Ambient Stable Radical Cations, Diradicaloid π-Dimeric Dications, Closed-Shell Dications, and Diradical Dications of Methylthio-Capped Rylenes.

PubMed

Qi, Qingbiao; Burrezo, Paula Mayorga; Phan, Hoa; Herng, Tun Seng; Gopalakrishna, Tullimilli Y; Zeng, Wangdong; Ding, Jun; Casado, Juan; Wu, Jishan

2017-06-01

Radical cations and dications of π-conjugated systems play vital roles in organic electronic devices, organic conductors, and conducting polymers. Their structures, charge and spin distribution, and mechanism of charge transport are of great interest. In this article, radical cations and dications of a series of newly synthesized methylthio-capped rylenes were synthesized and isolated. Their ground-state structures, physical properties, and solid-state packing were systematically investigated by various experimental methods, such as X-ray crystallographic analysis, UV/Vis/NIR absorption spectroscopy, (spectro-)electrochemistry, nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, superconducting quantum interference device, and Raman spectroscopy, assisted by DFT calculations. It was found that all the charged species show an exceptional stability under ambient air and light conditions due to the efficient spin and charge delocalization over the whole rylene backbone. The dication of hexarylene turned out to have an unusual open-shell singlet rather than closed-shell ground state, thus it can be described as a diradical dication. Dimerization was observed for the radical cations and even the dications in crystals due to the strong intermolecular antiferromagnetic spin-spin interaction and π-π interaction, which result in unique magnetic properties. Such intermolecular association was also observed in solution. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The ground and low-lying excited states and feasibility of laser cooling for GaH+ and InH+ cations

NASA Astrophysics Data System (ADS)

Zhang, Qing-Qing; Yang, Chuan-Lu; Wang, Mei-Shan; Ma, Xiao-Guang; Liu, Wen-Wang

2018-03-01

The potential energy curves and transition dipole moments of 12Σ+ and 12Π states of GaH+ and InH+ cations are performed by employing ab initio calculations. Based on the potential energy curves, the rotational and vibrational energy levels of the two states are obtained by solving the Schrödinger equation of nuclear movement. The spectroscopic parameters are deduced with the obtained rovibrational energy levels. The spin-orbit coupling effect of the 2Π states for both the GaH+ and InH+ cations are also calculated. The feasibility of laser cooling of GaH+ and InH+ cations are examined by using the results of the electronic and spectroscopic properties. The highly diagonal Franck-Condon factors and appropriate radiative lifetimes are determined by using the potential energy curves and transition dipole moments for the 2Π1/2, 3/2 ↔ 12Σ+ transitions. The results indicate that the 2Π1/2, 3/2 ↔ 12Σ+ transitions of both GaH+ and InH+ cations are appropriate for the close cycle transition of laser cooling. The optical scheme of the laser cooling is constructed for the GaH+ and InH+ cations.

Cation ordering and effect of biaxial strain in double perovskite CsRbCaZnCl 6

DOE PAGES

Pilania, G.; Uberuaga, B. P.

2015-03-19

Here, we investigate the electronic structure, energetics of cation ordering, and effect of biaxial strain on double perovskite CsRbCaZnCl 6 using first-principles calculations based on density functional theory. The two constituents (i.e., CsCaCl 3 and RbZnCl 3) forming the double perovskite exhibit a stark contrast. While CsCaCl 3 is known to exist in a cubic perovskite structure and does not show any epitaxial strain induced phase transitions within an experimentally accessible range of compressive strains, RbZnCl 3 is thermodynamically unstable in the perovskite phase and exhibits ultra-sensitive response at small epitaxial strains if constrained in the perovskite phase. We showmore » that combining the two compositions in a double perovskite structure not only improves overall stability but also the strain-polarization coupling of the material. Our calculations predict a ground state with P4/nmm space group for the double perovskite, where A-site cations (i.e., Cs and Rb) are layer-ordered and B-site cations (i.e., Ca and Zn) prefer a rocksalt type ordering. The electronic structure and bandgap in this system are shown to be quite sensitive to the B-site cation ordering and is minimally affected by the ordering of A-site cations. We find that at experimentally accessible compressive strains CsRbCaZnCl 6 can be phase transformed from its paraelectric ground state to an antiferroelectric state, where Zn atoms contribute predominantly to the polarization. Furthermore, both energy difference and activation barrier for a transformation between this antiferroelectric state and the corresponding ferroelectric configuration are predicted to be small. As a result, the computational approach presented here opens a new pathway towards a rational design of novel double perovskites with improved strain response and functionalities.« less

Threshold ionization spectroscopic investigation of supersonic jet-cooled, laser-desorbed Tryptophan

NASA Astrophysics Data System (ADS)

Taherkhani, Mehran; Armentano, Antonio; Černý, Jiří; Müller-Dethlefs, Klaus

2016-07-01

Tryptophan (Trp) was studied by two-colour Photoionization Efficiency (PIE) and Mass Analysed Threshold Ionization (MATI) spectroscopy using a laser desorption apparatus. Conformer A of Trp was excited into the S1 state (34,878 cm-1) and the second laser was scanned around the D0 cation ground and the D1 excited state. No ionization signal into the D0 state could be found, but a clear threshold was observed for the D1 state with an ionization energy of 66,704 ± 3 cm-1 (8.27 eV). This observation is explained in terms of the electronic configurations of the S1 and cationic states.

The EPR of the triplet state of aryl cations in crystals of diazonium salts

NASA Astrophysics Data System (ADS)

Kondratenko, P. A.; Shrubovich, E. V.; Shulga, S. Z.

The spectra of the electron paramagnetic resonance (EPR) of aryl cations possessing a principle triplet ground-state and orientated in a monocrystal of diazonium salts is studied. It is shown that two nonequivalent paramagnetic centers, which differ in orientation are formed within the crystal. A theoretic description of experimental results is possible only when allowing for the effect of low symmetry. This symmetry is invoked by the interactivity of the paramagnetic center of symmetry C(sub 2v) with the crystal field of symmetry C(sub i).

Vibronic spectra of the p-benzoquinone radical anion and cation: a matrix isolation and computational study.

PubMed

Piech, Krzysztof; Bally, Thomas; Ichino, Takatoshi; Stanton, John

2014-02-07

The electronic and vibrational absorption spectra of the radical anion and cation of p-benzoquinone (PBQ) in an Ar matrix between 500 and 40,000 cm(-1) are presented and discussed in detail. Of particular interest is the radical cation, which shows very unusual spectroscopic features that can be understood in terms of vibronic coupling between the ground and a very low-lying excited state. The infrared spectrum of PBQ˙(+) exhibits a very conspicuous and complicated pattern of features above 1900 cm(-1) that is due to this electronic transition, and offers an unusually vivid demonstration of the effects of vibronic coupling in what would usually be a relatively simple region of the electromagnetic spectrum associated only with vibrational transitions. As expected, the intensities of most of the IR transitions leading to levels that couple the ground to the very low-lying first excited state of PBQ˙(+) increase by large factors upon ionization, due to "intensity borrowing" from the D0 → D1 electronic transition. A notable exception is the antisymmetric C=O stretching vibration, which contributes significantly to the vibronic coupling, but has nevertheless quite small intensity in the cation spectrum. This surprising feature is rationalized on the basis of a simple perturbation analysis.

Epitaxially stabilized iridium spinel oxide without cations in the tetrahedral site

NASA Astrophysics Data System (ADS)

Kuriyama, Hiromichi; Matsuno, Jobu; Niitaka, Seiji; Uchida, Masaya; Hashizume, Daisuke; Nakao, Aiko; Sugimoto, Kunihisa; Ohsumi, Hiroyuki; Takata, Masaki; Takagi, Hidenori

2010-05-01

Single-crystalline thin film of an iridium dioxide polymorph Ir2O4 has been fabricated by the pulsed laser deposition of LixIr2O4 precursor and the subsequent Li-deintercalation using soft chemistry. Ir2O4 crystallizes in a spinel (AB2O4) without A cations in the tetrahedral site, which is isostructural to λ-MnO2. Ir ions form a pyrochlore sublattice, which is known to give rise to a strong geometrical frustration. This Ir spinel was found to be a narrow gap insulator, in remarkable contrast to the metallic ground state of rutile-type IrO2. We argue that an interplay of a strong spin-orbit coupling and a Coulomb repulsion gives rise to an insulating ground state as in a layered perovskite Sr2IrO4.

Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study.

PubMed

Gardiner, Sara H; Karsili, Tolga N V; Lipciuc, M Laura; Wilman, Edward; Ashfold, Michael N R; Vallance, Claire

2014-02-07

The photodissociation dynamics of ethyl bromide and ethyl iodide cations (C2H5Br(+) and C2H5I(+)) have been studied. Ethyl halide cations were formed through vacuum ultraviolet (VUV) photoionization of the respective neutral parent molecules at 118.2 nm, and were photolysed at a number of ultraviolet (UV) photolysis wavelengths, including 355 nm and wavelengths in the range from 236 to 266 nm. Time-of-flight mass spectra and velocity-map images have been acquired for all fragment ions and for ground (Br) and spin-orbit excited (Br*) bromine atom products, allowing multiple fragmentation pathways to be investigated. The experimental studies are complemented by spin-orbit resolved ab initio calculations of cuts through the potential energy surfaces (along the RC-Br/I stretch coordinate) for the ground and first few excited states of the respective cations. Analysis of the velocity-map images indicates that photoexcited C2H5Br(+) cations undergo prompt C-Br bond fission to form predominantly C2H5(+) + Br* products with a near-limiting 'parallel' recoil velocity distribution. The observed C2H3(+) + H2 + Br product channel is thought to arise via unimolecular decay of highly internally excited C2H5(+) products formed following radiationless transfer from the initial excited state populated by photon absorption. Broadly similar behaviour is observed in the case of C2H5I(+), along with an additional energetically accessible C-I bond fission channel to form C2H5 + I(+) products. HX (X = Br, I) elimination from the highly internally excited C2H5X(+) cation is deemed the most probable route to forming the C2H4(+) fragment ions observed from both cations. Finally, both ethyl halide cations also show evidence of a minor C-C bond fission process to form CH2X(+) + CH3 products.

Rationalization of the solvation effects on the AtO+ ground-state change.

PubMed

Ayed, Tahra; Réal, Florent; Montavon, Gilles; Galland, Nicolas

2013-09-12

(211)At radionuclide is of considerable interest as a radiotherapeutic agent for targeted alpha therapy in nuclear medicine, but major obstacles remain because the basic chemistry of astatine (At) is not well understood. The AtO(+) cationic form might be currently used for (211)At-labeling protocols in aqueous solution and has proved to readily react with inorganic/organic ligands. But AtO(+) reactivity must be hindered at first glance by spin restriction quantum rules: the ground state of the free cation has a dominant triplet character. Investigating AtO(+) clustered with an increasing number of water molecules and using various flavors of relativistic quantum methods, we found that AtO(+) adopts in solution a Kramers restricted closed-shell configuration resembling a scalar-relativistic singlet. The ground-state change was traced back to strong interactions, namely, attractive electrostatic interactions and charge transfer, with water molecules of the first solvation shell that lift up the degeneracy of the frontier π* molecular orbitals (MOs). This peculiarity brings an alternative explanation to the highly variable reproducibility reported for some astatine reactions: depending on the production protocols (with distillation in gas-phase or "wet chemistry" extraction), (211)At may or may not readily react.

Absorption and electroabsorption spectra of carotenoid cation radical and dication

NASA Astrophysics Data System (ADS)

Krawczyk, Stanisław

1998-05-01

Radical cations and dications of two carotenoids astaxanthin and canthaxanthin were prepared by oxidation with FeCl 3 in fluorinated alcohols at room temperature. Absorption and electroabsorption (Stark effect) spectra were recorded for astaxanthin cations in mixed frozen matrices at temperatures about 160 K. The D 0→D 2 transition in cation radical is at 835 nm. The electroabsorption spectrum for the D 0→D 2 transition exhibits a negative change of molecular polarizability, Δ α=-1.2·10 -38 C·m 2/V (-105 A 3), which seems to originate from the change in bond order alternation in the ground state rather than from the electric field-induced interaction of D 1 and D 2 excited states. Absorption spectrum of astaxanthin dication is located at 715-717 nm, between those of D 0→D 2 in cation radical and S 0→S 2 in neutral carotenoid. Its shape reflects a short vibronic progression and strong inhomogeneous broadening. The polarizability change on electronic excitation, Δ α=2.89·10 -38 C·m 2/V (260 A 3), is five times smaller than in neutral astaxanthin. This value reflects the larger energetic distance from the lowest excited state to the higher excited states than in the neutral molecule.

Nonadiabatic Photodynamics of a Retinal Model in Polar and Nonpolar Environment

PubMed Central

2013-01-01

The nonadiabatic photodynamics of the all-trans-2,4-pentadiene-iminium cation (protonated Schiff base 3, PSB3) and the all-trans-3-methyl-2,4-pentadiene-iminium cation (MePSB3) were investigated in the gas phase and in polar (aqueous) and nonpolar (n-hexane) solutions by means of surface hopping using a multireference configuration-interaction (MRCI) quantum mechanical/molecular mechanics (QM/MM) level. Spectra, lifetimes for radiationless deactivation to the ground state, and structural and electronic parameters are compared. A strong influence of the polar solvent on the location of the crossing seam, in particular in the bond length alternation (BLA) coordinate, is found. Additionally, inclusion of the polar solvent changes the orientation of the intersection cone from sloped in the gas phase to peaked, thus enhancing considerably its efficiency for deactivation of the molecular system to the ground state. These factors cause, especially for MePSB3, a substantial decrease in the lifetime of the excited state despite the steric inhibition by the solvent. PMID:23470211

Electron Transfer Dissociation: Effects of Cation Charge State on Product Partitioning in Ion/Ion Electron Transfer to Multiply Protonated Polypeptides

PubMed Central

Liu, Jian; McLuckey, Scott A.

2012-01-01

The effect of cation charge state on product partitioning in the gas-phase ion/ion electron transfer reactions of multiply protonated tryptic peptides, model peptides, and relatively large peptides with singly charged radical anions has been examined. In particular, partitioning into various competing channels, such as proton transfer (PT) versus electron transfer (ET), electron transfer with subsequent dissociation (ETD) versus electron transfer with no dissociation (ET,noD), and fragmentation of backbone bonds versus fragmentation of side chains, was measured quantitatively as a function of peptide charge state to allow insights to be drawn about the fundamental aspects of ion/ion reactions that lead to ETD. The ET channel increases relative to the PT channel, ETD increases relative to ET,noD, and fragmentation at backbone bonds increases relative to side-chain cleavages as cation charge state increases. The increase in ET versus PT with charge state is consistent with a Landau-Zener based curve-crossing model. An optimum charge state for ET is predicted by the model for the ground state-to-ground state reaction. However, when the population of excited product ion states is considered, it is possible that a decrease in ET efficiency as charge state increases will not be observed due to the possibility of the population of excited electronic states of the products. Several factors can contribute to the increase in ETD versus ET,noD and backbone cleavage versus side-chain losses. These factors include an increase in reaction exothermicity and charge state dependent differences in precursor and product ion structures, stabilities, and sites of protonation. PMID:23264749

Torsional, Vibrational and Vibration-Torsional Levels in the S_{1} and Ground Cationic D_{0}^{+} States of Para-Xylene

NASA Astrophysics Data System (ADS)

Gardner, Adrian M.; Tuttle, William Duncan; Groner, Peter; Wright, Timothy G.

2017-06-01

Insight gained from examining the "pure" torsional, vibrational and vibration-torsional (vibtor) levels of the single rotor molecules: toluene (methylbenzene) and para-fluorotoluene (pFT), is applied to the double rotor para-xylene (p-dimethylbenzene) molecule . Resonance-enhanced multiphoton ionization (REMPI) spectroscopy and zero-kinetic-energy (ZEKE) spectroscopy are employed in order to investigate the S_{1} and ground cationic states of para-xylene. Observed transitions are assigned in the full molecular symmetry group (G_{72}) for the first time. J. R. Gascooke, E. A. Virgo, and W. D. Lawrance, J. Chem. Phys., 143, 044313 (2015). A. M. Gardner, W. D. Tuttle, L. Whalley, A. Claydon, J. H. Carter and T. G. Wright, J. Chem. Phys., 145, 124307 (2016). A. M. Gardner, W. D. Tuttle, P. Groner and T. G. Wright, J. Chem. Phys., (2017, in press).

Structural investigations and the effect of strain on lead based double perovskites

NASA Astrophysics Data System (ADS)

Abbett, Brian; Fennie, Craig J.

2014-03-01

The A2 BB' O6 double perovskite structure, in which the B and B' ions are ordered (typically in a rocksalt configuration), provides a versatile platform to realize new properties such as multiferroicity. In particular, compounds with a lone-pair cation on the A-site, such as A=Pb2+, and magnetic B=Co, Mn, and diamagnetic B'= Te, Mo, W, Re, cations have been investigated experimentally, but as of yet none have been found to display ferroelectricity, although several are known to be antiferroelectric. Here we present a first-principles study of the structural and dielectric properties of this family of compounds. We resolve any conflicting reports in the literature as to the ground state structure of compounds and predict the ground state structure when no structural data is available. Additionally, we investigate the effect of epitaxial strain on the structural and magnetic properties.

Experimental Insights into Ground-State Selection of Quantum XY Pyrochlores

NASA Astrophysics Data System (ADS)

Hallas, Alannah M.; Gaudet, Jonathan; Gaulin, Bruce D.

2018-03-01

Extensive experimental investigations of the magnetic structures and excitations in the XY pyrochlores have been carried out over the past decade. Three families of XY pyrochlores have emerged: Yb2B2O7, Er2B2O7, and, most recently, [Formula: see text]Co2F7. In each case, the magnetic cation (either Yb, Er, or Co) exhibits XY anisotropy within the local pyrochlore coordinates, a consequence of crystal field effects. Materials in these families display rich phase behavior and are candidates for exotic ground states, such as quantum spin ice, and exotic ground-state selection via order-by-disorder mechanisms. In this review, we present an experimental summary of the ground-state properties of the XY pyrochlores, including evidence that they are strongly influenced by phase competition. We empirically demonstrate the signatures for phase competition in a frustrated magnet: multiple heat capacity anomalies, suppressed TN or TC, sample- and pressure-dependent ground states, and unconventional spin dynamics.

Excited state dynamics of the astaxanthin radical cation

NASA Astrophysics Data System (ADS)

Amarie, Sergiu; Förster, Ute; Gildenhoff, Nina; Dreuw, Andreas; Wachtveitl, Josef

2010-07-01

Femtosecond transient absorption spectroscopy in the visible and NIR and ultrafast fluorescence spectroscopy were used to examine the excited state dynamics of astaxanthin and its radical cation. For neutral astaxanthin, two kinetic components corresponding to time constants of 130 fs (decay of the S 2 excited state) and 5.2 ps (nonradiative decay of the S 1 excited state) were sufficient to describe the data. The dynamics of the radical cation proved to be more complex. The main absorption band was shifted to 880 nm (D 0 → D 3 transition), showing a weak additional band at 1320 nm (D 0 → D 1 transition). We found, that D 3 decays to the lower-lying D 2 within 100 fs, followed by a decay to D 1 with a time constant of 0.9 ps. The D 1 state itself exhibited a dual behavior, the majority of the population is transferred to the ground state in 4.9 ps, while a small population decays on a longer timescale of 40 ps. Both transitions from D 1 were found to be fluorescent.

Effects of zero point vibration on the reaction dynamics of water dimer cations following ionization.

PubMed

Tachikawa, Hiroto

2017-06-30

Reactions of water dimer cation (H2O)2+ following ionization have been investigated by means of a direct ab initio molecular dynamics method. In particular, the effects of zero point vibration and zero point energy (ZPE) on the reaction mechanism were considered in this work. Trajectories were run on two electronic potential energy surfaces (PESs) of (H2O)2+: ground state ( 2 A″-like state) and the first excited state ( 2 A'-like state). All trajectories on the ground-state PES lead to the proton-transferred product: H 2 O + (Wd)-H 2 O(Wa) → OH(Wd)-H 3 O + (Wa), where Wd and Wa refer to the proton donor and acceptor water molecules, respectively. Time of proton transfer (PT) varied widely from 15 to 40 fs (average time of PT = 30.9 fs). The trajectories on the excited-state PES gave two products: an intermediate complex with a face-to-face structure (H 2 O-OH 2 ) + and a PT product. However, the proton was transferred to the opposite direction, and the reverse PT was found on the excited-state PES: H 2 O(Wd)-H 2 O + (Wa) → H 3 O + (Wd)-OH(Wa). This difference occurred because the ionizing water molecule in the dimer switched between the ground and excited states. The reaction mechanism of (H2O)2+ and the effects of ZPE are discussed on the basis of the results. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhattacharyya, Swarnendu, E-mail: swarnendu.bhattacharyya@ch.tum.de; Domcke, Wolfgang, E-mail: wolfgang.domcke@ch.tum.de; Dai, Zuyang

A diabatic three-sheeted six-dimensional potential-energy surface has been constructed for the ground state and the lowest excited state of the PH{sub 3}{sup +} cation. Coupling terms of Jahn-Teller and pseudo-Jahn-Teller origin up to eighth order had to be included to describe the pronounced anharmonicity of the surface due to multiple conical intersections. The parameters of the diabatic Hamiltonian have been optimized by fitting the eigenvalues of the potential-energy matrix to ab initio data calculated at the CASSCF/MRCI level employing the correlation-consistent triple-ζ basis. The theoretical photoelectron spectrum of phosphine and the non-adiabatic nuclear dynamics of the phosphine cation have beenmore » computed by propagating nuclear wave packets with the multiconfiguration time-dependent Hartree method. The theoretical photoelectron bands obtained by Fourier transformation of the autocorrelation function agree well with the experimental results. It is shown that the ultrafast non-radiative decay dynamics of the first excited state of PH{sub 3}{sup +} is dominated by the exceptionally strong Jahn-Teller coupling of the asymmetric bending vibrational mode together with a hyperline of conical intersections with the electronic ground state induced by the umbrella mode. Time-dependent population probabilities have been computed for the three adiabatic electronic states. The non-adiabatic Jahn-Teller dynamics within the excited state takes place within ≈5 fs. Almost 80% of the excited-state population decay to the ground state within about 10 fs. The wave packets become highly complex and delocalized after 20 fs and no further significant transfer of electronic population seems to occur up to 100 fs propagation time.« less

First-principles theory of cation and intercalation ordering in Li xCoO 2

NASA Astrophysics Data System (ADS)

Wolverton, C.; Zunger, Alex

Several types of cation- and vacancy-ordering are of interest in the Li xCoO 2 battery cathode material since they can have a profound effect on the battery voltage. We present a first-principles theoretical approach which can be used to calculate both cation- and vacancy-ordering patterns at both zero and finite temperatures. This theory also provides quantum-mechanical predictions (i.e., without the use of any experimental input) of battery voltages of both ordered and disordered Li xCoO 2/Li cells from the energetics of the Li intercalation reactions. Our calculations allow us to search the entire configurational space to predict the lowest-energy ground-state structures, search for large voltage cathodes, explore metastable low-energy states, and extend our calculations to finite temperatures, thereby searching for order-disorder transitions and states of partial disorder. We present the first prediction of the stable spinel structure LiCo 2O 4 for the 50% delithiated Li 0.5CoO 2.

Resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of p-vinylaniline

NASA Astrophysics Data System (ADS)

Tzeng, Sheng Yuan; Dong, Changwu; Tzeng, Wen Bih

2012-10-01

We report the vibronic and cation spectra of p-vinylaniline, which are recorded by using the resonant two-photon ionization and the mass-analyzed threshold ionization spectroscopic techniques. The band origin of the S1 ← S0 electronic transition appears at 31,490 ± 2 cm-1 and the adiabatic ionization energy is determined to be 59,203 ± 5 cm-1. Due to the nature of the substituent, the amino and vinyl groups lead to lower electronic excitation and ionization energies by a few thousand wave numbers. Most of the observed active modes result from the in-plane ring deformation and substituent-sensitive vibrations of this molecule in the electronically excited S1 and cationic ground D0 states. By comparing the frequencies of the observed active vibrations, one may conclude that the molecular geometry and the vibrational coordinates of these modes of the p-vinylaniline cation in the D0 state resemble those of the neutral species in the S1 state.

Pulsed-field ionization zero electron kinetic energy spectrum of the ground electronic state of BeOBe+.

PubMed

Antonov, Ivan O; Barker, Beau J; Heaven, Michael C

2011-01-28

The ground electronic state of BeOBe(+) was probed using the pulsed-field ionization zero electron kinetic energy photoelectron technique. Spectra were rotationally resolved and transitions to the zero-point level, the symmetric stretch fundamental and first two bending vibrational levels were observed. The rotational state symmetry selection rules confirm that the ground electronic state of the cation is (2)Σ(g)(+). Detachment of an electron from the HOMO of neutral BeOBe results in little change in the vibrational or rotational constants, indicating that this orbital is nonbonding in nature. The ionization energy of BeOBe [65480(4) cm(-1)] was refined over previous measurements. Results from recent theoretical calculations for BeOBe(+) (multireference configuration interaction) were found to be in good agreement with the experimental data.

Theoretical calculations on the electron absorption spectra of selected Polycyclic Aromatic Hydrocarbons (PAH) and derivatives

NASA Technical Reports Server (NTRS)

Du, Ping

1993-01-01

As a theoretical component of the joint effort with the laboratory of Dr. Lou Allamandola to search for potential candidates for interstellar organic carbon compound that are responsible for the visible diffuse interstellar absorption bands (DIB's), quantum mechanical calculations were performed on the electron absorption spectra of selected polycyclic aromatic hydrocarbons (PAH) and derivatives. In the completed project, 15 different species of naphthalene, its hydrogen abstraction and addition derivatives, and corresponding cations and anions were studied. Using semiempirical quantum mechanical method INDO/S, the ground electronic state of each species was evaluated with restricted Hartree-Fock scheme and limited configuration interaction. The lowest energy spin state for each species was used for electron absorption calculations. Results indicate that these calculations are accurate enough to reproduce the spectra of naphthalene cation and anion observed in neon matrix. The spectral pattern of the hydrogen abstraction and addition derivatives predicted based on these results indicate that the electron configuration of the pi orbitals of these species is the dominant determinant. A combined list of 19 absorptions calculated from 4500 A to 10,400 A were compiled and suggested as potential candidates that are relevant for the DIB's absorptions. Continued studies on pyrene and derivatives revealed the ground state symmetries and multiplicities of its neutral, anionic, and cationic species. Spectral calculations show that the cation (B(sub 3g)-2) and the anion (A(sub u)-2) are more likely to have low energy absorptions in the regions between 10 kK and 20 kK, similar to naphthalene. These absorptions, together with those to be determined from the hydrogen abstraction and addition derivatives of pyrene, can be used to provide additional candidates and suggest experimental work in the search for interstellar compounds that are responsible for DIB's.

Ferromagnetic spin coupling in the chromium dimer cation: Measurements by photodissociation spectroscopy combined with coupled-cluster calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Egashira, Kazuhiro, E-mail: egashira@clusterlab.jp; Yamada, Yurika; Kita, Yukiumi

2015-02-07

The magnetic coupling of the chromium dimer cation, Cr{sub 2}{sup +}, has been an outstanding problem for decades. An optical absorption spectrum of Cr{sub 2}{sup +} has been obtained by photodissociation spectroscopy in the photon-energy range from 2.0 to 5.0 eV. Besides, calculations have been performed by the equation-of-motion coupled-cluster singles and doubles method for vertical excitation of the species. Their coincidence supports our assignment that the ground electronic state exhibits a ferromagnetic spin coupling, which is contrary to those of neutral and negatively charged dimers, Cr{sub 2} and Cr{sub 2}{sup −}, in their lowest spin states.

Encapsulation of a [Dy(OH2)8](3+) cation: magneto-optical and theoretical studies of a caged, emissive SMM.

PubMed

Al Hareri, M; Gavey, E L; Regier, J; Ras Ali, Z; Carlos, L D; Ferreira, R A S; Pilkington, M

2016-10-15

The first supramolecular cage formed by three benzo-15-crown-5 macrocycles encapsulating a [Dy(OH2)8](3+) guest cation is reported, with the Dy(iii) centre exhibiting local pseudo square antiprismatic D4d symmetry. The anisotropy barrier extracted from ac susceptibility studies, emission spectroscopy and ab initio calculations reveals that the second excited state Kramers doublet plays a key role in the magnetization dynamics due to the Ising character and near coparallel nature of the ground and first excited Kramers doublets.

Electronic structure of the benzene dimer cation

NASA Astrophysics Data System (ADS)

Pieniazek, Piotr A.; Krylov, Anna I.; Bradforth, Stephen E.

2007-07-01

The benzene and benzene dimer cations are studied using the equation-of-motion coupled-cluster model with single and double substitutions for ionized systems. The ten lowest electronic states of the dimer at t-shaped, sandwich, and displaced sandwich configurations are described and cataloged based on the character of the constituent fragment molecular orbitals. The character of the states, bonding patterns, and important features of the electronic spectrum are explained using qualitative dimer molecular orbital linear combination of fragment molecular orbital framework. Relaxed ground state geometries are obtained for all isomers. Calculations reveal that the lowest energy structure of the cation has a displaced sandwich structure and a binding energy of 20kcal/mol, while the t-shaped isomer is 6kcal/mol higher. The calculated electronic spectra agree well with experimental gas phase action spectra and femtosecond transient absorption in liquid benzene. Both sandwich and t-shaped structures feature intense charge resonance bands, whose location is very sensitive to the interfragment distance. Change in the electronic state ordering was observed between σ and πu states, which correlate to the B˜ and C˜ bands of the monomer, suggesting a reassignment of the local excitation peaks in the gas phase experimental spectrum.

Influences of the propyl group on the van der Waals structures of 4-propylaniline complexes with one and two argon atoms studied by electronic and cationic spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Zhijun; Gu, Quanli; Department of Chemistry, University of Oklahoma, Norman, Oklahoma 73019

2015-07-21

4-propylaniline complexes with one and two argon atoms formed in the molecular beam were studied in the first excited electronic state, S{sub 1}, using resonance enhanced two-photon ionization spectroscopy and in the cation ground state, D{sub 0}, using mass analyzed threshold ionization spectroscopy. The combination of electronic and cationic spectra of the clusters allows two conformations to be identified in both aniline-Ar{sub 1} and aniline-Ar{sub 2}, which are assigned to either the gauche configuration or anti-configuration of 4-propylaniline. The gauche isomer exhibits complex bands shifted 29 cm{sup −1} and 89 cm{sup −1} from the S{sub 1} origin bands and 83more » cm{sup −1} and 148 cm{sup −1} from the ionization potential assigned to the Ar{sub 1} and Ar{sub 2} complexes, respectively. For the anti-rotamer, the corresponding shifts actually become nearly additive, 53 cm{sup −1} and 109 cm{sup −1} for the S{sub 1} origin bands, and 61 cm{sup −1} and 125 cm{sup −1} for the ionization potentials. Ab initio calculations provide insights into the influences of the propyl and amino groups on the positions of the argon atoms within the clusters. In addition, the binding energy of one argon with the gauche isomer of 4-propylaniline has been measured to be 550 ± 5 cm{sup −1} in the D{sub 0} state, 496 ± 5 cm{sup −1} in the S{sub 1} state, and 467 ± 5 cm{sup −1} in the neutral ground state, S{sub 0}.« less

Interactions of NO and CO with Pd and Pt atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, G.W.; Carter, E.A.

1991-03-21

The authors report ab initio generalized valence bond and correlation-consistent configuration interaction studies of CO and NO interacting with Pd and Pt atoms. They find dramatically different bonding mechanisms for the two ligands, which are easily understood in terms of changes in the electronic structure of the metal and the ligand. CO bonds to both Pd and pt by a {sigma} donor/{pi} back-bonding mechanism, yielding linear geometries. Their calculations predict that the ground ({sup 1}{Sigma}{sup +}) state of PdCO is bound by 27 kcal/mol, while the ground ({sup 1}{Sigma}{sup +}) state of PtCO is bound by only 18.5 kcal/mol. Bymore » contrast, PdNO and PtNO are both bent, with the dominant bonding involving a covalent {sigma} bond between a singly occupied metal d{sigma} orbital and the singly occupied NO 2{pi}* orbital. While the ground ({sup 2}A{prime}) state of PtNO is strongly bound (D{sub e}(Pt-NO) {approximately} 20 kcal/mol), NO binds very weakly to Pd (D{sub e}(Pd-NO) {le} 4 kcal/mol). Linear excited states ({sup 2}{Sigma} and {sup 2}{Pi}) of PtNO and PdNO are predicted to be only weakly bound or unbound. However, corresponding linear cationic states ({sup 1}{Sigma}{sup +} and {sup 3}{Pi}) are strongly bound, but the cationic bent ({sup 1}A{prime}) states are still the ground states of PtNO{sup +} and PdNO{sup +}. These stark contrasts, in which NO binds strongly to Pt but weakly to Pd while CO binds much more strongly to Pd, are due to the preference for closed-shell species to bind strongly to other closed-shell species (e.g., CO to Pd) and for radicals to bind strongly to other radicals (e.g., NO to Pt).« less

First-principles theory of cation- and intercalation-ordering in Li_xCoO_2

NASA Astrophysics Data System (ADS)

Wolverton, C.; Zunger, Alex

1998-03-01

Using a combination of first-principles total energies, a cluster expansion technique, and Monte Carlo simulations, we present a first-principles theory which can predict both cation- and intercalation-ordering patterns at both zero and finite temperatures, and can provide first-principles predictions of battery voltages of Li_xCoO_2/Li cells. The classes of ordering problems that we study are the following: (i) The LiMO2 oxides (M=3d metal) form a series of structures based on an octahedrally-coordinated network with anions (O) on one fcc sublattice and cations (Li and M) on the other, leading to Li/Co ordering in LiCoO2 (x=1). We find the ground state is the CuPt or (111)-layered cation arrangment, in agreement with the observed structure. (ii) In battery applications, Li is (de)intercalated from the compound, creating a vacancy (denoted Box) that can be positioned in different lattice locations; Thus, Box/Co ordering in BoxCoO2 (x=0) is also of interest. We find the ground state for BoxCoO2 is also a (111)-layered structure, although a different stacking sequence (AAA) of close-packed layers is preferred. (iii) The vacancies left behind by Li extraction can form ordered vacancy compounds in partially de-lithiated Li_xCoO_2, leading to a Box/Li ordering problem (0<=x<=1). Our calculations agree with the observed voltage profiles in these systems, and predict the existence of new intercalation-ordered compounds. Supported by BES/OER/DMS under contract DE-AC36-83CH10093.

Non-classical behaviour of higher valence dopants in chromium (III) oxide by a Cr vacancy compensation mechanism

NASA Astrophysics Data System (ADS)

Carey, John J.; Nolan, Michael

2017-10-01

Modification of metal oxides with dopants that have a stable oxidation in their parent oxides which is higher than the host system is expected to introduce extra electrons into the material to improve carrier mobility. This is essential for applications in catalysis, SOFCs and solar energy materials. Density functional theory calculations are used to investigate the change in electronic and geometric structure of chromium (III) oxide by higher valence dopants, namely; Ce, Ti, V and Zr. For single metal doping, we find that the dopants with variable oxidation states, Ce, Ti and V, adopt a valence state of  +3, while Zr dopant has a  +4 oxidation state and reduces a neighbouring Cr cation. Chromium vacancy formation is greatly enhanced for all dopants, and favoured over oxygen vacancy formation. The Cr vacancies generate holes which oxidise Ce, Ti and V from  +3 to  +4, while also oxidising lattice oxygen sites. For Zr doping, the generated holes oxidise the reduced Cr2+ cation back to Cr3+ and also two lattice oxygen atoms. Three metal atoms in the bulk lattice facilitate spontaneous Cr vacancy from charge compensation. A non-classical compensation mechanism is observed for Ce, Ti and V; all three metals are oxidised from  +3 to  +4, which explains experimental observations that these metals have a  +4 oxidation state in Cr2O3. Charge compensation of the three Zr metals proceeds by a classical higher valence doping mechanism; the three dopants reduce three Cr cations, which are subsequently charge compensated by a Cr vacancy oxidising three Cr2+ to Cr3+. The compensated structures are the correct ground state electronic structure for these doped systems, and used as a platform to investigate cation/anion vacancy formation. Unlike the single metal doped bulks, preference is now given for oxygen vacancy formation over Cr vacancy formation, indicating that the dopants increase the reducibility of Cr2O3 with Ce doping showing the strongest enhancement. The importance of the correct ground state in determining the formation of defects is emphasised.

Spectroscopy of the UO+2 cation and the delayed ionization of UO2.

PubMed

Merritt, Jeremy M; Han, Jiande; Heaven, Michael C

2008-02-28

Vibronically resolved spectra for the UO+2 cation have been recorded using the pulsed field ionization zero electron kinetic energy (PFI-ZEKE) technique. For the ground state, long progressions in both the bending and symmetric stretch vibrations were observed. Bend and stretch progressions of the first electronically excited state were also observed, and the origin was found at an energy of 2678 cm(-1) above the ground state zero-point level. This observation is consistent with a recent theoretical prediction [Infante et al., J. Chem. Phys. 127, 124308 (2007)]. The ionization energy for UO2, derived from the PFI-ZEKE spectrum, namely, 6.127(1) eV, is in excellent agreement with the value obtained from an earlier photoionization efficiency measurement. Delayed ionization of UO2 in the gas phase has been reported previously [Han et al., J. Chem. Phys. 120, 5155 (2004)]. Here, we extend the characterization of the delayed ionization process by performing a quantitative study of the ionization rate as a function of the energy above the ionization threshold. The ionization rate was found to be 5 x 10(6) s(-1) at threshold, and increased linearly with increasing energy in the range investigated (0-1200 cm(-1)).

Intrinsic Defect Ferromagnetism: The case of Hafnium Oxide

NASA Astrophysics Data System (ADS)

Das Pemmaraju, Chaitanya

2005-03-01

In view of the recent experimental reports of intrinsic ferromagnetism in Hafnium Oxide (HfO2) thin film systems ootnotetextM. Venkatesan, C. B. Fitzgerald, J. M. D. Coey Nature 430, 630 (2004) Brief Communications, we carried out first principles investigations to look for magnetic structure in HfO2 possibly brought about by the presence of small concentrations of intrinsic point defects. Ab initio electronic structure calculations using Density Functional Theory (DFT) show that isolated cation vacancy sites in HfO2 lead to the formation of high spin defect states which couple ferromagnetically to each other. Interestingly, these high spin states are observed in the low symmetry monoclinic and tetragonal phases while the highly symmetric cubic flourite phase exhibits a non-magnetic ground state. Detailed studies of the electronic structure of cation vacancies in the three crystalline phases of Hafnia show that symmetry leading to orbitally degenerate defect levels is not a pre-requsite for ferromagnetism and that the interplay between Kinetic, Coulomb and Exchange energy together with favourable coupling to the Crystalline environment can lead to high spin ferromagnetic ground states even in extreme low symmetry systems like monoclinic HfO2. These findings open up a much wider class of systems to the possibility of intrinsic defect ferromagnetism.

Ab initio investigation of sulfur monofluoride and its singly charged cation and anion in their ground electronic state

NASA Astrophysics Data System (ADS)

Song, Li; Shan-Jun, Chen; Yan, Chen; Peng, Chen

2016-03-01

The SF radical and its singly charged cation and anion, SF+ and SF-, have been investigated on the MRCI/aug-cc-pVXZ (X = Q, 5, 6) levels of theory with Davidson correction. Both the core-valence correlation and the relativistic effect are considered. The extrapolating to the complete basis set (CBS) limit is adopted to remove the basis set truncation error. Geometrical parameters, potential energy curves (PECs), vibrational energy levels, spectroscopic constants, ionization potentials, and electron affinities of the ground electronic state for all these species are obtained. The information with respect to molecular characteristics of the SFn (n = -1, 0, +1) systems derived in this work will help to extend our knowledge and to guide further experimental or theoretical researches. Project supported by the National Natural Science Foundation of China (Grant Nos. 11304023 and 11447172), the Young and Middle-Aged Talent of Education Burea of Hubei Province, China (Grant No. Q20151307), and the Yangtze Youth Talents Fund of Yangtze University, China (Grant No. 2015cqr21).

Photo-fragmentation spectroscopy of benzylium and 1-phenylethyl cations

NASA Astrophysics Data System (ADS)

Féraud, Géraldine; Dedonder-Lardeux, Claude; Soorkia, Satchin; Jouvet, Christophe

2014-01-01

The electronic spectra of cold benzylium (C6H5-CH2+) and 1-phenylethyl (C6H5-CH-CH3+) cations have been recorded via photofragment spectroscopy. Benzylium and 1-phenylethyl cations produced from electrosprayed benzylamine and phenylethylamine solutions, respectively, were stored in a cryogenically cooled quadrupole ion trap and photodissociated by an OPO laser, scanned in parts of the UV and visible regions (600-225 nm). The electronic states and active vibrational modes of the benzylium and 1-phenylethyl cations as well as those of their tropylium or methyl tropylium isomers have been calculated with ab initio methods for comparison with the spectra observed. Sharp vibrational progressions are observed in the visible region while the absorption features are much broader in the UV. The visible spectrum of the benzylium cation is similar to that obtained in an argon tagging experiment [V. Dryza, N. Chalyavi, J. A. Sanelli, and E. J. Bieske, J. Chem. Phys. 137, 204304 (2012)], with an additional splitting assigned to Fermi resonances. The visible spectrum of the 1-phenylethyl cation also shows vibrational progressions. For both cations, the second electronic transition is observed in the UV, around 33 000 cm-1 (4.1 eV) and shows a broadened vibrational progression. In both cases the S2 optimized geometry is non-planar. The third electronic transition observed around 40 000 cm-1 (5.0 eV) is even broader with no apparent vibrational structures, which is indicative of either a fast non-radiative process or a very large change in geometry between the excited and the ground states. The oscillator strengths calculated for tropylium and methyl tropylium are weak. Therefore, these isomeric structures are most likely not responsible for these absorption features. Finally, the fragmentation pattern changes in the second and third electronic states: C2H2 loss becomes predominant at higher excitation energies, for both cations.

Distinguishing between relaxation pathways by combining dissociative ionization pump probe spectroscopy and ab initio calculations: a case study of cytosine.

PubMed

Kotur, Marija; Weinacht, Thomas C; Zhou, Congyi; Kistler, Kurt A; Matsika, Spiridoula

2011-05-14

We present a general method for tracking molecular relaxation along different pathways from an excited state down to the ground state. We follow the excited state dynamics of cytosine pumped near the S(0)-S(1) resonance using ultrafast laser pulses in the deep ultraviolet and probed with strong field near infrared pulses which ionize and dissociate the molecules. The fragment ions are detected via time of flight mass spectroscopy as a function of pump probe delay and probe pulse intensity. Our measurements reveal that different molecular fragments show different timescales, indicating that there are multiple relaxation pathways down to the ground state. We interpret our measurements with the help of ab initio electronic structure calculations of both the neutral molecule and the molecular cation for different conformations en route to relaxation back down to the ground state. Our measurements and calculations show passage through two seams of conical intersections between ground and excited states and demonstrate the ability of dissociative ionization pump probe measurements in conjunction with ab initio electronic structure calculations to track molecular relaxation through multiple pathways.

Ground and Excited-Electronic-State Dissociations of Hydrogen-Rich and Hydrogen-Deficient Tyrosine Peptide Cation Radicals

NASA Astrophysics Data System (ADS)

Viglino, Emilie; Lai, Cheuk Kuen; Mu, Xiaoyan; Chu, Ivan K.; Tureček, František

2016-09-01

We report a comprehensive study of collision-induced dissociation (CID) and near-UV photodissociation (UVPD) of a series of tyrosine-containing peptide cation radicals of the hydrogen-rich and hydrogen-deficient types. Stable, long-lived, hydrogen-rich peptide cation radicals, such as [AAAYR + 2H]+● and several of its sequence and homology variants, were generated by electron transfer dissociation (ETD) of peptide-crown-ether complexes, and their CID-MS3 dissociations were found to be dramatically different from those upon ETD of the respective peptide dications. All of the hydrogen-rich peptide cation radicals contained major (77%-94%) fractions of species having radical chromophores created by ETD that underwent photodissociation at 355 nm. Analysis of the CID and UVPD spectra pointed to arginine guanidinium radicals as the major components of the hydrogen-rich peptide cation radical population. Hydrogen-deficient peptide cation radicals were generated by intramolecular electron transfer in CuII(2,2 ':6 ',2 ″-terpyridine) complexes and shown to contain chromophores absorbing at 355 nm and undergoing photodissociation. The CID and UVPD spectra showed major differences in fragmentation for [AAAYR]+● that diminished as the Tyr residue was moved along the peptide chain. UVPD was found to be superior to CID in localizing Cα-radical positions in peptide cation radical intermediates.

Electrostatically driven resonance energy transfer in "cationic" biocompatible indium phosphide quantum dots.

PubMed

Devatha, Gayathri; Roy, Soumendu; Rao, Anish; Mallick, Abhik; Basu, Sudipta; Pillai, Pramod P

2017-05-01

Indium Phosphide Quantum Dots (InP QDs) have emerged as an alternative to toxic metal ion based QDs in nanobiotechnology. The ability to generate cationic surface charge, without compromising stability and biocompatibility, is essential in realizing the full potential of InP QDs in biological applications. We have addressed this challenge by developing a place exchange protocol for the preparation of cationic InP/ZnS QDs. The quaternary ammonium group provides the much required permanent positive charge and stability to InP/ZnS QDs in biofluids. The two important properties of QDs, namely bioimaging and light induced resonance energy transfer, are successfully demonstrated in cationic InP/ZnS QDs. The low cytotoxicity and stable photoluminescence of cationic InP/ZnS QDs inside cells make them ideal candidates as optical probes for cellular imaging. An efficient resonance energy transfer ( E ∼ 60%) is observed, under physiological conditions, between the cationic InP/ZnS QD donor and anionic dye acceptor. A large bimolecular quenching constant along with a linear Stern-Volmer plot confirms the formation of a strong ground state complex between the cationic InP/ZnS QDs and the anionic dye. Control experiments prove the role of electrostatic attraction in driving the light induced interactions, which can rightfully form the basis for future nano-bio studies between cationic InP/ZnS QDs and anionic biomolecules.

Slow Photoelectron Spectroscopy and State-Selected Unimolecular Decomposition of Ionized DNA Bases Analogues

NASA Astrophysics Data System (ADS)

Mahjoub, Ahmed; Hochlaf, Majdi; Poisson, Lionel; Garcia, Gustavo A.; Nahon, Laurent

2013-06-01

We studied the single-photon ionization of gas-phase 2-Piperidone (DNA basis analogue) and of its dimer using vacuum-ultraviolet (VUV) synchrotron radiation coupled to a velocity map imaging electron/ion coincidence spectrometer The slow photoelectron spectrum (SPES) of the monomer is dominated by the vibrational transitions to the ground state. These spectra are assigned with the help of theoretical calculations dealing with the equilibrium geometries, electronic-state patterns and evolutions, harmonic and anharmonic wavenumbers. After its formation, dimer is subject of intramolecular isomerization, H transfer and then unimolecular fragmentation processes. The near threshold photofragmentation pattern of the cationic 2-Piperidone cation and its dimer has been recorded. The experimental method yields the fragment intensity as a function of the internal energy deposited into the parent cation. In parallel, ab initio studies on ionic and neutral fragmentation products have been performed with the aim of determining the isomers of the ionic products observed experimentally as well as of their neutral counterparts. L. Nahon, N. De Oliveria,J. F. Gil,B. Pilette,O. Marcouillé, B. La garde and F. Polack Journal of Synchrotron Radiation {19}(4), 508-520; 2012

Taple-top imaging of the non-adiabatically driven isomerization in the acetylene cation

NASA Astrophysics Data System (ADS)

Beaulieu, Samuel; Ibrahim, Heide; Wales, Benji; Schmidt, Bruno E.; Thiré, Nicolas; Bisson, Éric; Hebeisen, Christoph T.; Wanie, Vincent; Giguere, Mathieu; Kieffer, Jean-Claude; Sanderson, Joe; Schuurman, Michael S.; Légaré, François

2014-05-01

One of the primary goals of modern ultrafast science is to follow nuclear and electronic evolution of molecules as they undergo a photo-chemical reaction. Most of the interesting dynamics phenomena in molecules occur when an electronically excited state is populated. When the energy difference between electronic ground and excited states is large, Free Electron Laser (FEL) and HHG-based VUV sources were, up to date, the only light sources able to efficiently initiate those non-adiabatic dynamics. We have developed a simple table-top approach to initiate those rich dynamics via multiphoton absorption. As a proof of principle, we studied the ultrafast isomerization of the acetylene cation. We have chosen this model system for isomerization since the internal conversion mechanism which leads to proton migration is still under debate since decades. Using 266 nm multiphoton absorption as a pump and 800 nm induced Coulomb Explosion as a probe, we have shoot the first high-resolution molecular movie of the non-adiabatically driven proton migration in the acetylene cation. The experimental results are in excellent agreement with high level ab initio trajectory simulations.

Experimental and ab initio characterization of HC3N+ vibronic structure. II. High-resolution VUV PFI-ZEKE spectroscopy.

PubMed

Gans, Bérenger; Lamarre, Nicolas; Broquier, Michel; Liévin, Jacques; Boyé-Péronne, Séverine

2016-12-21

Vacuum-ultraviolet pulsed-field-ionization zero-kinetic-energy photoelectron spectra of X + Π2←XΣ+1 and B + Π2←XΣ+1 transitions of the HC 3 14 N and HC 3 15 N isotopologues of cyanoacetylene have been recorded. The resolution of the photoelectron spectra allowed us to resolve the vibrational structures and the spin-orbit splittings in the cation. Accurate values of the adiabatic ionization potentials of the two isotopologues (E I /hc(HC 3 14 N)=93 909(2) cm -1 and E I /hc(HC 3 15 N)=93 912(2) cm -1 ), the vibrational frequencies of the ν 2 , ν 6 , and ν 7 vibrational modes, and the spin-orbit coupling constant (A SO = -44(2) cm -1 ) of the X + Π2 cationic ground state have been derived from the measurements. Using ab initio calculations, the unexpected structure of the B + Π2←XΣ+1 transition is tentatively attributed to a conical intersection between the A + and B + electronic states of the cation.

Excited-State Proton Transfer on the Surface of a Therapeutic Protein, Protamine.

PubMed

Awasthi, Ankur A; Singh, Prabhat K

2017-11-16

Proton transfer reactions on biosurfaces play an important role in a myriad of biological processes. Herein, the excited-state proton transfer reaction of 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) has been investigated in the presence of an important therapeutic protein, Protamine (PrS), using ground-state absorption, steady-state, and detailed time-resolved emission measurements. HPTS forms a 1:1 complex with Protamine with a high association constant of 2.6 × 10 4 M -1 . The binding of HPTS with Protamine leads to a significant modulation in the ground-state prototropic equilibrium causing a downward shift of 1.1 unit in the acidity constant (pK a ). In contrast to a large number of reports of slow proton transfer of HPTS on biosurfaces, interestingly, HPTS registers a faster proton transfer event in the presence of Protamine as compared to that of even the bulk aqueous buffer medium. Furthermore, the dimensionality of the proton diffusion process is also significantly reduced on the surface of Protamine that is in contrast to the behavior of HPTS in the bulk aqueous buffer medium, where the proton diffusion process is three-dimensional. The effect of ionic strength on the binding of HPTS toward PrS suggests a predominant role of electrostatic interaction between anionic HPTS and cationic Protamine, which is further supported by molecular docking simulations which predict that the most preferable binding site for HPTS on the surface of Protamine is surrounded by multiple cationic arginine residues.

Photo-fragmentation spectroscopy of benzylium and 1-phenylethyl cations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Féraud, Géraldine; Dedonder-Lardeux, Claude; Jouvet, Christophe, E-mail: christophe.jouvet@univ-amu.fr

The electronic spectra of cold benzylium (C{sub 6}H{sub 5}-CH{sub 2}{sup +}) and 1-phenylethyl (C{sub 6}H{sub 5}-CH-CH{sub 3}{sup +}) cations have been recorded via photofragment spectroscopy. Benzylium and 1-phenylethyl cations produced from electrosprayed benzylamine and phenylethylamine solutions, respectively, were stored in a cryogenically cooled quadrupole ion trap and photodissociated by an OPO laser, scanned in parts of the UV and visible regions (600–225 nm). The electronic states and active vibrational modes of the benzylium and 1-phenylethyl cations as well as those of their tropylium or methyl tropylium isomers have been calculated with ab initio methods for comparison with the spectra observed.more » Sharp vibrational progressions are observed in the visible region while the absorption features are much broader in the UV. The visible spectrum of the benzylium cation is similar to that obtained in an argon tagging experiment [V. Dryza, N. Chalyavi, J. A. Sanelli, and E. J. Bieske, J. Chem. Phys. 137, 204304 (2012)], with an additional splitting assigned to Fermi resonances. The visible spectrum of the 1-phenylethyl cation also shows vibrational progressions. For both cations, the second electronic transition is observed in the UV, around 33 000 cm{sup −1} (4.1 eV) and shows a broadened vibrational progression. In both cases the S{sub 2} optimized geometry is non-planar. The third electronic transition observed around 40 000 cm{sup −1} (5.0 eV) is even broader with no apparent vibrational structures, which is indicative of either a fast non-radiative process or a very large change in geometry between the excited and the ground states. The oscillator strengths calculated for tropylium and methyl tropylium are weak. Therefore, these isomeric structures are most likely not responsible for these absorption features. Finally, the fragmentation pattern changes in the second and third electronic states: C{sub 2}H{sub 2} loss becomes predominant at higher excitation energies, for both cations.« less

Vibrationally resolved photoelectron spectroscopy of electronic excited states of DNA bases: application to the ã state of thymine cation.

PubMed

Hochlaf, Majdi; Pan, Yi; Lau, Kai-Chung; Majdi, Youssef; Poisson, Lionel; Garcia, Gustavo A; Nahon, Laurent; Al Mogren, Muneerah Mogren; Schwell, Martin

2015-02-19

For fully understanding the light-molecule interaction dynamics at short time scales, recent theoretical and experimental studies proved the importance of accurate characterizations not only of the ground (D0) but also of the electronic excited states (e.g., D1) of molecules. While ground state investigations are currently straightforward, those of electronic excited states are not. Here, we characterized the à electronic state of ionic thymine (T(+)) DNA base using explicitly correlated coupled cluster ab initio methods and state-of-the-art synchrotron-based electron/ion coincidence techniques. The experimental spectrum is composed of rich and long vibrational progressions corresponding to the population of the low frequency modes of T(+)(Ã). This work challenges previous numerous works carried out on DNA bases using common synchrotron and VUV-based photoelectron spectroscopies. We provide hence a powerful theoretical and experimental framework to study the electronic structure of ionized DNA bases that could be generalized to other medium-sized biologically relevant systems.

D1((2)B2g) to D0((2)Au) Fluorescence from the Matrix-Isolated Perylene Cation Following Laser Excitation into the D5(2)B3g) and D2 ((2)B3g) Electronic States

NASA Technical Reports Server (NTRS)

Chillier, Xavier D. F.; Stone, Bradley M.; Joblin, Christine; Salama, Farid; Allamandola, Louis J.; DeVincenzi, Donald L. (Technical Monitor)

2001-01-01

Fluorescence spectra of the perylene cation, pumped by direct laser excitation via the D(sub 2)((2)B(sub 3g)) (left arrow) D(sub 0)((2)A(sub u)) and D(sub 5)(2)B(sub 3g)) (left arrow) D(sub 0)((2)A(sub u)) transitions, are presented. Direct excitation into the D5 or D2 states is followed by rapid non-radiative relaxation to D1 that, in turn,relaxes radiatively. Excitation spectroscopy across the D(sub 2)((2)B(sub 3g)) (left arrow) D(sub 0)((2)A(sub u)) transition near 730 nm shows that site splitting plays little or no role in determining the spectral substructure in the ion spectra. Tentative assignments for ground state vibrational frequencies are made by comparison of spectral intervals with calculated normal mode frequencies.

Molecular symmetry group analysis of the low-wavenumber torsions and vibration-torsions in the S1 state and ground state cation of p-xylene: An investigation using resonance-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy (ZEKE) spectroscopy

NASA Astrophysics Data System (ADS)

Gardner, Adrian M.; Tuttle, William D.; Groner, Peter; Wright, Timothy G.

2017-03-01

For the first time, a molecular symmetry group (MSG) analysis has been undertaken in the investigation of the electronic spectroscopy of p-xylene (p-dimethylbenzene). Torsional and vibration-torsional (vibtor) levels in the S1 state and ground state of the cation of p-xylene are investigated using resonance-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy (ZEKE) spectroscopy. In the present work, we concentrate on the 0-350 cm-1 region, where there are a number of torsional and vibtor bands and we discuss the assignment of this region. In Paper II [W. D. Tuttle et al., J. Chem. Phys. 146, 124309 (2017)], we examine the 350-600 cm-1 region where vibtor levels are observed as part of a Fermi resonance. The similarity of much of the observed spectral activity to that in the related substituted benzenes, toluene and para-fluorotoluene, is striking, despite the different symmetries. The discussion necessitates a consideration of the MSG of p-xylene, which has been designated G72, but we shall also designate [{3,3}]D2h and we include the symmetry operations, character table, and direct product table for this. We also discuss the symmetries of the internal rotor (torsional) levels and the selection rules for the particular electronic transition of p-xylene investigated here.

Interaction between the exchanged Mn2+ and Yb3+ ions confined in zeolite-Y and their luminescence behaviours

PubMed Central

Ye, Shi; Sun, Jiayi; Yi, Xiong; Wang, Yonggang; Zhang, Qinyuan

2017-01-01

Luminescent zeolites exchanged with two distinct and interacted emissive ions are vital but less-studied for the potential applications in white light emitting diodes, solar cells, optical codes, biomedicine and so on. Typical transition metal ion Mn2+ and lanthanide ion Yb3+ are adopted as a case study via their characteristic transitions and the interaction between them. The option is considered with that the former with d-d transition has a large gap between the first excited state 4T1 and the ground state 6A1 (normally >17,000 cm−1) while the latter with f-f transition has no metastable excited state above 10,000 cm−1, which requires the vicinity of these two ions for energy transfer. The results of various characterizations, including BET measurement, photoluminescence spectroscopy, solid-state NMR, and X-ray absorption spectroscopy, etc., show that Yb3+ would preferably enter into the zeolite-Y pores and introduction of Mn2+ would cause aggregation of each other. Herein, cation-cation repulsion may play a significant role for the high valence of Mn2+ and Yb3+ when exchanging the original cations with +1 valence. Energy transfer phenomena between Mn2+ and Yb3+ occur only at elevated contents in the confined pores of zeolite. The research would benefit the design of zeolite composite opto-functional materials. PMID:28393920

Interaction between the exchanged Mn2+ and Yb3+ ions confined in zeolite-Y and their luminescence behaviours

NASA Astrophysics Data System (ADS)

Ye, Shi; Sun, Jiayi; Yi, Xiong; Wang, Yonggang; Zhang, Qinyuan

2017-04-01

Luminescent zeolites exchanged with two distinct and interacted emissive ions are vital but less-studied for the potential applications in white light emitting diodes, solar cells, optical codes, biomedicine and so on. Typical transition metal ion Mn2+ and lanthanide ion Yb3+ are adopted as a case study via their characteristic transitions and the interaction between them. The option is considered with that the former with d-d transition has a large gap between the first excited state 4T1 and the ground state 6A1 (normally >17,000 cm-1) while the latter with f-f transition has no metastable excited state above 10,000 cm-1, which requires the vicinity of these two ions for energy transfer. The results of various characterizations, including BET measurement, photoluminescence spectroscopy, solid-state NMR, and X-ray absorption spectroscopy, etc., show that Yb3+ would preferably enter into the zeolite-Y pores and introduction of Mn2+ would cause aggregation of each other. Herein, cation-cation repulsion may play a significant role for the high valence of Mn2+ and Yb3+ when exchanging the original cations with +1 valence. Energy transfer phenomena between Mn2+ and Yb3+ occur only at elevated contents in the confined pores of zeolite. The research would benefit the design of zeolite composite opto-functional materials.

Study of crystal-field interaction in magnetic frustrated lead pyrochlore Gd2Pb2O7

NASA Astrophysics Data System (ADS)

Swarnakar, D.; Jana, Y. M.

2018-05-01

A fine tuning between the crystal field and the molecular field to adopt unique ground state in frustrated magnetic R2M2O7 pyrochlores structures is made by the variation of chemical pressure at R-site caused by substitution of nonmagnetic cation of M-site. Existence of larger cation at M-site increases the lattice parameter or nearest-neighbor bond distance between magnetic R-spins, and causes subtle changes to the local oxygen environment surrounding each R-ion, thereby reduces the chemical pressure at R-site which leads to a dramatic change in the crystal-field and molecular field. To investigate the effect of chemical pressure, the experimental results of powder magnetic susceptibility and isothermal magnetization of the frustrated compound Gd2Pb2O7 containing largest cation, e.g. lead (Pb), at M4+-sites were simulated and analyzed employing a D3d crystal-field (CF) and anisotropic molecular field at R-sites in the self- consistent mean-field approach. The second-ordered axial parameter B20 and total CF splitting of the ground multiplet Gd-ion in Gd2Pb2O7 are 477 cm-1 and 4.8 cm-1 respectively which are the lowest among their isomorphous counterparts, implying reduced effect of the crystal-field at Gd site in Gd2Pb2O7.

Epitaxial phase diagrams of SrTiO3, CaTiO3, and SrHfO3: Computational investigation including the role of antiferrodistortive and A -site displacement modes

NASA Astrophysics Data System (ADS)

Angsten, Thomas; Asta, Mark

2018-04-01

Ground-state epitaxial phase diagrams are calculated by density functional theory (DFT) for SrTiO3, CaTiO3, and SrHfO3 perovskite-based compounds, accounting for the effects of antiferrodistortive and A -site displacement modes. Biaxial strain states corresponding to epitaxial growth of (001)-oriented films are considered, with misfit strains ranging between -4 % and 4%. Ground-state structures are determined using a computational procedure in which input structures for DFT optimizations are identified as local minima in expansions of the total energy with respect to strain and soft-mode degrees of freedom. Comparison to results of previous DFT studies demonstrates the effectiveness of the computational approach in predicting ground-state phases. The calculated results show that antiferrodistortive octahedral rotations and associated A -site displacement modes act to suppress polarization and reduce the epitaxial strain energy. A projection of calculated atomic displacements in the ground-state epitaxial structures onto soft-mode eigenvectors shows that three ferroelectric and six antiferrodistortive displacement modes are dominant at all misfit strains considered, with the relative contributions from each varying systematically with the strain. Additional A -site displacement modes contribute to the atomic displacements in CaTiO3 and SrHfO3, which serve to optimize the coordination of the undersized A -site cation.

Vibration and Vibration-Torsion Levels of the S_{1} and Ground Cationic D_{0}^{+} States of Para-Fluorotoluene and Para-Xylene Below 1000 \\wn

NASA Astrophysics Data System (ADS)

Tuttle, William Duncan; Gardner, Adrian M.; Whalley, Laura E.; Wright, Timothy G.

2017-06-01

We have employed resonance-enhanced multiphoton ionisation (REMPI) spectroscopy and zero-kinetic-energy (ZEKE) spectroscopy to investigate the first excited electronic singlet (S_{1}) state and the cationic ground state (D_{0}^{+}) of para-fluorotoluene (pFT) and para-xylene (pXyl). Spectra have been recorded via a large number of selected intermediate levels, to support assignment of the vibration and vibration-torsion levels in these molecules and to investigate possible couplings. The study of levels in this region builds upon previous work on the lower energy regions of pFT and pXyl and here we are interested in how vibration-torsion (vibtor) levels might combine and interact with vibrational ones, and so we consider the possible couplings which occur. Comparisons between the spectra of the two molecules show a close correspondence, and the influence of the second methyl rotor in para-xylene on the onset of intramolecular vibrational redistribution (IVR) in the S_{1} state is a point of interest. This has bearing on future work which will need to consider the role of both more flexible side chains of substituted benzene molecules, and multiple side chains. A. M. Gardner, W. D. Tuttle, L. Whalley, A. Claydon, J. H. Carter and T. G. Wright, J. Chem. Phys., 145, 124307 (2016). A. M. Gardner, W. D. Tuttle, P. Groner and T. G. Wright, J. Chem. Phys., (2017, in press). W. D. Tuttle, A. M. Gardner, K. O'Regan, W. Malewicz and T. G. Wright, J. Chem. Phys., (2017, in press).

Evaluating the Nature of So-Called S*-State Feature in Transient Absorption of Carotenoids in Light-Harvesting Complex 2 (LH2) from Purple Photosynthetic Bacteria.

PubMed

Niedzwiedzki, Dariusz M; Hunter, C Neil; Blankenship, Robert E

2016-11-03

Carotenoids are a class of natural pigments present in all phototrophic organisms, mainly in their light-harvesting proteins in which they play roles of accessory light absorbers and photoprotectors. Extensive time-resolved spectroscopic studies of these pigments have revealed unexpectedly complex photophysical properties, particularly for carotenoids in light-harvesting LH2 complexes from purple bacteria. An ambiguous, optically forbidden electronic excited state designated as S* has been postulated to be involved in carotenoid excitation relaxation and in an alternative carotenoid-to-bacteriochlorophyll energy transfer pathway, as well as being a precursor of the carotenoid triplet state. However, no definitive and satisfactory origin of the carotenoid S* state in these complexes has been established, despite a wide-ranging series of studies. Here, we resolve the ambiguous origin of the carotenoid S* state in LH2 complex from Rba. sphaeroides by showing that the S* feature can be seen as a combination of ground state absorption bleaching of the carotenoid pool converted to cations and the Stark spectrum of neighbor neutral carotenoids, induced by temporal electric field brought by the carotenoid cation-bacteriochlorophyll anion pair. These findings remove the need to assign an S* state, and thereby significantly simplify the photochemistry of carotenoids in these photosynthetic antenna complexes.

Reduced graphene oxide and porphyrin. An interactive affair in 2-D.

PubMed

Wojcik, Aleksandra; Kamat, Prashant V

2010-11-23

Photoexcited cationic 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) (TMPyP) undergoes charge-transfer interaction with chemically reduced graphene oxide (RGO). Formation of the ground-state TMPyP-RGO complex in solution is marked by the red-shift of the porphyrin absorption band. This complexation was analyzed by Benesi-Hildebrand plot. Porphyrin fluorescence lifetime reduced from 5 to 1 ns upon complexation with RGO, indicating excited-state interaction between singlet excited porphyrin and RGO. Femtosecond transient absorption measurements carried out with TMPyP adsorbed on RGO film revealed fast decay of the singlet excited state, followed by the formation of a longer-living product with an absorption maximum around 515 nm indicating the formation of a porphyrin radical cation. The ability of TMPyP-RGO to undergo photoinduced charge separation was further confirmed from the photoelectrochemical measurements. TMPyP-RGO coated conducting glass electrodes are capable of generating photocurrent under visible excitation. These results are indicative of the electron transfer between photoexcited porphyrin and RGO. The role of graphene in accepting and shuttling electrons in light-harvesting assemblies is discussed.

Subfemtosecond quantum nuclear dynamics in water isotopomers.

PubMed

Rao, B Jayachander; Varandas, A J C

2015-05-21

Subfemtosecond quantum dynamics studies of all water isotopomers in the X̃ (2)B1 and à (2)A1 electronic states of the cation formed by Franck-Condon ionization of the neutral ground electronic state are reported. Using the ratio of the autocorrelation functions for the isotopomers as obtained from the solution of the time-dependent Schrödinger equation in a grid representation, high-order harmonic generation signals are calculated as a function of time. The results are found to be in agreement with the available experimental findings and with our earlier study for D2O(+)/H2O(+). Maxima are predicted in the autocorrelation function ratio at various times. Their origin and occurrence is explained by calculating expectation values of the bond lengths and bond angle of the water isotopomers as a function of time. The values so calculated for the (2)B1 and (2)A1 electronic states of the cation show quasiperiodic oscillations that can be associated with the time at which the nuclear wave packet reaches the minima of the potential energy surface, there being responsible for the peaks in the HHG signals.

Synchrotron-based valence shell photoionization of CH radical

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gans, B., E-mail: berenger.gans@u-psud.fr, E-mail: christian.alcaraz@u-psud.fr; Falvo, C.; Holzmeier, F.

2016-05-28

We report the first experimental observations of X{sup +} {sup 1}Σ{sup +}←X {sup 2}Π and a{sup +} {sup 3}Π←X {sup 2}Π single-photon ionization transitions of the CH radical performed on the DESIRS beamline at the SOLEIL synchrotron facility. The radical was produced by successive hydrogen-atom abstractions on methane by fluorine atoms in a continuous microwave discharge flow tube. Mass-selected ion yields and photoelectron spectra were recorded as a function of photon energy using a double imaging photoelectron/photoion coincidence spectrometer. The ion yield appears to be strongly affected by vibrational and electronic autoionizations, which allow the observation of high Rydberg statesmore » of the neutral species. The photoelectron spectra enable the first direct determinations of the adiabatic ionization potential and the energy of the first triplet state of the cation with respect to its singlet ground state. This work also brings valuable information on the complex electronic structure of the CH radical and its cation and adds new observations to complement our understanding of Rydberg states and autoionization processes.« less

Identification of four rotamers of m-methoxystyrene by resonant two-photon ionization and mass analyzed threshold ionization spectroscopy

NASA Astrophysics Data System (ADS)

Xu, Yanqi; Tzeng, Sheng Yuan; Shivatare, Vidya; Takahashi, Kaito; Zhang, Bing; Tzeng, Wen Bih

2015-03-01

We report the vibronic and cation spectra of four rotamers of m-methoxystyrene, recorded by using the two-color resonant two-photon ionization and mass-analyzed threshold ionization techniques. The excitation energies of the S1← S0 electronic transition are found to be 32 767, 32 907, 33 222, and 33 281 cm-1, and the corresponding adiabatic ionization energies are 65 391, 64 977, 65 114, and 64 525 cm-1 for these isomeric species. Most of the observed active vibrations in the electronically excited S1 and cationic ground D0 states involve in-plane ring deformation and substituent-sensitive bending motions. It is found that the relative orientation of the methoxyl with respect to the vinyl group does not influence the vibrational frequencies of the ring-substituent bending modes. The two dimensional potential energy surface calculations support our experimental finding that the isomerization is restricted in the S1 and D0 states.

Experimental and Quantum-Chemical Study of Electronically Excited States of Protolytic Isovanillin Species

NASA Astrophysics Data System (ADS)

Vusovich, O. V.; Tchaikovskaya, O. N.; Sokolova, I. V.; Vasil'eva, N. Yu.

2014-05-01

Methods of electronic spectroscopy and quantum chemistry are used to compare protolytic vanillin and isovanillin species. Three protolytic species: anion, cation, and neutral are distinguished in the ground state of the examined molecules. Vanillin and isovanillin in the ground state in water possess identical spectral characteristics: line positions and intensities in the absorption spectra coincide. Minima of the electrostatic potential demonstrate that the deepest isomer minimum is observed on the carbonyl oxygen atom. However, investigations of the fluorescence spectra show that the radiative properties of isomers differ. An analysis of results of quantum-chemical calculations demonstrate that the long-wavelength ππ* transition in the vanillin absorption spectra is formed due to electron charge transfer from the phenol part of the molecule to oxygen atoms of the methoxy and carbonyl groups, and in the isovanillin absorption spectra, it is formed only on the oxygen atom of the methoxy group. The presence of hydroxyl and carbonyl groups in the structure of the examined molecules leads to the fact that isovanillin in the ground S0 state, the same as vanillin, possesses acidic properties, whereas in the excited S1 state, they possess basic properties. A comparison of the рKа values of aqueous solutions demonstrates that vanillin possesses stronger acidic and basic properties in comparison with isovanillin.

High-resolution threshold photoionization of N2O

NASA Technical Reports Server (NTRS)

Wiedmann, R. T.; Grant, E. R.; Tonkyn, R. G.; White, M. G.

1991-01-01

Pulsed field ionization (PFI) has been used in conjunction with a coherent VUV source to obtain high-resolution threshold photoelectron spectra for the (000), (010), (020), and (100) vibrational states of the N2O(+) cation. Simulations for the rotational profiles of each vibronic level were obtained by fitting the Buckingham-Orr-Sichel equations using accurate spectroscopic constants for the ground states of the neutral and the ion. The relative branch intensities are interpreted in terms of the partial waves of the outgoing photoelectron to which the ionic core is coupled and in terms of the angular momentum transferred to the core.

Dissociation dynamics of 3- and 4-nitrotoluene radical cations: Coherently driven C-NO2 bond homolysis

NASA Astrophysics Data System (ADS)

Ampadu Boateng, Derrick; Gutsev, Gennady L.; Jena, Puru; Tibbetts, Katharine Moore

2018-04-01

Monosubstituted nitrotoluenes serve as important model compounds for nitroaromatic energetic molecules such as trinitrotoluene. This work investigates the ultrafast nuclear dynamics of 3- and 4-nitrotoluene radical cations using femtosecond pump-probe measurements and the results of density functional theory calculations. Strong-field adiabatic ionization of 3- and 4-nitrotoluene using 1500 nm, 18 fs pulses produces radical cations in the ground electronic state with distinct coherent vibrational excitations. In both nitrotoluene isomers, a one-photon excitation with the probe pulse results in NO2 loss to form C7H7+, which exhibits out-of-phase oscillations in yield with the parent molecular ion. The oscillations in 4-nitrotoluene with a period of 470 fs are attributed to the torsional motion of the NO2 group based on theoretical results showing that the dominant relaxation pathway in 4-nitrotoluene radical cations involves the rotation of the NO2 group away from the planar geometry. The distinctly faster oscillation period of 216 fs in 3-nitrotoluene is attributed to an in-plane bending motion of the NO2 and CH3 moieties based on analysis of the normal modes. These results demonstrate that coherent nuclear motions determine the probability of C-NO2 homolysis in the nitrotoluene radical cations upon optical excitation within several hundred femtoseconds of the initial ionization event.

First principles exploration of NiO and its ions NiO+ and NiO-

NASA Astrophysics Data System (ADS)

Sakellaris, Constantine N.; Mavridis, Aristides

2013-02-01

We present a high level ab initio study of NiO and its ions, NiO+ and NiO-. Employing variational multireference configuration interaction (MRCI) and single reference coupled-cluster methods combined with basis sets of quintuple quality, 54, 20, and 10 bound states of NiO, NiO+, and NiO- have been studied. For all these states, complete potential energy curves have been constructed at the MRCI level of theory; in addition, for the ground states of the three species core subvalence (3s23p6/Ni) and scalar relativistic effects have been taken into account. We report energetics, spectroscopic parameters, dipole moments, and spin-orbit coupling constants. The agreement with experiment is in the case of NiO good, but certain discrepancies that need further investigation have arisen in the case of the anion whose ground state remains computationally a tantalizing matter. The cation is experimentally almost entirely unexplored, therefore, the study of many states shall prove valuable to further investigators. The ground state symmetry, bond distances, and binding energies of NiO and NiO+ are (existing experimental values in parenthesis), X3Σ-(X3Σ-), re = 1.606 (1.62712) Å, D0 = 88.5 (89.2 ± 0.7) kcal/mol, and X4Σ-(?), re = 1.60(?) Å, D0 = 55 (62.4 ± 2.4) kcal/mol, respectively. The ground state of NiO- is 4Σ- (but 2Π experimentally) with D0 = 85-87 (89.2 ± 0.7) kcal/mol.

Hydrochemistry of the Mahomet Bedrock Valley Aquifer, East-Central Illinois: indicators of recharge and ground-water flow

USGS Publications Warehouse

Panno, S.V.; Hackley, Keith C.; Cartwright, K.; Liu, Chao-Li

1994-01-01

A conceptual model of the ground-water flow and recharge to the Mahomet Bedrock Valley Aquifer (MVA), east-central Illinois, was developed using major ion chemistry and isotope geochemistry. The MVA is a 'basal' fill in the east-west trending buried bedrock valley composed of clean, permeable sand and gravel to thicknesses of up to 61 m. It is covered by a thick sequence of glacial till containing thinner bodies of interbedded sand and gravel. Ground water from the MVA was found to be characterized by clearly defined geochemical regions with three distinct ground-water types. A fourth ground-water type was found at the confluence of the MVA and the Mackinaw Bedrock Valley Aquifer (MAK) to the west. Ground water in the Onarga Valley, a northeastern tributary of the MVA, is of two types, a mixed cation-SO42- type and a mixed cation-HCO3- type. The ground water is enriched in Na+, Ca2+, Mg2+, and SO42- which appears to be the result of an upward hydraulic gradient and interaction of deeper ground water with oxidized pyritic coals and shale. We suggest that recharge to the Onarga Valley and overlying aquifers is 100% from bedrock (leakage) and lateral flow from the MVA to the south. The central MVA (south of the Onarga Valley) is composed of relatively dilute ground water of a mixed cation-HCO3- type, with low total dissolved solids, and very low concentrations of Cl- and SO42-. Stratigraphic relationships of overlying aquifers and ground-water chemistry of these and the MVA suggest recharge to this region of the MVA (predominantly in Champaign County) is relatively rapid and primarily from the surface. Midway along the westerly flow path of the MVA (western MVA), ground water is a mixed cation-HCO3- type with relatively high Cl-, where Cl- increases abruptly by one to ??? two orders of magnitude. Data suggest that the increase in Cl- is the result of leakage of saline ground water from bedrock into the MVA. Mass-balance calculations indicate that approximately 9.5% of recharge in this area is from bedrock. Concentrations of Na+, HCO3-, As, and TDS also increase in the western MVA. Ground water in the MAK is of a Ca2+-HCO3- type. Mass-balance calculations, using Cl- as a natural, conservative tracer, indicate that approximately 17% of the ground water flowing from the confluence area is derived from the MVA.

Vibronic relaxation dynamics of o-dichlorobenzene in its lowest excited singlet state

NASA Astrophysics Data System (ADS)

Liu, Benkang; Zhao, Haiyan; Lin, Xiang; Li, Xinxin; Gao, Mengmeng; Wang, Li; Wang, Wei

2018-01-01

Vibronic dynamics of o-dichlorobenzene in its lowest excited singlet state, S1, is investigated in real time by using femtosecond pump-probe method, combined with time-of-flight mass spectroscopy and photoelectron velocity mapping technique. Relaxation processes for the excitation in the range of 276-252 nm can be fitted by single exponential decay model, while in the case of wavelength shorter than 252 nm two-exponential decay model must be adopted for simulating transient profiles. Lifetime constants of the vibrationally excited S1 states change from 651 ± 10 ps for 276 nm excitation to 61 ± 1 ps for 242 nm excitation. Both the internal conversion from the S1 to the highly vibrationally excited ground state S0 and the intersystem crossing from the S1 to the triplet state are supposed to play important roles in de-excitation processes. Exponential fitting of the de-excitation rates on the excitation energy implies such de-excitation process starts from the highly vibrationally excited S0 state, which is validated, by probing the relaxation following photoexcitation at 281 nm, below the S1 origin. Time-dependent photoelectron kinetic energy distributions have been obtained experimentally. As the excitation wavelength changes from 276 nm to 242 nm, different cationic vibronic vibrations can be populated, determined by the Franck-Condon factors between the large geometry distorted excited singlet states and final cationic states.

Primary photophysical properties of moxifloxacin--a fluoroquinolone antibiotic.

PubMed

Lorenzo, Fernando; Navaratnam, Suppiah; Edge, Ruth; Allen, Norman S

2008-01-01

The photophysical properties of the fluoroquinolone antibiotic moxifloxacin (MOX) were investigated in aqueous media. MOX in water, at pH 7.4, shows two intense absorption bands at 287 and 338 nm (epsilon = 44,000 and 17,000 dm(3) mol(-1) cm(-1), respectively). The absorption and emission properties of MOX are pH-dependent, pK(a) values for the protonation equilibria of both the ground (6.1 and 9.6) and excited singlet states (6.8 and 9.1) of MOX were determined spectroscopically. MOX fluoresces weakly, the quantum yield for fluorescence emission being maximum (0.07) at pH 8. Phosphorescence from the excited triplet state in frozen ethanol solution has a quantum yield of 0.046. Laser flash photolysis and pulse radiolysis studies have been carried out to characterize the transient species of MOX in aqueous solution. On laser excitation, MOX undergoes monophotonic photoionization with a quantum yield of 0.14. This leads to the formation of a long-lived cation radical whose absorption is maximum at 470 nm (epsilon(470) = 3400 dm(3) mol(-1) cm(-1)). The photoionization process releases hydrated electron which rapidly reacts (k = 2.8 x 10(10) dm(3) mol(-1) s(-1)) with ground state MOX, yielding a long-lived anion radical with maximum absorption at 390 nm (epsilon(390) = 2400 dm(3) mol(-1) cm(-1)). The cation radical of MOX is able to oxidize protein components tryptophan and tyrosine. The bimolecular rate constants for these reactions are 2.3 x 10(8) dm(3) mol(-1) s(-1) and 1.3 x 10(8) dm(3) mol(-1) s(-1), respectively. Singlet oxygen sensitized by the MOX triplet state was also detected only in oxygen-saturated D(2)O solutions, with a quantum yield of 0.075.

VUV Absorption Spectra of Gas-Phase Quinoline in the 3.5 - 10.7 eV Photon Energy Range.

PubMed

Leach, Sydney; Jones, Nykola C; Hoffmann, Søren Vrønning; Un, Sun

2018-06-16

The absorption spectrum of quinoline was measured in the gas phase between 3.5 and 10.7 eV using a synchrotron photon source. A large number of sharp and broad spectral features were observed, some of which have plasmon-type collective π-electron modes contributing to their intensities. Eight valence electronic transitions were assigned, considerably extending the number of π-π* transitions previously observed mainly in solution. The principal factor in solution red-shifts is found to be the Lorentz-Lorenz polarizability parameter. Rydberg bands, observed for the first time, are analysed into eight different series, converging to the D0 ground and two excited electronic states, D3 and D4, of the quinoline cation. The R1 series limit is 8.628 eV for the first ionization energy of quinoline, a value more precise than previously published. This value, combined with cation electronic transition data provides precise energies, respectively 10.623 eV and 11.355 eV, for the D3 and D4 states. The valence transition assignments are based on DFT calculations as well as on earlier Pariser-Parr-Pople SCF LCAO MO results. The relative quality of the P-P-P and DFT data is discussed. Both are far from spectroscopic accuracy concerning electronic excited states but were nevertheless useful for our assignments. Our time-dependent DFT calculations of quinoline are excellent for its ground state properties such as geometry, rotational constants, dipole moment and vibrational frequencies, which agree well with experimental observations. Vibrational components of the valence and Rydberg transitions mainly involve C-H bend and C=C and C=N stretch modes. Astrophysical applications of the VUV absorption of quinoline are briefly discussed.

Electrostatically driven resonance energy transfer in “cationic” biocompatible indium phosphide quantum dots† †Electronic supplementary information (ESI) available: Detailed experimental methods, the synthesis and characterization of QDs, bioimaging, stability studies, control experiments, and the calculation of various parameters involved in the resonance energy transfer process etc. See DOI: 10.1039/c7sc00592j Click here for additional data file.

PubMed Central

Devatha, Gayathri; Roy, Soumendu; Rao, Anish; Mallick, Abhik; Basu, Sudipta

2017-01-01

Indium Phosphide Quantum Dots (InP QDs) have emerged as an alternative to toxic metal ion based QDs in nanobiotechnology. The ability to generate cationic surface charge, without compromising stability and biocompatibility, is essential in realizing the full potential of InP QDs in biological applications. We have addressed this challenge by developing a place exchange protocol for the preparation of cationic InP/ZnS QDs. The quaternary ammonium group provides the much required permanent positive charge and stability to InP/ZnS QDs in biofluids. The two important properties of QDs, namely bioimaging and light induced resonance energy transfer, are successfully demonstrated in cationic InP/ZnS QDs. The low cytotoxicity and stable photoluminescence of cationic InP/ZnS QDs inside cells make them ideal candidates as optical probes for cellular imaging. An efficient resonance energy transfer (E ∼ 60%) is observed, under physiological conditions, between the cationic InP/ZnS QD donor and anionic dye acceptor. A large bimolecular quenching constant along with a linear Stern–Volmer plot confirms the formation of a strong ground state complex between the cationic InP/ZnS QDs and the anionic dye. Control experiments prove the role of electrostatic attraction in driving the light induced interactions, which can rightfully form the basis for future nano-bio studies between cationic InP/ZnS QDs and anionic biomolecules. PMID:28626557

H2O Nucleation Around Noble Metal Cations

NASA Astrophysics Data System (ADS)

Calaminici, Patrizia; Oropeza Alfaro, Pavel; Juarez Flores, Martin; Köster, Andreas; Beltran, Marcela; Ulises Reveles, J.; Khanna, Shiv N.

2008-03-01

First principle electronic structure calculations have been carried out to investigate the ground state geometry, electronic structure and binding energy of noble metal cations (H2O)n^+ clusters containing up to 10 H2O molecules. The calculations are performed with the density functional theory code deMon2k [1]. Due to the very flat potential energy surface of these systems special care to the numerical stability of energy and gradient calculation must be taken.Comparison of the results obtained with Cu^+, Ag^+ and Au^+ will be shown. This investigation provides insight into the structural arrangement of the water molecules around these metals and a microscopic understanding of the observed incremental binding energy in the case of the gold cation based on collision induced dissociation experiments. [1] A.M. Köster, P. Calaminici, M.E. Casida, R. Flores-Moreno, G. Geudtner, A. Goursot, T. Heine, A. Ipatov, F. Janetzko, J. Martin del Campo, S. Patchkovski, J.U. Reveles, A. Vela and D.R. Salahub, deMon2k, The deMon Developers, Cinvestav, 2006

Evaluating the nature of so-called S*-State feature in transient absorption of carotenoids in light-harvesting complex 2 (LH2) from purple photosynthetic bacteria

DOE PAGES

Niedzwiedzki, Dariusz M.; Hunter, C. Neil; Blankenship, Robert E.

2016-10-11

Carotenoids are a class of natural pigments present in all phototrophic organisms, mainly in their light-harvesting proteins in which they play roles of accessory light absorbers and photoprotectors. Extensive time-resolved spectroscopic studies of these pigments have revealed unexpectedly complex photophysical properties, particularly for carotenoids in light-harvesting LH2 complexes from purple bacteria. An ambiguous, optically forbidden electronic excited state designated as S* has been postulated to be involved in carotenoid excitation relaxation and in an alternative carotenoid-to-bacteriochlorophyll energy transfer pathway, as well as being a precursor of the carotenoid triplet state. However, no definitive and satisfactory origin of the carotenoid S*more » state in these complexes has been established, despite a wide-ranging series of studies. Here, we resolve the ambiguous origin of the carotenoid S* state in LH2 complex from Rba. sphaeroides by showing that the S* feature can be seen as a combination of ground state absorption bleaching of the carotenoid pool converted to cations and the Stark spectrum of neighbor neutral carotenoids, induced by temporal electric field brought by the carotenoid cation- bacteriochlorophyll anion pair. Lastly, these findings remove the need to assign an S* state, and thereby significantly simplify the photochemistry of carotenoids in these photosynthetic antenna complexes.« less

Evaluating the nature of so-called S*-State feature in transient absorption of carotenoids in light-harvesting complex 2 (LH2) from purple photosynthetic bacteria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Niedzwiedzki, Dariusz M.; Hunter, C. Neil; Blankenship, Robert E.

Carotenoids are a class of natural pigments present in all phototrophic organisms, mainly in their light-harvesting proteins in which they play roles of accessory light absorbers and photoprotectors. Extensive time-resolved spectroscopic studies of these pigments have revealed unexpectedly complex photophysical properties, particularly for carotenoids in light-harvesting LH2 complexes from purple bacteria. An ambiguous, optically forbidden electronic excited state designated as S* has been postulated to be involved in carotenoid excitation relaxation and in an alternative carotenoid-to-bacteriochlorophyll energy transfer pathway, as well as being a precursor of the carotenoid triplet state. However, no definitive and satisfactory origin of the carotenoid S*more » state in these complexes has been established, despite a wide-ranging series of studies. Here, we resolve the ambiguous origin of the carotenoid S* state in LH2 complex from Rba. sphaeroides by showing that the S* feature can be seen as a combination of ground state absorption bleaching of the carotenoid pool converted to cations and the Stark spectrum of neighbor neutral carotenoids, induced by temporal electric field brought by the carotenoid cation- bacteriochlorophyll anion pair. Lastly, these findings remove the need to assign an S* state, and thereby significantly simplify the photochemistry of carotenoids in these photosynthetic antenna complexes.« less

Electronic structure of the [MNH2]+ (M = Sc-Cu) complexes.

PubMed

Hendrickx, Marc F A; Clima, Sergiu

2006-11-23

B3LYP geometry optimizations for the [MNH2]+ complexes of the first-row transition metal cations (Sc+-Cu+) were performed. Without any exception the ground states of these unsaturated amide complexes were calculated to possess planar geometries. CASPT2 binding energies that were corrected for zero-point energies and including relativistic effects show a qualitative trend across the series that closely resembles the experimental observations. The electronic structures for the complexes of the early and middle transition metal cations (Sc+-Co+) differ from the electronic structures derived for the complexes of the late transition metal cations (Ni+ and Cu+). For the former complexes the relative higher position of the 3d orbitals above the singly occupied 2p(pi) HOMO of the uncoordinated NH2 induces an electron transfer from the 3d shell to 2p(pi). The stabilization of the 3d orbitals from the left to the right along the first-row transition metal series causes these orbitals to become situated below the HOMO of the NH2 ligand for Ni+ and Cu+, preventing a transfer from occurring in the [MNH2]+ complexes of these metal cations. Analysis of the low-lying states of the amide complexes revealed a rather unique characteristic of their electronic structures that was found across the entire series. Rather exceptionally for the whole of chemistry, pi-type interactions were calculated to be stronger than the corresponding sigma-type interactions. The origin of this extraordinary behavior can be ascribed to the low-lying sp2 lone pair orbital of the NH2 ligand with respect to the 3d level.

A photoelectron spectroscopic investigation of vinyl fluoride (C2H3F): the HeI, threshold and CIS photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Locht, R.; Leyh, B.; Dehareng, D.; Hottmann, K.; Baumgärtel, H.

2010-01-01

The threshold photoelectron spectrum (TPES) and the constant ion state (CIS) spectra of the individual ionic states of C2H3F have been recorded using synchrotron radiation. For comparison a well-resolved HeI photoelectron spectrum (HeI-PES) has also been measured and analysed in detail. The TPES has been measured between 9.5 eV and 35 eV photon energy. Numerous vibrational structures, reported for the first time, observed in the ground state and the six excited states of the cation are analysed. Quantum chemical calculations have been performed and provide strong support to the assignments. State-selected CIS spectra highlighted the major importance of autoionization for the production of almost all ionized states of C2H3F observed in this work.

Prototype electrostatic ground state approach to predicting crystal structures of ionic compounds: Application to hydrogen storage materials

NASA Astrophysics Data System (ADS)

Majzoub, E. H.; Ozoliņš, V.

2008-03-01

We have developed a procedure for crystal structure generation and prediction for ionic compounds consisting of a collection of cations and rigid complex anions. Our approach is based on global optimization of an energy functional consisting of the electrostatic and soft-sphere repulsive energies using Metropolis Monte Carlo (MMC) simulated annealing in conjunction with smoothing of the potential energy landscape via the distance scaling method. The resulting structures, or prototype electrostatic ground states (PEGS), are subsequently relaxed using first-principles density-functional theory (DFT) calculations to obtain accurate structural parameters and thermodynamic properties. This method is shown to produce the ground state structures of NaAlH4 and Mg(AlH4)2 , as well as the mixed cation alanate K2LiAlH6 . For LiAlH4 , the PEGS search produces a structure with a static DFT total energy equal to that of the experimentally observed structure; the latter is stabilized by vibrational contributions to the free energy. For mixed-valence hexa-alanates, XY AlH6 , where X=(Li,Na,K) , and Y=(Mg,Ca) , the PEGS method predicts six unsuspected structure types, which are not found in the existing structure databases. The PEGS search yields energies that are, on the average, better than the best database structures with the same number of atoms per unit cell, demonstrating the predictive power and usefulness of the PEGS structures. In addition to the recently synthesized LiMgAlH6 compound, we predict that LiCaAlH6 , NaCaAlH6 , and KCaAlH6 are also thermodynamically stable with respect to phase separation into other alanates and metal hydrides. In contrast, NaMgAlH6 and KMgAlH6 are slightly unstable (by less than 3kJ/mol ) relative to the phase separation into NaAlH4 , KAlH4 , and MgH2 . We suggest that solid-state ion-exchange reactions between X3AlH6 (X=Li,Na,K) and YCl2 (Y=Mg,Ca) could be used to synthesize the predicted mixed-valence hexa-alanates.

Search for an explanation for neutralization rates of atomic ion-ion reactions

NASA Astrophysics Data System (ADS)

Miller, Thomas M.; Wiens, Justin P.; Shuman, Nicholas S.; Viggiano, Albert A.

2016-09-01

We have measured well over a hundred rate coefficients k for cation-anion mutual neutralization reactions at thermal energies. For molecular ions, the k at 300 K tend not to vary more than a factor of two or three, presumably because a great many neutral states cross the incoming Coulombic potential energy curve. Atomic-atomic systems, for which there are few favorable curve crossings between the neutral and Coulombic curves, show variation of at least a factor of 60 in the measured k values at 300 K. For reactions involving the noble-gas cations, we assume that the final state is the lowest excited state of the neutral, plus the ground state of the neutralized anion, because otherwise the crossing distance R is so small that the curve-crossing probability is nil. We plotted measured k values (in cm3/s) vs the distance R (in bohr) at which the neutral and Coulombic curves cross, the found that the data are fairly well fit by a power law for k, 10-4R - 2 . 8 . The question is, is there a physical explanation for the observed dependence on R? We will discuss the data and the expectations of Landau-Zener theory. Supported by Air Force Office of Scientific Research (AFOSR-2303EP).

Kinetics of First-Row Transition Metal Cations (V+, Fe+, Co+) with OCS at Thermal Energies.

PubMed

Sweeny, Brendan C; Ard, Shaun G; Shuman, Nicholas S; Viggiano, Albert A

2018-05-03

The temperature-dependent kinetics for reactions of V + , Fe + , and Co + with OCS are measured using a selected ion flow tube apparatus heated to 300-600 K. All three reactions proceed solely by C-S activation at thermal energies, resulting in metal sulfide cation formation. Previously calculated reaction pathways were employed to inform statistical modeling of these reactions for comparison to the data. As surmised previously, all three reactions at thermal energies require spin crossing, with the Fe + reaction crossing once circumventing a prohibitive transition state, before crossing again to form ground state products. The Fe + and Co + reaction efficiencies increase with energy. For the Co + reaction, and to a lesser extent the Fe + reaction, the apparent activation energies are less than the reaction endothermicities, possibly indicating increasing diabatic behavior of the spin crossings with energy. The V + reaction was well modeled assuming an entirely adiabatic spin crossing, such that the resultant avoided crossing behaves similarly to a tight transition state. The subsequent reaction of VS + with OCS producing VS 2 + is also investigated; the rate-limiting transition state energy derived from statistical modeling is poorly reproduced by quantum calculations using a variety of methods, highlighting the large (1-2 eV) uncertainty in calculated energetics of transition-metal containing species.

Density functional theory and Raman spectroscopy applied to structure and vibrational mode analysis of 1,1',3,3'-tetraethyl-5,5',6,6'-tetrachloro- benzimidazolocarbocyanine iodide and its aggregate.

PubMed

Aydin, Metin; Dede, Özge; Akins, Daniel L

2011-02-14

We have measured electronic and Raman scattering spectra of 1,1',3,3'-tetraethyl-5,5',6,6'-tetrachloro-benzimidazolocarbocyanine iodide (TTBC) in various environments, and we have calculated the ground state geometric and spectroscopic properties of the TTBC cation in the gas and solution phases (e.g., bond distances, bond angles, charge distributions, and Raman vibrational frequencies) using density functional theory. Our structure calculations have shown that the ground state equilibrium structure of a cis-conformer lies ∼200 cm(-1) above that of a trans-conformer and both conformers have C(2) symmetry. Calculated electronic transitions indicate that the difference between the first transitions of the two conformers is about 130 cm(-1). Raman spectral assignments of monomeric- and aggregated-TTBC cations have been aided by density functional calculations at the same level of the theory. Vibrational mode analyses of the calculated Raman spectra reveal that the observed Raman bands above 700 cm(-1) are mainly associated with the in-plane deformation of the benzimidazolo moieties, while bands below 700 cm(-1) are associated with out-of-plane deformations of the benzimidazolo moieties. We have also found that for the nonresonance excited experimental Raman spectrum of aggregated-TTBC cation, the Raman bands in the higher-frequency region are enhanced compared with those in the nonresonance spectrum of the monomeric cation. For the experimental Raman spectrum of the aggregate under resonance excitation, however, we find new Raman features below 600 cm(-1), in addition to a significantly enhanced Raman peak at 671 cm(-1) that are associated with out-of-plane distortions. Also, time-dependent density functional theory calculations suggest that the experimentally observed electronic transition at ∼515 nm (i.e., 2.41 eV) in the absorption spectrum of the monomeric-TTBC cation predominantly results from the π → π∗ transition. Calculations are further interpreted as indicating that the observed shoulder in the absorption spectrum of TTBC in methanol at 494 nm (i.e., 2.51 eV) likely results from the ν(") = 0 → ν' = 1 transition and is not due to another electronic transition of the trans-conformer-despite the fact that measured and calculated NMR results (not provided here) support the prospect that the shoulder might be attributable to the 0-0 band of the cis-conformer.

Metal cation dependence of interactions with amino acids: bond dissociation energies of Rb(+) and Cs(+) to the acidic amino acids and their amide derivatives.

PubMed

Armentrout, P B; Yang, Bo; Rodgers, M T

2014-04-24

Metal cation-amino acid interactions are key components controlling the secondary structure and biological function of proteins, enzymes, and macromolecular complexes comprising these species. Determination of pairwise interactions of alkali metal cations with amino acids provides a thermodynamic vocabulary that begins to quantify these fundamental processes. In the present work, we expand a systematic study of such interactions by examining rubidium and cesium cations binding with the acidic amino acids (AA), aspartic acid (Asp) and glutamic acid (Glu), and their amide derivatives, asparagine (Asn) and glutamine (Gln). These eight complexes are formed using electrospray ionization and their bond dissociation energies (BDEs) are determined experimentally using threshold collision-induced dissociation with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy-dependent cross sections include consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. Quantum chemical calculations are conducted at the B3LYP, MP2(full), and M06 levels of theory using def2-TZVPPD basis sets, with results showing reasonable agreement with experiment. At 0 and 298 K, most levels of theory predict that the ground-state conformers for M(+)(Asp) and M(+)(Asn) involve tridentate binding of the metal cation to the backbone carbonyl, amino, and side-chain carbonyl groups, although tridentate binding to the carboxylic acid group and side-chain carbonyl is competitive for M(+)(Asn). For the two longer side-chain amino acids, Glu and Gln, multiple structures are competitive. A comparison of these results to those for the smaller alkali cations, Na(+) and K(+), provides insight into the trends in binding energies associated with the molecular polarizability and dipole moment of the side chain. For all four metal cations, the BDEs are inversely correlated with the size of the metal cation and follow the order Asp < Glu < Asn < Gln.

Vibrational structure of vinyl chloride cation studied by using one-photon zero-kinetic energy photoelectron spectroscopy.

PubMed

Zhang, Ping; Li, Juan; Mo, Yuxiang

2007-09-06

The vibrational structure of vinyl chloride cation, CH(2)CHCl+ (X(2)A' '), has been studied by vacuum ultraviolet (VUV) zero-kinetic energy (ZEKE) photoelectron spectroscopy. Among nine symmetric vibrational modes, the fundamental frequencies of six modes have been determined. The first overtone of the out-of-plane CH(2) twist vibrational mode has been also measured. In addition to these, the combination and overtone bands of the above vibrational modes about 4500 cm(-1) above the ground state have been observed in the ZEKE spectrum. The vibrational band intensities of the ZEKE spectrum can be described approximately by the Franck-Condon factors with harmonic approximation. The ZEKE spectrum has been assigned based on the harmonic frequencies and Franck-Condon factors from theoretical calculations. The ionization energy (IE) of CH(2)CHCl is determined as 80705.5 +/- 2.5 (cm(-1)) or 10.0062 +/- 0.0003 (eV).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tokár, K.; Derian, R.; Mitas, L.

Using explicitly correlated fixed-node quantum Monte Carlo and density functional theory (DFT) methods, we study electronic properties, ground-state multiplets, ionization potentials, electron affinities, and low-energy fragmentation channels of charged half-sandwich and multidecker vanadium-benzene systems with up to 3 vanadium atoms, including both anions and cations. It is shown that, particularly in anions, electronic correlations play a crucial role; these effects are not systematically captured with any commonly used DFT functionals such as gradient corrected, hybrids, and range-separated hybrids. On the other hand, tightly bound cations can be described qualitatively by DFT. A comparison of DFT and quantum Monte Carlo providesmore » an in-depth understanding of the electronic structure and properties of these correlated systems. The calculations also serve as a benchmark study of 3d molecular anions that require a balanced many-body description of correlations at both short- and long-range distances.« less

The geochemical evolution of aqueous sodium in the Black Creek Aquifer, Horry and Georgetown counties, South Carolina

USGS Publications Warehouse

Zack, Allen L.; Roberts, Ivan

1988-01-01

The Black Creek aquifer contains dilute seawater near the North Carolina State line, probably the result of incomplete flushing of ancient seawater. Data do not indicate that the dilute seawater has migrated toward areas of fresh ground-water withdrawals. The concentration of chloride in ground-water samples ranges from 5 to 720 milligrams per liter and that of sodium from 160 to 690 milligrams per liter. Ion-exchange reactions (sodium for calcium and fluoride for hydroxyl) occur with the calcium carbonate dissolution reaction which produces calcium, bicarbonate, and hydroxyl ions. The reaction sequence and stoichiometry result in an aqueous solution in which the sum of bicarbonate and chloride equivalents per liter is equal to the equivalents per liter of sodium. Calcium ions are exchanged for sodium ions derived from sodium-rich clays upgradient of the dilute seawater. The cation-exchange reaction equilibrates at a sodium concentration of 280 milligrams per liter. Amounts of sodium greater than 280 milligrams per liter are contributed from dilute seawater. The cation-exchange reaction approaches an equilibrium which represents a mass-action limit in terms of the ratio of sodium to calcium in solution versus the ratio of exchangeable sodium to calcium on clay surfaces. Where the limit of calcium carbonate solubility is approached and dissolution ceases, some precipitation of calcite probably takes place. The dissolution of calcite exposes fossil shark teeth which release fluoride ions to the ground water through anion exchange with aqueous hydroxyl ions.

Proton Transfers in a Channelrhodopsin-1 Studied by Fourier Transform Infrared (FTIR) Difference Spectroscopy and Site-directed Mutagenesis*

PubMed Central

Ogren, John I.; Yi, Adrian; Mamaev, Sergey; Li, Hai; Spudich, John L.; Rothschild, Kenneth J.

2015-01-01

Channelrhodopsin-1 from the alga Chlamydomonas augustae (CaChR1) is a low-efficiency light-activated cation channel that exhibits properties useful for optogenetic applications such as a slow light inactivation and a red-shifted visible absorption maximum as compared with the more extensively studied channelrhodopsin-2 from Chlamydomonas reinhardtii (CrChR2). Previously, both resonance Raman and low-temperature FTIR difference spectroscopy revealed that unlike CrChR2, CaChR1 under our conditions exhibits an almost pure all-trans retinal composition in the unphotolyzed ground state and undergoes an all-trans to 13-cis isomerization during the primary phototransition typical of other microbial rhodopsins such as bacteriorhodopsin (BR). Here, we apply static and rapid-scan FTIR difference spectroscopy along with site-directed mutagenesis to characterize the proton transfer events occurring upon the formation of the long-lived conducting P2380 state of CaChR1. Assignment of carboxylic C=O stretch bands indicates that Asp-299 (homolog to Asp-212 in BR) becomes protonated and Asp-169 (homolog to Asp-85 in BR) undergoes a net change in hydrogen bonding relative to the unphotolyzed ground state of CaChR1. These data along with earlier FTIR measurements on the CaChR1 → P1 transition are consistent with a two-step proton relay mechanism that transfers a proton from Glu-169 to Asp-299 during the primary phototransition and from the Schiff base to Glu-169 during P2380 formation. The unusual charge neutrality of both Schiff base counterions in the P2380 conducting state suggests that these residues may function as part of a cation selective filter in the open channel state of CaChR1 as well as other low-efficiency ChRs. PMID:25802337

Proton transfers in a channelrhodopsin-1 studied by Fourier transform infrared (FTIR) difference spectroscopy and site-directed mutagenesis.

PubMed

Ogren, John I; Yi, Adrian; Mamaev, Sergey; Li, Hai; Spudich, John L; Rothschild, Kenneth J

2015-05-15

Channelrhodopsin-1 from the alga Chlamydomonas augustae (CaChR1) is a low-efficiency light-activated cation channel that exhibits properties useful for optogenetic applications such as a slow light inactivation and a red-shifted visible absorption maximum as compared with the more extensively studied channelrhodopsin-2 from Chlamydomonas reinhardtii (CrChR2). Previously, both resonance Raman and low-temperature FTIR difference spectroscopy revealed that unlike CrChR2, CaChR1 under our conditions exhibits an almost pure all-trans retinal composition in the unphotolyzed ground state and undergoes an all-trans to 13-cis isomerization during the primary phototransition typical of other microbial rhodopsins such as bacteriorhodopsin (BR). Here, we apply static and rapid-scan FTIR difference spectroscopy along with site-directed mutagenesis to characterize the proton transfer events occurring upon the formation of the long-lived conducting P2 (380) state of CaChR1. Assignment of carboxylic C=O stretch bands indicates that Asp-299 (homolog to Asp-212 in BR) becomes protonated and Asp-169 (homolog to Asp-85 in BR) undergoes a net change in hydrogen bonding relative to the unphotolyzed ground state of CaChR1. These data along with earlier FTIR measurements on the CaChR1 → P1 transition are consistent with a two-step proton relay mechanism that transfers a proton from Glu-169 to Asp-299 during the primary phototransition and from the Schiff base to Glu-169 during P2 (380) formation. The unusual charge neutrality of both Schiff base counterions in the P2 (380) conducting state suggests that these residues may function as part of a cation selective filter in the open channel state of CaChR1 as well as other low-efficiency ChRs. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pandit, Shubhrangshu; Preston, Thomas J.; Orr-Ewing, Andrew J., E-mail: a.orr-ewing@bristol.ac.uk

Photodissociation of gaseous bromocyclopropane via its A-band continuum has been studied at excitation wavelengths ranging from 230 nm to 267 nm. Velocity-map images of ground-state bromine atoms (Br), spin-orbit excited bromine atoms (Br{sup ∗}), and C{sub 3}H{sub 5} hydrocarbon radicals reveal the kinetic energies of these various photofragments. Both Br and Br{sup ∗} atoms are predominantly generated via repulsive excited electronic states in a prompt photodissociation process in which the hydrocarbon co-fragment is a cyclopropyl radical. However, the images obtained at the mass of the hydrocarbon radical fragment identify a channel with total kinetic energy greater than that deduced frommore » the Br and Br{sup ∗} images, and with a kinetic energy distribution that exceeds the energetic limit for Br + cyclopropyl radical products. The velocity-map images of these C{sub 3}H{sub 5} fragments have lower angular anisotropies than measured for Br and Br{sup ∗}, indicating molecular restructuring during dissociation. The high kinetic energy C{sub 3}H{sub 5} signals are assigned to allyl radicals generated by a minor photochemical pathway which involves concerted C–Br bond dissociation and cyclopropyl ring-opening following single ultraviolet (UV)-photon absorption. Slow photofragments also contribute to the velocity map images obtained at the C{sub 3}H{sub 5} radical mass, but the corresponding slow Br atoms are not observed. These features in the images are attributed to C{sub 3}H{sub 5}{sup +} from the photodissociation of the C{sub 3}H{sub 5}Br{sup +} molecular cation following two-photon ionization of the parent compound. This assignment is confirmed by 118-nm vacuum ultraviolet ionization studies that prepare the molecular cation in its ground electronic state prior to UV photodissociation.« less

Evidence for concerted ring opening and C-Br bond breaking in UV-excited bromocyclopropane.

PubMed

Pandit, Shubhrangshu; Preston, Thomas J; King, Simon J; Vallance, Claire; Orr-Ewing, Andrew J

2016-06-28

Photodissociation of gaseous bromocyclopropane via its A-band continuum has been studied at excitation wavelengths ranging from 230 nm to 267 nm. Velocity-map images of ground-state bromine atoms (Br), spin-orbit excited bromine atoms (Br(∗)), and C3H5 hydrocarbon radicals reveal the kinetic energies of these various photofragments. Both Br and Br(∗) atoms are predominantly generated via repulsive excited electronic states in a prompt photodissociation process in which the hydrocarbon co-fragment is a cyclopropyl radical. However, the images obtained at the mass of the hydrocarbon radical fragment identify a channel with total kinetic energy greater than that deduced from the Br and Br(∗) images, and with a kinetic energy distribution that exceeds the energetic limit for Br + cyclopropyl radical products. The velocity-map images of these C3H5 fragments have lower angular anisotropies than measured for Br and Br(∗), indicating molecular restructuring during dissociation. The high kinetic energy C3H5 signals are assigned to allyl radicals generated by a minor photochemical pathway which involves concerted C-Br bond dissociation and cyclopropyl ring-opening following single ultraviolet (UV)-photon absorption. Slow photofragments also contribute to the velocity map images obtained at the C3H5 radical mass, but the corresponding slow Br atoms are not observed. These features in the images are attributed to C3H5 (+) from the photodissociation of the C3H5Br(+) molecular cation following two-photon ionization of the parent compound. This assignment is confirmed by 118-nm vacuum ultraviolet ionization studies that prepare the molecular cation in its ground electronic state prior to UV photodissociation.

Experimental and Computational Investigations of the Threshold Photoelectron Spectrum of the HCCN Radical

NASA Astrophysics Data System (ADS)

Gans, B.; Falvo, Cyril; Coudert, L. H.; Garcia, Gustavo A.; Küger, J.; Loison, J.-C.

2017-06-01

The HCCN radical, already detected in the interstellar medium, is also important for nitrile chemistry in Titan's atmosphere. Quite recently the photoionization spectrum of the radical has been recorded using mass selected threshold photoelectron (TPE) spectroscopy and this provided us with the first spectroscopic information about the HCCN} cation. Modeling such a spectrum requires accounting for the non-rigidity of HCCN and for the Renner-Teller effect in HCCN+. In its ^3A'' electronic ground state, HCCN is a non-rigid molecule as the potential for the \\angle{HCC} bending angle is very shallow. Vibronic couplings with the same bending angle leads, in the ^2Π electronic ground state of HCCN+, to a strong Renner-Teller effect giving rise to a bent ^2A' and a quasi-linear ^2A'' state. In this paper the photoionization spectrum of the HCCN radical is simulated. The model developped treats the \\angle{HCC} bending angle as a large amplitude coordinate in both the radical and the cation and accounts for the overall rotation and the Renner-Teller couplings. Gaussian quadrature are used to calculate matrix elements of the three potential energy functions retrieved through ab initio calculations and rovibrational operators going to infinity for the linear configuration are treated rigorously. The HCCN TPE spectrum is computed with the above model calculating all rotational components and choosing the appropriate lineshape. This synthetic spectrum will be shown in the paper and compared with the experimental one.^b Guélin and Cernicharo, A&A 244 (1991) L21 Loison et al., Icarus 247 (2015) 218 Garcia, Krüger, Gans, Falvo, Coudert, and Loison, J. Chem. Phys. (2017) submitted Koput, J. Phys. Chem. A 106 (2002) 6183 Zhao, Zhang, and Sun, J. Phys. Chem. A 112 (2008) 12125

Infrared spectroscopy of hydrated polycyclic aromatic hydrocarbon cations: naphthalene+-water.

PubMed

Chatterjee, Kuntal; Dopfer, Otto

2017-12-13

Polycyclic aromatic hydrocarbons (PAHs) are suggested to occur in interstellar media and ice grains. It is important to characterize hydrated PAHs and their cations to explore their stability in interstellar and biological media. Herein, the infrared photodissociation (IRPD) spectrum of the naphthalene + -H 2 O radical cation (Np + -H 2 O) recorded in the O-H and C-H stretch range is analysed by dispersion-corrected density functional theory calculations at the B3LYP-D3/aug-cc-pVTZ level to determine its structure and intermolecular bonding. Monohydration of Np + in its 2 A u ground electronic state leads to the formation of a bifurcated CHO ionic hydrogen bond (H-bond), in which the lone pairs of H 2 O bind to two adjacent CH proton donors of the two aromatic rings. The frequency-dependent branching ratios observed for IRPD of cold Np + -H 2 O-Ar clusters allows the estimation of the dissociation energy of Np + -H 2 O as D 0 ∼ 2800 ± 300 cm -1 . The monohydration motif of Np + differs qualitatively from that of the benzene cation in both structure and binding energy, indicating the strong influence of the multiple aromatic rings on the hydration of PAH + cations. This difference is rationalized by natural bond orbital analysis of the ionic H-bond motif. Comparison with neutral Np-H 2 O reveals the large change in structure and bond strength of the hydrated PAHs upon ionization. While neutral Np-H 2 O is stabilized by weak π H-bonds (OHπ, π-stacking), strong cation-dipole forces favour a planar bifurcated CHO ionic H-bond in Np + -H 2 O.

The structural diversity of ABS{sub 3} compounds with d{sup 0} electronic configuration for the B-cation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brehm, John A., E-mail: brehmj@sas.upenn.edu; Bennett, Joseph W.; Schoenberg, Michael Rutenberg

2014-06-14

We use first-principles density functional theory within the local density approximation to ascertain the ground state structure of real and theoretical compounds with the formula ABS{sub 3} (A = K, Rb, Cs, Ca, Sr, Ba, Tl, Sn, Pb, and Bi; and B = Sc, Y, Ti, Zr, V, and Nb) under the constraint that B must have a d{sup 0} electronic configuration. Our findings indicate that none of these AB combinations prefer a perovskite ground state with corner-sharing BS{sub 6} octahedra, but that they prefer phases with either edge- or face-sharing motifs. Further, a simple two-dimensional structure field map createdmore » from A and B ionic radii provides a neat demarcation between combinations preferring face-sharing versus edge-sharing phases for most of these combinations. We then show that by modifying the common Goldschmidt tolerance factor with a multiplicative term based on the electronegativity difference between A and S, the demarcation between predicted edge-sharing and face-sharing ground state phases is enhanced. We also demonstrate that, by calculating the free energy contribution of phonons, some of these compounds may assume multiple phases as synthesis temperatures are altered, or as ambient temperatures rise or fall.« less

Dynamic Electron Correlation Effects on the Ground State Potential Energy Surface of a Retinal Chromophore Model.

PubMed

Gozem, Samer; Huntress, Mark; Schapiro, Igor; Lindh, Roland; Granovsky, Alexander A; Angeli, Celestino; Olivucci, Massimo

2012-11-13

The ground state potential energy surface of the retinal chromophore of visual pigments (e.g., bovine rhodopsin) features a low-lying conical intersection surrounded by regions with variable charge-transfer and diradical electronic structures. This implies that dynamic electron correlation may have a large effect on the shape of the force fields driving its reactivity. To investigate this effect, we focus on mapping the potential energy for three paths located along the ground state CASSCF potential energy surface of the penta-2,4-dieniminium cation taken as a minimal model of the retinal chromophore. The first path spans the bond length alternation coordinate and intercepts a conical intersection point. The other two are minimum energy paths along two distinct but kinetically competitive thermal isomerization coordinates. We show that the effect of introducing the missing dynamic electron correlation variationally (with MRCISD) and perturbatively (with the CASPT2, NEVPT2, and XMCQDPT2 methods) leads, invariably, to a stabilization of the regions with charge transfer character and to a significant reshaping of the reference CASSCF potential energy surface and suggesting a change in the dominating isomerization mechanism. The possible impact of such a correction on the photoisomerization of the retinal chromophore is discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spiegel, G.W.

The kinetic solvent isotope effect, KSIE, (k/sub H/sub 2/O//k/sub D/sub 2/O/), at 25.0/sup 0/C and ionic strength, I, equal to 0.20 +- 0.02 M was measured for the nucleophilic displacement of iodine ion from iodomethane, iodoacetamide, and iodoacetate ion, thiophene from S-Methylthiophenium ion, and tosylate ion from methyl tosylate by bromide ion, chloride ion, acetate ion, hydroxide ion, water, ammonia, ethylenediamine, n-butylamine, piperazine, piperidine, quinuclidine, and 1,4-Diazabicyclo(2.2.2)octane (DABCO), and the monoprotonated cations of ethylenediamine, piperazine, and DABCO. By means of solvent partition measurements at 25.0/sup 0/C and I = 0.02 M between H/sub 2/O and D/sub 2/O and a commonmore » immiscible organic solvent, the ground state activity coefficients in D/sub 2/O, the solution in H/sub 2/O being chosen as the reference state, were determined for the nitrogen-containing nucleophiles (except ammonia) and the substrates methyl tosylate, iodoacetamide, and iodoacetic acid. The solubilities at 25.0/sup 0/C of the picrate and tetraphenylborate salts of the monoprotonated cationic forms of ethylenediamine, piperazine, and DABCO were measured to determine the activity coefficients in D/sub 2/O of these ions relative to an H/sub 2/O reference state. Applying the Eyring equation, the activity coefficients of the transition states in D/sub 2/O, reference state H/sub 2/O, were calculated.« less

Resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of 3,5-difluorophenol

NASA Astrophysics Data System (ADS)

Peng, Wei Chih; Wu, Pei Ying; Tzeng, Shen Yuan; Tzeng, Wen Bih

2018-05-01

The first electronic transition and adiabatic ionization energies of 3,5-difluorophenol (35DFP) have been identified as 37614 cm-1 and 72468 cm-1, respectively. These energy values of 35DFP are marginally higher than those of other positional isomers of difluorophenols (25DFP, 34DFP, and 24DFP). The observed active vibrations are primarily due to the in-plane and out-of-plane ring deformation and substituent-sensitive bending motions in the electronically excited (S1) and cationic ground (D0) states.

Use of ultrafast dispersed pump-dump-probe and pump-repump-probe spectroscopies to explore the light-induced dynamics of peridinin in solution.

PubMed

Papagiannakis, Emmanouil; Vengris, Mikas; Larsen, Delmar S; van Stokkum, Ivo H M; Hiller, Roger G; van Grondelle, Rienk

2006-01-12

Optical pump-induced dynamics of the highly asymmetric carotenoid peridinin in methanol was studied by dispersed pump-probe, pump-dump-probe, and pump-repump-probe transient absorption spectroscopy in the visible region. Dispersed pump-probe measurements show that the decay of the initially excited S2 state populates two excited states, the S1 and the intramolecular charge-transfer (ICT) state, at a ratio determined by the excitation wavelength. The ensuing spectral evolution occurs on the time scale of a few picoseconds and suggests the equilibration of these states. Dumping the stimulated emission of the ICT state with an additional 800-nm pulse after 400- and 530-nm excitation preferentially removes the ICT state contribution from the broad excited-state absorption, allowing for its spectral characterization. At the same time, an unrelaxed ground-state species, which has a subpicosecond lifetime, is populated. The application of the 800-nm pulse at early times, when the S2 state is still populated, led to direct generation of the peridinin cation, observed for the first time in a transient absorption experiment. The excited and ground electronic states manifold of peridinin has been reconstructed using target analysis; this approach combined with the measured multipulse spectroscopic data allows us to estimate the spectra and time scales of the corresponding transient states.

Unique role of ionic liquid [bmin][BF 4] during curcumin-surfactant association and micellization of cationic, anionic and non-ionic surfactant solutions

NASA Astrophysics Data System (ADS)

Patra, Digambara; Barakat, Christelle

2011-09-01

Hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroburate, modified the properties of aqueous surfactant solutions associated with curcumin. Because of potential pharmaceutical applications as an antioxidant, anti-inflammatory and anti-carcinogenic agent, curcumin has received ample attention as potential drug. The interaction of curcumin with various charged aqueous surfactant solutions showed it exists in deprotonated enol form in surfactant solutions. The nitro and hydroxyl groups of o-nitrophenol interact with the carbonyl and hydroxyl groups of the enol form of curcumin by forming ground state complex through hydrogen bonds and offered interesting information about the nature of the interactions between the aqueous surfactant solutions and curcumin depending on charge of head group of the surfactant. IL[bmin][BF 4] encouraged early formation of micelle in case of cationic and anionic aqueous surfactant solutions, but slightly prolonged micelle formation in the case of neutral aqueous surfactant solution. However, for curcumin IL [bmin][BF 4] favored strong association (7-fold increase) with neutral surfactant solution, marginally supported association with anionic surfactant solution and discouraged (˜2-fold decrease) association with cationic surfactant solution.

Structural evolution of the methane cation in subfemtosecond photodynamics

NASA Astrophysics Data System (ADS)

Mondal, T.; Varandas, A. J. C.

2015-07-01

An ab initio quantum dynamics study has been performed to explore the structural rearrangement of ground state CH 4+ in subfemtosecond resolved photodynamics. The method utilizes time-dependent wave-packet propagation on the X ˜ 2 T 2 electronic manifold of the title cation in full dimensionality, including nonadiabatic coupling of the three electronic sheets. Good agreement is obtained with recent experiments [Baker et al., Science 312, 424 (2006)] which use high-order harmonic generation to probe the attosecond proton dynamics. The novel results provide direct theoretical support of the observations while unravelling the underlying details. With the geometrical changes obtained by calculating the expectation values of the nuclear coordinates as a function of time, the structural evolution is predicted to begin through activation of the totally symmetric a1 and doubly degenerate e modes. While the former retains the original Td symmetry of the cation, the Jahn-Teller active e mode conducts it to a D2d structure. At ˜1.85 fs, the intermediate D2d structure is further predicted to rearrange to local C2v minimum geometry via Jahn-Teller active bending vibrations of t2 symmetry.

Femtosecond stimulated Raman evidence for charge-transfer character in pentacene singlet fission† †Electronic supplementary information (ESI) available: Actinic pump spectrum, discussion on ground state addition process, peak fitting procedure, transient absorption data, power dependence measurements, etalon pulse shaping, TIPS-pentacene FSRS data, and optimized geometry and frequency calculation results. See DOI: 10.1039/c7sc03496b

PubMed Central

Hart, Stephanie M.; Silva, W. Ruchira

2017-01-01

Singlet fission is a spin-allowed process in which an excited singlet state evolves into two triplet states. We use femtosecond stimulated Raman spectroscopy, an ultrafast vibrational technique, to follow the molecular structural evolution during singlet fission in order to determine the mechanism of this process. In crystalline pentacene, we observe the formation of an intermediate characterized by pairs of excited state peaks that are red- and blue-shifted relative to the ground state features. We hypothesize that these features arise from the formation of cationic and anionic species due to partial transfer of electron density from one pentacene molecule to a neighboring molecule. These observations provide experimental evidence for the role of states with significant charge-transfer character which facilitate the singlet fission process in pentacene. Our work both provides new insight into the singlet fission mechanism in pentacene and demonstrates the utility of structurally-sensitive time-resolved spectroscopic techniques in monitoring ultrafast processes. PMID:29675170

Static electric dipole polarizabilities of tri- and tetravalent U, Np, and Pu ions.

PubMed

Parmar, Payal; Peterson, Kirk A; Clark, Aurora E

2013-11-21

High-quality static electric dipole polarizabilities have been determined for the ground states of the hard-sphere cations of U, Np, and Pu in the III and IV oxidation states. The polarizabilities have been calculated using the numerical finite field technique in a four-component relativistic framework. Methods including Fock-space coupled cluster (FSCC) and Kramers-restricted configuration interaction (KRCI) have been performed in order to account for electron correlation effects. Comparisons between polarizabilities calculated using Dirac-Hartree-Fock (DHF), FSCC, and KRCI methods have been made using both triple- and quadruple-ζ basis sets for U(4+). In addition to the ground state, this study also reports the polarizability data for the first two excited states of U(3+/4+), Np(3+/4+), and Pu(3+/4+) ions at different levels of theory. The values reported in this work are the most accurate to date calculations for the dipole polarizabilities of the hard-sphere tri- and tetravalent actinide ions and may serve as reference values, aiding in the calculation of various electronic and response properties (for example, intermolecular forces, optical properties, etc.) relevant to the nuclear fuel cycle and material science applications.

Coupled electron-nuclear dynamics: Charge migration and charge transfer initiated near a conical intersection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mendive-Tapia, David; Vacher, Morgane; Bearpark, Michael J.

Coupled electron-nuclear dynamics, implemented using the Ehrenfest method, has been used to study charge migration with fixed nuclei, together with charge transfer when nuclei are allowed to move. Simulations were initiated at reference geometries of neutral benzene and 2-phenylethylamine (PEA), and at geometries close to potential energy surface crossings in the cations. Cationic eigenstates, and the so-called sudden approximation, involving removal of an electron from a correlated ground-state wavefunction for the neutral species, were used as initial conditions. Charge migration without coupled nuclear motion could be observed if the Ehrenfest simulation, using the sudden approximation, was started near a conicalmore » intersection where the states were both strongly coupled and quasi-degenerate. Further, the main features associated with charge migration were still recognizable when the nuclear motion was allowed to couple. In the benzene radical cation, starting from the reference neutral geometry with the sudden approximation, one could observe sub-femtosecond charge migration with a small amplitude, which results from weak interaction with higher electronic states. However, we were able to engineer large amplitude charge migration, with a period between 10 and 100 fs, corresponding to oscillation of the electronic structure between the quinoid and anti-quinoid cationic electronic configurations, by distorting the geometry along the derivative coupling vector from the D{sub 6h} Jahn-Teller crossing to lower symmetry where the states are not degenerate. When the nuclear motion becomes coupled, the period changes only slightly. In PEA, in an Ehrenfest trajectory starting from the D{sub 2} eigenstate and reference geometry, a partial charge transfer occurs after about 12 fs near the first crossing between D{sub 1}, D{sub 2} (N{sup +}-Phenyl, N-Phenyl{sup +}). If the Ehrenfest propagation is started near this point, using the sudden approximation without coupled nuclear motion, one observes an oscillation of the spin density – charge migration – between the N atom and the phenyl ring with a period of 4 fs. When the nuclear motion becomes coupled, this oscillation persists in a damped form, followed by an effective charge transfer after 30 fs.« less

Coupled electron-nuclear dynamics: Charge migration and charge transfer initiated near a conical intersection

NASA Astrophysics Data System (ADS)

Mendive-Tapia, David; Vacher, Morgane; Bearpark, Michael J.; Robb, Michael A.

2013-07-01

Coupled electron-nuclear dynamics, implemented using the Ehrenfest method, has been used to study charge migration with fixed nuclei, together with charge transfer when nuclei are allowed to move. Simulations were initiated at reference geometries of neutral benzene and 2-phenylethylamine (PEA), and at geometries close to potential energy surface crossings in the cations. Cationic eigenstates, and the so-called sudden approximation, involving removal of an electron from a correlated ground-state wavefunction for the neutral species, were used as initial conditions. Charge migration without coupled nuclear motion could be observed if the Ehrenfest simulation, using the sudden approximation, was started near a conical intersection where the states were both strongly coupled and quasi-degenerate. Further, the main features associated with charge migration were still recognizable when the nuclear motion was allowed to couple. In the benzene radical cation, starting from the reference neutral geometry with the sudden approximation, one could observe sub-femtosecond charge migration with a small amplitude, which results from weak interaction with higher electronic states. However, we were able to engineer large amplitude charge migration, with a period between 10 and 100 fs, corresponding to oscillation of the electronic structure between the quinoid and anti-quinoid cationic electronic configurations, by distorting the geometry along the derivative coupling vector from the D6h Jahn-Teller crossing to lower symmetry where the states are not degenerate. When the nuclear motion becomes coupled, the period changes only slightly. In PEA, in an Ehrenfest trajectory starting from the D2 eigenstate and reference geometry, a partial charge transfer occurs after about 12 fs near the first crossing between D1, D2 (N+-Phenyl, N-Phenyl+). If the Ehrenfest propagation is started near this point, using the sudden approximation without coupled nuclear motion, one observes an oscillation of the spin density - charge migration - between the N atom and the phenyl ring with a period of 4 fs. When the nuclear motion becomes coupled, this oscillation persists in a damped form, followed by an effective charge transfer after 30 fs.

Rigorous Relativistic Methods for Addressing {P}- and {T}-NONCONSERVATION in Heavy-Element Molecules

NASA Astrophysics Data System (ADS)

Fleig, Timo

2013-06-01

A new and rigorous method for accurate ab-initio calculations of the electron electric dipole moment {P,T}-odd interaction constant is presented. The approach uses string-based Configuration Interaction wavefunctions and Dirac four-component spinors as one-particle basis functions, and the {P,T}-odd constant is obtained as an expectation value over these correlated wavefunctions. The method has been applied to the HfF^+ molecular ion to determine spectroscopic constants for four low-lying electronic states. For one of these states (Ω = 1) we have determined a new accurate benchmark value for the effective electric field E_{ eff} correlating 34 valence and outer atomic core electrons and using wavefunction expansions with nearly 5 \\cdot 10^8 coefficients. For the Ω = 1 state of the ThO molecule the first ab-initio result for the electron EDM interaction constant is presented. Aspects of modern all-electron relativistic many-body approaches applicable to both atoms and molecules will be discussed, including perspectives for the treatment of other interesting candidate systems and {P}- or {P,T}-non-conserving effects in molecular systems. %Zero-kinetic-energy (ZEKE) photoelectron spectroscopy was used to probe the vibrational levels in the ground electronic state of the chlorobenzene cation using a two-color photoionization scheme via the S{_1} electronic state of the neutral. Exciting through different S{_1} vibrational levels has revealed mixing of some S{_1} normal coordinates in the ground state of the cation. A previously-identified Fermi resonance in the S{_1} state of the neutral is also confirmed by the ZEKE spectra. The adiabatic ionization energy is measured as 73 170±5 cm^{-1}. S. Knecht, H. J. Å. Jensen and T. Fleig J. Chem. Phys. {132}, 014108 (2010 T. Fleig, H. J. Å. Jensen, J. Olsen and L. Visscher J. Chem. Phys. {124}, 104106 (2006) T. Fleig and M. K. Nayak Phys. Rev. X {XXX}, XXXX (submitted). T. G. Wright, S. I. Panov and T. A. Miller J. Chem. Phys. {102}(12), XXXX March 1995.

In situ remediation process using divalent metal cations

DOEpatents

Brady, Patrick V.; Khandaker, Nadim R.; Krumhansl, James L.; Teter, David M.

2004-12-14

An in situ process for treating ambient solid materials (e.g., soils, aquifer solids, sludges) by adding one or more divalent metal cations to the ambient solid material. The added divalent metal cations, such as Cu.sup.2+ or Zn.sup.2+, combine with metal oxide/hydroxides (e.g., ferric oxide/hydroxide or aluminum oxide/hydroxide) already present in the ambient solid material to form an effective sorbent material having a large number of positively-charged surface complexes that binds and immobilizes anionic contaminant species (e.g., arsenic or chromate). Divalent metal cations can be added, for example, by injecting an aqueous solution of CuSO.sub.4 into an aquifer contaminated with arsenic or chromate. Also, sludges can be stabilized against leaching of anionic contaminants through the addition of divalent metal cations. Also, an inexpensive sorbent material can be easily formed by mixing divalent metal cations with soil that has been removed from the ground.

Femtosecond stimulated Raman evidence for charge-transfer character in pentacene singlet fission.

PubMed

Hart, Stephanie M; Silva, W Ruchira; Frontiera, Renee R

2018-02-07

Singlet fission is a spin-allowed process in which an excited singlet state evolves into two triplet states. We use femtosecond stimulated Raman spectroscopy, an ultrafast vibrational technique, to follow the molecular structural evolution during singlet fission in order to determine the mechanism of this process. In crystalline pentacene, we observe the formation of an intermediate characterized by pairs of excited state peaks that are red- and blue-shifted relative to the ground state features. We hypothesize that these features arise from the formation of cationic and anionic species due to partial transfer of electron density from one pentacene molecule to a neighboring molecule. These observations provide experimental evidence for the role of states with significant charge-transfer character which facilitate the singlet fission process in pentacene. Our work both provides new insight into the singlet fission mechanism in pentacene and demonstrates the utility of structurally-sensitive time-resolved spectroscopic techniques in monitoring ultrafast processes.

Removal of contaminants from landfill leachates by filtration through glauconitic greensands

USGS Publications Warehouse

Spoljaric, N.; Crawford, W.A.

1979-01-01

Passing landfill leachate through glauconitic greensand filters reduces the heavy metal cation content, lessens the unpleasant odor, and diminishes the murkiness of the leachate. The capability of the greensand to trap metal cations is increased by prolonging the contact time between the leachate and the greensand. Flushing the charged greensand filter with water does not cause significant release of cations back into solution, suggesting that polluted greensand might be disposed of at landfill sites without endangering the quality of either ground or surface water. ?? 1979 Springer Verlag New York Inc.

Excited state non-adiabatic dynamics of the smallest polyene, trans 1,3-butadiene. I. Time-resolved photoelectron-photoion coincidence spectroscopy

NASA Astrophysics Data System (ADS)

Boguslavskiy, Andrey E.; Schalk, Oliver; Gador, Niklas; Glover, William J.; Mori, Toshifumi; Schultz, Thomas; Schuurman, Michael S.; Martínez, Todd J.; Stolow, Albert

2018-04-01

The ultrafast excited state dynamics of the smallest polyene, trans-1,3-butadiene, were studied by femtosecond time-resolved photoelectron-photoion coincidence (TRPEPICO) spectroscopy. The evolution of the excited state wavepacket, created by pumping the bright 1Bu (ππ*) electronic state at its origin of 216 nm, is projected via one- and two-photon ionization at 267 nm onto several ionization continua. The results are interpreted in terms of Koopmans' correlations and Franck-Condon factors for the excited and cationic states involved. The known predissociative character of the cation excited states is utilized to assign photoelectron bands to specific continua using TRPEPICO spectroscopy. This permits us to report the direct observation of the famously elusive S1(21Ag) dark electronic state during the internal conversion of trans 1,3-butadiene. Our phenomenological analysis permits the spectroscopic determination of several important time constants. We report the overall decay lifetimes of the 11Bu and 21Ag states and observe the re-appearance of the hot ground state molecule. We argue that the apparent dephasing time of the S2(11Bu) state, which leads to the extreme breadth of the absorption spectrum, is principally due to large amplitude torsional motion on the 1Bu surface in conjunction with strong non-adiabatic couplings via conical intersections, whereupon nuclear wavepacket revivals to the initial Franck-Condon region become effectively impossible. In Paper II [W. J. Glover et al., J. Chem. Phys. 148, 164303 (2018)], ab initio multiple spawning is used for on-the-fly computations of the excited state non-adiabatic wavepacket dynamics and their associated TRPEPICO observables, allowing for direct comparisons of experiment with theory.

Excited state non-adiabatic dynamics of the smallest polyene, trans 1,3-butadiene. I. Time-resolved photoelectron-photoion coincidence spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boguslavskiy, Andrey E.; Schalk, Oliver; Gador, Niklas

The ultrafast excited state dynamics of the smallest polyene, trans-1,3-butadiene, were studied by femtosecond time-resolved photoelectron-photoion coincidence (TRPEPICO) spectroscopy. The evolution of the excited state wavepacket, created by pumping the bright 1B u (ππ*) electronic state at its origin of 216 nm, is projected via one- and two-photon ionization at 267 nm onto several ionization continua. The results are interpreted in terms of Koopmans’ correlations and Franck-Condon factors for the excited and cationic states involved. The known predissociative character of the cation excited states is utilized to assign photoelectron bands to specific continua using TRPEPICO spectroscopy. This permits us tomore » report the direct observation of the famously elusive S 1(2 1A g) dark electronic state during the internal conversion of trans 1,3-butadiene. Our phenomenological analysis permits the spectroscopic determination of several important time constants. We report the overall decay lifetimes of the 1 1B u and 2 1A g states and observe the re-appearance of the hot ground state molecule. We argue that the apparent dephasing time of the S 2(1 1B u) state, which leads to the extreme breadth of the absorption spectrum, is principally due to large amplitude torsional motion on the 1B u surface in conjunction with strong non-adiabatic couplings via conical intersections, whereupon nuclear wavepacket revivals to the initial Franck-Condon region become effectively impossible. Lastly, in Paper II [W. J. Glover et al., J. Chem. Phys. 148, 164303 (2018)], ab initio multiple spawning is used for on-the-fly computations of the excited state non-adiabatic wavepacket dynamics and their associated TRPEPICO observables, allowing for direct comparisons of experiment with theory.« less

Excited state non-adiabatic dynamics of the smallest polyene, trans 1,3-butadiene. I. Time-resolved photoelectron-photoion coincidence spectroscopy

DOE PAGES

Boguslavskiy, Andrey E.; Schalk, Oliver; Gador, Niklas; ...

2018-04-27

The ultrafast excited state dynamics of the smallest polyene, trans-1,3-butadiene, were studied by femtosecond time-resolved photoelectron-photoion coincidence (TRPEPICO) spectroscopy. The evolution of the excited state wavepacket, created by pumping the bright 1B u (ππ*) electronic state at its origin of 216 nm, is projected via one- and two-photon ionization at 267 nm onto several ionization continua. The results are interpreted in terms of Koopmans’ correlations and Franck-Condon factors for the excited and cationic states involved. The known predissociative character of the cation excited states is utilized to assign photoelectron bands to specific continua using TRPEPICO spectroscopy. This permits us tomore » report the direct observation of the famously elusive S 1(2 1A g) dark electronic state during the internal conversion of trans 1,3-butadiene. Our phenomenological analysis permits the spectroscopic determination of several important time constants. We report the overall decay lifetimes of the 1 1B u and 2 1A g states and observe the re-appearance of the hot ground state molecule. We argue that the apparent dephasing time of the S 2(1 1B u) state, which leads to the extreme breadth of the absorption spectrum, is principally due to large amplitude torsional motion on the 1B u surface in conjunction with strong non-adiabatic couplings via conical intersections, whereupon nuclear wavepacket revivals to the initial Franck-Condon region become effectively impossible. Lastly, in Paper II [W. J. Glover et al., J. Chem. Phys. 148, 164303 (2018)], ab initio multiple spawning is used for on-the-fly computations of the excited state non-adiabatic wavepacket dynamics and their associated TRPEPICO observables, allowing for direct comparisons of experiment with theory.« less

Spectroscopic Identification of the Carbyne Hydride Structure of the Dehydrogenation Product of Methane Activation by Osmium Cations

NASA Astrophysics Data System (ADS)

Armentrout, P. B.; Kuijpers, Stach E. J.; Lushchikova, Olga V.; Hightower, Randy L.; Boles, Georgia C.; Bakker, Joost M.

2018-04-01

The present work explores the structures of species formed by dehydrogenation of methane (CH4) and perdeuterated methane (CD4) by the 5d transition metal cation osmium (Os+). Using infrared multiple photon dissociation (IRMPD) action spectroscopy and density functional theory (DFT), the structures of the [Os,C,2H]+ and [Os,C,2D]+ products are explored. This study complements previous work on the related species formed by dehydrogenation of methane by four other 5d transition metal cations (M+ = Ta+, W+, Ir+, and Pt+). Osmium cations are formed in a laser ablation source, react with methane pulsed into a reaction channel downstream, and the resulting products spectroscopically characterized through photofragmentation using the Free-Electron Laser for IntraCavity Experiments (FELICE) in the 300-1800 cm-1 range. Photofragmentation was monitored by the loss of H2/D2. Comparison of the experimental spectra and DFT calculated spectra leads to identification of the ground state carbyne hydride, HOsCH+ (2A') as the species formed, as previously postulated theoretically. Further, a full description of the systematic spectroscopic shifts observed for deuterium labeling of these complexes, some of the smallest systems to be studied using IRMPD action spectroscopy, is achieved. A full rotational contour analysis explains the observed linewidths as well as the observation of doublet structures in several bands, consistent with previous observations for HIrCH+ (2A'). [Figure not available: see fulltext.

Structures and stability of metal-doped Ge nM (n = 9, 10) clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Wei; Lu, Wen-Cai; Xia, Lin-Hua

The lowest-energy structures of neutral and cationic Ge nM (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge 9 and Ge 10 clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Ge n clusters. However, the neutral and cationic FeGe 9,10,MnGe 9,10 and Ge 10Al are cage-like withmore » the metal atom encapsulated inside. Such cage-like transition metal doped Ge n clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge 9,10Fe and Ge 9Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.« less

Structures and stability of metal-doped Ge nM (n = 9, 10) clusters

DOE PAGES

Qin, Wei; Lu, Wen-Cai; Xia, Lin-Hua; ...

2015-06-26

The lowest-energy structures of neutral and cationic Ge nM (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge 9 and Ge 10 clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Ge n clusters. However, the neutral and cationic FeGe 9,10,MnGe 9,10 and Ge 10Al are cage-like withmore » the metal atom encapsulated inside. Such cage-like transition metal doped Ge n clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge 9,10Fe and Ge 9Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.« less

Transforming high-dimensional potential energy surfaces into sum-of-products form using Monte Carlo methods

NASA Astrophysics Data System (ADS)

Schröder, Markus; Meyer, Hans-Dieter

2017-08-01

We propose a Monte Carlo method, "Monte Carlo Potfit," for transforming high-dimensional potential energy surfaces evaluated on discrete grid points into a sum-of-products form, more precisely into a Tucker form. To this end we use a variational ansatz in which we replace numerically exact integrals with Monte Carlo integrals. This largely reduces the numerical cost by avoiding the evaluation of the potential on all grid points and allows a treatment of surfaces up to 15-18 degrees of freedom. We furthermore show that the error made with this ansatz can be controlled and vanishes in certain limits. We present calculations on the potential of HFCO to demonstrate the features of the algorithm. To demonstrate the power of the method, we transformed a 15D potential of the protonated water dimer (Zundel cation) in a sum-of-products form and calculated the ground and lowest 26 vibrationally excited states of the Zundel cation with the multi-configuration time-dependent Hartree method.

Structures and stability of metal-doped GenM (n = 9, 10) clusters

NASA Astrophysics Data System (ADS)

Qin, Wei; Lu, Wen-Cai; Xia, Lin-Hua; Zhao, Li-Zhen; Zang, Qing-Jun; Wang, C. Z.; Ho, K. M.

2015-06-01

The lowest-energy structures of neutral and cationic GenM (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge9 and Ge10 clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Gen clusters. However, the neutral and cationic FeGe9,10,MnGe9,10 and Ge10Al are cage-like with the metal atom encapsulated inside. Such cage-like transition metal doped Gen clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge9,10Fe and Ge9Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Hyewon; Cheong, S.W.; Kim, Bog G., E-mail: boggikim@pusan.ac.kr

We have studied the properties of SnO{sub 6} octahedra-containing perovskites and their derived structures using ab initio calculations with different density functionals. In order to predict the correct band gap of the materials, we have used B3LYP hybrid density functional, and the results of B3LYP were compared with those obtained using the local density approximation and generalized gradient approximation data. The calculations have been conducted for the orthorhombic ground state of the SnO{sub 6} containing perovskites. We also have expended the hybrid density functional calculation to the ASnO{sub 3}/A'SnO{sub 3} system with different cation orderings. We propose an empirical relationshipmore » between the tolerance factor and the band gap of SnO{sub 6} containing oxide materials based on first principles calculation. - Graphical abstract: (a) Structure of ASnO{sub 3} for orthorhombic ground state. The green ball is A (Ba, Sr, Ca) cation and the small (red) ball on edge is oxygen. SnO{sub 6} octahedrons are plotted as polyhedron. (b) Band gap of ASnO{sub 3} as a function of the tolerance factor for different density functionals. The experimental values of the band gap are marked as green pentagons. (c) ASnO{sub 3}/A'SnO{sub 3} superlattices with two types cation arrangement: [001] layered structure and [111] rocksalt structure, respectively. (d) B3LYP hybrid functional band gaps of ASnO{sub 3}, [001] ordered superlattices, and [111] ordered superlattices of ASnO{sub 3}/A'SnO{sub 3} as a function of the effective tolerance factor. Note the empirical linear relationship between the band gap and effective tolerance factor. - Highlights: • We report the hybrid functional band gap calculation of ASnO{sub 3} and ASnO{sub 3}/A'SnO{sub 3}. • The band gap of ASnO{sub 3} using B3LYP functional reproduces the experimental value. • We propose the linear relationship between the tolerance factor and the band gap.« less

Mechanistic insights into allosteric regulation of the A 2A adenosine G protein-coupled receptor by physiological cations

DOE PAGES

Ye, Libin; Neale, Chris Andrew; Sljoka, Adnan; ...

2018-04-10

Cations play key roles in regulating G-protein-coupled receptors (GPCRs), although their mechanisms are poorly understood. Here, 19F NMR is used to delineate the effects of cations on functional states of the adenosine A 2A GPCR. While Na + reinforces an inactive ensemble and a partial-agonist stabilized state, Ca 2+ and Mg 2+ shift the equilibrium toward active states. Positive allosteric effects of divalent cations are more pronounced with agonist and a G-protein-derived peptide. In cell membranes, divalent cations enhance both the affinity and fraction of the high affinity agonist-bound state. Molecular dynamics simulations suggest high concentrations of divalent cations bridgemore » specific extracellular acidic residues, bringing TM5 and TM6 together at the extracellular surface and allosterically driving open the G-protein-binding cleft as shown by rigidity-transmission allostery theory. Lastly, an understanding of cation allostery should enable the design of allosteric agents and enhance our understanding of GPCR regulation in the cellular milieu.« less

Mechanistic insights into allosteric regulation of the A 2A adenosine G protein-coupled receptor by physiological cations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Libin; Neale, Chris Andrew; Sljoka, Adnan

Cations play key roles in regulating G-protein-coupled receptors (GPCRs), although their mechanisms are poorly understood. Here, 19F NMR is used to delineate the effects of cations on functional states of the adenosine A 2A GPCR. While Na + reinforces an inactive ensemble and a partial-agonist stabilized state, Ca 2+ and Mg 2+ shift the equilibrium toward active states. Positive allosteric effects of divalent cations are more pronounced with agonist and a G-protein-derived peptide. In cell membranes, divalent cations enhance both the affinity and fraction of the high affinity agonist-bound state. Molecular dynamics simulations suggest high concentrations of divalent cations bridgemore » specific extracellular acidic residues, bringing TM5 and TM6 together at the extracellular surface and allosterically driving open the G-protein-binding cleft as shown by rigidity-transmission allostery theory. Lastly, an understanding of cation allostery should enable the design of allosteric agents and enhance our understanding of GPCR regulation in the cellular milieu.« less

Electronic and magnetic properties of RMnO3/AMnO3 heterostructures

NASA Astrophysics Data System (ADS)

Yu, Rong; Yunoki, Seiji; Dong, Shuai; Dagotto, Elbio

2009-09-01

The ground-state properties of RMnO3/AMnO3 (RMO/AMO) heterostructures (with R=La,Pr,… , a trivalent rare-earth cation and A=Sr,Ca,… , a divalent alkaline cation) are studied using a two-orbital double-exchange model including the superexchange coupling and Jahn-Teller lattice distortions. To describe the charge transfer across the interface, the long-range Coulomb interaction is taken into account at the mean-field level, by self-consistently solving the Poisson’s equation. The calculations are carried out numerically on finite clusters. We find that the state stabilized near the interface of the heterostructure is similar to the state of the bulk compound (R,A)MO at electronic density close to 0.5. For instance, a charge and orbitally ordered CE state is found at the interface if the corresponding bulk (R,A)MO material is a narrow-to-intermediate bandwidth manganite. But instead the interface regime accommodates an A-type antiferromagnetic state with a uniform x2-y2 orbital order, if the bulk (R,A)MO corresponds to a wide bandwidth manganite. We argue that these results explain some of the properties of long-period (RMO)m/(AMO)n superlattices, such as (PrMnO3)m/(CaMnO3)n and (LaMnO3)m/(SrMnO3)n . We also remark that the intermediate states in between the actual interface and the bulklike regimes of the heterostructure are dependent on the bandwidth and the screening of the Coulomb interaction. In these regions of the heterostructures, states are found that do not have an analog in experimentally known bulk phase diagrams. These new states of the heterostructures provide a natural interpolation between magnetically ordered states that are stable in the bulk at different electronic densities.

First-principles study of Ga-vacancy induced magnetism in β-Ga2O3.

PubMed

Yang, Ya; Zhang, Jihua; Hu, Shunbo; Wu, Yabei; Zhang, Jincang; Ren, Wei; Cao, Shixun

2017-11-01

First principles calculations based on density functional theory were performed to study the electronic structure and magnetic properties of β-Ga 2 O 3 in the presence of cation vacancies. We investigated two kinds of Ga vacancies at different symmetry sites and the consequent structural distortion and defect states. We found that both the six-fold coordinated octahedral site and the four-fold coordinated tetrahedral site vacancies can lead to a spin polarized ground state. Furthermore, the calculation identified a relationship between the spin polarization and the charge states of the vacancies, which might be explained by a molecular orbital model consisting of uncompensated O 2- 2p dangling bonds. The calculations for the two vacancy systems also indicated a potential long-range ferromagnetic order which is beneficial for spintronics application.

Application of environmental tracers to mixing, evolution, and nitrate contamination of ground water in Jeju Island, Korea

USGS Publications Warehouse

Koh, D.-C.; Plummer, Niel; Kip, Solomon D.; Busenberg, E.; Kim, Y.-J.; Chang, H.-W.

2006-01-01

Tritium/helium-3 (3H/3He) and chlorofluorocarbons (CFCs) were investigated as environmental tracers in ground water from Jeju Island (Republic of Korea), a basaltic volcanic island. Ground-water mixing was evaluated by comparing 3H and CFC-12 concentrations with lumped-parameter dispersion models, which distinguished old water recharged before the 1950s with negligible 3H and CFC-12 from younger water. Low 3H levels in a considerable number of samples cannot be explained by the mixing models, and were interpreted as binary mixing of old and younger water; a process also identified in alkalinity and pH of ground water. The ground-water CFC-12 age is much older in water from wells completed in confined zones of the hydro-volcanic Seogwipo Formation in coastal areas than in water from the basaltic aquifer. Major cation concentrations are much higher in young water with high nitrate than those in uncontaminated old water. Chemical evolution of ground water resulting from silicate weathering in basaltic rocks reaches the zeolite-smectite phase boundary. The calcite saturation state of ground water increases with the CFC-12 apparent (piston flow) age. In agricultural areas, the temporal trend of nitrate concentration in ground water is consistent with the known history of chemical fertilizer use on the island, but increase of nitrate concentration in ground water is more abrupt after the late 1970s compared with the exponential growth of nitrogen inputs. ?? 2005 Elsevier B.V. All rights reserved.

Full-dimensional quantum calculations of the dissociation energy, zero-point, and 10 K properties of H7+/D7+ clusters using an ab initio potential energy surface.

PubMed

Barragán, Patricia; Pérez de Tudela, Ricardo; Qu, Chen; Prosmiti, Rita; Bowman, Joel M

2013-07-14

Diffusion Monte Carlo (DMC) and path-integral Monte Carlo computations of the vibrational ground state and 10 K equilibrium state properties of the H7 (+)/D7 (+) cations are presented, using an ab initio full-dimensional potential energy surface. The DMC zero-point energies of dissociated fragments H5 (+)(D5 (+))+H2(D2) are also calculated and from these results and the electronic dissociation energy, dissociation energies, D0, of 752 ± 15 and 980 ± 14 cm(-1) are reported for H7 (+) and D7 (+), respectively. Due to the known error in the electronic dissociation energy of the potential surface, these quantities are underestimated by roughly 65 cm(-1). These values are rigorously determined for first time, and compared with previous theoretical estimates from electronic structure calculations using standard harmonic analysis, and available experimental measurements. Probability density distributions are also computed for the ground vibrational and 10 K state of H7 (+) and D7 (+). These are qualitatively described as a central H3 (+)/D3 (+) core surrounded by "solvent" H2/D2 molecules that nearly freely rotate.

Zero kinetic energy photoelectron spectroscopy of triphenylene.

PubMed

Harthcock, Colin; Zhang, Jie; Kong, Wei

2014-06-28

We report vibrational information of both the first electronically excited state and the ground cationic state of jet-cooled triphenylene via the techniques of resonantly enhanced multiphoton ionization (REMPI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. The first excited electronic state S1 of the neutral molecule is of A1' symmetry and is therefore electric dipole forbidden in the D3h group. Consequently, there are no observable Franck-Condon allowed totally symmetric a1' vibrational bands in the REMPI spectrum. All observed vibrational transitions are due to Herzberg-Teller vibronic coupling to the E' third electronically excited state S3. The assignment of all vibrational bands as e' symmetry is based on comparisons with calculations using the time dependent density functional theory and spectroscopic simulations. When an electron is eliminated, the molecular frame undergoes Jahn-Teller distortion, lowering the point group to C2v and resulting in two nearly degenerate electronic states of A2 and B1 symmetry. Here we follow a crude treatment by assuming that all e' vibrational modes resolve into b2 and a1 modes in the C2v molecular frame. Some observed ZEKE transitions are tentatively assigned, and the adiabatic ionization threshold is determined to be 63 365 ± 7 cm(-1). The observed ZEKE spectra contain a consistent pattern, with a cluster of transitions centered near the same vibrational level of the cation as that of the intermediate state, roughly consistent with the propensity rule. However, complete assignment of the detailed vibrational structure due to Jahn-Teller coupling requires much more extensive calculations, which will be performed in the future.

A repertoire of pyridinium-phenyl-methyl cross-talk through a cascade of intramolecular electrostatic interactions.

PubMed

Acharya, P; Plashkevych, O; Morita, C; Yamada, S; Chattopadhyaya, J

2003-02-21

Direct intramolecular cation-pi interaction between phenyl and pyridinium moieties in 1a(+) has been experimentally evidenced through pH-dependent (1)H NMR titration. The basicity of the pyridinyl group (pK(a) 2.9) in 1a can be measured both from the pH-dependent chemical shifts of the pyridinyl protons as well as from the protons of the neighboring phenyl and methyl groups as a result of electrostatic interaction between the phenyl and the pyridinium ion in 1a(+) at the ground state. The net result of this nearest neighbor electrostatic interaction is that the pyridinium moiety in 1a becomes more basic (pK(a) 2.92) compared to that in the standard 2a (pK(a) 2.56) as a consequence of edge-to-face cation (pyridinium)-pi (phenyl) interaction, giving a free energy of stabilization (DeltaDeltaG(o)pKa) of -2.1 kJ mol(-1). The fact that the pH-dependent downfield shifts of the phenyl and methyl protons give the pK(a) of the pyridine moiety of 1a also suggests that the nearest neighbor cation (pyridinium)-pi (phenyl) interaction also steers the CH (methyl)-pi (phenyl) interaction in tandem. This means that the whole pyridine-phenyl-methyl system in 1a(+) is electronically coupled at the ground state, cross-modulating the physicochemical property of the next neighbor by using the electrostatics as the engine, and the origin of this electrostatics is a far away point in the molecule-the pyridinyl-nitrogen. The relative chemical shift changes and the pK(a) differences show that the cation (pyridinium)-pi (phenyl) interaction is indeed more stable (DeltaDeltaG(o)pKa = -2.1 kJ mol(-1)) than that of the CH (methyl)-pi (phenyl) interaction (DeltaDeltaG(o)pKa = -0.8 kJ mol(-1)). Since the pK(a) of the pyridine moiety in 1a is also obtained through the pH-dependent shifts of both phenyl and methyl protons, it suggests that the net electrostatic mediated charge transfer from the phenyl to the pyridinium and its effect on the CH (methyl)-pi (phenyl) interaction corresponds to DeltaG(o)pKa of the pyridinium ion (approximately 17.5 kJ mol(-1)), which means that the aromatic characters of the phenyl and the pyridinium rings in 1a(+) have been cross-modulated owing to the edge-to-face interaction proportional to this DeltaG(o)pKa change.

Modulation of the Conformational Dynamics of Apo-Adenylate Kinase through a π-Cation Interaction.

PubMed

Halder, Ritaban; Manna, Rabindra Nath; Chakraborty, Sandipan; Jana, Biman

2017-06-15

Large-scale conformational transition from open to closed state of adenylate kinase (ADK) is essential for its catalytic cycle. Apo-ADK undergoes conformational transition in a way that closely resembles an open-to-closed conformational transition. Here, equilibrium simulations, free-energy simulations, and quantum mechanics/molecular mechanics (QM/MM) calculations in combination with several bioinformatics approaches have been used to explore the molecular origin of this conformational transition in apo-ADK. In addition to its conventional open state, Escherichia coli apo-ADK adopts conformations that resemble a closed-like intermediate, the "half-open-half-closed" (HOHC) state, and a π-cation interaction can account for the stability of this HOHC state. Energetics and the electronic properties of this π-cation interaction have been explored using QM/MM calculations. Upon rescinding the π-cation interaction, the conformational landscape of the apo-ADK changes completely. The apo-ADK population is shifted completely toward the open state. This π-cation interaction is highly conserved in bacterial ADK; the cationic guanidinium moiety of a conserved ARG interacts with the delocalized π-electron cloud of either PHE or TYR. Interestingly, this study demonstrates the modulation of a principal protein dynamics by a conserved specific π-cation interaction across different organisms.

MS-CASPT2 study of hole transfer in guanine-indole complexes using the generalized Mulliken-Hush method: effective two-state treatment.

PubMed

Butchosa, C; Simon, S; Blancafort, L; Voityuk, A

2012-07-12

Because hole transfer from nucleobases to amino acid residues in DNA-protein complexes can prevent oxidative damage of DNA in living cells, computational modeling of the process is of high interest. We performed MS-CASPT2 calculations of several model structures of π-stacked guanine and indole and derived electron-transfer (ET) parameters for these systems using the generalized Mulliken-Hush (GMH) method. We show that the two-state model commonly applied to treat thermal ET between adjacent donor and acceptor is of limited use for the considered systems because of the small gap between the ground and first excited states in the indole radical cation. The ET parameters obtained within the two-state GMH scheme can deviate significantly from the corresponding matrix elements of the two-state effective Hamiltonian based on the GMH treatment of three adiabatic states. The computed values of diabatic energies and electronic couplings provide benchmarks to assess the performance of less sophisticated computational methods.

(π−1) → (π−1), (π−1) emission spectra of chlorofluorobenzene cations in the gaseous phase and their lifetimes in the (0o) states

USGS Publications Warehouse

Maier, John Paul; Marthaler, O.; Mohraz, Manijeh; Shiley, R.H.

1980-01-01

The radiative decay of seventeen electronically excited chlorofluorobenzene cations in the gaseous phase has been detected. The reported emission spectra, which have been obtained using low energy electron beam excitation, are assigned to the B(??-1 ??? X(??-1 electronic transitions of these cations on the basis of their Ne(I) photoelectron spectra. In another sixteen chloroflourobenzene cations, the B ??? X radiative decay could not be detected, from which is inferred that the B states are now associated with Cl 3p(??-1 ionisation processes. The lifetimes of the studied cations in the lowest vibrational levels of the B(??-1 state have been measured. ?? 1980.

Sugar Radical Formation by a Proton Coupled Hole Transfer in 2′-Deoxyguanosine Radical Cation (2′-dG•+): A Theoretical Treatment

PubMed Central

Kumar, Anil; Sevilla, Michael D.

2009-01-01

Previous experimental and theoretical work has established that electronic excitation of a guanine cation radical in nucleosides or in DNA itself leads to sugar radical formation by deprotonation from the dexoxyribose sugar. In this work we investigate a ground electronic state pathway for such sugar radical formation in a hydrated one electron oxidized 2′-deoxyguanosine (dG•+ + 7H2O), using density functional theory (DFT) with the B3LYP functional and the 6-31G* basis set. We follow the stretching of the C5′-H bond in dG•+ to gain an understanding of the energy requirements to transfer the hole from the base to sugar ring and then to deprotonate to proton acceptor sites in solution and on the guanine ring. The geometries of reactant (dG•+ + 7H2O), transition state (TS) for deprotonation of C5′ site and product (dG(•C5′, N7-H+) + 7 H2O) were fully optimized. The zero point energy (ZPE) corrected activation energy (TS) for the proton transfer (PT) from C5′ is calculated to be 9.0 kcal/mol and is achieved by stretching the C5′-H bond by 0.13 Å from its equilibrium bond distance (1.099 Å). Remarkably, this small bond stretch is sufficient to transfer the “hole” (positive charge and spin) from guanine to the C5′ site on the deoxyribose group. Beyond the TS, the proton (H+) spontaneously adds to water to form a hydronium ion (H3O+) as an intermediate. The proton subsequently transfers to the N7 site of the guanine (product). The 9 kcal/mol barrier suggests slow thermal conversion of the cation radical to the sugar radical but also suggests that localized vibrational excitations would be sufficient to induce rapid sugar radical formation in DNA base cation radicals. PMID:19754084

Quality of water and chemistry of bottom sediment in the Rillito Creek basin, Tucson, Arizona, 1992-93

USGS Publications Warehouse

Tadayon, Saeid

1995-01-01

Physical and chemical data were collected from four surface-water sites, six ground-water sites, and two bottom-sediment sites during 1992-93. Specific conductance, hardness, alkalinity, and dissolved- solids concentrations generally were higher in ground water than in surface water. The median concentrations of dissolved major ions, with the exception of potassium, were higher in ground water than in surface water. In surface water and ground water, calcium was the dominant cation, and bicarbonate was the dominant anion. Concentrations of dissolved nitrite and nitrite plus nitrate in surface water and ground water did not exceed the U.S. Environmental Protection Agency maximum contaminant levels of 1 and 10 milligrams per liter for drinking water, respectively. Ammonium plus organic nitrogen in bottom sediment was detected at the highest concentration of any nitrogen species. Median values for most of the dissolved trace elements in surface water and ground water were below the detection levels. Dissolved trace elements in surface water and ground water did not exceed the U.S. Environmental Protection Agency maximum contaminant levels for drinking water. Trace-element concentrations in bottom sediment were similar to trace-element concentrations reported for soils of the western conterminous United States. Several organochlorine pesticides and priority pollutants were detected in surface-water and bottom-sediment samples; however, they did not exceed water-quality standards. Pesticides or priority pollutants were not detected in ground-water samples.

Charge dynamics of 57Fe probe atoms in La2Li0.5Cu0.5O4

NASA Astrophysics Data System (ADS)

Presniakov, I. A.; Sobolev, A. V.; Rusakov, V. S.; Moskvin, A. S.; Baranov, A. V.

2018-06-01

The objective of this study is to characterize the electronic state and local surrounding of 57Fe Mössbauer probe atoms within iron-doped layered perovskite La2Li0.5Cu0.5O4 containing transition metal in unusual formal oxidation states "+3". An approach based on the qualitative energy diagrams analysis and the calculations within the cluster configuration interaction method have been developed. It was shown that a large amount of charge is transferred via Cu-O bonds from the O: 2p bands to the Cu: 3d orbitals and the ground state is dominated by the d9L configuration ("Cu2+-O-" state). The dominant d9L ground state for the (CuO6) sublattice induces in the environment of the 57Fe probe cations a charge transfer Fe3+ + O-(L) → Fe4+ + O2-, which transforms "Fe3+" into "Fe4+" state. The experimental spectra in the entire temperature range 77-300 K were described with the use of the stochastic two-level model based on the assumption of dynamic equilibrium between two Fe3+↔Fe4+ valence states related to the iron atom in the [Fe(1)O4]4- center. The relaxation frequencies and activation energies of the corresponding charge fluctuations were estimated based on Mössbauer data. The results are discussed assuming a temperature-induced change in the electronic state of the [CuO4]5- clusters in the layered perovskite.

Carotenoid radical cation formation in LH2 of purple bacteria: a quantum chemical study.

PubMed

Wormit, Michael; Dreuw, Andreas

2006-11-30

In LH2 complexes of Rhodobacter sphaeroides the formation of a carotenoid radical cation has recently been observed upon photoexcitation of the carotenoid S2 state. To shed more light onto the yet unknown molecular mechanism leading to carotenoid radical formation in LH2, the interactions between carotenoid and bacteriochlorophyll in LH2 are investigated by means of quantum chemical calculations for three different carotenoids--neurosporene, spheroidene, and spheroidenone--using time-dependent density functional theory. Crossings of the calculated potential energy curve of the electron transfer state with the bacteriochlorophyll Qx state and the carotenoid S1 and S2 states occur along an intermolecular distance coordinate for neurosporene and spheroidene, but for spheroidenone no crossing of the electron transfer state with the carotenoid S1 state could be found. By comparison with recent experiments where no formation of a spheroidenone radical cation has been observed, a molecular mechanism for carotenoid radical cation formation is proposed in which it is formed via a vibrationally excited carotenoid S1 or S*state. Arguments are given why the formation of the carotenoid radical cation does not proceed via the Qx, S2, or higher excited electron transfer states.

Photoabsorption in sodium clusters: first principles configuration interaction calculations

NASA Astrophysics Data System (ADS)

Priya, Pradip Kumar; Rai, Deepak Kumar; Shukla, Alok

2017-05-01

We present systematic and comprehensive correlated-electron calculations of the linear photoabsorption spectra of small neutral closed- and open-shell sodium clusters (Nan, n = 2 - 6), as well as closed-shell cation clusters (Nan+, n = 3, 5). We have employed the configuration interaction (CI) methodology at the full CI (FCI) and quadruple CI (QCI) levels to compute the ground, and the low-lying excited states of the clusters. For most clusters, besides the minimum energy structures, we also consider their energetically close isomers. The photoabsorption spectra were computed under the electric-dipole approximation, employing the dipole-matrix elements connecting the ground state with the excited states of each isomer. Our calculations were tested rigorously for convergence with respect to the basis set, as well as with respect to the size of the active orbital space employed in the CI calculations. These calculations reveal that as far as electron-correlation effects are concerned, core excitations play an important role in determining the optimized ground state geometries of various clusters, thereby requiring all-electron correlated calculations. But, when it comes to low-lying optical excitations, only valence electron correlation effects play an important role, and excellent agreement with the experimental results is obtained within the frozen-core approximation. For the case of Na6, the largest cluster studied in this work, we also discuss the possibility of occurrence of plasmonic resonance in the optical absorption spectrum. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-70728-3

Stressor states and the cation crossroads.

PubMed

Weber, Karl T; Bhattacharya, Syamal K; Newman, Kevin P; Soberman, Judith E; Ramanathan, Kodangudi B; McGee, Jesse E; Malik, Kafait U; Hickerson, William L

2010-12-01

Neurohormonal activation involving the hypothalamic-pituitary-adrenal axis and adrenergic nervous and renin-angiotensin-aldosterone systems is integral to stressor state-mediated homeostatic responses. The levels of effector hormones, depending upon the degree of stress, orchestrate the concordant appearance of hypokalemia, ionized hypocalcemia and hypomagnesemia, hypozincemia, and hyposelenemia. Seemingly contradictory to homeostatic responses wherein the constancy of extracellular fluid would be preserved, upregulation of cognate-binding proteins promotes coordinated translocation of cations to injured tissues, where they participate in wound healing. Associated catecholamine-mediated intracellular cation shifts regulate the equilibrium between pro-oxidants and antioxidant defenses, a critical determinant of cell survival. These acute and chronic stressor-induced iterations in extracellular and intracellular cations are collectively referred to as the cation crossroads. Intracellular cation shifts, particularly excessive accumulation of Ca2+, converge on mitochondria to induce oxidative stress and raise the opening potential of their inner membrane permeability transition pores (mPTPs). The ensuing loss of cationic homeostasis and adenosine triphosphate (ATP) production, together with osmotic swelling, leads to organellar degeneration and cellular necrosis. The overall impact of iterations in extracellular and intracellular cations and their influence on cardiac redox state, cardiomyocyte survival, and myocardial structure and function are addressed herein.

Nuclear quantum effects on adsorption of H2 and isotopologues on metal ions

NASA Astrophysics Data System (ADS)

Savchenko, Ievgeniia; Gu, Bing; Heine, Thomas; Jakowski, Jacek; Garashchuk, Sophya

2017-02-01

The nuclear quantum effects on the zero-point energy (ZPE), influencing adsorption of H2 and isotopologues on metal ions, are examined using normal mode analysis of ab initio electronic structure results for complexes with 17 metal cations. The lightest metallic nuclei, Li and Be, are found to be the most 'quantum'. The largest selectivity in adsorption is predicted for Cu, Ni and Co ions. Analysis of the nuclear wavepacket dynamics on the ground state electronic potential energy surfaces (PES) performed for complexes of Li+ and Cu+2 with H2/D2/HD shows that the PES anharmonicity changes the ZPE by up to 9%.

Accurate sub-millimetre rest frequencies for HOCO+ and DOCO+ ions

NASA Astrophysics Data System (ADS)

Bizzocchi, L.; Lattanzi, V.; Laas, J.; Spezzano, S.; Giuliano, B. M.; Prudenzano, D.; Endres, C.; Sipilä, O.; Caselli, P.

2017-06-01

Context. HOCO+ is a polar molecule that represents a useful proxy for its parent molecule CO2, which is not directly observable in the cold interstellar medium. This cation has been detected towards several lines of sight, including massive star forming regions, protostars, and cold cores. Despite the obvious astrochemical relevance, protonated CO2 and its deuterated variant, DOCO+, still lack an accurate spectroscopic characterisation. Aims: The aim of this work is to extend the study of the ground-state pure rotational spectra of HOCO+ and DOCO+ well into the sub-millimetre region. Methods: Ground-state transitions have been recorded in the laboratory using a frequency-modulation absorption spectrometer equipped with a free-space glow-discharge cell. The ions were produced in a low-density, magnetically confined plasma generated in a suitable gas mixture. The ground-state spectra of HOCO+ and DOCO+ have been investigated in the 213-967 GHz frequency range; 94 new rotational transitions have been detected. Additionally, 46 line positions taken from the literature have been accurately remeasured. Results: The newly measured lines have significantly enlarged the available data sets for HOCO+ and DOCO+, thus enabling the determination of highly accurate rotational and centrifugal distortion parameters. Our analysis shows that all HOCO+ lines with Ka ≥ 3 are perturbed by a ro-vibrational interaction that couples the ground state with the v5 = 1 vibrationally excited state. This resonance has been explicitly treated in the analysis in order to obtain molecular constants with clear physical meaning. Conclusions: The improved sets of spectroscopic parameters provide enhanced lists of very accurate sub-millimetre rest frequencies of HOCO+ and DOCO+ for astrophysical applications. These new data challenge a recent tentative identification of DOCO+ towards a pre-stellar core. Supplementary tables are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A34

Monte Carlo simulations of disorder in ZnSn N 2 and the effects on the electronic structure

DOE PAGES

Lany, Stephan; Fioretti, Angela N.; Zawadzki, Paweł P.; ...

2017-08-10

In multinary compound semiconductors, cation disorder can decisively alter the electronic properties and impact potential applications. ZnSnN 2 is a ternary nitride of interest for photovoltaics, which forms in a wurtzite-derived crystal structure. In the ground state, every N anion is coordinated by two Zn and two Sn cations, thereby observing the octet rule locally. Using a motif-based model Hamiltonian, we performed Monte Carlo simulations that provide atomistic representations of ZnSnN 2 with varying degrees of cation disorder. Subsequent electronic structure calculations describe the evolution of band gaps, optical properties, and carrier localization effects as a function of the disorder.more » We find that octet-rule conserving disorder is practically impossible to avoid but perfectly benign, with hardly any effects on the electronic structure. In contrast, a fully random cation distribution would be very detrimental, but fortunately it is energetically highly unfavorable. A degree of disorder that can realistically be expected for nonequilibrium thin-film deposition leads to a moderate band-gap reduction and to moderate carrier localization effects. Comparing the simulated structures with experimental samples grown by sputtering, we find evidence that these samples indeed incorporate a certain degree of octet-rule violating disorder, which is reflected in the x-ray diffraction and in the optical absorption spectra. This study demonstrates that the electronic properties of ZnSnN 2 are dominated by changes of the local coordination environments rather than long-range ordering effects.« less

Monte Carlo simulations of disorder in ZnSn N 2 and the effects on the electronic structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lany, Stephan; Fioretti, Angela N.; Zawadzki, Paweł P.

In multinary compound semiconductors, cation disorder can decisively alter the electronic properties and impact potential applications. ZnSnN 2 is a ternary nitride of interest for photovoltaics, which forms in a wurtzite-derived crystal structure. In the ground state, every N anion is coordinated by two Zn and two Sn cations, thereby observing the octet rule locally. Using a motif-based model Hamiltonian, we performed Monte Carlo simulations that provide atomistic representations of ZnSnN 2 with varying degrees of cation disorder. Subsequent electronic structure calculations describe the evolution of band gaps, optical properties, and carrier localization effects as a function of the disorder.more » We find that octet-rule conserving disorder is practically impossible to avoid but perfectly benign, with hardly any effects on the electronic structure. In contrast, a fully random cation distribution would be very detrimental, but fortunately it is energetically highly unfavorable. A degree of disorder that can realistically be expected for nonequilibrium thin-film deposition leads to a moderate band-gap reduction and to moderate carrier localization effects. Comparing the simulated structures with experimental samples grown by sputtering, we find evidence that these samples indeed incorporate a certain degree of octet-rule violating disorder, which is reflected in the x-ray diffraction and in the optical absorption spectra. This study demonstrates that the electronic properties of ZnSnN 2 are dominated by changes of the local coordination environments rather than long-range ordering effects.« less

Fast, safe, and reliable methods for extraction of major inorganic cations from small quantities of woody plant tissues

Treesearch

Rakesh Minocha; Walter C. Shortle

1993-01-01

Two simple and fast methods for the extraction of major inorganic cations (Ca, Mg, Mn, K) from small quantities of stemwood and needles of woody plants were developed. A 3.2- or 6.4-mm cobalt drill bit was used to shave samples from disks and increment cores of stemwood. For ion extraction, wood (ground or shavings) or needles were either homogenzied using a Tekmar...

Revisiting the ground state of CoAl 2 O 4 : Comparison to the conventional antiferromagnet MnAl 2 O 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacDougall, Gregory J.; Aczel, Adam A.; Su, Yixi

The A-site spinel material CoAl 2O 4 is a physical realization of the frustrated diamond-lattice antiferromagnet, a model in which unique incommensurate or “spin-spiral-liquid” ground states are predicted. Our previous single-crystal neutron scattering study instead classified it as a “kinetically inhibited” antiferromagnet, where the long-ranged correlations of a collinear Néel ground state are blocked by the freezing of domain-wall motion below a first-order phase transition at T*=6.5 K. This study provides new data sets from a number of experiments, which support and expand this work in several important ways. We show that the phenomenology leading to the kinetically inhibited ordermore » is unaffected by sample measured and instrument resolution, while new low-temperature measurements reveal spin correlations are unchanging between T=2 K and 250 mK, consistent with a frozen state. Polarized diffuse neutron measurements show several interesting magnetic features, which can be entirely explained by the existence of short-ranged Néel order. Finally, and crucially, this paper presents some neutron scattering studies of single crystalline MnAl 2O 4, which acts as an unfrustrated analog to CoAl 2O 4 and shows all the hallmarks of a classical antiferromagnet with a continuous phase transition to Néel order at T N=39 K. Direct comparison between the two compounds indicates that CoAl 2O 4 is unique, not in the nature of high-temperature diffuse correlations, but rather in the nature of the frozen state below T*. Finally, the higher level of cation inversion in the MnAl 2O 4 sample indicates that this behavior is primarily an effect of greater next-nearest-neighbor exchange.« less

Revisiting the ground state of CoAl 2 O 4 : Comparison to the conventional antiferromagnet MnAl 2 O 4

DOE PAGES

MacDougall, Gregory J.; Aczel, Adam A.; Su, Yixi; ...

2016-11-17

The A-site spinel material CoAl 2O 4 is a physical realization of the frustrated diamond-lattice antiferromagnet, a model in which unique incommensurate or “spin-spiral-liquid” ground states are predicted. Our previous single-crystal neutron scattering study instead classified it as a “kinetically inhibited” antiferromagnet, where the long-ranged correlations of a collinear Néel ground state are blocked by the freezing of domain-wall motion below a first-order phase transition at T*=6.5 K. This study provides new data sets from a number of experiments, which support and expand this work in several important ways. We show that the phenomenology leading to the kinetically inhibited ordermore » is unaffected by sample measured and instrument resolution, while new low-temperature measurements reveal spin correlations are unchanging between T=2 K and 250 mK, consistent with a frozen state. Polarized diffuse neutron measurements show several interesting magnetic features, which can be entirely explained by the existence of short-ranged Néel order. Finally, and crucially, this paper presents some neutron scattering studies of single crystalline MnAl 2O 4, which acts as an unfrustrated analog to CoAl 2O 4 and shows all the hallmarks of a classical antiferromagnet with a continuous phase transition to Néel order at T N=39 K. Direct comparison between the two compounds indicates that CoAl 2O 4 is unique, not in the nature of high-temperature diffuse correlations, but rather in the nature of the frozen state below T*. Finally, the higher level of cation inversion in the MnAl 2O 4 sample indicates that this behavior is primarily an effect of greater next-nearest-neighbor exchange.« less

Ground-Water Conditions and Studies in the Albany Area of Dougherty County, Georgia, 2007

USGS Publications Warehouse

Gordon, Debbie W.

2008-01-01

The U.S. Geological Survey (USGS) has been working with the Albany Water, Gas, and Light Commission to monitor ground-water quality and availability since 1977. This report presents an overview of ground-water conditions and studies in the Albany area of Dougherty County, Georgia, during 2007. Historical data are also presented for comparison with 2007 data. Ongoing monitoring activities include continuous water-level recording in 24 wells and monthly water-level measurements in 5 wells. During 2007, water levels in 21 of the continuous-recording wells were below normal, corresponding to lower than average rainfall. Ground-water samples collected from the Upper Floridan aquifer indicate that nitrate levels have decreased or remained about the same since 2006. Water samples were collected from the Flint River and wells at the Albany wellfield, and data were plotted on a trilinear diagram to show the percent composition of selected major cations and anions. Ground-water constituents (major cations and anions) of the Upper Floridan aquifer at the Albany wellfield are distinctly different from those in the water of the Flint River. To improve the understanding of the ground-water flow system and nitrate movement in the Upper Floridan aquifer, the USGS is developing a ground-water flow model in the southwestern Albany area of Georgia. The model is being calibrated to simulate periods of dry (October 1999) and relatively wet (March 2001) hydrologic conditions. Preliminary water-level simulations indicate a generally good fit to measured water levels.

Limnological characteristics of selected lakes in the Nebraska sandhills, U.S.A., and their relation to chemical characteristics of adjacent ground water

USGS Publications Warehouse

La Baugh, J.W.

1986-01-01

Limnological characteristics of Crane, Hackberry, Island and Roundup Lakes, and chemical characteristics of shallow ground water, within the Crescent Lake National Wildlife Refuge, western Nebraska, were determined during a preliminary investigation of the interaction between lakes and ground water in this study area between 1980 and 1984. When ice cover was absent, the lakes were well-mixed vertically, regardless of season. Depth to which 1% of surface illumination penetrated was commonly less than 1m. Variability in light penetration, as measured by Secchidisk transparency, appeared to be unrelated to changes in algal biomass, even though algal biomass, measured as chlorophyll a, varied seasonally within a two-order-of-magnitude range. Blue-green algae were the most abundant phytoplankton; this condition occurred most often when the ratio of total nitrogen to total phosphorus in the lakes' water was less than 29. Although rotifers and copepod naupli commonly were the most abundant zooplankton in the lakes, cladocerans were dominant occasionally. Either sodium or calcium was the most abundant cation, and bicarbonate was the most abundant anion, in water from water-table wells and lakes sampled during the study. The second most abundant cation in the ground water was related to the location of the sampled well within the ground-water system. The lakes were a source of dissolved organic carbon seeping to ground water. Chemical and hydrologic data indicate there is interaction between lakes and ground water in the study area. ?? 1986.

Comparative electronic structure of a lanthanide and actinide diatomic oxide: Nd versus U

NASA Astrophysics Data System (ADS)

Krauss, M.; Stevens, W. J.

2003-01-01

Using a modified version of the Alchemy electronic structure code and relativistic pseudopotentials, the electronic structure of the ground and low lying excited states of UO, NdO, and NdO + have been calculated at the Hartree-Fock (HF) and multiconfiguration self-consistent field (MCSCF) levels of theory. Including results from an earlier study of UO + this provides the information for a comparative analysis of a lanthanide and an actinide diatomic oxide. UO and NdO are both described formally as M +2 O -2 and the cations as M +3 O -2 , but the HF and MCSCF calculations show that these systems are considerably less ionic due to large charge back-transfer in the πorbitals. The electronic states putatively arise from the ligand field (oxygen anion) perturbed f 4 , sf 3 , df 3 , sdf 2 , or s 2 f 2 states of M +2 and f 3 , sf 2 or df 2 states of M +3 . Molecular orbital results show a substantial stabilization of the sf 3 or s 2 f 2 configurations relative to the f 4 or df 3 configurations that are the even or odd parity ground states in the M +2 free ion. The compact f and d orbitals are more destabilized by the anion field than the diffuse s orbital. The ground states of the neutral species are dominated by orbitals arising from the M +2 sf 3 term, and all the potential energy curves arising from this configuration are similar, which allows an estimate of the vibrational frequencies for UO and NdO of 862 cm -1 and 836 cm -1 , respectively. For NdO + and UO + the excitation energies for the Ωstates were calculated with a valence configuration interaction method using ab initio effective spin-orbit operators to couple the molecular orbital configurations. The results for NdO + are very comparable with the results for UO + , and show the vibrational and electronic states to be interleaved.

Spectral studies of N-nonyl acridine orange in anionic, cationic and neutral surfactants

NASA Astrophysics Data System (ADS)

Wiosetek-Reske, Agnieszka M.; Wysocki, Stanisław

2006-08-01

The spectroscopic and photophysical properties of N-nonyl acridine orange - a metachromatic dye useful as a mitochondrial probe in living cells - are reported in water and microheterogeneous media: anionic sodium dodecylsulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB) and neutral octylophenylpolyoxyethylene ether (TX-100). The spectral changes of N-nonyl acridine orange were observed in the presence of varying amount of SDS, CTAB and TX-100 and indicated formation of a dye-surfactant complex. The spectral changes were also regarded to be caused by the incorporation of dye molecules to micelles. It was proved by calculated values Kb and f in the following order: Kb TX-100 > Kb CTAB > Kb SDS and fTX-100 > fCTAB > fSDS. NAO binds to the micelle regardless the micellar charge. There are two types of interactions between NAO and micelles: hydrophobic and electrostatic. The hydrophobic interactions play a dominant role in binding of the dye to neutral TX-100. The unexpected fact of the binding NAO to cationic CTAB can be explained by a dominant role of hydrophobic interactions over electrostatic repulsion. Therefore, the affinity of NAO to CTAB is smaller than TX-100. Electrostatic interactions play an important role in binding of NAO to anionic micelles SDS. We observed a prolonged fluorescence lifetime after formation of the dye-surfactant complex τSDS > τTX-100 > τCTAB > τwater, the dye being protected against water in this environment. TX-100 is found to stabilize the excited state of NAO which is more polar than the ground state. Spectroscopic and photophysical properties of NAO will be helpful for a better understanding of the nature of binding and distribution inside mammalian cells.

Theoretical Study of Group 14 M^{+}(^{2}P_{J})-RG Complexes (M^{+} = C^{+}, Si^{+}; RG = he - Ar)

NASA Astrophysics Data System (ADS)

Tuttle, William Duncan; Thorington, Rebecca L.; Wright, Timothy G.; Viehland, Larry A.

2017-06-01

The light group 14 cations are found in a wide variety of environments, with, for example, C^{+} ions thought to play a key role in the chemistry of the interstellar medium, while Si^{+} ions are an important component of the upper atmosphere of the Earth due to their presence in meteoroids. We calculate accurate interatomic potentials for a singly charged carbon cation and a singly charged silicon cation interacting with the rare gas atoms helium, neon and argon. The RCCSD(T) method is employed, with basis sets of quadruple-ζ and quintuple-ζ quality, and the energies counterpoise corrected and extrapolated to the basis set limit at each point. In all cases, we consider the lowest electronic states of the M^{+} atom, (^{2}P_{J}), interacting with the ground electronic state of the RG atom, (^{1}S_{0}), and compute potentials corresponding to the molecular terms, ^{2}Π and ^{2}Σ^{+}, as well as the spin-orbit levels which arise: ^{2}Π_{3/2}, ^{2}Π_{1/2} and ^{2}Σ_{1/2}^{+}. The potentials are employed to calculated spectroscopic constants and ion transport properties. S. Petrie and D. K. Bohme, Mass Spec. Rev., 26, 258 (2007). J. M. C. Plane, J. C. Gómez-Martin, W. Feng, and D. Janches, J. Geophys. Res. Atmos. 121, 3718 (2016). W. D. Tuttle, R. L. Thorington, L. A. Viehland and T. G. Wright, Mol. Phys. 113, 3767 (2015). W. D. Tuttle, R. L. Thorington, L. A. Viehland and T. G. Wright (in preparation). W. D. Tuttle, R. L. Thorington, L. A. Viehland and T. G. Wright, Mol. Phys. 115, 437 (2017).

Impact of the cation distribution homogeneity on the americium oxidation state in the U0.54Pu0.45Am0.01O2-x mixed oxide

NASA Astrophysics Data System (ADS)

Vauchy, Romain; Robisson, Anne-Charlotte; Martin, Philippe M.; Belin, Renaud C.; Aufore, Laurence; Scheinost, Andreas C.; Hodaj, Fiqiri

2015-01-01

The impact of the cation distribution homogeneity of the U0.54Pu0.45Am0.01O2-x mixed oxide on the americium oxidation state was studied by coupling X-ray diffraction (XRD), electron probe micro analysis (EPMA) and X-ray absorption spectroscopy (XAS). Oxygen-hypostoichiometric Am-bearing uranium-plutonium mixed oxide pellets were fabricated by two different co-milling based processes in order to obtain different cation distribution homogeneities. The americium was generated from β- decay of 241Pu. The XRD analysis of the obtained compounds did not reveal any structural difference between the samples. EPMA, however, revealed a high homogeneity in the cation distribution for one sample, and substantial heterogeneity of the U-Pu (so Am) distribution for the other. The difference in cation distribution was linked to a difference in Am chemistry as investigated by XAS, with Am being present at mixed +III/+IV oxidation state in the heterogeneous compound, whereas only Am(IV) was observed in the homogeneous compound. Previously reported discrepancies on Am oxidation states can hence be explained by cation distribution homogeneity effects.

Structures and stability of metal-doped Ge{sub n}M (n = 9, 10) clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Wei, E-mail: qinw@qdu.edu.cn; Xia, Lin-Hua; Zhao, Li-Zhen

The lowest-energy structures of neutral and cationic Ge{sub n}M (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge{sub 9} and Ge{sub 10} clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Ge{sub n} clusters. However, the neutral and cationic FeGe{sub 9,10},MnGe{sub 9,10} and Ge{sub 10}Al are cage-like withmore » the metal atom encapsulated inside. Such cage-like transition metal doped Ge{sub n} clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge{sub 9,10}Fe and Ge{sub 9}Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.« less

Vibrational assignment and structure of trinuclear oxo-centered of basic formate iron(III) and chromium(III) complexes: A density functional theory study

NASA Astrophysics Data System (ADS)

Kiana, Samaneh; Yazdanbakhsh, Mohammad; Jamialahmadi, Mina; Tayyari, Sayyed Faramarz

2014-09-01

[Fe3O(OOCH)6(H2O)3]OOCH·HCOOH, and [Cr3O(OOCH)6(H2O)3]OOCH·2.5HNO3 were synthesized and the molecular structure and vibrational assignments of their cations were investigated by means of density functional theory (DFT) calculations. The harmonic vibrational frequencies of [Fe3O(OOCH)6(H2O)3]+ and [Cr3O(OOCH)6(H2O)3]+ were obtained at the UB3LYP level using a series of basis sets. The topological properties of the charge distribution of both cations in their ground states are discussed in detail by means of natural bond orbital (NBO) theory and of [Fe3O(OOCH)6(H2O)3]+ by the quantum theory of atoms in molecules (AIM). The calculated geometrical parameters and vibrational frequencies were compared with the experimental results. The scaled theoretical frequencies and the structural parameters were found to be in good agreement with the experimental data.

Femtosecond pump-supercontinuum probe and transient lens spectroscopy of adonixanthin.

PubMed

Lenzer, Thomas; Schubert, Steffen; Ehlers, Florian; Lohse, Peter W; Scholz, Mirko; Oum, Kawon

2009-03-15

The ultrafast internal conversion (IC) dynamics of adonixanthin in organic solvents were studied by pump-supercontinuum probe (PSCP) and transient lens (TL) spectroscopy after photoexcitation to the S(2) state. Transient PSCP spectra in the range 344-768 nm provided the spectral evolution of the S(0)-->S(2) ground state bleach and S(1)-->S(n) excited state absorption. Time constants were tau(2) =115 and 111 fs for the S(2)-->S(1) IC and tau(1)=6.4 and 5.8 ps for the S(1)-->S(0) IC in acetone and methanol, respectively. There was only an insignificant polarity dependence of tau(1), underlining the negligible importance of intramolecular charge transfer (ICT) in the lowest-lying excited state of C(40) carotenoids with carbonyl substitution on the beta-ionone ring. A blueshift and a spectral narrowing of the S(1)-->S(n) ESA band, likely due to solvation dynamics, and formation of the adonixanthin radial cation at high pump energies via resonant two-photon ionization were found.

Evidence for Cation-Controlled Excited-State Localization in a Ruthenium Polypyridyl Compound.

PubMed

Beauvilliers, Evan E; Meyer, Gerald J

2016-08-01

The visible absorption and photoluminescence (PL) properties of the four neutral ruthenium diimine compounds [Ru(bpy)2(dcb)] (B2B), [Ru(dtb)2(dcb)] (D2B), [Ru(bpy)2(dcbq)] (B2Q), and [Ru(dtb)2(dcbq)] (D2Q), where bpy is 2,2'-bipyridine, dcb is 4,4'-(CO2(-))2-bpy, dtb is 4,4'-(tert-butyl)2-bpy, and dcbq is 4,4'-(CO2(-))2-2,2'-biquinoline, are reported in the presence of Lewis acidic cations present in fluid solutions at room temperature. In methanol solutions, the measured spectra were insensitive to the presence of these cations, while in acetonitrile a significant red shift in the PL spectra (≤1400 cm(-1)) was observed consistent with stabilization of the metal-to-ligand charge transfer (MLCT) excited state through Lewis acid-base adduct formation. No significant spectral changes were observed in control experiments with the tetrabutylammonium cation. Titration data with Li(+), Na(+), Mg(2+), Ca(2+), Zn(2+), Al(3+), Y(3+), and La(3+) showed that the extent of stabilization saturated at high cation concentration with magnitudes that scaled roughly with the cation charge-to-size ratio. The visible absorption spectra of D2Q was particularly informative due to the presence of two well-resolved MLCT absorption bands: (1) Ru → bpy, λmax ≈ 450 nm; and (2) Ru → dcbq, λmax ≈ 540 nm. The higher-energy band blue-shifted and the lower-energy band red-shifted upon cation addition. The PL intensity and lifetime of the excited state of B2B first increased with cation addition without significant shifts in the measured spectra, behavior attributed to a cation-induced change in the localization of the emissive excited state from bpy to dcb. The importance of excited-state localization and stabilization for solar energy conversion is discussed.

On the “alpha-phase” of Ca{sub 2−x}Sr{sub x}MnO{sub 4} and extending the chemistry of Sr{sub 7−y}Ca{sub y}Mn{sub 4}O{sub 15} to y>1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Craddock, Sarah; Senn, Mark S.

There has been renewed interest in the Ruddlesden-Popper phase (n=2) of composition Ca{sub n+1}Mn{sub n}O{sub 3} {sub n+1} in the light of recent research that has highlighted the nature of the improper ferroelectric ground state, which arises due to the couplings between specific combinations of MnO{sub 6} octahedral rotations and tilts. A fruitful route to control these octahedral degrees of freedom, and hence such desired physical properties, is through chemical substitution on the A–site cation i.e. Ca{sub 2−x}Sr{sub x}MnO{sub 4} for n =1, and in light of this, we have reinvestigated the chemistry of this solid solution. Here we focusmore » on a common impurity phase observed during this synthesis which has been termed the “alpha-phase” in the literature. We show that this impurity phase is actually comprised mainly of a structure related to Sr{sub 7}Mn{sub 4}O{sub 15} but is found here with significantly higher Ca substitution than previously believed possible. Sr{sub 7}Mn{sub 4}O{sub 15} is an interesting structural type in its own right, but has been mainly overlooked to date, exhibiting interesting physics related to low dimensional magnetic ordering and dimer interactions, and we show here that the structural type is a likely candidate for exhibiting a multiferroic ground state. The prospect of being able to tune the lattice and the exchange interactions through further chemical substitution is likely to lead to a renewed interest in this material. - Graphical abstract: Extending the chemistry of Sr{sub 7−y}Ca{sub y}Mn{sub 4}O{sub 15} beyond y>1, revealing highly anisotropic cation ordering and tunable magnetic properties. - Highlights: • Chemistry of the unique structural type Sr{sub 7}Mn{sub 4}O{sub 15} is extended to high Ca concentrations. • Cation occupancy model is determined, showing highly anisotropic solubility of Ca on the 7 unique Sr crystallographic sites. • Anomalies in the magnetic susceptibility data are discussed with reference to symmetry arguments pointing towards a possible novel multiferroic mechanism in this material.« less

Infrared spectroscopy of ionized corannulene in the gas phase.

PubMed

Alvaro Galué, Héctor; Rice, Corey A; Steill, Jeffrey D; Oomens, Jos

2011-02-07

The gas-phase infrared spectra of radical cationic and protonated corannulene were recorded by infrared multiple-photon dissociation (IRMPD) spectroscopy using the IR free electron laser for infrared experiments. Electrospray ionization was used to generate protonated corannulene and an IRMPD spectrum was recorded in a Fourier-transform ion cyclotron resonance mass spectrometer monitoring H-loss as a function of IR frequency. The radical cation was produced by 193-nm UV photoionization of the vapor of corannulene in a 3D quadrupole trap and IR irradiation produces H, H(2), and C(2)H(x) losses. Summing the spectral response of the three fragmentation channels yields the IRMPD spectrum of the radical cation. The spectra were analyzed with the aid of quantum-chemical calculations carried out at various levels of theory. The good agreement of theoretical and experimental spectra for protonated corannulene indicates that protonation occurs on one of the peripheral C-atoms, forming an sp(3) hybridized carbon. The spectrum of the radical cation was examined taking into account distortions of the C(5v) geometry induced by the Jahn-Teller effect as a consequence of the degenerate (2)E(1) ground electronic state. As indicated by the calculations, the five equivalent C(s) minima are separated by marginal barriers, giving rise to a dynamically distorted system. Although in general the character of the various computed vibrational bands appears to be in order, only a qualitative match to the experimental spectrum is found. Along with a general redshift of the calculated frequencies, the IR intensities of modes in the 1000-1250 cm(-1) region show the largest discrepancy with the harmonic predictions. In addition to CH "in-plane" bending vibrations, these modes also exhibit substantial deformation of the pentagonal inner ring, which may relate directly to the vibronic interaction in the radical cation.

Synthetic Control of Exciton Behavior in Colloidal Quantum Dots.

PubMed

Pu, Chaodan; Qin, Haiyan; Gao, Yuan; Zhou, Jianhai; Wang, Peng; Peng, Xiaogang

2017-03-08

Colloidal quantum dots are promising optical and optoelectronic materials for various applications, whose performance is dominated by their excited-state properties. This article illustrates synthetic control of their excited states. Description of the excited states of quantum-dot emitters can be centered around exciton. We shall discuss that, different from conventional molecular emitters, ground-state structures of quantum dots are not necessarily correlated with their excited states. Synthetic control of exciton behavior heavily relies on convenient and affordable monitoring tools. For synthetic development of ideal optical and optoelectronic emitters, the key process is decay of band-edge excitons, which renders transient photoluminescence as important monitoring tool. On the basis of extensive synthetic developments in the past 20-30 years, synthetic control of exciton behavior implies surface engineering of quantum dots, including surface cation/anion stoichiometry, organic ligands, inorganic epitaxial shells, etc. For phosphors based on quantum dots doped with transition metal ions, concentration and location of the dopant ions within a nanocrystal lattice are found to be as important as control of the surface states in order to obtain bright dopant emission with monoexponential yet tunable photoluminescence decay dynamics.

Ground and excited states of vanadium hydroxide isomers and their cations, VOH0,+ and HVO0,+

NASA Astrophysics Data System (ADS)

Miliordos, Evangelos; Harrison, James F.; Hunt, Katharine L. C.

2013-03-01

Employing correlation consistent basis sets of quadruple-zeta quality and applying both multireference configuration interaction and single-reference coupled cluster methodologies, we studied the electronic and geometrical structure of the [V,O,H]0,+ species. The electronic structure of HVO0,+ is explained by considering a hydrogen atom approaching VO0,+, while VOH0,+ molecules are viewed in terms of the interaction of V+,2+ with OH-. The potential energy curves for H-VO0,+ and V0,+-OH have been constructed as functions of the distance between the interacting subunits, and the potential energy curves have also been determined as functions of the H-V-O angle. For the stationary points that we have located, we report energies, geometries, harmonic frequencies, and dipole moments. We find that the most stable bent HVO0,+ structure is lower in energy than any of the linear HVO0,+ structures. Similarly, the most stable state of bent VOH is lower in energy than the linear structures, but linear VOH+ is lower in energy than bent VOH+. The global minimum on the potential energy surface for the neutral species is the tilde{X}^3A″ state of bent HVO, although the tilde{X}^5A″ state of bent VOH is less than 5 kcal/mol higher in energy. The global minimum on the potential surface for the cation is the tilde{X}^4Σ ^- state of linear VOH+, with bent VOH+ and bent HVO+ both more than 10 kcal/mol higher in energy. For the neutral species, the bent geometries exhibit significantly higher dipole moments than the linear structures.

The electronic structure of vanadium monochloride cation (VCl+): Tackling the complexities of transition metal species

NASA Astrophysics Data System (ADS)

DeYonker, Nathan J.; Halfen, DeWayne T.; Allen, Wesley D.; Ziurys, Lucy M.

2014-11-01

Six electronic states (X 4Σ-, A 4Π, B 4Δ, 2Φ, 2Δ, 2Σ+) of the vanadium monochloride cation (VCl+) are described using large basis set coupled cluster theory. For the two lowest quartet states (X 4Σ- and A 4Π), a focal point analysis (FPA) approach was used that conjoined a correlation-consistent family of basis sets up to aug-cc-pwCV5Z-DK with high-order coupled cluster theory through pentuple (CCSDTQP) excitations. FPA adiabatic excitation energies (T0) and spectroscopic constants (re, r0, Be, B0, bar De, He, ωe, v0, αe, ωexe) were extrapolated to the valence complete basis set Douglas-Kroll (DK) aug-cc-pV∞Z-DK CCSDT level of theory, and additional treatments accounted for higher-order valence electron correlation, core correlation, and spin-orbit coupling. Due to the delicate interplay between dynamical and static electronic correlation, single reference coupled cluster theory is able to provide the correct ground electronic state (X 4Σ-), while multireference configuration interaction theory cannot. Perturbations from the first- and second-order spin orbit coupling of low-lying states with quartet spin multiplicity reveal an immensely complex rotational spectrum relative to the isovalent species VO, VS, and TiCl. Computational data on the doublet manifold suggest that the lowest-lying doublet state (2Γ) has a Te of ˜11 200 cm-1. Overall, this study shows that laboratory and theoretical rotational spectroscopists must work more closely in tandem to better understand the bonding and structure of molecules containing transition metals.

Square-antiprismatic eight-coordinate complexes of divalent first-row transition metal cations: a density functional theory exploration of the electronic-structural landscape.

PubMed

Conradie, Jeanet; Patra, Ashis K; Harrop, Todd C; Ghosh, Abhik

2015-02-16

Density functional theory (in the form of the PW91, BP86, OLYP, and B3LYP exchange-correlation functionals) has been used to map out the low-energy states of a series of eight-coordinate square-antiprismatic (D2d) first-row transition metal complexes, involving Mn(II), Fe(II), Co(II), Ni(II), and Cu(II), along with a pair of tetradentate N4 ligands. Of the five complexes, the Mn(II) and Fe(II) complexes have been synthesized and characterized structurally and spectroscopically, whereas the other three are as yet unknown. Each N4 ligand consists of a pair of terminal imidazole units linked by an o-phenylenediimine unit. The imidazole units are the strongest ligands in these complexes and dictate the spatial disposition of the metal three-dimensional orbitals. Thus, the dx(2)-y(2) orbital, whose lobes point directly at the coordinating imidazole nitrogens, has the highest orbital energy among the five d orbitals, whereas the dxy orbital has the lowest orbital energy. In general, the following orbital ordering (in order of increasing orbital energy) was found to be operative: dxy < dxz = dyz ≤ dz(2) < dx(2)-y(2). The square-antiprism geometry does not lead to large energy gaps between the d orbitals, which leads to an S = 2 ground state for the Fe(II) complex. Nevertheless, the dxy orbital has significantly lower energy relative to that of the dxz and dyz orbitals. Accordingly, the ground state of the Fe(II) complex corresponds unambiguously to a dxy(2)dxz(1)dyz(1)dz(2)(1)dx(2)-y(2)(1) electronic configuration. Unsurprisingly, the Mn(II) complex has an S = 5/2 ground state and no low-energy d-d excited states within 1.0 eV of the ground state. The Co(II) complex, on the other hand, has both a low-lying S = 1/2 state and multiple low-energy S = 3/2 states. Very long metal-nitrogen bonds are predicted for the Ni(II) and Cu(II) complexes; these bonds may be too fragile to survive in solution or in the solid state, and the complexes may therefore not be isolable. Overall, the different exchange-correlation functionals provided a qualitatively consistent and plausible picture of the low-energy d-d excited states of the complexes.

IR signature of the photoionization-induced hydrophobic-->hydrophilic site switching in phenol-Arn clusters

NASA Astrophysics Data System (ADS)

Ishiuchi, Shun-ichi; Sakai, Makoto; Tsuchida, Yuji; Takeda, Akihiro; Kawashima, Yasutake; Dopfer, Otto; Müller-Dethlefs, Klaus; Fujii, Masaaki

2007-09-01

IR spectra of phenol-Arn (PhOH-Arn) clusters with n =1 and 2 were measured in the neutral and cationic electronic ground states in order to determine the preferential intermolecular ligand binding motifs, hydrogen bonding (hydrophilic interaction) versus π bonding (hydrophobic interaction). Analysis of the vibrational frequencies of the OH stretching motion, νOH, observed in nanosecond IR spectra demonstrates that neutral PhOH-Ar and PhOH -Ar2 as well as cationic PhOH +-Ar have a π-bound structure, in which the Ar atoms bind to the aromatic ring. In contrast, the PhOH +-Ar2 cluster cation is concluded to have a H-bound structure, in which one Ar atom is hydrogen-bonded to the OH group. This π →H binding site switching induced by ionization was directly monitored in real time by picosecond time-resolved IR spectroscopy. The π-bound νOH band is observed just after the ionization and disappears simultaneously with the appearance of the H-bound νOH band. The analysis of the picosecond IR spectra demonstrates that (i) the π →H site switching is an elementary reaction with a time constant of ˜7ps, which is roughly independent of the available internal vibrational energy, (ii) the barrier for the isomerization reaction is rather low(<100cm-1), (iii) both the position and the width of the H-bound νOH band change with the delay time, and the time evolution of these spectral changes can be rationalized by intracluster vibrational energy redistribution occurring after the site switching. The observation of the ionization-induced switch from π bonding to H bonding in the PhOH +-Ar2 cation corresponds to the first manifestation of an intermolecular isomerization reaction in a charged aggregate.

Electronic structures of superionic conductor Li3N

NASA Astrophysics Data System (ADS)

Aoki, Masaru; Ode, Yoshiyuki; Tsumuraya, Kazuo

2011-03-01

Lithium nitride is a superionic conductor with high Li conductivity. The compound has been studied extensively because of its potential utility as electrolyte in solid-state batteries. Though the mobility of the cations within the crystalline solid is high comparable to that of molten salts, the mechanism of the high mobility of the cations remains unsolved. To clarify the origin of the mobility we investigate the electronic states of the Li cations in the Li 3 N crystal with the first principles electronic structure analysis, focusing a correlation between the cations and the ionicities of the constituent atoms. We have found the existence of the covalent bonding between the Li atoms in the Li 3 N crystal in spite of the ionized states of the constituent atoms.

Alternative analytical forms to model diatomic systems based on the deformed exponential function.

PubMed

da Fonsêca, José Erinaldo; de Oliveira, Heibbe Cristhian B; da Cunha, Wiliam Ferreira; Gargano, Ricardo

2014-07-01

Using a deformed exponential function and the molecular-orbital theory for the simplest molecular ion, two new analytical functions are proposed to represent the potential energy of ground-state diatomic systems. The quality of these new forms was tested by fitting the ab initio electronic energies of the system LiH, LiNa, NaH, RbH, KH, H2, Li2, K2, H 2 (+) , BeH(+) and Li 2 (+) . From these fits, it was verified that these new proposals are able to adequately describe homonuclear, heteronuclear and cationic diatomic systems with good accuracy. Vibrational spectroscopic constant results obtained from these two proposals are in good agreement with experimental data.

State-to-state measurements of low-energy ion-molecule and ion-ion collisions by three dimensional momentum imaging

NASA Astrophysics Data System (ADS)

Urbain, Xavier

2016-09-01

While the measurement of total absolute cross sections remains challenging, the insight provided by differential cross sections and branching ratios is invaluable to assess the quality of theoretical predictions. Satisfactory agreement at the latter level gives better confidence in the proper identification of the reaction mechanism and key parameters. The three dimensional imaging of molecular dissociation, and more generally, the determination of all momentum vectors of the reaction products, gives direct access to the differential quantities of interest. For the prototype reaction of a proton colliding with H2, the secondary H2+current may be recorded to provide the total charge transfer yield. The dissociative charge transfer of the product ions with alkali targets leaves a characteristic signature in the total kinetic energy imparted to the H fragments. Its measurement is readily achieved by coincident detection on position sensitive detectors. This allows us to extract vibrational populations as a function of collision energy. A resonant enhancement of the charge transfer around 45 eV/amu is observed, that leaves the molecular ion in its vibrational ground state. Those observations are supported by state-of-the-art calculations. We have similarly explored the ionization of molecular oxygen by proton and alpha particle impact, at velocities characteristic of the solar wind. A somewhat more involved vibrational analysis of the O2+cations indicates a Franck-Condon like vibrational population of the ground electronic state from 50 eV to 10 keV, unlikely to modify the branching ratios of dissociative recombination, itself responsible for airglow emissions. More interestingly, a significant population of the 4Πu excited state is measured at velocities typical of the fast solar wind. Finally, we shall address the implementation of three dimensional imaging in merged ion-ion beam studies. Mutual neutralization involving anions and cations is a very efficient process, characterized by a uniquely defined initial state and a limited range of final states readily identified by the total kinetic energy released to the products. Detailed branching ratios may be obtained at near zero collision energy where the reaction rate is maximum and the system behaves as a quasi-molecule undergoing in flight dissociation. As an example, we shall discuss the mutual neutralization of C+ and various anions of the second and third row of the periodic table. This work was supported by the Fonds de la Recherche Scientifique - FNRS through IISN Contract No. 4.4504.10.

Estimates of natural ground-water discharge and characterization of water quality in Dry Valley, Washoe County, West-Central Nevada, 2002-2003

USGS Publications Warehouse

Berger, David L.; Maurer, Douglas K.; Lopes, Thomas J.; Halford, Keith J.

2004-01-01

The Dry Valley Hydrographic Area is being considered as a potential source area for additional water supplies for the Reno-Sparks area, which is about 25 miles south of Dry Valley. Current estimates of annual ground-water recharge to Dry Valley have a considerable range. In undeveloped valleys, such as Dry Valley, long-term ground-water discharge can be assumed the same as long-term ground-water recharge. Because estimating ground-water discharge has more certainty than estimating ground-water recharge from precipitation, the U.S. Geological Survey, in cooperation with Washoe County, began a three-year study to re-evaluate the ground-water resources by estimating natural ground-water discharge and characterize ground-water quality in Dry Valley. In Dry Valley, natural ground-water discharge occurs as subsurface outflow and by ground-water evapotranspiration. The amount of subsurface outflow from the upper part of Dry Valley to Winnemucca and Honey Lake Valleys likely is small. Subsurface outflow from Dry Valley westward to Long Valley, California was estimated using Darcy's Law. Analysis of two aquifer tests show the transmissivity of poorly sorted sediments near the western side of Dry Valley is 1,200 to 1,500 square feet per day. The width of unconsolidated sediments is about 4,000 feet between exposures of tuffaceous deposits along the State line, and decreases to about 1,500 feet (0.5 mile) west of the State line. The hydraulic gradient east and west of the State line ranges from 0.003 to 0.005 foot per foot. Using these values, subsurface outflow to Long Valley is estimated to be 50 to 250 acre-feet per year. Areas of ground-water evapotranspiration were field mapped and partitioned into zones of plant cover using relations derived from Landsat imagery acquired July 8, 2002. Evapotranspiration rates for each plant-cover zone were multiplied by the corresponding area and summed to estimate annual ground-water evapotranspiration. About 640 to 790 acre-feet per year of ground water is lost to evapotranspiration in Dry Valley. Combining subsurface-outflow estimates with ground-water evapotranspiration estimates, total natural ground-water discharge from Dry Valley ranges from a minimum of about 700 acre-feet to a maximum of about 1,000 acre-feet annually. Water quality in Dry Valley generally is good and primary drinking-water standards were not exceeded in any samples collected. The secondary standard for manganese was exceeded in three ground-water samples. One spring sample and two surface-water samples exceeded the secondary standard for pH. Dry Valley has two primary types of water chemistry that are distinguishable by cation ratios and related to the two volcanic-rock units that make up much of the surrounding mountains. In addition, two secondary types of water chemistry appear to have evolved by evaporation of the primary water types. Ground water near the State line appears to be an equal mixture of the two primary water chemistries and has as an isotopic characteristic similar to evaporated surface water.

The Broken Ring: Reduced Aromaticity in Lys-Trp Cations and High pH Tautomer Correlates with Lower Quantum Yield and Shorter Lifetimes

PubMed Central

2015-01-01

Several nonradiative processes compete with tryptophan fluorescence emission. The difficulty in spectral interpretation lies in associating specific molecular environmental features with these processes and thereby utilizing the fluorescence spectral data to identify the local environment of tryptophan. Here, spectroscopic and molecular modeling study of Lys-Trp dipeptide charged species shows that backbone-ring interactions are undistinguished. Instead, quantum mechanical ground state isosurfaces reveal variations in indole π electron distribution and density that parallel charge (as a function of pK1, pK2, and pKR) on the backbone and residues. A pattern of aromaticity-associated quantum yield and fluorescence lifetime changes emerges. Where quantum yield is high, isosurfaces have a charge distribution similar to the highest occupied molecular orbital (HOMO) of indole, which is the dominant fluorescent ground state of the 1La transition dipole moment. Where quantum yield is low, isosurface charge distribution over the ring is uneven, diminished, and even found off ring. At pH 13, the indole amine is deprotonated, and Lys-Trp quantum yield is extremely low due to tautomer structure that concentrates charge on the indole amine; the isosurface charge distribution bears scant resemblance to the indole HOMO. Such greatly diminished fluorescence has been observed for proteins where the indole nitrogen is hydrogen bonded, lending credence to the association of aromaticity changes with diminished quantum yield in proteins as well. Thus tryptophan ground state isosurfaces are an indicator of indole aromaticity, signaling the partition of excitation energy between radiative and nonradiative processes. PMID:24882092

PAH chemistry at eV internal energies. 1. H-shifted isomers

NASA Astrophysics Data System (ADS)

Trinquier, Georges; Simon, Aude; Rapacioli, Mathias; Gadéa, Florent Xavier

2017-06-01

The PAH family of organic compounds (polycyclic aromatic hydrocarbons), involved in several fields of chemistry, has received particular attention in astrochemistry, where their vibrational spectroscopy, thermodynamics, dynamics, and fragmentation properties are now abundantly documented. This survey aims at drawing trends for low spin-multiplicity surfaces of PAHs bearing internal energies in the range 1-10 eV. It addresses some typical alternatives to the ground-state regular structures of PAHs, making explicit possible intramolecular rearrangements leading to high-lying minima. These isomerisations should be taken into consideration when addressing PAH processing in astrophysical conditions. The first part of this double-entry study focuses on the hydrogen-shifted forms, which bear both a carbene center and a saturated carbon. It rests upon DFT calculations mainly performed on two emblematic PAH representatives, coronene and pyrene, in their neutral and mono- and multi-cationic states. Systematically searched for in neutral species, these H-shifted minima are lying 4-5 eV above the regular all-conjugated forms, and are separated by barriers of about 1 eV. General hydrogen-shifting is found to be easier for cationic species as the relative energies of their H-shifted minima are 1-1.5 eV lower than those for neutral species. As much as possible, classical knowledge and concepts of organic chemistry such as aromaticity and Clar's rules are invoked for result interpretation.

Uncovering the Roles of Oxygen in Cr(III) Photoredox Catalysis.

PubMed

Higgins, Robert F; Fatur, Steven M; Shepard, Samuel G; Stevenson, Susan M; Boston, David J; Ferreira, Eric M; Damrauer, Niels H; Rappé, Anthony K; Shores, Matthew P

2016-04-27

A combined experimental and theoretical investigation aims to elucidate the necessary roles of oxygen in photoredox catalysis of radical cation based Diels-Alder cycloadditions mediated by the first-row transition metal complex [Cr(Ph2phen)3](3+), where Ph2phen = bathophenanthroline. We employ a diverse array of techniques, including catalysis screening, electrochemistry, time-resolved spectroscopy, and computational analyses of reaction thermodynamics. Our key finding is that oxygen acts as a renewable energy and electron shuttle following photoexcitation of the Cr(III) catalyst. First, oxygen quenches the excited Cr(3+)* complex; this energy transfer process protects the catalyst from decomposition while preserving a synthetically useful 13 μs excited state and produces singlet oxygen. Second, singlet oxygen returns the reduced catalyst to the Cr(III) ground state, forming superoxide. Third, the superoxide species reduces the Diels-Alder cycloadduct radical cation to the final product and reforms oxygen. We compare the results of these studies with those from cycloadditions mediated by related Ru(II)-containing complexes and find that the distinct reaction pathways are likely part of a unified mechanistic framework where the photophysical and photochemical properties of the catalyst species lead to oxygen-mediated photocatalysis for the Cr-containing complex but radical chain initiation for the Ru congener. These results provide insight into how oxygen can participate as a sustainable reagent in photocatalysis.

Fusing Laser Reflectance and Image Data for Terrain Classification for Small Autonomous Robots

DTIC Science & Technology

2014-12-01

limit us to low power, lightweight sensors , and a maximum range of approximately 5 meters. Contrast these robot characteristics to typical terrain...classifi- cation work which uses large autonomous ground vehicles with sensors mounted high above the ground. Terrain classification for small autonomous...into predefined classes [10], [11]. However, wheeled vehicles offer the ability to use non-traditional sensors such as vibration sensors [12] and

XUV-induced reactions in benzene on sub-10 fs timescale: nonadiabatic relaxation and proton migration.

PubMed

Galbraith, M C E; Smeenk, C T L; Reitsma, G; Marciniak, A; Despré, V; Mikosch, J; Zhavoronkov, N; Vrakking, M J J; Kornilov, O; Lépine, F

2017-08-02

Unraveling ultrafast dynamical processes in highly excited molecular species has an impact on our understanding of chemical processes such as combustion or the chemical composition of molecular clouds in the universe. In this article we use short (<7 fs) XUV pulses to produce excited cationic states of benzene molecules and probe their dynamics using few-cycle VIS/NIR laser pulses. The excited states produced by the XUV pulses lie in an especially complex spectral region where multi-electronic effects play a dominant role. We show that very fast τ ≈ 20 fs nonadiabatic processes dominate the relaxation of these states, in agreement with the timescale expected for most excited cationic states in benzene. In the CH 3 + fragmentation channel of the doubly ionized benzene cation we identify pathways that involve structural rearrangement and proton migration to a specific carbon atom. Further, we observe non-trivial transient behavior in this fragment channel, which can be interpreted either in terms of propagation of the nuclear wavepacket in the initially excited electronic state of the cation or as a two-step electronic relaxation via an intermediate state.

The cyclopropene radical cation: Rovibrational level structure at low energies from high-resolution photoelectron spectra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vasilatou, K.; Michaud, J. M.; Baykusheva, D.

2014-08-14

The cyclopropene radical cation (c-C{sub 3}H{sub 4}{sup +}) is an important but poorly characterized three-membered-ring hydrocarbon. We report on a measurement of the high-resolution photoelectron and photoionization spectra of cyclopropene and several deuterated isotopomers, from which we have determined the rovibrational energy level structure of the X{sup ~+} {sup 2}B{sub 2} ground electronic state of c-C{sub 3}H{sub 4}{sup +} at low energies for the first time. The synthesis of the partially deuterated isotopomers always resulted in mixtures of several isotopomers, differing in their number of D atoms and in the location of these atoms, so that the photoelectron spectra ofmore » deuterated samples are superpositions of the spectra of several isotopomers. The rotationally resolved spectra indicate a C{sub 2v}-symmetric R{sub 0} structure for the ground electronic state of c-C{sub 3}H{sub 4}{sup +}. Two vibrational modes of c-C{sub 3}H{sub 4}{sup +} are found to have vibrational wave numbers below 300 cm{sup −1}, which is surprising for such a small cyclic hydrocarbon. The analysis of the isotopic shifts of the vibrational levels enabled the assignment of the lowest-frequency mode (fundamental wave number of ≈110 cm{sup −1} in c-C{sub 3}H{sub 4}{sup +}) to the CH{sub 2} torsional mode (ν{sub 8}{sup +}, A{sub 2} symmetry) and of the second-lowest-frequency mode (≈210 cm{sup −1} in c-C{sub 3}H{sub 4}{sup +}) to a mode combining a CH out-of-plane with a CH{sub 2} rocking motion (ν{sub 15}{sup +}, B{sub 2} symmetry). The potential energy along the CH{sub 2} torsional coordinate is flat near the equilibrium structure and leads to a pronounced anharmonicity.« less

Pyridine radical cation and its fluorine substituted derivatives

USGS Publications Warehouse

Bondybey, V.E.; English, J.H.; Shiley, R.H.

1982-01-01

The spectra and relaxation of the pyridine cation and of several of its fluorinated derivatives are studied in low temperature Ne matrices. The ions are generated by direct photoionization of the parent compounds. Of the compounds studied, laser induced → and → fluorescence is observed only for the 2, 6‐difluoropyridine cation. The analysis of the spectrum indicates that the ion is planar both in the and states. The large variety in the spectroscopic and relaxation behavior of fluoropyridine radical cations is explained in terms of their electronic structure and of the differential shifts of the individual electronic states caused by the fluorine substitution.

Discovery of the Ubiquitous Cation NS+ in Space Confirmed by Laboratory Spectroscopy

NASA Astrophysics Data System (ADS)

Cernicharo, J.; Lefloch, B.; Agúndez, M.; Bailleux, S.; Margulès, L.; Roueff, E.; Bachiller, R.; Marcelino, N.; Tercero, B.; Vastel, C.; Caux, E.

2018-02-01

We report the detection in space of a new molecular species that has been characterized spectroscopically and fully identified from astrophysical data. The observations were carried out with the IRAM 30 m telescope. The molecule is ubiquitous as its J=2\\to 1 transition has been found in cold molecular clouds, prestellar cores, and shocks. However, it is not found in the hot cores of Orion-KL and in the carbon-rich evolved star IRC+10216. Three rotational transitions in perfect harmonic relation J\\prime =2/3/5 have been identified in the prestellar core B1b. The molecule has a 1Σ electronic ground state and its J=2\\to 1 transition presents the hyperfine structure characteristic of a molecule containing a nucleus with spin 1. A careful analysis of possible carriers shows that the best candidate is NS+. The derived rotational constant agrees within 0.3%–0.7% with ab initio calculations. NS+ was also produced in the laboratory to unambiguously validate the astrophysical assignment. The observed rotational frequencies and determined molecular constants confirm the discovery of the nitrogen sulfide cation in space. The chemistry of NS+ and related nitrogen-bearing species has been analyzed by means of a time-dependent gas-phase model. The model reproduces well the observed NS/NS+ abundance ratio, in the range 30–50, and indicates that NS+ is formed by reactions of the neutral atoms N and S with the cations SH+ and NH+, respectively.

Analysis of X-ray adsorption edges: L 2,3 edge of FeCl 4 -

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bagus, Paul S.; Nelin, Connie J.; Ilton, Eugene S.

We describe a detailed analysis of the features of the X-ray adsorption spectra at the Fe L 2,3 edge of FeCl 4. The objective of this analysis is to explain the origin of the complex features in relation to properties of the wavefunctions, especially for the excited states. These properties include spin-orbit and ligand field splittings where a novel aspect of the dipole selection rules is applied to understand the influence of these splittings on the spectra. We also explicitly take account of the intermediate coupling of the open core and valence shell electrons. Our analysis also includes comparison ofmore » theory and experiment for the Fe L 2,3 edge and comparison of theoretical predictions for the Fe 3+ cation and FeCl 4-. The electronic structure is obtained from theoretical wavefunctions for the ground and excited states.« less

Ultraviolet photodissociation action spectroscopy of the N-pyridinium cation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hansen, Christopher S., E-mail: csh297@uowmail.edu.au; Trevitt, Adam J., E-mail: adamt@uow.edu.au; Blanksby, Stephen J.

2015-01-07

The S{sub 1}←S{sub 0} electronic transition of the N-pyridinium ion (C{sub 5}H{sub 5}NH{sup +}) is investigated using ultraviolet photodissociation (PD) spectroscopy of the bare ion and also the N{sub 2}-tagged complex. Gas-phase N-pyridinium ions photodissociate by the loss of molecular hydrogen (H{sub 2}) in the photon energy range 37 000–45 000 cm{sup −1} with structurally diagnostic ion-molecule reactions identifying the 2-pyridinylium ion as the exclusive co-product. The photodissociation action spectra reveal vibronic details that, with the aid of electronic structure calculations, support the proposal that dissociation occurs through an intramolecular rearrangement on the ground electronic state following internal conversion. Quantum chemical calculationsmore » are used to analyze the measured spectra. Most of the vibronic features are attributed to progressions of totally symmetric ring deformation modes and out-of-plane modes active in the isomerization of the planar excited state towards the non-planar excited state global minimum.« less

Grounding electrode and method of reducing the electrical resistance of soils

DOEpatents

Koehmstedt, Paul L.

1980-01-01

A first solution of an electrolyte is injected underground into a volume of soil having negative surface charges on its particles. A cationic surfactant suspended in this solution neutralizes these surface charges of the soil particles within the volume. Following the first solution, a cationic asphalt emulsion suspended in a second solution is injected into the volume. The asphalt emulsion diffuses through the volume and electrostatically bonds with additional soil surrounding the volume such that an electrically conductive water repellant shell enclosing the volume is formed. This shell prevents the leaching of electrolyte from the volume into the additional soil. The second solution also contains a dissolved deliquescent salt which draws water into the volume prior to the formation of the shell. When electrically connected to an electrical installation such as a power line tower, the volume constitutes a grounding electrode for the tower.

Metal-organic complexes in geochemical processes: temperature dependence of the standard thermodynamic properties of aqueous complexes between metal cations and dicarboxylate ligands

NASA Astrophysics Data System (ADS)

Prapaipong, Panjai; Shock, Everett L.; Koretsky, Carla M.

1999-10-01

By combining results from regression and correlation methods, standard state thermodynamic properties for aqueous complexes between metal cations and divalent organic acid ligands (oxalate, malonate, succinate, glutarate, and adipate) are evaluated and applied to geochemical processes. Regression of experimental standard-state equilibrium constants with the revised Helgeson-Kirkham-Flowers (HKF) equation of state yields standard partial molal entropies (S¯°) of aqueous metal-organic complexes, which allow determination of thermodynamic properties of the complexes at elevated temperatures. In cases where S¯° is not available from either regression or calorimetric measurement, the values of S¯° can be estimated from a linear correlation between standard partial molal entropies of association (ΔS¯°r) and standard partial molal entropies of aqueous cations (S¯°M). The correlation is independent of cation charge, which makes it possible to predict S¯° for complexes between divalent organic acids and numerous metal cations. Similarly, correlations between standard Gibbs free energies of association of metal-organic complexes (ΔḠ°r) and Gibbs free energies of formation (ΔḠ°f) for divalent metal cations allow estimates of standard-state equilibrium constants where experimental data are not available. These correlations are found to be a function of ligand structure and cation charge. Predicted equilibrium constants for dicarboxylate complexes of numerous cations were included with those for inorganic and other organic complexes to study the effects of dicarboxylate complexes on the speciation of metals and organic acids in oil-field brines. Relatively low concentrations of oxalic and malonic acids affect the speciation of cations more than similar concentrations of succinic, glutaric, and adipic acids. However, the extent to which metal-dicarboxylate complexes contribute to the speciation of dissolved metals depends on the type of dicarboxylic acid ligand; relative concentration of inorganic, mono-, and dicarboxylate ligands; and the type of metal cation. As an example, in the same solution, dicarboxylic acids have a greater influence on the speciation of Fe+2 and Mg+2 than on the speciation of Zn+2 and Mn+2.

The effect of dissolution of volcanic glass on the water chemistry in a tuffaceous aquifer, Rainier Mesa, Nevada

USGS Publications Warehouse

White, Art F.; Claassen, H.C.; Benson, Larry V.

1980-01-01

Geochemistry of ground water associated with the Tertiary tuffs within Rainier Mesa, southern Nevada, was investigated to determine the relative importance of glass dissolution in controlling water chemistry. Water samples were obtained both from interstitial pores in core sections and from free-flowing fractures. Cation com- positions showed that calcium and magnesium decreased as a function of depth in the mesa, as sodium increased. The maximum effect occurs within alteration zones containing clinoptilolite and montmorillonite, suggesting these minerals effectively remove bivalent cations from the system. Comparisons are made between compositions of ground waters found within Rainier Mesa that apparently have not reacted with secondary minerals and compositions of waters produced by experimental dissolution of vitric and crystalline tufts which comprise the principal aquifers in the area. The two tuff phases have the same bulk chemistry but produce aqueous solutions of different chemistry. Rapid parabolic dissolution of sodium and silica from, and the retention of, potassium within the vitric phase verify previous predictions concerning water compositions associated with vitric volcanic rocks. Parabolic dissolution of the crystalline phase results in solutions high in calcium and magnesium and low in silica. Extrapolation of the parabolic dissolution mechanism for the vitric tuff to long times successfully reproduces, at com- parable pH, cation ratios existing in Rainier Mesa ground water. Comparison of mass- transfer rates of the vitric and crystalline tuffs indicates that the apparent higher glass-surface to aqueous-volume ratio associated with the vitric rocks may account for dominance of the glass reaction.

Pentavalent neptunyl ([OΞNpΞO] +) cation–cation interactions in aqueous/polar organic mixed-solvent media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burn, Adam G.; Martin, Leigh R.; Nash, Kenneth L.

Bonding interactions between polyvalent cations and oxo-anions are well known and characterized by predictably favorable Gibbs energies in solution-phase coordination chemistry. In contrast, interactions between ions of like charge are generally expected to be repulsive and strongly influenced by cation solvation. An exception to this instinctive rule is found in the existence of complexes resulting from interactions of pentavalent actinyl cations ([O≡An≡O] +) with selected polyvalent cations. Such cation–cation complexes have been known to exist since the 1960s, when they were first reported by Sullivan and co-workers. The weak actinyl cation–cation complex, resulting from a bonding interaction between a pentavalentmore » linear dioxo actinyl cation donor and hexavalent actinyl or trivalent/tetravalent metal cation acceptor, has been most commonly seen in media in which water activities are reduced, principally highly-salted aqueous media. Such interactions of pentavalent actinides are of relevance in ongoing research that focuses on advanced nuclear fuel processing systems based on the upper oxidation states of americium. This investigation focuses on exploring the thermodynamic stability of complexes between selected highly-charged metal cations (Al 3+, Sc 3+, Cr 3+, Fe 3+, In 3+ and UO 2+ 2) and the pentavalent neptunyl cation (NpO + 2, whose coordination chemistry is similar to that of AmO + 2 while exhibiting significantly greater oxidation state stability) in aqueous–polar organic mixed-solvents. As a result, the Gibbs energies for the cation–cation complexation reactions are correlated with general features of electrostatic bonding models; the NpO + 2 • Cr 3+ complex exhibits unexpectedly strong interactions that may indicate significant covalency in the cation–cation bonding interaction.« less

Pentavalent neptunyl ([OΞNpΞO] +) cation–cation interactions in aqueous/polar organic mixed-solvent media

DOE PAGES

Burn, Adam G.; Martin, Leigh R.; Nash, Kenneth L.

2017-06-17

Bonding interactions between polyvalent cations and oxo-anions are well known and characterized by predictably favorable Gibbs energies in solution-phase coordination chemistry. In contrast, interactions between ions of like charge are generally expected to be repulsive and strongly influenced by cation solvation. An exception to this instinctive rule is found in the existence of complexes resulting from interactions of pentavalent actinyl cations ([O≡An≡O] +) with selected polyvalent cations. Such cation–cation complexes have been known to exist since the 1960s, when they were first reported by Sullivan and co-workers. The weak actinyl cation–cation complex, resulting from a bonding interaction between a pentavalentmore » linear dioxo actinyl cation donor and hexavalent actinyl or trivalent/tetravalent metal cation acceptor, has been most commonly seen in media in which water activities are reduced, principally highly-salted aqueous media. Such interactions of pentavalent actinides are of relevance in ongoing research that focuses on advanced nuclear fuel processing systems based on the upper oxidation states of americium. This investigation focuses on exploring the thermodynamic stability of complexes between selected highly-charged metal cations (Al 3+, Sc 3+, Cr 3+, Fe 3+, In 3+ and UO 2+ 2) and the pentavalent neptunyl cation (NpO + 2, whose coordination chemistry is similar to that of AmO + 2 while exhibiting significantly greater oxidation state stability) in aqueous–polar organic mixed-solvents. As a result, the Gibbs energies for the cation–cation complexation reactions are correlated with general features of electrostatic bonding models; the NpO + 2 • Cr 3+ complex exhibits unexpectedly strong interactions that may indicate significant covalency in the cation–cation bonding interaction.« less

Electrostatic transition state stabilization rather than reactant destabilization provides the chemical basis for efficient chorismate mutase catalysis.

PubMed

Burschowsky, Daniel; van Eerde, André; Ökvist, Mats; Kienhöfer, Alexander; Kast, Peter; Hilvert, Donald; Krengel, Ute

2014-12-09

For more than half a century, transition state theory has provided a useful framework for understanding the origins of enzyme catalysis. As proposed by Pauling, enzymes accelerate chemical reactions by binding transition states tighter than substrates, thereby lowering the activation energy compared with that of the corresponding uncatalyzed process. This paradigm has been challenged for chorismate mutase (CM), a well-characterized metabolic enzyme that catalyzes the rearrangement of chorismate to prephenate. Calculations have predicted the decisive factor in CM catalysis to be ground state destabilization rather than transition state stabilization. Using X-ray crystallography, we show, in contrast, that a sluggish variant of Bacillus subtilis CM, in which a cationic active-site arginine was replaced by a neutral citrulline, is a poor catalyst even though it effectively preorganizes chorismate for the reaction. A series of high-resolution molecular snapshots of the reaction coordinate, including the apo enzyme, and complexes with substrate, transition state analog and product, demonstrate that an active site, which is only complementary in shape to a reactive substrate conformer, is insufficient for effective catalysis. Instead, as with other enzymes, electrostatic stabilization of the CM transition state appears to be crucial for achieving high reaction rates.

Photofragment slice imaging studies of pyrrole and the Xe{center_dot}{center_dot}{center_dot}pyrrole cluster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rubio-Lago, L.; Zaouris, D.; Sakellariou, Y.

The photolysis of pyrrole has been studied in a molecular beam at wavelengths of 250, 240, and 193.3 nm, using two different carrier gases, He and Xe. A broad bimodal distribution of H-atom fragment velocities has been observed at all wavelengths. Near threshold at both 240 and 250 nm, sharp features have been observed in the fast part of the H-atom distribution. Under appropriate molecular beam conditions, the entire H-atom loss signal from the photolysis of pyrrole at both 240 and 250 nm (including the sharp features) disappear when using Xe as opposed to He as the carrier gas. Wemore » attribute this phenomenon to cluster formation between Xe and pyrrole, and this assumption is supported by the observation of resonance enhanced multiphoton ionization spectra for the (Xe{center_dot}{center_dot}{center_dot}pyrrole) cluster followed by photofragmentation of the nascent cation cluster. Ab initio calculations are presented for the ground states of the neutral and cationic (Xe{center_dot}{center_dot}{center_dot}pyrrole) clusters as a means of understanding their structural and energetic properties.« less

Atomic solid state energy scale: Universality and periodic trends in oxidation state

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pelatt, Brian D.; Kokenyesi, Robert S.; Ravichandran, Ram

2015-11-15

The atomic solid state energy (SSE) scale originates from a plot of the electron affinity (EA) and ionization potential (IP) versus band gap (E{sub G}). SSE is estimated for a given atom by assessing an average EA (for a cation) or an average IP (for an anion) for binary inorganic compounds having that specific atom as a constituent. Physically, SSE is an experimentally-derived average frontier orbital energy referenced to the vacuum level. In its original formulation, 69 binary closed-shell inorganic semiconductors and insulators were employed as a database, providing SSE estimates for 40 elements. In this contribution, EA and IPmore » versus E{sub G} are plotted for an additional 92 compounds, thus yielding SSE estimates for a total of 64 elements from the s-, p-, d-, and f-blocks of the periodic table. Additionally, SSE is refined to account for its dependence on oxidation state. Although most cations within the SSE database are found to occur in a single oxidation state, data are available for nine d-block transition metals and one p-block main group metal in more than one oxidation state. SSE is deeper in energy for a higher cation oxidation state. Two p-block main group non-metals within the SSE database are found to exist in both positive and negative oxidation states so that they can function as a cation or anion. SSEs for most cations are positioned above −4.5 eV with respect to the vacuum level, and SSEs for all anions are positioned below. Hence, the energy −4.5 eV, equal to the hydrogen donor/acceptor ionization energy ε(+/−) or equivalently the standard hydrogen electrode energy, is considered to be an absolute energy reference for chemical bonding in the solid state. - Highlights: • Atomic solid-state energies are estimated for 64 elements from experimental data. • The relationship between atomic SSEs and oxidation state is assessed. • Cations are positioned above and absolute energy of −4.5 eV and anions below.« less

Magnetoelectric properties of Pb free Bi2FeTiO6: A theoretical investigation

NASA Astrophysics Data System (ADS)

Patra, Lokanath; Ravindran, P.

2018-05-01

The structural, electronic, magnetic and ferroelectric properties of Pb free double perovskite multiferroic Bi2FeTiO6 are investigated using density functional theory within the general gradient approximation (GGA) method. Our structural optimization using total energy calculations for different potential structures show a minimum energy for a non-centrosymmetric rhombohedral structure with R3c space group. Bi2FeTiO6 is found to be an antiferromagnetic insulator with C-type magnetic ordering with bandgap value of 0.3 eV. The calculated magnetic moment of 3.52 μB at Fe site shows the high spin arrangement of 3d electrons which is also confirmed by our orbital projected density of states analysis. We have analyzed the characteristics of bonding present between the constituents of Bi2FeTiO6 with the help of calculated partial density of states and Born effective charges. The ground state of the nearest centrosymmetric structure is found to be a G-type antiferromagnet with half metallicity showing that by the application of external electric field we can not only get a polarized state but also change the magnetic ordering and electronic structure in the present compound indicating strong magnetoelectric coupling. The cation sites the coexistence of Bi 6s lone pair (bring disproportionate charge distribution) and Ti4+ d0 ions which brings covalency produces off-center displacement and favors a non-centrosymmetric ground state and thus ferroelectricity. Our Berry phase calculation gives a polarization of 48 µCcm-2 for Bi2FeTiO6.

Increasing Base Cations in Streams: Another Legacy of Deicing Salts?

NASA Astrophysics Data System (ADS)

Helton, A. M.; Barclay, J. R.; Bellucci, C.; Rittenhouse, C.

2017-12-01

Elevated use of deicing salts directly increases sodium chloride inputs to watersheds. Sodium can accumulate in soils over time and has the potential to leach other cations (e.g., calcium, magnesium, and potassium) from the soil through cation exchange. We hypothesize that increased use of deicing salts results in a legacy of soils depleted in non-sodium base cations with loss of cations to receiving waters. The goal of this project is to quantify temporal trends in base cations and chloride in streams and rivers across the United States. We used Weighted Regressions on Time, Discharge, and Season (WRTDS) to analyze trends in base cations. Our preliminary analysis of 10 rivers in Connecticut with chemical periods of record ranging from 24 - 64 years (median = 55 years), shows that the flux of base cations is increasing in all sites (25 - 366 103 meq ha-1 yr-1 yr-1), driven largely by increases in sodium (23 - 222 103 meq ha-1 yr-1 yr-1), the dominant cation in 7 of the sites. Chloride is also increasing at all sites (26 - 261 103 meq ha-1 yr-1 yr-1), which, in combination with salt use trends, suggests a road salt source for the increased sodium. Non-sodium cations are also increasing in 9 of the sites (8 - 54 103 meq ha-1 yr-1 yr-1), though they are not directly added with most deicing salts. We will compare these trends to other long-term sites across the United States, and quantify relationships between cation trends and land cover, road density, and snowfall.

Mesoporous titanium phosphate molecular sieves with ion-exchange capacity.

PubMed

Bhaumik, A; Inagaki, S

2001-01-31

Novel open framework molecular sieves, titanium(IV) phosphates named, i.e., TCM-7 and -8 (Toyota Composite Materials, numbers 7 and 8), with new mesoporous cationic framework topologies obtained by using both cationic and anionic surfactants are reported. The (31)P MAS NMR, UV-visible absorption, and XANES data suggest the tetrahedral state of P and Ti, and stabilization of the tetrahedral state of Ti in TCM-7/8 is due to the incorporation of phosphorus (at Ti/P = 1:1) vis-à-vis the most stable octahedral state of Ti in the pure mesoporous TiO(2). Mesoporous TCM-7 and -8 show anion exchange capacity due to the framework phosphonium cation and cation exchange capacity due to defective P-OH groups. The high catalytic activity in the liquid-phase partial oxidation of cyclohexene with a dilute H(2)O(2) oxidant supports the tetrahedral coordination of Ti in these materials.

Evaluation of the influence of ionization states and spacers in the thermotropic phase behaviour of amino acid-based cationic lipids and the transfection efficiency of their assemblies.

PubMed

Sarker, Satya Ranjan; Arai, Satoshi; Murate, Motohide; Takahashi, Hiroshi; Takata, Masaki; Kobayashi, Toshihide; Takeoka, Shinji

2012-01-17

The influence of both the ionization states and the hydrocarbon chain spacer of a series of amino acid-based cationic lipids was evaluated in terms of gene delivery efficiency and cytotoxicity to the COS-7 cell line and compared with that of Lipofectamine 2000. We synthesized a series of amino acid-based cationic lipids with different ionization states (i.e., -NH(2), -NH(3)(+)Cl(-) or -NH(3)(+)TFA(-)) in the lysine head group and different hydrocarbon chain spacers (i.e., 0, 3, 5 or 7 carbon atoms) between the hydrophilic head group and hydrophobic moieties. In the 3-carbon series, the cationic assemblies formed a micellar structure in the presence of -NH(3)(+)Cl(-) and a vesicular structure both in the presence of -NH(2) and -NH(3)(+)TFA(-). Differential scanning calorimetry (DSC) data revealed a significantly lower (8.1°C) gel-to-liquid crystalline phase transition temperature for cationic assemblies bearing -NH(3)(+)TFA(-) when compared to their -NH(2) counterparts. Furthermore, the zeta potential of cationic assemblies having -NH(3)(+)TFA(-) in the hydrophilic head group was maximum followed by -NH(3)(+)Cl(-) and -NH(2) irrespective of their hydrocarbon chain spacer length. The gene delivery efficiency in relation to the ionization states of the hydrophilic head group was as follows: -NH(3)(+)TFA(-)>-NH(3)(+)Cl(-)>-NH(2). Copyright © 2011 Elsevier B.V. All rights reserved.

Cation Selectivity in Biological Cation Channels Using Experimental Structural Information and Statistical Mechanical Simulation.

PubMed

Finnerty, Justin John; Peyser, Alexander; Carloni, Paolo

2015-01-01

Cation selective channels constitute the gate for ion currents through the cell membrane. Here we present an improved statistical mechanical model based on atomistic structural information, cation hydration state and without tuned parameters that reproduces the selectivity of biological Na+ and Ca2+ ion channels. The importance of the inclusion of step-wise cation hydration in these results confirms the essential role partial dehydration plays in the bacterial Na+ channels. The model, proven reliable against experimental data, could be straightforwardly used for designing Na+ and Ca2+ selective nanopores.

A comparative study of the Au + H{sub 2}, Au{sup +} + H{sub 2}, and Au{sup −} + H{sub 2} systems: Potential energy surfaces and dynamics of reactive collisions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dorta-Urra, Anaís; Zanchet, Alexandre; Roncero, Octavio

2015-04-21

In order to study the Au{sup −} + H{sub 2} collision, a new global potential energy surface (PES) describing the ground electronic state of AuH{sub 2}{sup −} system is developed and compared with the PESs of the neutral [Zanchet et al., J. Chem. Phys. 132, 034301 (2010)] and cationic systems [Anaís et al., J. Chem. Phys. 135, 091102 (2011)]. We found that Au{sup −} − H{sub 2} presents a H-Au-H insertion minimum attributed to the stabilization of the LUMO 3b{sub 2} orbital, which can be considered as the preamble of the chemisorption well appearing in larger gold clusters. While themore » LUMO orbital is stabilized, the HOMO 6a{sub 1} is destabilized, creating a barrier at the geometry where the energy orbitals’ curves are crossing. In the anion, this HOMO is doubly occupied, while in the neutral system is half-filled and completely empty in the cation, explaining the gradual disappearance of the well and the barrier as the number of electrons decreases. The cation presents a well in the entrance channel partially explained by electrostatic interactions. The three systems’ reactions are highly endothermic, by 1.66, 2.79, and 3.23 eV for AuH, AuH{sup +}, and AuH{sup −} products, respectively. The reaction dynamics is studied using quasi-classical trajectory method for the three systems. The one corresponding to the anionic system is new in this work. Collision energies between 1.00 and 8.00 eV, measured for the cation, are in good agreement with the simulated cross section for the AuH{sup +}. It was also found that the total fragmentation, in three atoms, competes becoming dominant at sufficiently high energy. Here, we study the competition between the two different reaction pathways for the anionic, cationic, and neutral species, explaining the differences using a simple model based on the topology of the potential energy surfaces.« less

Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barnes, J. C.; Fahrenbach, A. C.; Dyar, S. M.

2012-06-08

The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylene-bridged bipyridinium (P-BIPY2+) unit and a cyclobis (paraquat-p-phenylene) (CBPQT4+) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT4+ ring encircles the DNP unit. Reduction of the CBPQT4+ leads to the CBPQT2(•+) diradical dication while the P-BIPY2+ unit is reduced to its P-BIPY•+ radical cation. A radical-state co-conformation (RSCC) results from movement of the CBPQT2(•+) ring along the dumbbell to surround the P-BIPY•+ unit.more » This shuttling event induces IET to occur between the pyridinium redox centers of the P-BIPY•+ unit, a property which is absent between these redox centers in the free dumbbell and in the 1:1 complex formed between the CBPQT2(•+) ring and the radical cation of methyl-phenylene-viologen (MPV•+). Using electron paramagnetic resonance (EPR) spectroscopy, the process of IET was investigated by monitoring the line broadening at varying temperatures and determining the rate constant (kET = 1.33 × 107 s-1) and activation energy (ΔG‡ = 1.01 kcal mol-1) for electron transfer. These values were compared to the corresponding values predicted, using the optical absorption spectra and Marcus–Hush theory.« less

Computation of bedrock-aquifer recharge in northern Westchester County, New York, and chemical quality of water from selected bedrock wells

USGS Publications Warehouse

Wolcott, Stephen W.; Snow, Robert F.

1995-01-01

An empirical technique was used to calculate the recharge to bedrock aquifers in northern Westchester County. This method requires delineation of ground-water divides within the aquifer area and values for (1) the extent of till and exposed bedrock within the aquifer area, and (2) mean annual runoff. This report contains maps and data needed for calculation of recharge in any given area within the 165square-mile study area. Recharge was computed by this technique for a 93-square-mile part of the study area and used a ground-water-flow model to evaluate the reliability of the method. A two-layer, steady-state model of the selected area was calibrated. The area consists predominantly of bedrock overlain by small localized deposits of till and stratified drill Ground-water-level and streamflow data collected in mid-November 1987 were used for model calibration. The data set approximates average annual conditions. The model was calibrated from (1) estimates of recharge as computed through the empirical technique, and (2) a range of values for hydrologic properties derived from aquifer tests and published literature. Recharge values used for model simulation appear to be reasonable for average steady-state conditions. Water-quality data were collected from 53 selected bedrock wells throughout northern Westchester County to define the background ground-water quality. The constituents and properties for which samples were analyzed included major cations and anions, temperature, pH, specific conductance, and hardness. Results indicate little difference in water quality among the bedrock aquifers within the study area. Ground water is mainly the calcium-bicarbonate type and is moderately hard. Average concentrations of sodium, sulfate, chloride, nitrate, iron, and manganese were within acceptable limits established by the U.S. Environmental Protection Agency for domestic water supply.

Synthetic laser medium

DOEpatents

Stokowski, S.E.

1987-10-20

A laser medium is particularly useful in high average power solid state lasers. The laser medium includes a chromium dopant and preferably neodymium ions as codopant, and is primarily a gadolinium scandium gallium garnet, or an analog thereof. Divalent cations inhibit spiral morphology as large boules from which the laser medium is derived are grown, and a source of ions convertible between a trivalent state and a tetravalent state at a low ionization energy are in the laser medium to reduce an absorption coefficient at about one micron wavelength otherwise caused by the divalent cations. These divalent cations and convertible ions are dispersed in the laser medium. Preferred convertible ions are provided from titanium or cerium sources.

Synthetic laser medium

DOEpatents

Stokowski, Stanley E.

1989-01-01

A laser medium is particularly useful in high average power solid state lasers. The laser medium includes a chormium dopant and preferably neodymium ions as codopant, and is primarily a gadolinium scandium gallium garnet, or an analog thereof. Divalent cations inhibit spiral morphology as large boules from which the laser medium is derived are grown, and a source of ions convertible between a trivalent state and a tetravalent state at a low ionization energy are in the laser medium to reduce an absorption coefficient at about one micron wavelength otherwise caused by the divalent cations. These divalent cations and convertible ions are dispersed in the laser medium. Preferred convertible ions are provided from titanium or cerium sources.

Nonselective Currents and Channels in Plasma Membranes of Protoplasts from Coats of Developing Seeds of Bean1

PubMed Central

Zhang, Wen-Hao; Skerrett, Martha; Walker, N. Alan; Patrick, John W.; Tyerman, Stephen D.

2002-01-01

In developing bean (Phaseolus vulgaris) seeds, phloem-imported nutrients move in the symplast from sieve elements to the ground parenchyma cells where they are transported across the plasma membrane into the seed apoplast. To study the mechanisms underlying this transport, channel currents in ground parenchyma protoplasts were characterized using patch clamp. A fast-activating outward current was found in all protoplasts, whereas a slowly activating outward current was observed in approximately 25% of protoplasts. The two currents had low selectivity for univalent cations, but the slow current was more selective for K+ over Cl− (PK:PCl = 3.6–4.2) than the fast current (PK:PCl = 1.8–2.5) and also displayed Ca2+ selectivity. The slow current was blocked by Ba2+, whereas both currents were blocked by Gd3+ and La3+. Efflux of K+ from seed coat halves was inhibited 25% by Gd3+ and La3+ but was stimulated by Ba2+ and Cs+, suggesting that only the fast current may be a component in the pathway for K+ release. An “instantaneous” inward current observed in all protoplasts exhibited similar pharmacology and permeability for univalent cations to the fast outward current. In outside-out patches, two classes of depolarization-activated cation-selective channels were observed: one slowly activating of low conductance (determined from nonstationary noise to be 2.4 pS) and another with conductances 10-fold higher. Both channels occurred at high density. The higher conductance channel in 10 mm KCl had PK:PCl = 2.8. Such nonselective channels in the seed coat ground parenchyma cell could function to allow some of the efflux of phloem-imported univalent ions into the seed apoplast. PMID:11842143

High-pressure synthesis, crystal chemistry and physics of perovskites with small cations at the A site.

PubMed

Belik, Alexei A; Yi, Wei

2014-04-23

ABO3 perovskites with small cations at the A site (A = Sc(3+), In(3+) and Mn(2+) and B = Al(3+) and transition metals) are reviewed. They extend the corresponding families of perovskites with A(3+) = Y, La-Lu, and Bi and A(2+) = Cd, Ca, Sr and Ba and exhibit the largest structural distortions. As a result of these large distortions, they show, in many cases, distinct structural and magnetic properties. These are manifested in: B-site-ordered monoclinic structures of ScMnO3 and 'InMnO3'; an unusual superstructure of ScRhO3 and InRhO3; antiferromagnetic ground states and multiferroic properties of Sc2NiMnO6 and In2NiMnO6; two magnetic transitions in ScCrO3 and InCrO3 with very close transition temperatures; a Pnma-to-P-1 structural transition and k = (½, 0, ½) magnetic ordering in ScVO3; and incommensurate magnetic ordering of Mn(2+) spins in metallic MnVO3. A large number of simple ScBO3, InBO3 and MnBO3 perovskites has not been synthesized yet, and the number of experimental and theoretical works on each known ScBO3, InBO3 and MnBO3 perovskites counts to only one or two (except for ScAlO3). The synthesis, crystal chemistry and physics of perovskites with small cations at the A site is an emerging field in perovskite science.

Interfacial Electron Transfer at Sensitized Nanocrystalline TiO2 Electrolyte Interfaces: Influence of Surface Electric Fields and Lewis-Acidic Cations

NASA Astrophysics Data System (ADS)

Barr, Timothy J.

Interfacial electron transfer reactions facilitate charge separation and recombination in dye-sensitized solar cells (DSSCs). Understanding what controls these electron transfer reactions is necessary to develop efficient DSSCs. Gerischer proposed a theory for interfacial electron transfer where the rate constant was related to the energetic overlap between the donor and acceptor states. The present work focuses on understanding how the composition of the CH3CN electrolyte influenced this overlap. It was found that the identity of the electrolyte cation tuned the energetic position of TiO2 electron acceptor states, similar to how pH influences the flatband potential of bulk semiconductors in aqueous electrolytes. For example, the onset for absorption changes, that were attributed to electrons in the TiO2 thin film, were 0.5 V more positive in Mg2+ containing electrolyte than TBA+, where TBA+ is tetrabutylammonium. Similar studies performed on mesoporous, nanocrystalline SnO2 thin films reported a similar cation dependence, but also found evidence for electrons that did not absorb in the visible region that were termed ‘phantom electrons.’. Electron injection is known to generate surface electric fields on the order of 2 MV/cm. The rearrangement of cations in response to surface electric fields, termed screening, was investigated. It was found that magnitude of the electric field and the screening dynamics were dependent on the identity of the electrolyte cation. The rate of charge recombination to the anionic iodide/triiodide redox mediator correlated with the screening ability of the cation, and was initially thought to control charge recombination. However, it was difficult to determine whether electron diffusion or driving force were also cation dependent. Therefore, a in-lab built apparatus, termed STRiVE, was constructed that could disentangle the influence electron diffusion, driving force, and electric fields had on charge recombination. It was found that electron diffusion was independent of the electrolyte cation. Furthermore, charge recombination displayed the same cation-sensitivity using both anionic and cationic redox mediators, indicating electric fields did not cause the cation-dependence of charge recombination. Instead, it was found that the electrolyte cation tuned the energetic position of the TiO2 acceptor states and modulated the driving force for charge recombination.

Early events associated with the excited state proton transfer in 2-(2{sup '}-pyridyl)benzimidazole

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burai, Tarak Nath; Mukherjee, Tushar Kanti; Lahiri, Priyanka

2009-07-21

2-(2{sup '}-pyridyl)benzimidazole (2PBI) undergoes excited state proton transfer (ESPT) in acidic solutions, leading to a tautomer emission at 460 nm. This photoprocess has been studied using ultrafast fluorescence spectroscopic techniques in acidic neat aqueous solutions, in viscous mixtures of glycerol with water, as well as in sucrose solutions. The tautomer is found to be stabilized in the more viscous medium, leading to a greater relative quantum yield as well as lifetime. The long rise time in tautomer emission is not affected by viscosity though. Rather, it appears to have the same value as the long component of the decay ofmore » the cationic excited state (C*). In addition to the subnanosecond lifetime reported earlier, C* is found to exhibit a decay time of 2 ps. This is assigned to its protonation to form the nonfluorescent dication in its excited state (D*) considering the ground and excited state pK{sub a} values reported earlier. An additional rising component of 100 ps is observed in the region of C* emission. This is likely to arise from a structural change or charge redistribution in C* immediately after its creation and before the phototautomerization.« less

Electronic spectra of astrophysically interesting cations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maier, John P., E-mail: j.p.maier@unibas.ch; Rice, Corey A., E-mail: j.p.maier@unibas.ch; Mazzotti, Fabio J., E-mail: j.p.maier@unibas.ch

2015-01-22

The electronic spectra of polyacetylene cations were recorded at 20K in the laboratory in an ion trap instrument. These can then be compared with diffuse interstellar band (DIB) absorptions. Examination of recently published data shows that the attribution of a weak DIB at ∼506.9 nm to diacetylene cation is not justified. Study of the higher excited electronic states of polyacetylene cations shows that their widths can still be sufficiently narrow for consideration as DIB carriers.

The electronic structure of vanadium monochloride cation (VCl{sup +}): Tackling the complexities of transition metal species

DOE Office of Scientific and Technical Information (OSTI.GOV)

DeYonker, Nathan J., E-mail: ndyonker@memphis.edu; Halfen, DeWayne T.; Ziurys, Lucy M.

Six electronic states (X {sup 4}Σ{sup −}, A {sup 4}Π, B {sup 4}Δ, {sup 2}Φ, {sup 2}Δ, {sup 2}Σ{sup +}) of the vanadium monochloride cation (VCl{sup +}) are described using large basis set coupled cluster theory. For the two lowest quartet states (X {sup 4}Σ{sup −} and A {sup 4}Π), a focal point analysis (FPA) approach was used that conjoined a correlation-consistent family of basis sets up to aug-cc-pwCV5Z-DK with high-order coupled cluster theory through pentuple (CCSDTQP) excitations. FPA adiabatic excitation energies (T{sub 0}) and spectroscopic constants (r{sub e}, r{sub 0}, B{sub e}, B{sub 0}, D{sup ¯}{sub e}, H{sub e},more » ω{sub e}, v{sub 0}, α{sub e}, ω{sub e}x{sub e}) were extrapolated to the valence complete basis set Douglas-Kroll (DK) aug-cc-pV∞Z-DK CCSDT level of theory, and additional treatments accounted for higher-order valence electron correlation, core correlation, and spin-orbit coupling. Due to the delicate interplay between dynamical and static electronic correlation, single reference coupled cluster theory is able to provide the correct ground electronic state (X {sup 4}Σ{sup −}), while multireference configuration interaction theory cannot. Perturbations from the first- and second-order spin orbit coupling of low-lying states with quartet spin multiplicity reveal an immensely complex rotational spectrum relative to the isovalent species VO, VS, and TiCl. Computational data on the doublet manifold suggest that the lowest-lying doublet state ({sup 2}Γ) has a T{sub e} of ∼11 200 cm{sup −1}. Overall, this study shows that laboratory and theoretical rotational spectroscopists must work more closely in tandem to better understand the bonding and structure of molecules containing transition metals.« less

Cation Selectivity in Biological Cation Channels Using Experimental Structural Information and Statistical Mechanical Simulation

PubMed Central

Finnerty, Justin John

2015-01-01

Cation selective channels constitute the gate for ion currents through the cell membrane. Here we present an improved statistical mechanical model based on atomistic structural information, cation hydration state and without tuned parameters that reproduces the selectivity of biological Na+ and Ca2+ ion channels. The importance of the inclusion of step-wise cation hydration in these results confirms the essential role partial dehydration plays in the bacterial Na+ channels. The model, proven reliable against experimental data, could be straightforwardly used for designing Na+ and Ca2+ selective nanopores. PMID:26460827

A nitrogen-rich septage-effluent plume in a glacial aquifer, Cape Cod, Massachusetts, February 1990 through December 1992

USGS Publications Warehouse

Desimone, Leslie A.; Barlow, Paul M.; Howes, Brian L.

1996-01-01

Physical, chemical, and microbial processes controlled transport of a nitrogen-rich ground-water plume through a glacial aquifer. Lithologic heterogeneity and vertical head gradients influenced plume movement and geometry. Nitrate was the predominant nitrogen form and oxygen was depleted in the ground-water plume. However, denitrification transformed only 2 percent of plume nitrogen because of limited organic-carbon availability. Aerobic respiration, nitrification and cation exchange (unsaturated zone) and ammonium sorption (saturated zone) had larger effects.

Multi-State Vibronic Interactions in Fluorinated Benzene Radical Cations.

NASA Astrophysics Data System (ADS)

Faraji, S.; Köppel, H.

2009-06-01

Conical intersections of potential energy surfaces have emerged as paradigms for signalling strong nonadiabatic coupling effects. An important class of systems where some of these effects have been analyzed in the literature, are the benzene and benzenoid cations, where the electronic structure, spectroscopy, and dynamics have received great attention in the literature. In the present work a brief overview is given over our theoretical treatments of multi-mode and multi-state vibronic interactions in the benzene radical cation and some of its fluorinated derivatives. The fluorobenzene derivatives are of systematic interest for at least two different reasons. (1) The reduction of symmetry by incomplete fluorination leads to a disappearance of the Jahn-Teller effect present in the parent cation. (2) A specific, more chemical effect of fluorination consists in the energetic increase of the lowest σ-type electronic states of the radical cations. The multi-mode multi-state vibronic interactions between the five lowest electronic states of the fluorobenzene radical cations are investigated theoretically, based on ab initio electronic structure data, and employing the well-established linear vibronic coupling model, augmented by quadratic coupling terms for the totally symmetric vibrational modes. Low-energy conical intersections, and strong vibronic couplings are found to prevail within the set of tilde{X}-tilde{A} and tilde{B}-tilde{C}-tilde{D} cationic states, while the interactions between these two sets of states are found to be weaker and depend on the particular isomer. This is attributed to the different location of the minima of the various conical intersections occurring in these systems. Wave-packet dynamical simulations for these coupled potential energy surfaces, utilizing the powerful multi-configuration time-dependent Hartree method are performed. Ultrafast internal conversion processes and the analysis of the MATI and photo-electron spectra shed new light on the spectroscopy and fluorescence dynamics of these species. W. Domcke, D. R. Yarkony, and H. Köppel, Advanced Series in Physical Chemistry, World Scientific, Singapore (2004). M. H. Beck and A. Jäckle and G. A. Worth and H. -D. Meyer, Phys. Rep. 324, 1 (2000). S. Faraji, H. Köppel, (Part I) ; S. Faraji, H. Köppel, H.-D. Meyer, (Part II) J. Chem. Phys. 129, 074310 (2008).

Pharmaceuticals' sorptions relative to properties of thirteen different soils.

PubMed

Kodešová, Radka; Grabic, Roman; Kočárek, Martin; Klement, Aleš; Golovko, Oksana; Fér, Miroslav; Nikodem, Antonín; Jakšík, Ondřej

2015-04-01

Transport of human and veterinary pharmaceuticals in soils and consequent ground-water contamination are influenced by many factors, including compound sorption on soil particles. Here we evaluate the sorption isotherms for 7 pharmaceuticals on 13 soils, described by Freundlich equations, and assess the impact of soil properties on various pharmaceuticals' sorption on soils. Sorption of ionizable pharmaceuticals was, in many cases, highly affected by soil pH. The sorption coefficient of sulfamethoxazole was negatively correlated to soil pH, and thus positively related to hydrolytic acidity and exchangeable acidity. Sorption coefficients for clindamycin and clarithromycin were positively related to soil pH and thus negatively related to hydrolytic acidity and exchangeable acidity, and positively related to base cation saturation. The sorption coefficients for the remaining pharmaceuticals (trimethoprim, metoprolol, atenolol, and carbamazepine) were also positively correlated with the base cation saturation and cation exchange capacity. Positive correlations between sorption coefficients and clay content were found for clindamycin, clarithromycin, atenolol, and metoprolol. Positive correlations between sorption coefficients and organic carbon content were obtained for trimethoprim and carbamazepine. Pedotransfer rules for predicting sorption coefficients of various pharmaceuticals included hydrolytic acidity (sulfamethoxazole), organic carbon content (trimethoprimand carbamazepine), base cation saturation (atenolol and metoprolol), exchangeable acidity and clay content (clindamycin), and soil active pH and clay content (clarithromycin). Pedotransfer rules, predicting the Freundlich sorption coefficients, could be applied for prediction of pharmaceutical mobility in soils with similar soil properties. Predicted sorption coefficients together with pharmaceutical half-lives and other imputes (e.g., soil-hydraulic, geological, hydro-geological, climatic) may be used for assessing potential ground-water contamination. Copyright © 2014 Elsevier B.V. All rights reserved.

A pK change of acidic residues contributes to cation countertransport in the Ca-ATPase of sarcoplasmic reticulum. Role of H+ in Ca(2+)-ATPase countertransport.

PubMed

Yu, X; Hao, L; Inesi, G

1994-06-17

Proteoliposomal vesicles reconstituted with sarcoplasmic reticulum ATPase and exogenous lipids sustain ATP-dependent Ca2+ uptake and H+ ejection, as well as net charge displacement by Ca2+. We have studied the effect of lumenal (inner) and medium (extravesicular) pH variations on the countertransport ratios of H+ and Ca2+. We find that the Ca2+/H+ molar ratio is approximately 1 when the lumenal and medium pH is near neutrality, but changes with a specific pattern when the medium pH is varied in the presence of a constant lumenal pH and when the lumenal pH is varied in the presence of a constant medium pH. Empirical analysis of the experimental data shows that the apparent pK of the residue(s) releasing H+ into the medium is approximately 6.1, whereas the apparent pK of the residue(s) binding lumenal H+ is approximately 7.7. Assuming that the same acidic residues are involved in H+ and Ca2+ countertransport, our findings suggest a lower affinity for H+ in their outward orientation (prevalent in the ground state of the enzyme) and a higher affinity for H+ in lumenal orientation (prevalent in the phosphorylated state of the enzyme). Cyclic pK changes, coupled to ATP utilization, promote cation exchange, Ca2+ uptake, and H+ ejection by the vesicles. The stoichiometry of countertransport and net charge displacement is matched by a corresponding electrogenic behavior. A calculation of voltage development related to initial rates of charge transfer (dV/dt = (dQ/dt)/Cm) is given as a corrective replacement of a previous steady state calculation.

Nuclear quantum effects on adsorption of H 2 and isotopologues on metal ions

DOE PAGES

Savchenko, Ievgeniia; Gu, Bing; Heine, Thomas; ...

2017-01-03

The nuclear quantum effects on the zero-point energy (ZPE), influencing adsorption of Hmore » $$_2$$ and isotopologues on metal ions, are examined in this study using normal mode analysis of ab initio electronic structure results for complexes with 17 metal cations. To estimate for the anharmonicity, a nuclear wavepacket dynamics on the ground state electronic potential energy surfaces (PES) have been employed for complexes of Li$^+$ and Cu$$^{+2}$$ with H$$_2$$, D$$_2$$, HD. The dynamics analysis shows that incorporation of the PES anharmonicity changes the ZPE by up to 9%. Finally, the lightest metallic nuclei, Li and Be, are found to be the most 'quantum'. The largest selectivity in adsorption is predicted for Cu, Ni and Co ions.« less

Mn@Si14+: a singlet fullerene-like endohedrally doped silicon cluster.

PubMed

Ngan, Vu Thi; Pierloot, Kristine; Nguyen, Minh Tho

2013-04-21

The electronic structure of Mn@Si14(+) is determined using DFT and CASPT2/CASSCF(14,15) computations with large basis sets. The endohedrally Mn-doped Si cationic cluster has a D3h fullerene-like structure featuring a closed-shell singlet ground state with a singlet-triplet gap of ~1 eV. A strong stabilizing interaction occurs between the 3d(Mn) and the 2D-shell(Si14) orbitals, and a large amount of charge is transferred from the Si14 cage to the Mn dopant. The 3d(Mn) orbitals are filled by encapsulation, and the magnetic moment of Mn is completely quenched. Full occupation of [2S, 2P, 2D] shell orbitals by 18 delocalized electrons confers the doped Mn@Si14(+) cluster a spherically aromatic character.

Structure and dynamics of cationic membrane peptides and proteins: Insights from solid-state NMR

PubMed Central

Hong, Mei; Su, Yongchao

2011-01-01

Many membrane peptides and protein domains contain functionally important cationic Arg and Lys residues, whose insertion into the hydrophobic interior of the lipid bilayer encounters significant energy barriers. To understand how these cationic molecules overcome the free energy barrier to insert into the lipid membrane, we have used solid-state NMR spectroscopy to determine the membrane-bound topology of these peptides. A versatile array of solid-state NMR experiments now readily yields the conformation, dynamics, orientation, depth of insertion, and site-specific protein–lipid interactions of these molecules. We summarize key findings of several Arg-rich membrane peptides, including β-sheet antimicrobial peptides, unstructured cell-penetrating peptides, and the voltage-sensing helix of voltage-gated potassium channels. Our results indicate the central role of guanidinium-phosphate and guanidinium-water interactions in dictating the structural topology of these cationic molecules in the lipid membrane, which in turn account for the mechanisms of this functionally diverse class of membrane peptides. PMID:21344534

Questa baseline and pre-mining ground-water quality investigation. 5. Well installation, water-level data, and surface- and ground-water geochemistry in the Straight Creek drainage basin, Red River Valley, New Mexico, 2001-03

USGS Publications Warehouse

Naus, Cheryl A.; McCleskey, R. Blaine; Nordstrom, D. Kirk; Donohoe, Lisa C.; Hunt, Andrew G.; Paillet, Frederick L.; Morin, Roger H.; Verplanck, Philip L.

2005-01-01

The U.S. Geological Survey, in cooperation with the New Mexico Environment Department, is investigating the pre-mining ground-water chemistry at the Molycorp molybdenum mine in the Red River Valley, northern New Mexico. The primary approach is to determine the processes controlling ground-water chemistry at an unmined, off-site, proximal analog. The Straight Creek drainage basin, chosen for this purpose, consists of the same quartz-sericite-pyrite altered andesitic and rhyolitic volcanic rock of Tertiary age as the mine site. The weathered and rugged volcanic bedrock surface is overlain by heterogeneous debris-flow deposits that interfinger with alluvial deposits near the confluence of Straight Creek and the Red River. Pyritized rock in the upper part of the drainage basin is the source of acid rock drainage (pH 2.8-3.3) that infiltrates debris-flow deposits containing acidic ground water (pH 3.0-4.0) and bedrock containing water of circumneutral pH values (5.6-7.7). Eleven observation wells were installed in the Straight Creek drainage basin. The wells were completed in debris-flow deposits, bedrock, and interfingering debris-flow and Red River alluvial deposits. Chemical analyses of ground water from these wells, combined with chemical analyses of surface water, water-level data, and lithologic and geophysical logs, provided information used to develop an understanding of the processes contributing to the chemistry of ground water in the Straight Creek drainage basin. Surface- and ground-water samples were routinely collected for determination of total major cations and selected trace metals; dissolved major cations, selected trace metals, and rare-earth elements; anions and alkalinity; and dissolved-iron species. Rare-earth elements were determined on selected samples only. Samples were collected for determination of dissolved organic carbon, mercury, sulfur isotopic composition (34S and 18O of sulfate), and water isotopic composition (2H and 18O) during selected samplings. One set of ground-water samples was collected for helium-3/tritium and chlorofluorocarbon (CFC) age dating. Several lines of evidence indicate that surface water is the primary input to the Straight Creek ground-water system. Straight Creek streamflow and water levels in wells closest to the apex of the Straight Creek debris fan and closest to Straight Creek itself appear to respond to the same seasonal inputs. Oxygen and hydrogen isotopic compositions in Straight Creek surface water and ground water are similar, and concentrations of most dissolved constituents in most Straight Creek surface-water and shallow (debris-flow and alluvial) aquifer ground-water samples correlate strongly with sulfate (concentrations decrease linearly with sulfate in a downgradient direction). After infiltration of surface water, dilution along the flow path is the dominant mechanism controlling ground-water chemistry. However, concentrations of some constituents can be higher in ground water than can be accounted for by concentrations in Straight Creek surface water, and additional sources of these constituents must therefore be inferred. Constituents for which concentrations in ground water can be high relative to surface water include calcium, magnesium, strontium, silica, sodium, and potassium in ground water from debris-flow and alluvial aquifers and manganese, calcium, magnesium, strontium, sodium, and potassium in ground water from the bedrock aquifer. All ground water is a calcium sulfate type, often at or near gypsum saturation because of abundant gypsum in the aquifer material developed from co-existing calcite and pyrite mineralization. Calcite dissolution, the major buffering mechanism for bedrock aquifer ground water, also contributes to relatively higher calcium concentrations in some ground water. The main source of the second most abundant cation, magnesium, is probably dissolution of magnesium-rich carbonates or silicates. Strontium may also be

Electrochemistry of cations in diopsidic melt - Determining diffusion rates and redox potentials from voltammetric curves

NASA Technical Reports Server (NTRS)

Colson, Russell O.; Haskin, Larry A.; Crane, Daniel

1990-01-01

Results are presented on determinations of reduction potentials and their temperature dependence of selected ions in diopsidic melt, by using linear sweep voltammetry. Diffusion coefficients were measured for cations of Eu, Mn, Cr, and In. Enthalpies and entropies of reduction were determined for the cations V(V), Cr(3+), Mn(2+), Mn(3+), Fe(2+), Cu(2+), Mo(VI), Sn(IV), and Eu(3+). Reduction potentials were used to study the structural state of cations in the melt.

Dynamic study of excited state hydrogen-bonded complexes of harmane in cyclohexane-toluene mixtures.

PubMed

Carmona, Carmen; Balón, Manuel; Galán, Manuel; Guardado, Pilar; Muñoz, María A

2002-09-01

Photoinduced proton transfer reactions of harmane or 1-methyl-9H-pyrido[3,4-b]indole (HN) in the presence of the proton donor hexafluoroisopropanol (HFIP) in cyclohexane-toluene mixtures (CY-TL; 10% vol/vol of TL) have been studied. Three excited state species have been identified: a 1:2 hydrogen-bonded proton transfer complex (PTC), between the pyridinic nitrogen of the substrate and the proton donor, a hydrogen-bonded cation-like exciplex (CL*) with a stoichiometry of at least 1:3 and a zwitterionic exciplex (Z*). Time-resolved fluorescence measurements evidence that upon excitation of ground state PTC, an excited state equilibrium is established between PTC* and the cationlike exciplex, CL*, lambdaem approximately/= 390 nm. This excited state reaction is assisted by another proton donor molecule. Further reaction of CL* with an additional HFIP molecule produces the zwitterionic species, Z*, lambda(em) approximately/= 500 nm. From the analysis of the multiexponential decays, measured at different emission wavelengths and as a function of HFIP concentration, the mechanism of these excited state reactions has been established. Thus, three rate constants and three reciprocal lifetimes have been determined. The simultaneous study of 1,9-dimethyl-9H-pyrido[3,4-b]indole (MHN) under the same experimental conditions has helped to understand the excited state kinetics of these processes.

Scandium induced structural transformation and B′:B″ cationic ordering in Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} multiferroic ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mallesham, B.; Ranjith, R., E-mail: ranjith@iith.ac.in; Manivelraja, M.

2014-07-21

The current study explores non-magnetic Sc{sup 3+} induced structural transformation, evolution of local B-site cation ordering and associated effect on ferroelectric phase transition temperature T{sub max} (temperature corresponding to dielectric maxima) on increasing the atom percent of Sc substitution in [Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} (PFN)] ceramics. In this regard, the phase pure Pb[(Fe{sub 0.5−x}Sc{sub x})Nb{sub 0.5}]O{sub 3} ceramics with x varying from 0 to 0.5 were synthesized through solid state reaction route. The detailed structural analysis through Rietveld refinement confirms the room temperature transformation from a monoclinic Cm to rhombohedral R3m structure at x = 0.3 mol. % of Sc. Absorption spectra studies showmore » that there is a considerable increment in the bandgap at higher scandium content. Most interestingly, the T{sub max} exhibited an increment for lower scandium contents (x = 0.1 to 0.25) followed by a drop in T{sub max} (x = 0.3 to 0.5). Such anomalous behavior in T{sub max} is expected to arise due to the onset of B′, B″ local cation ordering beyond Sc content x = 0.25. The B-site cation ordering at and beyond x = 0.3 was also confirmed by the evolution of cation order induced Pb-O coupled vibrational mode in Raman scattering studies. In addition, the Mössbauer spectra of PFN (x = 0) and Pb(Fe{sub 0.4}Sc{sub 0.1}Nb{sub 0.5})O{sub 3} (x = 0.1) are reported to verify the spin state and oxidation state of iron. The lattice distortion due to the radius ratio difference between a Sc{sup 3+} cation and Fe{sup 3+} cation in low spin state is responsible for the structural transformation, which in turn facilitates a B′:B″ cation ordering.« less

State-resolved three-dimensional electron-momentum correlation in nonsequential double ionization of benzene

NASA Astrophysics Data System (ADS)

Winney, Alexander H.; Lin, Yun Fei; Lee, Suk Kyoung; Adhikari, Pradip; Li, Wen

2016-03-01

We report state-resolved electron-momentum correlation measurement of strong-field nonsequential double ionization in benzene. With a novel coincidence detection apparatus, highly efficient triple coincidence (electron-electron dication) and quadruple coincidence (electron-electron-cation-cation) are used to resolve the final ionic states and to characterize three-dimensional (3D) electron-momentum correlation. The primary states associated with dissociative and nondissociative dications are assigned. A 3D momentum anticorrelation is observed for the electrons in coincidence with dissociative benzene dication states whereas such a correlation is absent for nondissociative dication states.

Ground-water quality and geochemistry in Dayton, Stagecoach, and Churchill Valleys, western Nevada

USGS Publications Warehouse

Thomas, James M.; Lawrence, Stephen J.

1994-01-01

The U.S. Geological Survey investigated the quality of ground water in the Dayton, Stagecoach, and Churchill Valleys as part of the Carson River Basin National Water-Quality Assessment (NAWQA) pilot study. Four aquifer systems have been de- lineated in the study area. Principal aquifers are unconsolidated deposits at altitudes of less than 4,900 feet above sea level and more than 50 feet below land surface. Shallow aquifers are at altitudes of less than 4,900 feet and less than 50 feet below land surface. Upland aquifers are above 4,900 feet and provide recharge to the principal aquifers. Thermal aquifers, defined as those having a water temperature greater than 30 degrees Celsius, are also present. Ground water used in Dayton, Stagecoach, and Churchill Valleys is pumped from principal aquifers in unconsolidated basin-fill deposits. Ground water in these aquifers originates as precipitation in the adjacent mountains and is recharged by the Carson River and by underflow from adjacent upstream valleys. Ground-water flow is generally parallel to the direction of surface-water flow in the Carson River. Ground water is discharged by pumping, evapo- transpiration, and underflow into the Carson River. The results of geochemical modeling indicate that as ground water moves from upland aquifers in mountainous recharge areas to principal aquifers in basin-fill deposits, the following processes probably occur: (1) plagioclase feldspar, sodium chloride, gypsum (or pyrite), potassium feldspar, and biotite dissolve; (2) calcite precipitates; (3) kaolinite forms; (4) small amounts of calcium and magnesium in the water exchange for potassium on aquifer minerals; and (5) carbon dioxide is gained or lost. The geochemical models are consistent with (1) phases identified in basin- fill sediments; (2) chemical activity of major cations and silica; (3) saturation indices of calcite and amorphous silica; (4) phase relations for aluminosilicate minerals indicated by activity diagrams; and (5) results of optical, X-ray diffraction, and scanning-electron microscopy examination of mineral grains in the aquifer sediments. Sulfur-isotopic composition of ground- water samples also supports the models. In general, the quality of ground water in the study area meets Nevada State drinking-water standards and is acceptable for most uses. In addition to analysis for major ions, samples were analyzed for 22 inorganic trace elements, 3 nutrients, and 4 radionuclides. Selenium in 1 sample is the only constituent that exceeded Nevada State primary drinking-water standards. Nevada State secondary- drinking water standards were exceeded for fluoride in 1 sample, for iron in 7 samples, and for manganese in 19 samples. Minor constituent con- centrations are generally the result of local redox conditions, and are primarily from minerals in volcanic and marine metasedimentary rocks, metal- oxide coatings on mineral grains, and organic matter.

Orbital controlled band gap engineering of tetragonal BiFeO 3 for optoelectronic applications

DOE PAGES

Qiao, L.; Zhang, S.; Xiao, H. Y.; ...

2018-01-01

Bismuth ferrite BiFeO 3 (BFO) is an important ferroelectric material for thin-film optoelectronic sensing and potential photovoltaic applications. Its relatively large band gap, however, limits the conversion efficiency of BFO absorber-based PV devices. In this study, based on density functional theory calculations we demonstrate that with well-designed Fe-site elemental substitution, tetragonal BFO can exhibit a much lower fundamental band gap than conventional rhombohedral BFO without forming in-gap electronic states and unravel the underlying mechanisms. Cation atomic size, electronegativity, and crystallographic symmetry are evidenced as critical parameters to tailor the metal 3d – oxygen 2p orbital interactions and thus intrinsically modifymore » electronic structure, particularly, the shape and character of the valence and conduction band edges. With reduced band gap, improved mobility, and uncompromised ferroelectric and magnetic ground states, the present results provide a new strategy of designing high symmetry BFO for efficient optoelectronic applications.« less

Orbital controlled band gap engineering of tetragonal BiFeO 3 for optoelectronic applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiao, L.; Zhang, S.; Xiao, H. Y.

Bismuth ferrite BiFeO 3 (BFO) is an important ferroelectric material for thin-film optoelectronic sensing and potential photovoltaic applications. Its relatively large band gap, however, limits the conversion efficiency of BFO absorber-based PV devices. In this study, based on density functional theory calculations we demonstrate that with well-designed Fe-site elemental substitution, tetragonal BFO can exhibit a much lower fundamental band gap than conventional rhombohedral BFO without forming in-gap electronic states and unravel the underlying mechanisms. Cation atomic size, electronegativity, and crystallographic symmetry are evidenced as critical parameters to tailor the metal 3d – oxygen 2p orbital interactions and thus intrinsically modifymore » electronic structure, particularly, the shape and character of the valence and conduction band edges. With reduced band gap, improved mobility, and uncompromised ferroelectric and magnetic ground states, the present results provide a new strategy of designing high symmetry BFO for efficient optoelectronic applications.« less

Weak-field few-femtosecond VUV photodissociation dynamics of water isotopologues

NASA Astrophysics Data System (ADS)

Baumann, Arne; Bazzi, Sophia; Rompotis, Dimitrios; Schepp, Oliver; Azima, Armin; Wieland, Marek; Popova-Gorelova, Daria; Vendrell, Oriol; Santra, Robin; Drescher, Markus

2017-07-01

We present a joint experimental and theoretical study of the VUV-induced dynamics of H2O and its deuterated isotopologues in the first excited state (A ˜1B1 ) utilizing a VUV-pump VUV-probe scheme combined with a b initio classical trajectory calculations. 16-fs VUV pulses centered at 161 nm created by fifth-order harmonic generation are employed for single-shot pump-probe measurements. Combined with a precise determination of the VUV pulses' temporal profile, they provide the necessary temporal resolution to elucidate sub-10-fs dissociation dynamics in the 1+1 photon ionization time window. Ionization with a single VUV photon complements established strong-field ionization schemes by disclosing the molecular dynamics under perturbative conditions. Kinetic isotope effects derived from the pump-probe experiment are found to be in agreement with our by ab initio classical trajectory calculations, taking into account photoionization cross sections for the ground and first excited state of the water cation.

High-resolution threshold photoionization of N sub 2 O

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiedmann, R.T.; Grant, E.R.; Tonkyn, R.G.

1991-07-15

Pulsed field ionization (PFI) has been used in conjunction with a coherent vuv source to obtain high-resolution threshold photoelectron spectra for the (000), (010), (020), and (100) vibrational states of the N{sub 2}O{sup +} cation. Simulations for the rotational profiles of each vibronic level were obtained by fitting the Buckingham--Orr--Sichel equations (A. D. Buckingham, B. J. Orr, and J. M. Sichel, Philos. Trans. R. Soc. London, Ser. A {bold 268}, 147 (1970)) using accurate spectroscopic constants for the ground states of the neutral and the ion. The relative branch intensities are interpreted in terms of the partial waves of themore » outgoing photoelectron to which the ionic core is coupled and in terms of the angular momentum transferred to the core. The PFI technique also allows us to report an improved value for the ionization potential of N{sub 2}O of 103 963{plus minus}5 cm{sup {minus}1}.« less

Surprises in low dimensional spin 1/2 magnets - from crystal chemistry to microscopic magnetic models of complex oxides

NASA Astrophysics Data System (ADS)

Rosner, Helge

2011-03-01

A microscopic understanding of the structure-properties relation in crystalline materials is a main goal of modern solid state chemistry and physics. Due to their peculiar magnetism, low dimensional spin 1/2 systems are often highly sensitive to structural details. Seemingly unimportant structural details can be crucial for the magnetic ground state of a compound, especially in the case of competing interactions, frustration and near-degeneracy. Here, we present for selected, complex Cu 2+ systems that a first principles based approach can reliably provide the correct magnetic model, especially in cases where the interpretation of experimental data meets serious difficulties or fails. We demonstrate that the magnetism of low dimensional insulators crucially depends on the magnetically active orbitals which are determined by details of the ligand field of the magnetic cation. Our theoretical results are in very good agreement with thermodynamic and spectroscopic data and provide deep microscopic insight into topical low dimensional magnets.

G W (Γ ) method without the Bethe-Salpeter equation for photoabsorption energies of spin-polarized systems

NASA Astrophysics Data System (ADS)

Isobe, Tomoharu; Kuwahara, Riichi; Ohno, Kaoru

2018-06-01

The one-shot G W method, beginning with the local density approximation (LDA), enables one to calculate photoemission and inverse photoemission spectra. In order to calculate photoabsorption spectra, one had to additionally solve the Bethe-Salpeter equation (BSE) for the two-particle (electron-hole) Green's function, which doubly induces evaluation errors. It has been recently reported that the G W +BSE method significantly underestimates the experimental photoabsorption energies (PAEs) of small molecules. In order to avoid these problems, we propose to apply the G W (Γ ) method not to the neutral ground state but to the cationic state to calculate PAEs without solving the BSE, which allows a rigorous one-to-one correspondence between the photoabsorption peak and the "extended" quasiparticle level. We applied the self-consistent linearized G W Γ method including the vertex correction Γ to our method, and found that this method gives the PAEs of B, Na3, and Li3 to within 0.1 eV accuracy.

Electronic structure and optical spectra of semiconducting carbon nanotubes functionalized by diazonium salts

NASA Astrophysics Data System (ADS)

Ramirez, Jessica; Mayo, Michael L.; Kilina, Svetlana; Tretiak, Sergei

2013-02-01

We report density functional (DFT) calculations on finite-length semiconducting carbon nanotubes covalently and non-covalently functionalized by aryl diazonium moieties and their chlorinated derivatives. For these systems, we investigate (i) an accuracy of different functionals and basis sets, (ii) a solvent effect, and (iii) the impact of the chemical functionalization on optical properties of nanotubes. In contrast to B3LYP, only long-range-corrected functionals, such as CAM-B3LYP and wB97XD, properly describe the ground and excited state properties of physisorbed molecules. We found that physisorbed cation insignificantly perturbs the optical spectra of nanotubes. In contrast, covalently bound complexes demonstrate strong redshifts and brightening of the lowest exciton that is optically dark in pristine nanotubes. However, the energy and oscillator strength of the lowest state are dictated by the position of the molecule on the nanotube. Thus, if controllable and selective chemical functionalization is realized, the PL of nanotubes could be improved.

Generalized trends in the formation energies of perovskite oxides.

PubMed

Zeng, ZhenHua; Calle-Vallejo, Federico; Mogensen, Mogens B; Rossmeisl, Jan

2013-05-28

Generalized trends in the formation energies of several families of perovskite oxides (ABO3) and plausible explanations to their existence are provided in this study through a combination of DFT calculations, solid-state physics analyses and simple physical/chemical descriptors. The studied elements at the A site of perovskites comprise rare-earth, alkaline-earth and alkaline metals, whereas 3d and 5d metals were studied at the B site. We also include ReO3-type compounds, which have the same crystal structure of cubic ABO3 perovskites except without A-site elements. From the observations we extract the following four conclusions for the perovskites studied in the present paper: for a given cation at the B site, (I) perovskites with cations of identical oxidation state at the A site possess close formation energies; and (II) perovskites with cations of different oxidation states at the A site usually have quite different but ordered formation energies. On the other hand, for a given A-site cation, (III) the formation energies of perovskites vary linearly with respect to the atomic number of the elements at the B site within the same period of the periodic table, and the slopes depend systematically on the oxidation state of the A-site cation; and (IV) the trends in formation energies of perovskites with elements from different periods at the B site depend on the oxidation state of A-site cations. Since the energetics of perovskites is shown to be the superposition of the individual contributions of their constituent oxides, the trends can be rationalized in terms of A-O and B-O interactions in the ionic crystal. These findings reveal the existence of general systematic trends in the formation energies of perovskites and provide further insight into the role of ion-ion interactions in the properties of ternary compounds.

Neutral and cationic phosphoramide adducts of silicon tetrachloride: synthesis and characterization of their solution and solid-state structures.

PubMed

Denmark, Scott E; Eklov, Brian M

2008-01-01

The solution and solid-state structures of hexamethylphosphoramide (HMPA) adducts of tetrachlorosilane (SiCl4) are discussed. In solution, the meridional and facial isomers of the hexa-coordinate cationic complex 3 HMPASiCl3 + Cl(-) (2) predominate at all HMPA concentrations, and are in equilibrium with the hexa-coordinate neutral trans- and cis-2 HMPASiCl4 complexes (1), as well as the penta-coordinate cationic cis-2 HMPASiCl3 + Cl(-) (3). Single crystal X-ray analyses are reported for the ionized mer-3 HMPASiCl3 + HCl2 (-) and the neutral trans-2 HMPASiCl4 complexes.

Structural and spectroscopic features of proton hydrates in the crystalline state. Solid-state DFT study on HCl and triflic acid hydrates

NASA Astrophysics Data System (ADS)

Vener, M. V.; Chernyshov, I. Yu.; Rykounov, A. A.; Filarowski, A.

2018-01-01

Crystalline HCl and CF3SO3H hydrates serve as excellent model systems for protonated water and perfluorosulphonic acid membranes, respectively. They contain characteristic H3O+, H5О+2, H7О+3 and H3O+(H2O)3 (the Eigen cation) structures. The properties of these cations in the crystalline hydrates of strong monobasic acids are studied by solid-state density function theory (DFT). Simultaneous consideration of the HCl and CF3SO3H hydrates reveals the impact of the size of a counter ion and the crystalline environment on the structure and infrared active bands of the simplest proton hydrates. The H7O+3 structure is very sensitive to the size of the counter ion and symmetry of the local environment. This makes it virtually impossible to identify the specific features of H7O+3 in molecular crystals. The H3O+ ion can be treated as the Eigen-like cation in the crystalline state. Structural, infrared and electron-density features of H5О+2 and the Eigen cation are virtually insensitive to the size of the counter ion and the symmetry of the local crystalline environment. These cations can be considered as the simplest stable proton hydrates in the condensed phase. Finally, the influence of the Grimme correction on the structure and harmonic frequencies of the molecular crystals with short (strong) intermolecular O-H···O bonds is discussed.

Spectroscopic and Kinetic Characterization of Peroxidase-Like π-Cation Radical Pinch-Porphyrin-Iron(III) Reaction Intermediate Models of Peroxidase Enzymes.

PubMed

Hernández Anzaldo, Samuel; Arroyo Abad, Uriel; León García, Armando; Ramírez Rosales, Daniel; Zamorano Ulloa, Rafael; Reyes Ortega, Yasmi

2016-06-27

The spectroscopic and kinetic characterization of two intermediates from the H₂O₂ oxidation of three dimethyl ester [(proto), (meso), (deuteroporphyrinato) (picdien)]Fe(III) complexes ([FePPPic], [FeMPPic] and [FeDPPic], respectively) pinch-porphyrin peroxidase enzyme models, with s = 5/2 and 3/2 Fe(III) quantum mixed spin (qms) ground states is described herein. The kinetic study by UV/Vis at λmax = 465 nm showed two different types of kinetics during the oxidation process in the guaiacol test for peroxidases (1-3 + guaiacol + H₂O₂ → oxidation guaiacol products). The first intermediate was observed during the first 24 s of the reaction. When the reaction conditions were changed to higher concentration of pinch-porphyrins and hydrogen peroxide only one type of kinetics was observed. Next, the reaction was performed only between pinch-porphyrins-Fe(III) and H₂O₂, resulting in only two types of kinetics that were developed during the first 0-4 s. After this time a self-oxidation process was observed. Our hypotheses state that the formation of the π-cation radicals, reaction intermediates of the pinch-porphyrin-Fe(III) family with the ligand picdien [N,N'-bis-pyridin-2-ylmethyl-propane-1,3-diamine], occurred with unique kinetics that are different from the overall process and was involved in the oxidation pathway. UV-Vis, ¹H-NMR and ESR spectra confirmed the formation of such intermediates. The results in this paper highlight the link between different spectroscopic techniques that positively depict the kinetic traits of artificial compounds with enzyme-like activity.

Exciplex Formation between Silver Ions and the Lowest MLCT Excited State of the Tris(Bipyrazine)Ruthenium(2) Cation

DTIC Science & Technology

1988-07-11

OFFICE OF NAVAL RESEARCH Contract N00014-84-G-0201 Task No. 0051-865 0 Technical Report #21 Exciplex Formation Between Silver Ions and the Lowest...ELEMENT NO-. NO NO ~ ACCESSION NO 11. TITLE (include Security Classification) Exciplex Formation Between Silver Ions and the Lowest MLCT Excited State of... eXCiplexes with upIV to six silver ions per excited Cation. Lifetime, wavelength data are presented as a function of the [Agi/[Ru] ratio. An excited state

Advantage of low-temperature hydrothermal synthesis to grow stoichiometric crednerite crystals

NASA Astrophysics Data System (ADS)

Poienar, Maria; Martin, Christine; Lebedev, Oleg I.; Maignan, Antoine

2018-06-01

This work reports a new approach for the growth of stoichiometric crednerite CuMnO2 crystals. The hydrothermal reaction, starting from soluble metal sulphates as precursors, is assisted by ethylene glycol and the formation of crednerite is found to depend strongly on pH and temperature. This method allows obtaining small hexagonal platelets with the larger dimension about 1.0-1.5 μm and with a composition characterized by a Cu/Mn ratio of 1. Thus, these crystals differ from the needle-like millimetric ones obtained by the flux technique for which the composition departs from the expected one and is close to Cu1.04Mn0.96. This monitoring of the cationic composition in crednerite, using hydrothermal synthesis, is important as the Cu/Mn ratio controls the low temperature antiferromagnetic ground-state.

Single DNA molecules on freestanding and supported cationic lipid bilayers: diverse conformational dynamics controlled by the local bilayer properties

NASA Astrophysics Data System (ADS)

Herold, Christoph; Schwille, Petra; Petrov, Eugene P.

2016-02-01

We present experimental results on the interaction of DNA macromolecules with cationic lipid membranes with different properties, including freestanding membranes in the fluid and gel state, and supported lipid membranes in the fluid state and under conditions of fluid-gel phase coexistence. We observe diverse conformational dynamics of membrane-bound DNA molecules controlled by the local properties of the lipid bilayer. In case of fluid-state freestanding lipid membranes, the behaviour of DNA on the membrane is controlled by the membrane charge density: whereas DNA bound to weakly charged membranes predominantly behaves as a 2D random coil, an increase in the membrane charge density leads to membrane-driven irreversible DNA collapse and formation of subresolution-sized DNA globules. On the other hand, electrostatic binding of DNA macromolecules to gel-state freestanding membranes leads to completely arrested diffusion and conformational dynamics of membrane-adsorbed DNA. A drastically different picture is observed in case of DNA interaction with supported cationic lipid bilayers: When the supported bilayer is in the fluid state, membrane-bound DNA molecules undergo 2D translational Brownian motion and conformational fluctuations, irrespectively of the charge density of the supported bilayer. At the same time, when the supported cationic membrane shows fluid-gel phase coexistence, membrane-bound DNA molecules are strongly attracted to micrometre-sized gel-phase domains enriched with the cationic lipid, which results in 2D compaction of the membrane-bound macromolecules. This DNA compaction, however, is fully reversible, and disappears as soon as the membrane is heated above the fluid-gel coexistence. We also discuss possible biological implications of our experimental findings.

Experimental investigation of variations in morphology, composition and mixing-state of boundary layer aerosol: A balloon based study over urban environment (New Delhi)

NASA Astrophysics Data System (ADS)

Mishra, S. K.; Ahlawat, A.; Khosla, D.; Sharma, C.; Prasad, M. V. S. N.; Singh, Sukhvir; Gupta, B.; Tulsi; Sethi, D.; Sinha, P. R.; Ojha, D. K.; Wiedensohler, A.; Kotnala, R. K.

2018-07-01

The morphology, composition, and complex mixing states of aerosol are extremely important physico-chemical properties which are the major inputs to the optical/radiative models. Though, ground based observations of the said properties are abundant but the vertical profiles of the same are very much limited throughout the globe. The information on the vertical heterogeneity of the aforementioned properties over a polluted environment like Delhi will be very helpful to develop a better understanding of the thermodynamics of the lower atmosphere. In present study, we carried out a tethered balloon based field campaign in National Physical Laboratory (28° 38‧ 10″ N, 77° 10‧ 17″ E) from 21 to 27 February 2014 to explore the vertical distribution of the said properties. Based on the microscopic observations, the bubbly shaped sulfate particles number percentage is less (5%) on the ground, abundant (49%) on altitude <350 m and nearly absent on altitude >350 m. At 500 m altitude, particles were majorly of spiked shape with elongated dimension ∼ 3-4 μm. The number percentage of the aged fractals has been found to increase by 4% in the 100-350 m range against the ground observations. Based on the bulk composition of non-carbonaceous species, at 200 m altitude, we observed significant amount (74%) of the oxides of sulfur compared to that of ground observations (30%) that could be due to temperature inversion and air parcel movement from IGP (Indo Gangetic Plain). Various core-shell type particle configurations have been observed at different altitudes. At 200 m altitude, particles were majorly aged with anionic species (like S, Cl and HSO4) and cationic species (like C2H5). The bulk and individual particle level data generated over Delhi environment in this experiment may improve our understanding of boundary layer aerosol and could provide the scientific insights of their probable effects on low level cloud formation.

Preparing transition-metal clusters in known structural forms: the mass-analyzed threshold ionization spectrum of V3.

PubMed

Ford, Mark S; Mackenzie, Stuart R

2005-08-22

The first results are presented of a new experiment designed both to generate and characterize spectroscopically individual isomers of transition-metal cluster cations. As a proof of concept the one-photon mass-analyzed threshold ionization (MATI) spectrum of V3 has been recorded in the region of 44,000-45,000 cm-1. This study extends the range of a previous zero-kinetic-energy (ZEKE) photoelectron study of Yang et al. [Chem. Phys. Lett. 231, 177 (1994)] with which the current results are compared. The MATI spectra reported here exhibit surprisingly high resolution (0.2 cm-1) for this technique despite the use of large discrimination and extraction fields. Analysis of the rotational profile of the origin band allows assignment of the V3 ground state as and the V3+ ground state as , both with D3h geometry, in agreement with the density-functional theory study of the V3 ZEKE spectrum by Calaminici et al. [J. Chem. Phys. 114, 4036 (2001)]. There is also some evidence in the spectrum of transitions to the low-lying excited state of the ion. The vibrational structure observed in the MATI spectrum is, however, significantly different to and less extensive than that predicted in the density-functional theory study. Possible reasons for the discrepancies are discussed and an alternative assignment is proposed which results in revised values for the vibrational wave numbers of both the neutral and ionic states. These studies demonstrate the efficient generation of cluster ions in known structural (isomeric) forms and pave the way for the study of cluster reactivity as a function of geometrical structure.

Complete phase diagram of rare-earth nickelates from first-principles

NASA Astrophysics Data System (ADS)

Varignon, Julien; Grisolia, Mathieu N.; Íñiguez, Jorge; Barthélémy, Agnès; Bibes, Manuel

2017-12-01

The structural, electronic and magnetic properties of AMO3 perovskite oxides, where M is a 3d transition metal, are highly sensitive to the geometry of the bonds between the metal-d and oxygen-p ions (through octahedra rotations and distortions) and to their level of covalence. This is particularly true in rare-earth nickelates RNiO3 that display a metal-insulator transition with complex spin orders tunable by the rare-earth size, and are on the border line between dominantly ionic (lighter elements) and covalent characters (heavier elements). Accordingly, computing their ground state is challenging and a complete theoretical description of their rich phase diagram is still missing. Here, using first-principles simulations, we successfully describe the electronic and magnetic experimental ground state of nickelates. We show that the insulating phase is characterized by a split of the electronic states of the two Ni sites (i.e., resembling low-spin 4+ and high-spin 2+) with a concomitant shift of the oxygen-2p orbitals toward the depleted Ni cations. Therefore, from the point of view of the charge, the two Ni sites appear nearly identical whereas they are in fact distinct. Performing such calculations for several nickelates, we built a theoretical phase diagram that reproduces all their key features, namely a systematic dependence of the metal-insulator transition with the rare-earth size and the crossover between a second to first order transition for R = Pr and Nd. Finally, our results hint at strategies to control the electronic and magnetic phases of perovskite oxides by fine tuning of the level of covalence.

Entropy-stabilized oxides

PubMed Central

Rost, Christina M.; Sachet, Edward; Borman, Trent; Moballegh, Ali; Dickey, Elizabeth C.; Hou, Dong; Jones, Jacob L.; Curtarolo, Stefano; Maria, Jon-Paul

2015-01-01

Configurational disorder can be compositionally engineered into mixed oxide by populating a single sublattice with many distinct cations. The formulations promote novel and entropy-stabilized forms of crystalline matter where metal cations are incorporated in new ways. Here, through rigorous experiments, a simple thermodynamic model, and a five-component oxide formulation, we demonstrate beyond reasonable doubt that entropy predominates the thermodynamic landscape, and drives a reversible solid-state transformation between a multiphase and single-phase state. In the latter, cation distributions are proven to be random and homogeneous. The findings validate the hypothesis that deliberate configurational disorder provides an orthogonal strategy to imagine and discover new phases of crystalline matter and untapped opportunities for property engineering. PMID:26415623

Molecular Dynamics of Flexible Polar Cations in a Variable Confined Space: Toward Exceptional Two-Step Nonlinear Optical Switches.

PubMed

Xu, Wei-Jian; He, Chun-Ting; Ji, Cheng-Min; Chen, Shao-Li; Huang, Rui-Kang; Lin, Rui-Biao; Xue, Wei; Luo, Jun-Hua; Zhang, Wei-Xiong; Chen, Xiao-Ming

2016-07-01

The changeable molecular dynamics of flexible polar cations in the variable confined space between inorganic chains brings about a new type of two-step nonlinear optical (NLO) switch with genuine "off-on-off" second harmonic generation (SHG) conversion between one NLO-active state and two NLO-inactive states. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Evaluation of water quality and hydrogeochemistry of surface and groundwater, Tiruvallur District, Tamil Nadu, India

NASA Astrophysics Data System (ADS)

Krishna Kumar, S.; Hari Babu, S.; Eswar Rao, P.; Selvakumar, S.; Thivya, C.; Muralidharan, S.; Jeyabal, G.

2017-09-01

Water quality of Tiruvallur Taluk of Tiruvallur district, Tamil Nadu, India has been analysed to assess its suitability in relation to domestic and agricultural uses. Thirty water samples, including 8 surface water (S), 22 groundwater samples [15 shallow ground waters (SW) and 7 deep ground waters (DW)], were collected to assess the various physico-chemical parameters such as Temperature, pH, Electrical conductivity (EC), Total dissolved solids (TDS), cations (Ca, Mg, Na, K), anions (CO3, HCO3, Cl, SO4, NO3, PO4) and trace elements (Fe, Mn, Zn). Various irrigation water quality diagrams and parameters such as United states salinity laboratory (USSL), Wilcox, sodium absorption ratio (SAR), sodium percentage (Na %), Residual sodium carbonate (RSC), Residual Sodium Bicarbonate (RSBC) and Kelley's ratio revealed that most of the water samples are suitable for irrigation. Langelier Saturation Index (LSI) values suggest that the water is slightly corrosive and non-scale forming in nature. Gibbs plot suggests that the study area is dominated by evaporation and rock-water dominance process. Piper plot indicates the chemical composition of water, chiefly controlled by dissolution and mixing of irrigation return flow.

Molecular dynamics simulations of the structure and single-particle dynamics of mixtures of divalent salts and ionic liquids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gómez-González, Víctor; Docampo-Álvarez, Borja; Gallego, Luis J.

2015-09-28

We report a molecular dynamics study of the structure and single-particle dynamics of mixtures of a protic (ethylammonium nitrate) and an aprotic (1-butyl-3-methylimidazolium hexaflurophosphate [BMIM][PF{sub 6}]) room-temperature ionic liquids doped with magnesium and calcium salts with a common anion at 298.15 K and 1 atm. The solvation of these divalent cations in dense ionic environments is analyzed by means of apparent molar volumes of the mixtures, radial distribution functions, and coordination numbers. For the protic mixtures, the effect of salt concentration on the network of hydrogen bonds is also considered. Moreover, single-particle dynamics of the salt cations is studied by means ofmore » their velocity autocorrelation functions and vibrational densities of states, explicitly analyzing the influence of salt concentration, and cation charge and mass on these magnitudes. The effect of the valency of the salt cation on these properties is considered comparing the results with those for the corresponding mixtures with lithium salts. We found that the main structural and dynamic features of the local solvation of divalent cations in ionic liquids are similar to those of monovalent salts, with cations being localized in the polar nanoregions of the bulk mixture coordinated in monodentate and bidentate coordination modes by the [NO{sub 3}]{sup −} and [PF{sub 6}]{sup −} anions. However, stronger electrostatic correlations of these polar nanoregions than in mixtures with salts with monovalent cations are found. The vibrational modes of the ionic liquid (IL) are seen to be scarcely affected by the addition of the salt, and the effect of mass and charge on the vibrational densities of states of the dissolved cations is reported. Cation mass is seen to exert a deeper influence than charge on the low-frequency vibrational spectra, giving a red shift of the vibrational modes and a virtual suppression of the higher energy vibrational modes for the heavier Ca{sup 2+} cations. No qualitative difference with monovalent cations was found in what solvation is concerned, which suggests that no enhanced reduction of the mobility of these cations and their complexes in ILs respective to those of monovalent cations is to be expected.« less

Evaluating the Nature of So-Called S*-State Feature in Transient Absorption of Carotenoids in Light-Harvesting Complex 2 (LH2) from Purple Photosynthetic Bacteria

PubMed Central

2016-01-01

Carotenoids are a class of natural pigments present in all phototrophic organisms, mainly in their light-harvesting proteins in which they play roles of accessory light absorbers and photoprotectors. Extensive time-resolved spectroscopic studies of these pigments have revealed unexpectedly complex photophysical properties, particularly for carotenoids in light-harvesting LH2 complexes from purple bacteria. An ambiguous, optically forbidden electronic excited state designated as S* has been postulated to be involved in carotenoid excitation relaxation and in an alternative carotenoid-to-bacteriochlorophyll energy transfer pathway, as well as being a precursor of the carotenoid triplet state. However, no definitive and satisfactory origin of the carotenoid S* state in these complexes has been established, despite a wide-ranging series of studies. Here, we resolve the ambiguous origin of the carotenoid S* state in LH2 complex from Rba. sphaeroides by showing that the S* feature can be seen as a combination of ground state absorption bleaching of the carotenoid pool converted to cations and the Stark spectrum of neighbor neutral carotenoids, induced by temporal electric field brought by the carotenoid cation–bacteriochlorophyll anion pair. These findings remove the need to assign an S* state, and thereby significantly simplify the photochemistry of carotenoids in these photosynthetic antenna complexes. PMID:27726397

Lanthanide-organic complexes based on polyoxometalates: Solvent effect on the luminescence properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang Qun; Liu Shuxia, E-mail: liusx@nenu.edu.cn; Liang Dadong

2012-06-15

A series of lanthanide-organic complexes based on polyoxometalates (POMs) [Ln{sub 2}(DNBA){sub 4}(DMF){sub 8}][W{sub 6}O{sub 19}] (Ln=La(1), Ce(2), Sm(3), Eu(4), Gd(5); DNBA=3,5-dinitrobenzoate; DMF=N,N-dimethylformamide) has been synthesized. These complexes consist of [W{sub 6}O{sub 19}]{sup 2-} and dimeric [Ln{sub 2}(DNBA){sub 4}(DMF){sub 8}]{sup 2+} cations. The luminescence properties of 4 are measured in solid state and different solutions, respectively. Notably, the emission intensity increases gradually with the increase of solvent permittivity, and this solvent effect can be directly observed by electrospray mass spectrometry (ESI-MS). The analyses of ESI-MS show that the eight coordinated solvent DMF units of dimeric cation are active. They can movemore » away from dimeric cations and exchange with solvent molecules. Although the POM anions escape from 3D supramolecular network, the dimeric state structure of [Ln{sub 2}(DNBA){sub 4}]{sup 2+} remains unchanged in solution. The conservation of red luminescence is attributed to the maintenance of the aggregated state structures of dimeric cations. - Graphical abstract: 3D POMs-based lanthanide-organic complexes performed the solvent effect on the luminescence property. The origin of such solvent effect can be understood and explained on the basis of the existence of coordinated active sites by the studies of ESI-MS. Highlights: Black-Right-Pointing-Pointer The solvent effect on the luminescence property of POMs-based lanthanide-organic complexes. Black-Right-Pointing-Pointer ESI-MS analyses illuminate the correlation between the structure and luminescence property. Black-Right-Pointing-Pointer The dimeric cations have eight active sites of solvent coordination. Black-Right-Pointing-Pointer The aggregated state structure of dimer cation remains unchanged in solution. Black-Right-Pointing-Pointer Luminescence associating with ESI-MS is a new method for investigating the interaction of complex and solvent.« less

Cation and anion sequences in dark-adapted Balanus photoreceptor

PubMed Central

1977-01-01

Anion and cation permeabilities in dark-adapted Balanus photoreceptors were determined by comparing changes in the membrane potential in response to replacement of the dominant anion (Cl-) or cation (Na+) by test anions or cations in the superfusing solution. The anion permeability sequence obtained was PI greater than PSO4 greater than PBr greater than PCl greater than Pisethionate greater than Pmethanesulfonate. Gluconate, glucuronate, and glutamate generally appeared more permeable and propionate less permeable than Cl-. The alkali-metal cation permeability sequence obtained was PK greater than PRb greater than PCx greater than PNa approximately PLi. This corresponds to Eisenman's IV which is the same sequencethat has been obtained for other classes of nerve cells in the resting state. The values obtained for the permeability ratios of the alkali-metal cations are considered to be minimal. The membrane conductance measured by passing inward current pulses in the different test cations followed the sequence, GK greater than GRb greater than GCs greater than GNa greater than GLi. The conductance ratios obtained for a full substitution of the test cation agreed quite well with permeability ratios for all the alkali-metal cations except K+ which was generally higher. PMID:199688

Correlating valence state, site preference and co-substitution to the magnetoelastic properties of cobalt ferrite

NASA Astrophysics Data System (ADS)

Nlebedim, Cajetan; Jiles, David

2015-03-01

Understanding how to influence the physics of magnetism, especially the relationship between magnetic susceptibility and stress, can be very useful in designing non-contact stress and torque sensors using magnetoelastic materials. This is particularly important considering that materials rarely occur in states desirable for direct applications. In this work we show that the magnetoelastic properties of cobalt ferrite are strongly dependent on the valence states and site preferences of substituted cations. It was found that co-substitution of magnetic and non-magnetic cations, is key to achieving simultaneous improvement in magnetostriction amplitude and strain sensitivity to applied magnetic field. Nevertheless, Curie temperature decreased, irrespective of the valence state, site preference or co-substitution. This presentation will show why tetravalent Ge resulted in superior magnetostrictive properties compared to other tetravalent, trivalent and divalent cations substituted into the crystal lattice of cobalt ferrite. This work was supported by the U.S. DOE, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. The research was performed at Ames Laboratory, operated for the USDoE by Iowa State University (Contract #DE-AC02-07CH11358).

Ground and excited state dissociation dynamics of ionized 1,1-difluoroethene.

PubMed

Gridelet, E; Dehareng, D; Locht, R; Lorquet, A J; Lorquet, J C; Leyh, B

2005-09-22

The kinetic energy release distributions (KERDs) for the fluorine atom loss from the 1,1-difluoroethene cation have been recorded with two spectrometers in two different energy ranges. A first experiment uses dissociative photoionization with the He(I) and Ne(I) resonance lines, providing the ions with a broad internal energy range, up to 7 eV above the dissociation threshold. The second experiment samples the metastable range, and the average ion internal energy is limited to about 0.2 eV above the threshold. In both energy domains, KERDs are found to be bimodal. Each component has been analyzed by the maximum entropy method. The narrow, low kinetic energy components display for both experiments the characteristics of a statistical, simple bond cleavage reaction: constraint equal to the square root of the fragment kinetic energy and ergodicity index higher than 90%. Furthermore, this component is satisfactorily accounted for in the metastable time scale by the orbiting transition state theory. Potential energy surfaces corresponding to the five lowest electronic states of the dissociating 1,1-C2H2F2+ ion have been investigated by ab initio calculations at various levels. The equilibrium geometry of these states, their dissociation energies, and their vibrational wavenumbers have been calculated, and a few conical intersections between these surfaces have been identified. It comes out that the ionic ground state X2B1 is adiabatically correlated with the lowest dissociation asymptote. Its potential energy curve increases in a monotonic way along the reaction coordinate, giving rise to the narrow KERD component. Two states embedded in the third photoelectron band (B2A1 at 15.95 eV and C2B2 at 16.17 eV) also correlate with the lowest asymptote at 14.24 eV. We suggest that their repulsive behavior along the reaction coordinate be responsible for the KERD high kinetic energy contribution.

Potentiometric titration of thiols, cationic surfactants and halides using a solid-state silver-silver sulphide electrode.

PubMed

Pinzauti, S; Papeschi, G; La Porta, E

1983-01-01

A rugged, low resistance silver-silver sulphide solid-state electrode for determining pharmaceuticals as authentic samples or in dosage forms by potentiometric titration is described. Sodium tetraphenylborate, mercury(II) acetate and silver nitrate (0.01) M were employed as titrants in the analysis of cationic surfactants (cetylpyridinium chloride, benzethonium chloride, benzalkonium chloride and chlorhexidine salts), antithyroid drugs (methimazole and propylthiouracil) or sodium halides respectively.

Cation distribution and vacancies in nickel cobaltite.

PubMed

Loche, Danilo; Marras, Claudia; Carta, Daniela; Casula, Maria Francesca; Mountjoy, Gavin; Corrias, Anna

2017-06-28

Samples of nickel cobaltite, a mixed oxide occurring in the spinel structure which is currently extensively investigated because of its prospective application as ferromagnetic, electrocatalytic, and cost-effective energy storage material were prepared in the form of nanocrystals stabilized in a highly porous silica aerogel and as unsupported nanoparticles. Nickel cobaltite nanocrystals with average size 4 nm are successfully grown for the first time into the silica aerogel provided that a controlled oxidation of the metal precursor phases is carried out, consisting in a reduction under H 2 flow followed by mild oxidation in air. The investigation of the average oxidation state of the cations and of their distribution between the sites within the spinel structure, which is commonly described assuming the Ni cations are only located in the octahedral sites, has been carried out by X-ray absorption spectroscopy providing evidence for the first time that the unsupported nickel cobaltite sample has a Ni : Co molar ratio higher than the nominal ratio of 1 : 2 and a larger than expected average overall oxidation state of the cobalt and nickel cations. This is achieved retaining the spinel structure, which accommodates vacancies to counterbalance the variation in oxidation state.

On the permeation of large organic cations through the pore of ATP-gated P2X receptors

PubMed Central

Harkat, Mahboubi; Peverini, Laurie; Dunning, Kate; Beudez, Juline; Martz, Adeline; Calimet, Nicolas; Specht, Alexandre; Cecchini, Marco; Chataigneau, Thierry; Grutter, Thomas

2017-01-01

Pore dilation is thought to be a hallmark of purinergic P2X receptors. The most commonly held view of this unusual process posits that under prolonged ATP exposure the ion pore expands in a striking manner from an initial small-cation conductive state to a dilated state, which allows the passage of larger synthetic cations, such as N-methyl-d-glucamine (NMDG+). However, this mechanism is controversial, and the identity of the natural large permeating cations remains elusive. Here, we provide evidence that, contrary to the time-dependent pore dilation model, ATP binding opens an NMDG+-permeable channel within milliseconds, with a conductance that remains stable over time. We show that the time course of NMDG+ permeability superimposes that of Na+ and demonstrate that the molecular motions leading to the permeation of NMDG+ are very similar to those that drive Na+ flow. We found, however, that NMDG+ “percolates” 10 times slower than Na+ in the open state, likely due to a conformational and orientational selection of permeating molecules. We further uncover that several P2X receptors, including those able to desensitize, are permeable not only to NMDG+ but also to spermidine, a large natural cation involved in ion channel modulation, revealing a previously unrecognized P2X-mediated signaling. Altogether, our data do not support a time-dependent dilation of the pore on its own but rather reveal that the open pore of P2X receptors is wide enough to allow the permeation of large organic cations, including natural ones. This permeation mechanism has considerable physiological significance. PMID:28442564

Comparison of the effects of divalent cations on the noradrenaline-evoked cation current in rabbit portal vein smooth muscle cells

PubMed Central

Aromolaran, A S; Large, W A

1999-01-01

The facilitatory effects of external Ca2+, Sr2+ and Ba2+ (Cao2+, Sro2+ and Bao2+) on the noradrenaline-evoked non-selective cation current (Icat) were compared in rabbit portal vein smooth muscle cells using patch pipette techniques. All divalent cations tested potentiated the amplitude of Icat and the potency sequence was Cao2+ > Sro2+ > Bao2+. Cao2+ and Sro2+ increased the amplitude of Icat by about eight times whereas Bao2+ produced only a threefold facilitation. The current-voltage relationship of Icat was not changed by Cao2+, Sro2+ or Bao2+. From noise analysis the single channel conductance (γ) was approximately 10 pS in divalent cation-free solution but was about 20 pS with Cao2+, Sro2+ and Bao2+. From noise and voltage-jump experiments it was apparent that at least three kinetically resolvable channel states are associated with Icat in divalent cation-free solution. Cao2+ and Sro2+ produced marked changes in the characteristics of the power spectrum and relaxations of Icat in response to voltage steps, consistent with a shift in the equilibrium between the channel states, whereas Bao2+ produced minimal effects. The data show that Cao2+, Sro2+ and Bao2+ increase the amplitude of Icat, which results in part from an increase in the single channel conductance. In addition the results suggest that Cao2+ and Sro2+ alter the kinetic behaviour of the single channels whereas Bao2+ has little effect on the equilibrium between the channel states. PMID:10545143

Residence times and nitrate transport in ground water discharging to streams in the Chesapeake Bay Watershed

USGS Publications Warehouse

Lindsey, Bruce D.; Phillips, Scott; Donnelly, Colleen A.; Speiran, Gary K.; Plummer, Niel; Bohlke, John Karl; Focazio, Michael J.; Burton, William C.; Busenberg, Eurybiades

2003-01-01

One of the major water-quality problems in the Chesapeake Bay is an overabundance of nutrients from the streams and rivers that discharge to the Bay. Some of these nutrients are from nonpoint sources such as atmospheric deposition, agricultural manure and fertilizer, and septic systems. The effects of efforts to control nonpoint sources, however, can be difficult to quantify because of the lag time between changes at the land surface and the response in the base-flow (ground water) component of streams. To help resource managers understand the lag time between implementation of management practices and subsequent response in the nutrient concentrations in the base-flow component of streamflow, a study of ground-water discharge, residence time, and nitrate transport in springs throughout the Chesapeake Bay Watershed and in four smaller watersheds in selected hydrogeomorphic regions (HGMRs) was conducted. The four watersheds were in the Coastal Plain Uplands, Piedmont crystalline, Valley and Ridge carbonate, and Valley and Ridge siliciclastic HGMRs.A study of springs to estimate an apparent age of the ground water was based on analyses for concentrations of chlorofluorocarbons in water samples collected from 48 springs in the Chesapeake Bay Watershed. Results of the analysis indicate that median age for all the samples was 10 years, with the 25th percentile having an age of 7 years and the 75th percentile having an age of 13 years. Although the number of samples collected in each HGMR was limited, there did not appear to be distinct differences in the ages between the HGMRs. The ranges were similar between the major HGMRs above the Fall Line (modern to about 50 years), with only two HGMRs of small geographic extent (Piedmont carbonate and Mesozoic Lowland) having ranges of modern to about 10 years. The median values of all the HGMRs ranged from 7 to 11 years. Not enough samples were collected in the Coastal Plain for comparison. Spring samples showed slightly younger water under wet conditions than under dry conditions. The apparent age of water from wells, springs, and other ground-water discharge points in the four targeted watersheds was modern to 60 years, which was similar to the apparent ages from the spring study. In the Pocomoke River Watershed in the Coastal Plain Uplands HGMR, the apparent age of ground-water samples ranged from 0 to 60 years; the ages in the vicinity of the streams ranged from 0 to 23 years.The apparent ages of ground water in the Polecat Creek Watershed in the Piedmont crystalline HGMR ranged from 2 to 30 years. The apparent ages of water from wells in the Muddy Creek Watershed in the Valley and Ridge carbonate HGMR ranged from 10 to 20 years (except for a single sample that was 45 years). The ages in the East Mahantango Creek Watershed in the Valley and Ridge siliciclastic HGMR ranged from 0 to 50 years. The distribution in apparent age of water from wells in the targeted watersheds, however, generally is older than that for water from the springs. The median age of water from wells in the Muddy Creek Watershed, for example, was 15 years, compared to 11 years for the water from the springs in that watershed, and less than 10 years for water from all springs in the spring study. The similarity in the ranges in apparent age of water from the wells and from the springs shows that the samples from the targeted watersheds and springs have bracketed the range of apparent ages that would be expected in the shallow ground-water-flow systems throughout the Chesapeake Bay Watershed.The apparent age of water from individual wells does not necessarily represent the entire distribution of ages of the discharging ground water, and it is this distribution of ages that affects the response of nutrient concentrations in stream base flow. Nutrient-reduction scenarios were modeled for two watersheds for which the distribution of apparent ground-water ages was available, the East Mahantango Creek Watershed in the Valley and Ridge siliciclastic HGMR and the Locust Grove Watershed in the Coastal Plain Uplands HGMR. A nutrient-reduction scenario was created for East Mahantango Creek, where the average residence time was determined to be approximately 10 years on the basis of the output of particle tracking from a ground-water-flow model. This scenario showed decreases of nearly 50 percent in base-flow concentrations of nitrate in streams within the first year after the reduction in nitrogen input; smaller reductions in nitrate concentration occurred in each subsequent year. A second scenario for that same watershed, in which the same 10-year average residence time was assumed and an exponential model was used for analysis, showed that a 50-percent reduction in base-flow concentrations of nitrate could take up to 5 years. For the Locust Grove Watershed, in which an average residence time of 32 years was assumed, simulation with the exponential model showed that it may take more than 20 years to achieve a 50-percent reduction in base-flow concentra-tions of nitrate. Although it was not possible to construct such scenarios for all watersheds, these examples show the range of possible responses to changes in nutrient inputs in two very different types of watersheds.Findings from this study include information on factors that affect ground-water age, spatial distribution of ages, and nitrogen transport. In the East Mahantango Creek Watershed and the Polecat Creek Watershed, the residence time varied spatially depending on the position of the flow path, and temporally depending on the recharge conditions. Generally, ground water in areas near the stream had short residence times and the water in upland areas had longer residence times. Water traveling through deep layers had longer residence times than water traveling through shallow layers, and residence times were faster under high recharge conditions than low recharge conditions. Ground water in the Pocomoke Watershed exhibits a similar pattern: younger water discharges to small order streams in headwater basins and older water discharges to larger streams near the basin outlet.Factors affecting nitrogen transport in ground water include spatial and temporal variation in input sources, ground-water age, and aquifer processes that lead to denitrification. Spatial and temporal variations in nitrogen sources affect all the watersheds. Tributaries with higher inputs of nitrogen have higher concentrations in stream base flow. Areas where nitrogen application rates have increased over time show an age-nitrate relation in ground-water samples. The age-nitrate relation can be affected by denitrification, which occurs in Pocomoke and East Mahantango Creeks but is not evident in Polecat and Muddy Creeks. In East Mahantango Creek, the level of denitrification is significant in water with residence times greater than 20 years, but because this is a small component of overall ground-water discharge to a stream, it may not remove a significant quantity of nitrogen from the system. Denitrification in Pocomoke Creek is significant and appears to affect mostly older water discharging to streams. Therefore, if most of the nitrogen entering these two streams is associated with the discharge of younger ground water, denitrification may not greatly affect the overall nitrogen delivery to these streams.Other findings of this study show that nitrate in ground water discharging along preferential flow paths may not be affected by natural processes, such as denitrification or uptake by riparian vegetation. Seeps to swales and ditches beneath the north uplands at Polecat Creek indicate a shallow water table and discharge of young ground water whereas the absence of such seeps on the south side indicates a deep water table and a lack of young ground water. Similarly, discharge at the base of the slope and to the valley wetland south of the creek but not north of the creek indicates a different role for the riparian forest on the two sides of the creek. In many of the systems where water discharges at the base of slopes to wetlands, ditches have been dug to drain the valley. Such drainage circumvents possible removal of nitrate by riparian vegetation.Because ground-water residence times do not appear directly related to the HGMRs, the targeting of management practices will achieve the most rapid response in water quality if directed at 1) watersheds with large agricultural sources of nitrate, 2) areas with the shortest ground-water-flow paths and 3) areas not affected by significant denitrification. The fastest response in stream base-flow concentrations of nitrogen to implementation of management practices would be to implement practices in those areas with the highest loads rather than attempt to target practices on the basis of HGMR stratification. Overall findings of the study indicate that 1) ground-water contributions to nitrogen in streamflow are significant, 2) some response to management practices should be evident in base-flow concentrations of nitrogen and loads within 1 to 5 years in watersheds with the shortest average residence times, but response time may be closer to 20 years in watersheds with longer average ground-water residence times, 3) the majority of the response in ground-water discharge to any changes in management practices will be distributed over a 10-year time period even in the watersheds with the fastest response times, and 4) given that half the streamflow is from ground-water discharge and the other half is runoff or soil water, about 90 percent of total water being discharged to a stream will be less than about a decade old; therefore, full implementation of nutrient reductions may result in improved streamwater quality in about a decade. In the more-likely scenario of gradual source reduction, the reduction in concentrations of nitrate in streams and aquifers would take longer than the examples shown here.

Glyphosate sensitivity of 5-enol-pyruvylshikimate-3-phosphate synthase from Bacillus subtilis depends upon state of activation induced by monovalent cations.

PubMed

Fischer, R S; Rubin, J L; Gaines, C G; Jensen, R A

1987-07-01

The 5-enol-pyruvylshikimate-3-phosphate (EPSP) synthase from Bacillus subtilis was activated by monovalent cations, catalytic activity being negligible in the absence of monovalent cations. The order of cation effectiveness (NH4+ greater than K+ greater than Rb+ greater than Na+ = Cs+ = Li+) indicated that the extent of activation was directly related to the unhydrated cation radius. Ammonium salts, at physiological concentrations, were dramatically more effective than other cations. Activation by ammonium was instantaneous, was not influenced by the counter ion, and gave a hyperbolic saturation curve. Hill plots did not show detectable cooperativity in the binding of ammonium. Double-reciprocal plots indicated that ammonium increases the maximal velocity and decreases the apparent Michaelis constants of EPSP synthase with respect to both phosphoenol pyruvate (PEP) and shikimate 3-phosphate (S3P). A direct relationship between sensitivity to inhibition by glyphosate and the activation state of EPSP synthase was demonstrated. Hill plots indicated a single value for glyphosate binding throughout the range of ammonium activation. Double-reciprocal plots of substrate saturation data obtained with ammonium-activated enzyme in the presence of glyphosate showed glyphosate to behave as a competitive inhibitor with respect to PEP and as a mixed-type inhibitor relative to S3P. The increased glyphosate sensitivity of ammonium-activated EPSP synthase is attributed to a lowering of the inhibitor constant of glyphosate with respect to PEP. Erroneous underestimates of sensitivities of some bacterial EPSP synthases to inhibition by glyphosate may result from failure to recognize cation requirements of EPSP synthases.

The Renner-Teller effect in HCCCl(+)(X̃(2)Π) studied by zero-kinetic energy photoelectron spectroscopy and ab initio calculations.

PubMed

Sun, Wei; Dai, Zuyang; Wang, Jia; Mo, Yuxiang

2015-05-21

The spin-vibronic energy levels of the chloroacetylene cation up to 4000 cm(-1) above the ground state have been measured using the one-photon zero-kinetic energy photoelectron spectroscopic method. The spin-vibronic energy levels have also been calculated using a diabatic model, in which the potential energy surfaces are expressed by expansions of internal coordinates, and the Hamiltonian matrix equation is solved using a variational method with harmonic basis functions. The calculated spin-vibronic energy levels are in good agreement with the experimental data. The Renner-Teller (RT) parameters describing the vibronic coupling for the H-C≡C bending mode (ε4), Cl-C≡C bending mode (ε5), the cross-mode vibronic coupling (ε45) of the two bending vibrations, and their vibrational frequencies (ω4 and ω5) have also been determined using an effective Hamiltonian matrix treatment. In comparison with the spin-orbit interaction, the RT effect in the H-C≡C bending (ε4) mode is strong, while the RT effect in the Cl-C≡C bending mode is weak. There is a strong cross-mode vibronic coupling of the two bending vibrations, which may be due to a vibronic resonance between the two bending vibrations. The spin-orbit energy splitting of the ground state has been determined for the first time and is found to be 209 ± 2 cm(-1).

Modulation of inherent dynamical tendencies of the bisabolyl cation via preorganization in epi-isozizaene synthase.

PubMed

Pemberton, Ryan P; Ho, Krystina C; Tantillo, Dean J

2015-04-01

The relative importance of preorganization, selective transition state stabilization and inherent reactivity are assessed through quantum chemical and docking calculations for a sesquiterpene synthase ( epi -isozizaene synthase, EIZS). Inherent reactivity of the bisabolyl cation, both static and dynamic, appears to determine the pathway to product, although preorganization and selective binding of the final transition state structure in the multi-step carbocation cascade that forms epi -isozizaene appear to play important roles.

Structural distortions upon oxidation in heteroleptic [Cp(2)W(dmit)] tungsten dithiolene complex: combined structural, spectroscopic, and magnetic studies.

PubMed

Reinheimer, Eric W; Olejniczak, Iwona; Łapiński, Andrzej; Swietlik, Roman; Jeannin, Olivier; Fourmigué, Marc

2010-11-01

Four different cation radical salts are obtained upon electrocrystallization of [Cp(2)W(dmit)] (dmit = 1,3-dithiole-2-thione-4,5-dithiolato) in the presence of the BF(4)(-), PF(6)(-), Br(-), and [Au(CN)(2)](-) anions. In these formally d(1) cations, the WS(2)C(2) metallacycle is folded along the S···S hinge to different extents in the four salts, an illustration of the noninnocent character of the dithiolate ligand. Structural characteristics and the charge distribution on atoms, for neutral and ionized complexes with various folding angles, were calculated using DFT methods, together with the normal vibrational modes and theoretical Raman spectra. Raman spectra of neutral complex [Cp(2)W(dmit)] and its salts formed with BF(4)(-), AsF(6)(-), PF(6)(-), Br(-), and [Au(CN)(2)](-) anions were measured using the red excitation (λ = 632.8 nm). A correlation between the folding angle of the metallacycle and the Raman spectroscopic properties is analyzed. The bands attributed to the C═C and C-S stretching modes shift toward higher and lower frequencies by about 0.3-0.4 cm(-1) deg(-1), respectively. The solid state structural and magnetic properties of the three salts are analyzed and compared with those of the corresponding molybdenum complexes. Temperature dependence of the magnetic susceptibility shows the presence of one-dimensional antiferromagnetic interactions in the BF(4)(-), PF(6)(-), and [Au(CN)(2)](-) salts, while an antiferromagnetic ground state is identified in the Br(-) salt below T(Néel) = 7 K. Interactions are systematically weaker in the tungsten salts than in the isostructural molybdenum analogs, a consequence of the decreased spin density on the dithiolene ligand in the tungsten complexes.

Theoretical Study on the Catalytic Reduction Mechanism of NO by CO on Tetrahedral Rh4 Subnanocluster.

PubMed

Yang, Hua-Qing; Fu, Hong-Quan; Su, Ben-Fang; Xiang, Bo; Xu, Qian-Qian; Hu, Chang-Wei

2015-11-25

The catalytic mechanism of 2NO + 2CO → N2 + 2CO2 on Rh4 cluster has been systematically investigated on the ground and first excited states at the B3LYP/6-311+G(2d),SDD level. For the overall reaction of 2NO + 2CO → N2 + 2CO2, the main reaction pathways take place on the facet site rather than the edge site of the Rh4 cluster. The turnover frequency (TOF) determining transition states are characteristic of the second N-O bond cleavage with rate constant k4 = 1.403 × 10(11) exp (-181 203/RT) and the N-N bond formation for the intermediate N2O formation with rate constant k2 = 3.762 × 10(12) exp (-207 817/RT). The TOF-determining intermediates of (3)N(b)Rh4NO and (3)N(b)Rh4O(b)(NO) are associated with the nitrogen-atom molecular complex, which is in agreement with the experimental observation of surface nitrogen. On the facet site of Rh4 cluster, the formation of CO2 stems solely from the recombination of CO and O atom, while N2 originates partly from the recombination of two N atoms and partly from the decomposition of N2O. For the N-O bond cleavage or the synchronous N-O bond cleavage and C-O bond formation, the neutral Rh4 cluster exhibits better catalytic performance than the cationic Rh4(+) cluster. Alternatively, for N-N bond formation, the cationic Rh4(+) cluster possesses better catalytic performance than the neutral Rh4 cluster.

Metal bacteriochlorins which act as dual singlet oxygen and superoxide generators.

PubMed

Fukuzumi, Shunichi; Ohkubo, Kei; Zheng, Xiang; Chen, Yihui; Pandey, Ravindra K; Zhan, Riqiang; Kadish, Karl M

2008-03-06

A series of stable free-base, Zn(II) and Pd(II) bacteriochlorins containing a fused six- or five-member diketo- or imide ring have been synthesized as good candidates for photodynamic therapy sensitizers, and their electrochemical, photophysical, and photochemical properties were examined. Photoexcitation of the palladium bacteriochlorin affords the triplet excited state without fluorescence emission, resulting in formation of singlet oxygen with a high quantum yield due to the heavy atom effect of palladium. Electrochemical studies revealed that the zinc bacteriochlorin has the smallest HOMO-LUMO gap of the investigated compounds, and this value is significantly lower than the triplet excited-state energy of the compound in benzonitrile. Such a small HOMO-LUMO gap of the zinc bacteriochlorin enables intermolecular photoinduced electron transfer from the triplet excited state to the ground state to produce both the radical cation and the radical anion. The radical anion thus produced can transfer an electron to molecular oxygen to produce superoxide anion which was detected by electron spin resonance. The same photosensitizer can also act as an efficient singlet oxygen generator. Thus, the same zinc bacteriochlorin can function as a sensitizer with a dual role in that it produces both singlet oxygen and superoxide anion in an aprotic solvent (benzonitrile).

Electrostatic interactions guide the active site face of a structure-specific ribonuclease to its RNA substrate.

PubMed

Plantinga, Matthew J; Korennykh, Alexei V; Piccirilli, Joseph A; Correll, Carl C

2008-08-26

Restrictocin, a member of the alpha-sarcin family of site-specific endoribonucleases, uses electrostatic interactions to bind to the ribosome and to RNA oligonucleotides, including the minimal specific substrate, the sarcin/ricin loop (SRL) of 23S-28S rRNA. Restrictocin binds to the SRL by forming a ground-state E:S complex that is stabilized predominantly by Coulomb interactions and depends on neither the sequence nor structure of the RNA, suggesting a nonspecific complex. The 22 cationic residues of restrictocin are dispersed throughout this protein surface, complicating a priori identification of a Coulomb interacting surface. Structural studies have identified an enzyme-substrate interface, which is expected to overlap with the electrostatic E:S interface. Here, we identified restrictocin residues that contribute to binding in the E:S complex by determining the salt dependence [partial differential log(k 2/ K 1/2)/ partial differential log[KCl

Ionization-induced solvent migration in acetanilide-methanol clusters inferred from isomer-selective infrared spectroscopy.

PubMed

Weiler, Martin; Nakamura, Takashi; Sekiya, Hiroshi; Dopfer, Otto; Miyazaki, Mitsuhiko; Fujii, Masaaki

2012-12-07

We present the resonance-enhanced multiphoton ionization, infrared-ultraviolet hole burning (IR-UV HB), and IR dip spectra of the trans-acetanilide-methanol (AA-MeOH) cluster in the S(0), S(1), and cationic ground state (D(0)) in a supersonic jet. The IR-UV HB spectra demonstrate the co-existence of two isomers in S(0,1), in which MeOH binds either to the NH or the CO site of the peptide linkage in AA, denoted as AA(NH)-MeOH and AA(CO)-MeOH. When AA(CO)-MeOH is selectively ionized, its IR spectrum in D(0) is the same as that measured for AA(+) (NH)-MeOH. Thus, photoionization of AA(CO)-MeOH induces migration of MeOH from the CO to the NH site with 100% yield. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Glass-like phonon scattering from a spontaneous nanostructure in AgSbTe2.

PubMed

Ma, J; Delaire, O; May, A F; Carlton, C E; McGuire, M A; VanBebber, L H; Abernathy, D L; Ehlers, G; Hong, Tao; Huq, A; Tian, Wei; Keppens, V M; Shao-Horn, Y; Sales, B C

2013-06-01

Materials with very low thermal conductivity are of great interest for both thermoelectric and optical phase-change applications. Synthetic nanostructuring is most promising for suppressing thermal conductivity through phonon scattering, but challenges remain in producing bulk samples. In crystalline AgSbTe2 we show that a spontaneously forming nanostructure leads to a suppression of thermal conductivity to a glass-like level. Our mapping of the phonon mean free paths provides a novel bottom-up microscopic account of thermal conductivity and also reveals intrinsic anisotropies associated with the nanostructure. Ground-state degeneracy in AgSbTe2 leads to the natural formation of nanoscale domains with different orderings on the cation sublattice, and correlated atomic displacements, which efficiently scatter phonons. This mechanism is general and suggests a new avenue for the nanoscale engineering of materials to achieve low thermal conductivities for efficient thermoelectric converters and phase-change memory devices.

First principles study on structural, lattice dynamical and thermal properties of BaCeO3

NASA Astrophysics Data System (ADS)

Zhang, Qingping; Ding, Jinwen; He, Min

2017-09-01

BaCeO3 exhibits impressive application potentials on solid oxide fuel cell electrolyte, hydrogen separation membrane and photocatalyst, owing to its unique ionic and electronic properties. In this article, the electronic structures, phonon spectra and thermal properties of BaCeO3 in orthorhombic, rhombohedral and cubic phases are investigated based on density functional theory. Comparisons with reported experimental results are also presented. The calculation shows that orthorhombic structure is both energetically and dynamically stable under ground state, which is supported by the experiment. Moreover, charge transfer between cations and anions accompanied with phase transition is observed, which is responsible for the softened phonon modes in rhombohedral and cubic phases. Besides, thermal properties are discussed. Oxygen atoms contribute most to the specific heat. The calculated entropy and specific heat at constant pressure fit well with the experimental ones within the measured temperature range.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiong, Jie; Yan, Jiaqiang; Aczel, Adam A.

The structural, electrical, and magnetic properties of the double perovskite Ba 2LuReO 6 have been examined in this paper. It is an insulator whose temperature dependent conductivity is consistent with variable range hopping electrical transport. A transition to an antiferromagnet state with type I order occurs below T N = 31 K. High resolution time-of-flight neutron powder diffraction measurements show that it retains the cubic double perovskite structure down to 10 K. High intensity, low resolution neutron powder diffraction measurements confirm the antiferromagnetic order and indicate that cubic symmetry is still observed at 1.5 K. The small ordered moment ofmore » 0.34(4)μ B per Re is comparable to estimates of moments on 5d 2 ions in other antiferromagnetically ordered cubic double perovskites. Finally, comparisons with related double perovskites containing 5d 2 ions, such as Os 6+ and Re 5+, reveal that subtle changes in structure or electron configuration of the diamagnetic octahedral cations can have a large impact on the magnetic ground state, the size of the ordered moment, and the Néel temperature.« less

Removal of lead, cadmium, zinc, and copper from industrial wastewater by carbon developed from walnut, hazelnut, almond, pistachio shell, and apricot stone.

PubMed

Kazemipour, Maryam; Ansari, Mehdi; Tajrobehkar, Shabnam; Majdzadeh, Majdeh; Kermani, Hamed Reihani

2008-01-31

In this work, adsorption of copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd) that exist in industrial wastewater onto the carbon produced from nutshells of walnut, hazelnut, pistachio, almond, and apricot stone has been investigated. All the agricultural shell or stone used were ground, sieved to a defined size range, and carbonized in an oven. Time and temperature of heating were optimized at 15 min and 800 degrees C, respectively, to reach maximum removal efficiency. Removal efficiency was optimized regarding to the initial pH, flow rate, and dose of adsorbent. The maximum removal occurred at pH 6-10, flow rate of 3 mL/min, and 0.1g of the adsorbent. Capacity of carbon sources for removing cations will be considerably decreased in the following times of passing through them. Results showed that the cations studied significantly can be removed by the carbon sources. Efficiency of carbon to remove the cations from real wastewater produced by copper industries was also studied. Finding showed that not only these cations can be removed considerably by the carbon sources noted above, but also removing efficiency are much more in the real samples. These results were in adoption to those obtained by standard mixture synthetic wastewater.

Electronic Structure and Properties of Berkelium Iodates.

PubMed

Silver, Mark A; Cary, Samantha K; Garza, Alejandro J; Baumbach, Ryan E; Arico, Alexandra A; Galmin, Gregory A; Chen, Kuan-Wen; Johnson, Jason A; Wang, Jamie C; Clark, Ronald J; Chemey, Alexander; Eaton, Teresa M; Marsh, Matthew L; Seidler, Kevin; Galley, Shane S; van de Burgt, Lambertus; Gray, Ashley L; Hobart, David E; Hanson, Kenneth; Van Cleve, Shelley M; Gendron, Frédéric; Autschbach, Jochen; Scuseria, Gustavo E; Maron, Laurent; Speldrich, Manfred; Kögerler, Paul; Celis-Barros, Cristian; Páez-Hernández, Dayán; Arratia-Pérez, Ramiro; Ruf, Michael; Albrecht-Schmitt, Thomas E

2017-09-27

The reaction of 249 Bk(OH) 4 with iodate under hydrothermal conditions results in the formation of Bk(IO 3 ) 3 as the major product with trace amounts of Bk(IO 3 ) 4 also crystallizing from the reaction mixture. The structure of Bk(IO 3 ) 3 consists of nine-coordinate Bk III cations that are bridged by iodate anions to yield layers that are isomorphous with those found for Am III , Cf III , and with lanthanides that possess similar ionic radii. Bk(IO 3 ) 4 was expected to adopt the same structure as M(IO 3 ) 4 (M = Ce, Np, Pu), but instead parallels the structural chemistry of the smaller Zr IV cation. Bk III -O and Bk IV -O bond lengths are shorter than anticipated and provide further support for a postcurium break in the actinide series. Photoluminescence and absorption spectra collected from single crystals of Bk(IO 3 ) 4 show evidence for doping with Bk III in these crystals. In addition to luminescence from Bk III in the Bk(IO 3 ) 4 crystals, a broad-band absorption feature is initially present that is similar to features observed in systems with intervalence charge transfer. However, the high-specific activity of 249 Bk (t 1/2 = 320 d) causes oxidation of Bk III and only Bk IV is present after a few days with concomitant loss of both the Bk III luminescence and the broadband feature. The electronic structure of Bk(IO 3 ) 3 and Bk(IO 3 ) 4 were examined using a range of computational methods that include density functional theory both on clusters and on periodic structures, relativistic ab initio wave function calculations that incorporate spin-orbit coupling (CASSCF), and by a full-model Hamiltonian with spin-orbit coupling and Slater-Condon parameters (CONDON). Some of these methods provide evidence for an asymmetric ground state present in Bk IV that does not strictly adhere to Russel-Saunders coupling and Hund's Rule even though it possesses a half-filled 5f 7 shell. Multiple factors contribute to the asymmetry that include 5f electrons being present in microstates that are not solely spin up, spin-orbit coupling induced mixing of low-lying excited states with the ground state, and covalency in the Bk IV -O bonds that distributes the 5f electrons onto the ligands. These factors are absent or diminished in other f 7 ions such as Gd III or Cm III .

Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of bromobenzene and its perdeuterated isotopologue: Assignment of the vibrations of the S{sub 0}, S{sub 1}, and D{sub 0}{sup +} states of bromobenzene and the S{sub 0} and D{sub 0}{sup +} states of iodobenzene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrejeva, Anna; Tuttle, William D.; Harris, Joe P.

2015-12-28

We report vibrationally resolved spectra of the S{sub 1}←S{sub 0} transition of bromobenzene using resonance-enhanced multiphoton ionization spectroscopy. We study bromobenzene-h{sub 5} as well as its perdeuterated isotopologue, bromobenzene-d{sub 5}. The form of the vibrational modes between the isotopologues and also between the S{sub 0} and S{sub 1} electronic states is discussed for each species, allowing assignment of the bands to be achieved and the activity between states and isotopologues to be established. Vibrational bands are assigned utilizing quantum chemical calculations, previous experimental results, and isotopic shifts. Previous work and assignments of the S{sub 1} spectra are discussed. Additionally, themore » vibrations in the ground state cation, D{sub 0}{sup +}, are considered, since these have also been used by previous workers in assigning the excited neutral state spectra. We also examine the vibrations of iodobenzene in the S{sub 0} and D{sub 0}{sup +} states and comment on the previous assignments of these. In summary, we have been able to assign the corresponding vibrations across the whole monohalobenzene series of molecules, in the S{sub 0}, S{sub 1}, and D{sub 0}{sup +} states, gaining insight into vibrational activity and vibrational couplings.« less

Influence of cations on noncovalent interactions between 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved fulvic and humic acids.

PubMed

Gadad, Praveen; Nanny, Mark A

2008-12-01

The influence of cations (Na(+), Ca(2+) and Mg(2+)) on noncovalent interactions between 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved fulvic acids (FAs) (Norman landfill leachate fulvic acid (NLFA) and Suwannee River fulvic acid (SRFA)) and dissolved humic acids (HAs) (Suwannee River humic acid (SRHA) and Leonardite humic acid (LHA)) was examined using steady-state fluorescence spectroscopy at pH 4, 7 and 10 as a function of cation concentration (up to 25-100mM). Regardless of pH and cation concentration, PRODAN quenching by FA was unaffected by cations. However, interactions between PRODAN and HA decreased in the presence of cations at pH 7 and 10. Cation concentrations below the HA charge density resulted in the greatest decrease of PRODAN quenching, while very little additional decrease in PRODAN quenching occurred at cation concentrations above the HA charge density. This suggests that as the HA carboxylic acid functional groups form inner sphere complexes with divalent cations, intramolecular interactions result in a contraction of the HA molecular structure, thereby preventing PRODAN from associating with the condensed aromatic, electron accepting moieties inherent within HA molecules and responsible for PRODAN quenching. However, once the HA carboxylic acid functional groups are fully titrated with divalent cations, PRODAN quenching is no longer significantly influenced by the further addition of cations, even though these additional cations facilitate intermolecular interactions between the HA molecules to form supramolecular HA aggregates that can continue to increase in size. Regardless of FA and HA type, pH, cation type and concentration, the lack of blue-shifted fluorescence emission spectra indicated that micelle-like hydrophobic regions, amenable to PRODAN partitioning, were not formed by intra- and intermolecular interactions of FA and HA.

Tutorial Workshop on Robotics and Robot Control.

DTIC Science & Technology

1982-10-26

J^V7S US ARMY TANK-AUTOMOTIVE COMMAND, WARREN MICHIGAN US ARMY MATERIEL SYSTEMS ANALYSIS ACTIVITY, ABERDEEN PROVING GROUNDS, MARYLAND ^ V&S...Technology Pasadena, California 91103 M. Vur.kovic Senior Research Associate Institute for Technoeconomic Systems Department of Industrial...Further investigation of the action precedence graphs together with their appli- cation to more complex manipulator tasks and analysis of J2. their

Charge states of ions, and mechanisms of charge ordering transitions

NASA Astrophysics Data System (ADS)

Pickett, Warren E.; Quan, Yundi; Pardo, Victor

2014-07-01

To gain insight into the mechanism of charge ordering transitions, which conventionally are pictured as a disproportionation of an ion M as 2Mn+→M(n+1)+ + M(n-1)+, we (1) review and reconsider the charge state (or oxidation number) picture itself, (2) introduce new results for the putative charge ordering compound AgNiO2 and the dual charge state insulator AgO, and (3) analyze the cationic occupations of the actual (not formal) charge, and work to reconcile the conundrums that arise. We establish that several of the clearest cases of charge ordering transitions involve no disproportion (no charge transfer between the cations, and hence no charge ordering), and that the experimental data used to support charge ordering can be accounted for within density functional-based calculations that contain no charge transfer between cations. We propose that the charge state picture retains meaning and importance, at least in many cases, if one focuses on Wannier functions rather than atomic orbitals. The challenge of modeling charge ordering transitions with model Hamiltonians isdiscussed.

Synthesis, characterization, and tuning of the liquid crystal properties of ionic materials based on the cyclic polyoxothiometalate [{Mo4O4S4(H2O)3(OH)2}2(P8W48O184)](36-).

PubMed

Watfa, Nancy; Floquet, Sébastien; Terazzi, Emmanuel; Haouas, Mohamed; Salomon, William; Korenev, Vladimir S; Taulelle, Francis; Guénée, Laure; Hijazi, Akram; Naoufal, Daoud; Piguet, Claude; Cadot, Emmanuel

2015-02-14

A series of compounds resulting from the ionic association of a nanoscopic inorganic cluster of formula [K2NaxLiy{Mo4O4S4(OH)2(H2O)3}2(HzP8W48O184)]((34-x-y-z)-), 1, with several organic cations such as dimethyldioctadecylammonium DODA(+), trimethylhexadecylammonium TMAC16(+), alkylmethylimidazoliums mimCn(+) (n = 12-20) and alkyl-dimethylimidazoliums dmimCn(+) (n = 12 and 16) was prepared and characterized in the solid state by FT-IR, EDX, Elemental analysis, TGA and solid state NMR. The solid state NMR experiments performed on (1)H, (13)C and (31)P nuclei evidenced the interactions between the cations and 1 as well as the organization of the alkyl chains of the cations within the solid. Polarized optical microscopy, DSC and SA-XRD experiments implicated mesomorphic phases for DODA(+) and mimCn(+) salts of 1. The crystallographic parameters were determined and demonstrated that the inter-lamellar spacing could be controlled upon changing the length of the alkyl chain, a very interesting result if we consider the huge size of the inorganic cluster 1 and the simple nature of the cations.

Role of bond adaptability in the passivation of colloidal quantum dot solids.

PubMed

Thon, Susanna M; Ip, Alexander H; Voznyy, Oleksandr; Levina, Larissa; Kemp, Kyle W; Carey, Graham H; Masala, Silvia; Sargent, Edward H

2013-09-24

Colloidal quantum dot (CQD) solids are attractive materials for photovoltaic devices due to their low-cost solution-phase processing, high absorption cross sections, and their band gap tunability via the quantum size effect. Recent advances in CQD solar cell performance have relied on new surface passivation strategies. Specifically, cadmium cation passivation of surface chalcogen sites in PbS CQDs has been shown to contribute to lowered trap state densities and improved photovoltaic performance. Here we deploy a generalized solution-phase passivation strategy as a means to improving CQD surface management. We connect the effects of the choice of metal cation on solution-phase surface passivation, film-phase trap density of states, minority carrier mobility, and photovoltaic power conversion efficiency. We show that trap passivation and midgap density of states determine photovoltaic device performance and are strongly influenced by the choice of metal cation. Supported by density functional theory simulations, we propose a model for the role of cations, a picture wherein metals offering the shallowest electron affinities and the greatest adaptability in surface bonding configurations eliminate both deep and shallow traps effectively even in submonolayer amounts. This work illustrates the importance of materials choice in designing a flexible passivation strategy for optimum CQD device performance.

Trigonal Mn3 and Co3 Clusters Supported by Weak-Field Ligands: A Structural, Spectroscopic, Magnetic, and Computational Investigation into the Correlation of Molecular and Electronic Structure

PubMed Central

Fout, Alison R.; Xiao, Dianne J.; Zhao, Qinliang; Harris, T. David; King, Evan R.; Eames, Emily V.; Zheng, Shao-Liang; Betley, Theodore A.

2012-01-01

Transamination of divalent transition metal starting materials (M2(N(SiMe3)2)4, M = Mn, Co) with hexadentate ligand platforms RLH6 (RLH6 = MeC(CH2NPh-o-NR)3 where R = H, Ph, Mes (Mes = Mesityl)) or H,CyLH6 = 1,3,5-C6H9(NHPh-o-NH2)3 with added pyridine or tertiary phosphine co-ligands afforded trinuclear complexes of the type (RL)Mn3(py)3 and (RL)Co3(PMe2R’)3 (R’ = Me, Ph). While the sterically less encumbered ligand varieties, HL or PhL, give rise to local square-pyramidal geometries at each of the bound metal atoms, with four anilides forming an equatorial plane and an exogenous pyridine or phosphine in the apical site, the mesityl-substituted ligand (MesL) engenders local tetrahedral coordination. Both the neutral Mn3 and Co3 clusters feature S = 1/2 ground states, as determined by dc magnetometry, 1H NMR spectroscopy, and low-temperature EPR spectroscopy. Within the Mn3 clusters, the long internuclear Mn–Mn separations suggest minimal direct metal-metal orbital overlap. Accordingly, fits to variable-temperature magnetic susceptibility data reveal the presence of weak antiferromagnetic superexchange interactions through the bridging anilide ligands with exchange couplings ranging from J = −16.8 to −42 cm−1. Conversely, the short Co–Co interatomic distances suggest a significant degree of direct metal-metal orbital overlap, akin to the related Fe3 clusters. With the Co3 series, the S = 1/2 ground state can be attributed to population of a single molecular orbital manifold that arises from mixing of the metal- and o-phenylenediamide (OPDA) ligand-based frontier orbitals. Chemical oxidation of the neutral Co3 clusters affords diamagnetic cationic clusters of the type [(RL)Co3(PMe2R)3]+. DFT calculations on the neutral (S = ½) and cationic (S = 0) Co3 clusters reveal that oxidation occurs at an oribital with contributions from both the Co3 core and OPDA subunits. The predicted bond elongations within the ligand OPDA units are corroborated by the ligand bond perturbations observed by X-ray crystallography. PMID:22991939

The electrostatics of VDAC: implications for selectivity and gating.

PubMed

Choudhary, Om P; Ujwal, Rachna; Kowallis, William; Coalson, Rob; Abramson, Jeff; Grabe, Michael

2010-02-26

The voltage-dependent anion channel (VDAC) is the major pathway mediating the transfer of metabolites and ions across the mitochondrial outer membrane. Two hallmarks of the channel in the open state are high metabolite flux and anion selectivity, while the partially closed state blocks metabolites and is cation selective. Here we report the results from electrostatics calculations carried out on the recently determined high-resolution structure of murine VDAC1 (mVDAC1). Poisson-Boltzmann calculations show that the ion transfer free energy through the channel is favorable for anions, suggesting that mVDAC1 represents the open state. This claim is buttressed by Poisson-Nernst-Planck calculations that predict a high single-channel conductance indicative of the open state and an anion selectivity of 1.75--nearly a twofold selectivity for anions over cations. These calculations were repeated on mutant channels and gave selectivity changes in accord with experimental observations. We were then able to engineer an in silico mutant channel with three point mutations that converted mVDAC1 into a channel with a preference for cations. Finally, we investigated two proposals for how the channel gates between the open and the closed state. Both models involve the movement of the N-terminal helix, but neither motion produced the observed voltage sensitivity, nor did either model result in a cation-selective channel, which is observed experimentally. Thus, we were able to rule out certain models for channel gating, but the true motion has yet to be determined. Copyright (c) 2009. Elsevier Ltd. All rights reserved.

Low-Frequency Raman Modes of 2H-TaSe2 in the Charge Density Wave Phase

NASA Astrophysics Data System (ADS)

Chowdhury, Sugata; Simpson, J.; Einstein, T. L.; Hight Walker, A. R.; Theoretical Collaboration

With changes in temperatures, tantalum diselenide (2H-TaSe2) , a layered, transition metal chalcogenides (TMD) exhibits unique super-lattice structures. The metallic ground state changes to an incommensurate charge density wave (CDW) state at 122?K followed by a commensurate CDW state at 90?K, and eventually a superconducting state 0.14 K. These phase transitions are driven by strong electron-phonon coupling and favored by the particular form of the Fermi surface of these systems. Here we theoretically studied the structural origin of low-frequency Raman modes of bulk 2H-TaSe2\\ in the CDW phases. Our calculations reveal that changes observed in the Raman modes are associated with the thermal expansion in the basal plane of 2H-TaSe2. The Grüneisen parameters of these two Raman modes increase in the CDW phases. Changes in the lattice parameter ``a'' are large compared to ``c'' which induces strain along the a-axis. We compared our results with experimental data which show low-frequency Raman phonon modes are very sensitive to temperature and are not observed in the metallic room-temperature state. In addition, we found that cation displacement is more than anion in CDW phase. Our results may shed more light on exact nature of the CDW instability and optical properties in this system.

Excited state properties of the astaxanthin radical cation: A quantum chemical study

NASA Astrophysics Data System (ADS)

Dreuw, Andreas; Starcke, Jan Hendrik; Wachtveitl, Josef

2010-07-01

Using time-dependent density functional theory, the excited electronic states of the astaxanthin radical cation (AXT rad + ) are investigated. While the optically allowed excited D 1 and D 3 states are typical ππ∗ excited states, the D 2 and D 4 states are nπ∗ states. Special emphasis is put onto the influence of the carbonyl groups onto the excited states. For this objective, the excited states of four hypothetical carotenoids and zeaxanthin have been computed. Addition of a carbonyl group to a conjugated carbon double bond system does essentially not change the vertical excitation energies of the optically allowed ππ∗ states due to two counter-acting effects: the excitation energy should increase due to the -M-effect of the carbonyl group and at the same time decrease owing to the elongation of the conjugated double bond system by the carbonyl group itself.

Hydrogeologic controls of surface-water chemistry in the Adirondack region of New York State

USGS Publications Warehouse

Peters, N.E.; Driscoll, C.T.

1987-01-01

Relationships between surface-water discharge, water chemistry, and watershed geology were investigated to evaluate factors affecting the sensitivity of drainage waters in the Adirondack region of New York to acidification by atmospheric deposition. Instantaneous discharge per unit area was derived from relationships between flow and staff-gage readings at 10 drainage basins throughout the region. The average chemical composition of the waters was assessed from monthly samples collected from July 1982 through July 1984. The ratio of flow at the 50-percent exceedence level to the flow at the 95-percent exceedence level of flow duration was negatively correlated with mean values of alkalinity or acid-neutralizing capacity (ANC), sum of basic cations (SBC), and dissolved silica, for basins containing predominantly aluminosilicate minerals and little or no carbonate-bearing minerals. Low ratios are indicative of systems in which flow is predominately derived from surface- and ground-water storage, whereas high ratios are characteristic of watersheds with variable flow that is largely derived from surface runoff. In an evaluation of two representative surface-water sites, concentrations of ANC, SBC, and dissolved silica, derived primarily from soil mineral weathering reactions. decreased with increasing flow. Furthermore, the ANC was highest at low flow when the percentage of streamflow derived from ground water was maximum. As flow increased, the ANC decreased because the contribution of dilute surface runoff and lateral flow through the shallow acidic soil horizons to total flow increased. Basins having relatively high ground-water contributions to total flow, in general, have large deposits of thick till or stratified drift. A major factor controlling the sensitivity of these streams and lakes to acidification is the relative contribution of ground water to total discharge. ?? 1987 Martinus Nijhoff/Dr W. Junk Publishers.

Identification of Organics in Ice Grains from Enceladus

NASA Astrophysics Data System (ADS)

Khawaja, N.; Postberg, F.; Reviol, R.; Nölle, L.; Klenner, F.; Srama, R.

2015-12-01

The Cosmic Dust Analyzer (CDA) aboard the Cassini spacecraft performs in-situ measurements of the chemical composition of icy dust grains impinging onto the target surface. The instrument recorded cationic Time-of-Flight (ToF) mass spectra of organic-bearing ice grains emitted from Enceladus at different impact velocities causing different molecular fragmentation patterns [1,2]. Here we present a detailed analysis of these spectra (Type-2) to identify the composition of organic material embedded in Enceladus ice grains. The organic compounds display a great compositional diversity, which indicates varying contributions of several organic species. The spectra analysis is supported by a large-scale laboratory ground campaign yielding a library of analogue spectra for organic material embedded in a water ice matrix. To mimic the identified pattern of cationic fragments in organic enriched spectra we use a laboratory setup: Infrared Free Liquid MALDI ToF Mass Spectrometer (IR-FL-MALDI-ToF-MS). An infrared laser is used to disperse a liquid micro-beam of a water-solution to get cationic fragments. The laser energy is adjusted to simulate different impact velocities of ice particles on CDA [3]. So far we have identified characteristic fragment patterns of at least three classes of organic molecules: (i) aromatic species, (ii) amines, and (iii) carbonyl group species. (i) ice grains containing aromatic species are identified by a series of characteristic aromatic fragment cations (ii) ice grains containing amines are identified by a pronounced ammonium cation and (iii) ice grains containing carbonyl compounds are specified by a characteristic acylium cation in conjunction with certain others mass lines. Besides aromatic, amine and carbonyl species, Type-2 spectra also show contributions from other, yet un-specified, organic species. Typically, fragment cations of aromatic compounds are stable at impact velocities up-to 15km/s whereas cations of amines and carbonyl species are stable at velocities below 8km/s. Work is in progress to quantify concentrations of the identified species and to assign yet un-specified organic mass lines in Type 2 spectra. Ref: [1]Postberg et al., Icarus-193,2008. [2]Postberg et al., Nature-459,2009. [3]Beinsen, A., University of Göttingen, Dissertation (2011).

VUV photoionization and dissociative photoionization of the prebiotic molecule acetyl cyanide: Theory and experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bellili, A.; Hochlaf, M., E-mail: hochlaf@univ-mlv.fr, E-mail: martin.schwell@lisa.u-pec.fr; Schwell, M., E-mail: hochlaf@univ-mlv.fr, E-mail: martin.schwell@lisa.u-pec.fr

2014-10-07

The present combined theoretical and experimental investigation concerns the single photoionization of gas-phase acetyl cyanide and the fragmentation pathways of the resulting cation. Acetyl cyanide (AC) is inspired from both the chemistry of cyanoacetylene and the Strecker reaction which are thought to be at the origin of medium sized prebiotic molecules in the interstellar medium. AC can be formed by reaction from cyanoacetylene and water but also from acetaldehyde and HCN or the corresponding radicals. In view of the interpretation of vacuum ultraviolet (VUV) experimental data obtained using synchrotron radiation, we explored the ground potential energy surface (PES) of acetylmore » cyanide and of its cation using standard and recently implemented explicitly correlated methodologies. Our PES covers the regions of tautomerism (between keto and enol forms) and of the lowest fragmentation channels. This allowed us to deduce accurate thermochemical data for this astrobiologically relevant molecule. Unimolecular decomposition of the AC cation turns out to be very complex. The implications for the evolution of prebiotic molecules under VUV irradiation are discussed.« less

Alkalinity generation in snowmelt and rain runoff during short distance flow over rock

Treesearch

James L. Clayton

1998-01-01

High-elevation ecosystems in the western United States typically have patchy, discontinuous areas of surficial soils surrounded by large areas of rock outcrop, talus, and scree. Snowmelt and precipitation that percolate through soil increase in alkalinity, principally by increasing base cation concentration through cation exchange, and by decreasing acid anion...

Computational study of electronic, optical and thermoelectric properties of X3PbO (X = Ca, Sr, Ba) anti-perovskites

NASA Astrophysics Data System (ADS)

Hassan, M.; Arshad, I.; Mahmood, Q.

2017-11-01

We report the structural, electronic, optical and thermoelectric (TE) properties of X3PbO (X = Ca, Sr, Ba) anti-perovskites as a function of X cations belonging to the group IIA. The computations are done by using the most recently introduced modified Becke-Johnson potential. It has been observed that the cubic lattice constant increases as the cations change from Ca to Ba, consequently, the bulk modulus reduces. The bottom of conduction band shows strong hybridization between Pb-6p, O-2p and X-s states, in contrast, valence band maxima are mainly manufactured by Pb-6p states. The anti-perovskites exhibit narrow direct band gap that show an inverse relation to the static real dielectric constants that verifies Penn’s model. In addition, the X cations induced tuning of the absorption edge in the visible and the ultraviolet energy suggest optical device applications. The computed TE parameters have been found sensitive to the X cations and have been demonstrated to be best suited for the TE devices operating at high temperatures.

The special features of the crystal structure and properties of oxides with mixed conductivity based on lanthanum gallate

NASA Astrophysics Data System (ADS)

Politova, E. D.; Ivanov, S. A.; Kaleva, G. M.; Mosunov, A. V.; Rusakov, V. S.

2008-10-01

The paper presents a review of works on the synthesis, structural composition effects, phase transitions, and electrical conductivity properties of multicomponent solid solutions based on heterosubstituted lanthanum gallate (La,A)(Ga,M)O3 - y . High-temperature phase transitions and structural and charge ordering effects were studied. The presence of iron cations in different valence states was proved; the relative contents of these cations depended on the x parameter and nonstoichiometry parameter y of the base composition. For M = Fe, antiferromagnetic ordering was observed; its temperature interval was determined by the concentration of iron cations in the high-spin state. The total conductivity was found to increase as the concentration of transition metal cations grew because of an increase in the electronic conductivity component. The data on structural parameters and dc and ac conductivity substantiated the conclusion that the highest ionic conductivity and permeability to oxygen were characteristic of iron-containing oxides. The results obtained are evidence that crystal chemical factors play a determining role in the formation of the ion-conducting properties of anion-deficient perovskite-like oxides.

Surface-induced magnetism of the solids with impurities and vacancies

NASA Astrophysics Data System (ADS)

Morozovska, A. N.; Eliseev, E. A.; Glinchuk, M. D.; Blinc, R.

2011-04-01

Using the quantum-mechanical approach combined with the image charge method we calculated the lowest energy levels of the impurities and neutral vacancies with two electrons or holes located in the vicinity of flat surface of different solids. Unexpectedly we obtained that the magnetic triplet state is the ground state of the impurities and neutral vacancies in the vicinity of surface, while the nonmagnetic singlet is the ground state in the bulk, for e.g. He atom, Li+, Be++ ions, etc. The energy difference between the lowest triplet and singlet states strongly depends on the electron (hole) effective mass μ, dielectric permittivity of the solid ε2 and the distance from the surface z0. For z0=0 and defect charge ∣Z∣=2 the energy difference is more than several hundreds of Kelvins at μ=(0.5-1)me and ε2=2-10, more than several tens of Kelvins at μ=(0.1-0.2)me and ε2=5-10, and not more than several Kelvins at μ<0.1me and ε2>15 (me is the mass of a free electron). Pair interaction of the identical surface defects (two doubly charged impurities or vacancies with two electrons or holes) reveals the ferromagnetic spin state with the maximal exchange energy at the definite distance between the defects (∼5-25 nm). We estimated the critical concentration of surface defects and transition temperature of ferromagnetic long-range order appearance in the framework of percolation and mean field theories, and RKKY approach for semiconductors like ZnO. We obtained that the nonmagnetic singlet state is the lowest one for a molecule with two electrons formed by a pair of identical surface impurities (like surface hydrogen), while its next state with deep enough negative energy minimum is the magnetic triplet. The metastable magnetic triplet state appeared for such molecule at the surface indicates the possibility of metastable ortho-states of the hydrogen-like molecules, while they are absent in the bulk of material. The two series of spectral lines are expected due to the coexistence of ortho- and para-states of the molecules at the surface. We hope that obtained results could provide an alternative mechanism of the room temperature ferromagnetism observed in TiO2, HfO2, and In2O3 thin films with contribution of the oxygen vacancies. We expect that both anion and cation vacancies near the flat surface act as magnetic defects because of their triplet ground state and Hund's rule. The theoretical forecasts are waiting for experimental justification allowing for the number of the defects in the vicinity of surface is much larger than in the bulk of as-grown samples.

Cationic 1,2,3-Triazolium Alkynes: Components To Enhance 1,4-Regioselective Azide-Alkyne Cycloaddition Reactions.

PubMed

Monasterio, Zaira; Sagartzazu-Aizpurua, Maialen; Miranda, José I; Reyes, Yuri; Aizpurua, Jesus M

2016-02-19

4-Alkynyl-1,2,3-triazolium cations undergo thermal [3 + 2] cycloaddition reactions with azides roughly 50- to 100-fold faster than comparable noncharged alkynes. Further, the reaction is highly 1,4-regioselective (dr up to 99:1) owing to the selective stabilization of 1,4-TS transition states via conjugative π-acceptor assistance of the alkyne triazolium ring. The novel cationic triazolium alkynes also accelerate the CuAAC reaction to provide bis(1,2,3-triazoles) in an "ultrafast" way (<5 min).

Dynamics of photoexcited Ba+ cations in 4He nanodroplets

NASA Astrophysics Data System (ADS)

Leal, Antonio; Zhang, Xiaohang; Barranco, Manuel; Cargnoni, Fausto; Hernando, Alberto; Mateo, David; Mella, Massimo; Drabbels, Marcel; Pi, Martí

2016-03-01

We present a joint experimental and theoretical study on the desolvation of Ba+ cations in 4He nanodroplets excited via the 6p ← 6s transition. The experiments reveal an efficient desolvation process yielding mainly bare Ba+ cations and Ba+Hen exciplexes with n = 1 and 2. The speed distributions of the ions are well described by Maxwell-Boltzmann distributions with temperatures ranging from 60 to 178 K depending on the excitation frequency and Ba+ Hen exciplex size. These results have been analyzed by calculations based on a time-dependent density functional description for the helium droplet combined with classical dynamics for the Ba+. In agreement with experiment, the calculations reveal the dynamical formation of exciplexes following excitation of the Ba+ cation. In contrast to experimental observation, the calculations do not reveal desolvation of excited Ba+ cations or exciplexes, even when relaxation pathways to lower lying states are included.

Local electrostatic interactions determine the diameter of fusion pores

PubMed Central

Guček, Alenka; Jorgačevski, Jernej; Górska, Urszula; Rituper, Boštjan; Kreft, Marko; Zorec, Robert

2015-01-01

In regulated exocytosis vesicular and plasma membranes merge to form a fusion pore in response to stimulation. The nonselective cation HCN channels are involved in the regulation of unitary exocytotic events by at least 2 mechanisms. They can affect SNARE-dependent exocytotic activity indirectly, via the modulation of free intracellular calcium; and/or directly, by altering local cation concentration, which affects fusion pore geometry likely via electrostatic interactions. By monitoring membrane capacitance, we investigated how extracellular cation concentration affects fusion pore diameter in pituitary cells and astrocytes. At low extracellular divalent cation levels predominantly transient fusion events with widely open fusion pores were detected. However, fusion events with predominately narrow fusion pores were present at elevated levels of extracellular trivalent cations. These results show that electrostatic interactions likely help determine the stability of discrete fusion pore states by affecting fusion pore membrane composition. PMID:25835258

Selective monovalent cation association and exchange around Keplerate polyoxometalate macroanions in dilute aqueous solutions.

PubMed

Pigga, Joseph M; Teprovich, Joseph A; Flowers, Robert A; Antonio, Mark R; Liu, Tianbo

2010-06-15

The interaction between water-soluble Keplerate polyoxometalate {Mo(72)Fe(30)} macroions and small countercations is explored by laser light scattering, anomalous small-angle X-ray scattering (ASAXS), and isothermal titration calorimetry (ITC) techniques. The macroions are found to be able to select the type of associated counterions based upon the counterions' valence state and hydrated size, when multiple types of additional cations are present in solution (even among different monovalent cations). The preference goes to the cations with higher valences or smaller hydrated sizes if the valences are identical. This counterion exchange process changes the magnitude of the macroion-counterion interaction and, thus, is reflected in the dimension of the self-assembled {Mo(72)Fe(30)} blackberry supramolecular structures. The hydrophilic macroions exhibit a competitive recognition of various monovalent counterions in dilute solutions. A critical salt concentration (CSC) for each type of cation exists for the blackberry formation of {Mo(72)Fe(30)} macroions, above which the blackberry size increases significantly with the increasing total ionic strength in solution. The CSC values are much smaller for cations with higher valences and also decrease with the cations' hydrated size for various monovalent cations. The change of blackberry size corresponding to the change of ionic strength in solution is reversible.

Social Role Discovery in Human Events (Open Access)

DTIC Science & Technology

2013-10-03

to all people in the videos. We also present a novel YouTube social roles dataset with ground truth role annota- tions, and introduce annotations on a... nursing home [13], making role identifi- cation a difficult human task. Ideally, we would like to auto- matically discover such interaction-based role...34# $% &’$( ! Figure 2. Sample frames from different events in the YouTube Social

Impact of Wildfire on Solute Release in Forested Catchments, Jemez River, New Mexico, USA

NASA Astrophysics Data System (ADS)

Sanchez, R. A.; Meixner, T.; McIntosh, J. C.; Chorover, J.

2017-12-01

Wildfires represent a large disturbance to the hydrology and biogeochemistry of forested catchments. The number, size and severity of wildfires have significantly increased in the western United States since 1990. Nutrients and other elements (e.g. Ca) that were taken up and stored by biomass are released from burned vegetation during forest fires and transported downgradient via overland flow, shallow subsurface flow, and/or deep groundwater flow. Ash accumulations on hillslopes may also store particulate carbon and contain elevated concentrations of elements that maybe leached into surface and ground water over extended periods of time. In 2013, the Thompson Ridge wildfire burned headwater catchments in the Jemez River Basin Critical Zone Observatory (JRB-CZO) within the Valles Caldera National Preserve, New Mexico USA. The burn severity and area impacted were different in the three headwater catchments. This study investigated the impact of the wildfire on surface water quality, including how the fire-induced impacts evolved with time, and how biogeochemical processes controlled post-fire solute concentrations in the surface water. Comparison of pre- and post-fire surface water solute chemistry shows increases in major cations and anions following fire. Increases in nitrate and sulfate concentrations in streams after the wildfire were likely from leaching of burned biomass. The elevated NO3- and SO42- concentrations persisted for over two years, and were even higher during spring snowmelt. Meanwhile, base cation concentrations increased immediately, within a few weeks after the fire, likely related to leaching from combusted organic matter; and, over a period of approximately two months, base cation concentrations returned to pre-fire levels. Trace element behavior was also altered by fire. For example, while pre-fire aluminum concentrations in stream flow increased significantly during the wet seasons (snowmelt and monsoons), the post-fire observations do not show significant changes with increase in discharge.

Microsolvation of the 5-hydroxyindole cation (5HI+) with nonpolar and quadrupolar ligands: Infrared photodissociation spectra of 5HI+-Ln clusters with L = Ar and N2 (n ≤ 3)

NASA Astrophysics Data System (ADS)

Klyne, Johanna; Dopfer, Otto

2017-07-01

Solvation of biomolecules and their building blocks has a strong influence on their structure and function. Herein we characterize the initial microsolvation of the 5-hydroxyindole cation (5HI+) in its 2A″ ground electronic state with nonpolar and quadrupolar ligands (L = Ar, N2) by infrared photodissociation (IRPD) spectroscopy of cold and mass-selected 5HI+-Ln (n ≤ 3) clusters in a molecular beam and dispersion-corrected density functional theory calculations (B3LYP-D3/aug-cc-pVTZ). The isomer-selective OH and NH stretch frequency shifts (ΔνOH/NH) disentangle the competition between H-bonding to the acidic OH and NH groups and π-stacking to the conjugated bicyclic aromatic π-electron system, the intermolecular interaction strengths, and the cluster growth sequence. For 5HI+-Arn, H-bonding and π-stacking strongly compete, indicating that dispersion forces are important for the interaction of 5HI+ with nonpolar ligands. In contrast, for 5HI+-(N2)n clusters, the H-bonds are much stronger than the π-bonds and largely determine the initial solvation process. In all clusters, the OH…L bonds are stronger than the NH…L bonds followed by the π-bonds. The interaction of 5HI+ with N2 is roughly twice stronger than with Ar, mainly due to the additional quadrupole moment of N2. The nature and strength of the individual interactions are quantified by the noncovalent interaction approach. Comparison of 5HI+-L with the corresponding neutral clusters reveals the strong impact of ionization on the total and relative interaction strengths of the H-bonds and π-bonds. In addition, comparison of 5HI+-L with corresponding clusters of the phenol, indole, and pyrrole radical cations illustrates the effects of substitution of functional groups and the addition of aromatic rings to the various subunits of 5HI on the intermolecular potential.

Citrate, in collaboration with a guanidinium ion, as a generator of cubane-like complexes with a range of metal cations: synthesis, structures, and magnetic properties of [C(NH2)3]8[(M(II))4(cit)4].8H2O (M = Mg, Mn, Fe, Co, Ni, and Zn; cit = Citrate).

PubMed

Hudson, Timothy A; Berry, Kevin J; Moubaraki, Boujemaa; Murray, Keith S; Robson, Richard

2006-05-01

Aqueous reaction mixtures containing citric acid, guanidinium carbonate, and a range of metal cations (Mg2+, Mn2+, Fe2+, Co2+, Ni2+, and Zn2+) at room temperature give crystalline products of composition [C(NH2)3]8[(M(II))4(cit)4].8H2O (cit = citrate). In all cases, the crystals are suitable for single-crystal X-ray diffraction studies, which reveal that the compounds are isostructural (space group P4(2)/n; a approximately 16.2 A, and c approximately 11.5 A). As was intended, cubane-like [M4(cit)4]8- complex anions are present. The individual citrate units are chiral, but each cubane unit contains two of one hand and two of the other, related around an S4 axis. The cubane units are involved in no less than 40 H-bonding interactions with guanidinium cations and lattice water molecules. Detailed susceptibility and magnetization studies show that the intracluster magnetic coupling within the Mn(II), Fe(II), Co(II), and Ni(II) cubanes is very weak in all cases with J values of -0.82, -0.43, and -0.09 cm(-1) for the Mn, Fe, and Co species, respectively. A two-J model gave the best agreement with the susceptibility and high-field magnetization data for the Ni(II) case, over the whole temperature range studied, and the sign of the parameters, J12 = -0.3 cm(-1) and J13 = +2.97 cm(-1), correlated with the two Ni-(mu3-O)-Ni angles observed in the cluster structure. All members of the 3d-block [M4(cit)4]8- family have spin ground states, ST, of zero, with the higher ST levels just a few reciprocal centimeters away in energy.

Network topology for the formation of solvated electrons in binary CaO–Al2O3 composition glasses

PubMed Central

Akola, Jaakko; Kohara, Shinji; Ohara, Koji; Fujiwara, Akihiko; Watanabe, Yasuhiro; Masuno, Atsunobu; Usuki, Takeshi; Kubo, Takashi; Nakahira, Atsushi; Nitta, Kiyofumi; Uruga, Tomoya; Weber, J. K. Richard; Benmore, Chris J.

2013-01-01

Glass formation in the CaO–Al2O3 system represents an important phenomenon because it does not contain typical network-forming cations. We have produced structural models of CaO–Al2O3 glasses using combined density functional theory–reverse Monte Carlo simulations and obtained structures that reproduce experiments (X-ray and neutron diffraction, extended X-ray absorption fine structure) and result in cohesive energies close to the crystalline ground states. The O–Ca and O–Al coordination numbers are similar in the eutectic 64 mol % CaO (64CaO) glass [comparable to 12CaO·7Al2O3 (C12A7)], and the glass structure comprises a topologically disordered cage network with large-sized rings. This topologically disordered network is the signature of the high glass-forming ability of 64CaO glass and high viscosity in the melt. Analysis of the electronic structure reveals that the atomic charges for Al are comparable to those for Ca, and the bond strength of Al–O is stronger than that of Ca–O, indicating that oxygen is more weakly bound by cations in CaO-rich glass. The analysis shows that the lowest unoccupied molecular orbitals occurs in cavity sites, suggesting that the C12A7 electride glass [Kim SW, Shimoyama T, Hosono H (2011) Science 333(6038):71–74] synthesized from a strongly reduced high-temperature melt can host solvated electrons and bipolarons. Calculations of 64CaO glass structures with few subtracted oxygen atoms (additional electrons) confirm this observation. The comparable atomic charges and coordination of the cations promote more efficient elemental mixing, and this is the origin of the extended cage structure and hosted solvated (trapped) electrons in the C12A7 glass. PMID:23723350

Network topology for the formation of solvated electrons in binary CaO-Al2O3 composition glasses.

PubMed

Akola, Jaakko; Kohara, Shinji; Ohara, Koji; Fujiwara, Akihiko; Watanabe, Yasuhiro; Masuno, Atsunobu; Usuki, Takeshi; Kubo, Takashi; Nakahira, Atsushi; Nitta, Kiyofumi; Uruga, Tomoya; Weber, J K Richard; Benmore, Chris J

2013-06-18

Glass formation in the CaO-Al2O3 system represents an important phenomenon because it does not contain typical network-forming cations. We have produced structural models of CaO-Al2O3 glasses using combined density functional theory-reverse Monte Carlo simulations and obtained structures that reproduce experiments (X-ray and neutron diffraction, extended X-ray absorption fine structure) and result in cohesive energies close to the crystalline ground states. The O-Ca and O-Al coordination numbers are similar in the eutectic 64 mol % CaO (64CaO) glass [comparable to 12CaO·7Al2O3 (C12A7)], and the glass structure comprises a topologically disordered cage network with large-sized rings. This topologically disordered network is the signature of the high glass-forming ability of 64CaO glass and high viscosity in the melt. Analysis of the electronic structure reveals that the atomic charges for Al are comparable to those for Ca, and the bond strength of Al-O is stronger than that of Ca-O, indicating that oxygen is more weakly bound by cations in CaO-rich glass. The analysis shows that the lowest unoccupied molecular orbitals occurs in cavity sites, suggesting that the C12A7 electride glass [Kim SW, Shimoyama T, Hosono H (2011) Science 333(6038):71-74] synthesized from a strongly reduced high-temperature melt can host solvated electrons and bipolarons. Calculations of 64CaO glass structures with few subtracted oxygen atoms (additional electrons) confirm this observation. The comparable atomic charges and coordination of the cations promote more efficient elemental mixing, and this is the origin of the extended cage structure and hosted solvated (trapped) electrons in the C12A7 glass.

Hydrochemical facies and ground-water flow patterns in northern part of Atlantic Coastal Plain

USGS Publications Warehouse

Back, William

1966-01-01

Flow patterns of fresh ground water shown on maps and in cross sections have been deduced from available water-level data. These patterns are controlled by the distribution of the higher landmasses and by the depth to either bedrock or to the salt-water interface. The mapping of hydrochemical facies shows that at shallow depths within the Coastal Plain (less than about 200 ft) the calcium-magnesium cation facies generally predominates. The bicarbonate anion facies occurs within more of the shallow Coastal Plain sediments than does the sulfate or the chloride facies. In deeper formations, the sodium chloride character predominates. The lower dissolved-solids content of the ground water in New Jersey indicates less upward vertical leakage than in Maryland and Virginia, where the shallow formations contain solutions of higher concentration.

Theoretical analyses of the effects on the linear and quadratic nonlinear optical properties of N-arylation of pyridinium groups in stilbazolium dyes.

PubMed

Coe, Benjamin J; Beljonne, David; Vogel, Henryk; Garín, Javier; Orduna, Jesús

2005-11-10

N-Arylation of the pyridinium electron acceptor unit in stilbazolium chromophores has been found by previous experimental hyper-Rayleigh scattering and electronic Stark effect (electroabsorption) spectroscopic studies to lead to substantial increases in the static first hyperpolarizability beta(0). We show here that INDO/SCI calculations on the isolated cations trans-4'-(dimethylamino)-N-R-4-stilbazolium (R = methyl 1, phenyl 2, 2,4-dinitrophenyl 3, or 2-pyrimidyl 4) predict only slight red-shifts in the energy of the intramolecular charge-transfer (ICT) transition and accompanying relatively small changes in beta(0) on moving along the series. The inclusion of acetonitrile solvent using a polarizable continuum model affords a somewhat better agreement with the experimental data, especially the red-shifting of the ICT transition and the increase in beta(0) on going from 1 to 4. Time-dependent density functional theory (TD-DFT), finite field, and coupled perturbed Hartree-Fock calculations reproduce even more closely the empirical data and trends; the latter two approaches lead to the highest quadratic nonlinear optical (NLO) response of the studied chromophores for 3, for which the predicted beta(0) is ca. 50-100% larger than that of the analogous N-methylated cation 1. Although the TD-DFT and INDO/SCI approaches give quite different results for ground- and excited-state dipole moments, the overall conclusions of these two methods regarding the ICT absorption and NLO responses are similar.

Structural and vibrational spectral investigations of melaminium glutarate monohydrate by FTIR, FT-Raman and DFT methods.

PubMed

Arjunan, V; Marchewka, M K; Raj, Arushma; Yang, Haifeng; Mohan, S

2015-01-25

Melaminium glutarate monohydrate has been synthesised and FTIR and FT-Raman spectral investigations are carried out. The molecular geometry and vibrational frequencies of melaminium glutarate monohydrate in the ground state have been determined by using B3LYP method with 6-31++G(**), 6-31++G and cc-pVDZ basis sets. The stability of the system, inter molecular hydrogen bonding and the electron donor-acceptor interactions of the complex have been investigated by using natural bonding orbital analysis. It reveals that the N-H⋯O and O-H⋯O intermolecular interactions significantly influence crystal packing of this molecular complex. The glutarate anion forms hydrogen bonds to the melaminium cation as the proton donor of the type N-H⋯O with a distance (N⋯O)=2.51 Å. It is also linked by other hydrogen bonds to the water molecule of the type O-H⋯O with (O⋯O)=2.82 Å and to the amino (NH2) group of melaminium cation of the type N-H⋯O with (N⋯O)=2.82 Å as the proton acceptor. The electrostatic potential of the complex is in the range +1.892e×10(-2) to -1.892e×10(-2). The limits of total electron density of the complex is +6.679e×10(-2) to -6.679e×10(-2). Copyright © 2014 Elsevier B.V. All rights reserved.

Structural and vibrational spectral investigations of melaminium glutarate monohydrate by FTIR, FT-Raman and DFT methods

NASA Astrophysics Data System (ADS)

Arjunan, V.; Marchewka, M. K.; Raj, Arushma; Yang, Haifeng; Mohan, S.

2015-01-01

Melaminium glutarate monohydrate has been synthesised and FTIR and FT-Raman spectral investigations are carried out. The molecular geometry and vibrational frequencies of melaminium glutarate monohydrate in the ground state have been determined by using B3LYP method with 6-31++G**, 6-31++G and cc-pVDZ basis sets. The stability of the system, inter molecular hydrogen bonding and the electron donor-acceptor interactions of the complex have been investigated by using natural bonding orbital analysis. It reveals that the Nsbnd H⋯O and Osbnd H⋯O intermolecular interactions significantly influence crystal packing of this molecular complex. The glutarate anion forms hydrogen bonds to the melaminium cation as the proton donor of the type Nsbnd H⋯O with a distance (N⋯O) = 2.51 Å. It is also linked by other hydrogen bonds to the water molecule of the type Osbnd H⋯O with (O⋯O) = 2.82 Å and to the amino (sbnd NH2) group of melaminium cation of the type Nsbnd H⋯O with (N⋯O) = 2.82 Å as the proton acceptor. The electrostatic potential of the complex is in the range +1.892e × 10-2 to -1.892e × 10-2. The limits of total electron density of the complex is +6.679e × 10-2 to -6.679e × 10-2.

Multistate λ-local-elevation umbrella-sampling (MS-λ-LEUS): method and application to the complexation of cations by crown ethers.

PubMed

Bieler, Noah S; Tschopp, Jan P; Hünenberger, Philippe H

2015-06-09

An extension of the λ-local-elevation umbrella-sampling (λ-LEUS) scheme [ Bieler et al. J. Chem. Theory Comput. 2014 , 10 , 3006 ] is proposed to handle the multistate (MS) situation, i.e. the calculation of the relative free energies of multiple physical states based on a single simulation. The key element of the MS-λ-LEUS approach is to use a single coupling variable Λ controlling successive pairwise mutations between the states of interest in a cyclic fashion. The Λ variable is propagated dynamically as an extended-system variable, using a coordinate transformation with plateaus and a memory-based biasing potential as in λ-LEUS. Compared to other available MS schemes (one-step perturbation, enveloping distribution sampling and conventional λ-dynamics) the proposed method presents a number of important advantages, namely: (i) the physical states are visited explicitly and over finite time periods; (ii) the extent of unphysical space required to ensure transitions is kept minimal and, in particular, one-dimensional; (iii) the setup protocol solely requires the topologies of the physical states; and (iv) the method only requires limited modifications in a simulation code capable of handling two-state mutations. As an initial application, the absolute binding free energies of five alkali cations to three crown ethers in three different solvents are calculated. The results are found to reproduce qualitatively the main experimental trends and, in particular, the experimental selectivity of 18C6 for K(+) in water and methanol, which is interpreted in terms of opposing trends along the cation series between the solvation free energy of the cation and the direct electrostatic interactions within the complex.

The Generation of Dehydroalanine Residues in Protonated Polypeptides: Ion/Ion Reactions for Introducing Selective Cleavages

NASA Astrophysics Data System (ADS)

Peng, Zhou; Bu, Jiexun; McLuckey, Scott A.

2017-09-01

We examine a gas-phase approach for converting a subset of amino acid residues in polypeptide cations to dehydroalanine (Dha). Subsequent activation of the modified polypeptide ions gives rise to specific cleavage N-terminal to the Dha residue. This process allows for the incorporation of selective cleavages in the structural characterization of polypeptide ions. An ion/ion reaction within the mass spectrometer between a multiply protonated polypeptide and the sulfate radical anion introduces a radical site into the multiply protonated polypeptide reactant. Subsequent collisional activation of the polypeptide radical cation gives rise to radical side chain loss from one of several particular amino acid side chains (e.g., leucine, asparagine, lysine, glutamine, and glutamic acid) to yield a Dha residue. The Dha residues facilitate preferential backbone cleavages to produce signature c- and z-ions, demonstrated with cations derived from melittin, mechano growth factor (MGF), and ubiquitin. The efficiencies for radical side chain loss and for subsequent generation of specific c- and z-ions have been examined as functions of precursor ion charge state and activation conditions using cations of ubiquitin as a model for a small protein. It is noted that these efficiencies are not strongly dependent on ion trap collisional activation conditions but are sensitive to precursor ion charge state. Moderate to low charge states show the greatest overall yields for the specific Dha cleavages, whereas small molecule losses (e.g., water/ammonia) dominate at the lowest charge states and proton catalyzed amide bond cleavages that give rise to b- and y-ions tend to dominate at high charge states. [Figure not available: see fulltext.

The tetravalent organic cation spermine causes the gating of the IRK1 channel expressed in murine fibroblast cells.

PubMed Central

Ishihara, K; Hiraoka, M; Ochi, R

1996-01-01

1. The activation kinetics of the IRK1 channel stably expressed in L cells (a murine fibroblast cell line) were studied under the whole-cell voltage clamp. Without polyamines or Mg2+ in the pipettes, inward currents showed an exponential activation on hyperpolarization. The steep inward rectification of the currents around the reversal potential (Erev) could be described by the open-close transition of the channel with first-order kinetics. 2. When the tetravalent organic cation spermine (Spm) was added in the pipettes, the activation kinetics changed; this was explicable by the increase in the closing rate constant. The activation of the currents observed without Spm or Mg2+ in the pipettes was ascribed to the unblocking of the 'endogenous-Spm block'. 3. In the presence of the divalent cation putrescine (Put) or of Mg2+ in the pipettes, a different non-conductive state suppressed the outward currents on depolarization; the channels instantaneously changed to the open state on repolarization. As the depolarization was prolonged, this non-conductive state was replaced by the non-conductive state that shows an exponential activation on repolarization. This phenomenon was attributed to the redistribution of the channels from the Put- or Mg(2+)-blocked state to the 'endogenous Spm-blocked state' during depolarization. 4. In the presence of the trivalent cation spermidine (Spd) in the pipettes, two different non-conductive states occurred, showing a faster and a slower activation on repolarization. The rectification around Erev was mainly due to the non-conductive state showing a faster activation, which appeared to be the Spd-blocked state. During depolarization, redistribution of the channels to the 'endogenous Spm-blocked state' also occurred. 5. In the presence of Spd, Put or Mg2+ in the pipettes, the voltage dependence of the activation time constant reflecting the unblocking of the 'endogenous Spm' was shifted in the hyperpolarizing direction. 6. Our results suggest that the 'intrinsic gating' that shows the time-dependent activation on repolarization, and that is responsible for the inward rectification around Erev, reflects the blocking kinetics of the tetravalent Spm. PMID:8866861

The interplay of ion crosslinking, free ion content, and polymer mobility in PEO-based single-ion conductors

NASA Astrophysics Data System (ADS)

Lin, Kan-Ju; Maranas, Janna

2010-03-01

We use molecular dynamics simulation to study ion clustering and dynamics in ion containing polymers. This PEO based single-ion conducting ionomer serves as a model system for understanding cation transport in solid state polymer electrolytes (SPEs). Although small-angle x-ray scattering does not show an ionomer peak, we observer various cation-anion complexes in the simulation, suggesting ionomer backbones are crosslinked through ion complexes. These crosslinks reduce the adjacent PEO mobility resulting in a symmetric mobility gradient along the PEO chain. We vary the cation-anion interaction in the simulation to observe the interplay of cation-anion association, polymer mobility and cation motion. Cation-anion association controls the number of free ions, which is important in ionic conductivity when these materials are used as SPEs. Polymer mobility controls how fast the free ions are able to move through the SPE. High conductivity requires both a high free ion content and fast polymer motion. To understand the connection between the two, we ``tune'' the force field in order to manipulate the free ion content and observe the influence on PEO dynamics.

Clusterization Effects in III-V Nitrides: Nitrogen Vacancies, and Si and Mg Impurities in Aluminum Nitride and Gallium Nitride

NASA Astrophysics Data System (ADS)

Gubanov, V. A.; Pentaleri, E. A.; Boekema, C.; Fong, C. Y.; Klein, B. M.

1997-03-01

We have investigated clusterization of nitrogen vacancies and Si and Mg doping impurities in zinc-blende aluminum nitride (c-AlN) and gallium nitride (c-GaN) by the tight-binding LMTO technique. The calculations used 128-site supercells. Si and Mg atoms replacing ions in both the cation and anion sublattices of the host lattices of the host crystals have been considered. The Mg impurity at cation sites is found to form partially occupied states at the valence-band edge, and may result in p-type conductivity. When Si substitutes for Ga, the impurity band is formed at the conduction-band edge, resulting in n-type conductivity. Si impurities at cation sites, and Mg impurity at anion sites are able to form resonance states in the gap. The influence of impurity clusterization in the host lattice and interstitial sites on electronic properties of c-AlN and c-GaN crystals are modeled. The changes in vacancy- and impurity-state energies, bonding type, localization, density of states at the Fermi level in different host lattices, their dependence on impurity/vacancy concentration are analyzed and compared with the experimental data.

Barbiturates Bind in the GLIC Ion Channel Pore and Cause Inhibition by Stabilizing a Closed State*♦

PubMed Central

Fourati, Zaineb; Ruza, Reinis Reinholds; Laverty, Duncan; Drège, Emmanuelle; Delarue-Cochin, Sandrine; Joseph, Delphine; Koehl, Patrice; Smart, Trevor; Delarue, Marc

2017-01-01

Barbiturates induce anesthesia by modulating the activity of anionic and cationic pentameric ligand-gated ion channels (pLGICs). Despite more than a century of use in clinical practice, the prototypic binding site for this class of drugs within pLGICs is yet to be described. In this study, we present the first X-ray structures of barbiturates bound to GLIC, a cationic prokaryotic pLGIC with excellent structural homology to other relevant channels sensitive to general anesthetics and, as shown here, to barbiturates, at clinically relevant concentrations. Several derivatives of barbiturates containing anomalous scatterers were synthesized, and these derivatives helped us unambiguously identify a unique barbiturate binding site within the central ion channel pore in a closed conformation. In addition, docking calculations around the observed binding site for all three states of the receptor, including a model of the desensitized state, showed that barbiturates preferentially stabilize the closed state. The identification of this pore binding site sheds light on the mechanism of barbiturate inhibition of cationic pLGICs and allows the rationalization of several structural and functional features previously observed for barbiturates. PMID:27986812

Reconnaissance data for selected herbicides, two atrazine metabolities, and nitrate in surface water of the Midwestern United States, 1989-90

USGS Publications Warehouse

Scribner, E.A.; Thurman, E.M.; Goolsby, D.A.; Meyer, M.T.; Mills, M.S.; Pomes, M.L.

1993-01-01

Water-quality data were collected from 147 rivers and streams during 1989-90 to assess selected preemergent herbicides, two atrazine metabolites, and nitrate in 10 Midwestern States. This report includes a description of the sampling design, data collection techniques, laboratory and analytical methods, and a compilation of constituent concentrations and quality-assurance data. All water samples were collected by depth-integrating techniques at three to five locations across the wetted perimeter of each stream. Sites were sampled three times in l989--before application of herbi- cides, during the first major runoff after appli- cation of herbicides, and in the fall during a low-flow period when ground water contributed to most of the streamflow. About 50 sites were selected by a stratified random procedure and resampled for both pre- and post-application herbicide concen- trations in 1990 to verify the 1989 results. Laboratory analyses consisted of both enzyme-linked immunosorbent assay (ELISA) with confirmation by gas chromatography-mass spectrometry (GC/MS). The data are useful in studying herbicide transport, in comparison of the spatial distribution of the post-application concentrations of 11 herbicides and 2 atrazine metabolites (deethylatrazine and deisopropylatrazine) in streams and rivers at a regional scale. It is also useful in examination of annual persistence of herbicides and two metabolites in surface water, and in the assessment of atrazine metabolites as indicators of surface- and ground- water interaction. The reconnaissance data are contained in this report and are also available on computer diskette from the U.S. Geological Survey in Lawrence, Kansas.

The role of electronegativity on the extent of nitridation of group 5 metals as revealed by reactions of tantalum cluster cations with ammonia molecules.

PubMed

Arakawa, Masashi; Ando, Kota; Fujimoto, Shuhei; Mishra, Saurabh; Patwari, G Naresh; Terasaki, Akira

2018-05-10

Reactions of the free tantalum cation, Ta+, and tantalum cluster cations, Tan+ (n = 2-10), with ammonia are presented. The reaction of the monomer cation, Ta+, with two molecules of NH3 leads to the formation of TaN2H2+ along with release of two H2 molecules. The dehydrogenation occurs until the formal oxidation number of the tantalum atom reaches +5. On the other hand, all the tantalum cluster cations, Tan+, react with two molecules of NH3 and form TanN2+ with the release of three H2 molecules. Further exposure to ammonia showed that TanNmH+ and TanNm+ are produced through successive reactions; a pure nitride and three H2 molecules are formed for every other NH3 molecule. The nitridation occurred until the formal oxidation number of the tantalum atoms reaches +5 as in the case of TaN2H2+ in contrast to other group 5 elements, i.e., vanadium and niobium, which have been reported to produce nitrides with lower oxidation states. The present results on small gas-phase metal-nitride clusters show correlation with their bulk properties: tantalum is known to form bulk nitrides in the oxidation states of either +5 (Ta3N5) or +3 (TaN), whereas vanadium and niobium form nitrides in the oxidation state of +3 (VN and NbN). Along with DFT calculations, these findings reveal that nitridation is driven by the electron-donating ability of group 5 elements, i.e., electronegativity of the metal plays a key role in determining the composition of the metal nitrides.

Effect of Alkali Metal Cations on Slow Inactivation of Cardiac Na+ Channels

PubMed Central

Townsend, Claire; Horn, Richard

1997-01-01

Human heart Na+ channels were expressed transiently in both mammalian cells and Xenopus oocytes, and Na+ currents measured using 150 mM intracellular Na+. The kinetics of decaying outward Na+ current in response to 1-s depolarizations in the F1485Q mutant depends on the predominant cation in the extracellular solution, suggesting an effect on slow inactivation. The decay rate is lower for the alkali metal cations Li+, Na+, K+, Rb+, and Cs+ than for the organic cations Tris, tetramethylammonium, N-methylglucamine, and choline. In whole cell recordings, raising [Na+]o from 10 to 150 mM increases the rate of recovery from slow inactivation at −140 mV, decreases the rate of slow inactivation at relatively depolarized voltages, and shifts steady-state slow inactivation in a depolarized direction. Single channel recordings of F1485Q show a decrease in the number of blank (i.e., null) records when [Na+]o is increased. Significant clustering of blank records when depolarizing at a frequency of 0.5 Hz suggests that periods of inactivity represent the sojourn of a channel in a slow-inactivated state. Examination of the single channel kinetics at +60 mV during 90-ms depolarizations shows that neither open time, closed time, nor first latency is significantly affected by [Na+]o. However raising [Na+]o decreases the duration of the last closed interval terminated by the end of the depolarization, leading to an increased number of openings at the depolarized voltage. Analysis of single channel data indicates that at a depolarized voltage a single rate constant for entry into a slow-inactivated state is reduced in high [Na+]o, suggesting that the binding of an alkali metal cation, perhaps in the ion-conducting pore, inhibits the closing of the slow inactivation gate. PMID:9234168

Hydrology and cycling of nitrogen and phosphorus in Little Bean Marsh : a remnant riparian wetland along the Missouri River in Platte County, Missouri, 1996-97

USGS Publications Warehouse

Blevins, Dale W.

2004-01-01

The lack of concurrent water-quality and hydrologic data on riparian wetlands in the Midwestern United States has resulted in a lack of knowledge about the water-quality functions that these wetlands provide. Therefore, Little Bean Marsh, a remnant riparian wetland along the Missouri River, was investigated in 1996 and 1997 primarily to determine the magnitude and character of selected water-quality benefits that can be produced in such a wetland and to identify critical processes that can be managed in remnant or restored riparian wetlands for amelioration of water quality. Little Bean Marsh averages 69 hectares in size, has a maximum depth of about 1 meter, and the majority of the marsh is covered by macrophytes. In 1997, 41 percent of the water received by Little Bean Marsh was from direct precipitation, 14 percent was from ground-water seepage, 30 percent from watershed runoff, and 15 percent was backflow from Bean Lake. Although, Little Bean Marsh was both a ground-water recharge and discharge area, discharge to the marsh was three times the recharge to ground water. Ground-water levels closely tracked marsh water levels indicating a strong hydraulic connection between ground water and the marsh. Reduced surface runoff and ground-water availability are stabilizing influences on marsh hydrology and probably contribute to the persistence of emergent vegetation. The rapid hydraulic connection between Little Bean Marsh and ground water indicates that the hydrologic regime of most wetlands along the lower Missouri River is largely a function of the altitude of the marsh bottom relative to the altitude of the water table. More water was lost from the marsh through evapotranspiration (59 percent) than all other pathways combined. This is partially because the transpiration process of abundant macrophytes can greatly contribute to the evapotranspiration above that lost from open water surfaces. Surface outflow accounted for 36 percent and ground-water seepage accounted for only 5 percent of the losses. Large residence times allows the marsh to greatly affect water quality before water escapes as ground-water recharge or surface outflow. The shallowness of Little Bean Marsh and ion exclusion during ice formation caused the highest specific conductances of 1,100 to 1,300 microsiemens per centimeter at 25 degrees Celsius to occur during the winter. This concentration of dissolved solutes under ice can make wetlands more vulnerable to toxic contaminants than deeper surface-water bodies. Dissolved oxygen was less than 5 mg/L (milligrams per liter) for 3 to 4 months and near 0 mg/L for about 1 month in summer. Despite depths of less than 1 meter, temperature stratification persisted more than 3 months during the summers of 1996 and 1997, preventing mixing and contributing to periods of anoxia. Shallow depths and extended periods of anoxia in the marsh limit the ability of some organisms to escape high-temperature stress. Turbidity in Little Bean Marsh usually was low for several reasons: sediment loadings from the largely flood-plain drainage were low, emergent vegetation shade out algae and shield the water from wind, and high concentrations of bivalent cations increase flocculation rates of inorganic suspended material. The high concentrations of bivalent cations was largely because of a substantial amount of ground-water seepage into the marsh. Dissolved organic nitrogen was the dominant nitrogen species in Little Bean Marsh. Denitrification and biotic uptake kept more than 62 percent of nitrate (NO3) and 43 percent of ammonium (NH4) concentrations in marsh samples less than a detection limit of 0.005 mg/L. This contrasts with the Missouri River where inorganic NO3 dominates. Consequently, artificial flood-plain drainage that bypasses riparian wetlands likely deliver substantially more biotically available inorganic nitrogen to receiving waters than surface water that has been routed through a remnant wetland. Aver

Enzyme architecture: optimization of transition state stabilization from a cation-phosphodianion pair.

PubMed

Reyes, Archie C; Koudelka, Astrid P; Amyes, Tina L; Richard, John P

2015-04-29

The side chain cation of R269 lies at the surface of l-glycerol 3-phosphate dehydrogenase (GPDH) and forms an ion pair to the phosphodianion of substrate dihydroxyacetone phosphate (DHAP), which is buried at the nonpolar protein interior. The R269A mutation of GPDH results in a 110-fold increase in K(m) (2.8 kcal/mol effect) and a 41,000-fold decrease in k(cat) (6.3 kcal/mol effect), which corresponds to a 9.1 kcal/mol destabilization of the transition state for GPDH-catalyzed reduction of DHAP by NADH. There is a 6.7 kcal/mol stabilization of the transition state for the R269A mutant GPDH-catalyzed reaction by 1.0 M guanidinium ion, and the transition state for the reaction of the substrate pieces is stabilized by an additional 2.4 kcal/mol by their covalent attachment at wildtype GPDH. These results provide strong support for the proposal that GPDH invests the 11 kcal/mol intrinsic phosphodianion binding energy of DHAP in trapping the substrate at a nonpolar active site, where strong electrostatic interactions are favored, and obtains a 9 kcal/mol return from stabilizing interactions between the side chain cation and transition state trianion. We propose a wide propagation for the catalytic motif examined in this work, which enables strong transition state stabilization from enzyme-phosphodianion pairs.

Singlet and doublet states UV-vis spectrum and electronic properties of 3-methylchrysene and 4-methylchrysene in glass matrix.

PubMed

Husain, Mudassir M; Tandon, H C; Varadwaj, Pradeep R

2008-03-01

The ultraviolet-visual spectrum of 3-methylchrysene, 4-methylchrysene and their radical cations formed by ultraviolet radiations, were measured in glass matrix at the room temperature. In the measured singlet state spectrum we were able to identify the alpha, p, beta, beta' (Clar's) or (1)L(b), (1)L(a)(1)B(b), (1)B(a) (Platt's notation) bands. The presence of alpha, beta or (1)L(b), (1)B(b) was confirmed by calculating their wavelength ratio lambda(alpha)/lambda(beta). Since matrix induces perturbation in the measured spectrum; it becomes necessary to take into account the perturbation while computing the spectrum. An effort has been made in this work to simulate the electronic spectrum in the same environment as is measured. This study presents the first calculated spectrum of these systems and their cations in glass matrix by semi empirical methods. To observe the magnitude of perturbation and hence to see the spectral shift in glass matrix, the spectrum was calculated in the free state as well. Spectral properties such as frontier orbitals gap, dipole moment, mean polarizabilities and its tensors were also computed both in glass matrix and free state using semiemperical method. The measured bands of 3-methylchrysene cation at wavelength 416.50 and 473.85 nm closely match with the available diffuse intersteallar bands (DIBs) at 417.55 and 472.64 nm, respectively. Also the observed 474.85 nm band of 4-methylchrysene cation matches the DIB at 476.00 nm.

Increase of the pharmacological and pharmacokinetic efficacy of negatively charged polypeptide recombinant hirudin in rats via parenteral route by association with cationic liposomes.

PubMed

Meng, Meng; Liu, Yu; Wang, Yi-Bo; Wang, Jian-Cheng; Zhang, Hua; Wang, Xue-Qing; Zhang, Xuan; Lu, Wan-Liang; Zhang, Qiang

2008-06-04

Two biodegradable cationic lipids, stearylamine and DC-Chol, were chosen to investigate the effect of cationic lipids on the in vitro and in vivo characteristics of hydrophilic proteins or peptides of low isoelectric point. Thrombin inhibitor recombinant hirudin variant-2 (rHV2) was selected as the model drug. The cationic lipids were found to achieve higher entrapment efficiency of rHV2 in liposomes than zwitterionic lipids. The positively charged liposomes became less positive and relatively stable in serum after loading rHV2. The cationic liposomes induced sustained release of rHV2 in the presence of plasma, significantly prolonged the antithrombotic efficacy and plasma level of rHV2 after intravenous injection in rats in comparison with neutral lipid liposomes, especially for stearylamine group. Both clotting times correlated well with plasma rHV2 levels. No serious adverse events were observed and physical state of rats was satisfactory for all the formulations. Electrostatic interaction between negative charge of rHV2 and cationic liposomes was confirmed and it might affect all the characteristics of rHV2 loaded cationic vehicles. The findings suggest that cationic liposomes may be a potential sustained-release delivery system for parenteral administration of hydrophilic proteins or peptides with low isoelectric point to prolong efficacy and improve bioavailability.

U.S. Geological Survey Georgia Water Science Center and Albany Water, Gas, and Light Commission Cooperative Water Program-Summary of Activities, July 2005 through June 2006

USGS Publications Warehouse

Gordon, Debbie W.

2006-01-01

The U.S. Geological Survey (USGS) has been working with the Albany Water, Gas, and Light Commission to monitor ground-water quality and availability since 1977. This report presents the findings for July 2005 through June 2006 and summarizes the ground-water and surface-water conditions for 2005. Water levels in 14 wells were continuously monitored in Dougherty County, Georgia. Water levels in 12 of those wells were above normal, one was normal, and one was below normal. Ground-water samples collected from the Upper Floridan aquifer indicate that nitrate levels have increased in 13 wells and decreased in two wells from a year earlier. A sample also was collected from the Flint River. A trilinear diagram showing the percent composition of selected major cations and anions indicates that the ground-water quality of the Upper Floridan aquifer at the Albany wellfield is distinctly different from the water quality of the Flint River. To improve the understanding of the ground-water flow system and nitrate movement in the Upper Floridan aquifer, the USGS is developing a ground-water flow model in the southwest Albany area, Georgia.

Control of cerium oxidation state through metal complex secondary structures

DOE PAGES

Levin, Jessica R.; Dorfner, Walter L.; Carroll, Patrick J.; ...

2015-08-11

A series of alkali metal cerium diphenylhydrazido complexes, M x(py) y[Ce(PhNNPh) 4], M = Li, Na, and K, x = 4 (Li and Na) or 5 (K), and y = 4 (Li), 8 (Na), or 7 (K), were synthesized to probe how a secondary coordination sphere would modulate electronic structures at a cerium cation. The resulting electronic structures of the heterobimetallic cerium diphenylhydrazido complexes were found to be strongly dependent on the identity of the alkali metal cations. When M = Li + or Na +, the cerium(III) starting material was oxidized with concomitant reduction of 1,2-diphenylhydrazine to aniline. Reductionmore » of 1,2-diphenylhydrazine was not observed when M = K +, and the complex remained in the cerium(III) oxidation state. Oxidation of the cerium(III) diphenylhydrazido complex to the Ce( IV) diphenylhydrazido one was achieved through a simple cation exchange reaction of the alkali metals. As a result, UV-Vis spectroscopy, FTIR spectroscopy, electrochemistry, magnetic susceptibility, and DFT studies were used to probe the oxidation state and the electronic changes that occurred at the metal centre.« less

Fragmentation of tetrahydrofuran molecules by H(+), C(+), and O(+) collisions at the incident energy range of 25-1000 eV.

PubMed

Wasowicz, Tomasz J; Pranszke, Bogusław

2015-01-29

We have studied fragmentation processes of the gas-phase tetrahydrofuran (THF) molecules in collisions with the H(+), C(+), and O(+) cations. The collision energies have been varied between 25 and 1000 eV and thus covered a velocity range from 10 to 440 km/s. The following excited neutral fragments of THF have been observed: the atomic hydrogen H(n), n = 4-9, carbon atoms in the 2p3s (1)P1, 2p4p (1)D2, and 2p4p (3)P states and vibrationally and rotationally excited diatomic CH fragments in the A(2)Δ and B(2)Σ(-) states. Fragmentation yields of these excited fragments have been measured as functions of the projectile energy (velocity). Our results show that the fragmentation mechanism depends on the projectile cations and is dominated by electron transfer from tetrahydrofuran molecules to cations. It has been additionally hypothesized that in the C(+)+THF collisions a [C-C4H8O](+) complex is formed prior to dissociation. The possible reaction channels involved in fragmentation of THF under the H(+), C(+), and O(+) cations impact are also discussed.

Rotationally resolved state-to-state photoionization and photoelectron study of titanium carbide and its cation (TiC/TiC⁺).

PubMed

Luo, Zhihong; Huang, Huang; Chang, Yih-Chung; Zhang, Zheng; Yin, Qing-Zhu; Ng, C Y

2014-10-14

Titanium carbide and its cation (TiC/TiC(+)) have been investigated by the two-color visible (VIS)-ultraviolet (UV) resonance-enhanced photoionization and pulsed field ionization-photoelectron (PFI-PE) methods. Two visible excitation bands for neutral TiC are observed at 16,446 and 16,930 cm(-1). Based on rotational analyses, these bands are assigned as the respective TiC((3)Π1) ← TiC(X(3)Σ(+)) and TiC((3)Σ(+)) ← TiC(X(3)Σ(+)) transition bands. This assignment supports that the electronic configuration and term symmetry for the neutral TiC ground state are …7σ(2)8σ(1)9σ(1)3π(4) (X(3)Σ(+)). The rotational constant and the corresponding bond distance of TiC(X(3)Σ(+); v″ = 0) are determined to be B0″ = 0.6112(10) cm(-1) and r0″ = 1.695(2) Å, respectively. The rotational analyses of the VIS-UV-PFI-PE spectra for the TiC(+)(X; v(+) = 0 and 1) vibrational bands show that the electronic configuration and term symmetry for the ionic TiC(+) ground state are …7σ(2)8σ(1)3π(4) (X(2)Σ(+)) with the v(+) = 0 → 1 vibrational spacing of 870.0(8) cm(-1) and the rotational constants of B(e)(+) = 0.6322(28) cm(-1), and α(e)(+) = 0.0085(28) cm(-1). The latter rotational constants yield the equilibrium bond distance of r(e)(+) = 1.667(4) Å for TiC(+)(X(2)Σ(+)). The cleanly rotationally resolved VIS-UV-PFI-PE spectra have also provided a highly precise value of 53 200.2(8) cm(-1) [6.5960(1) eV] for the adiabatic ionization energy (IE) of TiC. This IE(TiC) value along with the known IE(Ti) has made possible the determination of the difference between the 0 K bond dissociation energy (D0) of TiC(+)(X(2)Σ(+)) and that of TiC(X(3)Σ(+)) to be D0(Ti(+)-C) - D0(Ti-C) = 0.2322(2) eV. Similar to previous experimental observations, the present state-to-state PFI-PE study of the photoionization transitions, TiC(+)(X(2)Σ(+); v(+) = 0 and 1, N(+)) ← TiC((3)Π1; v', J'), reveals a strong decreasing trend for the photoionization cross section as |ΔN(+)| = |N(+) - J'| is increased. The maximum |ΔN(+)| change of 7 observed here is also consistent with the previous experimental results for the 3d transition-metal carbides, oxides, and nitrides. However, the VIS-UV-PFI-PE spectra for TiC(+)(X(2)Σ(+); v(+) = 0 and 1, N(+)) are found to display only the negative ΔN(+) (N(+)-J'≤ 0) transitions, indicating that the cross sections for the formation of positive ΔN(+) (N(+)-J' > 0) transitions by both the channel coupling mechanism and direct photoionization are negligibly small.

Spectroscopic parameters, vibrational levels, transition dipole moments and transition probabilities of the 9 low-lying states of the NCl+ cation

NASA Astrophysics Data System (ADS)

Yin, Yuan; Shi, Deheng; Sun, Jinfeng; Zhu, Zunlue

2018-03-01

This work calculates the potential energy curves of 9 Λ-S and 28 Ω states of the NCl+ cation. The technique employed is the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson correction. The Λ-S states are X2Π, 12Σ+, 14Π, 14Σ+, 14Σ-, 24Π, 14Δ, 16Σ+, and 16Π, which are yielded from the first two dissociation channels of NCl+ cation. The Ω states are generated from these Λ-S states. The 14Π, 14Δ, 16Σ+, and 16Π states are inverted with the spin-orbit coupling effect included. The 14Σ+, 16Σ+, and 16Π states are very weakly bound, whose well depths are only several-hundred cm- 1. One avoided crossing of PECs occurs between the 12Σ+ and 22Σ+ states. To improve the quality of potential energy curves, core-valence correlation and scalar relativistic corrections are included. The potential energies are extrapolated to the complete basis set limit. The spectroscopic parameters and vibrational levels are calculated. The transition dipole moments are computed. The Franck-Condon factors, Einstein coefficients, and radiative lifetimes of many transitions are determined. The spectroscopic approaches are proposed for observing these states according to the transition probabilities. The spin-orbit coupling effect on the spectroscopic and vibrational properties is evaluated. The spectroscopic parameters, vibrational levels, transition dipole moments, as well as transition probabilities reported in this paper could be considered to be very reliable.

Cation effects on phosphatidic acid monolayers at various pH conditions.

PubMed

Zhang, Ting; Cathcart, Matthew G; Vidalis, Andrew S; Allen, Heather C

2016-10-01

The impact of pH and cations on phase behavior, stability, and surface morphology for dipalmitoylphosphatidic acid (DPPA) monolayers was investigated. At pH<10, DPPA monolayers on water are predominantly populated by neutral species and display the highest packing density. Cations are found to expand and stabilize the monolayer in the following order of increasing magnitude at pH 5.6: Na + >K + ∼Mg 2+ >Ca 2+ . Additionally, cation complexation is tied to the pH and protonation state of DPPA, which are the primary factors controlling the monolayer surface behavior. The binding affinity of cations to the headgroup and thus deprotonation capability of the cation, ranked in the order of Ca 2+ >Mg 2+ >Na + >K + , is found to be well explained by the law of matching water affinities. Nucleation of surface 3D lipid structures is observed from Ca 2+ , Mg 2+ , and Na + , but not from K + , consistent with the lowest binding affinity of K + . Unraveling cation and pH effects on DPPA monolayers is useful in further understanding the surface properties of complex systems such as organic-coated marine aerosols where organic films are directly influenced by the pH and ionic composition of the underlying aqueous phase. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Rotational relaxation of CF+(X1Σ) in collision with He(1S)

NASA Astrophysics Data System (ADS)

Denis-Alpizar, O.; Inostroza, N.; Castro Palacio, J. C.

2018-01-01

The carbon monofluoride cation (CF+) has been detected recently in Galactic and extragalactic regions. Therefore, excitation rate coefficients of this molecule in collision with He and H2 are necessary for a correct interpretation of the astronomical observations. The main goal of this work is to study the collision of CF+ with He in full dimensionality at the close-coupling level and to report a large set of rotational rate coefficients. New ab initio interaction energies at the CCSD(T)/aug-cc-pv5z level of theory were computed, and a three-dimensional potential energy surface was represented using a reproducing kernel Hilbert space. Close-coupling scattering calculations were performed at collisional energies up to 1600 cm-1 in the ground vibrational state. The vibrational quenching cross-sections were found to be at least three orders of magnitude lower than the pure rotational cross-sections. Also, the collisional rate coefficients were reported for the lowest 20 rotational states of CF+ and an even propensity rule was found to be in action only for j > 4. Finally, the hyperfine rate coefficients were explored. These data can be useful for the determination of the interstellar conditions where this molecule has been detected.

Type I antiferromagnetic order in Ba 2LuReO 6: Exploring the role of structural distortions in double perovskites containing 5d 2 ions

DOE PAGES

Xiong, Jie; Yan, Jiaqiang; Aczel, Adam A.; ...

2017-12-02

The structural, electrical, and magnetic properties of the double perovskite Ba 2LuReO 6 have been examined in this paper. It is an insulator whose temperature dependent conductivity is consistent with variable range hopping electrical transport. A transition to an antiferromagnet state with type I order occurs below T N = 31 K. High resolution time-of-flight neutron powder diffraction measurements show that it retains the cubic double perovskite structure down to 10 K. High intensity, low resolution neutron powder diffraction measurements confirm the antiferromagnetic order and indicate that cubic symmetry is still observed at 1.5 K. The small ordered moment ofmore » 0.34(4)μ B per Re is comparable to estimates of moments on 5d 2 ions in other antiferromagnetically ordered cubic double perovskites. Finally, comparisons with related double perovskites containing 5d 2 ions, such as Os 6+ and Re 5+, reveal that subtle changes in structure or electron configuration of the diamagnetic octahedral cations can have a large impact on the magnetic ground state, the size of the ordered moment, and the Néel temperature.« less

Drug Discovery of Antimicrobial Photosensitizers Using Animal Models

PubMed Central

Sharma, Sulbha K.; Dai, Tianhong; Kharkwal, Gitika B.; Huang, Ying-Ying; Huang, Liyi; Bil De Arce, Vida J.; Tegos, George P.; Hamblin, Michael R.

2012-01-01

Antimicrobial photodynamic therapy (aPDT) is an emerging alternative to antibiotics motivated by growing problems with multi-drug resistant pathogens. aPDT uses non-toxic dyes or photosensitizers (PS) in combination with harmless visible of the correct wavelength to be absorbed by the PS. The excited state PS can form a long-lived triplet state that can interact with molecular oxygen to produce reactive oxygen species such as singlet oxygen and hydroxyl radical that kill the microbial cells. To obtain effective PS for treatment of infections it is necessary to use cationic PS with positive charges that are able to bind to and penetrate different classes of microbial cells. Other drug design criteria require PS with high absorption coefficients in the red/near infra-red regions of the spectrum where light penetration into tissue is maximum, high photostability to minimize photobleaching, and devising compounds that will selectively bind to microbial cells rather than host mammalian cells. Several molecular classes fulfill many of these requirements including phenothiazinium dyes, cationic tetrapyrroles such as porphyrins, phthalocyanines and bacteriochlorins, cationic fullerenes and cationic derivatives of other known PS. Larger structures such as conjugates between PS and cationic polymers, cationic nanoparticles and cationic liposomes that contain PS are also effective. In order to demonstrate in vivo efficacy it is necessary to use animal models of localized infections in which both PS and light can be effectively delivered into the infected area. This review will cover a range of mouse models we have developed using bioluminescent pathogens and a sensitive low light imaging system to non-invasively monitor the progress of the infection in real time. Effective aPDT has been demonstrated in acute lethal infections and chronic biofilm infections; in infections caused by Gram-positive, Gram-negative bacteria and fungi; in infections in wounds, third degree burns, skin abrasions and soft-tissue abscesses. This range of animal models also represents a powerful aid in antimicrobial drug discovery. PMID:21504410

Liquid-like cationic sub-lattice in copper selenide clusters

NASA Astrophysics Data System (ADS)

White, Sarah L.; Banerjee, Progna; Jain, Prashant K.

2017-02-01

Super-ionic solids, which exhibit ion mobilities as high as those in liquids or molten salts, have been employed as solid-state electrolytes in batteries, improved thermoelectrics and fast-ion conductors in super-capacitors and fuel cells. Fast-ion transport in many of these solids is supported by a disordered, `liquid-like' sub-lattice of cations mobile within a rigid anionic sub-lattice, often achieved at high temperatures or pressures via a phase transition. Here we show that ultrasmall clusters of copper selenide exhibit a disordered cationic sub-lattice under ambient conditions unlike larger nanocrystals, where Cu+ ions and vacancies form an ordered super-structure similar to the bulk solid. The clusters exhibit an unusual cationic sub-lattice arrangement wherein octahedral sites, which serve as bridges for cation migration, are stabilized by compressive strain. The room-temperature liquid-like nature of the Cu+ sub-lattice combined with the actively tunable plasmonic properties of the Cu2Se clusters make them suitable as fast electro-optic switches.

Phase behavior in quaternary ammonium ionic liquid-propanol solutions: Hydrophobicity, molecular conformations, and isomer effects

NASA Astrophysics Data System (ADS)

Abe, Hiroshi; Kohki, Erica; Nakada, Ayumu; Kishimura, Hiroaki

2017-07-01

In ionic liquids (ILs), the effects of a quaternary ammonium cation containing a hydroxyl group were investigated and compared with the effect of a standard quaternary ammonium cation. The cation possessing a hydroxyl group is choline, Chol+, and the anion is bis(trifluoromethylsulfonyl)imide, TFSI-. Crystal polymorphism of pure [Chol][TFSI] was observed upon both cooling and heating by simultaneous X-ray diffraction and differential scanning calorimetry measurements. In contrast, [N3111][TFSI] (N3111+: N-trimethyl-N-propylammonium), a standard IL, demonstrated simple crystallization upon cooling. By adding 1-propanol or 2-propanol, the phase behaviors of the [Chol][TFSI]-based and [N3111][TFSI]-based mixtures were clearly distinguished. By Raman spectroscopy, the TFSI- anion conformers in the liquid state were shown to vary according to the propanol concentration, propanol isomer, and type of cation. The anomalous behaviors of pure [Chol][TFSI] and its mixtures are derived from hydrogen bonding of the hydroxyl group of Chol+ cation coupled with the hydrophobicity and packing efficiency of propanol.

The translational, rotational, and vibrational energy effects on the chemical reactivity of water cation H2O+(X 2B1) in the collision with deuterium molecule D2

NASA Astrophysics Data System (ADS)

Xu, Yuntao; Xiong, Bo; Chang, Yih Chung; Ng, C. Y.

2013-07-01

By employing the newly established vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) double quadrupole-double octopole ion guide apparatus, we have examined the translational, rotational, and vibrational energy effects on the chemical reactivity of water cation H2O+(X2B1) in the collision with deuterium molecule D2. The application of a novel electric-field pulsing scheme to the VUV laser PFI-PI ion source has enabled the preparation of a rovibrationally selected H2O+(X2B1; v_1^ + v_2^ + v_3^ +; N+Ka+Kc+) ion beam with not only high internal-state selectivity and high intensity but also high translational energy resolution. Despite the unfavorable Franck-Condon factors, we are able to prepare the excited vibrational states (v_1^ + v_2^ + v_3^ +) = (100) and (020) along with the (000) ground vibrational state, for collisional studies, where v_1^ +, v_2^ +, and v_3^ + represent the symmetric stretching, bending, and asymmetric stretching modes of H2O+(X2B1). We show that a range of rotational levels from N+Ka+Kc+ = 000 to 322, covering a rotational energy range of 0-200 cm-1 of these vibrational states, can also be generated for absolute integral cross section (σ) measurements at center-of-mass collision energies (Ecms) from thermal energies to 10.00 eV. The Ecm dependences of the σ values are consistent with the prediction of the orbiting model, indicating that translational energy significantly hinders the chemical reactivity of H2O+(X2B1). Rotational enhancements are observed at Ecm < 0.30 eV for all the three vibrational states, (000), (100), and (020). While the σ values for (100) are found to be only slightly below those for (000), the σ values for (020) are lower than those for (000) and (100) by up to 20% at Ecm ≤ 0.20 eV, indicative of vibrational inhibition at low Ecm by excitation of the (020) mode. Rationalizations are proposed for the observed rotational enhancements and the bending vibrational inhibition. Rigorous theoretical calculations are needed to interpret the wealth of rovibrationally selected cross sections obtained in the present study.

Derivation of the RPA (Random Phase Approximation) Equation of ATDDFT (Adiabatic Time Dependent Density Functional Ground State Response Theory) from an Excited State Variational Approach Based on the Ground State Functional.

PubMed

Ziegler, Tom; Krykunov, Mykhaylo; Autschbach, Jochen

2014-09-09

The random phase approximation (RPA) equation of adiabatic time dependent density functional ground state response theory (ATDDFT) has been used extensively in studies of excited states. It extracts information about excited states from frequency dependent ground state response properties and avoids, thus, in an elegant way, direct Kohn-Sham calculations on excited states in accordance with the status of DFT as a ground state theory. Thus, excitation energies can be found as resonance poles of frequency dependent ground state polarizability from the eigenvalues of the RPA equation. ATDDFT is approximate in that it makes use of a frequency independent energy kernel derived from the ground state functional. It is shown in this study that one can derive the RPA equation of ATDDFT from a purely variational approach in which stationary states above the ground state are located using our constricted variational DFT (CV-DFT) method and the ground state functional. Thus, locating stationary states above the ground state due to one-electron excitations with a ground state functional is completely equivalent to solving the RPA equation of TDDFT employing the same functional. The present study is an extension of a previous work in which we demonstrated the equivalence between ATDDFT and CV-DFT within the Tamm-Dancoff approximation.

Structure and ionic diffusion of alkaline-earth ions in mixed cation glasses A 2O–2MO–4SiO 2 with molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Konstantinou, Konstantinos; Sushko, Petr; Duffy, Dorothy M.

2015-05-15

A series of mixed cation silicate glasses of the composition A2O – 2MO – 4SiO2, with A=Li,Na,K and M=Ca,Sr,Ba has been investigated by means of molecular dynamics simulations in order to understand the effect of the nature of the cations on the mobility of the alkaline-earth ions within the glass network. The size of the alkaline-earth cation was found to affect the inter-atomic distances, the coordination number distributions and the bond angle distributions , whereas the medium-range order was almost unaffected by the type of the cation. All the alkaline-earth cations contribute to lower vibrational frequencies but it is observedmore » that that there is a shift to smaller frequencies and the vibrational density of states distribution gets narrower as the size of the alkaline-earth increases. The results from our modeling for the ionic diffusion of the alkaline-earth cations are in a qualitative agreement with the experimental observations in that there is a distinct correlation between the activation energy for diffusion of alkaline earth-ions and the cation radii ratio. An asymmetrical linear behavior in the diffusion activation energy with increasing size difference is observed. The results can be described on the basis of a theoretical model that relates the diffusion activation energy to the electrostatic interactions of the cations with the oxygens and the elastic deformation of the silicate network.« less

Changes in biogeochemical cycling following forest defoliation by pine wilt disease in Kiryu experimental catchment in Japan

NASA Astrophysics Data System (ADS)

Tokuchi, Naoko; Ohte, Nobuhito; Hobara, Satoru; Kim, Su-Jin; Masanori, Katsuyama

2004-10-01

Changes in nutrient budgets and hydrological processes due to the natural disturbance of pine wilt disease (PWD) were monitored in a small, forested watershed in Japan. The disturbance caused changes in soil nitrogen transformations. Pre-disturbance, mineralized nitrogen remained in the form of NH4+, whereas in disturbed areas most mineralized nitrogen was nitrified. Stream NO3- concentrations increased following PWD. There was a delay between time of disturbance and the increase of NO3- in ground and stream waters. Stream concentrations of NO3- and cations (Ca2+ + Mg2+) were significantly correlated from 1994 to 1996, whereas the correlation among NO3-, H+, and SO42- was significant only in 1995. Although both cation exchange and SO42- adsorption buffered protons, cation exchange was the dominant and continuous mechanism for acid buffering. SO42- adsorption was variable and highly pH dependent. The disturbance also resulted in slight delayed changes of input-output nutrient balances. The nitrogen contribution to PWD litter inputs was 7.39 kmol ha-1, and nitrogen loss from streamwater was less than 0.5 kmol ha-1 year-1 throughout the observation period. This large discrepancy suggested substantial nitrogen immobilization.

Learning from data to design functional materials without inversion symmetry

PubMed Central

Balachandran, Prasanna V.; Young, Joshua; Lookman, Turab; Rondinelli, James M.

2017-01-01

Accelerating the search for functional materials is a challenging problem. Here we develop an informatics-guided ab initio approach to accelerate the design and discovery of noncentrosymmetric materials. The workflow integrates group theory, informatics and density-functional theory to uncover design guidelines for predicting noncentrosymmetric compounds, which we apply to layered Ruddlesden-Popper oxides. Group theory identifies how configurations of oxygen octahedral rotation patterns, ordered cation arrangements and their interplay break inversion symmetry, while informatics tools learn from available data to select candidate compositions that fulfil the group-theoretical postulates. Our key outcome is the identification of 242 compositions after screening ∼3,200 that show potential for noncentrosymmetric structures, a 25-fold increase in the projected number of known noncentrosymmetric Ruddlesden-Popper oxides. We validate our predictions for 19 compounds using phonon calculations, among which 17 have noncentrosymmetric ground states including two potential multiferroics. Our approach enables rational design of materials with targeted crystal symmetries and functionalities. PMID:28211456

(CaO)(FeSe): A layered wide-gap oxychalcogenide semiconductor

DOE PAGES

Han, Fei; Wang, Di; Malliakas, Christos D.; ...

2015-07-20

A new iron-oxychalcogenide (CaO)(FeSe) was obtained which crystallizes in the orthorhombic space group Pnma (No. 62) with a = 5.9175(12) Å, b = 3.8797(8) Å, c = 13.170(3) Å. The unique structure of (CaO)(FeSe) is built up of a quasi-two-dimensional network of corrugated infinite layers of corner-shared FeSe 2O 2 tetrahedra that extend in the ab-plane. The FeSe 2O 2 layers stack along the c-axis with Ca 2+ cations sandwiched between the layers. Optical spectroscopy and resistivity measurements reveal semiconducting behavior with an indirect optical band gap of around 1.8 eV and an activation energy of 0.19(1) eV. Furthermore, electronicmore » band structure calculations at the density function level predict a magnetic configuration as ground state and confirm the presence of an indirect wide gap in (CaO)(FeSe).« less

Effect of Sulfuric and Triflic Acids on the Hydration of Vanadium Cations: An ab Initio Study.

PubMed

Sepehr, Fatemeh; Paddison, Stephen J

2015-06-04

Vanadium redox flow batteries (VRFBs) may be a promising solution for large-scale energy storage applications, but the crossover of any of the redox active species V(2+), V(3+), VO(2+), and VO2(+) through the ion exchange membrane will result in self-discharge of the battery. Hence, a molecular level understanding of the states of vanadium cations in the highly acidic environment of a VRFB is needed. We examine the effects of sulfuric and triflic (CF3SO3H) acids on the hydration of vanadium species as they mimic the electrolyte and functional group of perfluorosulfonic acid (PFSA) membranes. Hybrid density functional theory in conjunction with a continuum solvation model was utilized to obtain the local structures of the hydrated vanadium cations in proximity to H2SO4, CF3SO3H, and their conjugate anions. The results indicate that none of these species covalently bond to the vanadium cations. The hydration structure of V(3+) is more distorted than that of V(2+) in an acidic medium. The oxo-group of VO2(+) is protonated by either acid, in contrast to VO(2+) which is not protonated. The atomic partial charge of the four oxidation states of vanadium varies from +1.7 to +2.0. These results provide the local solvation structures of vanadium cations in the VRFBs environment that are directly related to the electrolytes stability and diffusion of vanadium ions into the membrane.

Role of charge screening and delocalization for lipophilic cation permeability of model and mitochondrial membranes.

PubMed

Trendeleva, Tatiana A; Sukhanova, Evgenia I; Rogov, Anton G; Zvyagilskaya, Renata A; Seveina, Inna I; Ilyasova, Tatiana M; Cherepanov, Dmitry A; Skulachev, Vladimir P

2013-09-01

The effects of the mitochondria-targeted lipophilic cation dodecyltriphenylphosphonium (C12TPP, the charge is delocalized and screened by bulky hydrophobic residues) and those of lipophilic cations decyltriethylammonium bromide and cetyltrimethylammonium bromide (C10TEA and C16TMA, the charges are localized and screened by less bulky residues) on bilayer planar phospholipid membranes and tightly-coupled mitochondria from the yeast Yarrowia lipolytica have been compared. In planar membranes, C12TPP was found to generate a diffusion potential as if it easily penetrates these membranes. In the presence of palmitate, C12TPP induced H(+) permeability like plastoquinonyl decyltriphenilphosphonium that facilitates transfer of fatty acid anions (Severin et al., PNAS, 2010, 107, 663-668). C12TPP was shown to stimulate State 4 respiration of mitochondria and caused a mitochondrial membrane depolarization with a half-maximal effect at 6μM. Besides, C12TPP profoundly potentiated the uncoupling effect of endogenous or added fatty acids. C10TEA and C16TMA inhibited State 4 respiration and decreased the membrane potential, though at much higher concentrations than C12TPP, and they did not promote the uncoupling action of fatty acids. These relationships were modeled by molecular dynamics. They can be explained by different membrane permeabilities for studied cations, which in turn are due to different availabilities of the positive charge in these cations to water dipoles. Copyright © 2012 Elsevier B.V. All rights reserved.

Impact of shelterbelts of different age on the content of nitrates and phosphates in ground water

NASA Astrophysics Data System (ADS)

Jaskulska, Renata; Wojciech Szajdak, Lech

2010-05-01

The investigations were carried out in the Agroecological Landscape Park situated 40 km South-West of Poznań in the upper Obra River watershed, Poland. The arable land constitutes 70%, shelterbelts and small afforestations about 14% and meadows and pastures about 12%. Shelterbelts belong to very efficient biogeochemical barriers. They decrease the migration of chemical compounds between ecosystems. The direction of ground water flow was from the adjoining cultivated field towards shelterbelts. Two shelterbelts of different humus guantity in surface layer soils were investigated. The age and species composition of plant was taken under consideration. The first one is 160-year-old shelterbelt, where predominant species is Robinia pseudoacacia, Quercus rober and Alnus glutinosa and is characterized by a well-developed humus level. The other one is 14-year-old shelterbelt. It includes 13 species of trees (Quercus petrea, Larix deciduas, Pinus silvestri, Populus nigra, Sorbus aucuparia) and reveals a small amount of humus. The soils are minerals, grey-brown podzolic in surface layer soils compound from light loamy sands and weakly loamy sands. The contents of N-NO3-, P-PO4-3, were investigated in the ground water under shelterbelts and adjoining cultivated fields. In addition, cationic sorptive capacity, specific surface areas, TOC were determined in soils. The smallest concentrations of nitrates (3.35 mg×l-1) and phosphates (0.02 mg×l-1) were observed in ground water under the 160-year-old shelterbelt. The physicochemical properties of soils under 160-year-old shelterbelt: specific surface areas (20.3 m2×g-1), cationic sorptive capacity (24.8 cmol(+)×kg-1), TOC (4.3%) was higher than in 14-year-old shelterbelt and in adjoining cultivated fields. The results revealed, that the 160-year-old shelterbelt characterizing developed humus more effectively than 14-year-old shelterbelt decreases the amounts of chemical compounds in ground water and sufficiently fulfils the function such as biogeochemical barrier in agricultural landscape. This work was supported by a grant No. N N305 229535 founded by Polish Ministry of Education.

Estimation of electronegativity values of elements in different valence states.

PubMed

Li, Keyan; Xue, Dongfeng

2006-10-05

The electronegativities of 82 elements in different valence states and with the most common coordination numbers have been quantitatively calculated on the basis of an effective ionic potential defined by the ionization energy and ionic radius. It is found that for a given cation, the electronegativity increases with increasing oxidation state and decreases with increasing coordination number. For the transition-metal cations, the electronegativity of the low-spin state is higher than that of the high-spin state. The ligand field stabilization, the first filling of p orbitals, the transition-metal contraction, and especially the lanthanide contraction are well-reflected by the relative values of our proposed electronegativity. This new scale is useful for us to estimate some quantities (e.g., the Lewis acid strength for the main group elements and the hydration free energy for the first transition series) and predict the structure and property of materials.

Simultaneous Analysis of Monovalent Anions and Cations with a Sub-Microliter Dead-Volume Flow-Through Potentiometric Detector for Ion Chromatography

PubMed Central

Dumanli, Rukiye; Attar, Azade; Erci, Vildan; Isildak, Ibrahim

2016-01-01

A microliter dead-volume flow-through cell as a potentiometric detector is described in this article for sensitive, selective and simultaneous detection of common monovalent anions and cations in single column ion chromatography for the first time. The detection cell consisted of less selective anion- and cation-selective composite membrane electrodes together with a solid-state composite matrix reference electrode. The simultaneous separation and sensitive detection of sodium (Na+), potassium (K+), ammonium (NH4+), chloride (Cl−) and nitrate (NO3−) in a single run was achieved by using 98% 1.5 mM MgSO4 and 2% acetonitrile eluent with a mixed-bed ion-exchange separation column without suppressor column system. The separation and simultaneous detection of the anions and cations were completed in 6 min at the eluent flow-rate of 0.8 mL/min. Detection limits, at S/N = 3, were ranged from 0.2 to 1.0 µM for the anions and 0.3 to 3.0 µM for the cations, respectively. The developed method was successfully applied to the simultaneous determination of monovalent anions and cations in several environmental and biological samples. PMID:26786906

A kinetic study of ferrocenium cation decomposition utilizing an integrated electrochemical methodology composed of cyclic voltammetry and amperometry.

PubMed

Singh, Archana; Chowdhury, Debarati Roy; Paul, Amit

2014-11-21

A novel, easy, quick, and inexpensive integrated electrochemical methodology composed of cyclic voltammetry and amperometry has been developed for the determination of the kinetic stability of higher oxidation states for inorganic complexes. In this study, ferrocene and its derivatives have been used as model systems and the corresponding ferrocenium cations were generated in situ during the electrochemical experiments to determine their kinetic stabilities. The study found that the ferrocenium cations decompose following the first-order kinetics at 27 ± 3 °C in the presence of ambient oxygen and water. The half-lives of the ferrocenium, carboxylate ferrocenium, and decamethyl ferrocenium cations were found to be 1.27 × 10(3), 1.52 × 10(3), and ≫11.0 × 10(3) s, respectively, in acetonitrile solvent having a 0.5 M tetrabutylammonium hexafluorophosphate electrolyte. These results are in agreement with the previous reports, i.e. the ferrocenium cation is unstable whereas the decamethyl ferrocenium cation has superior stability. The new methodology has been established by performing various experiments using different concentrations of ferrocene, variable scan rates in cyclic voltammetry, different time periods for amperometry, and in situ spectroelectrochemical experiments.

The Minimal Pharmacophore for Silent Agonism of the α7 Nicotinic Acetylcholine Receptor

PubMed Central

Chojnacka, Kinga; Horenstein, Nicole A.

2014-01-01

The minimum pharmacophore for activation of the human α7 nicotinic acetylcholine receptor (nAChR) is the tetramethylammonium cation. Previous work demonstrated that larger quaternary ammonium compounds, such as diethyldimethylammonium or 1-methyl quinuclidine, were α7-selective partial agonists, but additional increase in the size of the ammonium cation or the quinuclidine N-alkyl group by a single carbon to an N-ethyl group led to a loss of efficacy for ion channel activation. We report that although such compounds are ineffective at inducing the normal channel open state, they nonetheless regulate the induction of specific conformational states normally considered downstream of channel activation. We synthesized several panels of quaternary ammonium nAChR ligands that systematically varied the size of the substituents bonded to the central positively charged nitrogen atom. In these molecular series, we found a correlation between the molecular volume of the ligand and/or charge density, and the receptor’s preferred distribution among conformational states including the closed state, the active state, a nonconducting state that could be converted to an activated state by a positive allosteric modulator (PAM), and a PAM-insensitive nonconducting state. We hypothesize that the changes of molecular volume of an agonist’s cationic core subtly impact interactions at the subunit interface constituting the orthosteric binding site in such a way as to regulate the probability of conversions among the conformational states. We define a new minimal pharmacophore for the class of compounds we have termed “silent agonists,” which are able to induce allosteric modulator-dependent activation but not the normal activated state. PMID:24990939

Consequences of acid strength for isomerization and elimination catalysis on solid acids.

PubMed

Macht, Josef; Carr, Robert T; Iglesia, Enrique

2009-05-13

We address here the manner in which acid catalysis senses the strength of solid acids. Acid strengths for Keggin polyoxometalate (POM) clusters and zeolites, chosen because of their accurately known structures, are described rigorously by their deprotonation energies (DPE). Mechanistic interpretations of the measured dynamics of alkane isomerization and alkanol dehydration are used to obtain rate and equilibrium constants and energies for intermediates and transition states and to relate them to acid strength. n-Hexane isomerization rates were limited by isomerization of alkoxide intermediates on bifunctional metal-acid mixtures designed to maintain alkane-alkene equilibrium. Isomerization rate constants were normalized by the number of accessible protons, measured by titration with 2,6-di-tert-butylpyridine during catalysis. Equilibrium constants for alkoxides formed by protonation of n-hexene increased slightly with deprotonation energies (DPE), while isomerization rate constants decreased and activation barriers increased with increasing DPE, as also shown for alkanol dehydration reactions. These trends are consistent with thermochemical analyses of the transition states involved in isomerization and elimination steps. For all reactions, barriers increased by less than the concomitant increase in DPE upon changes in composition, because electrostatic stabilization of ion-pairs at the relevant transition states becomes more effective for weaker acids, as a result of their higher charge density at the anionic conjugate base. Alkoxide isomerization barriers were more sensitive to DPE than for elimination from H-bonded alkanols, the step that limits 2-butanol and 1-butanol dehydration rates; the latter two reactions showed similar DPE sensitivities, despite significant differences in their rates and activation barriers, indicating that slower reactions are not necessarily more sensitive to acid strength, but instead reflect the involvement of more unstable organic cations at their transition states. These compensating effects from electrostatic stabilization depend on how similar the charge density in these organic cations is to that in the proton removed. Cations with more localized charge favor strong electrostatic interactions with anions and form more stable ionic structures than do cations with more diffuse charges. Ion-pairs at elimination transition states contain cations with higher local charge density at the sp(2) carbon than for isomerization transition states; as a result, these ion-pairs recover a larger fraction of the deprotonation energy, and, consequently, their reactions become less sensitive to acid strength. These concepts lead us to conclude that the energetic difficulty of a catalytic reaction, imposed by gas-phase reactant proton affinities in transition state analogues, does not determine its sensitivity to the acid strength of solid catalysts.

Exploring Closed-Shell Cationic Phenalenyl: From Catalysis to Spin Electronics.

PubMed

Mukherjee, Arup; Sau, Samaresh Chandra; Mandal, Swadhin K

2017-07-18

The odd alternant hydrocarbon phenalenyl (PLY) can exist in three different forms, a closed-shell cation, an open-shell radical, and a closed-shell anion, using its nonbonding molecular orbital (NBMO). The chemistry of PLY-based molecules began more than five decades ago, and so far, the progress has mainly involved the open-shell neutral radical state. Over the last two decades, we have witnessed the evolution of a range of PLY-based radicals generating an array of multifunctional materials. However, it has been admitted that the practical applications of PLY radicals are greatly challenged by the low stability of the open-shell (radical) state. Recently, we took a different route to establish the utility of these PLY molecules using the closed-shell cationic state. In such a design, the closed-shell unit of PLY can readily accept free electrons, stabilizing in its NBMO upon generation of the open-shell state of the molecule. Thus, one can synthetically avoid the unstable open-shell state but still take advantage of this state by in situ generating the radical through external electron transfer or spin injection into the empty NBMO. It is worth noting that such approaches using closed-shell phenalenyl have been missing in the literature. This Account focuses on our recent developments using the closed-shell cationic state of the PLY molecule and its application in broad multidisciplinary areas spanning from catalysis to spin electronics. We describe how this concept has been utilized to develop a variety of homogeneous catalysts. For example, this concept was used in designing an iron(III) PLY-based electrocatalyst for a single-compartment H 2 O 2 fuel cell, which delivered the best electrocatalytic activity among previously reported iron complexes, organometallic catalysts for various homogeneous organic transformations (hydroamination and polymerization), an organic Lewis acid catalyst for the ring opening of epoxides, and transition-metal-free C-H functionalization catalysts. Moreover, this concept of using the empty NBMO present in the closed-shell cationic state of the PLY moiety to capture electron(s) was further extended to an entirely different area of spin electronics to design a PLY-based spin-memory device, which worked by a spin-filtration mechanism using an organozinc compound based on a PLY backbone deposited over a ferromagnetic substrate. In this Account, we summarize our recent efforts to understand how this unexplored closed-shell state of the phenalenyl molecule, which has been known for over five decades, can be utilized in devising an array of materials that not only are important from an organometallic chemistry or organic chemistry point of view but also provide new understanding for device physics.

Hydrogen Sulfide as a Scavenger of Sulfur Atomic Cation.

PubMed

Fortenberry, Ryan C; Trabelsi, Tarek; Francisco, Joseph S

2018-06-07

The well-studied hydrogen sulfide molecule is shown here for the first time to form a S-S bond barrierlessly with sulfur atomic cation to produce stable H 2 SS + , a compound for which there is nearly no literature data. Previous work has shown that the reaction of hydrogen sulfide with neutral atomic sulfur will likely only take place at high pressures. Conversely, this work shows that hydrogen sulfide will readily bind with atomic sulfur cation first through the 1 4 A″ state from association of H 2 S with S + ( 4 S) and then will relax to the nearly degenerate 1 2 A' or 1 2 A″ states. S + ( 4 S) + H 2 S lies 29.5 kcal/mol above the 1 4 A″ H 2 SS + minimum. The 1 4 A″ H 2 SS + minimum in the S-S bond is also directly intersected by the doublet potential energy surface. As the S-S bond shortens in the association, the 1 2 A' and 1 2 A″ states split, falling 33.5 and 26.4 kcal/mol, respectively, below the 1 4 A″ state. Hence, this work is opening the door for novel synthesis of S-S bonds or potential removal of the common H 2 S toxin/pollutant through concatenation and subsequent precipitation.

Sub-femtosecond quantum dynamics of the strong-field ionization of water to the X ̃(2)B1 and Ã(2)A1 states of the cation.

PubMed

Jayachander Rao, B; Varandas, A J C

2015-03-07

Motivated by recent efforts to achieve sub-femtosecond structural resolution in various molecular systems, we have performed a femtosecond quantum dynamics study of the water cation in the X ̃(2)B1 and Ã(2)A1 electronic states. Autocorrelation functions for H2O(+) and D2O(+) are calculated for such electronic states by solving numerically the time-dependent Schrödinger equation. From the ratio of the squared autocorrelation functions of D2O(+) and H2O(+), the high-order harmonic generation signals are calculated. Substantial vibrational dynamics is found in the Ã(2)A1 state as compared to the one in X ̃(2)B1, which supports recent experimental findings of Farrell et al., Phys. Rev. Lett., 2011, 107, 083001. Maxima in the above ratio are also predicted at ∼1.1 fs and ∼1.6 fs for the X ̃(2)B1 and Ã(2)A1 states, respectively. The expectation values of the positions of the atoms in H2O(+) as a function of time reveal a strong excitation of the bending mode in the Ã(2)A1 state, which explains the observed vibrational dynamics. The peaks in the ratios of the squared autocorrelation functions are also explained in terms of the evolving geometries of the water cation.

Cationic surfactant assisted sonochemical synthesis of Nd3+ doped Zn2SiO4 nanostructures for solid state lighting applications

NASA Astrophysics Data System (ADS)

Basavaraj, R. B.; Malleshappa, J.; Darshan, G. P.; Prasad, B. Daruka; Nagabhushana, H.

2018-04-01

For the first time cationic surfactant assisted ultrasound synthesis route has been used for the preparation of pure and Nd3+ (0.5-9 mol %) doped Zn2SiO4 nanophosphors. The shape, size and morphology of the products were tuned by controlling the various experimental parameters. The final product was well characterized by sophisticated techniques viz. powder X-ray diffraction (PXRD), Ultraviolet visible spectroscopy (UV-Vis) and photoluminescence (PL). The powder X-ray diffraction patterns confirmed that the synthesized samples exhibit hexagonal phase without any impurity. The DRS spectra showed major peaks at 275, 360, 529, 586, 680, 742 and 806 nm due to the transitions of the 4f electrons of Nd3+ from the ground-state 4I9/2 to 2F5/2, 4D3/2 + 4D5/2 + 2I11/2, 2K13/2 + 4G7/2 + 4G9/2, 4G5/2 + 2G7/2, 4F7/2 + 4S3/2, 4F5/2 + 2H9/2 and 4F3/2 respectively. The band energy gap (Eg) of the samples were estimated and found to be in the range 5.32 - 5.52 eV. Under 421 nm excitation, PL spectra exhibit strong near ultraviolet emission peaks at˜444 nm, 459 nm and 520 nm were attributed to 2P3/2 → 4I13/2, 2P3/2 → 4I15/2, 1I6 → 3H4, 2P1/2 → 4I9/2 and 4G7/2 → 4I9/2 transitions respectively. The photometric studies indicate that the synthesized Zn2SiO4: Nd3+ nanophosphors can be tuned from blue to pale green by varying the dopant concentration. The current synthesis route is rapid, environmentally benign, cost-effective and useful for industrial applications such as solid state lighting and display devices.

Theoretical study of hyperfine coupling constants and electron spin g factors for X2Σ diatomics from Groups 1 and 2

NASA Astrophysics Data System (ADS)

Bruna, Pablo J.; Grein, Friedrich

The ESR parameters of the cations Be 2 + , Mg 2 + , Ca 2 + , BeMg + , BeCa + , MgCa + and the mixed radicals ZBe, ZMg, ZCa (Z = Li, Na, K), all having a X 2 Σu + (1 σg 2 1 σu )/X 2 Sigma + (1 σ2 2 σ) ground state, have been studied theoretically. The A iso and A dip constants have been calculated with UHF, CISD, MP2, B3LYP, PW91PW91 wavefunctions, and 6-311+G(2df) basis sets. The electron spin g factors (magnetic moment μs) have been evaluated from correlated (MRDCI) wavefunctions, using a Hamiltonian based on Breit-Pauli theory with perturbation expansions up to second order, and 6-311+ G(2d) basis sets. As expected for s-rich radicals, the hyperfine spectra are governed by the A iso terms. Both Δg|| and Δg Υ̂values are negative, but Δg|| lies close to zero. For Δg Υ̂, the coupling with 1 2 Π(u) dominates the sum-over-states expansions. Although the singly occupied MOs (SOMO) are mostly of s character, the | Δg Υ̂| are relatively large, up to 5200 ppm for cationic, and up to 7850 ppm for neutral radicals. These large values are caused by low excitation energies and high magnetic transition moments, the latter due to the fact that the σ*( s - s ) SOMO has the same nodal properties as a p σorbital. Of the radicals considered here, an ESR spectrum is available only for Mg2+. Our theoretical A iso of-287 MHz reproduces well the matrix result (-291 MHz). Calculated values of-10 ppm for Deltag|| and of-1280 ppm for Deltag Υ̂give an average < Δg> =-860 ppm that lies within the experimental range of-600( ±300) ppm in Ne, and of-1300( ±500) ppm in Ar matrices.

Spectrofluorimetric determination of stoichiometry and association constants of the complexes of harmane and harmine with beta-cyclodextrin and chemically modified beta-cyclodextrins.

PubMed

Martín, L; León, A; Olives, A I; Del Castillo, B; Martín, M A

2003-06-13

The association characteristics of the inclusion complexes of the beta-carboline alkaloids harmane and harmine with beta-cyclodextrin (beta-CD) and chemically modified beta-cyclodextrins such as hydroxypropyl-beta-cyclodextrin (HPbeta-CD), 2,3-di-O-methyl-beta-cyclodextrin (DMbeta-CD) and 2,3,6-tri-O-methyl-beta-cyclodextrin (TMbeta-CD) are described. The association constants vary from 112 for harmine/DMbeta-CD to 418 for harmane/HPbeta-CD. The magnitude of the interactions between the host and the guest molecules depends on the chemical and geometrical characteristics of the guest molecules and therefore the association constants vary for the different cyclodextrin complexes. The steric hindrance is higher in the case of harmine due to the presence of methoxy group on the beta-carboline ring. The association obtained for the harmane complexes is stronger than the one observed for harmine complexes except in the case of harmine/TMbeta-CD. Important differences in the association constants were observed depending on the experimental variable used in the calculations (absolute value of fluorescence intensity or the ratio between the fluorescence intensities corresponding to the neutral and cationic forms). When fluorescence intensity values were considered, the association constants were higher than when the ratio of the emission intensity for the cationic and neutral species was used. These differences are a consequence of the co-existence of acid-base equilibria in the ground and in excited states together with the complexation equilibria. The existence of a proton transfer reaction in the excited states of harmane or harmine implies the need for the experimental dialysis procedure for separation of the complexes from free harmane or harmine. Such methodology allows quantitative results for stoichiometry determinations to be obtained, which show the existence of both 1:1 and 1:2 beta-carboline alkaloid:CD complexes with different solubility properties.

Is the ground state of Yang-Mills theory Coulombic?

NASA Astrophysics Data System (ADS)

Heinzl, T.; Ilderton, A.; Langfeld, K.; Lavelle, M.; Lutz, W.; McMullan, D.

2008-08-01

We study trial states modelling the heavy quark-antiquark ground state in SU(2) Yang-Mills theory. A state describing the flux tube between quarks as a thin string of glue is found to be a poor description of the continuum ground state; the infinitesimal thickness of the string leads to UV artifacts which suppress the overlap with the ground state. Contrastingly, a state which surrounds the quarks with non-Abelian Coulomb fields is found to have a good overlap with the ground state for all charge separations. In fact, the overlap increases as the lattice regulator is removed. This opens up the possibility that the Coulomb state is the true ground state in the continuum limit.

Ground-water resources data for Warren County, Pennsylvania

USGS Publications Warehouse

Moore, M.E.; Buckwalter, T.F.

1996-01-01

This report presents lithologic, hydrologic, and chemical data collected during a study of the ground-water resources of Warren County, Pa. The study was conducted during 1983-90 by the U.S. Geological Survey, in cooperation with the Pennsylvania Department of Conservation and Natural Resources, Bureau of Topographic and Geologic Survey, and the Warren County Commissioners. The data include information on aquifers, water levels, and yields for about 600 wells, and records for 57 springs. Descriptions of aquifer lithology and chemical analyses of water samples collected at well and spring sites are provided. Chemical analyses include major cations, anions, nutrients, and selected trace elements. Also included are data on concentrations of volatile organic compounds, dissolved methane, ethane, propane, and total organic carbon. The report presents a summary of the source and significance of selected chemical constituents in ground water, a listing of Federal drinking water standards, and information on selected methods of removing or reducing concentrations of undesirable chemical constituents from water. Daily ground- water levels for five observation wells are tabulated. Maps of Warren County show the location of townships, boroughs, and 7-1/2-minute quadrangles. Data-collection sites are shown on 18 figures. A glossary is provided for readers unfamiliar with ground-water terminology.

Monovalent Cation Activation of the Radical SAM Enzyme Pyruvate Formate-Lyase Activating Enzyme.

PubMed

Shisler, Krista A; Hutcheson, Rachel U; Horitani, Masaki; Duschene, Kaitlin S; Crain, Adam V; Byer, Amanda S; Shepard, Eric M; Rasmussen, Ashley; Yang, Jian; Broderick, William E; Vey, Jessica L; Drennan, Catherine L; Hoffman, Brian M; Broderick, Joan B

2017-08-30

Pyruvate formate-lyase activating enzyme (PFL-AE) is a radical S-adenosyl-l-methionine (SAM) enzyme that installs a catalytically essential glycyl radical on pyruvate formate-lyase. We show that PFL-AE binds a catalytically essential monovalent cation at its active site, yet another parallel with B 12 enzymes, and we characterize this cation site by a combination of structural, biochemical, and spectroscopic approaches. Refinement of the PFL-AE crystal structure reveals Na + as the most likely ion present in the solved structures, and pulsed electron nuclear double resonance (ENDOR) demonstrates that the same cation site is occupied by 23 Na in the solution state of the as-isolated enzyme. A SAM carboxylate-oxygen is an M + ligand, and EPR and circular dichroism spectroscopies reveal that both the site occupancy and the identity of the cation perturb the electronic properties of the SAM-chelated iron-sulfur cluster. ENDOR studies of the PFL-AE/[ 13 C-methyl]-SAM complex show that the target sulfonium positioning varies with the cation, while the observation of an isotropic hyperfine coupling to the cation by ENDOR measurements establishes its intimate, SAM-mediated interaction with the cluster. This monovalent cation site controls enzyme activity: (i) PFL-AE in the absence of any simple monovalent cations has little-no activity; and (ii) among monocations, going down Group 1 of the periodic table from Li + to Cs + , PFL-AE activity sharply maximizes at K + , with NH 4 + closely matching the efficacy of K + . PFL-AE is thus a type I M + -activated enzyme whose M + controls reactivity by interactions with the cosubstrate, SAM, which is bound to the catalytic iron-sulfur cluster.

Sn Cation Valency Dependence in Cation Exchange Reactions Involving Cu2-xSe Nanocrystals

PubMed Central

2014-01-01

We studied cation exchange reactions in colloidal Cu2-xSe nanocrystals (NCs) involving the replacement of Cu+ cations with either Sn2+ or Sn4+ cations. This is a model system in several aspects: first, the +2 and +4 oxidation states for tin are relatively stable; in addition, the phase of the Cu2-xSe NCs remains cubic regardless of the degree of copper deficiency (that is, “x”) in the NC lattice. Also, Sn4+ ions are comparable in size to the Cu+ ions, while Sn2+ ones are much larger. We show here that the valency of the entering Sn ions dictates the structure and composition not only of the final products but also of the intermediate steps of the exchange. When Sn4+ cations are used, alloyed Cu2–4ySnySe NCs (with y ≤ 0.33) are formed as intermediates, with almost no distortion of the anion framework, apart from a small contraction. In this exchange reaction the final stoichiometry of the NCs cannot go beyond Cu0.66Sn0.33Se (that is Cu2SnSe3), as any further replacement of Cu+ cations with Sn4+ cations would require a drastic reorganization of the anion framework, which is not possible at the reaction conditions of the experiments. When instead Sn2+ cations are employed, SnSe NCs are formed, mostly in the orthorhombic phase, with significant, albeit not drastic, distortion of the anion framework. Intermediate steps in this exchange reaction are represented by Janus-type Cu2-xSe/SnSe heterostructures, with no Cu–Sn–Se alloys. PMID:25340627

Switchable antifouling coatings and uses thereof

DOEpatents

Denton, Michele L. Baca; Dirk, Shawn M.; Johnson, Ross Stefan

2017-02-28

The present invention relates to antifouling coatings capable of being switched by using heat or ultraviolet light. Prior to switching, the coating includes an onium cation component having antimicrobial and antibacterial properties. Upon switching, the coating is converted to a conjugated polymer state, and the cationic component is released with any adsorbed biofilm layer. Thus, the coatings herein have switchable and releasable properties. Methods of making and using such coatings are also described.

Closed Loop System Identification with Genetic Algorithms

NASA Technical Reports Server (NTRS)

Whorton, Mark S.

2004-01-01

High performance control design for a flexible space structure is challenging since high fidelity plant models are di.cult to obtain a priori. Uncertainty in the control design models typically require a very robust, low performance control design which must be tuned on-orbit to achieve the required performance. Closed loop system identi.cation is often required to obtain a multivariable open loop plant model based on closed-loop response data. In order to provide an accurate initial plant model to guarantee convergence for standard local optimization methods, this paper presents a global parameter optimization method using genetic algorithms. A minimal representation of the state space dynamics is employed to mitigate the non-uniqueness and over-parameterization of general state space realizations. This control-relevant system identi.cation procedure stresses the joint nature of the system identi.cation and control design problem by seeking to obtain a model that minimizes the di.erence between the predicted and actual closed-loop performance.

Excited triplet state of N-(9-methylpurin-6-yl)pyridinium cation as an efficient photosensitizer in the oxidation of sulfur-containing amino acids. Laser flash and steady-state photolysis studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marciniak, B.; Hug, G.L.; Bobrowski, K.

1995-01-11

In this paper, we present and discuss the results of a detailed mechanistic study of the photosensitized oxidation of sulfur-containing amino acids by N-(9-methylpurin-6-yl)pyridinium cations in aqueous solution. The results provide data on the photoreactivity of the pyridinium salts (derived from the purine bases) in the presence of the electron donors such as sulfur-containing organic compounds and give new experimental evidence for the general mechanism of the sensitized photooxidation of thioethers proposed previously. 39 refs., 6 figs., 2 tabs.

Electromers of the benzene dimer radical cation.

PubMed

Błoch-Mechkour, Anna; Bally, Thomas

2015-04-28

The well-studied benzene dimer radical cation, which is prototypical for this class of species, has been reinvestigated computationally. Thereby it turned out that both the σ-hemibonded and the half-shifted sandwich structures of the benzene dimer cation, which had been independently proposed, represent stationary points on the B2PLYP-D potential energy surfaces. However, these structures belong to distinct electronic states, both of which are associated with potential surfaces that are very flat with regard to rotation of the two benzene rings in an opposite sense relative to each other. The surfaces of these two "electromers" of the benzene dimer cation are separated by only 3-4 kcal mol(-1) and do not intersect along the rotation coordinate, which represents a rather unique electronic structure situation. When moving on either of the two surfaces the title complex is an extremely fluxional species, in spite of its being bound by over 20 kcal mol(-1).

Ground-Water Quality in the Genesee River Basin, New York, 2005-2006

USGS Publications Warehouse

Eckhardt, David A.V.; Reddy, J.E.; Tamulonis, Kathryn L.

2007-01-01

Water samples were collected from 7 community water system wells and 15 private domestic wells throughout the Genesee River Basin in New York State (downstream from the Pennsylvania border) from October 2005 through March 2006 and analyzed to characterize the chemical quality of ground water in the basin. The wells were selected to represent areas of greatest ground-water use and to provide a representative sampling from the 2,439 square-mile basin area in New York. Samples were analyzed for five physical properties and 226 constituents that included nutrients, major inorganic ions, trace elements, radionuclides, pesticides, volatile organic compounds, and bacteria. The results show that ground water used for drinking water is generally of good quality in the Genesee River Basin, although concentrations of seven constituents exceeded drinking water standards. The cations that were detected in the highest concentrations were calcium, magnesium, and sodium; the anions that were detected in the greatest concentrations were bicarbonate, chloride, and sulfate. The predominant nutrient was nitrate, and nitrate concentrations were greater in samples from sand and gravel aquifers than in samples from bedrock aquifers. The trace elements barium, boron, cobalt, copper, and nickel were detected in every sample; the highest concentrations were barium, boron, chromium, iron, manganese, strontium, and lithium. Fourteen pesticides including seven pesticide degradates were detected in water from 12 of the 22 wells, but none of the concentrations exceeded Maximum Contaminant Levels (MCLs). Eight volatile organic compounds (VOCs) were detected in six samples, but none of the concentrations exceeded MCLs. Seven chemical analytes and three types of bacteria were present in concentrations that exceeded Federal and New York State water-quality standards, which are typically identical. Sulfate concentrations exceeded the U.S. Environmental Protection Agency (USEPA) Secondary Maximum Contaminant Level (SMCL) of 250 milligrams per liter (mg/L) in three samples; the chloride SMCL (250 mg/L) was exceeded in one sample. Sodium concentrations exceeded the USEPA Drinking Water Health Advisory of 60 mg/L in five samples. The SMCL for iron (300 ug/L) was exceeded in 11 filtered samples; the USEPA SMCL for manganese (50 ug/L) was exceeded in 10 filtered samples, and the New York State MCL (300 ug/L) was exceeded in 1 filtered sample. The MCL for aluminum (200 ug/L) was exceeded in 1 sample, and the MCL for arsenic (10 ug/L) was exceeded in 1 sample. Radon-222 exceeded the proposed USEPA MCL of 300 picocuries per liter in 16 samples. Any detection of total coliform or fecal coliform bacteria is considered a violation of New York State health regulations; in this study, total coliform was detected in eight samples; fecal coliform was detected in two samples, and Escherichia coli was detected in one sample.

An ultrafast spectroscopic and quantum mechanical investigation of multiple emissions in push-pull pyridinium derivatives bearing different electron donors.

PubMed

Carlotti, B; Benassi, E; Cesaretti, A; Fortuna, C G; Spalletti, A; Barone, V; Elisei, F

2015-08-28

A joint experimental and theoretical approach, involving state-of-the-art femtosecond fluorescence up-conversion measurements and quantum mechanical computations including vibronic effects, was employed to get a deep insight into the excited state dynamics of two cationic dipolar chromophores (Donor-π-Acceptor(+)) where the electron deficient portion is a N-methyl pyridinium and the electron donor a trimethoxyphenyl or a pyrene, respectively. The ultrafast spectroscopic investigation, and the time resolved area normalised emission spectra in particular, revealed a peculiar multiple emissive behaviour and allowed the distinct emitting states to be remarkably distinguished from solvation dynamics, occurring in water in a similar timescale. The two and three emissions experimentally detected for the trimethoxyphenyl and pyrene derivatives, respectively, were associated with specific local emissive minima in the potential energy surface of S1 on the ground of quantum-mechanical calculations. A low polar and planar Locally Excited (LE) state together with a highly polar and Twisted Intramolecular Charge Transfer (TICT) state is identified to be responsible for the dual emission of the trimethoxyphenyl compound. Interestingly, the more complex photobehaviour of the pyrenyl derivative was explained considering the contribution to the fluorescence coming not only from the LE and TICT states but also from a nearly Planar Intramolecular Charge Transfer (PICT) state, with both the TICT and the PICT generated from LE by progressive torsion around the quasi-single bond between the methylpyridinium and the ethene bridge. These findings point to an interconversion between rotamers for the pyrene compound taking place in its excited state against the Non-equilibrated Excited Rotamers (NEER) principle.

[The nature of pacemaker activity].

PubMed

Kabakov, A Iu

1991-01-01

A general equation of the membrane resting potential (RP) has been derived for closed cell membrane (CM) model. It is shown that Na,K-ATPase of cardiomyocytes is in the antielectrogenic phase. A hypothesis is proposed: a pacemaker cell is an excitable cell, which has RP corresponding to the given activity of Na,K-ATPase and non-activated cationic conductivities of CM higher than the activation threshold of Na-channels. The equation of the equipotential levels of the membrane RP on the surface of the cationic conductivities has been derived. It is shown that the substances (e. g. neuromediator) that change the membrane cation permeability are able to depolarize or to hyperpolarize CM. The direction of polarization is dependent on the state of the cell electrogenic system. The following factors promote the hyperpolarizing effect of the magnifying cation permeability substances: 1) high activity of Na,K-ATPase, 2) low background cation permeability of CM (among their number the integrity of CM) and 3) high ratio of the potassium permeability alteration in respect to that of sodium which is evoked by the substance (delta gK/delta gNa).

A Cation-containing Polymer Anion Exchange Membrane based on Poly(norbornene)

NASA Astrophysics Data System (ADS)

Beyer, Frederick; Price, Samuel; Ren, Xiaoming; Savage, Alice

Cation-containing polymers are being studied widely for use as anion exchange membranes (AEMs) in alkaline fuel cells (AFCs) because AEMs offer a number of potential benefits including allowing a solid state device and elimination of the carbonate poisoning problem. The successful AEM will combine high performance from several orthogonal properties, having robust mechanical strength even when wet, high hydroxide conductivity, and the high chemical stability required for long device lifetimes. In this study, we have synthesized a model cationic polymer that combines three of the key advantages of Nafion. The polymer backbone based on semicrystalline atactic poly(norbornene) offers good mechanical properties. A flexible, ether-based tether between the backbone and fixed cation charged species (quaternary ammonium) should provide the low-Tg, hydrophilic environment required to facilitate OH- transport. Finally, methyl groups have been added at the beta position relative to the quaternary ammonium cation to prevent Hoffman elimination, one mechanism by which AEMs are neutralized in a high pH environment. In this poster, we will present our findings on mechanical properties, morphology, charge transport, and chemical stability of this material.

Nongeminate Radiative Recombination of Free Charges in Cation-Exchanged PbS Quantum Dot Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marshall, Ashley R.; Beard, Matthew C.; Johnson, Justin C.

2016-06-01

Using photoluminescence (PL) spectroscopy we explore the radiative recombination pathways in PbS quantum dots (QDs) synthesized by two methods. We compare conventionally synthesized PbS from a PbO precursor to PbS synthesized using cation-exchange from CdS QDs. We show that strongly coupled films of PbS QDs from the cation-exchange luminesce with significant efficiency at room temperature. This is in stark contrast to conventional PbS QDs, which have exceedingly weak room temperature emission. Moreover, the power dependence of the emission is quadratic, indicating bimolecular radiative recombination that is reasonably competitive with trap-assisted recombination, a feature previously unreported in coupled PbS QD films.more » We interpret these results in terms of a greatly reduced defect concentration for cation-exchanged QDs that mitigates the influence of trap-assisted recombination. Cation-exchanged QDs have recently been employed in highly efficient and air-stable lead chalcogenide QD devices, and the reduced number of trap states inferred here may lead to improved current collection and higher open circuit voltage.« less

Nongeminate radiative recombination of free charges in cation-exchanged PbS quantum dot films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marshall, Ashley R.; Beard, Matthew C.; Johnson, Justin C.

2016-06-01

Using photoluminescence (PL) spectroscopy we explore the radiative recombination pathways in PbS quantum dots (QDs) synthesized by two methods. We compare conventionally synthesized PbS from a PbO precursor to PbS synthesized using cation-exchange from CdS QDs. We show that strongly coupled films of PbS QDs from the cation-exchange luminesce with significant efficiency at room temperature. This is in stark contrast to conventional PbS QDs, which have exceedingly weak room temperature emission. Moreover, the power dependence of the emission is quadratic, indicating bimolecular radiative recombination that is reasonably competitive with trap-assisted recombination, a feature previously unreported in coupled PbS QD films.more » We interpret these results in terms of a greatly reduced defect concentration for cation-exchanged QDs that mitigates the influence of trap-assisted recombination. Cation-exchanged QDs have recently been employed in highly efficient and air-stable lead chalcogenide QD devices, and the reduced number of trap states inferred here may lead to improved current collection and higher open circuit voltage.« less

Hydrogeology of the northern segment of the Edwards aquifer, Austin region, Texas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Senger, R.K.; Collins, E.W.; Kreitler, C.W.

1990-01-01

This book reports on geologic mapping and fracture analysis of Lower Cretaceous Edwards aquifer strata conducted to provide a better understanding of the geology of the Balcones Fault Zone as it relates to the hydrogeology of the aquifer's northern segment. Hydrochemical, water-level, and precipitation data were studied to evaluate ground-water flow characteristics, recharge and discharge mechanisms, and the hydrochemical evolution of ground water in the Edwards aquifer. The authors found that ground water generally flows eastward, and main discharge of the unconfined, fast-flowing system occurs along fractures through springs and seeps at the major creeks and rivers in the Georgetownmore » area. Some recharge water moves downdip past these springs into a confined section farther east, along a much reduced hydraulic gradient, and discharges by leaking through the confining units. Hydrochemistry of Edwards ground water indicates an evolution from a Ca-HCO{sub 3} and Ca-Mg-HCO{sub 3} to a mixed-cation-HCO{sub 3} farther downdip to a Na-HCO{sub 3}, and finally to a Na-mixed-anion-type water.« less

Theoretical investigation of the reaction of Mn+ with ethylene oxide.

PubMed

Li, Yuanyuan; Guo, Wenyue; Zhao, Lianming; Liu, Zhaochun; Lu, Xiaoqing; Shan, Honghong

2012-01-12

The potential energy surfaces of Mn(+) reaction with ethylene oxide in both the septet and quintet states are investigated at the B3LYP/DZVP level of theory. The reaction paths leading to the products of MnO(+), MnO, MnCH(2)(+), MnCH(3), and MnH(+) are described in detail. Two types of encounter complexes of Mn(+) with ethylene oxide are formed because of attachments of the metal at different sites of ethylene oxide, i.e., the O atom and the CC bond. Mn(+) would insert into a C-O bond or the C-C bond of ethylene oxide to form two different intermediates prior to forming various products. MnO(+)/MnO and MnH(+) are formed in the C-O activation mechanism, while both C-O and C-C activations account for the MnCH(2)(+)/MnCH(3) formation. Products MnO(+), MnCH(2)(+), and MnH(+) could be formed adiabatically on the quintet surface, while formation of MnO and MnCH(3) is endothermic on the PESs with both spins. In agreement with the experimental observations, the excited state a(5)D is calculated to be more reactive than the ground state a(7)S. This theoretical work sheds new light on the experimental observations and provides fundamental understanding of the reaction mechanism of ethylene oxide with transition metal cations.

Structures of Hydrated Alkali Metal Cations, M+(H2O)nAr (m = Li, Na, K, rb and Cs, n = 3-5), Using Infrared Photodissociation Spectroscopy and Thermodynamic Analysis

NASA Astrophysics Data System (ADS)

Ke, Haochen; van der Linde, Christian; Lisy, James M.

2014-06-01

Alkali metal cations play vital roles in chemical and biochemical systems. Lithium is widely used in psychiatric treatment of manic states and bipolar disorder; Sodium and potassium are essential elements, having major biological roles as electrolytes, balancing osmotic pressure on body cells and assisting the electroneurographic signal transmission; Rubidium has seen increasing usage as a supplementation for manic depression and depression treatment; Cesium doped compounds are used as essential catalysts in chemical production and organic synthesis. Since hydrated alkali metal cations are ubiquitous and the basic form of the alkali metal cations in chemical and biochemical systems, their structural and thermodynamic properties serve as the foundation for modeling more complex chemical and biochemical processes, such as ion transport and ion size-selectivity of ionophores and protein channels. By combining mass spectrometry and infrared photodissociation spectroscopy, we have characterized the structures and thermodynamic properties of the hydrated alkali metal cations, i.e. M+(H2O)nAr, (M = Li, Na, K, Rb and Cs, n = 3-5). Ab initio calculations and RRKM-EE (evaporative ensemble) calculations were used to assist in the spectral assignments and thermodynamic analysis. Results showed that the structures of hydrated alkali metal cations were determined predominantly by the competition between non-covalent interactions, i.e. the water---water hydrogen bonding interactions and the water---cation electrostatic interactions. This balance, however, is very delicate and small changes, i.e. different cations, different levels of hydration and different effective temperatures clearly impact the balance.

Electrical properties of AC{sub 3}B{sub 4}O{sub 12}-type perovskite ceramics with different cation vacancies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Guizhong; Chen, Zhi; Sun, Xiaojun

2015-05-15

Highlights: • AC{sub 3}B{sub 4}O{sub 12} perovskite with different concentration cation vacancies were prepared. • Cell parameter decreases with the increase of concentration of cation vacancies. • PTCO and CTO remain high dielectric permittivity but depress loss greatly. • Dielectric loss associates with cation vacancies and motion of oxygen vacancies. - Abstract: AC{sub 3}B{sub 4}O{sub 12}-type perovskite CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO), □{sub 0.34}Pr{sub 0.67}Cu{sub 3}Ti{sub 4}O{sub 12} (PCTO), □{sub 1}Cu{sub 3}Ta{sub 2}Ti{sub 2}O{sub 12} (CTTO), □{sub 2}Cu{sub 2}Ta{sub 4}O{sub 12} (CTO) ceramics with different concentration cation vacancies were prepared through traditional solid state reaction method. X-ray diffraction analysis indicatedmore » that CCTO and PCTO are perovskite cubic with space group Im-3 (no. 204) while CTTO and CTO are Pm-3 (no. 200). Cell parameter of the samples dramatically increases with the increase of cation vacancies. Dielectric permittivity of them maintains very high value of ∼10{sup 4} from room temperature to 550 K but the dielectric loss is depressed with the increase of cation vacancies in the same space group. The dielectric properties and conductivity behavior were described by the Debye relaxation and the universal dielectric response, respectively. The effect mechanism of cation vacancy and crystal structure on carrier transposition were discussed.« less

Shape of Multireference, Equation-of-Motion Coupled-Cluster, and Density Functional Theory Potential Energy Surfaces at a Conical Intersection.

PubMed

Gozem, Samer; Melaccio, Federico; Valentini, Alessio; Filatov, Michael; Huix-Rotllant, Miquel; Ferré, Nicolas; Frutos, Luis Manuel; Angeli, Celestino; Krylov, Anna I; Granovsky, Alexander A; Lindh, Roland; Olivucci, Massimo

2014-08-12

We report and characterize ground-state and excited-state potential energy profiles using a variety of electronic structure methods along a loop lying on the branching plane associated with a conical intersection (CI) of a reduced retinal model, the penta-2,4-dieniminium cation (PSB3). Whereas the performance of the equation-of-motion coupled-cluster, density functional theory, and multireference methods had been tested along the excited- and ground-state paths of PSB3 in our earlier work, the ability of these methods to correctly describe the potential energy surface shape along a CI branching plane has not yet been investigated. This is the focus of the present contribution. We find, in agreement with earlier studies by others, that standard time-dependent DFT (TDDFT) does not yield the correct two-dimensional (i.e., conical) crossing along the branching plane but rather a one-dimensional (i.e., linear) crossing along the same plane. The same type of behavior is found for SS-CASPT2(IPEA=0), SS-CASPT2(IPEA=0.25), spin-projected SF-TDDFT, EOM-SF-CCSD, and, finally, for the reference MRCISD+Q method. In contrast, we found that MRCISD, CASSCF, MS-CASPT2(IPEA=0), MS-CASPT2(IPEA=0.25), XMCQDPT2, QD-NEVPT2, non-spin-projected SF-TDDFT, and SI-SA-REKS yield the expected conical crossing. To assess the effect of the different crossing topologies (i.e., linear or conical) on the PSB3 photoisomerization efficiency, we discuss the results of 100 semiclassical trajectories computed by CASSCF and SS-CASPT2(IPEA=0.25) for a PSB3 derivative. We show that for the same initial conditions, the two methods yield similar dynamics leading to isomerization quantum yields that differ by only a few percent.

The fragmentation of ethanol cation under an electric field: An ab initio/RRKM study

NASA Astrophysics Data System (ADS)

Lu, Hsiu-Feng; Li, F.-Y.; Lin, Chun-Chin; Nagaya, K.; Chao, Ito; Lin, S. H.

2007-08-01

We present a theoretical study of ethanol cation under an electric field due to the existence of laser field in order to understand the influence of electric field on the mass spectrum of ethanol. The electric field was applied to the four major reaction channels of an ethanol cation, such as the conversion between C 2H 5OH + and c-C 2H 5OH +, CH 3-elimination and two α-H-eliminations, respectively. The correlation between product distribution and field strength is quite complex due to the different responses of the reactants and transition states toward the external electric field. This makes the product distribution change as field strength varies.

Frustration under pressure: Exotic magnetism in new pyrochlore oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiebe, C. R.; Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2; Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1

2015-04-01

Pyrochlore structures, of chemical formula A{sub 2}B{sub 2}O{sub 7} (A and B are typically trivalent and tetravalent ions, respectively), have been the focus of much activity in the condensed matter community due to the ease of substitution of rare earth and transition metal ions upon the two interpenetrating corner-shared tetrahedral lattices. Over the last few decades, superconductivity, spin liquid states, spin ice states, glassy states in the absence of chemical disorder, and metal-insulator transitions have all been discovered in these materials. Geometric frustration plays a role in the relevant physics of all of these phenomena. In the search for newmore » pyrochlore materials, it is the R{sub A}/R{sub B} cation radius ratio which determines the stability of the lattice over the defect fluorite structure in the lower limit. Under ambient pressure, the pyrochlores are stable for 1.36 ≤ R{sub A}/R{sub B} ≤ 1.71. However, using high pressure synthesis techniques (1-10 GPa of pressure), metastable pyrochlores exist up to R{sub A}/R{sub B} = 2.30. Many of these compounds are stable on a timescale of years after synthesis, and provide a means to greatly enhance exchange, and thus test theories of quantum magnetism and search for new phenomena. Within this article, we review new pyrochlore compounds synthesized via high pressure techniques and show how the ground states are extremely sensitive to chemical pressure.« less

Conformation-Specific Infrared and Ultraviolet Spectroscopy of α-METHYLBENZYL Radical: Probing the State-Dependent Effects of Methyl Rocking against a Radical Site

NASA Astrophysics Data System (ADS)

Kidwell, Nathanael M.; Mehta, Deepali N.; Zwier, Timothy S.; Reilly, Neil J.; Kokkin, Damian L.; McCarthy, Michael C.

2012-06-01

Combustion processes involve a myriad of complex reaction pathways which connect smaller precursors to larger polyaromatic hydrocarbons, many of which are still unknown. In particular, benzyl-type radicals play an important role in combustible fuels due to their intrinsic resonance stabilization and consequent increase in relative concentration. Here, we present a study of the vibronic spectroscopy of α-Methylbenzyl radical (α-MeBz), in which the orientation of the methyl group adjacent to the radical site responds to the electronic interaction extending from the conjugated π-system. Probing the isolated radical, produced in an electrical discharge under jet-cooled conditions, the two-color resonant two-photon ionization, fluorescence excitation, and dispersed fluorescence spectra were obtained in order to determine the ground and excited state barriers to internal rotation and the angular change associated with electronic excitation. Resonant ion-dip infrared spectroscopy (RIDIRS) has also been implemented to elucidate the infrared signatures in the alkyl and aromatic CH stretch regions in order to probe in a complementary way the state-dependent conformational preferences of α-MeBz. We will show that the D0- and D1-RIDIR spectra report sensitively on the strong coupling between the CH stretch vibrations and the C_α-C_β torsional geometry. Furthermore, photoionization efficiency scans were carried out to reveal the adiabatic ionization threshold of α-MeBz and the quantized levels present in the radical cation state.

Space Fence Ground-Based Radar System Increment 1 (Space Fence Inc 1)

DTIC Science & Technology

2015-12-01

Net - Centric Data Strategy and Net-Centric Services Strategy, and the principles and rules identified in the DoD IEA, excepting tactical and...Centric Data Strategy and Net- Centric Services Strategy, and the principles and rules identified in the DoD IEA, excepting tactical and non-IP...Strategy, and the principles and rules identified in the DoD IEA, excepting tactical and non-IP communi- cations. Compliant with TBD Space Fence must

An Independent Evaluation of the Engineer Proving Ground.

DTIC Science & Technology

1995-03-01

includes such prestigious hotels as the Ritz - Carlton . The Reston/Dulles corridor includes a major international airport. As such, one would expect...Development Plan 2-9 Next Steps 2-10 Chapter 3. Market Analysis of Planned EPG Land Uses 3-1 Office Space 3-1 Housing 3-10 Hotels /Motels 3-13... hotel and retail space. The proposed land use allo- cation is currently under review by Fairfax County. Table 2-1 summarizes the Army’s proposed

An Analysis of the Centaur Ground Processing System at the Kennedy Space Center/Cape Canaveral AFS.

DTIC Science & Technology

1985-12-01

SPONSORING 8tn OFF ICE SYMBOL 9 . PROCUREMENT INSTRUMENT IDENTIFiCATION NUMBER 0 RG4NICATICN II appsicable, * cADDRESS C-;t,. S:sI. and~ /11’ L,a,, .0...The PERT Network................8 2. The SLAM Model................. 9 F. Outline of the Paper................13 Ii. The Shuttle/Centaur G System...104 9 . AWAIT NODE..................104 10. FREE NODE...................105 11. ASSIGN NODE..................105 w 12. COLCT NODE

The Shock and Vibration Digest. Volume 17. Number 7

DTIC Science & Technology

1985-07-01

WORDS: Violins, Modal analysis Centro de Estudios c Investigaciones Tec- nicas de Guipu’coa, Barrio Ibaeta SIN, The vibrational behavior of a violin is...necessary in the transaction of business required by law of the De - partment of the Navy. Funds for printing of this publi- cation have been approved by...ground motion, amplified by the and much work has been done to improve dynamic response of a structure, that do elastomers. Other systems have been de

Nitranilic acid hexahydrate, a novel benchmark system of the Zundel cation in an intrinsically asymmetric environment: spectroscopic features and hydrogen bond dynamics characterised by experimental and theoretical methods.

PubMed

Molčanov, Krešimir; Stare, Jernej; Vener, Mikhail V; Kojić-Prodić, Biserka; Mali, Gregor; Grdadolnik, Jože; Mohaček-Grošev, Vlasta

2014-01-21

Nitranilic acid (2,5-dihydroxy-3,6-dinitro-2,5-cyclohexadiene-1,4-dione) as a strong dibasic acid in acidic aqueous media creates the Zundel cation, H5O2(+). The structural unit in a crystal comprises (H5O2)2(+) (2,5-dihydroxy-3,6-dinitro-1,4-benzoquinonate)(2-) dihydrate where the Zundel cation reveals no symmetry, being an ideal case for studying proton dynamics and its stability. The Zundel cation and proton transfer dynamics are studied by variable-temperature X-ray diffraction, IR and solid-state NMR spectroscopy, and various quantum chemical methods, including periodic DFT calculations, ab initio molecular dynamics simulation, and quantization of nuclear motion along three fully coupled internal coordinates. The Zundel cation features a short H-bond with the O···O distance of 2.433(2) Å with an asymmetric placement of hydrogen. The proton potential is of a single well type and, due to the non-symmetric surroundings, of asymmetric shape. The formation of the Zundel cation is facilitated by the electronegative NO2 groups. The employed spectroscopic techniques supported by calculations confirm the presence of a short H-bond with a complex proton dynamics.

Density-Functional-Theory Modeling of Cation Diffusion in Bulk La 1 - x Sr x MnO 3 ± δ ( x = 0.0 – 0.25 ) for Solid-Oxide Fuel-Cell Cathodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Yueh-Lin; Duan, Yuhua; Morgan, Dane

In this work, the A - and B -site cation migration pathways involving defect complexes in bulk La 1-xSr xMnO 3±δ (LSM) at x = 0.0-0.25 are investigated based on density-functional-theory modeling for solid-oxide fuel-cell (SOFC) cathode applications. We propose a dominant A -site cation migration mechanism which involves an A -site cation (e.g., Lamore » $$x\\atop{A}$$) V A"' of a V A"' -V B"' cluster, where La$$x\\atop{A}$$, V A"' and V B"' are La 3+, A-site vacancy, and B-site vacancy in bulk LSM, respectively, and V A"' -V B"' is the first nearest-neighbor V A"' and V B"' pair. This hop exhibits an approximately 1.6-eV migration barrier as compared to approximately 2.9 eV of the La$$x\\atop{A}$$ hop into a V A"'. This decrease in the cation migration barrier is attributed to the presence of the V B"' relieving the electrostatic repulsion and steric constraints to the migrating A-site cations in the transition-state image configurations.« less

Density-Functional-Theory Modeling of Cation Diffusion in Bulk La 1 - x Sr x MnO 3 ± δ ( x = 0.0 – 0.25 ) for Solid-Oxide Fuel-Cell Cathodes

DOE PAGES

Lee, Yueh-Lin; Duan, Yuhua; Morgan, Dane; ...

2017-10-04

In this work, the A - and B -site cation migration pathways involving defect complexes in bulk La 1-xSr xMnO 3±δ (LSM) at x = 0.0-0.25 are investigated based on density-functional-theory modeling for solid-oxide fuel-cell (SOFC) cathode applications. We propose a dominant A -site cation migration mechanism which involves an A -site cation (e.g., Lamore » $$x\\atop{A}$$) V A"' of a V A"' -V B"' cluster, where La$$x\\atop{A}$$, V A"' and V B"' are La 3+, A-site vacancy, and B-site vacancy in bulk LSM, respectively, and V A"' -V B"' is the first nearest-neighbor V A"' and V B"' pair. This hop exhibits an approximately 1.6-eV migration barrier as compared to approximately 2.9 eV of the La$$x\\atop{A}$$ hop into a V A"'. This decrease in the cation migration barrier is attributed to the presence of the V B"' relieving the electrostatic repulsion and steric constraints to the migrating A-site cations in the transition-state image configurations.« less

The iron-isotope fractionation dictated by the carboxylic functional: An ab-initio investigation

NASA Astrophysics Data System (ADS)

Ottonello, G.; Vetuschi Zuccolini, M.

2008-12-01

The ground-state geometries, electronic energies and vibrational properties of carboxylic complexes of iron were investigated both in vacuo and under the effect of a reaction field, to determine thermodynamic properties of iron-acetates and the role of the carboxylic functional on the isotopic imprinting of this metal in metalorganic complexation. The electronic energy, zero point corrections and thermal corrections of these substances at variational state were investigated at the DFT/B3LYP level of theory with different basis set expansions and the effect of the reaction field on the variational structures was investigated through the Polarized Continuun Model. Thermochemical cycle calculations, combined with solvation energy calculations and appropriate scaling from absolute to conventional properties allowed to compute the Gibbs free energy of formation from the elements of the investigated aqueous species and to select the best procedure to be applied in the successive vibrational analysis. The best compliance with the few existing thermodynamic data for these substances was obtained by coupling the gas phase calculations at DFT/B3LYP level with the [6-31G(d,p)]-[6-31G+(d,p)] (for cations and neutral molecules - anions; respectively) with solvation calculations adopting atomic radii optimized for the HF/6-31G(d) level of theory (UAHF). A vibrational analysis conducted on 54Fe, 56Fe, 57Fe and 58Fe gaseous isotopomers yielded reduced partition function ratios which increased not only with the nominal valence of the central cation, as expected, but, more importantly, with the extent of the complexation operated by the organic functional. Coupling thermodynamic data with separative effects it was shown that this last is controlled, as expected, by the relative bond strength of the complex in both aggregation states. Through the Integral Equation Formalism of the Polarized Continuum Model (IEFPCM) the effect of the ionic strength of the solution and of a T-dependent permittivity on the energy and separative effects of the solvated metalorganic complexes were analyzed in detail. The solvent effect in the standard state (hypothetical one-molal solution referred to infinite dilution; T = 298.15 K, P = 1 bar) is a limited reduction of the separative effects of all the isotopomeric couples. With an increase in T (and the concomitant decrease in the dielectric constant of the solvent) this effect diminishes progressively.

Rapid Discovery of Tribological Materials with Improved Performance Using Materials Informatics

DTIC Science & Technology

2014-03-10

of New Solid State Lubricants The recursive portioning model illustrated in Fig. 3 has been applied to about 500 compounds from the FileMakerPro...neighboring cation. Based on this assumption, the large cationic charge of mineral compounds indicates the number of anions tends to be larger than the...The formation of bond types is highly dependent on the difference of electronegativity (EN) between the two elements in the compound . For instance

State of Washington, Aquatic Plant Management Program: Design Memorandum.

DTIC Science & Technology

1979-10-01

3 days after appit- cation, fed ior 90 da- fo11-nIng haorst1ing equipment catIon. Swimming shouldt oe aplication . oring narventing opa- restricted...labor, maintenance, profit, capitalization of equipment costs, and mobilization -demobilization. 2/Local administrative costs are $2,000 for 100 acres...rental of two boats at a cost of $64/day each, mobilization - demobilization of equipment, and a capability of treating 100 acres/day. 2/The treatment boat

Analysis of ground-water-quality data of the Upper Colorado River basin, water years 1972-92

USGS Publications Warehouse

Apodaca, L.E.

1998-01-01

As part of the U.S. Geological Survey's National Water-Quality Assessment program, an analysis of the existing ground-water-quality data in the Upper Colorado River Basin study unit is necessary to provide information on the historic water-quality conditions. Analysis of the historical data provides information on the availability or lack of data and water-quality issues. The information gathered from the historical data will be used in the design of ground-water-quality studies in the basin. This report includes an analysis of the ground-water data (well and spring data) available for the Upper Colorado River Basin study unit from water years 1972 to 1992 for major cations and anions, metals and selected trace elements, and nutrients. The data used in the analysis of the ground-water quality in the Upper Colorado River Basin study unit were predominantly from the U.S. Geological Survey National Water Information System and the Colorado Department of Public Health and Environment data bases. A total of 212 sites representing alluvial aquifers and 187 sites representing bedrock aquifers were used in the analysis. The available data were not ideal for conducting a comprehensive basinwide water-quality assessment because of lack of sufficient geographical coverage.Evaluation of the ground-water data in the Upper Colorado River Basin study unit was based on the regional environmental setting, which describes the natural and human factors that can affect the water quality. In this report, the ground-water-quality information is evaluated on the basis of aquifers or potential aquifers (alluvial, Green River Formation, Mesaverde Group, Mancos Shale, Dakota Sandstone, Morrison Formation, Entrada Sandstone, Leadville Limestone, and Precambrian) and land-use classifications for alluvial aquifers.Most of the ground-water-quality data in the study unit were for major cations and anions and dissolved-solids concentrations. The aquifer with the highest median concentrations of major ions was the Mancos Shale. The U.S. Environmental Protection Agency secondary maximum contaminant level of 500 milligrams per liter for dissolved solids in drinking water was exceeded in about 75 percent of the samples from the Mancos Shale aquifer. The guideline by the Food and Agriculture Organization of the United States for irrigation water of 2,000 milligrams per liter was also exceeded by the median concentration from the Mancos Shale aquifer. For sulfate, the U.S. Environmental Protection Agency proposed maximum contaminant level of 500 milligrams per liter for drinking water was exceeded by the median concentration for the Mancos Shale aquifer. A total of 66 percent of the sites in the Mancos Shale aquifer exceeded the proposed maximum contaminant level.Metal and selected trace-element data were available for some sites, but most of these data also were below the detection limit. The median concentrations for iron for the selected aquifers and land-use classifications were below the U.S. Environmental Protection Agency secondary maximum contaminant level of 300 micrograms per liter in drinking water. Median concentration of manganese for the Mancos Shale exceeded the U.S. Environmental Protection Agency secondary maximum contaminant level of 50 micrograms per liter in drinking water. The highest selenium concentrations were in the alluvial aquifer and were associated with rangeland. However, about 22 percent of the selenium values from the Mancos Shale exceeded the U.S. Environmental Protection Agency maximum contaminant level of 50 micrograms per liter in drinking water.Few nutrient data were available for the study unit. The only nutrient species presented in this report were nitrate-plus-nitrite as nitrogen and orthophosphate. Median concentrations for nitrate-plus-nitrite as nitrogen were below the U.S. Environmental Protection Agency maximum contaminant level of 10 milligrams per liter in drinking water except for 0.02 percent of the sites in the al

Formation and fragmentation of quadruply charged molecular ions by intense femtosecond laser pulses.

PubMed

Yatsuhashi, Tomoyuki; Nakashima, Nobuaki

2010-07-22

We investigated the formation and fragmentation of multiply charged molecular ions of several aromatic molecules by intense nonresonant femtosecond laser pulses of 1.4 mum with a 130 fs pulse duration (up to 2 x 10(14) W cm(-2)). Quadruply charged states were produced for 2,3-benzofluorene and triphenylene molecular ion in large abundance, whereas naphthalene and 1,1'-binaphthyl resulted only in up to triply charged molecular ions. The laser wavelength was nonresonant with regard to the electronic transitions of the neutral molecules, and the degree of fragmentation was strongly correlated with the absorption of the singly charged cation radical. Little fragmentation was observed for naphthalene (off-resonant with cation), whereas heavy fragmentation was observed in the case of 1,1'-binaphthyl (resonant with cation). The degree of H(2) (2H) and 2H(2) (4H) elimination from molecular ions increased as the charge states increased in all the molecules examined. A striking difference was found between triply and quadruply charged 2,3-benzofluorene: significant suppression of molecular ions with loss of odd number of hydrogen was observed in the quadruply charged ions. The Coulomb explosion of protons in the quadruply charged state and succeeding fragmentation resulted in the formation of triply charged molecular ions with an odd number of hydrogens. The hydrogen elimination mechanism in the highly charged state is discussed.

Electronic Structure of p- and n-Type Doping Impurities in Cubic Gallium Nitride

NASA Astrophysics Data System (ADS)

Pentaleri, E. A.; Gubanov, V. A.; Fong, C. Y.; Klein, B. M.

1996-03-01

LMTO-TB calculations were performed to investigate the electronic structure of C, Be, Mg, Si, Zn, and Cd substitutional impurities in cubic GaN (c-GaN). The calculations used 128-site supercells consisting of 64-atoms. Empty spheres of two types occupied the remaining sites. Semi-core Ga 3d states were treated explicitly as valence states. Both amphoteric substitutions were considered for C and Si impurities, while only cation-site substitutions were considered for Be, Mg, Zn, and Cd. All metal impurities formed partially occupied impurity states at the VB edge, which may result in p-type conductivity. C and Si impurities substituted at anion sites form sharp resonances in the gap, and are inactive in creating either p- or n-type carriers. Likewise, cation-site C substitutions introduce to the middle of the band gap strongly localized states that are inactive in carrier formation. Cation-site Si substitutions form an impurity sub-band at the CB edge, leading to n-type conductivity. The DOS at the Fermi level for each impurity-doped c-GaN crystal is used to estimate the most effective p-type doping impurities. The wave-function composition, space, and energy localization is analyzed for different impurities via projections onto the orbital basis and atomic coordinational spheres, and by examining calculated charge-density distributions.

Molecular Dynamics Simulation Study of Solvent and State of Charge Effects on Solid-Phase Structure and Counterion Binding in a Nitroxide Radical Containing Polymer Energy Storage Material

DOE PAGES

Kemper, Travis W.; Gennett, Thomas; Larsen, Ross E.

2016-10-19

Here we performed molecular dynamics simulations to understand the effects of solvent swelling and state of charge (SOC) on the redox active, organic radical cathode material poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA). We show that the polar solvent acetonitrile primarily solvates the nitroxide radical without disrupting the packing of the (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) pendant groups of PTMA. We also simulated bulk PTMA in different SOC, 25%, 50%, 75%, and 100%, by converting the appropriate number of TEMPO groups to the cation charge state and adding BF 4 - counterions to the simulation. At each SOC the packing of PTMA, the solvent, and the counterionsmore » were examined. The binding of the anion to the nitroxide cation site was examined using the potential of mean force and found to be on the order of tens of meV, with a binding energy that decreased with increasing SOC. Additionally, we found that the cation state is stabilized by the presence of a nearby anion by more than 1 eV, and the implications of this stabilization on charge transport are discussed. Finally, we describe the implications of our results for how the SOC of an organic electrode affects electron and anion charge transport during the charging and discharging processes.« less

Ground-state splitting of ultrashallow thermal donors with negative central-cell corrections in silicon

NASA Astrophysics Data System (ADS)

Hara, Akito; Awano, Teruyoshi

2017-06-01

Ultrashallow thermal donors (USTDs), which consist of light element impurities such as carbon, hydrogen, and oxygen, have been found in Czochralski silicon (CZ Si) crystals. To the best of our knowledge, these are the shallowest hydrogen-like donors with negative central-cell corrections in Si. We observed the ground-state splitting of USTDs by far-infrared optical absorption at different temperatures. The upper ground-state levels are approximately 4 meV higher than the ground-state levels. This energy level splitting is also consistent with that obtained by thermal excitation from the ground state to the upper ground state. This is direct evidence that the wave function of the USTD ground state is made up of a linear combination of conduction band minimums.

Postsynthetic Doping of MnCl2 Molecules into Preformed CsPbBr3 Perovskite Nanocrystals via a Halide Exchange-Driven Cation Exchange.

PubMed

Huang, Guangguang; Wang, Chunlei; Xu, Shuhong; Zong, Shenfei; Lu, Ju; Wang, Zhuyuan; Lu, Changgui; Cui, Yiping

2017-08-01

Unlike widely used postsynthetic halide exchange for CsPbX 3 (X is halide) perovskite nanocrystals (NCs), cation exchange of Pb is of a great challenge due to the rigid nature of the Pb cationic sublattice. Actually, cation exchange has more potential for rendering NCs with peculiar properties. Herein, a novel halide exchange-driven cation exchange (HEDCE) strategy is developed to prepare dually emitting Mn-doped CsPb(Cl/Br) 3 NCs via postsynthetic replacement of partial Pb in preformed perovskite NCs. The basic idea for HEDCE is that the partial cation exchange of Pb by Mn has a large probability to occur as a concomitant result for opening the rigid halide octahedron structure around Pb during halide exchange. Compared to traditional ionic exchange, HEDCE is featured by proceeding of halide exchange and cation exchange at the same time and lattice site. The time and space requirements make only MnCl 2 molecules (rather than mixture of Mn and Cl ions) capable of doping into perovskite NCs. This special molecular doping nature results in a series of unusual phenomenon, including long reaction time, core-shell structured mid states with triple emission bands, and dopant molecules composition-dependent doping process. As-prepared dual-emitting Mn-doped CsPb(Cl/Br) 3 NCs are available for ratiometric temperature sensing. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Properties of complexes formed by Na(+), Mg(2+), and Fe(2+) binding with benzene molecules.

PubMed

Kolakkandy, Sujitha; Pratihar, Subha; Aquino, Adelia J A; Wang, Hai; Hase, William L

2014-10-09

A theoretical investigation was performed to study cation-π interactions in complexes of benzene (Bz) with cations, that is, M(z+)(Bz)n for M(z+) = Na(+), Mg(2+), Fe(2+) and n = 1-3, using MP2 theory with the 6-31+G* and 6-311++G** basis sets and the DFT/(B3LYP and B3LYP-D)/6-311++G** methods. Binding energies and structures of the complexes are reported. The splitting between the quintet and single states of the Fe(2+) complexes was found to depend on the number of benzene molecules in the complex and the complex's structure. All of the M(z+)(Bz) complexes prefer a half-sandwich geometry. A geometry with the cation sandwiched between the two benzene rings was found for the M(z+)(Bz)2 complexes, with the benzene rings either in an eclipsed or staggered conformation. An approximate cyclic structure, with the cation at its center, was found for three benzene molecules interacting with the cation. The cation-benzene binding energy is substantial and equal to 22, 108, and 151 kcal/mol for the Na(+)(Bz), Mg(2+)(Bz), and Fe(2+)(Bz) complexes, respectively. The strength of the interaction of the cation with an individual benzene molecule decreases as the number of benzene molecules bound to the cation increases; for example, it is 108 kcal/mol for Mg(2+)(Bz), but only 71 kcal/mol for Mg(2+)(Bz)3. There is a range of values for the M(z+)(Bz)n intermolecular vibrational frequencies; for example, they are ∼230-360 and ∼10-330 cm(-1) for the Mg(2+)(Bz) and Mg(2+)(Bz)3 complexes, respectively. Binding of the cation to benzene both red and blue shifts the benzene vibrational frequencies. This shifting is larger for the Mg(2+) and Fe(2+) complexes, as compared to those for Na(+), as a result of the former's stronger cation-benzene binding. The present study is an initial step to understand the possible importance of cation-π interactions for polycyclic aromatic hydrocarbon aggregation processes during soot formation.

Effect of Viscosity and Polar Properties of Solvent on Dynamics of Photoinduced Charge Transfer in BTA-1 Cation — Derivative of Thioflavin T

NASA Astrophysics Data System (ADS)

Gogoleva, S. D.; Stsiapura, V. I.

2018-05-01

It was found that the spectral and fluorescent properties of BTA-1C cation in protic and aprotic solvents differ. It was shown that for solutions in long-chain alcohols viscosity is the main factor that determines the dynamics of intramolecular charge transfer in the excited state of the BTA-1C molecule. In the case of aprotic solvents a correlation was found between the rate constant of twisted intramolecular charge transfer (TICT) during rotation of fragments of the molecule in relation to each other in the excited state and the solvent relaxation rate: k TICT 1/τ S .

Ionic configuration of copper ferrimanganites Cu 0.5Mn xFe 2.5- xO 4

NASA Astrophysics Data System (ADS)

Lenglet, M.; Kasperek, J.; Hannoyer, B.; Lopitaux, J.; d'Huysser, A.; Tellier, J. C.

1992-06-01

Mössbauer spectrometry, neutron diffraction, XANES, and XPS have led to the determination of the cation distributions of the system Cu 0.5Mn xFe 2.5- xO 4 (0≤ x≤1.5). The three cations are present in both tetrahedral and octahedral sites, and the relative number of Fe ions on A- and B-sites remains nearly constant in the whole range of x. It appears that for x≤0.5 manganese is divalent and copper is in its two oxidation states. For x>0.5 copper and iron are respectively divalent and trivalent; the manganese is in +2 and +3 oxydation states.

Entropy of the Bose-Einstein-condensate ground state: Correlation versus ground-state entropy

NASA Astrophysics Data System (ADS)

Kim, Moochan B.; Svidzinsky, Anatoly; Agarwal, Girish S.; Scully, Marlan O.

2018-01-01

Calculation of the entropy of an ideal Bose-Einstein condensate (BEC) in a three-dimensional trap reveals unusual, previously unrecognized, features of the canonical ensemble. It is found that, for any temperature, the entropy of the Bose gas is equal to the entropy of the excited particles although the entropy of the particles in the ground state is nonzero. We explain this by considering the correlations between the ground-state particles and particles in the excited states. These correlations lead to a correlation entropy which is exactly equal to the contribution from the ground state. The correlations themselves arise from the fact that we have a fixed number of particles obeying quantum statistics. We present results for correlation functions between the ground and excited states in a Bose gas, so as to clarify the role of fluctuations in the system. We also report the sub-Poissonian nature of the ground-state fluctuations.

Redox chemistry of nickel(II) complexes supported by a series of noninnocent β-diketiminate ligands.

PubMed

Takaichi, June; Morimoto, Yuma; Ohkubo, Kei; Shimokawa, Chizu; Hojo, Takayuki; Mori, Seiji; Asahara, Haruyasu; Sugimoto, Hideki; Fujieda, Nobutaka; Nishiwaki, Nagatoshi; Fukuzumi, Shunichi; Itoh, Shinobu

2014-06-16

Nickel complexes of a series of β-diketiminate ligands ((R)L(-), deprotonated form of 2-substituted N-[3-(phenylamino)allylidene]aniline derivatives (R)LH, R = Me, H, Br, CN, and NO2) have been synthesized and structurally characterized. One-electron oxidation of the neutral complexes [Ni(II)((R)L(-))2] by AgSbF6 or [Ru(III)(bpy)3](PF6)3 (bpy = 2,2'-bipyridine) gave the corresponding metastable cationic complexes, which exhibit an EPR spectrum due to a doublet species (S = 1/2) and a characteristic absorption band in near IR region ascribable to a ligand-to-ligand intervalence charge-transfer (LLIVCT) transition. DFT calculations have indicated that the divalent oxidation state of nickel ion (Ni(II)) is retained, whereas one of the β-diketiminate ligands is oxidized to give formally a mixed-valence complex, [Ni(II)((R)L(-))((R)L(•))](+). Thus, the doublet spin state of the oxidized cationic complex can be explained by taking account of the antiferromagnetic interaction between the high-spin nickel(II) ion (S = 1) and the organic radical (S = 1/2) of supporting ligand. A single-crystal structure of one of the cationic complexes (R = H) has been successfully determined to show that both ligands in the cationic complex are structurally equivalent. On the basis of theoretical analysis of the LLIVCT band and DFT calculations as well as the crystal structure, the mixed-valence complexes have been assigned to Robin-Day class III species, where the radical spin is equally delocalized between the two ligands to give the cationic complex, which is best described as [Ni(II)((R)L(0.5•-))2](+). One-electron reduction of the neutral complexes with decamethylcobaltocene gave the anionic complexes when the ligand has the electron-withdrawing substituent (R = CN, NO2, Br). The generated anionic complexes exhibited EPR spectra due to a doublet species (S = 1/2) but showed no LLIVCT band in the near-IR region. Thus, the reduced complexes are best described as the d(9) nickel(I) complexes supported by two anionic β-diketiminate ligands, [Ni(I)((R)L(-))2](-). This conclusion was also supported by DFT calculations. Substituent effects on the electronic structures of the three oxidation states (neutral, cationic, and anionic) of the complexes are systematically evaluated on the basis of DFT calculations.

Ground-state densities from the Rayleigh-Ritz variation principle and from density-functional theory.

PubMed

Kvaal, Simen; Helgaker, Trygve

2015-11-14

The relationship between the densities of ground-state wave functions (i.e., the minimizers of the Rayleigh-Ritz variation principle) and the ground-state densities in density-functional theory (i.e., the minimizers of the Hohenberg-Kohn variation principle) is studied within the framework of convex conjugation, in a generic setting covering molecular systems, solid-state systems, and more. Having introduced admissible density functionals as functionals that produce the exact ground-state energy for a given external potential by minimizing over densities in the Hohenberg-Kohn variation principle, necessary and sufficient conditions on such functionals are established to ensure that the Rayleigh-Ritz ground-state densities and the Hohenberg-Kohn ground-state densities are identical. We apply the results to molecular systems in the Born-Oppenheimer approximation. For any given potential v ∈ L(3/2)(ℝ(3)) + L(∞)(ℝ(3)), we establish a one-to-one correspondence between the mixed ground-state densities of the Rayleigh-Ritz variation principle and the mixed ground-state densities of the Hohenberg-Kohn variation principle when the Lieb density-matrix constrained-search universal density functional is taken as the admissible functional. A similar one-to-one correspondence is established between the pure ground-state densities of the Rayleigh-Ritz variation principle and the pure ground-state densities obtained using the Hohenberg-Kohn variation principle with the Levy-Lieb pure-state constrained-search functional. In other words, all physical ground-state densities (pure or mixed) are recovered with these functionals and no false densities (i.e., minimizing densities that are not physical) exist. The importance of topology (i.e., choice of Banach space of densities and potentials) is emphasized and illustrated. The relevance of these results for current-density-functional theory is examined.

Questa baseline and pre-mining ground-water quality investigation. 14. Interpretation of ground-water geochemistry in catchments other than the Straight Creek catchment, Red River Valley, Taos County, New Mexico, 2002-2003

USGS Publications Warehouse

Nordstrom, D. Kirk; McCleskey, R. Blaine; Hunt, Andrew G.; Naus, Cheryl A.

2005-01-01

The U.S. Geological Survey, in cooperation with the New Mexico Environment Department, is investigating the pre-mining ground-water chemistry at the Molycorp molybdenum mine in the Red River Valley, New Mexico. The primary approach is to determine the processes controlling ground-water chemistry at an unmined, off-site but proximal analog. The Straight Creek catchment, chosen for this purpose, consists of the same Tertiary-age quartz-sericite-pyrite altered andesite and rhyolitic volcanics as the mine site. Straight Creek is about 5 kilometers east of the eastern boundary of the mine site. Both Straight Creek and the mine site are at approximately the same altitude, face south, and have the same climatic conditions. Thirteen wells in the proximal analog drainage catchment were sampled for ground-water chemistry. Eleven wells were installed for this study and two existing wells at the Advanced Waste-Water Treatment (AWWT) facility were included in this study. Eight wells were sampled outside the Straight Creek catchment: one each in the Hansen, Hottentot, and La Bobita debris fans, four in a well cluster in upper Capulin Canyon (three in alluvial deposits and one in bedrock), and an existing well at the U.S. Forest Service Questa Ranger Station in Red River alluvial deposits. Two surface waters from the Hansen Creek catchment and two from the Hottentot drainage catchment also were sampled for comparison to ground-water compositions. In this report, these samples are evaluated to determine if the geochemical interpretations from the Straight Creek ground-water geochemistry could be extended to other ground waters in the Red River Valley , including the mine site. Total-recoverable major cations and trace metals and dissolved major cations, selected trace metals, anions, alkalinity; and iron-redox species were determined for all surface- and ground-water samples. Rare-earth elements and low-level As, Bi, Mo, Rb, Re, Sb, Se, Te, Th, U, Tl, V, W, Y, and Zr were determined on selected samples. Dissolved organic carbon (DOC), mercury, sulfate stable isotope composition (d34S and d18O of sulfate), stable isotope composition of water (d2H and d18O of water) were measured for selected samples. Chlorofluorocarbons (CFC) and 3He and 3H were measured for age dating on selected samples. Linear regressions from the Straight Creek ground-water data were used to compare ground-water chemistry trends in non-Straight Creek ground waters with Straight Creek alluvial ground-water chemistry dilution trends. Most of the solute trends for the ground waters are similar to those for Straight Creek but there are some notable exceptions. In lithologies that contain substantial pyrite mineralization, acid waters form with similar chemistries to those in Straight Creek and all the waters tend to be calcium-sulfate type. Hottentot ground waters contain substantially lower calcium concentrations relative to those in Straight Creek. This anomaly results from the exposure of rhyolite porphyry in the Hottentot scar and weathering zone. The rhyolite contains less calcium than the altered andesites and tuffs in the Straight Creek catchment and probably does not have the abundant gypsum and calcite. The Hansen ground waters have reached gypsum saturation and have similar calcium, magnesium, and beryllium concentrations as Straight Creek ground waters but have lower concentrations of fluoride, manganese, zinc, cobalt, nickel, copper, and lithium. Lower concentrations of elements related to mineralization at Hansen likely reflect the more distal location of Hansen with respect to intrusive centers that provided the heat source for hydrothermal alteration. The other ground water with water chemistry trends that are outside the Straight Creek trends was from an alluvial well from Capulin Canyon (CC2A). Although it had pH values near 6.0 and most major ions similar to the other Capulin Canyon ground waters, it contained high concentrations

Activation by divalent cations of a Ca2+-activated K+ channel from skeletal muscle membrane.

PubMed

Oberhauser, A; Alvarez, O; Latorre, R

1988-07-01

Several divalent cations were studied as agonists of a Ca2+-activated K+ channel obtained from rat muscle membranes and incorporated into planar lipid bilayers. The effect of these agonists on single-channel currents was tested in the absence and in the presence of Ca2+. Among the divalent cations that activate the channel, Ca2+ is the most effective, followed by Cd2+, Sr2+, Mn2+, Fe2+, and Co2+. Mg2+, Ni2+, Ba2+, Cu2+, Zn2+, Hg2+, and Sn2+ are ineffective. The voltage dependence of channel activation is the same for all the divalent cations. The time-averaged probability of the open state is a sigmoidal function of the divalent cation concentration. The sigmoidal curves are described by a dissociation constant K and a Hill coefficient N. The values of these parameters, measured at 80 mV are: N = 2.1, K = 4 X 10(-7) mMN for Ca2+; N = 3.0, K = 0.02 mMN for Cd2+; N = 1.45, K = 0.63 mMN for Sr2+; N = 1.7, K = 0.94 mMN for Mn2+; N = 1.1, K = 3.0 mMN for Fe2+; and N = 1.1 K = 4.35 mMN for Co2+. In the presence of Ca2+, the divalent cations Cd2+, Co2+, Mn2+, Ni2+, and Mg2+ are able to increase the apparent affinity of the channel for Ca2+ and they increase the Hill coefficient in a concentration-dependent fashion. These divalent cations are only effective when added to the cytoplasmic side of the channel. We suggest that these divalent cations can bind to the channel, unmasking new Ca2+ sites.

Loading capacity and interaction of DNA binding on catanionic vesicles with different cationic surfactants.

PubMed

Xu, Lu; Chen, Jingfei; Feng, Lei; Dong, Shuli; Hao, Jingcheng

2014-12-07

Cationic and anionic (catanionic) vesicles were constructed from the mixtures of sodium laurate (SL) and alkyltrimethylammonium bromide (CnTAB, n = 12, 14, and 16) and were used to control the loading capacity of DNA. The binding saturation point (BSP) of DNA to catanionic vesicles increases with the chain length of cationic surfactants, which is at 1.0, 1.3 and 1.5 for CnTAB with n = 12, 14, and 16, respectively. Our measurements showed that the loading capacity and affinity of DNA can be controlled by catanionic vesicles. It increases with the chain length of cationic surfactants. Because of a large reduction in surface charge density, catanionic vesicles are prone to undergo re-aggregation or fusion with the addition of DNA. DNA molecules can still maintain original coil state during the interaction with catanionic CnTAL vesicles. (1)H NMR data reveals that the obvious dissociation of anionic ions, L(-), from catanionic C14TAL vesicles is due to the interaction with DNA; however, this phenomenon cannot be observed in C12TAB-SL vesicles. Agarose gel electrophoresis (AGE) results demonstrate that the electrostatic interaction between the two oppositely charged cationic and anionic surfactants is stronger than that between DNA and cationic surfactant, CnTAB (n = 12, 14, and 16). Not only is the dissociation of L(-) simply determined by the charge competition, but it also depends largely on the variations in the surface charge density as well as the cationic and anionic surfactant competing ability in geometry configuration of catanionic vesicles. The complicated interaction between DNA and catanionic vesicles induces the deformation of cationic vesicles. Our results should provide clear guidance for choosing more proper vectors for DNA delivery and gene therapy in cell experiments.

Structure of 1:1 complex of 1-naphthylmethyl ester of monensin A with sodium perchlorate studied by X-ray, FT-IR and ab initio methods

NASA Astrophysics Data System (ADS)

Huczyński, Adam; Janczak, Jan; Brzezinski, Bogumil

2012-12-01

A new crystalline complex formed between 1-naphthylmethyl ester of the naturally occurring antibiotic - monensin A (MON8) with sodium perchlorate has been obtained and studied using X-ray crystallography and FT-IR spectroscopy. The X-ray data of the complex show that MON8 forms a pseudo-cyclic structure stabilised by one weak intramolecular hydrogen bond and the sodium cation co-ordinated by two oxygen atoms of hydroxyl groups and four etheric oxygen atoms in the hydrophilic sphere. Within this structure the oxygen atoms of the ester groups are not involved in the coordination of sodium cation. In contrast to the solid state structure of the complex, in acetonitrile solution an equilibrium between two structures, in which the oxygen atom of the carbonyl ester group is either involved or not involved in the complexation of the sodium cation, is found. In acetonitrile this equilibrium is shifted towards the latter structure i.e. the structure existing in the solid state. The gas-phase structure of [MON8sbnd Na]+ cation as shown the ab initio MO calculations is comparable with the crystal one. Three-dimensional molecular electrostatic potential calculated for the neutral MON8 and [MON8sbnd Na]+ molecules is helpful for understanding the structural aspects of the sodium complex formation.

Installation Restoration Program. Stage 1. King Salmon Airport , King Salmon, Alaska

DTIC Science & Technology

1989-08-29

DESCRIPTION SOILS, SEDIMENTS , SLU_ SOLIDS TREATMENT ] CONSTITUENTS OR CON., SOLIDO /F/CATION, FIXATION" - STABILIZATION AND FIX/ STABILIZATION FORM...are consistently present in site media _il, sediment , surface, and ground-I waters), and are potentially toxic to humans and the eni--ent. Suggested...Seep IV-76 4.1.5.2.3 North Barrel Bluff IV-76 4.1.5.2.4 South Barrel Bluff IV-94 4.1.6 Sediment Investigation IV-94 4.1.6.1 Eskimo Creek Seep IV-94

Cation ordering/disordering kinetics in Ba3CoNb2O9: An in situ study using synchrotron x-ray powder diffraction

NASA Astrophysics Data System (ADS)

Mallinson, P. M.; Claridge, J. B.; Rosseinsky, M. J.; Ibberson, R. M.; Wright, J. P.; Fitch, A. N.; Price, T.; Iddles, D. M.

2007-11-01

In situ synchrotron x-ray powder diffraction has been used to study the kinetics of cation ordering and disordering in the microwave dielectric electroceramic Ba3CoNb2O9 with a time resolution of 15s. The method enables the order/disorder temperature (To /d) in this material of 1430°C to be directly observed. The changes in the rate and degree of cation ordering and in the growth of ordered domains between samples ordered from standard precursor material and then subsequently reordered following an annealing period above To /d show that small changes in precursor order state and phase assemblage strongly influence the final domain size.

ION EXCHANGE PROCESS FOR THE RECOVERY AND PURIFICATION OF MATERIALS

DOEpatents

Long, R.S.; Bailes, R.H.

1958-04-15

A process for the recovery of certain metallic ions from aqueous solutions by ion exchange techniques is described. It is applicable to elements such as vanadium, chromium, nnanganese, and the like, which are capable of forming lower valent cations soluble in aqueous solutions and which also form ldgher valent anions soluble in aqueous acidic solutions. For example, small amounts of vanadium occurring in phosphoric acid prepared from phosphate rock may be recovered by reducing the vanadium to a trivalent cation adsorbing; the vanadium in a cationic exchange resin, then treating the resin with a suitable oxidizing agent to convert the adsorbed vanadium to a higher valent state, and finally eluting; the vanadium as an anion from the resin by means of an aqueous acidic solution.

The role of organic solvent radical cations in separations ligand degradation

DOE PAGES

Mezyk, Stephen P.; Mincher, Bruce J.; Dhiman, Surajdevprakash B.; ...

2015-11-04

The dodecane radical cation reaction rate constant with CMPO was measured using ps electron pulse radiolysis/absorption spectroscopy as k = (1.30 ± 0.11) x 1010 M -1 s -1 in dodecane/0.10 M CH 2Cl 2 solution. No reactivity increase occurred when these solutions were pre-contacted with nitric acid, similar to the behavior observed for TODGA. To corroborate these kinetic data with steady-state radiolysis measurements, where acid pre contacted CMPO showed significantly less degradation, it is proposed that the dodecane radical cation always reacts directly with TODGA, but for CMPO the charge-transfer occurs with the CMPO•HNO 3 complex formed in themore » acid contacted solvent.« less

Isolation, characterization, and computational studies of the novel [Mo3(mu3-Br)2(mu-Br)3Br6]2- cluster anion.

PubMed

Paraskevopoulou, Patrina; Makedonas, Christodoulos; Psaroudakis, Nikolaos; Mitsopoulou, Christiana A; Floros, Georgios; Seressioti, Andriana; Ioannou, Marinos; Sanakis, Yiannis; Rath, Nigam; Gómez García, Carlos J; Stavropoulos, Pericles; Mertis, Konstantinos

2010-03-01

The novel trimolybdenum cluster [Mo(3)(mu(3)-Br)(2)(mu-Br)(3)Br(6)](2-) (1, {Mo(3)}(9+), 9 d-electrons) has been isolated from the reaction of [Mo(CO)(6)] with 1,2-C(2)H(4)Br(2) in refluxing PhCl. The compound has been characterized in solution by electrospray ionization mass spectrometry (ESI-MS), UV-vis spectroscopy, cyclic voltammetry, and in the solid state by X-ray analysis (counter-cations: (n-Bu)(4)N(+) (1), Et(4)N(+), Et(3)BzN(+)), electron paramagnetic resonance (EPR), magnetic susceptibility measurements, and infrared spectroscopy. The least disordered (n-Bu)(4)N(+) salt crystallizes in the monoclinic space group C2/c, a = 20.077(2) A, b = 11.8638(11) A, c = 22.521(2) A, alpha = 90 deg, beta = 109.348(4) deg, gamma = 90 deg, V = 5061.3(9) A(3), Z = 4 and contains an isosceles triangular metal arrangement, which is capped by two bromine ligands. Each edge of the triangle is bridged by bromine ions. The structure is completed by six terminal bromine ligands. According to the magnetic measurements and the EPR spectrum the trimetallic core possesses one unpaired electron. Electrochemical data show that oxidation by one electron of 1 is reversible, thus proceeding with retention of the trimetallic core, while the reduction is irreversible. The effective magnetic moment of 1 (mu(eff), 1.55 mu(B), r.t.) is lower than the spin-only value (1.73 mu(B)) for S = 1/2 systems, most likely because of high spin-orbit coupling of Mo(III) and/or magnetic coupling throughout the lattice. The ground electronic state of 1 was studied using density functional theory techniques under the broken symmetry formalism. The ground state is predicted to exhibit strong antiferromagnetic coupling between the three molybdenum atoms of the core. Moreover, our calculated data predict two broken symmetry states that differ only by 0.4 kcal/mol (121 cm(-1)). The antiferromagnetic character is delocalized over three magnetic orbitals populated by three electrons. The assignment of the infrared spectra is also provided.

Single-Walled Carbon Nanotubes: Mimics of Biological Ion Channels.

PubMed

Amiri, Hasti; Shepard, Kenneth L; Nuckolls, Colin; Hernández Sánchez, Raúl

2017-02-08

Here we report on the ion conductance through individual, small diameter single-walled carbon nanotubes. We find that they are mimics of ion channels found in natural systems. We explore the factors governing the ion selectivity and permeation through single-walled carbon nanotubes by considering an electrostatic mechanism built around a simplified version of the Gouy-Chapman theory. We find that the single-walled carbon nanotubes preferentially transported cations and that the cation permeability is size-dependent. The ionic conductance increases as the absolute hydration enthalpy decreases for monovalent cations with similar solid-state radii, hydrated radii, and bulk mobility. Charge screening experiments using either the addition of cationic or anionic polymers, divalent metal cations, or changes in pH reveal the enormous impact of the negatively charged carboxylates at the entrance of the single-walled carbon nanotubes. These observations were modeled in the low-to-medium concentration range (0.1-2.0 M) by an electrostatic mechanism that mimics the behavior observed in many biological ion channel-forming proteins. Moreover, multi-ion conduction in the high concentration range (>2.0 M) further reinforces the similarity between single-walled carbon nanotubes and protein ion channels.

Alternative solution model for the ternary carbonate system CaCO3 - MgCO3 - FeCO3 - II. Calibration of a combined ordering model and mixing model

USGS Publications Warehouse

McSwiggen, P.L.

1993-01-01

Earlier attempts at solution models for the ternary carbonate system have been unable to adequately accommodate the cation ordering which occurs in some of the carbonate phases. The carbonate solution model of this study combines a Margules type of interaction model with a Bragg-Williams type of ordering model. The ordering model determines the equilibrium state of order for a crystal, from which the cation distribution within the lattice can be obtained. The interaction model addresses the effect that mixing different cation species within a given cation layer has on the total free energy of the system. An ordering model was derived, based on the Bragg-Williams approach; it is applicable to ternary systems involving three cations substituting on two sites, and contains three ordering energy parameters (WCaMg, WCaFe, and WCaMgFe). The solution model of this study involves six Margules-type interaction parameters (W12, W21, W13, W31, W23, and W32). Values for the two sets of energy parameters were calculated from experimental data and from compositional relationships in natural assemblages. ?? 1993 Springer-Verlag.

Effects of Zinc Gluconate and 2 Other Divalent Cationic Compounds on Olfactory Function in Mice

PubMed Central

Duncan-Lewis, Christopher A; Lukman, Roy L; Banks, Robert K

2011-01-01

Intranasal application of zinc gluconate has commonly been used to treat the common cold. The safety of this treatment, however, has come into question recently. In addition to a United States recall of a homeopathic product that contains zinc gluconate, abundant literature reports cytotoxic effects of zinc on the olfactory epithelium. Additional research suggests that divalent cations (such as zinc) can block ion channels that facilitate the transduction of odors into electrical signals on the olfactory epithelium. The purpose of the current study was 2-fold: to confirm whether zinc gluconate causes anosmia and to reveal whether any other divalent cationic compounds produce a similar effect. Groups of mice underwent a buried food-pellet test to gauge olfactory function and then were nasally irrigated with 1 of 3 divalent cationic compounds. When tested after treatment, mice irrigated with zinc gluconate and copper gluconate experienced a marked increase in food-finding time, indicating that they had lost their ability to smell a hidden food source. Control mice irrigated with saline had a significantly lower increase in times. These results confirm that zinc gluconate can cause anosmia and reveal that multiple divalent cations can negatively affect olfaction. PMID:22330252

Observation of decreasing resistivity of amorphous indium gallium zinc oxide thin films with an increasing oxygen partial pressure

NASA Astrophysics Data System (ADS)

Singh, Anup K.; Adhikari, Sonachand; Gupta, Rajeev; Deepak

2017-01-01

We have investigated the electrical resistivity behavior in amorphous indium gallium zinc oxide (a-IGZO) thin films. It is well known that resistivity increases as the film is deposited at a higher and higher oxygen partial pressure; we also record the same. However, in process we have discovered a remarkable region, in the oxygen deficient condition, that the resistivity shows an inverse behavior. This leads to the possibility that resistive films, suitable for thin film transistors, can also be obtained in oxygen deficient deposition conditions. Optical spectroscopic investigation could discern between a-IGZO films grown in oxygen deficient and oxygen rich conditions. The related resistivity behavior could be correlated to the presence of sub-bandgap states in films deposited in oxygen deficiency. These subgap states appear to be due to defects arising from local variations around the cations or oxygen atoms. The likely cause is an increase in Ga relative to In around O atom and the nature of cation-cation interaction when an oxygen atom is missing.

Influence of the Selectivity Filter Properties on Proton Selectivity in the Influenza A M2 Channel.

PubMed

Dudev, Todor; Grauffel, Cédric; Lim, Carmay

2016-10-05

The homotetrameric M2 proton channel of influenza A plays a crucial role in the viral life cycle and is thus an important therapeutic target. It selectively conducts protons against a background of other competing cations whose concentrations are up to a million times greater than the proton concentration. Its selectivity is largely determined by a constricted region of its open pore known as the selectivity filter, which is lined by four absolutely conserved histidines. While the mechanism of proton transport through the channel has been studied, the physical principles underlying the selectivity for protons over other cations in the channel's His 4 selectivity filter remain elusive. Furthermore, it is not known if proton selectivity absolutely requires all four histidines with two of the four histidines protonated and if other titratable amino acid residues in lieu of the histidines could bind protons and how they affect proton selectivity. Here, we elucidate how the competition between protons and rival cations such as Na + depends on the selectivity filter's (1) histidine protonation state, (2) solvent exposure, (3) oligomeric state (the number of protein chains and thus the number of His ligands), and (4) ligand composition by evaluating the free energies for replacing monovalent Na + with H 3 O + in various model selectivity filters. We show that tetrameric His 4 filters are more proton-selective than their trimeric His 3 counterparts, and a dicationic His 4 filter where two of the four histidines are protonated is more proton-selective than tetrameric filters with other charge states/composition (different combinations of His protonation states or different metal-ligating ligands). The [His 4 ] 2+ filter achieves proton selectivity by providing suboptimal binding conditions for rival cations such as Na + , which prefers a neutral or negatively charged filter instead of a dicationic one, and three rather than four ligands with oxygen-ligating atoms.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ho, M.; Shi, W; Rinaldo-Mathis, A

Inhibition of human purine nucleoside phosphorylase (PNP) stops growth of activated T-cells and the formation of 6-oxypurine bases, making it a target for leukemia, autoimmune disorders, and gout. Four generations of ribocation transition-state mimics bound to PNP are structurally characterized. Immucillin-H (K*{sub i} = 58 pM, first-generation) contains an iminoribitol cation with four asymmetric carbons. DADMe-Immucillin-H (K*{sub i} = 9 pM, second-generation), uses a methylene-bridged dihydroxypyrrolidine cation with two asymmetric centers. DATMe-Immucillin-H (K*{sub i} = 9 pM, third-generation) contains an open-chain amino alcohol cation with two asymmetric carbons. SerMe-ImmH (K*{sub i} = 5 pM, fourth-generation) uses achiral dihydroxyaminoalcohol seramide asmore » the ribocation mimic. Crystal structures of PNPs establish features of tight binding to be; (1) ion-pair formation between bound phosphate (or its mimic) and inhibitor cation, (2) leaving-group interactions to N1, O6, and N7 of 9-deazahypoxanthine, (3) interaction between phosphate and inhibitor hydroxyl groups, and (4) His257 interacting with the 5{prime}-hydroxyl group. The first generation analogue is an imperfect fit to the catalytic site with a long ion pair distance between the iminoribitol and bound phosphate and weaker interactions to the leaving group. Increasing the ribocation to leaving-group distance in the second- to fourth-generation analogues provides powerful binding interactions and a facile synthetic route to powerful inhibitors. Despite chemical diversity in the four generations of transition-state analogues, the catalytic site geometry is almost the same for all analogues. Multiple solutions in transition-state analogue design are available to convert the energy of catalytic rate enhancement to binding energy in human PNP.« less

The Cation-π Interaction Enables a Halo-Tag Fluorogenic Probe for Fast No-Wash Live Cell Imaging and Gel-Free Protein Quantification.

PubMed

Liu, Yu; Miao, Kun; Dunham, Noah P; Liu, Hongbin; Fares, Matthew; Boal, Amie K; Li, Xiaosong; Zhang, Xin

2017-03-21

The design of fluorogenic probes for a Halo tag is highly desirable but challenging. Previous work achieved this goal by controlling the chemical switch of spirolactones upon the covalent conjugation between the Halo tag and probes or by incorporating a "channel dye" into the substrate binding tunnel of the Halo tag. In this work, we have developed a novel class of Halo-tag fluorogenic probes that are derived from solvatochromic fluorophores. The optimal probe, harboring a benzothiadiazole scaffold, exhibits a 1000-fold fluorescence enhancement upon reaction with the Halo tag. Structural, computational, and biochemical studies reveal that the benzene ring of a tryptophan residue engages in a cation-π interaction with the dimethylamino electron-donating group of the benzothiadiazole fluorophore in its excited state. We further demonstrate using noncanonical fluorinated tryptophan that the cation-π interaction directly contributes to the fluorogenicity of the benzothiadiazole fluorophore. Mechanistically, this interaction could contribute to the fluorogenicity by promoting the excited-state charge separation and inhibiting the twisting motion of the dimethylamino group, both leading to an enhanced fluorogenicity. Finally, we demonstrate the utility of the probe in no-wash direct imaging of Halo-tagged proteins in live cells. In addition, the fluorogenic nature of the probe enables a gel-free quantification of fusion proteins expressed in mammalian cells, an application that was not possible with previously nonfluorogenic Halo-tag probes. The unique mechanism revealed by this work suggests that incorporation of an excited-state cation-π interaction could be a feasible strategy for enhancing the optical performance of fluorophores and fluorogenic sensors.

Electrospray ionization tandem mass spectrometry of ammonium cationized polyethers.

PubMed

Nasioudis, Andreas; Heeren, Ron M A; van Doormalen, Irene; de Wijs-Rot, Nicolette; van den Brink, Oscar F

2011-05-01

Quaternary ammonium salts (Quats) and amines are known to facilitate the MS analysis of high molar mass polyethers by forming low charge state adduct ions. The formation, stability, and behavior upon collision-induced dissociation (CID) of adduct ions of polyethers with a variety of Quats and amines were studied by electrospray ionization quadrupole time-of-flight, quadrupole ion trap, and linear ion trap tandem mass spectrometry (MS/MS). The linear ion trap instrument was part of an Orbitrap hybrid mass spectrometer that allowed accurate mass MS/MS measurements. The Quats and amines studied were of different degree of substitution, structure, and size. The stability of the adduct ions was related to the structure of the cation, especially the amine's degree of substitution. CID of singly/doubly charged primary and tertiary ammonium cationized polymers resulted in the neutral loss of the amine followed by fragmentation of the protonated product ions. The latter reveals information about the monomer unit, polymer sequence, and endgroup structure. In addition, the detection of product ions retaining the ammonium ion was observed. The predominant process in the CID of singly charged quaternary ammonium cationized polymers was cation detachment, whereas their doubly charged adduct ions provided the same information as the primary and tertiary ammonium cationized adduct ions. This study shows the potential of specific amines as tools for the structural elucidation of high molar mass polyethers. © American Society for Mass Spectrometry, 2011

Conventional empirical law reverses in the phase transitions of 122-type iron-based superconductors

DOE PAGES

Yu, Zhenhai; Wang, Lin; Wang, Luhong; ...

2014-11-24

Phase transition of solid-state materials is a fundamental research topic in condensed matter physics, materials science and geophysics. It has been well accepted and widely proven that isostructural compounds containing different cations undergo same pressure-induced phase transitions but at progressively lower pressures as the cation radii increases. However, we discovered that this conventional law reverses in the structural transitions in 122-type iron-based superconductors. In this report, a combined low temperature and high pressure X-ray diffraction (XRD) measurement has identified the phase transition curves among the tetragonal (T), orthorhombic (O) and the collapsed-tetragonal (cT) phases in the structural phase diagram ofmore » the iron-based superconductor AFe 2As 2 (A = Ca, Sr, Eu, and Ba). As a result, the cation radii dependence of the phase transition pressure (T → cT) shows an opposite trend in which the compounds with larger ambient radii cations have a higher transition pressure.« less

Femtosecond pump-probe photoionization-photofragmentation spectroscopy: photoionization-induced twisting and coherent vibrational motion of azobenzene cation.

PubMed

Ho, Jr-Wei; Chen, Wei-Kan; Cheng, Po-Yuan

2009-10-07

We report studies of ultrafast dynamics of azobenzene cation using femtosecond photoionization-photofragmentation spectroscopy. In our experiments, a femtosecond pump pulse first produces an ensemble of azobenzene cations via photoionization of the neutrals. A delayed probe pulse then brings the evolving ionic system to excited states that ultimately undergo ion fragmentation. The dynamics is followed by monitoring either the parent-ion depletion or fragment-ion formation as a function of the pump-probe delay time. The observed transients for azobenzene cation are characterized by a constant ion depletion modulated by a rapidly damped oscillatory signal with a period of about 1 ps. Theoretical calculations suggest that the oscillation arises from a vibration motion along the twisting inversion coordinate involving displacements in CNNC and phenyl-ring torsions. The oscillation is damped rapidly with a time constant of about 1.2 ps, suggesting that energy dissipation from the active mode to bath modes takes place in this time scale.

Occurrence of hexavalent chromium in ground water in the western Mojave Desert, California

USGS Publications Warehouse

Ball, J.W.; Izbicki, J.A.

2004-01-01

About 200 samples from selected public supply, domestic, and observation wells completed in alluvial aquifers underlying the western Mojave Desert were analyzed for total dissolved Cr and Cr(VI). Because Cr(VI) is difficult to preserve, samples were analyzed by 3 methods. Chromium(VI) was determined in the field using both a direct colorimetric method and EPA method 218.6, and samples were speciated in the field for later analysis in the laboratory using a cation-exchange method developed for the study described in this paper. Comparison of the direct colorimetric method and EPA method 218.6 with the new cation-exchange method yielded r2 values of 0.9991 and 0.9992, respectively. Total dissolved Cr concentrations ranged from less than the 0.1 ??g/l detection limit to 60 ??g/l, and almost all the Cr present was Cr(VI). Near recharge areas along the mountain front pH values were near neutral, dissolved O2 concentrations were near saturation, and Cr(VI) concentrations were less than the 0.1 ??g/l detection limit. Chromium(VI) concentrations and pH values increased downgradient as long as dissolved O 2 was present. However, low Cr(VI) concentrations were associated with low dissolved O2 concentrations near ground-water discharge areas along dry lakes. Chromium(VI) concentrations as high as 60 ??g/l occurred in ground water from the Sheep Creek fan alluvial deposits weathered from mafic rock derived from the San Gabriel Mountains, and Cr(VI) concentrations as high as about 36 ??g/l were present in ground water from alluvial deposits weathered from less mafic granitic, metamorphic, and volcanic rocks. Chromium(III) was the predominant form of Cr only in areas where dissolved O2 concentrations were less than 1 mg/l and was detected at a median concentration of 0.1 ??g/l, owing to its low solubility in water of near-neutral pH. Depending on local hydrogeologic conditions and the distribution of dissolved O2, Cr(VI) concentrations may vary considerably with depth. Samples collected under pumping conditions from different depths within wells show that Cr(VI) concentrations can range from less than the 0.1 ??g/l detection limit to 36 ??g/l in a single well and that dissolved O2 concentrations likely control the concentration and redox speciation of Cr in ground water.

Normal and Inverse Ferrite Spinels: A Set of Solid State Chemistry Related Experiments.

ERIC Educational Resources Information Center

Chaumont, C.; Burgard, M.

1979-01-01

Presents one of the themes of a French chemistry college laboratory course, which concerns the field of solid state chemistry and is focused on the study of the cation distribution in the case of certain spinel ferrites. (HM)

Small RNA Sequencing Reveals Dlk1-Dio3 Locus-Embedded MicroRNAs as Major Drivers of Ground-State Pluripotency.

PubMed

Moradi, Sharif; Sharifi-Zarchi, Ali; Ahmadi, Amirhossein; Mollamohammadi, Sepideh; Stubenvoll, Alexander; Günther, Stefan; Salekdeh, Ghasem Hosseini; Asgari, Sassan; Braun, Thomas; Baharvand, Hossein

2017-12-12

Ground-state pluripotency is a cell state in which pluripotency is established and maintained through efficient repression of endogenous differentiation pathways. Self-renewal and pluripotency of embryonic stem cells (ESCs) are influenced by ESC-associated microRNAs (miRNAs). Here, we provide a comprehensive assessment of the "miRNome" of ESCs cultured under conditions favoring ground-state pluripotency. We found that ground-state ESCs express a distinct set of miRNAs compared with ESCs grown in serum. Interestingly, most "ground-state miRNAs" are encoded by an imprinted region on chromosome 12 within the Dlk1-Dio3 locus. Functional analysis revealed that ground-state miRNAs embedded in the Dlk1-Dio3 locus (miR-541-5p, miR-410-3p, and miR-381-3p) promoted pluripotency via inhibition of multi-lineage differentiation and stimulation of self-renewal. Overall, our results demonstrate that ground-state pluripotency is associated with a unique miRNA signature, which supports ground-state self-renewal by suppressing differentiation. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Ground water investigations in Utah to June 30, 1936: A part of Chapter 8 in Twentieth biennial report of the State Engineer to the governor of Utah: 1935-1936

USGS Publications Warehouse

Taylor, G.H.; Thomas, H.E.

1936-01-01

During the past few years of drouth the importance of ground-water supplies has become more fully appreciated. During this time, because of subnormal replenishment of the ground-water reservoirs and the increased withdrawals from wells, the ground-water levels have declined in most developed areas in the State, a condition which has made the well owners acutely aware that ground water is not inexhaustible. Numerous cases of contention between well owners resulted in increased demands for adequate regulation of the appropriation and use of ground water. Realizing that more information concerning the ground water of the State was imperative, not only to administer the ground-water regulations but to prepare for the conservation and replenishment of existing supplies and development of new supplies, the State Legislature enacted, during its 1935 session, Senate Bill 206, which authorized the State Engineer to make an investigation of the ground water of the State. To provide for the expenses of the investigation, the bill allotted /$10,000 to the State Engineer, this sum to be matched by a State or Federal organization, and the investigation to be carried out co-operatively during the biennium beginning July 1, 1935. A co-operative agreement between the State Engineer and the United States Geological Survey was made on July 1, 1935.

Local Environment Sensitivity of the Cu K-Edge XANES Features in Cu-SSZ-13: Analysis from First-Principles.

PubMed

Zhang, Renqin; McEwen, Jean-Sabin

2018-05-22

Cu K-edge X-ray absorption near-edge spectra (XANES) have been widely used to study the properties of Cu-SSZ-13. In this Letter, the sensitivity of the XANES features to the local environment for a Cu + cation with a linear configuration and a Cu 2+ cation with a square-linear configuration in Cu-SSZ-13 is reported. When a Cu + cation is bonded to H 2 O or NH 3 in a linear configuration, the XANES has a strong peak at around 8983 eV. The intensity of this peak decreases as the linear configuration is broken. As for the Cu 2+ cations in a square-planar configuration with a coordination number of 4, two peaks at around 8986 and 8993 eV are found. An intensity decrease for both peaks at around 8986 and 8993 eV is found in an NH 3 _4_Z 2 Cu model as the N-Cu-N angle changes from 180 to 100°. We correlate these features to the variation of the 4p state by PDOS analysis. In addition, the feature peaks for both the Cu + cation and Cu 2+ cation do not show a dependence on the Cu-N bond length. We further show that the feature peaks also change when the coordination number of the Cu cation is varied, while these feature peaks are independent of the zeolite topology. These findings help elucidate the experimental XANES features at an atomic and an electronic level.

Impact of metal cations on the electrocatalytic properties of Pt/C nanoparticles at multiple phase interfaces.

PubMed

Durst, Julien; Chatenet, Marian; Maillard, Frédéric

2012-10-05

Proton-exchange membrane fuel cells (PEMFCs) use carbon-supported nanoparticles based on platinum and its alloys to accelerate the rate of the sluggish oxygen-reduction reaction (ORR). The most common metals alloyed to Pt include Co, Ni and Cu, and are thermodynamically unstable in the PEMFC environment. Their dissolution yields the formation and redistribution of metal cations (M(y+)) within the membrane electrode assembly (MEA). Metal cations can also contaminate the MEA when metallic bipolar plates are used as current collectors. In each case, the electrical performance of the PEMFC severely decreases, an effect that is commonly attributed to the poisoning of the sulfonic acid groups of the perfluorosulfonated membrane (PEM) and the resulting decrease of the proton transport properties. However, the impact of metal cations on the kinetics of electrochemical reactions involving adsorption/desorption and bond-breaking processes remains poorly understood. In this paper, we use model electrodes to highlight the effect of metal cations on Pt/C nanoparticles coated or not with a perfluorosulfonated ionomer for the CO electrooxidation reaction and the oxygen reduction reaction. We show that metal cations negatively impact the ORR kinetics and the mass-transport resistance of molecular oxygen. However, the specific adsorption of sulfonate groups of the Nafion® ionomer locally modifies the double layer structure and increases the tolerance to metal cations, even in the presence of sulphate ions in the electrolyte. The survey is extended by using an ultramicroelectrode with cavity and a solid state cell (SSC) specifically developed for this study.

Ground-Water Quality in the Delaware River Basin, New York, 2001 and 2005-2006

USGS Publications Warehouse

Nystrom, Elizabeth A.

2007-01-01

The Federal Clean Water Act Amendments of 1977 require that States monitor and report on the quality of ground water and surface water. To satisfy part of these requirements, the U.S. Geological Survey and New York State Department of Environmental Conservation have developed a program in which ground-water quality is assessed in 2 to 3 of New York State's 14 major basins each year. To characterize the quality of ground water in the Delaware River Basin in New York, water samples were collected from December 2005 to February 2006 from 10 wells finished in bedrock. Data from 9 samples collected from wells finished in sand and gravel in July and August 2001 for the National Water Quality Assessment Program also are included. Ground-water samples were collected and processed using standard U.S. Geological Survey procedures. Samples were analyzed for more than 230 properties and compounds, including physical properties, major ions, nutrients, trace elements, radon-222, pesticides and pesticide degradates, volatile organic compounds, and bacteria. Concentrations of most compounds were less than drinking-water standards established by the U.S. Environmental Protection Agency and New York State Department of Health; many of the organic analytes were not detected in any sample. Drinking-water standards that were exceeded at some sites include those for color, turbidity, pH, aluminum, arsenic, iron, manganese, radon-222, and bacteria. pH ranged from 5.6 to 8.3; the pH of nine samples was less than the U.S. Environmental Protection Agency secondary drinking-water standard range of 6.5 to 8.5. Water in the basin is generally soft to moderately hard (hardness 120 milligrams per liter as CaCO3 or less). The cation with the highest median concentration was calcium; the anion with the highest median concentrations was bicarbonate. Nitrate was the predominant nutrient detected but no sample exceeded the 10 mg/L U.S. Environmental Protection Agency maximum contaminant level. The trace elements detected with the highest median concentrations were strontium and iron in unfiltered water and strontium and barium in filtered water. Concentrations of trace elements in several samples exceeded U.S. Environmental Protection Agency secondary drinking-water standards, including aluminum (50-200 micrograms per liter, three wells), arsenic (10 micrograms per liter, one well), iron (300 micrograms per liter, three wells), and manganese (50 micrograms per liter, four wells). The median concentration of radon-222 was 1,580 picoCuries per liter. Radon-222 is not currently regulated, but the U.S. Environmental Protection Agency has proposed a maximum contaminant level of 300 picoCuries per liter along with an alternative maximum contaminant level of 4,000 picoCuries per liter, to be in effect in states that have programs to address radon in indoor air. Concentrations of radon-222 exceeded the proposed maximum contaminant level in all 19 of the samples and exceeded the proposed alternative maximum contaminant level in 1 sample. Eleven pesticides and pesticide degradates were detected in samples from ten wells; all were herbicides or herbicide degradates. Three volatile organic compounds were detected, including disinfection byproducts such as trichloromethane and gasoline components or additives such as methyl tert-butyl ether. No pesticides, pesticide degradates, or volatile organic compounds were detected above established limits. Coliform bacteria were detected in samples from five wells, four of which were finished in sand and gravel; Escherichia coli was not detected in any sample.

Preliminary appraisal of the hydrology of the Red Oak area, Latimer County, Oklahoma

USGS Publications Warehouse

Marcher, M.V.; Bergman, D.L.; Stoner, J.D.; Blumer, S.P.

1983-01-01

Bed rock in the Red Oak area consists of shale, siltstone, and sandstone of the McAlester and Savanna Formations of Pennsylvanian age. Water in bedrock occurs in bedding planes, joints, and fractures and is confined. The potentiometric surface generally is less than 20 feet below the land surface. Wells yield enough water for domestic and stock use, but larger amounts of ground water are not available. Ground water commonly is a sodium or mixed cation carbonate/bicarbonate type with dissolved-solids concentrations ranging from 321 to 714 milligrams per liter. Although variable in quality, ground water generally is suitable for domestic use. No relationship between water chemistry and well depth or location is apparent. Brazil Creek, the principal stream in the area, has no flow 15 percent of the time, and flow is less than 1 cubic foot per second about 25 percent of the time. Water in Brazil Creek is a mixed cation carbonate/bicarbonate type. Dissolved-solids concentrations in Brazil Creek upstream from areas of old and recent mining ranged from 31 to 99 milligrams per liter with a mean of 58 milligrams per liter, whereas concentrations downstream from the mine areas ranged from 49 to 596 milligrams per liter with a mean of 132 milligrams per liter. Water in Brazil and Rock Creeks had concentrations of cadmium, chromium, lead, and mercury that exceeded maximum contaminant levels established by the U.S. Environmental Protection Agency at least once during the 1979-81 water years. Maximum suspended-sediment discharge, in tons per day, was 2,500 for Brazil Creek and 3,318 for Rock Creek. Silt-clay particles (diameters less than 0.062 millimeter) were the dominant sediment size. A significant hydrologic effect of surface mining is creation of additional water storage in mine ponds; one such pond supplies water for the town of Red Oak. Other effects or potential effects of surface mining include changes in rock permeability and ground-water storage, changes in drainage patterns, and changes in the chemical quality and sediment loads of streams.

Synthesis, crystal structure, vibrational spectroscopy, optical properties and theoretical studies of a new organic-inorganic hybrid material: [((CH3)2NH2)(+)]6·[(BiBr6)(3-)]2.

PubMed

Ben Ahmed, A; Feki, H; Abid, Y

2014-12-10

A new organic-inorganic hybrid material, [((CH3)2NH2)(+)]6·[(BiBr6)(3-)]2, has been synthesized and characterized by X-ray diffraction, FT-IR, Raman spectroscopy and UV-Visible absorption. The studied compound crystallizes in the triclinic system, space group P1¯ with the following parameters: a=8.4749(6)(Å), b=17.1392(12)(Å), c=17.1392(12)(Å), α=117.339(0)°, β=99.487(0)°, γ=99.487(0)° and Z=2. The crystal lattice is composed of a two discrete (BiBr6)(3-) anions surrounded by six ((CH3)2NH2)(+) cations. Complex hydrogen bonding interactions between (BiBr6)(3-) and organic cations from a three-dimensional network. Theoretical calculations were performed using density functional theory (DFT) for studying the molecular structure, vibrational spectra and optical properties of the investigated molecule in the ground state. The full geometry optimization of designed system is performed using DFT method at B3LYP/LanL2DZ level of theory using the Gaussian03. The optimized geometrical parameters obtained by DFT calculations are in good agreement with single crystal XRD data. The vibrational spectral data obtained from FT-IR and Raman spectra are assigned based on the results of the theoretical calculations. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complements with the experimental findings. The simulated spectra satisfactorily coincide with the experimental UV-Visible spectrum. The results show good consistent with the experiment and confirm the contribution of metal orbital to the HOMO-LUMO boundary. Copyright © 2014 Elsevier B.V. All rights reserved.

Optical backbone-sidechain charge transfer transitions in proteins sensitive to secondary structure and modifications.

PubMed

Mandal, I; Paul, S; Venkatramani, R

2018-04-17

The absorption of light by proteins can induce charge transfer (CT) transitions in the UV-visible range of the electromagnetic spectrum. Metal-ligand complexes or active site prosthetic groups which absorb in the visible region exhibit prominent CT transitions. Furthermore, the protein backbone also exhibits CT transitions in the far UV range. In this manuscript, we present a detailed computational study of new near UV-visible CT transitions that involve amino acids with charged side chains. Specifically, using time dependent density functional theory calculations, we examine the absorption spectra of naturally charged amino acids (Lys, Glu, Arg, Asp and His), extracted from solution phase protein structures generated by classical molecular dynamics simulations, and phosphorylated amino acids (Tyr, Thr and Ser) from experimentally determined protein structures. We show that amino acids with charged sidechains present a directed electronic donor-bridge-acceptor paradigm, with the lowest energy optical excitations demonstrating peptide backbone-sidechain charge separations. The UV-visible spectral range of the backbone-sidechain CT transitions is determined by the chemical nature of the donor, bridge and acceptor groups within each amino acid, amino acid conformation and the protein secondary structure where the amino acids are located. Photoinduced CT occurs in opposite directions for the anionic and cationic amino acids along the ground state dipole moment vector for the chromophores. We find that photoinduced charge separation is more facile for the anionic amino acids (Asp, Glu, pSer, pThr and pTyr) relative to that for the cationic amino acids (Lys, Arg and Hsp). Our results provide a foundation for the development of spectroscopic markers based on the recently proposed Protein Charge Transfer Spectra (ProCharTS) which are relevant for the study of DNA-binding or intrinsically disordered proteins that are rich in charged amino acids.

Counterintuitive electron localisation from density-functional theory with polarisable solvent models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dale, Stephen G., E-mail: sdale@ucmerced.edu; Johnson, Erin R., E-mail: erin.johnson@dal.ca

2015-11-14

Exploration of the solvated electron phenomena using density-functional theory (DFT) generally results in prediction of a localised electron within an induced solvent cavity. However, it is well known that DFT favours highly delocalised charges, rendering the localisation of a solvated electron unexpected. We explore the origins of this counterintuitive behaviour using a model Kevan-structure system. When a polarisable-continuum solvent model is included, it forces electron localisation by introducing a strong energetic bias that favours integer charges. This results in the formation of a large energetic barrier for charge-hopping and can cause the self-consistent field to become trapped in local minimamore » thus converging to stable solutions that are higher in energy than the ground electronic state. Finally, since the bias towards integer charges is caused by the polarisable continuum, these findings will also apply to other classical polarisation corrections, as in combined quantum mechanics and molecular mechanics (QM/MM) methods. The implications for systems beyond the solvated electron, including cationic DNA bases, are discussed.« less

Experimental-Theoretical Approach to the Adsorption Mechanisms for Anionic, Cationic, and Zwitterionic Surfactants at the Calcite-Water Interface.

PubMed

Durán-Álvarez, Agustín; Maldonado-Domínguez, Mauricio; González-Antonio, Oscar; Durán-Valencia, Cecilia; Romero-Ávila, Margarita; Barragán-Aroche, Fernando; López-Ramírez, Simón

2016-03-22

The adsorption of surfactants (DTAB, SDS, and CAPB) at the calcite-water interface was studied through surface zeta potential measurements and multiscale molecular dynamics. The ground-state polarization of surfactants proved to be a key factor for the observed behavior; correlation was found between adsorption and the hard or soft charge distribution of the amphiphile. SDS exhibits a steep aggregation profile, reaching saturation and showing classic ionic-surfactant behavior. In contrast, DTAB and CAPB featured diversified adsorption profiles, suggesting interplay between supramolecular aggregation and desorption from the solid surface and alleviating charge buildup at the carbonate surface when bulk concentration approaches CMC. This manifests as an adsorption profile with a fast initial step, followed by a metastable plateau and finalizing with a sharp decrease and stabilization of surface charge. Suggesting this competition of equilibria, elicited at the CaCO3 surface, this study provides atomistic insight into the adsorption mechanism for ionic surfactants on calcite, which is in accordance with experimental evidence and which is a relevant criterion for developing enhanced oil recovery processes.

Analysis of spin-Hamiltonian and molecular orbital coefficients of Cu2+ doped C8H11KO8 single crystal through EPR technique

NASA Astrophysics Data System (ADS)

Juliet sheela, K.; Krishnan, S. Radha; Shanmugam, V. M.; Subramanian, P.

2018-04-01

Electron paramagnetic resonance (EPR) studies have been investigated at X-band microwave frequency on Cu2+ ion incorporated into the single crystal of potassium succinate-succinic acid (KSSA) at room temperature. The angular variation of the EPR spectra has shown two magnetically in-equivalent Cu2+ sites in the KSSA single crystal system. The spin Hamiltonian parameters g and A are determined which reveals that the site I and site II occupied in rhombic and axial local field symmetry around the impurity ion. Among the two paramagnetic impurity ions, sites one occupies at substituitional position in the place of monovalent cation (K+) in the crystal whereas the other enters in its lattice interstitially by the correlation of EPR and crystal structure data. From the calculated principle values gxx, gyy, gzz and Axx, Ayy, Azz of both the sites, the admixture coefficients and molecular orbital coefficients were evaluated which gives the information of ground state wave function and types of bonding of impurity ions with the ligands.

Unexpected Actinyl Cation-Directed Structural Variation in Neptunyl(VI) A-Type Tri-lacunary Heteropolyoxotungstate Complexes

DOE PAGES

Berg, John M.; Gaunt, Andrew J.; May, Iain; ...

2015-04-22

A-type tri-lacunary heteropolyoxotungstate anions (e.g., [PW 9O 34] 9-, [AsW 9O 34] 9-, [SiW 9O 34] 10- and [GeW 9O 34] 10-) are multi-dentate oxygen donor ligands that readily form sandwich complexes with actinyl cations ({UO 2} 2+, {NpO 2} +, {NpO 2} 2+ & {PuO 2} 2+) in near neutral/slightly alkaline aqueous solutions. Two or three actinyl cations are sandwiched between two trilacunary anions, with additional cations (Na +, K + or NH 4 +) also often held within the cluster. Studies thus far have indicated that it is these additional +I cations, rather than the specific actinylmore » cation, that direct the structural variation in the complexes formed. We now report the structural characterization of the neptunyl (VI) cluster complex (NH 4) 13 [Na(NpO 2) 2(A-α- PW 9O 34) 2]·12H 2O. The anion in this complex, [Na(NpO 2) 2(PW 9O 34) 2] 13-, contains one Na + cation and two {NpO 2} 2+ cations held between two [PW 9O 34] 9- anions – with an additional partial occupancy NH 4 + or {NpO 2} 2+ cation also present. In the analogous uranium (VI) system, under similar reaction conditions that includes an excess of NH 4Cl in the parent solution, it was previously shown that [(NH 4) 2(U VIO 2) 2(A-PW 9O 34) 2] 12- is the dominant species in both solution and the crystallized salt. Spectroscopic studies provide further proof of differences in the observed chemistry for the {NpO 2} 2+/[PW 9O 34] 9- and {UO 2} 2+/[PW 9O 34] 9- systems, both in solution and in solid state complexes crystallized from comparable salt solutions. The work revealed that varying the actinide element (Np vs. U) can indeed measurably impact structure and complex stability in the cluster chemistry of actinyl (VI) cations with A-type tri-lacunary heteropolyoxotungstate anions.« less

Classical many-particle systems with unique disordered ground states

NASA Astrophysics Data System (ADS)

Zhang, G.; Stillinger, F. H.; Torquato, S.

2017-10-01

Classical ground states (global energy-minimizing configurations) of many-particle systems are typically unique crystalline structures, implying zero enumeration entropy of distinct patterns (aside from trivial symmetry operations). By contrast, the few previously known disordered classical ground states of many-particle systems are all high-entropy (highly degenerate) states. Here we show computationally that our recently proposed "perfect-glass" many-particle model [Sci. Rep. 6, 36963 (2016), 10.1038/srep36963] possesses disordered classical ground states with a zero entropy: a highly counterintuitive situation . For all of the system sizes, parameters, and space dimensions that we have numerically investigated, the disordered ground states are unique such that they can always be superposed onto each other or their mirror image. At low energies, the density of states obtained from simulations matches those calculated from the harmonic approximation near a single ground state, further confirming ground-state uniqueness. Our discovery provides singular examples in which entropy and disorder are at odds with one another. The zero-entropy ground states provide a unique perspective on the celebrated Kauzmann-entropy crisis in which the extrapolated entropy of a supercooled liquid drops below that of the crystal. We expect that our disordered unique patterns to be of value in fields beyond glass physics, including applications in cryptography as pseudorandom functions with tunable computational complexity.

Effect of clay in controlling the non-fluorescence H-dimeric states of a cationic dye Nile Blue Chloride (NBC) in hybrid Langmuir-Blodgett (LB) film

NASA Astrophysics Data System (ADS)

Debnath, Chandan; Shil, Ashis; Hussain, S. A.; Bhattacharjee, D.

2018-01-01

Present communication reports the effect of amphiphilic matrices and nano-clay platelets on the aggregation properties of a water soluble cationic fluorescent dye Nile Blue Chloride (NBC) in Langmuir-Blodgett (LB) films. In-situ Brewster Angle Microscopic (BAM) studies showed distinct domain structures of complex and hybrid Langmuir monolayer at the air-water interface. UV-vis absorption spectra showed non-fluorescent H-dimeric band in concentrated aqueous solution of NBC and in complex LB film of NBC with stearic acid. By changing various parameters, a great control over H-dimeric states has been achieved in clay incorporated hybrid LB films. These films can act as efficient fluorescence probe.

Electron localization and magnetism in SrRuO3 with non-magnetic cation substitution

NASA Astrophysics Data System (ADS)

Tong, W.; Huang, F.-Q.; Chen, I.-W.

2011-03-01

The destruction of the ferromagnetism of alloyed SrRuO3 can be caused by electron localization at the substitution sites. Among all the non-magnetic cations that enter the B site, Zr4 + is the least disruptive to conductivity and ferromagnetism. This is because Zr4 + does not cause any charge disorder, and its empty d electron states which are poorly matched in energy with the Ru t2g4 states cause the least resonance scattering of Ru's d electrons. Conducting Sr(Ru, Zr)O3 may be used as an electrode for perovskite-based thin film devices, while its insulating counterpart provides unprecedented magnetoresistance, seldom seen in other non-manganite and non-cobaltite perovskites.

Distribution and source of barium in ground water at Cattaraugus Indian Reservation, southwestern New York

USGS Publications Warehouse

Moore, R.B.; Staubitz, W.W.

1984-01-01

High concentrations of dissolved barium have been found in ground water from bedrock wells on the Seneca Nation of Indians Reservation on Cattaraugus Creek in southwestern New York. Concentrations in 1982 were as high as 23.0 milligrams per liter , the highest found reported from any natural ground-water system in the world. The highest concentrations are in a bedrock aquifer and in small lenses of saturated gravel between bedrock and the overlying till. The bedrock aquifer is partly confined by silt, clay, and till. The high barium concentrations are attributed to dissolution of the mineral barite (BaSO4), which is present in the bedrock and possibly in overlying silt, clay, or till. The dissolution of barite seems to be controlled by action of sulfate-reducing bacteria, which alter the BaSO4 equilibrium by removing sulfate ions and permitting additional barite to dissolve. Ground water from the surficial, unconsolidated deposits and surface water in streams contain little or no barium. Because barium is chemically similar to calcium, it probably could be removed by cation exchange or treatments similar to those used for water softening. (USGS)

Preparation and Analysis of RNA Crystals

NASA Technical Reports Server (NTRS)

Todd, Paul

2000-01-01

The crystallization of RiboNucleic Acids (RNA) was studied from the standpoint of mechanisms of crystal growth in three tasks: (1) preparation of high-quality crystals of oligonuclotides for X-ray diffraction, (2) finding pathways to the growth of high-quality crystals for X-ray diffraction and (3) investigation of mechanisms of action of inertial acceleration on crystal growth. In these tasks: (1) RNA crystals were prepared and studied by X-ray diffraction; (2) a pathway to high-quality crystals was discovered and characterized; a combination of kinetic and equilibrium factors could be optimized as described below; and (3) an interplay between purity and gravity was found in a combination of space and ground experiments with nucleic acids and proteins. Most significantly, the rate of concentration of precipitant and RNA can be controlled by membrane-based methods of water removal or by diffusion of multivalent cations across an interface stabilized by a membrane. Oligonucleotide solutions are electrokinetically stabilized colloids, and crystals can form by the controlled addition of multivalent cations.

Preparation of cation exchanger from lemon and sorption of divalent heavy metals.

PubMed

Arslanoglu, Hasan; Soner Altundogan, H; Tumen, Fikret

2008-05-01

A cation exchanging material was developed from lemon by modifying the pectic-cellulosic substances in the lemon peel by lemon juice having citric acid. For this purpose, chopped lemon removed from seeds and yellow skin was heated in two stages, firstly at 50 degrees C for 24h and subsequently at 120 degrees C for 2h. The material obtained was ground, repeatedly washed with water and dried. Lemon peel and lemon resin obtained were characterized through physicochemical analyses and FTIR spectroscopy. Heavy metal binding performance of this material was determined by removal tests conducted by using 10mM solutions of divalent metals. Experimental results show that the resin prepared from lemon is effective especially for Pb and Cu removals. For a lemon resin dosage of 10 g l(-1), sorption affinity of divalent metal ions is found to be in an order of Pb>Cu>Ni>Fe>Cd>Zn>Co>Mn. Typically, sorption capacities are about 0.87 and 0.43 mmol g(-1) for Pb and Mn, respectively.

Quantum Simulation of Helium Hydride Cation in a Solid-State Spin Register.

PubMed

Wang, Ya; Dolde, Florian; Biamonte, Jacob; Babbush, Ryan; Bergholm, Ville; Yang, Sen; Jakobi, Ingmar; Neumann, Philipp; Aspuru-Guzik, Alán; Whitfield, James D; Wrachtrup, Jörg

2015-08-25

Ab initio computation of molecular properties is one of the most promising applications of quantum computing. While this problem is widely believed to be intractable for classical computers, efficient quantum algorithms exist which have the potential to vastly accelerate research throughput in fields ranging from material science to drug discovery. Using a solid-state quantum register realized in a nitrogen-vacancy (NV) defect in diamond, we compute the bond dissociation curve of the minimal basis helium hydride cation, HeH(+). Moreover, we report an energy uncertainty (given our model basis) of the order of 10(-14) hartree, which is 10 orders of magnitude below the desired chemical precision. As NV centers in diamond provide a robust and straightforward platform for quantum information processing, our work provides an important step toward a fully scalable solid-state implementation of a quantum chemistry simulator.

Interaction of ammonium with birnessite: Evidence of a chemical and structural transformation in alkaline aqueous medium

NASA Astrophysics Data System (ADS)

Boumaiza, Hella; Coustel, Romain; Despas, Christelle; Ruby, Christian; Bergaoui, Latifa

2018-02-01

The ammonium cation interaction with Na-birnessite in aqueous alkaline medium was studied. Solution and solid analysis give evidence that birnessite is not only acting as a cationic exchanger toward NH4+. The surface analysis performed by XPS showed that N1s spectra are characterized by the existence of two different environments: one assignable to an interlayer NH4+ and the second to a chemisorbed N-species. Structural and chemical transformations were observed on birnessite with nitrogen mass balance deficit. The monitoring of NH4+, Na+, Mn2+, NO3- and NO2- and solid changes (average oxidation state of Mn, cation exchange capacity, solid nitrogen content and symmetry evolution identified by XRD and FTIR) indicate unambiguously that NH4+ reacts chemically with the birnessite.

Bond angle variations in XH3 [X = N, P, As, Sb, Bi]: the critical role of Rydberg orbitals exposed using a diabatic state model.

PubMed

Reimers, Jeffrey R; McKemmish, Laura K; McKenzie, Ross H; Hush, Noel S

2015-10-14

Ammonia adopts sp(3) hybridization (HNH bond angle 108°) whereas the other members of the XH3 series PH3, AsH3, SbH3, and BiH3 instead prefer octahedral bond angles of 90-93°. We use a recently developed general diabatic description for closed-shell chemical reactions, expanded to include Rydberg states, to understand the geometry, spectroscopy and inversion reaction profile of these molecules, fitting its parameters to results from Equation of Motion Coupled-Cluster Singles and Doubles (EOM-CCSD) calculations using large basis sets. Bands observed in the one-photon absorption spectrum of NH3 at 18.3 eV, 30 eV, and 33 eV are reassigned from Rydberg (formally forbidden) double excitations to valence single-excitation resonances. Critical to the analysis is the inclusion of all three electronic states in which two electrons are placed in the lone-pair orbital n and/or the symmetric valence σ* antibonding orbital. An illustrative effective two-state diabatic model is also developed containing just three parameters: the resonance energy driving the high-symmetry planar structure, the reorganization energy opposing it, and HXH bond angle in the absence of resonance. The diabatic orbitals are identified as sp hybrids on X; for the radical cations XH3(+) for which only 2 electronic states and one conical intersection are involved, the principle of orbital following dictates that the bond angle in the absence of resonance is acos(-1/5) = 101.5°. The multiple states and associated multiple conical intersection seams controlling the ground-state structure of XH3 renormalize this to acos[3 sin(2)(2(1/2)atan(1/2))/2 - 1/2] = 86.7°. Depending on the ratio of the resonance energy to the reorganization energy, equilibrium angles can vary from these limiting values up to 120°, and the anomalously large bond angle in NH3 arises because the resonance energy is unexpectedly large. This occurs as the ordering of the lowest Rydberg orbital and the σ* orbital swap, allowing Rydbergization to compresses σ* to significantly increase the resonance energy. Failure of both the traditional and revised versions of the valence-shell electron-pair repulsion (VSEPR) theory to explain the ground-state structures in simple terms is attributed to exclusion of this key physical interaction.

Effects of five years of frequent N additions, with or without acidity, on the growth and below-ground dynamics of a young Sitka spruce stand growing on an acid peat: implications for sustainability

NASA Astrophysics Data System (ADS)

Stutter, M. I.; Alam, M. S.; Langan, S. J.; Woodin, S. J.; Smart, R. P.; Cresser, M. S.

2004-06-01

An experiment comparing effects of sulphuric acid and reduced N deposition on soil water quality and on chemical and physical growth indicators for forest ecosystems is described. Six H2SO4 and (NH4)2SO4 treatment loads, from 0 - 44 and 0 - 25 kmolc ha-1 yr-1, respectively, were applied to outdoor microcosms of Pinus sylvestris seedlings in 3 acid to intermediate upland soils (calc-silicate, quartzite and granite) for 2 years. Different soil types responded similarly to H2SO4 loads, resulting in decreased leachate pH, but differently to reduced N inputs. In microcosms of calc-silicate soil, nitrification of NH4 resulted in lower pH and higher cation leaching than in acid treatments. By contrast, in quartzite and granite soils, (NH4)2SO4 promoted direct cation leaching, although leachate pH increased. The results highlighted the importance of soil composition on the nature of the cations leached, the SO4 adsorption capacities and microbial N transformations. Greater seedling growth on calc-silicate soils under both treatment types was related to sustained nutrient availability. Reductions in foliar P and Mg with higher N treatments were observed for seedlings in the calc-silicate soil. There were few treatment effects on quartzite and granite microcosm tree seedlings since P limitation precluded seedling growth responses to treatments. Hence, any benefits of N deposition to seedlings on quartzite and granite soils appeared limited by availability of co-nutrients, exacerbated by rapid depletion of soil exchangeable base cations.

Ground-Water Quality in Western New York, 2006

USGS Publications Warehouse

Eckhardt, David A.V.; Reddy, James E.; Tamulonis, Kathryn L.

2008-01-01

Water samples were collected from 7 production wells and 26 private residential wells in western New York from August through December 2006 and analyzed to characterize the chemical quality of ground water. Wells at 15 of the sites were screened in sand and gravel aquifers, and 18 were finished in bedrock aquifers. The wells were selected to represent areas of greatest ground-water use and to provide a geographical sampling from the 5,340-square-mile study area. Samples were analyzed for 5 physical properties and 219 constituents that included nutrients, major inorganic ions, trace elements, radionuclides, pesticides, volatile organic compounds (VOC), phenolic compounds, organic carbon, and bacteria. Results indicate that ground water used for drinking supply is generally of acceptable quality, although concentrations of some constituents or bacteria exceeded at least one drinking-water standard at 27 of the 33 wells. The cations that were detected in the highest concentrations were calcium, magnesium, and sodium; anions that were detected in the highest concentrations were bicarbonate, chloride, and sulfate. The predominant nutrients were nitrate and ammonia; nitrate concentrations were higher in samples from sand and gravel aquifers than in samples from bedrock. The trace elements barium, boron, copper, lithium, nickel, and strontium were detected in every sample; the trace elements with the highest concentrations were barium, boron, iron, lithium, manganese, and strontium. Eighteen pesticides, including 9 pesticide degradates, were detected in water from 14 of the 33 wells, but none of the concentrations exceeded State or Federal Maximum Contaminant Levels (MCLs). Fourteen volatile organic compounds were detected in water from 12 of the 33 wells, but none of the concentrations exceeded MCLs. Eight chemical analytes and three types of bacteria were detected in concentrations that exceeded Federal and State drinking-water standards, which are typically identical. Sulfate concentrations exceeded the U.S. Environmental Protection Agency (USEPA) Secondary Maximum Contaminant Level (SMCL) of 250 milligrams per liter (mg/L) in three samples, and chloride concentrations exceeded the SMCL of 250 mg/L in two samples. Sodium concentrations exceeded the USEPA Drinking Water Health Advisory of 60 mg/L in nine samples. Iron concentrations exceeded the SMCL of 300 ug/L (micrograms per liter) in 14 filtered samples, and manganese exceeded the USEPA SMCL of 50 ug/L in 15 filtered samples, as well as the New York State MCL of 300 ug/L in 1 filtered sample. Arsenic exceeded the USEPA MCL of 10 ug/L in two samples, aluminum exceeded the SMCL for aluminum of 50 ug/L in one sample, and lead exceeded the MCL of 15 ug/L in one sample. Radon-222 exceeded the proposed USEPA MCL of 300 picocuries per liter in 24 samples. Any detection of coliform bacteria indicates a violation of New York State health regulations; total coliform was detected in 12 samples, and Escherichia coli was detected in 2 samples. The plate counts for heterotrophic bacteria exceeded the MCL (500 colony-forming units per milliliter) in four samples.

Classification of matrix-product ground states corresponding to one-dimensional chains of two-state sites of nearest neighbor interactions

NASA Astrophysics Data System (ADS)

Fatollahi, Amir H.; Khorrami, Mohammad; Shariati, Ahmad; Aghamohammadi, Amir

2011-04-01

A complete classification is given for one-dimensional chains with nearest-neighbor interactions having two states in each site, for which a matrix product ground state exists. The Hamiltonians and their corresponding matrix product ground states are explicitly obtained.

L-Edge Xanes Measurements of the Oxidation State of Tungsten in Iron Bearing and Iron Free Silicate Glasses

NASA Technical Reports Server (NTRS)

Danielson, L. R.; Righter, K.; Sutton, S.; Newville, M.

2008-01-01

Tungsten is important in constraining core formation of the Earth because this element is a moderately siderophile element (depleted 10 relative to chondrites) and, as a member of the Hf-W isotopic system, it is useful in constraining the timing of core formation. A number of previous experimental studies have been carried out to determine the silicate solubility and metal-silicate partitioning behavior of W, including its concomitant oxidation state. However, results of previous studies are inconsistent on whether W occurs as W(4+) or W(6+). It is assumed that W(4+) is the cation valence relevant to core formation. Given the sensitivity to silicate composition of high valence cations, knowledge of the oxidation state of W over a wide range of fO2 is critical to understanding the oxidation state of the mantle and core formation processes. This study seeks to measure the W valence and change in valence state over the range of fO2 most relevant to core formation, around IW-2.

Exponentially-Biased Ground-State Sampling of Quantum Annealing Machines with Transverse-Field Driving Hamiltonians

NASA Technical Reports Server (NTRS)

Mandra, Salvatore

2017-01-01

We study the performance of the D-Wave 2X quantum annealing machine on systems with well-controlled ground-state degeneracy. While obtaining the ground state of a spin-glass benchmark instance represents a difficult task, the gold standard for any optimization algorithm or machine is to sample all solutions that minimize the Hamiltonian with more or less equal probability. Our results show that while naive transverse-field quantum annealing on the D-Wave 2X device can find the ground-state energy of the problems, it is not well suited in identifying all degenerate ground-state configurations associated to a particular instance. Even worse, some states are exponentially suppressed, in agreement with previous studies on toy model problems [New J. Phys. 11, 073021 (2009)]. These results suggest that more complex driving Hamiltonians are needed in future quantum annealing machines to ensure a fair sampling of the ground-state manifold.

Adsorption of reovirus by minerals and soils.

PubMed Central

Moore, R S; Taylor, D H; Reddy, M M; Sturman, L S

1982-01-01

Adsorption of [35S]methionine-labeled reovirus by 30 dry soils, minerals, and finely ground rocks suspended in synthetic freshwater at pH 7 was investigated to determine the conditions necessary for optimum virus removal during land application of wastewaters. All of the minerals and soils studied were excellent adsorbents of reovirus, with greater than 99% of the virus adsorbed after 1 h at 4 degrees C. Thereafter, virus remaining in suspension was significantly inactivated, and within 24 h a three to five log10 reduction in titer occurred. The presence of divalent cations, i.e., Ca2+ and Mg2+, in synthetic freshwater enhanced removal, whereas soluble organic matter decreased the amount of virus adsorbed in secondary effluent. The amount of virus adsorbed by these substrates was inversely correlated with the amount of organic matter, capacity to adsorb cationic polyelectrolyte, and electrophoretic mobility. Adsorption increased with increasing available surface area, as suspended infectivity was reduced further by the more finely divided substrates. However, the organic content of the soils reduced the level of infectious virus adsorbed below that expected from surface area measurements alone. The inverse correlation between virus adsorption and substrate capacity for cationic polyelectrolyte indicates that the adsorption of infectious reovirus particles is predominately a charged colloidal particle-charged surface interaction. Thus, adsorption of polyelectrolyte may be useful in predicting the fate of viruses during land application of sewage effluents and sludges. PMID:7149717

Kinetic Monte Carlo Simulation of Oxygen and Cation Diffusion in Yttria-Stabilized Zirconia

NASA Technical Reports Server (NTRS)

Good, Brian

2011-01-01

Yttria-stabilized zirconia (YSZ) is of interest to the aerospace community, notably for its application as a thermal barrier coating for turbine engine components. In such an application, diffusion of both oxygen ions and cations is of concern. Oxygen diffusion can lead to deterioration of a coated part, and often necessitates an environmental barrier coating. Cation diffusion in YSZ is much slower than oxygen diffusion. However, such diffusion is a mechanism by which creep takes place, potentially affecting the mechanical integrity and phase stability of the coating. In other applications, the high oxygen diffusivity of YSZ is useful, and makes the material of interest for use as a solid-state electrolyte in fuel cells. The kinetic Monte Carlo (kMC) method offers a number of advantages compared with the more widely known molecular dynamics simulation method. In particular, kMC is much more efficient for the study of processes, such as diffusion, that involve infrequent events. We describe the results of kinetic Monte Carlo computer simulations of oxygen and cation diffusion in YSZ. Using diffusive energy barriers from ab initio calculations and from the literature, we present results on the temperature dependence of oxygen and cation diffusivity, and on the dependence of the diffusivities on yttria concentration and oxygen sublattice vacancy concentration. We also present results of the effect on diffusivity of oxygen vacancies in the vicinity of the barrier cations that determine the oxygen diffusion energy barriers.

Solid state nuclear magnetic resonance investigation of polymer backbone dynamics in poly(ethylene oxide) based lithium and sodium polyether-ester-sulfonate ionomers.

PubMed

Roach, David J; Dou, Shichen; Colby, Ralph H; Mueller, Karl T

2013-05-21

Polymer backbone dynamics of single ion conducting poly(ethylene oxide) (PEO)-based ionomer samples with low glass transition temperatures (T(g)) have been investigated using solid-state nuclear magnetic resonance. Experiments detecting (13)C with (1)H decoupling under magic angle spinning (MAS) conditions identified the different components of the polymer backbone (PEO spacer and isophthalate groups) and their relative mobilities for a suite of lithium- and sodium-containing ionomer samples with varying cation contents. Variable temperature (203-373 K) (1)H-(13)C cross-polarization MAS (CP-MAS) experiments also provided qualitative assessment of the differences in the motions of the polymer backbone components as a function of cation content and identity. Each of the main backbone components exhibit distinct motions, following the trends expected for motional characteristics based on earlier Quasi Elastic Neutron Scattering and (1)H spin-lattice relaxation rate measurements. Previous (1)H and (7)Li spin-lattice relaxation measurements focused on both the polymer backbone and cation motion on the nanosecond timescale. The studies presented here assess the slower timescale motion of the polymer backbone allowing for a more comprehensive understanding of the polymer dynamics. The temperature dependences of (13)C linewidths were used to both qualitatively and quantitatively examine the effects of cation content and identity on PEO spacer mobility. Variable contact time (1)H-(13)C CP-MAS experiments were used to further assess the motions of the polymer backbone on the microsecond timescale. The motion of the PEO spacer, reported via the rate of magnetization transfer from (1)H to (13)C nuclei, becomes similar for T≳1.1 T(g) in all ionic samples, indicating that at similar elevated reduced temperatures the motions of the polymer backbones on the microsecond timescale become insensitive to ion interactions. These results present an improved picture, beyond those of previous findings, for the dependence of backbone dynamics on cation density (and here, cation identity as well) in these amorphous PEO-based ionomer systems.

Cation Distribution and Magnetism in Quenched ZnFe2O4

NASA Astrophysics Data System (ADS)

Yuan, Qiao; Pan, Linlin; Liu, Run; Wang, Jingming; Liao, Zuzhen; Qin, Lili; Bi, Jian; Gao, Daojiang; Wu, Jiangtao

2018-03-01

Spinel ferrites constitute one of the most important families of magnets; their properties are believed to be highly dependent on cation occupancy. Zinc ferrite materials synthesized by various methods are usually reported to exhibit enhanced magnetism, but the mechanism underlying such enhancement remains poorly understood, with at least three effects being considered, namely cation distribution, oxygen vacancies, and surface spin disorder. We report herein the individual influence of cation distribution on the magnetic properties of zinc ferrite microparticles, synthesized by solid-state reaction with a fast (200 K/s) quench process. Based on structure analyses including x-ray powder diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy, Mössbauer spectroscopy, and magnetic measurements, it is concluded that the as-prepared samples exhibited different cation distribution with inversion degree increasing from approximately 0.18 to 0.28 with increasing calcination temperature from 800°C to 1200°C. The magnetism measured at 2 K was found to be enhanced with increase of the inversion degree, while that measured at 300 K was found to be independent of inversion degree. The mechanism of the enhanced magnetization is that the indirect interaction between A and B site at low temperature is stronger than that between two nearest B sites.

Cation Distribution and Magnetism in Quenched ZnFe2O4

NASA Astrophysics Data System (ADS)

Yuan, Qiao; Pan, Linlin; Liu, Run; Wang, Jingming; Liao, Zuzhen; Qin, Lili; Bi, Jian; Gao, Daojiang; Wu, Jiangtao

2018-07-01

Spinel ferrites constitute one of the most important families of magnets; their properties are believed to be highly dependent on cation occupancy. Zinc ferrite materials synthesized by various methods are usually reported to exhibit enhanced magnetism, but the mechanism underlying such enhancement remains poorly understood, with at least three effects being considered, namely cation distribution, oxygen vacancies, and surface spin disorder. We report herein the individual influence of cation distribution on the magnetic properties of zinc ferrite microparticles, synthesized by solid-state reaction with a fast (200 K/s) quench process. Based on structure analyses including x-ray powder diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy, Mössbauer spectroscopy, and magnetic measurements, it is concluded that the as-prepared samples exhibited different cation distribution with inversion degree increasing from approximately 0.18 to 0.28 with increasing calcination temperature from 800°C to 1200°C. The magnetism measured at 2 K was found to be enhanced with increase of the inversion degree, while that measured at 300 K was found to be independent of inversion degree. The mechanism of the enhanced magnetization is that the indirect interaction between A and B site at low temperature is stronger than that between two nearest B sites.

Structural Modifications and Photophysical Studies of Fluorescent Conjugated Polymers for Solid State Sensor Development

NASA Astrophysics Data System (ADS)

Chen, Anting

Fluorescent conjugated polymers (FCPs) represent an exciting area of research in chemosensors and biosensors. Previously, the polymer tmeda-PPETE, N,N,N'-trimethylethylenediamino (tmeda) receptors on a poly[2,5-thiophenediyl-1,2-ethynediyl-1,4-phenylenediyl-1,2-ethynediyl] (PPETE) backbone, showed significant quenching when copper(II) was added. Tmeda-PPETE polymer preloaded with copper(II) was found to be a fluorescent "turn-on" sensor for iron cations. Additional investigation of this metallopolymer revealed a selective sensory system toward carbonate and phosphorus anions through a competitive binding of copper(II) between the polymer tmeda-PPETE and the anions. Fluorescent turn-on response under systematically varied pH was affected by the equilibrium shift of the ionization of polyprotic ions. A sterically hindered pentiptycene group was introduced to the PPETE polymer backbone aiming to reduce aggregation and self-quenching in the solid state. A new FCP, tmeda-PPpETE (poly[(pentiptycene ethynylene)-alt-(thienylene ethynylene)] with tmeda receptors, has been designed and synthesized via Sonogashira cross-coupling reaction. Absorption and emission spectra of tmeda-PPpETE showed blue shifting from tmeda-PPETE, suggesting increased rigidity of polymer backbone. Tmeda-PPpETE showed a high selectivity towards copper(II) with improved sensitivity compared to tmeda-PPETE. The fluorescent quenching response is over 120-fold at emission maximum, and the detection limit is 1.04 ppb, significantly lower than the EPA action level of 1.3 ppm for copper(II). A small turn-off fluorescent response of tmeda-PPpETE was also observed upon addition of iron cations. To further investigate the interaction between pentiptycene containing polymers and iron cations, tmpda-PPpETE containing N,N,N'-trimethylpropylenediamino (tmpda) receptors was designed and synthesized. The absorption and emission spectra for tmpda-PPpETE were analogous to those of tmeda-PPpETE, with a higher quantum yield for tmpda-PPpETE. The cation selectivity test in solution showed selective fluorescent quenching for iron cations. Investigation of the polymer-iron interaction showed that two binding mechanisms were involved. This is the first report of pentiptycene-derived polymer participating in a metal complex formation. By using 1,3,5-triethynylbenzene as the linker group, a network of PPETE polymer backbone loaded with tmeda receptors was designed and synthesized. This transformed the linear FCP, tmeda-PPETE into a network polymer. Two derivatives of this polymer were also successfully synthesized. The metal cation selectivity test showed similar fluorescent response as tmeda-PPETE, which revealed the potential in developing solid state sensors.

Direct observation of a photochemical activation energy: a case study of acetone photodissociation

NASA Astrophysics Data System (ADS)

Koch, Markus; Heim, Pascal; Thaler, Bernhard; Kitzler, Markus; Ernst, Wolfgang E.

2017-06-01

The ability to observe and quantify the conversion of electronic potential energy to vibrational kinetic energy in a molecule after photoexcitation is essential to understand and control the outcome of photoinduced molecular fragmentation. We exploit the high selectivity of photoelectron-photoion coincidence detection to distinguish different relaxation channels and observe the fragmentation behavior of each channel. We demonstrate the concept by investigating the fragmentation of gas-phase acetone molecules initiated by three-photon excitation to high lying Rydberg states between 9.0 and 9.5 eV above the ground state. By applying variations of the photon energy, pulse duration (100-200 fs) and pulse energy, we are able to fully characterize the fragmentation process. Rydberg states between 5s and 8s are populated, which undergo ultrafast internal conversion to lower states. The corresponding non-adiabatic dynamics in the neutral molecule cause the conversion of electronic to vibrational energy, leading to fragmentation. Our scheme allows us to directly measure the activation energy for fragmentation of acetone to an acetyl ion and a methyl radical, which we determine to be (0.79 ± 0.04) eV. Longer laser pulses result in an increased fragment-to-parent ratio, representing a higher probability for relaxation because the relaxation time constants are comparable to the pulse duration. Upon excitation to Rydberg states at 9.5 eV we surprisingly observe reduced fragmentation, although ˜2 eV are coupled into vibrational energy, indicating that different relaxation pathways become active, which results in a change of the redistribution of vibrational energy within the molecule. Fragmentation due to subsequent excitation of the cation is found to play a minor role.

Orbital stability and energy estimate of ground states of saturable nonlinear Schrödinger equations with intensity functions in R2

NASA Astrophysics Data System (ADS)

Lin, Tai-Chia; Wang, Xiaoming; Wang, Zhi-Qiang

2017-10-01

Conventionally, the existence and orbital stability of ground states of nonlinear Schrödinger (NLS) equations with power-law nonlinearity (subcritical case) can be proved by an argument using strict subadditivity of the ground state energy and the concentration compactness method of Cazenave and Lions [4]. However, for saturable nonlinearity, such an argument is not applicable because strict subadditivity of the ground state energy fails in this case. Here we use a convexity argument to prove the existence and orbital stability of ground states of NLS equations with saturable nonlinearity and intensity functions in R2. Besides, we derive the energy estimate of ground states of saturable NLS equations with intensity functions using the eigenvalue estimate of saturable NLS equations without intensity function.

Symmetry-breaking dynamics of the finite-size Lipkin-Meshkov-Glick model near ground state

NASA Astrophysics Data System (ADS)

Huang, Yi; Li, Tongcang; Yin, Zhang-qi

2018-01-01

We study the dynamics of the Lipkin-Meshkov-Glick (LMG) model with a finite number of spins. In the thermodynamic limit, the ground state of the LMG model with an isotropic Hamiltonian in the broken phase breaks to a mean-field ground state with a certain direction. However, when the spin number N is finite, the exact ground state is always unique and is not given by a classical mean-field ground state. Here, we prove that when N is large but finite, through a tiny external perturbation, a localized state which is close to a mean-field ground state can be prepared, which mimics spontaneous symmetry breaking. Also, we find the localized in-plane spin polarization oscillates with two different frequencies ˜O (1 /N ) , and the lifetime of the localized state is long enough to exhibit this oscillation. We numerically test the analytical results and find that they agree very well with each other. Finally, we link the phenomena to quantum time crystals and time quasicrystals.

Optical Feshbach resonances and ground-state-molecule production in the RbHg system

NASA Astrophysics Data System (ADS)

Borkowski, Mateusz; Muñoz Rodriguez, Rodolfo; Kosicki, Maciej B.; Ciuryło, Roman; Żuchowski, Piotr S.

2017-12-01

We present the prospects for photoassociation, optical control of interspecies scattering lengths, and, finally, the production of ultracold absolute ground-state molecules in the Rb+Hg system. We use the state-of-the-art ab initio methods for the calculations of ground- [CCSD(T)] and excited-state (EOM-CCSD) potential curves. The RbHg system, thanks to the wide range of stable Hg bosonic isotopes, offers possibilities for mass tuning of ground-state interactions. The optical lengths describing the strengths of optical Feshbach resonances near the Rb transitions are favorable even at large laser detunings. Ground-state RbHg molecules can be produced with efficiencies ranging from about 20% for deeply bound to at least 50% for weakly bound states close to the dissociation limit. Finally, electronic transitions with favorable Franck-Condon factors can be found for the purposes of a STIRAP transfer of the weakly bound RbHg molecules to the absolute ground state using commercially available lasers.

Water-quality assessment of the Rio Grande Valley, Colorado, New Mexico, and Texas : shallow ground-water quality and land use in the Albuquerque area, central New Mexico, 1993

USGS Publications Warehouse

Anderholm, Scott K.

1997-01-01

This report describes the quality of shallow ground water and the relations between land use and the quality of that shallow ground water in an urban area in and adjacent to Albuquerque, New Mexico. Water samples were collected from 24 shallow wells. Samples were analyzed for selected common constituents, nutrients, trace elements, radionuclides, volatile organic compounds, and pesticides. The study area, which is in the Albuquerque Basin in central New Mexico, was limited to the Rio Grande flood plain; depth to water in this area generally is less than 25 feet. The amount and composition of recharge to the shallow ground-water system are important factors that affect shallow ground-water composition in this area. Important sources of recharge that affect shallow ground-water quality in the area include infiltration of surface water, which is used in agricultural land-use areas to irrigate crops, and infiltration of septic-system effluent in residential areas. Agricultural land use represents about 28 percent of the area, and residential land use represents about 35 percent of the total study area. In most of the study area, agricultural land use is interspersed with residential land use and neither is the dominant land use in the area. Land use in the study area historically has been changing from agricultural to urban. The composition of shallow ground water in the study area varies considerably. The dissolved solids concentration in shallow ground water in the study area ranges from 272 to 1,650 milligrams per liter, although the relative percentages of selected cations and anions do not vary substantially. Calcium generally is the dominant cation and bicarbonate generally is the dominant anion. Concentrations of nutrients generally were less than 1 milligram per liter. The concentration of many trace elements in shallow ground water was below or slightly above 1 microgram per liter and there was little variation in the concentrations. Barium, iron, manganese, molybdenum, and uranium were the only trace elements analyzed for that had median concentrations greater than 5 micrograms per liter. Volatile organic compounds were detected in 5 of 24 samples. Cis-1,2-dichloroethene and 1,1-dichloroethane were the most commonly detected volatile organic compounds (detected in two samples each). Pesticides were detected in 8 of 24 samples. Prometon was the most commonly detected pesticide (detected in 5 of 24 samples). Concentrations of volatile organic compounds and pesticides detected were much smaller than any U.S. Environmental Protection Agency standards that have been established. Infiltration of surface water and the evaporation or transpiration of this water, which partially is the result of past and present agricultural land use, seem to affect the concentrations of common constituents in shallow ground water in the study area. The small excess chloride in shallow ground water relative to surface water that has been affected by evaporation or transpiration could be due to mixing of shallow ground water with small amounts of precipitation/bulk deposition or septic-system effluent. Infiltration of septic-system effluent (residential land use) has affected the shallow ground-water composition in parts of the study area on the basis of the small dissolved oxygen concentrations, large dissolved organic carbon concentrations, and excess chloride. Despite the loading of nitrogen to the shallow ground-water system as the result of infiltration of septic-system effluent, the small nitrogen concentrations in shallow ground water probably are due to the small dissolved oxygen concentrations and relatively large dissolved organic carbon concentrations. The small concentrations and lack of variation of most trace elements indicate that land use has not substantially affected the concentration

MRCI study on transition dipole moments and transition probabilities of 18 low-lying states of CP+ cation

NASA Astrophysics Data System (ADS)

Zhou, Dan; Wang, Kedong; Li, Xue

2018-07-01

This study calculates the potential energy curves of 18 Λ-S and 50 Ω states, which arise from the C(3Pg) + P+(3Pg) dissociation channel of the CP+ cation. The calculations are made using the CASSCF method, followed by the icMRCI approach with the Davidson correction. Core-valence correlation and scalar relativistic corrections, as well as extrapolation to the complete basis set limit are included. The transition dipole moments are computed for 25 pairs of Λ-S states. The spin-orbit coupling effect on the spectroscopic and vibrational properties is evaluated. The Franck-Condon factors and Einstein coefficients of emissions are calculated. Radiative lifetimes are obtained for several vibrational levels of some states. The transitions are evaluated and spectroscopic measurement schemes for observing these Λ-S states are proposed. The potential energy curves, spectroscopic constants, vibrational levels, transition dipole moments, and transition probabilities reported in this paper can be considered to be very accurate and reliable. Because no experimental observations are currently available, the results obtained here can be used as guidelines for the detection of these states in appropriate spectroscopy experiments, in particular for observations in stellar atmospheres and in interstellar space.

Ground-water quality in east-central Idaho valleys

USGS Publications Warehouse

Parliman, D.J.

1982-01-01

From May through November 1978, water quality, geologic, and hydrologic data were collected for 108 wells in the Lemhi, Pahsimeroi, Salman River (Stanley to Salmon), Big Lost River, and Little Lost River valleys in east-central Idaho. Data were assembled to define, on a reconnaissance level, water-quality conditions in major aquifers and to develop an understanding of factors that affected conditions in 1978 and could affect future ground-water quality. Water-quality characteristics determined include specific conductance, pH, water temperature, major dissolved cations, major dissolved anions, and coliform bacteria. Concentrations of hardness, nitrite plus nitrate, coliform bacteria, dissolved solids, sulfate, chloride, fluoride , iron, calcium, magnesium, sodium, potassium or bicarbonate exceed public drinking water regulation limits or were anomalously high in some water samples. Highly mineralized ground water probably is due to the natural composition of the aquifers and not to surface contamination. Concentrations of coliform bacteria that exceed public drinking water limits and anomalously high dissolved nitrite-plus-nitrite concentrations are from 15- to 20-year old irrigation wells in heavily irrigated or more densely populated areas of the valleys. Ground-water quality and quantity in most of the study area are sufficient to meet current (1978) population and economic demands. Ground water in all valleys is characterized by significant concentrations of calcium, magnesium, and bicarbonate plus carbonate ions. Variations in the general trend of ground-water composition (especially in the Lemhi Valley) probably are most directly related to variability in aquifer lithology and proximity of sampling site to source of recharge. (USGS)

Ab-Initio Calculation of Electronic Structure of Lead Halide Perovskites with Formamidinium Cation as an Active Material for Perovskite Solar Cells

NASA Astrophysics Data System (ADS)

Indari, E. D.; Wungu, T. D. K.; Hidayat, R.

2017-07-01

Organic lead halide perovskite material based solar cells show impressive power conversion efficiencies, which can reach above 19 percent for perovskite solar cell with methyl-ammonium cations. These efficiencies are originated from efficient photoexcitation and charge carrier transport and not observed in conventional perovskite crystals. In this preliminary research work, we therefore performed Density Functional Theory (DFT) calculation of formamidinium lead iodide (FAPI), an alternative to methyl-ammonium lead iodide (MAPI), to predict their electronic structure and density of state (DOS). The calculation result at the most stable lattice parameters show a good agreement with the experiment results. The obtained band gap energy is 1.307 eV. The valence band is dominantly formed by the 5p orbitals of I- anions, while the conduction band is dominantly formed by the 6p orbitals of Pb2+ cations. The DOS of valence band of this perovskite seems smaller compared to the case of methyl-ammonium lead iodide perovskite, which then may explain the observation of smaller power conversion efficiencies in perovskite solar cells with this formamidinium cations.

Structure and performance of cationic assembly dispersed in amphoteric surfactants solution as a shampoo for hair damaged by coloring.

PubMed

Nagahara, Yasuo; Nishida, Yuichi; Isoda, Masanori; Yamagata, Yoshifumi; Nishikawa, Naoki; Takada, Koji

2007-01-01

In recent years, hair coloring gains popularity as a trend of consumer's hair care. This coloring frequently damages hair. In response to this, a new shampoo-base was developed for repairing hair damaged by coloring. The new shampoo-base was prepared by dispersing cationic assembly in a solution of amphoteric surfactants. The mixture of behenyl trimethyl ammonium chloride (C22TAC) and behenyl alcohol (C22OH) was applied as the cationic assembly, which are dispersed in amido propyl betaine laurate (LPB) solution. LPB, which behaves as an amphoteric surfactant, was used as the wash-base. It was verified from the results on the measurements of DSC, calorimeter polarization, cryo-SEM and X-ray diffraction that the cationic assembly has a crystalline structure in the LPB solution. The new shampoo-base was highly efficient to change the color-damaged hair from hydrophilic to hydrophobic. The friction level of the hair washed with the new shampoo-base recovered to the same state as that of healthy hair. The exfoliation of cuticle was reduced after washing with the new shampoo-base.

The doping sites in Eu2+-doped AIBIIPO4 phosphors and their consequence on the photoluminescence excitation spectra

NASA Astrophysics Data System (ADS)

Amer, M.; Boutinaud, P.

2018-02-01

The energy corresponding to the excitation edge in Eu2+-doped phosphate phosphors of the type AIBIIPO4 (AI = monovalent cation, BII = divalent cation) is calculated from the knowledge of two crystal-structure-related factors he(X(i)) and Fc(X(i)) which are connected respectively to the crystal field splitting (CFS) and the centroid energy (Ec) of the excited 4f65d1 electron configuration of Eu2+. The calculation is carried out for each cation site X(i) available for Eu2+ in 25 different compositions of AIBIIPO4 including NaZnPO4-Eu2+ for which the luminescence is firstly reported. Our results indicate (1) that is it possible to identify the nature of the cation site that contributes to the excitation edge of Eu2+ in AIBIIPO4 within an accuracy of±1000 cm-1 and (2) that the method can be used as a tool for the predictive design of AIBIIPO4 - Eu2+ phosphors applicable in solid state LED-based lighting.

Specific cationic emission of cisplatin following ionization by swift protons

NASA Astrophysics Data System (ADS)

Moretto-Capelle, Patrick; Champeaux, Jean-Philippe; Deville, Charlotte; Sence, Martine; Cafarelli, Pierre

2016-05-01

We have investigated collision-induced ionization and fragmentation by 100 keV protons of the radio sensitizing molecule cisplatin, which is used in cancer treatments. A large emission of HCl+ and NH2+ is observed, but surprisingly, no cationic fragments containing platinum are detected, in contrast to ionization-dissociation induced by electronic collision. Theoretical investigations show that the ionization processes take place on platinum and on chlorine atoms. We propose new ionization potentials for cisplatin. Dissociation limits corresponding to the measured fragmentation mass spectrum have been evaluated and the theoretical results show that the non-observed cationic fragments containing platinum are mostly associated with low dissociation energies. We have also investigated the reaction path for the hydrogen transfer from the NH3 group to the Cl atom, as well as the corresponding dissociation limits from this tautomeric form. Here again the cations containing platinum correspond to lower dissociation limits. Thus, the experimental results suggest that excited states, probably formed via inner-shell ionization of the platinum atom of the molecule, correlated to higher dissociation limits are favored.

Superionic state in double-layer capacitors with nanoporous electrodes.

PubMed

Kondrat, S; Kornyshev, A

2011-01-19

In recent experiments (Chmiola et al 2006 Science 313 1760; Largeot et al 2008 J. Am. Chem. Soc. 130 2730) an anomalous increase of the capacitance with a decrease of the pore size of a carbon-based porous electric double-layer capacitor has been observed. We explain this effect by image forces which exponentially screen out the electrostatic interactions of ions in the interior of a pore. Packing of ions of the same sign becomes easier and is mainly limited by steric interactions. We call this state 'superionic' and suggest a simple model to describe it. The model reveals the possibility of a voltage-induced first order transition between a cation(anion)-deficient phase and a cation(anion)-rich phase which manifests itself in a jump of capacitance as a function of voltage.

Strain Manipulated Magnetic Properties in ZnO and GaN Induced by Cation Vacancy

NASA Astrophysics Data System (ADS)

Gai, Yanqin; Jiang, Jiaping; Wu, Yuxi; Tang, Gang

2016-07-01

The effects of isotropic strains on the magnetic properties in ZnO and GaN induced by cation vacancies are comparatively investigated by density functional theory calculations. The magnetic moments and the couplings between vacancies in different charged states are calculated as a function of strains. The modulation of strain on the magnetic properties relies on the materials and the charge states of cation vacancies in them. As the occurrence of charge transfer in ZnO: V Zn under compression, the coupling between V_{{Zn}}0 is antiferromagnetic (AFM) and it could be stabilized by strains. Tensions can strengthen the ferromagnetic (FM) coupling between V_{{Zn}}0 but weaken that of V_{{Ga}}^{ - } . The neutral V Ga are always AFM coupling under strains from -6 to +6% and could be stabilized by compressions. The interactions between V_{{Ga}}^{ - } are always FM with ignorable variations under strains; however, the FM couplings between V_{{Ga}}^{2 - } could be strengthened by compressions. These varying trends of magnetic coupling under strains are interpreted by the band coupling models. Therefore, strain-engineering provides a route to manipulate and design high Curie temperature ferromagnetism derived and mediated by intrinsic defect for spintronic applications.

Quantum chemical studies of a model for peptide bond formation. 3. Role of magnesium cation in formation of amide and water from ammonia and glycine

NASA Technical Reports Server (NTRS)

Oie, T.; Loew, G. H.; Burt, S. K.; MacElroy, R. D.

1984-01-01

The SN2 reaction between glycine and ammonia molecules with magnesium cation Mg2+ as a catalyst has been studied as a model reaction for Mg(2+)-catalyzed peptide bond formation using the ab initio Hartree-Fock molecular orbital method. As in previous studies of the uncatalyzed and amine-catalyzed reactions between glycine and ammonia, two reaction mechanisms have been examined, i.e., a two-step and a concerted reaction. The stationary points of each reaction including intermediate and transition states have been identified and free energies calculated for all geometry-optimized reaction species to determine the thermodynamics and kinetics of each reaction. Substantial decreases in free energies of activation were found for both reaction mechanisms in the Mg(2+)-catalyzed amide bond formation compared with those in the uncatalyzed and amine-catalyzed amide bond formation. The catalytic effect of the Mg2+ cation is to stabilize both the transition states and intermediate, and it is attributed to the neutralization of the developing negative charge on the electrophile and formation of a conformationally flexible nonplanar five-membered chelate ring structure.

Compositional and Ionic-Size Controls on the Diffusion of Divalent Cations in Garnet: Insights from Atomistic Simulations

NASA Astrophysics Data System (ADS)

Carlson, W. D.

2012-12-01

Divalent cations in garnet (Mg, Fe, Mn, Ca) diffuse at rates that depend strongly on the host-crystal composition and on the ionic radius of the diffusant. Understanding of the nanoscale basis for these behaviors comes from atomistic simulations that calculate energies in the static limit for the defects and transition-state configurations associated with each diffusive step. Diffusion of divalent cations requires (a) creation of a cation-vacancy defect in a dodecahedral site and of a charge-compensating oxygen-vacancy defect that may or may not be in close spatial association; (b) except in the case of self-diffusion, creation of an impurity defect in which a foreign atom replaces the normal atom in a dodecahedral site adjacent to the vacancy; and (c) during the diffusive process, motion of the diffusing atom to a 'saddlepoint' position that represents the transition-state configuration. Comparisons of the system's energy in these various states, in structures of different composition and for ions of different ionic size, allows assessment of the nanoscale controls on diffusion kinetics. Molecular-statics calculations quantify defect energies and identify the transition-state configuration: the maximum energy along the diffusion path between two adjacent dodecahedral sites results when the diffusing ion is surrounded symmetrically by the six oxygen atoms that lie between the two sites. Across the range of end-member compositions, self-diffusion coefficients measured at identical conditions, and the tracer diffusivity of a single ion measured at identical conditions, can each vary by five orders of magnitude or more. Measured activation energies for these motions, however, are all equivalent to within ±6%. Calculated activation energies are in agreement with observations, in that they vary by only ±10%. Calculated vacancy-formation energies, on the other hand, are significantly larger in expanded structures; for example, that energy is greater for Prp than for Grs by ~ 470 kJ/mol. Thus in expanded structures, much higher vacancy concentrations can be produced at the same energetic cost, greatly enhancing rates of diffusion. The primary explanation for the more rapid diffusion of divalent cations in structures with larger cell dimensions therefore comes not from reduced saddlepoint strain energies in more compliant structures, but instead from the smaller energy required to create vacancy defects. Diffusivities of divalent cations exhibit a curious parabolic dependence on ionic size: for each structure, an optimally-sized ion exists, close in size to the dominant ion, that exhibits the fastest diffusion. Larger ions — and enigmatically, smaller ions — both diffuse more slowly. Calculated impurity-defect energies show that undersized impurity ions are bound more tightly in their sites, but the effects are too small in comparison to corresponding reductions in strain energy for the transition-state configuration to account for observed rate differences. Calculated vacancy-association energies reveal a slight tendency for vacancies to associate preferentially with larger impurity ions, but again the effect appears to be too small to provide a full explanation for observed behaviors.

Ground-state energies of the nonlinear sigma model and the Heisenberg spin chains

NASA Technical Reports Server (NTRS)

Zhang, Shoucheng; Schulz, H. J.; Ziman, Timothy

1989-01-01

A theorem on the O(3) nonlinear sigma model with the topological theta term is proved, which states that the ground-state energy at theta = pi is always higher than the ground-state energy at theta = 0, for the same value of the coupling constant g. Provided that the nonlinear sigma model gives the correct description for the Heisenberg spin chains in the large-s limit, this theorem makes a definite prediction relating the ground-state energies of the half-integer and the integer spin chains. The ground-state energies obtained from the exact Bethe ansatz solution for the spin-1/2 chain and the numerical diagonalization on the spin-1, spin-3/2, and spin-2 chains support this prediction.

Radioactive ion detector

DOEpatents

Bower, Kenneth E.; Weeks, Donald R.

1997-01-01

Apparatus for detecting the presence, in aqueous media, of substances which emit alpha and/or beta radiation and determining the oxidation state of these radioactive substances, that is, whether they are in cationic or anionic form. In one embodiment, a sensor assembly has two elements, one comprised of an ion-exchange material which binds cations and the other comprised of an ion-exchange material which binds anions. Each ion-exchange element is further comprised of a scintillation plastic and a photocurrent generator. When a radioactive substance to which the sensor is exposed binds to either element and emits alpha or beta particles, photons produced in the scintillation plastic illuminate the photocurrent generator of that element. Sensing apparatus senses generator output and thereby indicates whether cationic species or anionic species or both are present and also provides an indication of species quantity.

Radioactive ion detector

DOEpatents

Bower, K.E.; Weeks, D.R.

1997-08-12

Apparatus for detecting the presence, in aqueous media, of substances which emit alpha and/or beta radiation and determining the oxidation state of these radioactive substances, that is, whether they are in cationic or anionic form. In one embodiment, a sensor assembly has two elements, one comprised of an ion-exchange material which binds cations and the other comprised of an ion-exchange material which binds anions. Each ion-exchange element is further comprised of a scintillation plastic and a photocurrent generator. When a radioactive substance to which the sensor is exposed binds to either element and emits alpha or beta particles, photons produced in the scintillation plastic illuminate the photocurrent generator of that element. Sensing apparatus senses generator output and thereby indicates whether cationic species or anionic species or both are present and also provides an indication of species quantity. 2 figs.

The [C{sub 6}H{sub 10}]{sup {sm{underscore}bullet}+} hypersurface: The parent radical cation Diels-Alder reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffmann, M.; Schaefer, H.F. III

1999-07-21

Various possible reaction pathways between ethene and butadiene radical cation (cis- and trans-), have been investigated at different levels of theory up to UCCSD(T)/DZP/UMP2(fc)/DZP and with density functional theory at B3LYP/DZP. A stepwise addition involving open chain intermediates and leading to the Diels-Alder product, the cyclohexene radical cation, was found to have a total activation barrier {Delta}G{sup 298{ne}} = 6.3 kcal mol{sup {minus}1} and a change in free Gibbs energy, {Delta}G{sup 298}, of {minus}33.5 kcal mol{sup {minus}1}. On the E{degree} potential energy surface, all transition states are lower in energy than separated ethene and butadiene, the exothermicity {Delta}E = -45.6more » kcal mol{sup {minus}1}. A more direct path could be characterized as stepwise with one intermediate only at the SCF level but not at electron-correlated levels and hence might actually be a concerted strongly asynchronous addition with a very small or no activation barrier (UCCSD(T)/DZP/UHF/6-31G* gives a {Delta}G{sup 298{ne}} of 0.8 kcal mol{sup {minus}1}). The critical step for another alternative, the cyclobutanation-vinylcyclobutane/cyclohexene rearrangement, is a 1,3-alkyl shift which involves a barrier ({Delta}G{sup 298{ne}}) only 1.7 kcal mol{sup {minus}1} higher than that of stop use addition for both cis-, and trans-butadiene radical cation. However, from the (ethene and trans-butadiene) reactions, ring expansion of the vinylcyclobutane radical cation intermediate, to a methylene cyclopentane radical cation, requires an activation only 1.3 kcal mol{sup {minus}1} larger than for (trans-butadiene radical). While cis/trans isomerization of free butadiene radical cation requires a high activation (24.9 kcal mol{sup {minus}1}), a reaction sequence involving addition of ethene (to stepwise give an open chain intermediate and vinyl cyclobutane radical cation) has a barrier of only 3.5 kcal mol{sup {minus}1} ({Delta}G{sup 298{ne}}). This sequence also makes ethene and butadiene radical cations to exchange terminal methylene groups.« less

POLYMERIZATION OF /cap alpha/-METHYLSTYRENE BY ELECTRON IRRADIATION (in German)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Braun, D.; Heufer, G.; Seufert, W.

1964-01-01

Ampoules of alpha -methylstyrene sealed under vacuum were irradiated with 1-Mev electrons in a type JS Van de Graaff generator; comparative experiments with gamma rays were carried out with a /sup 60/Co source of 3000 deg C. High doses of electrons (ca. 10/sup 8/ rad) are necessary for polymerization. The conversion is graphed as a function of dose at 0 deg C; it reaches a maximum plateau of 65% at 4 x 10/sup 8/ rad; this may point to radiolysis of the polymer at doses above this. Polymerization conversion increases with decreasing dose rate, when dose and temperature are heldmore » constant; and conversion increases with decreasing temperature (22% at --22 deg C; 10% at 15 deg C; <1% at 60 deg C), as has been found with gamma rays. In the solid state between --40 deg C and --80 deg C the maximum yield is only about 5%. The molecular weights of all poly- alpha -methylstyrenes thus formed lie between 3000 and 12,000, independently of dose rate and temperature. All polymethylstyrenes formed in the liquid state have approximately the same tacticity independent of temperature (isotactic about 20%; syndiotactic about 80%). This corresponds to the tacticity of polymers formed cationically with Lewis acids. In the solid state the tacticity is: isotactic 38%, syndiotactic, 62%, comparable with the tacticity of anionic polymerization. In the liquid state the tacticity and the sensitivity towards water indicate a cationic mechanism for the reaction. NMR studies also indicate a cationic mechanism. (BBB)« less

40 CFR 141.401 - Sanitary surveys for ground water systems.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 23 2011-07-01 2011-07-01 false Sanitary surveys for ground water...) WATER PROGRAMS (CONTINUED) NATIONAL PRIMARY DRINKING WATER REGULATIONS Ground Water Rule § 141.401 Sanitary surveys for ground water systems. (a) Ground water systems must provide the State, at the State's...

Sang-Don Han | NREL

Science.gov Websites

between 1) electrolyte material structure (i.e., solvent/anion structure and solvation state of cations presence of organic foulants," Desalination (2009). "Influence of the heterogeneous structure on

Chemistry of alkali cation exchanged faujasite and mesoporous NaX using alkyl halides and phosphates

NASA Astrophysics Data System (ADS)

Lee, Min-Hong

The purpose of this work was to increase the reactivity of Faujasite X (NaX) zeolite toward the reactive decontamination of materials subject to nucleophilic attack by means of zeolite cation optimization and by means of the synthesis of mesoporous Faujasite X. Primary alkyl halides and trialkyl phosphates have been the test materials on which the cation-optimized and mesoporous zeolites have been tested. In the alkali cation optimization work, reactions of methyl iodide and 1-chloropropane with alkali metal cation exchanged Faujasite zeolite X were investigated at room temperature. The reactivity of the framework and the product formation were shown to depend on zeolite framework counter-cation. A quantitative study of zeolite product formation has been carried out, primarily using solid-state NMR spectroscopy. Large alkali cations showed preference toward substitution chemistry. In contrast, alkyl halide exposed LiX and NaX zeolites underwent both substitution and elimination. Subsequently introduced water molecules led to hydrolysis of framework species that was sensitive to framework counter-cation. The mesoporous NaX zeolites work undertakes to test whether an improvement in surface chemical reactivity can be achieved by introducing mesopores into the already reactive nucleophilic microporous NaX zeolite. Incorporation of the polydiallyl dimethyl ammonium chloride (PDADMAC) template and the formation of mesopores in Faujasite X zeolite (NaX) were successful and well-characterized. The mesopores are proposed to have occurred from incorporation of the cationic PDADMAC polymer into the zeolite by compensating zeolite framework charge. Subsequent sodium cation exchange of calcined mesoporous NaX was shown to restore the chemical reactivity characteristic of as-synthesized NaX. Trialkyl organophosphorous compounds underwent substitution reactions. The reactivity of both microporous and mesoporous Faujasite zeolite X and the product formation was shown to depend on the length of the alkyl chain. Although introduced mesopores alleviated the limited reagent diffusion to reactive sites due to the microporosity of the NaX zeolites, no marked improvement in the product yields was achieved with either the 1-chloroalkanes or the trialkyl phosphates test compounds, regardless of alkyl chain length. The disappointing results have been attributed to lack of substantial net increase in the numbers of zeolite nucleophilic sites accompanying mesopore introduction.

Interactions between cations and peat organic matter monitored with NMR wideline, static and FFC NMR relaxometry

NASA Astrophysics Data System (ADS)

Schaumann, Gabriele E.; Conte, Pellegrino; Jäger, Alexander; Alonzo, Giuseppe; Bertmer, Marko

2010-05-01

The molecular size of humic substances is still under debate and is believed to range up to several hundred thousands Dalton, although a number of recent studies suggest much lower molecular weights. Nowadays an increasing number of authors suggest a model of molecular aggregates. One explanation why results on the molecular mass of humic materials are contradictory, may be that individual OM molecules are linked via intermolecular interactions, by bridges of water molecules or by cations bridging cation exchange sites (Schaumann, 2006a, b). Properties of such cross-linked systems can be similar to macromolecular systems revealing covalent cross-links. In this context, multivalent cations play an important ecological role, serving as reversible cross-linking agent. Formation and disruption of such cation bridges may close or open sorption sites in soil organic matter. Although cross-linking by multivalent cations has been proposed in many studies, the cross-linking effect has not yet been demonstrated on the molecular scale. The objective of this study was to investigate the interactions between cations and peat organic matter using NMR wideline techniques as well as static and fast field cycling (FFC) NMR relaxometry. Peat treated with solutions containing either Na+, Ca2+ or Al3+ was investigated in air-dried state for longitudinal relaxation times (T1) and NMR wideline characteristics. T1 distributions were separated into two Gaussian functions which were interpreted to represent two proton populations belonging to two environments of differing mobility. The relaxation rates (R1 = T1-1) in the cation treated samples spread over a range of 87-123 s-1 (R1a: fast component) and 32-42 s-1 (R1b: slow component). The rates in all treatments are significantly different from each other. and decrease in the order conditioned sample > desalinated sample > Na-treated sample. The treatment with multivalent cations affects R1a and R1b in different ways and needs more detailed explanation. Wideline proton NMR spectra can be used to quantify proton containing material, mainly water, based on their mobility. Spectra were decomposed into a Gaussian and Lorentzian line and changes to mobility after heat treatment indicate the water binding strength. In this study, differences in the various NMR parameters on the cation treatments will be presented and discussed with respect to the crosslinking hypothesis.

Ground-state and Thermodynamic Properties of an S = 1 Kitaev Model

NASA Astrophysics Data System (ADS)

Koga, Akihisa; Tomishige, Hiroyuki; Nasu, Joji

2018-06-01

We study the ground-state and thermodynamic properties of an S = 1 Kitaev model. We first clarify the existence of global parity symmetry in addition to the local symmetry on each plaquette, which enables us to perform large-scale calculations on up to 24 sites. It is found that the ground state should be singlet, and its energy is estimated as E/N ˜ -0.65J, where J is the Kitaev exchange coupling. We find that the lowest excited state belongs to the same subspace as the ground state, and that the gap decreases monotonically with increasing system size, which suggests that the ground state of the S = 1 Kitaev model is gapless. Using the thermal pure quantum states, we clarify the finite temperature properties characteristic of the Kitaev models with S ≤ 2.

On the ground state of Yang-Mills theory

NASA Astrophysics Data System (ADS)

Bakry, Ahmed S.; Leinweber, Derek B.; Williams, Anthony G.

2011-08-01

We investigate the overlap of the ground state meson potential with sets of mesonic-trial wave functions corresponding to different gluonic distributions. We probe the transverse structure of the flux tube through the creation of non-uniform smearing profiles for the string of glue connecting two color sources in Wilson loop operator. The non-uniformly UV-regulated flux-tube operators are found to optimize the overlap with the ground state and display interesting features in the ground state overlap.

Theoretical investigations on the d-p hybridized aromaticity, photoelectron spectroscopy and neutral salts of the LaX2- (X=Al, Ga, In) clusters.

PubMed

Chen, Jing; Yang, Huan; Wang, Jing; Cheng, Shi-Bo

2018-05-30

We present an extensive density functional theory (DFT) calculations on the geometrical and electronic structures of the triatomic LaX 2 - (X=Al, Ga, In) clusters. Various trail structures and spin states have been attempted to determine the lowest-energy geometries of these La-doped metal clusters. The ground states of all three clusters are calculated to possess the trigonal structures with the singlet multiplicities. The calculations on molecular orbitals (MOs) and nucleus-independent chemical shift (NICS) values have been performed to examine the aromatic characteristics of the LaX 2 - (X=Al, Ga, In) clusters. The present calculations disclose that all these metal clusters are doubly aromatic, namely d-p hybridized σ and π aromaticity resulting from the effective overlap between the 5d atomic orbital of the La atom and the p orbitals of the IIIA group elements. Theoretical vertical detachment energies (VDEs) were also calculated to simulate the photoelectron spectra (PES) of the clusters. In addition, by adding the alkali cations (Li + and Na + ) into the LaX 2 - (X=Al, Ga, In) clusters, the geometries and electronic structures of the corresponding neutral salts have also been investigated to gain more insights in the potential of using these aromatic anions as building blocks. Copyright © 2018 Elsevier B.V. All rights reserved.

First principles study of structural, electronic and magnetic properties of SnGe n (0, ±1) ( n = 1–17) clusters

NASA Astrophysics Data System (ADS)

Djaadi, Soumaia; Eddine Aiadi, Kamal; Mahtout, Sofiane

2018-04-01

The structures, relative stability and magnetic properties of pure Ge n +1, neutral cationic and anionic SnGe n (n = 1–17) clusters have been investigated by using the first principles density functional theory implemented in SIESTA packages. We find that with the increasing of cluster size, the Ge n +1 and SnGe n (0, ±1) clusters tend to adopt compact structures. It has been also found that the Sn atom occupied a peripheral position for SnGe n clusters when n < 12 and occupied a core position for n > 12. The structural and electronic properties such as optimized geometries, fragmentation energy, binding energy per atom, HOMO–LUMO gaps and second-order differences in energy of the pure Ge n +1 and SnGe n clusters in their ground state are calculated and analyzed. All isomers of neutral SnGe n clusters are generally nonmagnetic except for n = 1 and 4, where the total spin magnetic moments is 2μ b. The total (DOS) and partial density of states of these clusters have been calculated to understand the origin of peculiar magnetic properties. The cluster size dependence of vertical ionization potentials, vertical electronic affinities, chemical hardness, adiabatic electron affinities and adiabatic ionization potentials have been calculated and discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lackner, Florian; Chatterley, Adam S.; Pemmaraju, C. D.

Femtosecond extreme ultraviolet transient absorption spectroscopy is used to explore strong-field ionization induced dynamics in selenophene (C 4H 4Se). The dynamics are monitored in real-time from the viewpoint of the Se atom by recording the temporal evolution of element-specific spectral features near the Se 3d inner-shell absorption edge (~58 eV). The interpretation of the experimental results is supported by first-principles time-dependent density functional theory calculations. The experiments simultaneously capture the instantaneous population of stable molecular ions, the emergence and decay of excited cation states, and the appearance of atomic fragments. The experiments reveal, in particular, insight into the strong-field inducedmore » ring-opening dynamics in the selenophene cation, which are traced by the emergence of non-cyclic molecules as well as the liberation of Se + ions within an overall time scale of approximately 170 fs. In this study, we propose that both products may be associated with dynamics on the same electronic surfaces but with different degrees of vibrational excitation. The time-dependent inner-shell absorption features provide direct evidence for a complex relaxation mechanism that may be approximated by a two-step model, whereby the initially prepared, excited cyclic cation decays within τ 1 = 80 ± 30 fs into a transient molecular species, which then gives rise to the emergence of bare Se + and ring-open cations within an additional τ 2 = 80 ± 30 fs. The combined experimental and theoretical results suggest a close relationship between σ* excited cation states and the observed ring-opening reactions. In conclusion, the findings demonstrate that the combination of femtosecond time-resolved core-level spectroscopy with ab initio estimates of spectroscopic signatures provide new insights into complex, ultrafast photochemical reactions such as ring-opening dynamics in organic molecules in real-time and with simultaneous sensitivity for electronic and structural rearrangements.« less

Direct observation of ring-opening dynamics in strong-field ionized selenophene using femtosecond inner-shell absorption spectroscopy

DOE PAGES

Lackner, Florian; Chatterley, Adam S.; Pemmaraju, C. D.; ...

2016-12-21

Femtosecond extreme ultraviolet transient absorption spectroscopy is used to explore strong-field ionization induced dynamics in selenophene (C 4H 4Se). The dynamics are monitored in real-time from the viewpoint of the Se atom by recording the temporal evolution of element-specific spectral features near the Se 3d inner-shell absorption edge (~58 eV). The interpretation of the experimental results is supported by first-principles time-dependent density functional theory calculations. The experiments simultaneously capture the instantaneous population of stable molecular ions, the emergence and decay of excited cation states, and the appearance of atomic fragments. The experiments reveal, in particular, insight into the strong-field inducedmore » ring-opening dynamics in the selenophene cation, which are traced by the emergence of non-cyclic molecules as well as the liberation of Se + ions within an overall time scale of approximately 170 fs. In this study, we propose that both products may be associated with dynamics on the same electronic surfaces but with different degrees of vibrational excitation. The time-dependent inner-shell absorption features provide direct evidence for a complex relaxation mechanism that may be approximated by a two-step model, whereby the initially prepared, excited cyclic cation decays within τ 1 = 80 ± 30 fs into a transient molecular species, which then gives rise to the emergence of bare Se + and ring-open cations within an additional τ 2 = 80 ± 30 fs. The combined experimental and theoretical results suggest a close relationship between σ* excited cation states and the observed ring-opening reactions. In conclusion, the findings demonstrate that the combination of femtosecond time-resolved core-level spectroscopy with ab initio estimates of spectroscopic signatures provide new insights into complex, ultrafast photochemical reactions such as ring-opening dynamics in organic molecules in real-time and with simultaneous sensitivity for electronic and structural rearrangements.« less

pH Lowering Ability of Sphagnum.

ERIC Educational Resources Information Center

Glime, Janice M.; Li, Yenhung

1998-01-01

States that the ecological role of Sphagnum species in peatlands is enormous. Presents a cation exchange experiment and background information on the characteristics and economic importance of Sphagnum. Contains 42 references. (DDR)

Dynamics of Ionic Liquid-Assisted Refolding of Denatured Cytochrome c: A Study of Preferential Interactions toward Renaturation.

PubMed

Singh, Upendra Kumar; Patel, Rajan

2018-05-25

In vitro refolding of denatured protein and the influence of the alkyl chain on the refolding of a protein were tested using long chain imidazolium chloride salts, 1-methyl-3-octylimidazolium chloride [C 8 mim][Cl], and 1-decyl-3-methylimidazolium chloride [C 10 mim][Cl]. The horse heart cytochrome c (h-cyt c) was denatured by urea and guanidinium hydrochloride (GdnHCl), as well as by base-induced denaturation at pH 13, to provide a broad overview of the overall refolding behavior. The variation in the alkyl chain of the ionic liquids (ILs) showed a profound effect on the refolding of denatured h-cyt c. The ligand-induced refolding was correlated to understand the mechanism of the conformational stability of proteins in aqueous solutions of ILs. The results showed that the long chain ILs having the [C 8 mim] + and [C 10 mim] + cations promote the refolding of alkali-denatured h-cyt c. The IL having the [C 10 mim] + cation efficiently refolded the alkali-denatured h-cyt c with the formation of the MG state, whereas the IL having the [C 8 mim] + cation, which is known to be compatible for protein stability, shows slight refolding and forms a different transition state. The lifetime results show successful refolding of alkaline-denatured h-cyt c by both of the ILs, however, more refolding was observed in the case of [C 10 mim][Cl], and this was correlated with the fast and medium lifetimes (τ 1 and τ 2 ) obtained, which show an increase accompanied by an increase in secondary structure. The hydrophobic interactions plays an important role in the refolding of chemically and alkali-denatured h-cyt c by long chain imidazolium ILs. The formation of the MG state by [C 10 mim][Cl] was also confirmed, as some regular structure exists far below the CMC of IL. The overall results suggested that the [C 10 mim] + cation bound to the unfolded h-cyt c triggers its refolding by electrostatic and hydrophobic interactions that stabilize the MG state.

Welding fixture for joining bar-wound stator conductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Souza, Urban J.; Rhoads, Frederick W.; Hanson, Justin

A fixture assembly for welding a plurality of stator wire end pairs may include an anvil, a movable clamp configured to translate between an unclamped state and a clamped state, a first grounding electrode, and a second grounding electrode. The movable clamp may be configured to urge the plurality of stator wire ends against the anvil when in the clamped state. The moveable clamp includes a separator feature that generally extends toward the anvil. Each of the first grounding electrode and second grounding electrodes may be configured to translate between a clamped state and an unclamped state. When in themore » clamped state, each of the first and second grounding electrodes is configured to urge a pair of the plurality of stator wire end pairs against the separator feature.« less

Catalog of Reports, Decisions and Opinions, Testimonies and Speeches, GAO Documents 113171-113401. Volume 5. Number 10.

DTIC Science & Technology

1980-10-01

the various medical centers transmute such liability to the Government. The agency spent must be critically examined to determine whether they can...edu- pational hazards, sexual harassment, and working mothers. cation exist as those identified by the States. In trying to get States to increase the

Easily Testable PLA-Based Finite State Machines

DTIC Science & Technology

1989-03-01

PLATYPUS (20]. Then, justifi- type 1, 4 and 5 can be guaranteed to be testable via cation paths are obtained from the STG using simple logic...next state lines is found, if such a vector par that is gnrt d y the trupt eexists, using PLATYPUS [20]. pair that is generated by the first corrupted

Preformation probability inside α emitters around the shell closures Z = 50 and N = 82

NASA Astrophysics Data System (ADS)

Seif, W. M.; Ismail, M.; Zeini, E. T.

2017-05-01

The preformation of an α-particle as a distinct entity inside the α-emitter is the first move towards α-decay. We investigate the α-particle preformation probability (S α ) in ordinary and exotic α-decays. We consider favored and unfavored decays at which the α-emitters and the produced daughter nuclides are in their ground or isomeric states. The study of 244 α-decay modes with 52≤slant Z≤slant 81 and 53≤slant N≤slant 112 is accomplished using the preformed cluster model. The preformation probabilities were estimated from the experimental half-lives and the computed decay widths based on the Wentzel-Kramers-Brillouin tunneling penetrability and knocking frequency, and the Skyrme-SLy4 interaction potential. We found that the favored α-decay mode from a ground state to an isomeric state shows larger α-preformation probability than the favored and unfavored decays of the same isotope but from isomeric to ground states. The favored decay mode from isomeric- to ground-state exhibits rather less S α relative to the other decay modes from the same nuclide. The favored decay modes between two isomeric states tend to yield larger S α and less partial half-life compared with the favored and unfavored decays from the same nuclides but between two ground states. For the decays involving two ground states, the preformation probability is larger for the favored decay modes than for the unfavored ones. The unfavored α-decay modes from ground- to isomeric-states are rare. The unfavored decay modes from isomeric- to ground-states show less S α than that for the favored decays from the ground states of the same emitters. The unfavored α-decay modes between two isomeric states exhibit larger S α than the other α-decay modes from the same isomers.

Biomass production, forage quality, and cation uptake of Quail bush, four-wing saltbush, and seaside barley irrigated with moderately saline-sodic water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bauder, J.W.; Browning, L.S.; Phelps, S.D.

2008-07-01

The study reported here investigated capacity of Atriplex lentiformis (Torr.) S. Wats. (Quail bush), Atriplex X aptera A. Nels. (pro sp.) (Wytana four-wing saltbush), and Hordeum marinum Huds. (seaside barley) to produce biomass and crude protein and take up cations when irrigated with moderately saline-sodic water, in the presence of a shallow water table. Water tables were established at 0.38, 0.76, and 1.14m below the surface in sand-filled columns. The columns were then planted to the study species. Study plants were irrigated for 224 days; irrigation water was supplied every 7 days equal to water lost to evapotranspiration (ET) plusmore » 100mL (the volume of water removed in the most previous soil solution sampling). Water representing one of two irrigation sources was used: Powder River (PR) or coalbed natural gas (CBNG) wastewater. Biomass production did not differ significantly between water quality treatments but did differ significantly among species and water table depth within species. Averaged across water quality treatments, Hordeum marinum produced 79% more biomass than A. lentiformis and 122% more biomass than Atriplex X aptera, but contained only 11% crude protein compared to 16% crude protein in A. lentiformis and 14% crude protein in Atriplex X aptera. Atriplex spp. grown in columns with the water table at 0.38m depth produced more biomass, took up less calcium on a percentage basis, and took up more sodium on a percentage basis than when grown with the water table at a deeper depth. Uptake of cations by Atriplex lentiformis was approximately twice the uptake of cations by Atriplex X aptera and three times that of H. marinum. After 224 days of irrigation, crop growth, and cation uptake, followed by biomass harvest, EC and SAR of shallow groundwater in columns planted to A. lentiformis were less than EC and SAR of shallow ground water in columns planted to either of the other species.« less

Hydrogeochemical survey of groundwater for selected areas in the Arabian Shield and in cover rocks, Kingdom of Saudi Arabia

USGS Publications Warehouse

McHugh, John B.; Miller, W. Roger

1989-01-01

In the spring of 1984, a hydrogeochemical survey was conducted in the Kingdom of Saudi Arabia to test ground water as a sampling medium in exploration for mineral deposits. Eighty-one water samples (mostly from wells) were collected. The samples were analysed for the presence and concentration of major cations and anions, as well as a suite of trace elements. Most of the water samples contained high concentrations of dissolved salts. The majority of the samples showed no significant amounts of the trace elements. A few well-water samples contained moderately anomalous concentrations of zinc, molybdenum, and uranium. These anomalies could be due to salinity effects, contamination, or the proximity of mineral sources. This survey has established some baseline water-chemistry data, especially for the trace metals, which to date have not been reported in ground water in the Kingdom of Saudi Arabia.

Location and valence state of strontium cations on the framework of a carbon dioxide selective porous silicoaluminophosphate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Li; Rivera-Ramos, Milton E.; Hernández-Maldonado, Arturo J.

2014-05-28

A Sr{sup 2+}-SAPO-34 material that displays superior CO2 adsorption selectivity and capacity was characterized via XPS and UV-vis spectroscopy to elucidate the valence state of strontium cations and framework silicon environment. Most importantly, the location of the strontium has been estimated from a Rietveld refinement analysis of synchrotron diffraction data. The XPS analysis indicated that the apparent valence state of the strontium is less than 2, an indication of its interaction with the large anionic framework. Furthermore, UV-vis tests pointed to changes in the silicon environment, plausibly related to this valence state or framework faulting. For the refinement, the analysismore » found that strontium occupied two unique sites: a site Sr1 slightly displaced from six-membered rings and a site Sr2 positioned at the top or bottom of the eight-membered rings. The latter position favors the interaction of the alkaline earth metal with CO{sub 2}, probably resulting in an enhanced electric field-quadrupole moment interaction.« less

Magnetic Modes in Rare Earth Perovskites: A Magnetic-Field-Dependent Inelastic Light Scattering study.

PubMed

Saha, Surajit; Cao, Bing-Chen; Motapothula, M; Cong, Chun-Xiao; Sarkar, Tarapada; Srivastava, Amar; Sarkar, Soumya; Patra, Abhijeet; Ghosh, Siddhartha; Ariando; Coey, J M D; Yu, Ting; Venkatesan, T

2016-11-15

Here, we report the presence of defect-related states with magnetic degrees of freedom in crystals of LaAlO 3 and several other rare-earth based perovskite oxides using inelastic light scattering (Raman spectroscopy) at low temperatures in applied magnetic fields of up to 9 T. Some of these states are at about 140 meV above the valence band maximum while others are mid-gap states at about 2.3 eV. No magnetic impurity could be detected in LaAlO 3 by Proton-Induced X-ray Emission Spectroscopy. We, therefore, attribute the angular momentum-like states in LaAlO 3 to cationic/anionic vacancies or anti-site defects. Comparison with the other rare earth perovskites leads to the empirical rule that the magnetic-field-sensitive transitions require planes of heavy elements (e.g. lanthanum) and oxygen without any other light cations in the same plane. These magnetic degrees of freedom in rare earth perovskites with useful dielectric properties may be tunable by appropriate defect engineering for magneto-optic applications.

Origin of High Electronic Quality in Solar Cell Absorber CH3NH3PbI3

NASA Astrophysics Data System (ADS)

Yin, Wanjian; Shi, Tingting; Wei, Suhua; Yan, Yanfa

Thin-film solar cells based on CH3NH3PbI3 halide perovskites have recently shown remarkable performance. First-principle calculations and molecular dynamic simulations show that the structure of pristine CH3NH3PbI3 is much more disordered than the inorganic archetypal thin-film semiconductor CdTe. However, the structural disorders from thermal fluctuation, point defects and grain boundaries introduce rare deep defect states within the bandgaps; therefore, the material has high electronic quality. We have further shown that this unusually high electronic quality is attributed to the unique electronic structures of halide perovskite: the strong coupling between cation lone-pair Pb s orbitals and anion p orbitals and the large atomic size of constitute cation atoms. We further found that although CH3NH3PbI3 GBs do not introduce a deep gap state, the defect level close to the VBM can still act as a shallow hole trap state. Cl and O can spontaneously segregate into GBs and passivate those defect levels and deactivate the trap state.

Magnetic order and magnetoelectric properties of R2CoMn O6 perovskites (R =Ho , Tm, Yb, and Lu)

NASA Astrophysics Data System (ADS)

Blasco, J.; García-Muñoz, J. L.; García, J.; Subías, G.; Stankiewicz, J.; Rodríguez-Velamazán, J. A.; Ritter, C.

2017-07-01

We present a detailed study on the magnetic structure and magnetoelectric properties of several double perovskites R2CoMn O6 (R =Ho , Tm, Yb, and Lu). All of these samples show an almost perfect (˜94 %) ordering of C o2 + and M n4 + cations in the unit cell. Our research reveals that the magnetic ground state strongly depends on the R size. For samples with larger R (Ho and Tm), the ground state is formed by a ferromagnetic order (F type) of C o2 + and M n4 + moments, while R either remains mainly disordered (Ho) or is coupled antiferromagnetically (Tm) to the Co/Mn sublattice. For samples with smaller R (Yb or Lu), competitive interactions lead to the formation of an E -type arrangement for the C o2 + and M n4 + moments with a large amount of extended defects such as stacking faults. The Y b3 + is partly ordered at very low temperature. The latter samples undergo a metamagnetic transition from the E into the F type, which is coupled to a negative magnetodielectric effect. Actually, the real part of dielectric permittivity shows an anomaly at the magnetic transition for the samples exhibiting an E -type order. This anomaly is absent in samples with F -type order, and, accordingly, it vanishes coupled to the metamagnetic transition for R =Yb or Lu samples. At room temperature, the huge values of the dielectric constant reveal the presence of Maxwell-Wagner depletion layers. Pyroelectric measurements reveal a high polarization at low temperature, but the onset of pyroelectric current is neither correlated to the kind of magnetic ordering nor to the magnetic transition. Our study identified the pyroelectric current as thermally stimulated depolarization current and electric-field polarization curves show a linear behavior at low temperature. Therefore, no clear ferroelectric transition occurs in these compounds.

Elaboration, Rietveld refinements and vibrational spectroscopic study of Na₁-xKxCaPb₃(PO₄)₃ lacunar apatites (0 ⩽ x ⩽ 1).

PubMed

Lahrich, S; Elmhammedi, M A; Manoun, B; Tamraoui, Y; Mirinioui, F; Azrour, M; Lazor, P

2015-06-15

Synthesis of apatites, Na1-xKxCaPb3(PO4)3 0 ⩽ x ⩽ 1, with anion vacancy were carried out using solid state reactions. The solid solution of apatite-type structure crystallize in the hexagonal system, space group P63/m (No. 176). Rietveld refinements showed that around 90% of Pb(2+) cations are located in the (6h) sites, the left amount of Pb(2+) cations are located in the (4f) sites; 27-31% of Ca(2+) cations are located in the (6h) sites, the left amount of Ca(2+) cations are located in the (4f) sites. The ninefold coordination sites (4f) are also occupied by the K(+) and Na(+) monovalent ions. The structure can be described as built up from [PO4](3-) tetrahedra and Pb(2+)/Ca(2+) of sixfold coordination cavities (6h positions), which delimit void hexagonal tunnels running along [001]. These tunnels are connected by cations of mixed sites (4f) which are half occupied by Pb(2+)/Ca(2+) and half by Na(+)/K(+) mixed cations. The assignment of the observed frequencies in the Raman and infrared spectra is discussed on the basis of a unit cell group analysis and by comparison with other apatites. Vibrational spectra of all the compositions are similar and show some linear shifts of the frequencies as a function of the composition toward lower values due the substitutions of Na(+) by K(+) with a larger radius. Copyright © 2015 Elsevier B.V. All rights reserved.

Gamma ray induced decomposition of double nitrates of lanthanum and cerium with some mono and bivalent cations in solid state

NASA Astrophysics Data System (ADS)

Kulkarni, S. P.; Garg, A. N.

Gamma ray induced decomposition of two series of double nitrates; 2M INO 3⋯Ln(NO 3) 3⋯ x H 2O (where MI = NH+4, Na+, K+, Rb+, Cs+; LnIII = La3+, Ce3+ and x = 2 or 4) and 3M II(NO 3) 2·2Ln III(NO 3) 3⋯24H 2O (where MII = Mg2+, Co2+, Zn2+; LnIII = La3+, Ce3+) has been studied in solid state over a wide absorbed dose range at room temperature. G(NO -2) values have been found to depend on the absorbed dose and the nature of cation in both the series of double salts. Radiation sensitivity of lanthanum double nitrates with monovalent cations at an absorbed dose of 158 kGy follows the order NH +4 < Rb + ≅ Cs + < Na + < K + and those of cerium NH +4 < Rb +

New donor-acceptor conjugates based on a trifluorenylporphyrin linked to a redox-switchable ruthenium unit.

PubMed

Merhi, Areej; Zhang, Xu; Yao, Dandan; Drouet, Samuel; Mongin, Olivier; Paul, Frédéric; Williams, J A Gareth; Fox, Mark A; Paul-Roth, Christine O

2015-05-28

Reactions of the 16-electron ruthenium complex [Ru(dppe)2Cl][PF6] with metal-free and zinc ethynylphenyltrifluorenylporphyrins and respectively, gave the new dyads and with ethynylruthenium group as a potential electron donor and the porphyrin as a potential electron acceptor. The redox properties of the porphyrins were investigated by cyclic voltammetry and UV spectroelectrochemistry (SEC), which reveal that the monocation and monoanion of metal-free porphyrin are stable under these conditions whereas the formation of the corresponding radical cation or anion of the zinc porphyrin was accompanied by partial decomplexation of the zinc ion. Oxidations of the dyads and gave stable radical cations as probed using IR, NIR and UV SEC methods. These cations show similar NIR and IR bands to those reported for the known 17-electron [Ru(dppe)2(C[triple bond, length as m-dash]CPh)Cl](+) radical cation. Remarkably, the dyad has four stable redox states +2/+1/0/-1 where the second oxidation and first reduction processes take place at the porphyrin unit. Simulated absorption spectra on at optimised geometries obtained by TD-DFT computations with the CAM-B3LYP functional are shown to be in very good agreement with the observed UV absorption spectra of . The spectra of and their oxidised and reduced species were interpreted with the aid of the TD-DFT data. Fluorescence measurements reveal that the dyads and are only weakly emitting compared to and , indicative of quenching of the porphyrinic singlet excited state by the ruthenium centre.

Heme Regulates Allosteric Activation of the Slo1 BK Channel

PubMed Central

Horrigan, Frank T.; Heinemann, Stefan H.; Hoshi, Toshinori

2005-01-01

Large conductance calcium-dependent (Slo1 BK) channels are allosterically activated by membrane depolarization and divalent cations, and possess a rich modulatory repertoire. Recently, intracellular heme has been identified as a potent regulator of Slo1 BK channels (Tang, X.D., R. Xu, M.F. Reynolds, M.L. Garcia, S.H. Heinemann, and T. Hoshi. 2003. Nature. 425:531–535). Here we investigated the mechanism of the regulatory action of heme on heterologously expressed Slo1 BK channels by separating the influences of voltage and divalent cations. In the absence of divalent cations, heme generally decreased ionic currents by shifting the channel's G–V curve toward more depolarized voltages and by rendering the curve less steep. In contrast, gating currents remained largely unaffected by heme. Simulations suggest that a decrease in the strength of allosteric coupling between the voltage sensor and the activation gate and a concomitant stabilization of the open state account for the essential features of the heme action in the absence of divalent ions. At saturating levels of divalent cations, heme remained similarly effective with its influence on the G–V simulated by weakening the coupling of both Ca2+ binding and voltage sensor activation to channel opening. The results thus show that heme dampens the influence of allosteric activators on the activation gate of the Slo1 BK channel. To account for these effects, we consider the possibility that heme binding alters the structure of the RCK gating ring and thereby disrupts both Ca2+- and voltage-dependent gating as well as intrinsic stability of the open state. PMID:15955873

The NorM MATE transporter from N. gonorrhoeae: insights into drug and ion binding from atomistic molecular dynamics simulations.

PubMed

Leung, Yuk Ming; Holdbrook, Daniel A; Piggot, Thomas J; Khalid, Syma

2014-07-15

The multidrug and toxic compound extrusion transporters extrude a wide variety of substrates out of both mammalian and bacterial cells via the electrochemical gradient of protons and cations across the membrane. The substrates transported by these proteins include toxic metabolites and antimicrobial drugs. These proteins contribute to multidrug resistance in both mammalian and bacterial cells and are therefore extremely important from a biomedical perspective. Although specific residues of the protein are known to be responsible for the extrusion of solutes, mechanistic details and indeed structures of all the conformational states remain elusive. Here, we report the first, to our knowledge, simulation study of the recently resolved x-ray structure of the multidrug and toxic compound extrusion transporter, NorM from Neisseria gonorrhoeae (NorM_NG). Multiple, atomistic simulations of the unbound and bound forms of NorM in a phospholipid lipid bilayer allow us to identify the nature of the drug-protein/ion-protein interactions, and secondly determine how these interactions contribute to the conformational rearrangements of the protein. In particular, we identify the molecular rearrangements that occur to enable the Na(+) ion to enter the cation-binding cavity even in the presence of a bound drug molecule. These include side chain flipping of a key residue, GLU-261 from pointing toward the central cavity to pointing toward the cation binding side when bound to a Na(+) ion. Our simulations also provide support for cation binding in the drug-bound and apo states of NorM_NG. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

The NorM MATE Transporter from N. gonorrhoeae: Insights into Drug and Ion Binding from Atomistic Molecular Dynamics Simulations

PubMed Central

Leung, Yuk Ming; Holdbrook, Daniel A.; Piggot, Thomas J.; Khalid, Syma

2014-01-01

The multidrug and toxic compound extrusion transporters extrude a wide variety of substrates out of both mammalian and bacterial cells via the electrochemical gradient of protons and cations across the membrane. The substrates transported by these proteins include toxic metabolites and antimicrobial drugs. These proteins contribute to multidrug resistance in both mammalian and bacterial cells and are therefore extremely important from a biomedical perspective. Although specific residues of the protein are known to be responsible for the extrusion of solutes, mechanistic details and indeed structures of all the conformational states remain elusive. Here, we report the first, to our knowledge, simulation study of the recently resolved x-ray structure of the multidrug and toxic compound extrusion transporter, NorM from Neisseria gonorrhoeae (NorM_NG). Multiple, atomistic simulations of the unbound and bound forms of NorM in a phospholipid lipid bilayer allow us to identify the nature of the drug-protein/ion-protein interactions, and secondly determine how these interactions contribute to the conformational rearrangements of the protein. In particular, we identify the molecular rearrangements that occur to enable the Na+ ion to enter the cation-binding cavity even in the presence of a bound drug molecule. These include side chain flipping of a key residue, GLU-261 from pointing toward the central cavity to pointing toward the cation binding side when bound to a Na+ ion. Our simulations also provide support for cation binding in the drug-bound and apo states of NorM_NG. PMID:25028887

Stability of Ruddlesden–Popper-structured oxides in humid conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lehtimäki, M.; Yamauchi, H.; Karppinen, M., E-mail: maarit.karppinen@aalto.fi

2013-08-15

Some of layered transition-metal oxides are known to react with atmospheric humidity to form through topotactic intercalation reactions new water-containing layered structures. Here we investigate the influence of oxygen content (7−δ) of the Ruddlesden–Popper-structured Sr{sub 3}FeMO{sub 7−δ} (M=Ni, Mn, Ti) oxides on the water-intercalation reaction. It is found that their oxygen contents influence greatly the reactivity of the phases with water. Other factors possibly affecting the reactivity are discussed on the basis of the present data in combination with a comprehensive review of previous works on Ruddlesden–Popper and related layered oxide phases. - Graphical abstract: Many of the Ruddlesden–Popper-structured A{submore » 3}B{sub 2}O{sub 7−δ} oxides readily react with water via intercalation reactions. Three possible factors affecting the water intercalation are identified: oxygen content of the phase, ionic radius of cation A and valence state of cation B. The resultant layered water-derivative phases can be categorised into two groups, depending on the crystal symmetry of the phase. Highlights: • Ruddlesden–Popper oxides A{sub 3}B{sub 2}O{sub 7−δ} often accommodate water via intercalation reaction. • The lower the oxygen content 7−δ is the more readily the intercalation reaction occurs. • The second factor promoting the reaction is the large size of cation A. • The third possible factor is the high valence state of cation B. • Resultant water-derivatives can be categorised into two groups depending on symmetry.« less

Ab initio investigation of the thermodynamics of cation distribution and of the electronic and magnetic structures in the LiMn2O4 spinel

NASA Astrophysics Data System (ADS)

Santos-Carballal, David; Ngoepe, Phuti E.; de Leeuw, Nora H.

2018-02-01

The spinel-structured lithium manganese oxide (LiMn2O4 ) is a material currently used as cathode for secondary lithium-ion batteries, but whose properties are not yet fully understood. Here, we report a computational investigation of the inversion thermodynamics and electronic behavior of LiMn2O4 derived from spin-polarized density functional theory calculations with a Hubbard Hamiltonian and long-range dispersion corrections (DFT+U-D3). Based on the analysis of the configurational free energy, we have elucidated a partially inverse equilibrium cation distribution for the LiMn2O4 spinel. This equilibrium degree of inversion is rationalized in terms of the crystal field stabilization effects and the difference between the size of the cations. We compare the atomic charges with the oxidation numbers for each degree of inversion. We found segregation of the Mn charge once these ions occupy the tetrahedral and octahedral sites of the spinel. We have obtained the atomic projections of the electronic band structure and density of states, showing that the normal LiMn2O4 has half-metallic properties, while the fully inverse spinel is an insulator. This material is in the ferrimagnetic state for the inverse and partially inverse cation arrangement. The optimized lattice and oxygen parameters, as well as the equilibrium degree of inversion, are in agreement with the available experimental data. The partial equilibrium degree of inversion is important in the interpretation of the lithium ion migration and surface properties of the LiMn2O4 spinel.

Highly planar diarylamine-fused porphyrins and their remarkably stable radical cations† †Electronic supplementary information (ESI) available. CCDC 1469154–1469160. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc02721k Click here for additional data file. Click here for additional data file.

PubMed Central

Fukui, Norihito; Cha, Wonhee; Shimizu, Daiki; Oh, Juwon

2017-01-01

Oxidative fusion reactions of meso-phenoxazino Ni(ii) porphyrin were found to be temperature dependent, giving rise to either a doubly phenylene-fused product at room temperature or a singly phenoxazine-fused product at 70 °C. The latter was further oxidized to a doubly phenoxazine-fused Ni(ii) porphyrin, which was subsequently converted to the corresponding free base porphyrin and Zn(ii) porphyrin. Compared to previously reported diphenylamine-fused porphyrins that displayed a molecular twist, doubly phenoxazine-fused porphyrins exhibited distinctly different properties owing to their highly planar structures, such as larger fluorescence quantum yields, formation of an offset face-to-face dimer both in solution and the solid state, and the generation of a mixed-valence π-radical cation dimer upon electrochemical oxidation. One-electron oxidation of the phenoxazine-fused Ni(ii) porphyrin with Magic Blue gave the corresponding radical cation, which was certainly stable and could be isolated by separation over a silica gel column but slowly chlorinated at the reactive β-positions in the solid state. This finding led to us to examine β,β′-dichlorinated phenoxazine-fused and diphenylamine-fused Ni(ii) porphyrins, which, upon treatment with Magic Blue, provided remarkably stable radical cations to an unprecedented level. It is actually possible to purify these radical cations by silica gel chromatography, and they can be stored for over 6 months without any sign of deterioration. Moreover, they exhibited no degradation even after the CH2Cl2 solution was washed with water. However, subtle structural differences (planar versus partly twisted) led to different crystal packing structures and solid-state magnetic properties. PMID:28451165

Enhancement of short-pulse recombination-pumped gain by soft-x-ray photoionization of the ground state

NASA Astrophysics Data System (ADS)

Apruzese, J. P.; Umstadter, D.

1996-02-01

The gain achieved in lasing to the ground state following short-pulse field ionization by a pump laser is highly transient. It will usually persist for only tens of picoseconds because of the rapid filling and negligible emptying of the ground state. Employing a detailed atomic model of lasing in hydrogen, we show that the removal of ground-state population by an appropriate broadband ionizing radiation field can enhance and prolong the gain in such a laser.

Effect of temperature on the single-particle ground-state energy of a polar quantum dot with Gaussian confinement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jahan, Luhluh K., E-mail: luhluhjahan@gmail.com; Chatterjee, Ashok

2016-05-23

The temperature and size dependence of the ground-state energy of a polaron in a Gaussian quantum dot have been investigated by using a variational technique. It is found that the ground-state energy increases with increasing temperature and decreases with the size of the quantum dot. Also, it is found that the ground-state energy is larger for a three-dimensional quantum dot as compared to a two-dimensional dot.

Summary of Ground-Water-Quality Data in the Anacostia River Watershed, Washington, D.C., September - December 2005

USGS Publications Warehouse

Klohe, Cheryl A.; Debrewer, Linda M.

2007-01-01

The U.S. Geological Survey, in cooperation with the District Department of the Environment (formerly the District of Columbia, Department of Health, Environmental Health Administration), conducted a ground-water-quality investigation in the Anacostia River watershed within Washington, D.C. Samples were collected and analyzed from 17 ground-water monitoring wells located within the study area from September through December 2005. Samples were analyzed for a variety of constituents including major ions, nutrients, volatile organic compounds, semivolatile organic compounds, pesticides and degradates, oil and grease, phenols, total polychlorinated biphenyls, and other selected constituents. The concentrations of major ions in the study area indicate that the ground water is predominantly calcium-bicarbonate type water, with some wells containing a higher percentage of milliequivalents per liter of iron (cation), and chloride or sulfate (anions). Concentrations of nitrogen were generally less than 1 milligram per liter, and concentrations of phosphorus were generally less than 0.5 milligrams per liter. Twelve of 79 pesticides and degradates were detected at 6 out of 17 wells. Volatile organic compounds (predominantly gasoline oxygenates and solvents) were detected in 9 of the 17 wells. Two semivolatile organic compounds, (bis(2-ethylhexyl) phthalate and total phenols), out of the 51 analyzed, were detected in the study area.

A calix[4]arene strapped calix[4]pyrrole: an ion-pair receptor displaying three different cesium cation recognition modes.

PubMed

Kim, Sung Kuk; Sessler, Jonathan L; Gross, Dustin E; Lee, Chang-Hee; Kim, Jong Seung; Lynch, Vincent M; Delmau, Laetitia H; Hay, Benjamin P

2010-04-28

An ion-pair receptor, the calix[4]pyrrole-calix[4]arene pseudodimer 2, bearing a strong anion-recognition site but not a weak cation-recognition site, has been synthesized and characterized by standard spectroscopic means and via single-crystal X-ray diffraction analysis. In 10% CD(3)OD in CDCl(3) (v/v), this new receptor binds neither the Cs(+) cation nor the F(-) anion when exposed to these species in the presence of other counterions; however, it forms a stable 1:1 solvent-separated CsF complex when exposed to these two ions in concert with one another in this same solvent mixture. In contrast to what is seen in the case of a previously reported crown ether "strapped" calixarene-calixpyrrole ion-pair receptor 1 (J. Am. Chem. Soc. 2008, 130, 13162-13166), where Cs(+) cation recognition takes place within the crown, in 2.CsF cation recognition takes place within the receptor cavity itself, as inferred from both single-crystal X-ray diffraction analyses and (1)H NMR spectroscopic studies. This binding mode is supported by calculations carried out using the MMFF94 force field model. In 10% CD(3)OD in CDCl(3) (v/v), receptor 2 shows selectivity for CsF over the Cs(+) salts of Cl(-), Br(-), and NO(3)(-) but will bind these other cesium salts in the absence of fluoride, both in solution and in the solid state. In the case of CsCl, an unprecedented 2:2 complex is observed in the solid state that is characterized by two different ion-pair binding modes. One of these consists of a contact ion pair with the cesium cation and chloride anion both being bound within the central binding pocket and in direct contact with one another. The other mode involves a chloride anion bound to the pyrrole NH protons of a calixpyrrole subunit and a cesium cation sandwiched between two cone shaped calix[4]pyrroles originating from separate receptor units. In contrast to what is seen for CsF and CsCl, single-crystal X-ray structural analyses and (1)H NMR spectroscopic studies reveal that receptor 2 forms a 1:1 complex with CsNO(3), with the ions bound in the form of a contact ion pair. Thus, depending on the counteranion, receptor 2 is able to stabilize three different ion-pair binding modes with Cs(+), namely solvent-bridged, contact, and host-separated.

Analytical approach to the multi-state lasing phenomenon in quantum dot lasers

NASA Astrophysics Data System (ADS)

Korenev, V. V.; Savelyev, A. V.; Zhukov, A. E.; Omelchenko, A. V.; Maximov, M. V.

2013-03-01

We introduce an analytical approach to describe the multi-state lasing phenomenon in quantum dot lasers. We show that the key parameter is the hole-to-electron capture rate ratio. If it is lower than a certain critical value, the complete quenching of ground-state lasing takes place at high injection levels. At higher values of the ratio, the model predicts saturation of the ground-state power. This explains the diversity of experimental results and their contradiction to the conventional rate equation model. Recently found enhancement of ground-state lasing in p-doped samples and temperature dependence of the ground-state power are also discussed.

Structure Effect of Squarylium Cyanine Dyes on Third-Order Optical Nonlinearities in Ground and Excited States

NASA Astrophysics Data System (ADS)

Liu, Xu-chun; Xu, Gang; Si, Jin-hai; Ye, Pei-xian; Lin, Tong; Peng, Bi-xian

1999-08-01

A series of squarylium cyanine dyes with different substituents were synthesized and the third-order optical nonlinearities of their ground and excited states were investigated by backward degenerate four-wave-mixing. For the ground state, the molecular hyperpolarizability γg increases with the red-shift of the absorption peak λmaxab of the squaraine with different substituents, whereas for the excited-state molecular hyperpolarizability γe, the nonlinear enhancement γe/γg decreases, which may indicate that in the excited state the electron accepting-donating ability of different substituents changes in the reverse order compared with the order in the ground state.

The influence of constitutional isomerism and change on molecular recognition processes.

PubMed

Williams, Avril R; Northrop, Brian H; Houk, Kendall N; Stoddart, J Fraser; Williams, David J

2004-10-25

Three constitutionally isomeric bis(naphthylmethyl)ammonium ions, in which the two naphthyl groups are substituted 1) both at their 1-positions, 2) one at its 1-position and the other at its 2-position, and 3) both at their 2-positions, have been investigated separately in solution for their propensities to undergo spontaneous self-assembly with three different [24]crown-8 derivatives, namely, pyrido[24]crown-8 (P24C8), dipyrido[24]crown-8 (DP24C8) and dibenzo[24]crown-8 (DB24C8), in turn to form [2]pseudorotaxanes. The strengths of the 1:1 complexes depend on the composition of the secondary dialkylammonium ions and on the nature of the crown ether hosts; generally, as far as the guest cation is concerned, the 1/1- and 2/2-isomers form stronger complexes, as indicated by stability constant measurements, than the 1/2-isomer and, as far as the crown ethers are concerned, the more flexible P24C8 is a much more efficient host than either DP24C8 or DB24C8. The rates of formation of the [2]pseudorotaxanes are fast (i.e., taking no more than a few minutes) in solution with the exception of one case, that is, in which the crown ether host is DB24C8 and the guest cation is the 1/1-isomer, when it can take upwards of one month for the complexation-decomplexation equilibrium to be established at room temperature. In all cases, the equilibrium between complexed and uncomplexed species is slow on the NMR timescale, allowing the determination of stability constants to be made readily using the single-point method. X-ray crystallography and molecular modeling have been used to gain insight into ground and transition state interactions, respectively, in some of the [2]pseudorotaxanes. The relative stabilities of the three [2]pseudorotaxanes formed by each guest cation in the presence of the three crown ether hosts were also evaluated in solution by competition experiments that were monitored by (1)H NMR spectroscopy. By and large the results of the competition experiments could be predicted on the basis of the derived stability constants for the individual [2]pseudorotaxanes.

How Single-site Mutation Affects HP Lattice Proteins

NASA Astrophysics Data System (ADS)

Shi, Guangjie; Landau, David P.; Vogel, Thomas; Wüst, Thomas; Li, Ying Wai

2014-03-01

We developed a heuristic method based on Wang-Landauand multicanonical sampling for determining the ground-state degeneracy of HP lattice proteins . Our algorithm allowed the most precise estimations of the (sometimes substantial) ground-state degeneracies of some widely studied HP sequences. We investigated the effects of single-site mutation on specific long HP lattice proteins comprehensively, including structural changes in ground-states, changes of ground-state degeneracy and thermodynamic properties of the systems. Both extremely sensitive and insensitive cases have been observed; consequently, properties such as specific heat, tortuosities etc. may be either largely unaffected or may change significantly due to mutation. More interestingly, mutation can even induce a lower ground-state energy in a few cases. Supported by NSF.

Do the cations in clay and the polymer matrix affect quantum dot fluorescent properties?

PubMed

Wei, Wenjun; Liu, Cui; Liu, Jiyan; Liu, Xueqing; Zou, Linling; Cai, Shaojun; Shi, Hong; Cao, Yuan-Cheng

2016-06-01

This paper studied the effects of cations and polymer matrix on the fluorescent properties of quantum dots (QDs). The results indicated that temperature has a greater impact on fluorescence intensity than clay cations (mainly K(+) and Na(+) ). Combined fluorescence lifetime and steady-state spectrometer tests showed that QD lifetimes all decreased when the cation concentration was increased, but the quantum yields were steady at various cation concentrations of 0, 0.05, 0.5 and 1 M. Poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA) and diepoxy resin were used to study the effects of polymers on QD lifetime and quantum yield. The results showed that the lifetime for QDs 550 nm in PEO and PVA was 17.33 and 17.12 ns, respectively; for the epoxy resin, the lifetime was 0.74 ns, a sharp decrease from 24.47 ns. The quantum yield for QDs 550 nm changed from 34.22% to 7.45% and 7.81% in PEO and PVA, respectively; for the epoxy resin the quantum yield was 2.25%. QDs 580 nm and 620 nm showed the same results as QDs 550 nm. This study provides useful information on the design, synthesis and application of QDs-polymer luminescent materials. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

Structural chemistry and magnetic properties of the perovskite Sr{sub 3}Fe{sub 2}TeO{sub 9}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Yawei; Hunter, Emily C.; Battle, Peter D., E-mail: peter.battle@chem.ox.ac.uk

2016-10-15

A polycrystalline sample of perovskite-like Sr{sub 3}Fe{sub 2}TeO{sub 9} has been prepared in a solid-state reaction and studied by a combination of electron microscopy, Mössbauer spectroscopy, magnetometry, X-ray diffraction and neutron diffraction. The majority of the reaction product is shown to be a trigonal phase with a 2:1 ordered arrangement of Fe{sup 3+} and Te{sup 6+} cations. However, the sample is prone to nano-twinning and tetragonal domains with a different pattern of cation ordering exist within many crystallites. Antiferromagnetic ordering exists in the trigonal phase at 300 K and Sr{sub 3}Fe{sub 2}TeO{sub 9} is thus the first example of amore » perovskite with 2:1 trigonal cation ordering to show long-range magnetic order. At 300 K the antiferromagnetic phase coexists with two paramagnetic phases which show spin-glass behaviour below ~80 K. - Graphical abstract: Sr{sub 3}Fe{sub 2}TeO{sub 9} has a 2:1 ordered arrangement of Fe{sup 3+} and Te{sup 6+} cations over the octahedral sites of a perovskite structure and is antiferromagnetic at room temperature. - Highlights: • 2:1 Cation ordering in a trigonal perovskite. • Magnetically ordered trigonal perovskite. • Intergrowth of nanodomains in perovskite microstructure.« less

Understanding the On-Off Switching Mechanism in Cationic Tetravalent Group-V-Based Fluoride Molecular Sensors Using Orbital Analysis.

PubMed

Usui, Kosuke; Ando, Mikinori; Yokogawa, Daisuke; Irle, Stephan

2015-12-24

The precise control of on-off switching is essential to the design of ideal molecular sensors. To understand the switching mechanism theoretically, we selected as representative example a 9-anthryltriphenylstibonium cation, which was reported as a fluoride ion sensor. In this molecule, the first excited singlet state exhibits two minimum geometries, where one of them is emissive and the other one dark. The excited state at the geometry with bright emission is of π-π* character, whereas it is of π-σ* character at the "dark" geometry. Geometry changes in the excited state were identified by geometry optimization and partial potential energy surface (PES) mapping. We also studied Group V homologues of this molecule. A barrierless relaxation pathway after vertical excitation to the "dark" geometry was found for the Sb-containing compound on the excited-states PES, whereas barriers appear in the case of P and As. Molecular orbital analysis suggests that the σ* orbital of the antimony compound is stabilized along such relaxation and that the excited state changes its nature correspondingly. Our results indicate that the size of the central atom is crucial for the design of fluoride sensors with this ligand framework.

Stat3 phosphorylation is required for embryonic stem cells ground state maintenance in 2i culture media.

PubMed

Wang, Dan; Sang, Hui; Zhang, Kaiyue; Nie, Yan; Zhao, Shuang; Zhang, Yan; He, Ningning; Wang, Yuebing; Xu, Yang; Xie, Xiaoyan; Li, Zongjin; Liu, Na

2017-05-09

Embryonic stem cells (ES cells) can be maintained its undifferentiated state with feeder cells or LIF, which can activate Jak/Stat3 pathway. Recently, it has been reported a new culture condition comprising serum-free medium with ERK and GSK3β inhibitors (2i) could drive ES cells into a state of pluripotency more like inner cell mass (ICM) in mouse blastocysts called ground state. However, although 2i could sustain ES cells self-renewal, LIF is routinely added. The roles of Stat3 activation are still unclear now. Here we investigated whether Jak/Stat3 might also contribute to the induction of ground state pluripotency. We introduced a lentiviral construct with 7-repeat Stat3-binding sequence to drive Renilla luciferase into ES cells, which can be used as a reporter to detect Stat3 activation by noninvasive bioluminescence imaging. Using this ES cells, we investigated the role of Stat3 activation in ground state maintenance. The results showed that Stat3 could be activated by 2i. Stattic, a chemical inhibitor of Stat3 phosphorylation, could effectively inhibit Stat3 activation in ES cells. When Stat3 activation was suppressed, ground state related genes were down regulated, and ES cells could not be maintained the ground state pluripotency even in 2i medium. All of these results indicate Stat3 activation is required in ground state maintenance.

Pathways of nutrient loading and impacts on plant diversity in a New York peatland

USGS Publications Warehouse

Drexler, J.Z.; Bedford, B.L.

2002-01-01

Nutrient loading is a subtle, yet serious threat to the preservation of high diversity wetlands such as peatlands. Pathways of nutrient loading and impacts on plant diversity in a small peatland in New York State, USA were determined by collecting and analyzing a suite of hydrogeological, hydro-chemical, soil, and vegetation data. Piezometer clusters within an intensive network constituted hydro-chemical sampling points and focal points for randomly selected vegetation quadrats and soil-coring locations. Hydrogeological data and nutrient analyses showed that P and K loading occurred chiefly by means of overland flow from an adjacent farm field, whereas N loading occurred predominantly through ground-water flow from the farm field. Redundancy analysis and polynomial regression showed that nutrients, particularly total P in peat, total K in peat, extractable NH4-N, and NO3-N flux in ground water, were strongly negatively correlated with plant diversity measures at the site. No other environmental variables except vegetation measures associated with eutrophication demonstrated such a strong relationship with plant diversity. Nitrate loading over 4 mg m -2 day-1 was associated with low plant diversity, and Ca fluxes between 80 and 130 mg m-2 day-1 were associated with high plant diversity. Areas in the site with particularly low vascular plant and bryophyte species richness and Shannon-Wiener diversity (H') occurred adjacent to the farm field and near a hillside spring. High H' and species richness of vascular plants and bryophytes occurred in areas that were further removed from agriculture, contained no highly dominant vegetation, and were situated directly along the ground-water flow paths of springs. These areas were characterized by relatively constant water levels and consistent, yet moderate fluxes of base cations and nutrients. Overall, this study demonstrates that knowledge of site hydrogeology is crucial for determining potential pathways of nutrient loading and for developing relationships between nutrient inflows and wetland plant diversity. ?? 2002, The Society of Wetland Scientists.

Solving Quantum Ground-State Problems with Nuclear Magnetic Resonance

PubMed Central

Li, Zhaokai; Yung, Man-Hong; Chen, Hongwei; Lu, Dawei; Whitfield, James D.; Peng, Xinhua; Aspuru-Guzik, Alán; Du, Jiangfeng

2011-01-01

Quantum ground-state problems are computationally hard problems for general many-body Hamiltonians; there is no classical or quantum algorithm known to be able to solve them efficiently. Nevertheless, if a trial wavefunction approximating the ground state is available, as often happens for many problems in physics and chemistry, a quantum computer could employ this trial wavefunction to project the ground state by means of the phase estimation algorithm (PEA). We performed an experimental realization of this idea by implementing a variational-wavefunction approach to solve the ground-state problem of the Heisenberg spin model with an NMR quantum simulator. Our iterative phase estimation procedure yields a high accuracy for the eigenenergies (to the 10−5 decimal digit). The ground-state fidelity was distilled to be more than 80%, and the singlet-to-triplet switching near the critical field is reliably captured. This result shows that quantum simulators can better leverage classical trial wave functions than classical computers PMID:22355607