Studies of Diamonds Using Electron Paramagnetic Resonance and Other Techniques

NASA Astrophysics Data System (ADS)

Zhang, Shigang

Studies of impurities/defects in diamonds grown with the high-temperature high-pressure technique (HTHP) and B- and P-doped diamond films using fast ion implantation and chemical evaporation have been carried out. The main technique employed in the study is electron paramagnetic resonance (EPR). Raman, laser and X-ray fluorescence are also used to characterize the samples. While other commonly used techniques such as infrared (IR) spectroscopy detect no nitrogen in an isotopically enriched ^ {12}C diamond, the clear EPR spectrum consistently measures a nitrogen concentration of about 0.05ppm by calibration against a few standards. The ^{12}C diamond is evaluated to be ideal for optical window application and studies of diamond properties. Neither the EPR lineshape nor the second moment supports a random nitrogen distribution in the ^{12}C diamond. Instead, the average nitrogen distance is found to be larger than the of the random nitrogen distribution. The g-tensor for substitutional nitrogen is found to be axially symmetric along the (111) direction with g_| - g_| = 0.00002(5). In the study of a HTHP IIb blue semiconducting diamond, neutral N is measured with a concentration of 0.02ppm. The result is not well understood since neutral nitrogen is expected to lose its extra electron to boron due to electron-hole recombination. Further studies are suggested to better understand this result. EPR studies of two sets of P-doped diamond films grown using fast ion implantation and chemical incorporation reveal that defect levels caused by diamond doping are still too high for semiconductor applications. As expected, P doping causes a defect level two orders of magnitude higher than B doping, which can be explained by the relatively larger size of P than B. The theoretical analysis based on EPR hyperfine interaction suggest that P forms a shallow donor in diamond and that the electron density at the P site is |psi(0)|^2 = 0.27 times 10^{24} cm^ {-3}. This is consistent

High-Frequency Electron Paramagnetic Resonance Spectroscopy of Nitroxide-Functionalized Nanodiamonds in Aqueous Solution.

PubMed

Akiel, R D; Stepanov, V; Takahashi, S

2017-06-01

Nanodiamond (ND) is an attractive class of nanomaterial for fluorescent labeling, magnetic sensing of biological molecules, and targeted drug delivery. Many of those applications require tethering of target biological molecules on the ND surface. Even though many approaches have been developed to attach macromolecules to the ND surface, it remains challenging to characterize dynamics of tethered molecule. Here, we show high-frequency electron paramagnetic resonance (HF EPR) spectroscopy of nitroxide-functionalized NDs. Nitroxide radical is a commonly used spin label to investigate dynamics of biological molecules. In the investigation, we developed a sample holder to overcome water absorption of HF microwave. Then, we demonstrated HF EPR spectroscopy of nitroxide-functionalized NDs in aqueous solution and showed clear spectral distinction of ND and nitroxide EPR signals. Moreover, through EPR spectral analysis, we investigate dynamics of nitroxide radicals on the ND surface. The demonstration sheds light on the use of HF EPR spectroscopy to investigate biological molecule-functionalized nanoparticles.

Retrospective Reconstruction of Radiation Doses of Chernobyl Liquidators by Electron Paramagnetic Resonance

DTIC Science & Technology

1997-12-01

Armed Forces Rad I Research Institute Retrospective Reconstruction of Radiation Doses of Chernobyl Liquidators by Electron Paramagnetic Resonance A...of Radiation Doses of Chernobyl Liquidators by Electron Paramagnetic Resonance Authored by Scientific Center of Radiation Medicine Academy of Medical...libraries associated with the U.S. Government’s Depository Library System. Preface On April 26, 1986, Reactor #4 at the Chernobyl Nuclear Power Plant near

Point defects in crystalline zircon (zirconium silicate), ZrSiO4: electron paramagnetic resonance studies

NASA Astrophysics Data System (ADS)

Tennant, W. C.; Claridge, R. F. C.; Walsby, C. J.; Lees, N. S.

This article outlines the present state of knowledge of paramagnetic defects in crystalline zircon as obtained mainly, but not exclusively, from electron paramagnetic resonance (EPR) studies in crystalline zircon (zirconium silicate, ZrSiO4). The emphasis is on single-crystal studies where, in principle, unambiguous analysis is possible. Firstly, the crystallography of zircon is presented. Secondly, the relationships between available crystal-site symmetries and the symmetries of observed paramagnetic species in zircon, and how these observations lead to unambiguous assignments of point-group symmetries for particular paramagnetic species are detailed. Next, spin-Hamiltonian (SH) analysis is discussed with emphasis on the symmetry relationships that necessarily exist amongst the Laue classes of the crystal sites in zircon, the paramagnetic species occupying those sites and the SH itself. The final sections of the article then survey the results of EPR studies on zircon over the period 1960-2002.

ELECTRON PARAMAGNETIC RESONANCE AND BAKING STUDIES ON GAMMA-IRRADIATED FLOUR

SciTech Connect

Lee, C.C.

1962-03-01

The irradiation of flour (from Western Canadian hard red spring wheat) at its usual moisture level of 12 to 14% with up to 10/sup 6/ rads of Co/sup 60/ gamma rays gave no observable electron paramagnetic resonance (EPR) spectrum. However, after reduction of the moisture contert to 8 or 4%, irradiation resulted in EPR absorption indicating presence of radioinduced free radicals, which were destroyed rapidly in the presence of water vapor. With the irradiated flour kept in a sealed tube, the EPR spectrum faded with time. The fading was quite rapid for the first few days and then proceeded moremore » slowly. Irradiation resulted in a moderate increase in baked bread loaf volume at fairly low radiation dosages, followed by a gradual decrease in loaf volume at higher dosages (0.25 Mrad). Also, loaf volume tended to decrease as the elapsed time between irradiation and baking increased. This finding, when considered with the fading of the EPR spectrum, indicated that the EPR-detectable free radicals in the irradiated flour did not cause a strengthenlng of the gluten to produce an increase in loaf volume, as the radicals disappeared on becoming stable compounds. (H.H.D.)« less

The Effect of Electronic Paramagnetism on Nuclear Magnetic Resonance Frequencies in Metals

DOE R&D Accomplishments Database

Townes, C. H.; Herring, C.; Knight, W. D.

1950-09-22

Observations on the shifts of nuclear resonances in metals ( Li{sup 7}, Na{sup 23}, Cu {sup 63}, Be{sup 9}, Pb{sup 207}, Al{sup 27}, and Ca{sup 69} ) due to free electron paramagnetism; comparison with theoretical values.

Measurement of electron paramagnetic resonance using terahertz time-domain spectroscopy.

PubMed

Kozuki, Kohei; Nagashima, Takeshi; Hangyo, Masanori

2011-12-05

We present a frequency-domain electron spin resonance (ESR) measurement system using terahertz time-domain spectroscopy. A crossed polarizer technique is utilized to increase the sensitivity in detecting weak ESR signals of paramagnets caused by magnetic dipole transitions between magnetic sublevels. We demonstrate the measurements of ESR signal of paramagnetic copper(II) sulfate pentahydrate with uniaxial anisotropy of the g-factor under magnetic fields up to 10 T. The lineshape of the obtained ESR signals agrees well with the theoretical predictions for a powder sample with the uniaxial anisotropy.

Strongly driven electron spins using a Ku band stripline electron paramagnetic resonance resonator

NASA Astrophysics Data System (ADS)

Yap, Yung Szen; Yamamoto, Hiroshi; Tabuchi, Yutaka; Negoro, Makoto; Kagawa, Akinori; Kitagawa, Masahiro

2013-07-01

This article details our work to obtain strong excitation for electron paramagnetic resonance (EPR) experiments by improving the resonator's efficiency. The advantages and application of strong excitation are discussed. Two 17 GHz transmission-type, stripline resonators were designed, simulated and fabricated. Scattering parameter measurements were carried out and quality factor were measured to be around 160 and 85. Simulation results of the microwave's magnetic field distribution are also presented. To determine the excitation field at the sample, nutation experiments were carried out and power dependence were measured using two organic samples at room temperature. The highest recorded Rabi frequency was rated at 210 MHz with an input power of about 1 W, which corresponds to a π/2 pulse of about 1.2 ns.

Mesostructure, electron paramagnetic resonance, and magnetic properties of polymer carbon black composites

NASA Astrophysics Data System (ADS)

Brosseau, C.; Molinié, P.; Boulic, F.; Carmona, F.

2001-06-01

Electron paramagnetic resonance (EPR) has now become firmly established as one of the methods of choice for analyzing the carbon network over a range of different volume fraction of the carbon black in the composite, i.e., below and above the respective conduction threshold concentration. In the present article, two types of carbon blacks, having very different primary structures, surface areas, and percolation thresholds, were used; Raven 7000 (of high surface area and high percolation threshold volume fraction) and Y50A (of low surface area and low percolation threshold volume fraction). A semiquantitative image analysis of the microstructure from transmission electron microscopy reveals information about the spatial distribution of the carbon aggregates and agglomerates inside the composite. We observe that the apparent surface of agglomerates increases significantly with increasing carbon black content for the two types of blacks investigated. Adsorbed oxygen on the carbon black cristallites and dynamic coalescence under mixing conditions can be responsible for the broadening of the dispersed phase surface distribution. The interagglomerate distance in two samples of concentrations fabsorption EPR spectra, at temperatures between 105 and 300 K, of the composite samples containing Raven 7000 can be described by a linear superposition of two distinct Lorentzian (one broad and the other narrow) resonance lines and a single (narrow) Lorentzian resonance line for composite samples containing Y50A. The spins giving rise to the EPR signal reside in the carbon black particles. In Raven 7000, the significant difference in linewidth between the two signals demonstrates a different environment where the restriction of the motion of the

Electron paramagnetic resonance of natural and gamma-irradiated alunite and kaolin mineral powders

NASA Astrophysics Data System (ADS)

Koksal, F.; Koseoglu, R.; Saka, I.; Basaran, E.; Sener, F.

2004-06-01

Natural alunite and kaolin minerals obtained from West Anatolia were investigated by electron paramagnetic resonance (EPR) in natural and gamma-irradiated states at room temperature and at 113 K. The paramagnetic centres at ambient temperature in natural alunite were attributed to the (C) over dot H 2OH, (C) over dot O-3(-), (S) over dot O-2(-), (C) over dot O-2(-) and [AlO4 ](0) radicals. In natural kaolin, the paramagnetic centres were attributed to the (C) over dot O-3(-), (S) over dot O-2(-) (C) over dot O-2(-) and [AlO4](0) radicals. The gamma-irradiation does not produce any detectable effects on these radicals. At 113 K, the lines for (C) over dot H2OH could not be observed well, probably due to the anisotropic behaviour of the hyperfine interaction of the methylene protons, but the lines for [AlO4](0) centres were found to be perfectly observable at above 20 mW microwave power in both alunite and kaolin powders before and after gamma-irradiation. The EPR parameters of the observed paramagnetic centres were reported.

Interpretation of the Electron Paramagnetic Resonance Spectra of Copper(II)-Tyrosine Complex

NASA Astrophysics Data System (ADS)

Xu, Xiao-Hui; Kuang, Min-Quan

2017-12-01

The electron paramagnetic resonance (EPR) spectra of [Cu(l-tyrosine)2]n (CuA) were interpreted based on the fourth-order perturbation treatments where the contributions due to the local distortion, ligand orbit and spin-orbit coupling were included. The calculated band transitions d_{x^2} - y^2 to dxy (≈16412 cm-1) and d_{z^2} (≈14845 cm-1) agree well with the band analysis results (d_{x^2} - y^2 \\to d_{xy} ≈16410 and d_{x^2} - y^2 \\to d_{z^2} ≈14850 cm-1). The unresolved separations d_{x^2} - y^2 \\to d_{xz} and d_{x^2} - y^2 \\to d_{yz} in the absorption spectra were evaluated as 26283 and 26262 cm-1, respectively. For CuA, copper chromophores in 1,3-diaminorpropane isophtalate copper(II) complex (CuB) and N-methyl-1,2-diaminoetaane-bis copper(II) polymer (CuC), the transition d_{x^2} - y^2 \\to d_{xy} (=E1≈10Dq) suffered an increase with a decrease in R̅L which was evaluated as the mean value of the copper-ligand bond lengths. The correlations between the tetragonal elongation ratio ρ (=(Rz-R̅L)/R̅L) (or the ratio G=(gz-ge)/((gx+gy)/2-ge)) and the g isotropy gav (=(gx+gy+gz)/3) (or the covalency factor N) for CuA, CuB and CuC were acquired and all the results were discussed.

Optical detection of electron paramagnetic resonance in room-temperature electron-irradiated ZnO

SciTech Connect

Vlasenko, L.S.; Watkins, G.D.

The dominant defect observed in the photoluminescence (PL) of room-temperature electron-irradiated ZnO by optical detection of electron paramagnetic resonance (ODEPR) is determined to be the positively charged oxygen vacancy (V{sub O}{sup +}). Its spectrum, labeled L3, was previously observed in a 4.2 K in situ irradiation study [Yu. V. Gorelkinskii and G. D. Watkins, Phys. Rev. B 69, 115212 (2004)], but it was thought there not to be stable at room temperature and was not identified. Here it is found to be stable to 400 deg. C, where it disappears. It is observed as a competing process (negative signal) tomore » the dominant PL band produced by the irradiation at {approx}700 nm, but is positive in a weaker band at {approx}600 nm. Models are presented for its electrical level position in the gap to explain the results. Two other ODEPR signals are also detected, one of which is tentatively identified as also associated with the oxygen vacancy.« less

Electron paramagnetic resonance and FT-IR spectroscopic studies of glycine anhydride and betaine hydrochloride

NASA Astrophysics Data System (ADS)

Halim Başkan, M.; Kartal, Zeki; Aydın, Murat

2015-12-01

Gamma irradiated powders of glycine anhydride and betaine hydrochloride have been investigated at room temperature by electron paramagnetic resonance (EPR). In these compounds, the observed paramagnetic species were attributed to the R1 and R2 radicals, respectively. It was determined that the free electron interacted with environmental protons and 14N nucleus in both radicals. The EPR spectra of gamma irradiated powder samples remained unchanged at room temperature for two weeks after irradiation. Also, the Fourier Transform Infrared (FT-IR), FT-Raman and thermal analyses of both compounds were investigated. The functional groups in the molecular structures of glycine anhydride and betaine hydrochloride were identified by vibrational spectroscopies (FT-IR and FT-Raman).

A 1-2 GHz pulsed and continuous wave electron paramagnetic resonance spectrometer

NASA Astrophysics Data System (ADS)

Quine, Richard W.; Rinard, George A.; Ghim, Barnard T.; Eaton, Sandra S.; Eaton, Gareth R.

1996-07-01

A microwave bridge has been constructed that performs three types of electron paramagnetic resonance experiments: continuous wave, pulsed saturation recovery, and pulsed electron spin echo. Switching between experiment types can be accomplished via front-panel switches without moving the sample. Design features and performance of the bridge and of a resonator used in testing the bridge are described. The bridge is constructed of coaxial components connected with semirigid cable. Particular attention has been paid to low-noise design of the preamplifier and stability of automatic frequency control circuits. The bridge incorporates a Smith chart display and phase adjustment meter for ease of tuning.

Electron paramagnetic resonance of gamma-irradiated single crystals of 3-nitroacetanilide

NASA Astrophysics Data System (ADS)

Aşik, Biray

2008-06-01

The electron paramagnetic resonance of single crystals of 3-nitroacetanilide has been observed and analyzed for different orientations of the crystal in the magnetic field, after being damaged at 300 K by γ-irradiation. The crystals have been investigated between 123 and 300 K. The spectra were found to be temperature independent. The irradiation of 3-nitroacetanilide by γ-rays produces radicals at the nitrogen atoms in the molecule. The principal values of the hyperfine coupling tensor of the unpaired electron and the principal values of the g-tensor were determined.

Paramagnetic Defects in Electron-Irradiated Yttria-Stabilized Zirconia: Effect of Yttria Content

SciTech Connect

Costantini, Jean-Marc; Beuneu, Francois; Morrison-Smith, Sarah

2011-01-01

We have studied the effect of the yttria content on the paramagnetic centres in electron-irradiated yttria-stabilized zirconia (ZrO2: Y3+) or YSZ. Single crystals with 9.5 mol% or 18 mol% Y2O3 were irradiated with electrons of 1.0, 1.5, 2.0 and 2.5 MeV. The paramagnetic centre production was studied by X-band EPR spectroscopy. The same paramagnetic centres were identified for both chemical compositions, namely two electron centres, i.e. i) F+-type centres (involving singly ionized oxygen vacancies), and ii) so-called T centres (Zr3+ in a trigonal symmetry site), and hole-centres. A strong effect is observed on the production of hole-centres which are stronglymore » enhanced when doubling the yttria content. However, no striking effect is found on the electron centres (except the enhancement of an extra line associated to the F+-type centres). It is concluded that hole-centres are produced by inelastic interactions, whereas F+-type centres are produced by elastic collisions with no effect of the yttria content on the defect production rate. In the latter case, the threshold displacement energy (Ed) of oxygen is estimated from the electron-energy dependence of the F+-type centre production rate, with no significant effect of the yttria content on Ed. An Ed value larger than 120 eV is found. Accordingly, classical molecular dynamics (MD) simulations with a Buckingham-type potential show that Ed values for Y and O are likely to be in excess of 200 eV. Due to the difficulty in displacing O or Y atoms, the radiation-induced defects may alternatively be a result of Zr atom displacements for Ed = 80 1 eV with subsequent defect re-arrangement.« less

Study of ultrasonic attenuation in f-electron systems in the paramagnetic limit of Coulomb interaction

SciTech Connect

Shadangi, Asit Ku., E-mail: asitshad@iopb.res.in; Rout, G. C., E-mail: gcr@iopb.res.in

2015-05-15

We report here a microscopic model study of ultrasonic attenuation in f-electron systems based on Periodic Anderson Model in which Coulomb interaction is considered within a mean-field approximation for a weak interaction. The Phonon is coupled to the conduction band and f-electrons. The phonon Green's function is calculated by Zubarev's technique of the Green's function method. The temperature dependent ultrasonic attenuation co-efficient is calculated from the imaginary part of the phonon self-energy in the dynamic and long wave length limit. The f-electron occupation number is calculated self-consistently in paramagnetic limit of Coulomb interaction. The effect of the Coulomb interaction onmore » ultrasonic attenuation is studied by varying the phonon coupling parameters to the conduction and f-electrons, hybridization strength, the position of f-level and the Coulomb interaction Strength. Results are discussed on the basis of experimental results.« less

Degradation of edible oil during food processing by ultrasound: electron paramagnetic resonance, physicochemical, and sensory appreciation.

PubMed

Pingret, Daniella; Durand, Grégory; Fabiano-Tixier, Anne-Sylvie; Rockenbauer, Antal; Ginies, Christian; Chemat, Farid

2012-08-08

During ultrasound processing of lipid-containing food, some off-flavors can be detected, which can incite depreciation by consumers. The impacts of ultrasound treatment on sunflower oil using two different ultrasound horns (titanium and pyrex) were evaluated. An electron paramagnetic resonance study was performed to identify and quantify the formed radicals, along with the assessment of classical physicochemical parameters such as peroxide value, acid value, anisidine value, conjugated dienes, polar compounds, water content, polymer quantification, fatty acid composition, and volatiles profile. The study shows an increase of formed radicals in sonicated oils, as well as the modification of physicochemical parameters evidencing an oxidation of treated oils.

Hyperfine Interactions in the Electron Paramagnetic Resonance Spectra of Point Defects in Wide-Band-Gap Semiconductors

DTIC Science & Technology

2014-09-18

compensation) during growth due to their preferred trivalent charge states. The electron paramagnetic resonance spectrum of the singly ionized chromium ...neutral nitrogen acceptor in ZnO . . . . . . . . . . . . . . . . . . 45 16 Spectrum of the singly ionized chromium acceptor in TiO2 . . . . . . . . . 49...is a single crystal of magnesium oxide that has been doped with chromium . Chromium Cr3+ substitutes for magnesium Mg2+ and creates a paramagnetic

High-Yield Spin Labeling of Long RNAs for Electron Paramagnetic Resonance Spectroscopy.

PubMed

Kerzhner, Mark; Matsuoka, Hideto; Wuebben, Christine; Famulok, Michael; Schiemann, Olav

2018-05-10

Site-directed spin labeling is a powerful tool for investigating the conformation and dynamics of biomacromolecules such as RNA. Here we introduce a spin labeling strategy based on click chemistry in solution that, in combination with enzymatic ligation, allows highly efficient labeling of complex and long RNAs with short reaction times and suppressed RNA degradation. With this approach, a 34-nucleotide aptamer domain of the preQ1 riboswitch and an 81-nucleotide TPP riboswitch aptamer could be labeled with two labels in several positions. We then show that conformations of the preQ1 aptamer and its dynamics can be monitored in the absence and presence of Mg 2+ and a preQ1 ligand by continuous wave electron paramagnetic resonance spectroscopy at room temperature and pulsed electron-electron double resonance spectroscopy (PELDOR or DEER) in the frozen state.

Paramagnetic defects in electron-irradiated yttria-stabilized zirconia: Effect of yttria content

SciTech Connect

Costantini, Jean-Marc; Beuneu, Francois; Morrison-Smith, Sarah E.

2011-12-20

We have studied the effect of the yttria content on the paramagnetic centres in electron-irradiated yttria-stabilized zirconia (ZrO2: Y3+) or YSZ. Single crystals with 9.5 mol% or 18 mol% Y2O3 were irradiated with electrons of 1.0, 1.5, 2.0 and 2.5 MeV. The paramagnetic centre production was studied by X-band EPR spectroscopy. The same paramagnetic centres were identified for both chemical compositions, namely two electron centres, i.e. i) F+-type centres (involving singly ionized oxygen vacancies), and ii) so-called T centres (Zr3+ in a trigonal symmetry site), and hole-centres. A strong effect is observed on the production of hole-centres which are stronglymore » enhanced when doubling the yttria content. However, no striking effect is found on the electron centres (except the enhancement of an extra line associated to the F+-type centres). It is concluded that hole-centres are produced by inelastic interactions, whereas F+-type centres are produced by elastic collisions with no effect of the yttria content on the defect production rate. In the latter case, the threshold displacement energy (Ed) of oxygen is estimated from the electron-energy dependence of the F+-type centre production rate, with no significant effect of the yttria content on Ed. An Ed value larger than 120 eV is found. Accordingly, classical molecular dynamics (MD) simulations with a Buckingham-type potential show that Ed values for Y and O are likely to be in excess of 200 eV. It is concluded that F+-type centres might be actually oxygen divacancies (F2+-type centres). Due to the difficulty in displacing O or Y atoms, the radiation-induced defects may alternatively be a result of Zr atom displacements for Ed = 80 ± 1 eV with subsequent defect re-arrangement.« less

Carbon-related platinum defects in silicon: An electron paramagnetic resonance study of high spin states

NASA Astrophysics Data System (ADS)

Scheerer, O.; Höhne, M.; Juda, U.; Riemann, H.

1997-10-01

In this article, we report about complexes in silicon investigated by electron paramagnetic resonance (EPR). In silicon doped with C and Pt we detected two different complexes: cr-1Pt (cr: carbon-related, 1Pt: one Pt atom) and cr-3Pt. The complexes have similar EPR properties. They show a trigonal symmetry with effective g-values geff,⊥=2g⊥≈4 and geff,‖=g‖≈2 (g⊥, g‖ true g-values). The g-values can be explained by a spin Hamiltonian with large fine-structure energy (electron spin S=3/2) and smaller Zeeman interaction. The participation of platinum in the complexes is proved by the hyperfine interaction. From experiments with varying carbon concentration we conclude that the complexes contain carbon. Atomistic models based on the Watkins vacancy-model for substitutional Pt were developed.

Study of the effects of hydroxyapatite nanocrystal codoping by pulsed electron paramagnetic resonance methods

NASA Astrophysics Data System (ADS)

Gafurov, M. R.; Biktagirov, T. B.; Mamin, G. V.; Shurtakova, D. V.; Klimashina, E. S.; Putlyaev, V. I.; Orlinskii, S. B.

2016-03-01

The effect of codoping of hydroxyapatite (HAP) nanocrystals with average sizes of 35 ± 15 nm during "wet" synthesis by CO 3 2- carbonate anions and Mn2+ cations on relaxation characteristics (for the times of electron spin-spin relaxation) of the NO 3 2- nitrate radical anion has been studied. By the example of HAP, it has been demonstrated that the electron paramagnetic resonance (EPR) is an efficient method for studying anion-cation (co)doping of nanoscale particles. It has been shown experimentally and by quantummechanical calculations that simultaneous introduction of several ions can be energetically more favorable than their separate inclusion. Possible codoping models have been proposed, and their energy parameters have been calculated.

Electrochemistry and electron paramagnetic resonance spectroscopy of cytochrome c and its heme-disrupted analogs.

PubMed

Novak, David; Mojovic, Milos; Pavicevic, Aleksandra; Zatloukalova, Martina; Hernychova, Lenka; Bartosik, Martin; Vacek, Jan

2018-02-01

Cytochrome c (cyt c) is one of the most studied conjugated proteins due to its electron-transfer properties and ability to regulate the processes involved in homeostasis or apoptosis. Here we report an electrochemical strategy for investigating the electroactivity of cyt c and its analogs with a disrupted heme moiety, i.e. apocytochrome c (acyt c) and porphyrin cytochrome c (pcyt c). The electrochemical data are supplemented with low-temperature and spin-probe electron paramagnetic resonance (EPR) spectroscopy. The main contribution of this report is a complex evaluation of cyt c reduction and oxidation at the level of surface-localized amino acid residues and the heme moiety in a single electrochemical scan. The electrochemical pattern of cyt c is substantially different to both analogs acyt c and pcyt c, which could be applicable in further studies on the redox properties and structural stability of cytochromes and other hemeproteins. Copyright © 2017 Elsevier B.V. All rights reserved.

Electron Paramagnetic Resonance of a Single NV Nanodiamond Attached to an Individual Biomolecule

NASA Astrophysics Data System (ADS)

Teeling-Smith, Richelle M.; Jung, Young Woo; Scozzaro, Nicolas; Cardellino, Jeremy; Rampersaud, Isaac; North, Justin A.; Šimon, Marek; Bhallamudi, Vidya P.; Rampersaud, Arfaan; Johnston-Halperin, Ezekiel; Poirier, Michael G.; Hammel, P. Chris

2016-05-01

A key limitation of electron paramagnetic resonance (EPR), an established and powerful tool for studying atomic-scale biomolecular structure and dynamics is its poor sensitivity, samples containing in excess of 10^12 labeled biomolecules are required in typical experiments. In contrast, single molecule measurements provide improved insights into heterogeneous behaviors that can be masked by ensemble measurements and are often essential for illuminating the molecular mechanisms behind the function of a biomolecule. We report EPR measurements of a single labeled biomolecule that merge these two powerful techniques. We selectively label an individual double-stranded DNA molecule with a single nanodiamond containing nitrogen-vacancy (NV) centers, and optically detect the paramagnetic resonance of NV spins in the nanodiamond probe. Analysis of the spectrum reveals that the nanodiamond probe has complete rotational freedom and that the characteristic time scale for reorientation of the nanodiamond probe is slow compared to the transverse spin relaxation time. This demonstration of EPR spectroscopy of a single nanodiamond labeled DNA provides the foundation for the development of single molecule magnetic resonance studies of complex biomolecular systems.

Electron paramagnetic resonance (EPR) spectroscopy characterization of wheat grains from plants of different water stress tolerance.

PubMed

Łabanowska, Maria; Filek, Maria; Kurdziel, Magdalena; Bednarska, Elżbieta; Dłubacz, Aleksandra; Hartikainen, Helina

2012-09-01

Grains of five genotypes of wheat (four Polish and one Finnish), differing in their tolerance to drought stress were chosen for this investigation. Electron paramagnetic resonance spectroscopy allowed observation of transition metal ions (Mn, Fe, Cu) and different types of stable radicals, including semiquinone centers, present in seed coats, as well as several types of carbohydrate radicals found mainly in the inner parts of grains. The content of paramagnetic metal centers was higher in sensitive genotypes (Radunia, Raweta) than in tolerant ones (Parabola, Nawra), whereas the Finnish genotype (Manu) exhibited intermediate amounts. Similarly, the concentrations of both types of radicals, carbohydrates and semiquinone were significantly higher in the grains originating from more sensitive wheat genotypes. The nature of carbohydrate radicals and their concentrations were confronted with the kinds and amounts of sugars found by the biochemical analyses and microscopy observations. It is suggested that some long lived radicals (semiquinone and starch radicals) occurring in grains could be indicators of stress resistance of wheat plants. Copyright © 2012 Elsevier GmbH. All rights reserved.

300 MHz continuous wave electron paramagnetic resonance spectrometer for small animal in vivo imaging

NASA Astrophysics Data System (ADS)

Koscielniak, J.; Devasahayam, N.; Moni, M. S.; Kuppusamy, P.; Yamada, K.; Mitchell, J. B.; Krishna, M. C.; Subramanian, S.

2000-11-01

Design and construction of an electron paramagnetic resonance (EPR) spectrometer, operating in the continuous wave mode in the radio frequency (rf) region, and capable of performing spectroscopy and in vivo imaging of paramagnetic spin probes is described. A resonant frequency of 300 MHz was chosen to provide the required sensitivity at nontoxic levels of commonly used spin probes and penetration of the rf in small animals. Three major components, the magnet, the radio frequency signal detection bridge, and the data acquisition module are described in this article. Integration of a rapid scan capability to reduce imaging time is also described. Two- and three-dimensional EPR images of the spin probe distribution in phantom objects as well as from in vivo experiments are reported. From the EPR images, morphology of some internal organs could be recognized. EPR images of the spin probe distribution in mice suggest differences in perfusion of the spin probe between normal and tumor regions. Addition of a spectral dimension to spatial images should enable differentiation of oxygen status in normal and pathological conditions.

Characterisation of β-tricalcium phosphate-based bone substitute materials by electron paramagnetic resonance spectroscopy

NASA Astrophysics Data System (ADS)

Matković, Ivo; Maltar-Strmečki, Nadica; Babić-Ivančić, Vesna; Dutour Sikirić, Maja; Noethig-Laslo, Vesna

2012-10-01

β-TCP based materials are frequently used as dental implants. Due to their resorption in the body and direct contact with tissues, in order to inactivate bacteria, fungal spores and viruses, they are usually sterilized by γ-irradiation. However, the current literature provides little information about effects of the γ-irradiation on the formation and stability of the free radicals in the bone graft materials during and after sterilization procedure. In this work five different bone graft substitution materials, composed of synthetic beta tricalcium phosphate (β-TCP) and hydroxyapatite (HAP) present in the market were characterized by electron paramagnetic resonance (EPR) spectroscopy, X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Paramagnetic species Mn2+, Fe3+, trapped H-atoms and CO2- radicals were detected in the biphasic material (60% HAP, 40% β-TCP), while in β-TCP materials only Mn2+ andor trapped hydrogen atoms were detected. EPR analysis revealed the details of the structure of these materials at the atomic level. The results have shown that EPR spectroscopy is a method which can be used to improve the quality control of bone graft materials after syntering, processing and sterilization procedure.

Measurement of Rate Constants for Homodimer Subunit Exchange Using Double Electron-Electron Resonance and Paramagnetic Relaxation Enhancements

PubMed Central

Yang, Yunhuang; Ramelot, Theresa A.; Ni, Shuisong; McCarrick, Robert M.; Kennedy, Michael A.

2013-01-01

Here, we report novel methods to measure rate constants for homodimer subunit exchange using double electron-electron resonance (DEER) electron paramagnetic resonance spectroscopy measurements and nuclear magnetic resonance spectroscopy based paramagnetic relaxation enhancement (PRE) measurements. The techniques were demonstrated using the homodimeric protein Dsy0195 from the strictly anaerobic bacterium Desulfitobacterium hafniense Y51. At specific times following mixing site-specific MTSL-labeled Dsy0195 with uniformly 15N-labeled Dsy0195, the extent of exchange was determined either by monitoring the decrease of MTSL-labeled homodimer from the decay of the DEER modulation depth or by quantifying the increase of MTSL-labeled/15N-labeled heterodimer using PREs. Repeated measurements at several time points following mixing enabled determination of the homodimer subunit dissociation rate constant, k−1;, which was 0.037 ± 0.005 min−1 derived from DEER experiments with a corresponding half-life time of 18.7 minutes. These numbers agreed with independent measurements obtained from PRE experiments. These methods can be broadly applied to protein-protein and protein-DNA complex studies. PMID:23180051

Systematic approach to cutoff frequency selection in continuous-wave electron paramagnetic resonance imaging

NASA Astrophysics Data System (ADS)

Hirata, Hiroshi; Itoh, Toshiharu; Hosokawa, Kouichi; Deng, Yuanmu; Susaki, Hitoshi

2005-08-01

This article describes a systematic method for determining the cutoff frequency of the low-pass window function that is used for deconvolution in two-dimensional continuous-wave electron paramagnetic resonance (EPR) imaging. An evaluation function for the criterion used to select the cutoff frequency is proposed, and is the product of the effective width of the point spread function for a localized point signal and the noise amplitude of a resultant EPR image. The present method was applied to EPR imaging for a phantom, and the result of cutoff frequency selection was compared with that based on a previously reported method for the same projection data set. The evaluation function has a global minimum point that gives the appropriate cutoff frequency. Images with reasonably good resolution and noise suppression can be obtained from projections with an automatically selected cutoff frequency based on the present method.

Study of free radicals in gamma irradiated cellulose of cultural heritage materials using Electron Paramagnetic Resonance

NASA Astrophysics Data System (ADS)

Kodama, Yasko; Rodrigues, Orlando, Jr.; Garcia, Rafael Henrique Lazzari; Santos, Paulo de Souza; Vasquez, Pablo A. S.

2016-07-01

Main subject of this article was to study room temperature stable radicals in Co-60 gamma irradiated contemporary paper using Electron Paramagnetic Resonance spectrometer (EPR). XRD was used to study the effect of ionizing radiation on the morphology of book paper. SEM images presented regions with cellulose fibers and regions with particles agglomeration on the cellulose fibers. Those agglomerations were rich in calcium, observed by EDS. XRD analysis confirmed presence of calcium carbonate diffraction peaks. The main objective of this study was to propose a method using conventional kinetics chemical reactions for the observed radical formed by ionizing radiation. Therefore, further analyses were made to study the half-life and the kinetics of the free radical created. This method can be suitably applied to study radicals on cultural heritage objects.

A new pulse width reduction technique for pulsed electron paramagnetic resonance spectroscopy.

PubMed

Ohba, Yasunori; Nakazawa, Shigeaki; Kazama, Shunji; Mizuta, Yukio

2008-03-01

We present a new technique for a microwave pulse modulator that generates a short microwave pulse of approximately 1ns for use in an electron paramagnetic resonance (EPR) spectrometer. A quadruple-frequency multiplier that generates a signal of 16-20GHz from an input of 4-5GHz was employed to reduce the rise and fall times of the pulse prepared by a PIN diode switch. We examined the transient response characteristics of a commercial frequency multiplier and found that the device can function as a multiplier for pulsed signal even though it was designed for continuous wave operation. We applied the technique to a Ku band pulsed EPR spectrometer and successfully observed a spin echo signal with a broad excitation bandwidth of approximately 1.6mT using 80 degrees pulses of 1.5ns.

Comparison of pulse sequences for R1-based electron paramagnetic resonance oxygen imaging.

PubMed

Epel, Boris; Halpern, Howard J

2015-05-01

Electron paramagnetic resonance (EPR) spin-lattice relaxation (SLR) oxygen imaging has proven to be an indispensable tool for assessing oxygen partial pressure in live animals. EPR oxygen images show remarkable oxygen accuracy when combined with high precision and spatial resolution. Developing more effective means for obtaining SLR rates is of great practical, biological and medical importance. In this work we compared different pulse EPR imaging protocols and pulse sequences to establish advantages and areas of applicability for each method. Tests were performed using phantoms containing spin probes with oxygen concentrations relevant to in vivo oxymetry. We have found that for small animal size objects the inversion recovery sequence combined with the filtered backprojection reconstruction method delivers the best accuracy and precision. For large animals, in which large radio frequency energy deposition might be critical, free induction decay and three pulse stimulated echo sequences might find better practical usage. Copyright © 2015 Elsevier Inc. All rights reserved.

Electron paramagnetic resonance of globin proteins - a successful match between spectroscopic development and protein research

NASA Astrophysics Data System (ADS)

Van Doorslaer, Sabine; Cuypers, Bert

2018-02-01

At the start of the twenty-first century, the research into the haem-containing globins got a considerable impetus with the discovery of three new mammalian globins: neuroglobin, cytoglobin and androglobin. Globins are by now found in all kingdoms of life and, in many cases, their functions are still under debate. This revival in globin research increased the demand for adequate physico-chemical research tools to determine the structure-function relationships of these proteins. From early days onwards, electron paramagnetic resonance (EPR) has been used in globin research. In recent decades, the field of EPR has been revolutionised with the introduction of many new pulsed and high-field EPR techniques. In this review, we highlight how EPR has become an essential tool in globin research, and how globins equally provide ideal model systems to push technical developments in EPR.

Growth Kinetics of the S Sub H Center on Magnesium Oxide Using Electron Paramagnetic Resonance

NASA Technical Reports Server (NTRS)

Jayne, J. P.

1971-01-01

Electron paramagnetic resonance spectroscopy was used to study the growth of S sub H centers on magnesium oxide powder which had hydrogen adsorbed on its surface. The centers were produced by ultraviolet radiation. The effects of both radiation intensity and hydrogen pressure were also studied. At constant hydrogen pressure and radiation dose, the initial S sub H center growth rate was found to be zero order. Beyond the initial region the growth rate deviated from zero order and finally approached saturation. The results are interpreted in terms of a model which assumes that the S sub H center is a hydrogen atom associated with a surface vacancy. Saturation appears to result from a limited supply of surface vacancies.

Studying metal impurities (Mn2+, Cu2+, Fe3+) in calcium phosphates by electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Iskhakova, K.; Murzakhanov, F.; Mamin, G.; Putlyaev, V.; Klimashina, E.; Fadeeva, I.; Fomin, A.; Barinov, S.; Maltsev, A.; Bakhteev, S.; Yusupov, R.; Gafurov, M.; Orlinskii, S.

2018-05-01

Calcium phosphates (CaP) are exploited in many fields of science, including geology, chemistry, biology and medicine due to their abundance in the nature and presence in the living organism. Various analytical and biochemical methods are used for controlling their chemical content, structure, morphology, etc. Unfortunately, magnetic resonance techniques are usually not even considered as necessary tools for CaP inspection. Some aspects of application of the commercially realized electron paramagnetic resonance (EPR) approaches for characterization of CaP powders and ceramics (including the nanosized materails) such as hydroxyapatite and tricalcium phosphates of biogenic and synthetic origins containing intrinsic impurities or intentional dopants are demonstrated. The key features and advantages of the EPR techniques for CaP based materials characterization that could compliment the data obtained with the recognized analytical methods are pointed out.

Theoretical calculations of Electron Paramagnetic Resonance parameters of liquid phase Orotic acid radical

NASA Astrophysics Data System (ADS)

Sarikaya, Ebru Karakaş; Dereli, Ömer

2017-02-01

To obtain liquid phase molecular structure, conformational analysis of Orotic acid was performed and six conformers were determined. For these conformations, eight possible radicals were modelled by using Density Functional Theory computations with respect to molecular structure. Electron Paramagnetic Resonance parameters of these model radicals were calculated and then they were compared with the experimental ones. Geometry optimizations of the molecule and modeled radicals were performed using Becke's three-parameter hybrid-exchange functional combined with the Lee-Yang-Parr correlation functional of Density Functional Theory and 6-311++G(d,p) basis sets in p-dioxane solution. Because Orotic acid can be mutagenic in mammalian somatic cells and it is also mutagenic for bacteria and yeast, it has been studied.

Imaging thiol redox status in murine tumors in vivo with rapid-scan electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Epel, Boris; Sundramoorthy, Subramanian V.; Krzykawska-Serda, Martyna; Maggio, Matthew C.; Tseytlin, Mark; Eaton, Gareth R.; Eaton, Sandra S.; Rosen, Gerald M.; Kao, Joseph P. Y.; Halpern, Howard J.

2017-03-01

Thiol redox status is an important physiologic parameter that affects the success or failure of cancer treatment. Rapid scan electron paramagnetic resonance (RS EPR) is a novel technique that has shown higher signal-to-noise ratio than conventional continuous-wave EPR in in vitro studies. Here we used RS EPR to acquire rapid three-dimensional images of the thiol redox status of tumors in living mice. This work presents, for the first time, in vivo RS EPR images of the kinetics of the reaction of 2H,15N-substituted disulfide-linked dinitroxide (PxSSPx) spin probe with intracellular glutathione. The cleavage rate is proportional to the intracellular glutathione concentration. Feasibility was demonstrated in a FSa fibrosarcoma tumor model in C3H mice. Similar to other in vivo and cell model studies, decreasing intracellular glutathione concentration by treating mice with L-buthionine sulfoximine (BSO) markedly altered the kinetic images.

Characterization of radiation-induced damage in high performance polymers by electron paramagnetic resonance imaging spectroscopy

NASA Technical Reports Server (NTRS)

Suleman, Naushadalli K.

1992-01-01

The potential for long-term human activity beyond the Earth's protective magnetosphere is limited in part by the lack of detailed information on the effectiveness and performance of existing structural materials to shield the crew and spacecraft from highly penetrating space radiations. The two radiations of greatest concern are high energy protons emitted during solar flares and galactic cosmic rays which are energetic ions ranging from protons to highly oxidized iron. Although the interactions of such high-energy radiations with matter are not completely understood at this time, the effects of the incident radiation are clearly expected to include the formation of paramagnetic spin centers via ionization and bond-scission reactions in the molecular matrices of structural materials. Since this type of radiation damage is readily characterized by Electron Paramagnetic Resonance (EPR) spectroscopy, the NASA Langley Research Center EPR system was repaired and brought on-line during the 1991 ASEE term. A major goal of the 1992 ASEE term was to adapt the existing core of the LaRC EPR system to meet the requirements for EPR Imaging--a powerful new technique which provides detailed information on the internal structure of materials by mapping the spatial distribution of unpaired spin density in bulk media. Major impetus for this adaptation arises from the fact that information derived from EPRI complements other methods such as scanning electron microscopy which primarily characterize surface phenomena. The modification of the EPR system has been initiated by the construction of specially designed, counterwound Helmholtz coils which will be mounted on the main EPR electromagnet. The specifications of the coils have been set to achieve a static linear magnetic field gradient of 10 gauss/mm/amp along the principal (Z) axis of the Zeeman field. Construction is also in progress of a paramagnetic standard in which the spin distribution is known in all three dimensions. This

Electron paramagnetic resonance of a 10B-containing heterocyclic radical

NASA Astrophysics Data System (ADS)

Eaton, Sandra S.; Ngendahimana, Thacien; Eaton, Gareth R.; Jupp, Andrew R.; Stephan, Douglas W.

2018-05-01

Electron paramagnetic resonance measurements for a 10B-containing heterocyclic phenanthrenedione radical, (C6F5)2B(O2C14H8), were made at X-band in 9:1 toluene:dichloromethane from 10 to 293 K and in toluene from 180 to 293 K. In well-deoxygenated 0.1 mM toluene solution at room temperature hyperfine couplings to 10B, four pairs of protons and five pairs of fluorines contribute to a continuous wave spectrum with many resolved lines. Hyperfine couplings were adjusted to provide the best fit for spectra of the radical enriched in 10B and the analogous radical synthesized with 10,11B in natural abundance, resulting in small refinements of the hyperfine coupling constants previously reported for the natural abundance sample. Electron spin relaxation rates at temperatures between 15 and 293 K were similar for samples containing 10B and natural isotope abundance. Analysis of electron spin echo envelope modulation and hyperfine correlation spectroscopy data at 80 K found Axx = -7.5 ± 0.3, Ayy = -8.5 ± 0.3, and Azz = -10.8 ± 0.3 MHz for 11B, which indicates small spin density on the boron. The spin echo and hyperfine spectroscopy data for the 10B -containing radical are consistent with the factor of 2.99 smaller hyperfine values for 10B than for 11B.

Ageing and thermal recovery of paramagnetic centers induced by electron irradiation in yttria-stabilized zirconia

NASA Astrophysics Data System (ADS)

Costantini, J. M.; Beuneu, F.

We have used electron spin resonance spectroscopy to study the defects induced in yttria-stabilized zirconia (YSZ) single crystals by 2.5-MeV electron irradiations. Two paramagnetic centers are produced: the first one with an axial <111> symmetry is similar to the trigonal Zr3+ electron center (T center) found after X-ray irradiation or thermo-chemical reduction, whereas the second one is a new oxygen hole center with an axial <100> symmetry different from the orthorhombic O- center induced by X-ray irradiation. At a fluence around 10(18) e/cm(2) , both centers are bleached out near 600 K, like the corresponding X-ray induced defects. At a fluence around 10(19) e/cm(2) , defects are much more stable, since complete thermal bleaching occurs near 1000 K. Accordingly, ageing of as-irradiated samples shows that high-dose defects at more stable than the low-dose ones.

Anisotropic rotational diffusion studied by passage saturation transfer electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Robinson, Bruce H.; Dalton, Larry R.

1980-01-01

The stochastic Liouville equation for the spin density matrix is modified to consider the effects of Brownian anisotropic rotational diffusion upon electron paramagnetic resonance (EPR) and saturation transfer electron paramagnetic resonance (ST-EPR) spectra. Spectral shapes and the ST-EPR parameters L″/L, C'/C, and H″/H defined by Thomas, Dalton, and Hyde at X-band microwave frequencies [J. Chem. Phys. 65, 3006 (1976)] are examined and discussed in terms of the rotational times τ∥ and τ⊥ and in terms of other defined correlation times for systems characterized by magnetic tensors of axial symmetry and for systems characterized by nonaxially symmetric magnetic tensors. For nearly axially symmetric magnetic tensors, such as nitroxide spin labels studied employing 1-3 GHz microwaves, ST-EPR spectra for systems undergoing anisotropic rotational diffusion are virtually indistinguishable from spectra for systems characterized by isotropic diffusion. For nonaxially symmetric magnetic tensors, such as nitroxide spin labels studied employing 8-35 GHz microwaves, the high field region of the ST-EPR spectra, and hence the H″/H parameter, will be virtually indistinguishable from spectra, and parameter values, obtained for isotropic diffusion. On the other hand, the central spectral region at x-band microwave frequencies, and hence the C'/C parameter, is sensitive to the anisotropic diffusion model provided that a unique and static relationship exists between the magnetic and diffusion tensors. Random labeling or motion of the spin label relative to the biomolecule whose hydrodynamic properties are to be investigated will destroy spectral sensitivity to anisotropic motion. The sensitivity to anisotropic motion is enhanced in proceeding to 35 GHz with the increased sensitivity evident in the low field half of the EPR and ST-EPR spectra. The L″/L parameter is thus a meaningful indicator of anisotropic motion when compared with H″/H parameter analysis. However

Polynuclear water-soluble dinitrosyl iron complexes with cysteine or glutathione ligands: electron paramagnetic resonance and optical studies.

PubMed

Vanin, Anatoly F; Poltorakov, Alexander P; Mikoyan, Vasak D; Kubrina, Lyudmila N; Burbaev, Dosymzhan S

2010-09-15

Electron paramagnetic resonance and optical spectrophotometric studies have demonstrated that low-molecular dinitrosyl iron complexes (DNICs) with cysteine or glutathione exist in aqueous solutions in the form of paramagnetic mononuclear (capital EM, Cyrillic-DNICs) and diamagnetic binuclear complexes (B-DNICs). The latter represent Roussin's red salt esters and can be prepared by treatment of aqueous solutions of Fe(2+) and thiols (small er, Cyrilliccapital EN, Cyrillic 7.4) with gaseous nitric oxide (NO) at the thiol:Fe(2+) ratio 1:1. capital EM, Cyrillic-DNICs are synthesized under identical conditions at the thiol:Fe(2+) ratios above 20 and produce an EPR signal with an electronic configuration {Fe(NO)(2)}(7) at g(aver.)=2.03. At neutral pH, aqueous solutions contain both M-DNICs and B-DNICs (the content of the latter makes up to 50% of the total DNIC pool). The concentration of B-DNICs decreases with a rise in pH; at small er, Cyrilliccapital EN, Cyrillic 9-10, the solutions contain predominantly M-DNICs. The addition of thiol excess to aqueous solutions of B-DNICs synthesized at the thiol:Fe(2+) ratio 1:2 results in their conversion into capital EM, Cyrillic-DNICs, the total amount of iron incorporated into M-DNICs not exceeding 50% of the total iron pool in B-DNICs. Air bubbling of cys-capital EM, Cyrillic-DNIC solutions results in cysteine oxidation-controlled conversion of capital EM, Cyrillic-DNICs first into cys-B-DNICs and then into the EPR-silent compound capital HA, Cyrillic able to generate a strong absorption band at 278 nm. In the presence of glutathione or cysteine excess, compound capital HA, Cyrillic is converted into B-DNIC/M-DNIC and is completely decomposed under effect of the Fe(2+) chelator small o, Cyrillic-phenanthroline or N-methyl-d-glucamine dithiocarbamate (MGD). Moreover, MGD initiates the synthesis of paramagnetic mononitrosyl iron complexes with MGD. It is hypothesized that compound capital HA, Cyrillic represents a polynuclear

One- and two-dimensional pulse electron paramagnetic resonance spectroscopy: concepts and applications.

PubMed

Van Doorslaer, S; Schweiger, A

2000-06-01

During the last two decades, the possibilities of pulse electron paramagnetic resonance (EPR) and pulse electron nuclear double resonance (ENDOR) spectroscopy have increased tremendously. While at the beginning of the 1980s pulse-EPR and ENDOR applications were still a rarity, the techniques are now very frequently applied in chemistry, physics, materials science, biology and mineralogy. This is mainly due to the considerable efforts invested in the last few years on instrument development and pulse-sequence design. Pulse-EPR spectrometers are now commercially available, which enables many research groups to use these techniques. In this work, an overview of state-of-the-art pulse EPR and ENDOR spectroscopy is given. The rapid expansion of the field, however, does not allow us to give an exhaustive record of all the pulse methods introduced so far. After a brief and very qualitative description of the basic principles of pulse EPR, we discuss some of the experiments in more detail and illustrate the potential of the methods with a number of selected applications.

New developments in high field electron paramagnetic resonance with applications in structural biology

NASA Astrophysics Data System (ADS)

Bennati, Marina; Prisner, Thomas F.

2005-02-01

Recent developments in microwave technologies have led to a renaissance of electron paramagnetic resonance (EPR) due to the implementation of new spectrometers operating at frequencies >=90 GHz. EPR at high fields and high frequencies (HF-EPR) has been established up to THz (very high frequency (VHF) EPR) in continuous wave (cw) operation and up to about 300 GHz in pulsed operation. To date, its most prominent application field is structural biology. This review article first gives an overview of the theoretical basics and the technical aspects of HF-EPR methodologies, such as cw and pulsed HF-EPR, as well as electron nuclear double resonance at high fields (HF-ENDOR). In the second part, the article illustrates different application areas of HF-EPR in studies of protein structure and function. In particular, HF-EPR has delivered essential contributions to disentangling complex spectra of radical cofactors or reaction intermediates in photosynthetic reaction centres, radical enzymes (such as ribonucleotide reductase) and in metalloproteins. Furthermore, HF-EPR combined with site-directed spin labelling in membranes and soluble proteins provides new methods of investigating complex molecular dynamics and intermolecular distances.

Electron paramagnetic resonance study of neutral Mg acceptors in β-Ga2O3 crystals

NASA Astrophysics Data System (ADS)

Kananen, B. E.; Halliburton, L. E.; Scherrer, E. M.; Stevens, K. T.; Foundos, G. K.; Chang, K. B.; Giles, N. C.

2017-08-01

Electron paramagnetic resonance (EPR) is used to directly observe and characterize neutral Mg acceptors ( M gGa0 ) in a β-Ga2O3 crystal. These acceptors, best considered as small polarons, are produced when the Mg-doped crystal is irradiated at or near 77 K with x rays. During the irradiation, neutral acceptors are formed when holes are trapped at singly ionized Mg acceptors ( M gGa- ). Unintentionally present Fe3+ (3d5) and Cr3+ (3d3) transition-metal ions serve as the corresponding electron traps. The hole is localized in a nonbonding p orbital on a threefold-coordinated oxygen ion adjacent to an Mg ion at a sixfold-coordinated Ga site. These M gGa0 acceptors (S = 1/2) have a slightly anisotropic g matrix (principal values are 2.0038, 2.0153, and 2.0371). There is also partially resolved 69Ga and 71Ga hyperfine structure resulting from unequal interactions with the two Ga ions adjacent to the hole. With the magnetic field along the a direction, hyperfine parameters are 2.61 and 1.18 mT for the 69Ga nuclei at the two inequivalent neighboring Ga sites. The M gGa0 acceptors thermally convert back to their nonparamagnetic M gGa- charge state when the temperature of the crystal is raised above approximately 250 K.

Electron Paramagnetic Resonance Study of a Photosynthetic Microbial Mat and Comparison with Archean Cherts

NASA Astrophysics Data System (ADS)

Bourbin, M.; Derenne, S.; Gourier, D.; Rouzaud, J.-N.; Gautret, P.; Westall, F.

2012-12-01

Organic radicals in artificially carbonized biomass dominated by oxygenic and non-oxygenic photosynthetic bacteria, Microcoleus chthonoplastes-like and Chloroflexus-like bacteria respectively, were studied by Electron Paramagnetic Resonance (EPR) spectroscopy. The two bacteria species were sampled in mats from a hypersaline lake. They underwent accelerated ageing by cumulative thermal treatments to induce progressive carbonization of the biological material, mimicking the natural maturation of carbonaceous material of Archean age. For thermal treatments at temperatures higher than 620 °C, a drastic increase in the EPR linewidth is observed in the carbonaceous matter from oxygenic photosynthetic bacteria and not anoxygenic photosynthetic bacteria. This selective EPR linewidth broadening reflects the presence of a catalytic element inducing formation of radical aggregates, without affecting the molecular structure or the microstructure of the organic matter, as shown by Raman spectroscopy and Transmission Electron Microscopy. For comparison, we carried out an EPR study of organic radicals in silicified carbonaceous rocks (cherts) from various localities, of different ages (0.42 to 3.5 Gyr) and having undergone various degrees of metamorphism, i.e. various degrees of natural carbonization. EPR linewidth dispersion for the most primitive samples was quite significant, pointing to a selective dipolar broadening similar to that observed for carbonized bacteria. This surprising result merits further evaluation in the light of its potential use as a marker of past bacterial metabolisms, in particular oxygenic photosynthesis, in Archean cherts.

Effect of the lattice dynamics on the electronic structure of paramagnetic NiO within the disordered local moment picture

NASA Astrophysics Data System (ADS)

Mozafari, Elham; Alling, Björn; Belov, Maxim P.; Abrikosov, Igor A.

2018-01-01

Using the disordered local moments approach in combination with the ab initio molecular dynamics method, we simulate the behavior of a paramagnetic phase of NiO at finite temperatures to investigate the effect of magnetic disorder, thermal expansion, and lattice vibrations on its electronic structure. In addition, we study its lattice dynamics. We verify the reliability of our theoretical scheme via comparison of our results with available experiment and earlier theoretical studies carried out within static approximations. We present the phonon dispersion relations for the paramagnetic rock-salt (B1) phase of NiO and demonstrate that it is dynamically stable. We observe that including the magnetic disorder to simulate the paramagnetic phase has a small yet visible effect on the band gap. The amplitude of the local magnetic moment of Ni ions from our calculations for both antiferromagnetic and paramagnetic phases agree well with other theoretical and experimental values. We demonstrate that the increase of temperature up to 1000 K does not affect the electronic structure strongly. Taking into account the lattice vibrations and thermal expansion at higher temperatures have a major impact on the electronic structure, reducing the band gap from ˜3.5 eV at 600 K to ˜2.5 eV at 2000 K. We conclude that static lattice approximations can be safely employed in simulations of the paramagnetic state of NiO up to relatively high temperatures (˜1000 K), but as we get closer to the melting temperature vibrational effects become quite large and therefore should be included in the calculations.

Electron paramagnetic resonance image reconstruction with total variation and curvelets regularization

NASA Astrophysics Data System (ADS)

Durand, Sylvain; Frapart, Yves-Michel; Kerebel, Maud

2017-11-01

Spatial electron paramagnetic resonance imaging (EPRI) is a recent method to localize and characterize free radicals in vivo or in vitro, leading to applications in material and biomedical sciences. To improve the quality of the reconstruction obtained by EPRI, a variational method is proposed to inverse the image formation model. It is based on a least-square data-fidelity term and the total variation and Besov seminorm for the regularization term. To fully comprehend the Besov seminorm, an implementation using the curvelet transform and the L 1 norm enforcing the sparsity is proposed. It allows our model to reconstruct both image where acquisition information are missing and image with details in textured areas, thus opening possibilities to reduce acquisition times. To implement the minimization problem using the algorithm developed by Chambolle and Pock, a thorough analysis of the direct model is undertaken and the latter is inverted while avoiding the use of filtered backprojection (FBP) and of non-uniform Fourier transform. Numerical experiments are carried out on simulated data, where the proposed model outperforms both visually and quantitatively the classical model using deconvolution and FBP. Improved reconstructions on real data, acquired on an irradiated distal phalanx, were successfully obtained.

Some recent multi-frequency electron paramagnetic resonance results on systems relevant for dosimetry and dating.

PubMed

Callens, F; Vanhaelewyn, G; Matthys, P

2002-04-01

Electron Paramagnetic Resonance (EPR) applications like e.g. EPR dosimetry and dating, are usually performed at X-band frequencies because of practical reasons (cost, sample size, etc.). However, it is increasingly recognized that the radiation-induced EPR signals are strongly composite, what might affect dose/age estimates. A few recent examples from both the dosimetry and dating field, illustrating the problems, will be presented. The involved spectra are mainly due to carbonate-derived radicals (CO2-, CO3(3-), etc.). Measurements at higher microwave frequencies are often recommended to improve the insight into the spectra and/or the practical signal quantification. Recent results at Q- and W-band frequencies will show that a multi-frequency approach indeed opens many interesting perspectives in this field but also that each frequency may have specific (dis)advantages depending on the EPR probe and application involved. The discussion will concern carbonate-containing apatite single crystals, shells, modern and fossil tooth enamel.

Electronic paramagnetic resonance (EPR) for the study of ascorbyl radical and lipid radicals in marine organisms.

PubMed

González, Paula Mariela; Aguiar, María Belén; Malanga, Gabriela; Puntarulo, Susana

2013-08-01

Electron paramagnetic resonance (EPR) spectroscopy detects the presence of radicals of biological interest, such as ascorbyl radical (A(•)) and lipid radicals. A(•) is easily detectable by EPR even in aqueous solution at room-temperature. Under oxidative conditions leading to changes in total ascorbate (AH(-)) content, the A(•)/AH(-) ratio could be used to estimate early oxidative stress in the hydrophilic milieu. This methodology was applied to a wide range of aquatic systems including algae, sea urchin, limpets, bivalves and fish, under physiological and oxidative stress conditions as well. The A(•)/AH(-) ratio reflected the state of one part of the oxidative defense system and provided an early and simple diagnosis of environmental stressing conditions. Oxidative damage to lipids was assessed by the EPR-sensitive adduct formation that correlates well with cell membrane damage with no interference from other biological compounds. Probe instability, tissue metabolism, and lack of spin specificity are drawback factors for employing EPR for in vivo determination of free radicals. However, the dependability of this technique, mostly by combining it with other biochemical strategies, enhances the value of these procedures as contributors to the knowledge of oxidative condition in aquatic organisms. Copyright © 2013 Elsevier Inc. All rights reserved.

Free radicals produced by the oxidation of gallic acid: An electron paramagnetic resonance study.

PubMed

Eslami, Angelique C; Pasanphan, Wanvimol; Wagner, Brett A; Buettner, Garry R

2010-08-05

Gallic acid (3,4,5-trihydroxybenzoic acid) is found in a wide variety of plants; it is extensively used in tanning, ink dyes, as well as in the manufacturing of paper. The gallate moiety is a key component of many functional phytochemicals. In this work electron paramagnetic spectroscopy (EPR) was used to detect the free radicals generated by the air-oxidation of gallic acid. We found that gallic acid produces two different radicals as a function of pH. In the pH range between 7-10, the spectrum of the gallate free radical is a doublet of triplets (aH = 1.00 G, aH = 0.23 G, aH = 0.28 G). This is consistent with three hydrogens providing hyperfine splitting. However, in a more alkaline environment, pH >10, the hyperfine splitting pattern transforms into a 1:2:1 pattern (aH (2) = 1.07 G). Using D2O as a solvent, we demonstrate that the third hydrogen (i.e. aH = 0.28 G) at lower pH is a slowly exchanging hydron, participating in hydrogen bonding with two oxygens in ortho position on the gallate ring. The pKa of this proton has been determined to be 10. This simple and novel approach permitted the understanding of the prototropic equilibrium of the semiquinone radicals generated by gallic acid, a ubiquitous compound, allowing new insights into its oxidation and subsequent reactions.

Electron Paramagnetic Resonance Imaging of the Spatial Distribution of Free Radicals in PMR-15 Polyimide Resins

NASA Technical Reports Server (NTRS)

Ahn, Myong K.; Eaton, Sandra S.; Eaton, Gareth R.; Meador, Mary Ann B.

1997-01-01

Prior studies have shown that free radicals generated by heating polyimides above 300 C are stable at room temperature and are involved in thermo-oxidative degradation in the presence of oxygen gas. Electron paramagnetic resonance imaging (EPRI) is a technique to determine the spatial distribution of free radicals. X-band (9.5 GHz) EPR images of PMR-15 polyimide were obtained with a spatial resolution of approximately 0.18 mm along a 2-mm dimension of the sample. In a polyimide sample that was not thermocycled, the radical distribution was uniform along the 2-mm dimension of the sample. For a polyimide sample that was exposed to thermocycling in air for 300 1-h cycles at 335 C, one-dimensional EPRI showed a higher concentration of free radicals in the surface layers than in the bulk sample. A spectral-spatial two-dimensional image showed that the EPR lineshape of the surface layer remained the same as that of the bulk. These EPRI results suggest that the thermo-oxidative degradation of PMR-15 resin involves free radicals present in the oxygen-rich surface layer.

Electron Paramagnetic Resonance Imaging of the Spatial Distribution of Free Radicals in PMR-15 Polyimide Resins

NASA Technical Reports Server (NTRS)

Ahn, Myong K.; Eaton, Sandra S.; Eaton, Gareth R.; Meador, Mary Ann B.

1997-01-01

Prior studies have shown that free radicals generated by heating polyimides above 300 C are stable at room temperature and are involved in thermo-oxidative degradation in the presence of oxygen gas. Electron Paramagnetic Resonance Imaging (EPRI) is a technique to determine the spatial distribution of free radicals. X-band (9.5 GHz) EPR images of PMR-15 polyimide were obtained with a spatial resolution of about 0.18 mm along a 2 mm dimension of the sample. In a polyimide sample that was not thermocycled, the radical distribution was uniform along the 2 mm dimension of the sample. For a polyimide sample that was exposed to thermocycling in air for 300 one-hour cycles at 335 C, one-dimensional EPRI showed a higher concentration of free radicals in the surface layers than in the bulk sample. A spectral-spatial two-dimensional image showed that the EPR lineshape of the surface layer remained the same as that of the bulk. These EPRI results suggest that the thermo-oxidative degradation of PMR-15 resin involves free radicals present in the oxygen-rich surface layer.

Evaluation of sub-microsecond recovery resonators for In Vivo Electron Paramagnetic Resonance Imaging

PubMed Central

F, Hyodo; S, Subramanian; N, Devasahayam; R, Murugesan; K, Matsumoto; JB, Mitchell; MC, Krishna

2008-01-01

Time-domain (TD) electron paramagnetic resonance (EPR) imaging at 300 MHz for in vivo applications requires resonators with recovery times less than 1 microsecond after pulsed excitation to reliably capture the rapidly decaying free induction decay (FID). In this study, we tested the suitability of the Litz foil coil resonator (LCR), commonly used in MRI, for in vivo EPR/EPRI applications in the TD mode and compared with parallel coil resonator (PCR). In TD mode, the sensitivity of LCR was lower than that of the PCR. However, in continuous wave (CW) mode, the LCR showed better sensitivity. The RF homogeneity was similar in both the resonators. The axis of the RF magnetic field is transverse to the cylindrical axis of the LCR, making the resonator and the magnet co-axial. Therefore, the loading of animals, and placing of the anesthesia nose cone and temperature monitors was more convenient in the LCR compared to the PCR whose axis is perpendicular to the magnet axis. PMID:18042414

Axially uniform resonant cavity modes for potential use in electron paramagnetic resonance spectroscopy

NASA Astrophysics Data System (ADS)

Mett, Richard R.; Froncisz, Wojciech; Hyde, James S.

2001-11-01

This article is concerned with cylindrical transverse electric TE011 and rectangular TE102 microwave cavity resonators commonly used in electron paramagnetic resonance (EPR) spectroscopy. In the cylindrical mode geometry considered here, the sample is along the z axis of the cylinder, dielectric disks of 1/4 wavelength thickness are placed at each end wall, and the diameter of the cylinder is set at the cutoff condition for propagation of microwave energy in a cylindrical waveguide at the desired microwave frequency. The microwave magnetic field is exactly uniform along the sample in the region between the dielectric disks and the resonant frequency is independent of the length of the cylinder without limit. The rectangular TE102 geometry is analogous, but here the microwave magnetic field is exactly uniform in a plane. A uniform microwave field along a line sample is highly advantageous in EPR spectroscopy compared with the usual sinusoidal variation, and these geometries are called "uniform field" modes. Extensive theoretical analysis as well as finite element calculation of field patterns are presented. The perturbation of field patterns caused by sample insertion as functions of the overall length of the resonator and diameter of the sample is analyzed. The article is intended to provide a basis for design of practical structures in the range of 10 to 100 GHz.

New method to measure the carbamoylating activity of nitrosoureas by electron paramagnetic resonance spectroscopy.

PubMed

Gadzheva, V; Ichimori, K; Raikov, Z; Nakazawa, H

1997-08-01

A new method for measuring the carbamoylating activity of nitrosoureas and isocyanates using electron paramagnetic resonance (EPR) spectroscopy is described. The extent and time course of carbamoylation reaction of chloroethyl isocyanate and a series of 9 nitrosoureas toward amino group of 4-amino-2,2,6,6-tetramethyl-piperidine-1-oxyl were examined with both the EPR method and the HPLC method which has been proposed by Brubaker et al. [Biochem. Pharmacol. 35:2359 (1986)]. Spin-labeled nitrosoureas we synthesized are included in this study since they have less toxicity or more efficiency than commercially available drug in some cases. The concentration of carbamoylated product was easily determined with the EPR spectra. There is a very high correlation (r = 0.982, t = 2.58, N = 10, p < 0.001) between the EPR and HPLC methods. Spin-labeled nitrosoureas showed lower carbamoylating activity than non-labeled analogues. The carbamoylating activity for these nitrosourea depended on the reactivity of isocyanate intermediate and almost independent of their half life. This rapid and simple EPR method is suitable for the detailed investigation of the rate and extent of carbamoylation reaction.

Oxygen-related 1-platinum defects in silicon: An electron paramagnetic resonance study

NASA Astrophysics Data System (ADS)

Juda, U.; Scheerer, O.; Höhne, M.; Riemann, H.; Schilling, H.-J.; Donecker, J.; Gerhardt, A.

1996-09-01

A monoclinic 1-platinum defect recently detected was investigated more thoroughly by electron paramagnetic resonance (EPR). The defect is one of the dominating defects in platinum doped silicon. With a perfect reproducibility it is observed in samples prepared from n-type silicon as well as from p-type silicon, in float zone (FZ) silicon as well as in Czochralski (Cz) silicon. Its concentration varies with the conditions of preparation and nearly reaches that of isolated substitutional platinum in Cz silicon annealed for 2 h at 540 °C after quenching from the temperature of platinum diffusion. Because of its concentration which in Cz-Si exceeds that in FZ-Si the defect is assumed to be oxygen-related though a hyperfine structure with 17O could not be resolved. The defect causes a level close to the valence band. This is concluded from variations of the Fermi level and from a discussion of the spin Hamiltonian parameters. In photo-EPR experiments the defect is coupled to recently detected acceptorlike self-interstitial related defects (SIRDs); their level position turns out to be near-midgap. These defects belong to the lifetime limiting defects in Pt-doped Si.

Integration of digital signal processing technologies with pulsed electron paramagnetic resonance imaging

PubMed Central

Pursley, Randall H.; Salem, Ghadi; Devasahayam, Nallathamby; Subramanian, Sankaran; Koscielniak, Janusz; Krishna, Murali C.; Pohida, Thomas J.

2006-01-01

The integration of modern data acquisition and digital signal processing (DSP) technologies with Fourier transform electron paramagnetic resonance (FT-EPR) imaging at radiofrequencies (RF) is described. The FT-EPR system operates at a Larmor frequency (Lf) of 300 MHz to facilitate in vivo studies. This relatively low frequency Lf, in conjunction with our ~10 MHz signal bandwidth, enables the use of direct free induction decay time-locked subsampling (TLSS). This particular technique provides advantages by eliminating the traditional analog intermediate frequency downconversion stage along with the corresponding noise sources. TLSS also results in manageable sample rates that facilitate the design of DSP-based data acquisition and image processing platforms. More specifically, we utilize a high-speed field programmable gate array (FPGA) and a DSP processor to perform advanced real-time signal and image processing. The migration to a DSP-based configuration offers the benefits of improved EPR system performance, as well as increased adaptability to various EPR system configurations (i.e., software configurable systems instead of hardware reconfigurations). The required modifications to the FT-EPR system design are described, with focus on the addition of DSP technologies including the application-specific hardware, software, and firmware developed for the FPGA and DSP processor. The first results of using real-time DSP technologies in conjunction with direct detection bandpass sampling to implement EPR imaging at RF frequencies are presented. PMID:16243552

Training effects on ROS production determined by electron paramagnetic resonance in master swimmers.

PubMed

Mrakic-Sposta, Simona; Gussoni, Maristella; Porcelli, Simone; Pugliese, Lorenzo; Pavei, Gaspare; Bellistri, Giuseppe; Montorsi, Michela; Tacchini, Philippe; Vezzoli, Alessandra

2015-01-01

Acute exercise induces an increase in Reactive Oxygen Species (ROS) production dependent on exercise intensity with highest ROS amount generated by strenuous exercise. However, chronic repetition of exercise, that is, exercise training, may reduce exercise-induced oxidative stress. Aim of this study was to evaluate the effects of 6-weeks high-intensity discontinuous training (HIDT), characterized by repeated variations of intensity and changes of redox potential, on ROS production and antioxidant capacity in sixteen master swimmers. Time course changes of ROS generation were assessed by Electron Paramagnetic Resonance in capillary blood by a microinvasive approach. An incremental arm-ergometer exercise (IE) until exhaustion was carried out at both before (PRE) and after (POST) training (Trg) period. A significant (P < 0.01) increase of ROS production from REST to the END of IE in PRE Trg (2.82 ± 0.66 versus 3.28 ± 0.66 µmol·min(-1)) was observed. HIDT increased peak oxygen consumption (36.1 ± 4.3 versus 40.6 ± 5.7 mL·kg(-1)·min(-1) PRE and POST Trg, resp.) and the antioxidant capacity (+13%) while it significantly decreased the ROS production both at REST (-20%) and after IE (-25%). The observed link between ROS production, adaptive antioxidant defense mechanisms, and peak oxygen consumption provides new insight into the correlation between ROS response pathways and muscle metabolic function.

Electron paramagnetic resonance field-modulation eddy-current analysis of silver-plated graphite resonators

NASA Astrophysics Data System (ADS)

Mett, Richard R.; Anderson, James R.; Sidabras, Jason W.; Hyde, James S.

2005-09-01

Magnetic field modulation is often introduced into a cylindrical TE011 electron paramagnetic resonance (EPR) cavity through silver plating over a nonconductive substrate. The plating thickness must be many times the skin depth of the rf and smaller than the skin depth of the modulation. We derive a parameter that quantifies the modulation field penetration and find that it also depends on resonator dimensions. Design criteria based on this parameter are presented graphically. This parameter is then used to predict the behavior of eddy currents in substrates of moderate conductivity, such as graphite. The conductivity of the graphite permits improved plating uniformity and permits use of electric discharge machining (EDM) techniques to make the resonator. EDM offers precision tolerances of 0.005 mm and is suitable for small, complicated shapes that are difficult to machine by other methods. Analytic predictions of the modulation penetration are compared with the results of finite-element simulations. Simulated magnetic field modulation uniformity and penetration are shown for several elemental coils and structures including the plated graphite TE011 cavity. Fabrication and experimental testing of the structure are discussed. Spatial inhomogeneity of the modulation phase is also investigated by computer simulation. We find that the modulation phase is uniform to within 1% over the TE011 cavity. Structures of lower symmetry have increased phase nonuniformity.

Antioxidant and radical-scavenging activities of Slovak honeys - An electron paramagnetic resonance study.

PubMed

Zalibera, Michal; Staško, Andrej; Šlebodová, Anna; Jančovičová, Viera; Čermáková, Tatiana; Brezová, Vlasta

2008-09-15

The antioxidant properties of 15 honey samples from different floral sources and various Slovak regions were investigated by means of electron paramagnetic resonance spectroscopy. Cation radical of ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) diammonium salt), DPPH (1,1-diphenyl-2-picrylhydrazyl) and hydroxyl radicals generated by the photochemical decomposition of hydrogen peroxide were used as oxidants. The antioxidant activities found with ABTS(+), expressed as trolox equivalent antioxidant capacity (TEAC), ranged from 0.15 to 1.14mmolkg(-1), and those determined with DPPH, from 0.04 to 0.32mmolkg(-1). TEAC values correlated well with results found by elimination of DPPH, and both values revealed a linear relationship with the concentration of phenolics obtained with the Folin-Ciocalteu phenol test (expressed as gallic acid equivalents, GAE). The colour coordinates (CIE L(∗)a(∗)b(∗)), as well as reflectance spectra determined for original honeys using a white background, demonstrated that the colour difference (ΔE(∗)) and coordinate b(∗) interrelate with TEAC values. The radical-scavenging capacities (RSC) of the honey samples determined in the experiments with photochemically decomposed hydrogen peroxide, generating reactive OH radicals in the presence of spin trapping agent, differ from those found with ABTS(+) and DPPH. Here, probably, the reactive OH radicals, having higher redox potential, are scavenged by a variety of compounds not effective with ABTS(+) and DPPH (e.g., saccharides, proteins). Copyright © 2008 Elsevier Ltd. All rights reserved.

Structural investigation and electron paramagnetic resonance of vanadyl doped alkali niobium borate glasses.

PubMed

Agarwal, A; Sheoran, A; Sanghi, S; Bhatnagar, V; Gupta, S K; Arora, M

2010-03-01

Glasses with compositions xNb(2)O(5).(30-x)M(2)O.69B(2)O(3) (where M=Li, Na, K; x=0, 4, 8 mol%) doped with 1 mol% V(2)O(5) have been prepared using normal melt quench technique. The IR transmission spectra of the glasses have been studied over the range 400-4000 cm(-1). The changes caused by the addition of Nb(2)O(5) on the structure of these glasses have been reported. The electron paramagnetic resonance spectra of VO(2+) ions in these glasses have been recorded in X-band (9.14 GHz) at room temperature (300 K). The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that the resultant resonance spectra contain hyperfine structures (hfs) due to V(4+) ions which exist as VO(2+) ions in octahedral coordination with a tetragonal compression in the present glasses. The tetragonality of V(4+)O(6) complex decreases with increasing concentration of Nb(2)O(5). The 3d(xy) orbit contracts with increase in Nb(2)O(5):M(2)O ratio. Values of the theoretical optical basicity, Lambda(th), have also been reported. Copyright 2009 Elsevier B.V. All rights reserved.

A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces

PubMed Central

Sidabras, Jason W.; Varanasi, Shiv K.; Mett, Richard R.; Swarts, Steven G.; Swartz, Harold M.; Hyde, James S.

2014-01-01

A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg2+ doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown. PMID:25362434

A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces.

PubMed

Sidabras, Jason W; Varanasi, Shiv K; Mett, Richard R; Swarts, Steven G; Swartz, Harold M; Hyde, James S

2014-10-01

A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg(2+) doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown.

Complex-formation between reduced xanthine oxidase and purine substrates demonstrated by electron paramagnetic resonance

PubMed Central

Pick, Frances M.; Bray, R. C.

1969-01-01

The origin of the Rapid molybdenum electron-paramagnetic-resonance signals, which are obtained on reducing xanthine oxidase with purine or with xanthine, and whose parameters were measured by Bray & Vänngård (1969), was studied. It is concluded that these signals represent complexes of reduced enzyme with substrate molecules. Xanthine forms one complex at high concentrations and a different one at low concentrations. Purine forms a complex indistinguishable from the low-concentration xanthine complex. There are indications that some other substrates also form complexes, but uric acid, a reaction product, does not appear to do so. The possible significance of the complexes in the catalytic cycle of the enzyme is discussed and it is suggested that they represent substrate molecules bound at the reduced active site, waiting their turn to react there, when the enzyme has been reoxidized. Support for this role for the complexes was deduced from experiments in which frozen samples of enzyme–xanthine mixtures, prepared by the rapid-freezing method, were warmed until the signals began to change. Under these conditions an increase in amplitude of the Very Rapid signal took place. Data bearing on the origin of the Slow molybdenum signal are also discussed. This signal disappears only slowly in the presence of oxygen, and its appearance rate is unaffected by change in the concentration of dithionite. It is concluded that, like other signals from the enzyme, it is due to Mov but that a slow change of ligand takes place before it is seen. The Slow species, like the Rapid, seems capable of forming complexes with purines. PMID:4310056

Tooth Retrospective Dosimetry Using Electron Paramagnetic Resonance: Influence of Irradiated Dental Composites

PubMed Central

Desmet, Céline M.; Djurkin, Andrej; Dos Santos-Goncalvez, Ana Maria; Dong, Ruhong; Kmiec, Maciej M.; Kobayashi, Kyo; Rychert, Kevin; Beun, Sébastien; Leprince, Julian G.; Leloup, Gaëtane; Levêque, Philippe; Gallez, Bernard

2015-01-01

In the aftermath of a major radiological accident, the medical management of overexposed individuals will rely on the determination of the dose of ionizing radiations absorbed by the victims. Because people in the general population do not possess conventional dosimeters, after the fact dose reconstruction methods are needed. Free radicals are induced by radiations in the tooth enamel of victims, in direct proportion to dose, and can be quantified using Electron Paramagnetic Resonance (EPR) spectrometry, a technique that was demonstrated to be very appropriate for mass triage. The presence of dimethacrylate based restorations on teeth can interfere with the dosimetric signal from the enamel, as free radicals could also be induced in the various composites used. The aim of the present study was to screen irradiated composites for a possible radiation-induced EPR signal, to characterize it, and evaluate a possible interference with the dosimetric signal of the enamel. We investigated the most common commercial composites, and experimental compositions, for a possible class effect. The effect of the dose was studied between 10 Gy and 100 Gy using high sensitivity X-band spectrometer. The influence of this radiation-induced signal from the composite on the dosimetric signal of the enamel was also investigated using a clinical L-Band EPR spectrometer, specifically developed in the EPR center at Dartmouth College. In X-band, a radiation-induced signal was observed for high doses (25-100 Gy); it was rapidly decaying, and not detected after only 24h post irradiation. At 10 Gy, the signal was in most cases not measurable in the commercial composites tested, with the exception of 3 composites showing a significant intensity. In L-band study, only one irradiated commercial composite influenced significantly the dosimetric signal of the tooth, with an overestimation about 30%. In conclusion, the presence of the radiation-induced signal from dental composites should not

Electron paramagnetic resonance method for the quantitative assay of ketoconazole in pharmaceutical preparations.

PubMed

Morsy, Mohamed A; Sultan, Salah M; Dafalla, Hatim

2009-08-15

In this study, electron paramagnetic resonance (EPR) is used, for the first time, as an analytical tool for the quantitative assay of ketoconazole (KTZ) in drug formulations. The drug was successfully characterized by the prominent signals by two radical species produced as a result of its oxidation with 400 microg/mL cerium(IV) in 0.10 mol dm(-3) sulfuric acid. The EPR signal of the reaction mixture was measured in eight capillary tubes housed in a 4 mm EPR sample tube. The radical stability was investigated by obtaining multi-EPR scans of each KTZ sample solution at time intervals of 2.5 min of the reaction mixing time. The plot of the disappearance of the radical species show that the disappearance is apparently of zero order. The zero-time intercept of the EPR signal amplitude, which should be proportional to the initial radical concentration, is linear in the sample concentration in the range between 100 and 400 microg/mL, with a correlation coefficient, r, of 0.999. The detection limit was determined to be 11.7 +/- 2.5 microg/mL. The method newly adopted was fully validated following the United States Pharmacopeia (USP) monograph protocol in both the generic and the proprietary forms. The method is very accurate, such that we were able to measure the concentration at confidence levels of 99.9%. The method was also found to be suitable for the assay of KTZ in its tablet and cream pharmaceutical preparations, as no interferences were encountered from excipients of the proprietary drugs. High specificity, simplicity, and rapidity are the merits of the present method compared to the previously reported methods.

Nitric oxide improves membrane fluidity of erythrocytes in essential hypertension: An electron paramagnetic resonance investigation.

PubMed

Tsuda, K; Kimura, K; Nishio, I; Masuyama, Y

2000-09-07

It has been shown that rheological abnormality might be an etiological factor in hypertension. Recent studies have revealed that human erythrocytes possess a nitric oxide (NO) synthase and that this activation might be involved in the regulation of rheological properties of erythrocytes. The present study was undertaken to investigate the role of NO in the regulation of membrane functions of erythrocytes in patients with essential hypertension by means of an electron paramagnetic resonance (EPR) and spin-labeling method. The NO donor S-nitroso-N-acetylpenicillamine (SNAP) decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (h(0)/h(-1)) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner. The finding indicated that the NO donor increased the membrane fluidity of erythrocytes. In addition, the effect of SNAP was significantly potentiated by 8-bromo-cyclic guanosine monophosphate. By contrast, the change of the fluidity induced by SNAP was reversed in the presence of L-N(G)-nitroarginine methyl ester and asymmetric dimethyl L-arginine. In patients with essential hypertension, the membrane fluidity of erythrocytes was significantly lower than in the normotensive subjects. The effect of SNAP was more pronounced in essential hypertension than in normotensive subjects. These results showed that NO increased the membrane fluidity and decreased the rigidity of cell membranes. Furthermore, the greater effect of NO on the fluidity in essential hypertension suggests that NO might actively participate in the regulation of rheological behavior of erythrocytes and have a crucial role in the improvement of microcirculation in hypertension. Copyright 2000 Academic Press.

Electron paramagnetic resonance study of lipid and protein membrane components of erythrocytes oxidized with hydrogen peroxide

PubMed Central

Mendanha, S.A.; Anjos, J.L.V.; Silva, A.H.M.; Alonso, A.

2012-01-01

Electron paramagnetic resonance (EPR) spectroscopy of spin labels was used to monitor membrane dynamic changes in erythrocytes subjected to oxidative stress with hydrogen peroxide (H2O2). The lipid spin label, 5-doxyl stearic acid, responded to dramatic reductions in membrane fluidity, which was correlated with increases in the protein content of the membrane. Membrane rigidity, associated with the binding of hemoglobin (Hb) to the erythrocyte membrane, was also indicated by a spin-labeled maleimide, 5-MSL, covalently bound to the sulfhydryl groups of membrane proteins. At 2% hematocrit, these alterations in membrane occurred at very low concentrations of H2O2 (50 µM) after only 5 min of incubation at 37°C in azide phosphate buffer, pH 7.4. Lipid peroxidation, suggested by oxidative hemolysis and malondialdehyde formation, started at 300 µM H2O2 (for incubation of 3 h), which is a concentration about six times higher than those detected with the probes. Ascorbic acid and α-tocopherol protected the membrane against lipoperoxidation, but did not prevent the binding of proteins to the erythrocyte membrane. Moreover, the antioxidant (+)-catechin, which also failed to prevent the cross-linking of cytoskeletal proteins with Hb, was very effective in protecting erythrocyte ghosts from lipid peroxidation induced by the Fenton reaction. This study also showed that EPR spectroscopy can be useful to assess the molecular dynamics of red blood cell membranes in both the lipid and protein domains and examine oxidation processes in a system that is so vulnerable to oxidation. PMID:22473321

Study of nanostructural organization of ionic liquids by electron paramagnetic resonance spectroscopy.

PubMed

Merunka, Dalibor; Peric, Mirna; Peric, Miroslav

2015-02-19

The X-band electron paramagnetic resonance spectroscopy (EPR) of a stable, spherical nitroxide spin probe, perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (pDTO) has been used to study the nanostructural organization of a series of 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids (ILs) with alkyl chain lengths from two to eight carbons. By employing nonlinear least-squares fitting of the EPR spectra, we have obtained values of the rotational correlation time and hyperfine coupling splitting of pDTO to high precision. The rotational correlation time of pDTO in ILs and squalane, a viscous alkane, can be fit very well to a power law functionality with a singular temperature, which often describes a number of physical quantities measured in supercooled liquids. The viscosity of the ILs and squalane, taken from the literature, can also be fit to the same power law expression, which means that the rotational correlation times and the ionic liquid viscosities have similar functional dependence on temperature. The apparent activation energy of both the rotational correlation time of pDTO and the viscous flow of ILs and squalane increases with decreasing temperature; in other words, they exhibit strong non-Arrhenius behavior. The rotational correlation time of pDTO as a function of η/T, where η is the shear viscosity and T is the temperature, is well described by the Stokes-Einstein-Debye (SED) law, while the hydrodynamic probe radii are solvent dependent and are smaller than the geometric radius of the probe. The temperature dependence of hyperfine coupling splitting is the same in all four ionic liquids. The value of the hyperfine coupling splitting starts decreasing with increasing alkyl chain length in the ionic liquids in which the number of carbons in the alkyl chain is greater than four. This decrease together with the decrease in the hydrodynamic radius of the probe indicates a possible existence of nonpolar nanodomains.

Electron Paramagnetic Resonance Measurements of Reactive Oxygen Species by Cyclic Hydroxylamine Spin Probes.

PubMed

Dikalov, Sergey I; Polienko, Yuliya F; Kirilyuk, Igor

2018-05-20

Oxidative stress contributes to numerous pathophysiological conditions such as development of cancer, neurodegenerative, and cardiovascular diseases. A variety of measurements of oxidative stress markers in biological systems have been developed; however, many of these methods are not specific, can produce artifacts, and do not directly detect the free radicals and reactive oxygen species (ROS) that cause oxidative stress. Electron paramagnetic resonance (EPR) is a unique tool that allows direct measurements of free radical species. Cyclic hydroxylamines are useful and convenient molecular probes that readily react with ROS to produce stable nitroxide radicals, which can be quantitatively measured by EPR. In this work, we critically review recent applications of various cyclic hydroxylamine spin probes in biology to study oxidative stress, their advantages, and the shortcomings. Recent Advances: In the past decade, a number of new cyclic hydroxylamine spin probes have been developed and their successful application for ROS measurement using EPR has been published. These new state-of-the-art methods provide improved selectivity and sensitivity for in vitro and in vivo studies. Although cyclic hydroxylamine spin probes EPR application has been previously described, there has been lack of translation of these new methods into biomedical research, limiting their widespread use. This work summarizes "best practice" in applications of cyclic hydroxylamine spin probes to assist with EPR studies of oxidative stress. Additional studies to advance hydroxylamine spin probes from the "basic science" to biomedical applications are needed and could lead to better understanding of pathological conditions associated with oxidative stress. Antioxid. Redox Signal. 28, 1433-1443.

A mass spectrometry and electron paramagnetic resonance study of photochemical and thermal aging of triterpenoid varnishes.

PubMed

Dietemann, P; Kälin, M; Zumbühl, S; Knochenmuss, R; Wülfert, S; Zenobi, R

2001-05-01

Photochemical and thermal aging of triterpenoid dammar and mastic resins used as varnishes on paintings were studied using graphite-assisted laser desorption/ionization mass spectrometry. This extends an earlier study on similar materials (Zumbühl et al., Anal. Chem. 1998, 70, 707-715) that focused on photoaging. Progressive aging results in development of groups of signals spaced by 14 and 16 Da, indicating incorporation of oxygen as well as simultaneous loss of hydrogen. Oligomers up to tetramers are formed, while cleavage reactions lead to increased signal intensities in the mass ranges between the oligomers and below the monomers. No major differences were found between the mass spectra of samples aged in light or darkness, except that deterioration was faster in light. Electron paramagnetic resonance spectroscopy revealed similar and significant amounts of radicals in films of dammar stored either in light or in darkness. It is concluded that oxidative radical reactions also take place in darkness and that differences in light and dark aging pathways are minor, although rates may differ. These findings lead to a unified explanation for yellowing of natural resin varnishes, one of the major degenerative changes in the appearance of paintings. It is also shown that the commercially available, nominally fresh resins are already in an advanced stage of oxidation and degradation. Energy-rich substances are formed upon irradiation with sunlight and are believed to restart the autoxidative chain reactions, regardless of storage conditions. As a result, varnishes are oxidized quite quickly (months) even when kept in darkness.

Optimal dielectric and cavity configurations for improving the efficiency of electron paramagnetic resonance probes

NASA Astrophysics Data System (ADS)

Elnaggar, Sameh Y.; Tervo, Richard; Mattar, Saba M.

2014-08-01

An electron paramagnetic resonance (EPR) spectrometer’s lambda efficiency parameter (Λ) is one of the most important parameters that govern its sensitivity. It is studied for an EPR probe consisting of a dielectric resonator (DR) in a cavity (CV). Expressions for Λ are derived in terms of the probe’s individual DR and CV components, Λ1 and Λ2 respectively. Two important cases are considered. In the first, a probe consisting of a CV is improved by incorporating a DR. The sensitivity enhancement depends on the relative rather than the absolute values of the individual components. This renders the analysis general. The optimal configuration occurs when the CV and DR modes are nearly degenerate. This configuration guarantees that the probe can be easily coupled to the microwave bridge while maintaining a large Λ. It is shown that for a lossy CV with a small quality factor Q2, one chooses a DR that has the highest filling factor, η1, regardless of its Λ1 and Q1. On the other hand, if the CV has a large Q2, the optimum DR is the one which has the highest Λ1. This is regardless of its η1 and relative dielectric constant, ɛr. When the quality factors of both the CV and DR are comparable, the lambda efficiency is reduced by a factor of √{2}. Thus the signal intensity for an unsaturated sample is cut in half. The second case is the design of an optimum shield to house a DR. Besides preventing radiation leakage, it is shown that for a high loss DR, the shield can actually boost Λ above the DR value. This can also be very helpful for relatively low efficiency dielectrics as well as lossy samples, such as polar liquids.

A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces

SciTech Connect

Sidabras, Jason W.; Varanasi, Shiv K.; Hyde, James S.

2014-10-15

A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is eithermore » surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg{sup 2+} doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown.« less

Characterization of iron, manganese, and copper synthetic hydroxyapatites by electron paramagnetic resonance spectroscopy

NASA Technical Reports Server (NTRS)

Sutter, B.; Wasowicz, T.; Howard, T.; Hossner, L. R.; Ming, D. W.

2002-01-01

The incorporation of micronutrients (e.g., Fe, Mn, Cu) into synthetic hydroxyapatite (SHA) is proposed for slow release of these nutrients to crops in NASA's Advanced Life Support (ALS) program for long-duration space missions. Separate Fe3+ (Fe-SHA), Mn2+ (Mn-SHA), and Cu2+ (Cu-SHA) containing SHA materials were synthesized by a precipitation method. Electron paramagnetic resonance (EPR) spectroscopy was used to determine the location of Fe3+, Mn2+, and Cu2+ ions in the SHA structure and to identify other Fe(3+)-, Mn(2+)-, and Cu(2+)-containing phases that formed during precipitation. The EPR parameters for Fe3+ (g=4.20 and 8.93) and for Mn2+ (g=2.01, A=9.4 mT, D=39.0 mT and E=10.5 mT) indicated that Fe3+ and Mn2+ possessed rhombic ion crystal fields within the SHA structure. The Cu2+ EPR parameters (g(z)=2.488, A(z)=5.2 mT) indicated that Cu2+ was coordinated to more than six oxygens. The rhombic environments of Fe3+ and Mn2+ along with the unique Cu2+ environment suggested that these metals substituted for the 7 or 9 coordinate Ca2+ in SHA. The EPR analyses also detected poorly crystalline metal oxyhydroxides or metal-phosphates associated with SHA. The Fe-, Mn-, and Cu-SHA materials are potential slow release sources of Fe, Mn, and Cu for ALS and terrestrial cropping systems.

Electron paramagnetic resonance and density-functional theory studies of Cu(II)-bis(oxamato) complexes.

PubMed

Bräuer, Björn; Weigend, Florian; Fittipaldi, Maria; Gatteschi, Dante; Reijerse, Edward J; Guerri, Annalisa; Ciattini, Samuele; Salvan, Georgeta; Rüffer, Tobias

2008-08-04

In this work we present the investigation of the influence of electronic and structural variations induced by varying the N,N'-bridge on the magnetic properties of Cu(II)- bis(oxamato) complexes. For this study the complexes [Cu(opba)] (2-) ( 1, opba = o-phenylene- bis(oxamato)), [Cu(nabo)] (2-) ( 2, nabo = 2,3-naphthalene- bis(oxamato)), [Cu(acbo)] (2-) ( 3, acbo = 2,3-anthrachinone- bis(oxamato)), [Cu(pba)] (2-) ( 4, pba = propylene- bis(oxamato)), [Cu(obbo)] (2-) ( 5, obbo = o-benzyl- bis(oxamato)), and [Cu(npbo)] (2-) ( 6, npbo = 1,8-naphthalene- bis(oxamato)), and the respective structurally isomorphic Ni(II) complexes ( 8- 13) have been prepared as ( (n)Bu 4N) (+) salts. The new complex ( (n)Bu 4N) 2[Cu(R-bnbo)].2H 2O ( 7, R-bnbo = (R)-1,1'-binaphthalene-2,2'- bis(oxamato)) was synthesized and is the first chiral complex in the series of Cu(II)-bis(oxamato) complexes. The molecular structure of 7 has been determined by single crystal X-ray analysis. The Cu(II) ions of the complexes 1- 7 are eta (4)(kappa (2) N, kappa (2) O) coordinated with a more or less distorted square planar geometry for 1- 6 and a distorted tetrahedral geometry for 7. Using pulsed Electron Nuclear Double Resonance on complex 6, detailed information about the relative orientation of the hyperfine ( A) and nuclear quadrupole tensors ( Q) of the coordinating nitrogens with respect to the g tensor were obtained. Electron Paramagnetic Resonance studies in the X, Q, and W-band at variable temperatures were carried out to extract g and A values of N ligands and Cu ion for 1- 7. The hyperfine values were interpreted in terms of spin population on the corresponding atoms. The obtained trends of the spin population for the monomeric building blocks were shown to correlate to the trends obtained in the dependence of the exchange interaction of the corresponding trinuclear complexes on their geometry.

Study of the oxidized and non- oxidized bitumen modified with additive «Adgezolin» by using electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Mukhamatdinov, I.; Gafurov, M.; Kemalov, A.; Rodionov, A.; Mamin, G.; Fakhretdinov, P.

2018-05-01

Cationic surfactant (adhesion additive) «Adgezolin» has been developed. It is shown that introduction of «Adgezolin» into the oxidized bitumen increases the relative amount of asphaltenes and monocyclearomatic hydrocarbons. By means of electron paramagnetic resonance (EPR) it is demonstrated that the introduction of additive «Adgezolin» increases the number of paramagnetic «free» carbon radicals (FR) in the oxidized bitumen and decreases that in the unoxidized species. In both types of bitumen shift from the Lorentzian to Gaussian EPR lineshape of FR is obtained that could be connected with as an increase of the samples homogeneity. It is supposed that while in the oxygenated bitumens introduction of additives leads to the disaggregation of asphaltene-resins compounds, in the unoxidized samples the balance is shifted towards formation of di-radicals.

Structure and dynamics in B12 enzyme catalysis revealed by electron paramagnetic resonance spectroscopy

NASA Astrophysics Data System (ADS)

Warncke, Kurt

2009-03-01

Challenges to the understanding of how protein structure and dynamics contribute to catalysis in enzymes, and the use of time-resolved electron paramagnetic resonance (EPR) spectroscopic techniques to address the challenges, are examined in the context of the coenzyme B12-dependent enzyme, ethanolamine ammonia-lyase (EAL), from Salmonella typhimurium. EAL conducts the homolytic cleavage of the coenzyme cobalt-carbon bond, intraprotein radical migration (5-6 å), and hydrogen atom transfers, which enable the core radical-mediated rearrangement reaction. Thermodynamic and activation parameters are measured in two experimental systems, which were developed to isolate sub-sequences from the multi-step catalytic cycle, as follows: (1) A dimethylsulfoxide (DMSO)/water cryosolvent system is used to prepare the kinetically-arrested enzyme/coenzyme/substrate ternary complex in fluid solution at 230 K.[1] Temperature-step initiated cobalt-carbon bond cleavage and radical pair separation to form the Co(II)-substrate radical pair are monitored by using time-resolved, full-spectrum EPR spectroscopy (234<=T<=250 K).[1] (2) The Co(II)-substrate radical pair is cryotrapped in frozen aqueous solution at T<150 K, and then promoted to react by a temperature step. The reaction of the substrate radical along the native pathway to form the diamagnetic bound products is monitored by using time-resolved, full-spectrum EPR spectroscopy (187<=T<=217 K).[2] High temporal resolution is achieved, because the reactions are dramatically slowed at the low temperatures, relative to the initiation and spectrum acquistion times. The results are combined with high resolution structures of the reactant centers, obtained by pulsed-EPR spectroscopies,[3] and the protein, obtained by structural proteomics[4] and EPR and electron spin echo envelope modulation (ESEEM) in combination with site directed mutagenesis,[5] to approach a molecular level description of protein contributions to catalysis in EAL. [4

Unravelling electronic and structural requisites of triplet-triplet energy transfer by advanced electron paramagnetic resonance and density functional theory

NASA Astrophysics Data System (ADS)

Di Valentin, M.; Salvadori, E.; Barone, V.; Carbonera, D.

2013-10-01

Advanced electron paramagnetic resonance (EPR) techniques, in combination with Density Functional theory (DFT), have been applied to the comparative study of carotenoid triplet states in two major photosynthetic antenna complexes, the Peridinin-chlorophyll a-protein of dinoflagellates and the light-harvesting complex II of higher plants. Carotenoid triplet states are populated by triplet-triplet energy transfer (TTET) from chlorophyll molecules to photoprotect the system from singlet oxygen formation under light-stress conditions. The TTET process is strongly dependent on the relative arrangement and on the electronic properties of the triplet states involved. The proposed spectroscopic approach exploits the concept of spin conservation during TTET, which leads to recognisable spin polarisation effects in the time-resolved and field-swept echo-detected EPR spectra. The electron spin polarisation produced at the carotenoid acceptor site depends on the initial polarisation of the chlorophyll donor and on the relative geometrical arrangement of the donor-acceptor zero-field splitting axes. We have demonstrated that a proper analysis of the spectra in the framework of spin angular momentum conservation allows to derive the pathways of TTET and to gain insight into the structural requirements of this mechanism for those antenna complexes, whose X-ray structure is available. We have further proved that this method, developed for natural antenna complexes of known X-ray structure, can be extended to systems lacking structural information in order to derive the relative arrangement of the partners in the energy transfer process. The structural requirements for efficient TTET, obtained from time-resolved and pulse EPR, have been complemented by a detailed description of the electronic structure of the carotenoid triplet state, provided by pulse Electron-Nuclear DOuble Resonance (ENDOR) experiments. Triplet-state hyperfine couplings of the α- and β-protons of the

Measurement of free radicals using electron paramagnetic resonance spectroscopy during open aorto-iliac arterial reconstruction.

PubMed

Majewski, Wacław; Krzyminiewski, Ryszard; Stanisić, Michał; Iskra, Maria; Krasiński, Zbigniew; Nowak, Marek; Dobosz, Bernadeta

2014-11-27

Aortic cross-clamping during abdominal aortic aneurysm (AAA) open repair leads to development of ischemia-reperfusion injury. Electron paramagnetic resonance spectroscopy (EPR) spin-trapping is a valuable method of direct measurement of free radicals. The objective of the study was to evaluate the results of EPR as a direct method of free radical measurement and degree of inflammatory response in open operative treatment of patients with AAA and aorto-iliac occlusive disease (AIOD). The study was performed on a group of 32 patients with AAA and 25 patients with AIOD scheduled for open repair. Peripheral venous blood for EPR spectroscopy and for SOD, GPx, ox-LDL, Il-6, TNF-alfa, CRP, and HO-1 were harvested. Selected parameters were established accordingly to specified EPR and immunohistochemical methods and analyzed between groups by Mann-Whitney U test and Wilcoxon matched-pairs signed-ranks test with Bonferroni correction. Free radicals level was correlated with the time of the aortic cross-clamping after the reperfusion of he first and second leg in AAA (r=0.7; r=0.47). ox-LDL in AAA decreased 5 min after reperfusion of the first leg (32.99 U/L, range: 14.09-77.12) and 5 min after reperfusion of the second leg (26.75 U/L, range: 11.56-82.12) and 24 h after the operation (25.85 U/L, range: 14.29-49.70). HO-1 concentration increased to above the level before intervention 24 h after surgery. The activities of GPx and SOD decreased 5 min after the first-leg reperfusion in AAA. Twenty-four hours after surgery, inflammatory markers increased in AAA to CRP was 14.76 ml/l (0.23-38.55), IL-6 was 141.22 pg/ml (84.3-591.03), TNF-alfa was 6.82 pg/ml (1.76-80.01) and AIOD: CRP was 18.44 mg/l (2.56-33.14), IL-6: 184.1 pg/ml (128.46-448.03), TNF-alfa was 7.74 pg/ml (1.74-74.74). EPR spin-trapping demonstrates temporarily elevated level of free radicals in early phase of reperfusion, leading to decrease antioxidants in AAA. Elevated free radical levels decreased 24 h after

Scaling craters in carbonates: Electron paramagnetic resonance analysis of shock damage

NASA Technical Reports Server (NTRS)

Polanskey, Carol A.; Ahrens, Thomas J.

1994-01-01

Carbonate samples from the 8.9-Mt nuclear (near-surface explosion) crater, OAK, and a terrestrial impact crater, Meteor Crater, were analyzed for shock damage using electron paramagnetic resonance (EPR). Samples from below the OAK apparent crater floor were obtained from six boreholes, as well as ejecta recovered from the crater floor. The degree of shock damage in the carbonate material was assessed by comparing the sample spectra to the spectra of Solenhofen and Kaibab limestone, which had been skocked to known pressures. Analysis of the OAK Crater borehole samples has identified a thin zone of allocthonous highly shocked (10-13 GPa) carbonate material underneath the apparent crater floor. This approx. 5- to 15-m-thick zone occurs at a maximum depth of approx. 125 m below current seafloor at the borehole, sited at the initial position of the OAK explosive, and decreases in depth towards the apparent crater edge. Because this zone of allocthonous shocked rock delineates deformed rock below, and a breccia of mobilized sand and collapse debris above, it appears to outline the transient crater. The transient crater volume inferred in this way is found to by 3.2 +/- 0.2 times 10(exp 6)cu m, which is in good agreement with a volume of 5.3 times 10(exp 6)cu m inferred from gravity scaling of laboratory experiments. A layer of highly shocked material is also found near the surface outside the crater. The latter material could represent a fallout ejecta layer. The ejecta boulders recovered from the present crater floor experienced a range of shock pressures from approx. 0 to 15 GPa with the more heavily shocked samples all occurring between radii of 360 and approx. 600 m. Moreover, the fossil content, lithology and Sr isotopic composition all demonstrate that the initial position of the bulk of the heavily shocked rock ejecta sampled was originally near surface rock at initial depths in the 32 to 45-m depth (below sea level) range. The EPR technique is also sensitive to

Studying lipid-protein interactions with electron paramagnetic resonance spectroscopy of spin-labeled lipids.

PubMed

Páli, Tibor; Kóta, Zoltán

2013-01-01

Spin label electron paramagnetic resonance (EPR) of lipid-protein interactions reveals crucial features of the structure and assembly of integral membrane proteins. Spin label EPR spectroscopy is the technique of choice to characterize the protein-solvating lipid shell in its highly dynamic nature, because the EPR spectra of lipids that are spin labeled close to the terminal methyl end of their acyl chains display two spectral components, those corresponding to lipids directly contacting the protein and those corresponding to lipids in the bulk fluid bilayer regions of the membrane. In this chapter, typical spin label EPR procedures are presented that allow determination of the stoichiometry of interaction of spin-labeled lipids with the intra-membranous region of membrane proteins or polypeptides, as well as the association constant of the spin-labeled lipid with respect to the host lipid. The lipids giving rise to the so-called immobile spectral component in the EPR spectrum of such samples are identified as the motionally restricted first-shell lipids solvating membrane proteins in biomembranes. Stoichiometry and selectivity are directly related to the structure of the intra-membranous sections of membrane-associated proteins or polypeptides and can be used to study the state of assembly of such proteins in the membrane. Since these characteristics of lipid-protein interactions are discussed in detail in the literature [see Marsh (Eur Biophys J 39:513-525, 2010) for a most recent review], here we focus more on how to spin label model and biomembranes and how to measure and analyze the two-component EPR spectra of spin-labeled lipids in phospholipid bilayers that contain proteins or polypeptides. After a description of how to prepare spin-labeled model and native biological membranes, we present the reader with computational procedures for determining the molar fraction of motionally restricted lipids when both, one, or none of the pure isolated-mobile or

Electron paramagnetic resonance studies on conformation states and metal ion exchange properties of vanadium bromoperoxidase

SciTech Connect

de Boer, E.; Boon, K.; Wever, R.

An electron paramagnetic resonance (EPR) study was carried out to examine structural aspects of vanadium-containing bromoperoxidase from the brown seaweed Ascophyllum nodosum. At high pH, the reduced form of bromoperoxidase showed an apparently axially symmetric EPR signal with 16 hyperfine lines. When the pH was lowered, a new EPR spectrum was formed. When EPR spectra of the reduced enzyme were recorded in the pH range from 4.2 to 8.4, it appeared that these changes were linked to a functional group with an apparent pK/sub a/ of about 5.4. In D/sub 2/O this value for the pK/sub a/ was 5.3. Itmore » is suggested that these effects arise from protonation of histidine or aspartate/glutamate residues near the metal ion. The values for the isotropic hyperfine coupling constant of the reduced enzyme at both high and low pH are also consistent with a ligand field containing nitrogen and/or oxygen donor atoms. When reduced bromoperoxidase was dissolved in D/sub 2/O or H/sub 2//sup 17/O instead of H/sub 2//sup 16/O, vanadium (IV) hyperfine line widths were markedly affected, demonstrating that water is a ligand of the metal ion. Together with previous work these findings suggest that vanadium (IV) is not involved in catalytic turnover and confirm the model in which the vanadium (V) ion of the native enzyme only serves to bind both hydrogen peroxide and bromide. After excess vanadate was added to a homogeneous preparation of purified bromoperoxidase, the extent of vanadium bound to the protein increased from 0.5 to 1.1, with a concomitant enhancement of enzymic activity. Finally, it is demonstrated that both vanadate (VO/sub 4//sup 3 -/) and molybdate (MoO/sub 4//sup 2 -/) compete for the same site on apobromoperoxidase.« less

Electron paramagnetic resonance g-tensors from state interaction spin-orbit coupling density matrix renormalization group

NASA Astrophysics Data System (ADS)

Sayfutyarova, Elvira R.; Chan, Garnet Kin-Lic

2018-05-01

We present a state interaction spin-orbit coupling method to calculate electron paramagnetic resonance g-tensors from density matrix renormalization group wavefunctions. We apply the technique to compute g-tensors for the TiF3 and CuCl42 - complexes, a [2Fe-2S] model of the active center of ferredoxins, and a Mn4CaO5 model of the S2 state of the oxygen evolving complex. These calculations raise the prospects of determining g-tensors in multireference calculations with a large number of open shells.

Conventional electron paramagnetic resonance of Mn2+ in synthetic hydroxyapatite at different concentrations of the doped manganese

NASA Astrophysics Data System (ADS)

Murzakhanov, F.; Mamin, G.; Voloshin, A.; Klimashina, E.; Putlyaev, V.; Doronin, V.; Bakhteev, S.; Yusupov, R.; Gafurov, M.; Orlinskii, S.

2018-05-01

Powders of synthetic hydroxyapatite doped with Mn2+ ions in concentrations from 0.05 till 5 wt. % were investigated by conventional electron paramagnetic resonance (EPR). The parameters of the spin-Hamiltonian are derived. Partially resolved hyperfine structure in the magnetic fields corresponding to g ≈ 4.3 and g ≈ 9.4 is observed. The narrowing of the central peak with concentration is reported. A possibility to use the linewidth and intensity of the central peak for concentration measurements are discussed. The results could be used for the identification and qualification of Mn2+ in oil, mining and ore formations.

Changes in mitochondrial functioning with electromagnetic radiation of ultra high frequency as revealed by electron paramagnetic resonance methods.

PubMed

Burlaka, Anatoly; Selyuk, Marina; Gafurov, Marat; Lukin, Sergei; Potaskalova, Viktoria; Sidorik, Evgeny

2014-05-01

To study the effects of electromagnetic radiation (EMR) of ultra high frequency (UHF) in the doses equivalent to the maximal permitted energy load for the staffs of the radar stations on the biochemical processes that occur in the cell organelles. Liver, cardiac and aorta tissues from the male rats exposed to non-thermal UHF EMR in pulsed and continuous modes were studied during 28 days after the irradiation by the electron paramagnetic resonance (EPR) methods including a spin trapping of superoxide radicals. The qualitative and quantitative disturbances in electron transport chain (ETC) of mitochondria are registered. A formation of the iron-nitrosyl complexes of nitric oxide (NO) radicals with the iron-sulphide (FeS) proteins, the decreased activity of FeS-protein N2 of NADH-ubiquinone oxidoreductase complex and flavo-ubisemiquinone growth combined with the increased rates of superoxide production are obtained. (i) Abnormalities in the mitochondrial ETC of liver and aorta cells are more pronounced for animals radiated in a pulsed mode; (ii) the alterations in the functioning of the mitochondrial ETC cause increase of superoxide radicals generation rate in all samples, formation of cellular hypoxia, and intensification of the oxide-initiated metabolic changes; and (iii) electron paramagnetic resonance methods could be used to track the qualitative and quantitative changes in the mitochondrial ETC caused by the UHF EMR.

Cathodoluminescence, laser ablasion inductively coupled plasma mass spectrometry, electron probe microanalysis and electron paramagnetic resonance analyses of natural sphalerite

USGS Publications Warehouse

Karakus, M.; Hagni, R.D.; Koenig, A.; Ciftc, E.

2008-01-01

Natural sphalerite associated with copper, silver, lead-zinc, tin and tungsten deposits from various world-famous mineral deposits have been studied by cathodoluminescence (CL), laser ablasion inductively coupled plasma mass spectrometry (LA-ICP-MS), electron probe microanalysis (EPMA) and electron paramagnetic resonance (EPR) to determine the relationship between trace element type and content and the CL properties of sphalerite. In general, sphalerite produces a spectrum of CL colour under electron bombardment that includes deep blue, turquoise, lime green, yellow-orange, orange-red and dull dark red depending on the type and concentration of trace quantities of activator ions. Sphalerite from most deposits shows a bright yellow-orange CL colour with ??max centred at 585 nm due to Mn2+ ion, and the intensity of CL is strongly dependent primarily on Fe2+ concentration. The blue emission band with ??max centred at 470-490 nm correlates with Ga and Ag at the Tsumeb, Horn Silver, Balmat and Kankoy mines. Colloform sphalerite from older well-known European lead-zinc deposits and late Cretaceous Kuroko-type VMS deposits of Turkey shows intense yellowish CL colour and their CL spectra are characterised by extremely broad emission bands ranging from 450 to 750 nm. These samples are characterised by low Mn (<10 ppm) and Ag (<1 ppm), and they are enriched in Tl (1-30 ppm) and Pb (80-1500 ppm). Strong green CL is produced by sphalerite from the Balmat-Edwards district. Amber, lime-green and red-orange sphalerite produced weak orange-red CL at room temperatures, with several emission bands centred at 490, 580, 630, 680, 745, with ??max at 630 nm being the strongest. These emission bands are well correlated with trace quantities of Sn, In, Cu and Mn activators. Sphalerite from the famous Ogdensburg and Franklin mines exhibited brilliant deep blue and orange CL colours and the blue CL may be related to Se. Cathodoluminescence behaviour of sphalerite serves to characterise ore

Cryogen-free superconducting magnet system for multifrequency electron paramagnetic resonance up to 12.1 T

NASA Astrophysics Data System (ADS)

Smirnov, Alex I.; Smirnova, Tatyana I.; MacArthur, Ryan L.; Good, Jeremy A.; Hall, Renny

2006-03-01

Multifrequency and high field/high frequency (HF) electron paramagnetic resonance (EPR) is a powerful spectroscopy for studying paramagnetic spin systems ranging from organic-free radicals to catalytic paramagnetic metal ion centers in metalloproteins. Typically, HF EPR experiments are carried out at resonant frequencies ν =95-300GHz and this requires magnetic fields of 3.4-10.7T for electronic spins with g ≈2.0. Such fields could be easily achieved with superconducting magnets, but, unlike NMR, these magnets cannot operate in a persistent mode in order to satisfy a wide range of resonant fields required by the experiment. Operating and maintaining conventional passively cooled superconducting magnets in EPR laboratories require frequent transfer of cryogens by trained personnel. Here we describe and characterize a versatile cryogen-free magnet system for HF EPR at magnetic fields up to 12.1T that is suitable for ramping the magnetic field over the entire range, precision scans around the target field, and/or holding the field at the target value. We also demonstrate that in a nonpersistent mode of operation the magnetic field can be stabilized to better than 0.3ppm/h over 15h period by employing a transducer-controlled power supply. Such stability is sufficient for many HF EPR experiments. An important feature of the system is that it is virtually maintenance-free because it is based on a cryogen-free technology and therefore does not require any liquid cryogens (liquid helium or nitrogen) for operation. We believe that actively cooled superconducting magnets are ideally suited for a wide range of HF EPR experiments including studies of spin-labeled nucleic acids and proteins, single-molecule magnets, and metalloproteins.

Reactive oxygen species' role in endothelial dysfunction by electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Wassall, Cynthia D.

The endothelium is a single layer of cells lining the arteries and is involved in many physiological reactions which are responsible for vascular tone. Free radicals are important participants in these chemical reactions in the endothelium. Here we quantify free radicals, ex vivo, in biological tissue with continuous wave electron paramagnetic resonance (EPR). In all of the experiments in this thesis, we use a novel EPR spin trapping technique that has been developed for tissue segments. EPR spin trapping is often considered the 'gold standard' in reactive oxygen species (ROS) detection because of its sensitivity and non-invasive nature. In all experiments, tissue was placed in physiological saline solution with 190-mM PBN (N-tert -butyl-α-phenylnitrone), 10% by volume dimethyl-sulphoxide (DMSO) for cryopreservation, and incubated in the dark for between 30 minutes up to 2 hours at 37°C while gently being stirred. Tissue and supernatant were then loaded into a syringe and frozen at -80°C until EPR analysis. In our experiments, the EPR spectra were normalized with respect to tissue volume. Conducting experiments at liquid nitrogen temperature leads to some experimental advantages. The freezing of the spin adducts renders them stable over a longer period, which allows ample time to analyze tissue samples for ROS. The dielectric constant of ice is greatly reduced over its liquid counterpart; this property of water enables larger sample volumes to be inserted into the EPR cavity without overloading it and leads to enhanced signal detection. Due to Maxwell-Boltzmann statistics, the population difference goes up as the temperature goes down, so this phenomenon enhances the signal intensity as well. With the 'gold standard' assertion in mind, we investigated whether slicing tissue to assay ROS that is commonly used in fluorescence experiments will show more free radical generation than tissue of a similar volume that remains unsliced. Sliced tissue exhibited a 76

Domain structure in biphenyl incommensurate phase II observed by electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Véron, A.; Emery, J.; Spiesser, M.

1994-11-01

The domain structure in incommensurate phase II of single biphenyl crystal has been observed by investigations of the optically excited states of the Electronic Paramagnetic Resonance (E.P.R.) deuterated naphthalene molecular probes which substitute biphenyl molecules. Our results confirm that this phase is a 1q bi-domain one. The analysis of the spectra obtained in X band (9.5 GHz) experiments, in relation with the spin Hamiltonian parameter properties permits us to show that the E.P.R. probe rotates around a direction perpendicular to its long axis while the biphenyl molecule undergoes a twist movement around this axis. They also account for a regime which is like a “ multi-soliton " regime while the modulation is a plane wave one in the pure single crystal. The two molecules of the high temperature cell do not exactly experience the saure displacement field in the incommensurate phase and consequently the two domains can be distinguished. The spin Hamiltonian parameters which characterize the E.P.R. probes have been determined in the incommensurate phase II of biphenyl. La structure en domaines de la phase II du biphényle est mise en évidence par les investigations dans les états photo-excités des molécules de naphtalène deutéré, utilisées comme sondes de Résonance Paramagnétique Electronique, se substituant de manière diluée dans le mono-cristal de biphényle. Ceci confirme que cette phase est 1q bi-domaine. L'analyse des spectres obtenus dans des expériences en bande X (9.5 GHz) en relation avec les propriétés de l'hamiltonien de spin permet de montrer que la sonde moléculaire tourne autour d'une direction perpendiculaire à son grand axe alors que la molécule de biphényle subit un mouvement de twist autour de cet axe. Les résultats montrent que ces sondes rendent compte d'un régime qui est comme un régime “ multi-solitons " alors que la modulation est plane dans le cristal pur. Les deux molécules sondes de la cellule �

A portable version of the program of nettar and villafranca for the simulation of electron paramagnetic resonance spectra of powders

NASA Astrophysics Data System (ADS)

Soulié, Edgar; Gaugenot, Jacques

1995-04-01

Nettar and Villafranca wrote in the FORTRAN programming language a computer program which simulates the electron paramagnetic resonance (EPR) spectra of powders (Journal of Magnetic Resonance, vol. 64 (1985) pp. 61-65). The spin Hamiltonian which their program can handle includes the Zeeman electronic interaction, the fine interaction up to the sixth order in the electron spin, a general hyperfine interaction, an isotropic nuclear Zeeman term; anisotropic ligand hyperfine terms are treated to first order in perturbation. The above Hamiltonian, without the ligand hyperfine terms, is treated exactly, i.e. the resonance equation for a transition between states labeled i and j is solved numerically: h.ν=Ei(H)-Ej(H).

Hyperfine Structure and Exchange Narrowing of Paramagnetic Resonance

DOE R&D Accomplishments Database

Townes, C. H.; Turkevich, J.

1950-01-01

Discussion of electronic paramagnetic resonance for the free radical ?, ?-diphenyl ?-picryl hydrazyl as observed by its effect on the transmission of microwave through a TE{sub 01} cavity with a small amount of the free radical placed approximately on the axis of the cavity; the half-width of this resonance at half maximum absorption was 1.45 oersteds.

Theory for electron transfer from a mixed-valence dimer with paramagnetic sites to a mononuclear acceptor

NASA Astrophysics Data System (ADS)

Bominaar, E. L.; Achim, C.; Borshch, S. A.

1999-06-01

Polynuclear transition-metal complexes, such as Fe-S clusters, are the prosthetic groups in a large number of metalloproteins and serve as temporary electron storage units in a number of important redox-based biological processes. Polynuclearity distinguishes clusters from mononuclear centers and confers upon them unique properties, such as spin ordering and the presence of thermally accessible excited spin states in clusters with paramagnetic sites, and fractional valencies in clusters of the mixed-valence type. In an earlier study we presented an effective-mode (EM) analysis of electron transfer from a binuclear mixed-valence donor with paramagnetic sites to a mononuclear acceptor which revealed that the cluster-specific attributes have an important impact on the kinetics of long-range electron transfer. In the present study, the validity of these results is tested in the framework of more detailed theories which we have termed the multimode semiclassical (SC) model and the quantum-mechanical (QM) model. It is found that the qualitative trends in the rate constant are the same in all treatments and that the semiclassical models provide a good approximation of the more rigorous quantum-mechanical description of electron transfer under physiologically relevant conditions. In particular, the present results corroborate the importance of electron transfer via excited spin states in reactions with a low driving force and justify the use of semiclassical theory in cases in which the QM model is computationally too demanding. We consider cases in which either one or two donor sites of a dimer are electronically coupled to the acceptor. In the case of multiconnectivity, the rate constant for electron transfer from a valence-delocalized (class-III) donor is nonadditive with respect to transfer from individual metal sites of the donor and undergoes an order-of-magnitude change by reversing the sign of the intradimer metal-metal resonance parameter (β). In the case of

X-band Electron Paramagnetic Resonance Investigation of Stable Organic Radicals Present under Cold Stratification in 'Fuji' Apple Seeds.

PubMed

Nakagawa, Kouichi; Matsumoto, Kazuhiro; Chaiserm, Nattakan; Priprem, Aroonsri

2017-01-01

We investigated stable organic radicals formed in response to cold stratification in 'Fuji' apple seeds using X-band (9 GHz) electron paramagnetic resonance (EPR) technique. This technique primarily detected two paramagnetic species in each seed. These two different radical species were assigned as a stable organic radical and Mn 2+ species based on the g values and hyperfine components. Signal from the stable radicals was noted at a g value of about 2.00 and was strong and relatively stable. Significant radical intensity changes were observed in apple seeds on refrigeration along with water supplementation. The strongest radical intensity and a very weak Mn 2+ signal were also observed for the seeds kept in moisture-containing sand in a refrigerator. Noninvasive EPR of the radicals present in each seed revealed that the stable radicals were located primarily in the seed coat. These results indicate that the significant radical intensity changes in apple seeds under refrigeration for at least 90 days followed by water supplementation for one week, can be related to cold stratification of the seeds.

Magnetic resonance force microscopy of paramagnetic electron spins at millikelvin temperatures.

PubMed

Vinante, A; Wijts, G; Usenko, O; Schinkelshoek, L; Oosterkamp, T H

2011-12-06

Magnetic resonance force microscopy (MRFM) is a powerful technique to detect a small number of spins that relies on force detection by an ultrasoft magnetically tipped cantilever and selective magnetic resonance manipulation of the spins. MRFM would greatly benefit from ultralow temperature operation, because of lower thermomechanical noise and increased thermal spin polarization. Here we demonstrate MRFM operation at temperatures as low as 30 mK, thanks to a recently developed superconducting quantum interference device (SQUID)-based cantilever detection technique, which avoids cantilever overheating. In our experiment, we detect dangling bond paramagnetic centres on a silicon surface down to millikelvin temperatures. Fluctuations of such defects are supposedly linked to 1/f magnetic noise and decoherence in SQUIDs, as well as in several superconducting and single spin qubits. We find evidence that spin diffusion has a key role in the low-temperature spin dynamics.

Electron paramagnetic resonance of Nb-doped BaTiO3 ceramics with positive temperature coefficient of resistivity

NASA Astrophysics Data System (ADS)

Jida, Shin'suke; Miki, Toshikatsu

1996-11-01

Paramagnetic centers in Nb-doped BaTiO3 ceramics are measured at 77-500 K by electron paramagnetic resonance (EPR) for investigating the role of the centers on the well-known positive temperature coefficient of resistivity (PTCR) effect (PTCR at the Curie temperature). EPR detects four signals; an anisotropically broad singlet signal at g=2.005, a sextet signal due to Mn2+, a Cr3+ signal, and a Ti3+ signal. The former two signals arise in the rhombohedral and cubic phases, but disappear in the tetragonal and orthorhombic phases. The Cr3+ signal appears in all of the phases, while the Ti3+ signal is detected only at low temperatures. The singlet signal also arises in undoped, barium-deficient BaTiO3 ceramics, therefore the signal is attributable to barium-vacancy-associated centers rather than Nb4+ ions or Fe3+ ions proposed by several authors. In this article, we propose that the singlet signal is due to vacancy-pairs of VBa-F+ type, i.e., the vacancy pair of VBa-VO capturing one electron. The electrical resistivity data show a polaronic character of low-temperature conduction and a high resistivity jump around the Curie temperature. The low-temperature polaronic conduction is explained in terms of electron-hopping between Ti4+ and Ti3+ ions. The resistivity jump at the Curie temperature occurs along with the EPR intensity increase of the singlet signal, the Mn2+ signal and the Cr3+ signal. We conclude that the PTCR of Nb-doped BaTiO3 ceramics is strongly associated with the trap activation of the VBa-VO vacancy-pairs and manganese centers at the tetragonal-to-cubic transition.

"Dark" Singlet Oxygen and Electron Paramagnetic Resonance Spin Trapping as Convenient Tools to Assess Photolytic Drug Degradation.

PubMed

Persich, Peter; Hostyn, Steven; Joie, Céline; Winderickx, Guy; Pikkemaat, Jeroen; Romijn, Edwin P; Maes, Bert U W

2017-05-01

Forced degradation studies are an important tool for a systematic assessment of decomposition pathways and identification of reactive sites in active pharmaceutical ingredients (APIs). Two methodologies have been combined in order to provide a deeper understanding of singlet oxygen-related degradation pathways of APIs under light irradiation. First, we report that a "dark" singlet oxygen test enables the investigation of drug reactivity toward singlet oxygen independently of photolytic irradiation processes. Second, the photosensitizing properties of the API producing the singlet oxygen was proven and quantified by spin trapping and electron paramagnetic resonance analysis. A combination of these techniques is an interesting addition to the forced degradation portfolio as it can be used for (1) revealing unexpected degradation pathways of APIs due to singlet oxygen, (2) clarifying photolytic drug-drug interactions in fixed-dose combinations, and (3) synthesizing larger quantities of hardly accessible oxidative drug degradants. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Theoretical Studies of the Electron Paramagnetic Resonance Parameters and Local Structure for VO2+ in Oxyfluoroborate Glasses

NASA Astrophysics Data System (ADS)

Zhang, Huaming; Yu, Xiaopeng; Xiao, Wenbo

2017-12-01

The electron paramagnetic resonance parameters (g factors g ‖, g ⊥ and hyperfine structure constants A ‖, A ⊥) of a tetragonal V4+ center in oxyfluoroborate glasses (20Li2O-10Li2F2-70B2O3) are theoretically investigated by using the perturbation formulas for a 3d1 ion in tetragonally compressed octahedra. The calculated results are in good agreement with the experimental data. Local structure parameters of [VO6]8- clusters are obtained from the calculation (i.e., R‖ ≈ 1.74 Å and R⊥ ≈ 1.985 Å for the metal-ligand distances parallel and perpendicular to the C4 axis, respectively). It is shown that the local structure around the V4+ ion possesses a compressed tetragonal distortion along C 4 axis. The signs of the hyperfine structure constants A‖ and A ⊥ for V4+ centers in oxyfluoroborate glasses were also suggested in the discussion.

X-Band Rapid-Scan Electron Paramagnetic Resonance of Radiation-Induced Defects in Tooth Enamel

PubMed Central

Yu, Zhelin; Romanyukha, Alexander; Eaton, Sandra S.; Eaton, Gareth R.

2015-01-01

X-band rapid-scan electron paramagnetic resonance (EPR) spectra from tooth enamel samples irradiated with doses of 0.5, 1 and 10 Gy had substantially improved signal-to-noise relative to conventional continuous wave EPR. The radiation-induced signal in 60 mg of a tooth enamel sample irradiated with a 0.5 Gy dose was readily characterized in spectra recorded with 34 min data acquisition times. The coefficient of variance of the calculated dose for a 1 Gy irradiated sample, based on simulation of the first-derivative spectra for three replicates as the sum of native and radiation-induced signals, was 3.9% for continuous wave and 0.4% for rapid scan. PMID:26207683

Electronic phase separation in insulating (Ga, Mn) As with low compensation: super-paramagnetism and hopping conduction

NASA Astrophysics Data System (ADS)

Yuan, Ye; Wang, Mao; Xu, Chi; Hübner, René; Böttger, Roman; Jakiela, Rafal; Helm, Manfred; Sawicki, Maciej; Zhou, Shengqiang

2018-03-01

In the present work, low compensated insulating (Ga,Mn)As with 0.7% Mn is obtained by ion implantation combined with pulsed laser melting. The sample shows variable-range hopping transport behavior with a Coulomb gap in the vicinity of the Fermi energy, and the activation energy is reduced by an external magnetic field. A blocking super-paramagnetism is observed rather than ferromagnetism. Below the blocking temperature, the sample exhibits a colossal negative magnetoresistance. Our studies confirm that the disorder-induced electronic phase separation occurs in (Ga,Mn)As samples with a Mn concentration in the insulator-metal transition regime, and it can account for the observed superparamagnetism and the colossal magnetoresistance.

A compensating point defect in carbon-doped GaN substrates studied with electron paramagnetic resonance spectroscopy

NASA Astrophysics Data System (ADS)

Willoughby, W. R.; Zvanut, M. E.; Paudel, Subash; Iwinska, M.; Sochacki, T.; Bockowski, M.

2018-04-01

Electron paramagnetic resonance (EPR) spectroscopy was used to investigate a type of point defect present in 1019 cm-3 carbon-doped GaN substrates grown by hydride vapor phase epitaxy. A broad, isotropic resonance at g ˜ 1.987 was observed at 3.5 K, and the EPR intensity increased with illumination at energies greater than 2.75 eV and decreased with photon energies greater than 0.95 eV. The latter is consistent with a deep level of 0.95 eV above the valence band maximum and implies that the associated defect likely participates in donor compensation. The ionization energy for this defect is close to the predicted value for the (-/0) transition level of CN and transition levels associated with Ga vacancies such as VGa and VGa-ON-2H.

Superoxide Anion Radical Production in the Tardigrade Paramacrobiotus richtersi, the First Electron Paramagnetic Resonance Spin-Trapping Study.

PubMed

Savic, Aleksandar G; Guidetti, Roberto; Turi, Ana; Pavicevic, Aleksandra; Giovannini, Ilaria; Rebecchi, Lorena; Mojovic, Milos

2015-01-01

Anhydrobiosis is an adaptive strategy that allows withstanding almost complete body water loss. It has been developed independently by many organisms belonging to different evolutionary lines, including tardigrades. The loss of water during anhydrobiotic processes leads to oxidative stress. To date, the metabolism of free radicals in tardigrades remained unclear. We present a method for in vivo monitoring of free radical production in tardigrades, based on electron paramagnetic resonance and spin-trap DEPMPO, which provides simultaneous identification of various spin adducts (i.e., different types of free radicals). The spin trap can be easily absorbed in animals, and tardigrades stay alive during the measurements and during 24-h monitoring after the treatment. The results show that hydrated specimens of the tardigrade Paramacrobiotus richtersi produce the pure superoxide anion radical ((•)O2(-)). This is an unexpected result, as all previously examined animals and plants produce both superoxide anion radical and hydroxyl radical ((•)OH) or exclusively hydroxyl radical.

Detection of undistorted continuous wave (CW) electron paramagnetic resonance (EPR) spectra with non-adiabatic rapid sweep (NARS) of the magnetic field

PubMed Central

Kittell, Aaron W.; Camenisch, Theodore G.; Ratke, Joseph J.; Sidabras, Jason W.; Hyde, James S.

2011-01-01

A continuous wave (CW) electron paramagnetic resonance (EPR) spectrum is typically displayed as the first harmonic response to the application of 100 kHz magnetic field modulation, which is used to enhance sensitivity by reducing the level of 1/f noise. However, magnetic field modulation of any amplitude causes spectral broadening and sacrifices EPR spectral intensity by at least a factor of two. In the work presented here, a CW rapid-scan spectroscopic technique that avoids these compromises and also provides a means of avoiding 1/f noise is developed. This technique, termed non-adiabatic rapid sweep (NARS) EPR, consists of repetitively sweeping the polarizing magnetic field in a linear manner over a spectral fragment with a small coil at a repetition rate that is sufficiently high that receiver noise, microwave phase noise, and environmental microphonics, each of which has 1/f characteristics, are overcome. Nevertheless, the rate of sweep is sufficiently slow that adiabatic responses are avoided and the spin system is always close to thermal equilibrium. The repetitively acquired spectra from the spectral fragment are averaged. Under these conditions, undistorted pure absorption spectra are obtained without broadening or loss of signal intensity. A digital filter such as a moving average is applied to remove high frequency noise, which is approximately equivalent in bandwidth to use of an integrating time constant in conventional field modulation with lock-in detection. Nitroxide spectra at L- and X-band are presented. PMID:21741868

Optical and electron paramagnetic resonance studies of the excited triplet states of UV-B absorbers: 2-ethylhexyl salicylate and homomenthyl salicylate.

PubMed

Sugiyama, Kazuto; Tsuchiya, Takumi; Kikuchi, Azusa; Yagi, Mikio

2015-09-26

The energy levels and lifetimes of the lowest excited triplet (T1) states of UV-B absorbers, 2-ethylhexyl salicylate (EHS) and homomenthyl salicylate (HMS), and their deprotonated anions (EHS(-) and HMS(-)) were determined through measurements of phosphorescence and electron paramagnetic resonance (EPR) spectra in rigid solutions at 77 K. The observed T1 energies of EHS and HMS are higher than those of butylmethoxydibenzoylmethane, the most widely used UV-A absorber, and octyl methoxycinnamate, the most widely used UV-B absorber. The T1 states of EHS, HMS, EHS(-) and HMS(-) were assigned to almost pure (3)ππ* state from the observed T1 lifetimes and zero-field splitting parameters. EHS and HMS with an intramolecular hydrogen bond show a photoinduced phosphorescence enhancement in ethanol at 77 K. The EPR signals of the T1 states of EHS and HMS also increase in intensity with UV-irradiation time (photoinduced EPR enhancement). The T1 lifetimes of EHS and HMS at room temperature were determined through triplet-triplet absorption measurements in ethanol. The quantum yields of singlet oxygen production by EHS and HMS were determined by using time-resolved near-IR phosphorescence.

Development of an electron paramagnetic resonance methodology for studying the photo-generation of reactive species in semiconductor nano-particle assembled films

NASA Astrophysics Data System (ADS)

Twardoch, Marek; Messai, Youcef; Vileno, Bertrand; Hoarau, Yannick; Mekki, Djamel E.; Felix, Olivier; Turek, Philippe; Weiss, Jean; Decher, Gero; Martel, David

2018-06-01

An experimental approach involving electron paramagnetic resonance is proposed for studying photo-generated reactive species in semiconductor nano-particle-based films deposited on the internal wall of glass capillaries. This methodology is applied here to nano-TiO2 and allows a semi-quantitative analysis of the kinetic evolutions of radical production using a spin scavenger probe.

Development of double-pulse lasers ablation system and electron paramagnetic resonance spectroscopy for direct spectral analysis of manganese doped PVA polymer

NASA Astrophysics Data System (ADS)

Khalil, A. A. I.; Morsy, M. A.; El-Deen, H. Z.

2017-11-01

Series of manganese-co-precipitated poly (vinyl alcohol) (PVA) polymer were quantitatively and qualitatively analyzed using laser ablation system (LAS) based on double-pulse laser induced breakdown spectroscopy (DP-LIBS) and electron paramagnetic resonance (EPR) spectroscopy. The collinear nanosecond laser beams of 266 and 1064 nm were optimized to focus on the surface of the PVA polymer target. Both laser beams were employed to estimate the natural properties of the excited Mn-PVA plasma, such as electron number density (Ne), electron temperature (Te), and Mn concentration. Individual transition lines of manganese (Mn), carbon (C), lithium (Li), hydrogen (H) and oxygen (O) atoms are identified based on the NIST spectral database. The results show better responses with DP-LIBS than the single-pulse laser induced breakdown spectroscopy (SP-LIBS). On the other hand, the EPR investigation shows characteristic broad peak of Mn-nano-particles (Mn-NPs) in the range of quantum dots of superparamagnetic materials. The line width (peak-to-peak, ΔHpp) and g-value of the observed Mn-EPR peak are ∼20 mT and 2.0046, respectively. The intensities of Mn-emission line at a wavelength 403.07 nm and the Mn-EPR absorption peak were used to accurate quantify the Mn-content in the polymer matrix. The results produce linear trends within the studied concentration range with regression coefficient (R2) value of ∼0.99, and limit of detection (LOD) of 0.026 mol.% and 0.016 mol.%, respectively. The LOD values are at a fold change of about -0.2 of the studied lowest mol.%. The proposed protocols of trace element detection are of significant advantage and can be applied to the other metal analysis.

Electron-paramagnetic-resonance studies of leghaemoglobins from soya-bean and cowpea root nodules. Identification of nitrosyl-leghaemoglobin in crude leghaemoglobin preparations

PubMed Central

Maskall, C. Sidney; Gibson, John F.; Dart, Peter J.

1977-01-01

1. Leghaemoglobins from soya-bean (Glycine max) and cowpea (Vigna unguiculata) root nodules were purified by chromatography on DEAE-cellulose phosphate columns at pH8.0 and pH5.8, to avoid the relatively low pH (5.2) commonly used to purify these proteins. 2. E.p.r. (electron-paramagnetic-resonance) spectra of the fluoride, azide, hydroxide and cyanide complexes of these ferric leghaemoglobins were very similar to the spectra of the corresponding myoglobin derivatives, indicating that the immediate environment of the iron in leghaemoglobin and myoglobin is similar, an imidazole moiety of histidine being the proximal ligand to the haem iron [cf. Appleby, Blumberg, Peisach, Wittenberg & Wittenberg (1976) J. Biol. Chem. 251, 6090–6096]. 3. E.p.r. spectra of the acid-metleghaemoglobins showed prominent high-spin features very near g=6 and g=2 and, unlike myoglobin, small low-spin absorptions near g=2.26, 2.72 and 3.14. The width of the g=6 absorption derivative at 10–20K was about 4–4.5mT, similar to the value for acid-methaemoglobin. In contrast, a recently published (Appleby et al., 1976) spectrum of acid-metleghaemoglobin a had less high-spin character and a much broader absorption derivative around g=6. 4. E.p.r. spectra of ferric leghaemoglobin nicotinate and imidazole complexes suggest that the low-spin absorption near g=3.14 can be attributed to a trace of ferric leghaemoglobin nicotinate, and those near g=2.26 and 2.72 are from an endogenous dihistidyl haemichrome. 5. A large e.p.r. signal at g=2 in all samples of crude leghaemoglobin was shown to be from nitrosyl-leghaemoglobin. A soya-bean sample contained 27±3% of the latter. A previously unidentified form of soya-bean ferrous leghaemoglobin a was shown to be its nitrosyl derivative. If this is not an artifact, and occurs in the root nodule, the nitrosyl radical may interfere with the function of leghaemoglobin. PMID:23110

Ethylene Glycol Quenching of Nitrogenase Catalysis: An Electron Paramagnetic Resonance Spectroscopic Study of Nitrogenase Turnover States and CO Bonding.

PubMed

Hales, Brian J

2015-07-14

Most hydrophilic organic solvents inhibit enzymatic activity. Nitrogenase is shown to be approximately 3 times more sensitive to organic inhibition than most other soluble enzymes. Ethylene glycol (EG) is demonstrated to rapidly inhibit nitrogenase activity without uncoupling ATP hydrolysis. Our data suggest the mechanism of inhibition is EG's blocking of binding of MgATP to the nitrogenase Fe protein. EG quenching allows, for the first time, the observation of the relaxation of the intermediate reaction states at room temperature. Electron paramagnetic resonance (EPR) spectroscopy is used to monitor the room-temperature decay of the nitrogenase turnover states following EG quenching of catalytic activity. The return of the intermediate states to the resting state occurs in multiple phases over 2 h. During the initial stage, nitrogenase still possesses the ability to generate CO-induced EPR signals even though catalytic activity has ceased. During the last phase of relaxation, the one-electron reduced state of the MoFe protein (E1) relaxes to the resting state (E0) in a slow first-order reaction.

A Ku band pulsed electron paramagnetic resonance spectrometer using an arbitrary waveform generator for quantum control experiments at millikelvin temperatures

SciTech Connect

Yap, Yung Szen, E-mail: yungszen@utm.my; Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor; Tabuchi, Yutaka

2015-06-15

We present a 17 GHz (Ku band) arbitrary waveform pulsed electron paramagnetic resonance spectrometer for experiments down to millikelvin temperatures. The spectrometer is located at room temperature, while the resonator is placed either in a room temperature magnet or inside a cryogen-free dilution refrigerator; the operating temperature range of the dilution unit is from ca. 10 mK to 8 K. This combination provides the opportunity to perform quantum control experiments on electron spins in the pure-state regime. At 0.6 T, spin echo experiments were carried out using γ-irradiated quartz glass from 1 K to 12.3 mK. With decreasing temperatures, wemore » observed an increase in spin echo signal intensities due to increasing spin polarizations, in accordance with theoretical predictions. Through experimental data fitting, thermal spin polarization at 100 mK was estimated to be at least 99%, which was almost pure state. Next, to demonstrate the ability to create arbitrary waveform pulses, we generate a shaped pulse by superposing three Gaussian pulses of different frequencies. The resulting pulse was able to selectively and coherently excite three different spin packets simultaneously—a useful ability for analyzing multi-spin system and for controlling a multi-qubit quantum computer. By applying this pulse to the inhomogeneously broadened sample, we obtain three well-resolved excitations at 8 K, 1 K, and 14 mK.« less

Quantitative determination of copper in a glass matrix using double pulse laser induced breakdown and electron paramagnetic resonance spectroscopic techniques.

PubMed

Khalil, Ahmed A I; Morsy, Mohamed A

2016-07-01

A series of lithium-lead-borate glasses of a variable copper oxide loading were quantitatively analyzed in this work using two distinct spectroscopic techniques, namely double pulse laser induced breakdown spectroscopy (DP-LIBS) and electron paramagnetic resonance (EPR). DP-LIBS results measured upon a combined nanosecond lasers irradiation running at 266nm and 1064nm pulses of a collinear configuration directed to the surface of borate glass samples with a known composition. This arrangement was employed to predict the electron's temperature (Te) and density (Ne) of the excited plasma from the recorded spectra. The intensity of elements' responses using this scheme is higher than that of single-pulse laser induced breakdown spectroscopy (SP-LIBS) setup under the same experimental conditions. On the other hand, the EPR data shows typical Cu (II) EPR-signals in the borate glass system that is networked at a distorted tetragonal Borate-arrangement. The signal intensity of the Cu (II) peak at g⊥=2.0596 has been used to quantify the Cu-content accurately in the glass matrix. Both techniques produced linear calibration curves of Cu-metals in glasses with excellent linear regression coefficient (R(2)) values. This study establishes a good correlation between DP-LIBS analysis of glass and the results obtained using EPR spectroscopy. The proposed protocols prove the great advantage of DP-LIBS system for the detection of a trace copper on the surface of glasses. Copyright © 2016 Elsevier B.V. All rights reserved.

Electron paramagnetic resonance investigation on modulatory effect of 17beta-estradiol on membrane fluidity of erythrocytes in postmenopausal women.

PubMed

Tsuda, K; Kinoshita, Y; Kimura, K; Nishio, I; Masuyama, Y

2001-08-01

Many studies have shown that estrogen may exert cardioprotective effects and reduce the risk of hypertension and coronary events. On the other hand, it has been proposed that cell membrane abnormalities play a role in the pathophysiology of hypertension, although it is not clear whether estrogen would influence membrane function in essential hypertension. The present study was performed to investigate the effects of 17beta-estradiol (E(2)) on membrane fluidity of erythrocytes in normotensive and hypertensive postmenopausal women. We determined the membrane fluidity of erythrocytes by means of an electron paramagnetic resonance and spin-labeling method. In an in vitro study, E(2) significantly decreased the order parameter for 5-nitroxide stearate and the peak height ratio for 16-nitroxide stearate obtained from electron paramagnetic resonance spectra of erythrocyte membranes in normotensive postmenopausal women. The finding indicates that E(2) might increase the membrane fluidity of erythrocytes. The effect of E(2) was significantly potentiated by the NO donor, S-nitroso-N-acetylpenicillamine, and a cGMP analogue, 8-bromo-cGMP. In contrast, the change in the membrane fluidity evoked by E(2) was attenuated in the presence of the NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester, and asymmetric dimethyl-L-arginine. In hypertensive postmenopausal women, the membrane fluidity of erythrocytes was significantly lower than that in normotensive postmenopausal women. The effect of E(2) on membrane fluidity was significantly more pronounced in the erythrocytes of hypertensive postmenopausal women than in the erythrocytes of normotensive postmenopausal women. The results of the present study showed that E(2) significantly increased the membrane fluidity and improved the microviscosity of erythrocyte membranes, partially mediated by an NO- and cGMP-dependent pathway. Furthermore, the greater action of E(2) in hypertension might be consistent with the hypothesis that E

Defects in paramagnetic Co-doped ZnO films studied by transmission electron microscopy

SciTech Connect

Kovacs, Andras; Ney, A.; Duchamp, Martial

2013-12-23

We have studied planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al2O3) and the Co:ZnO/Al2O3 interface structure at atomic resolution using aberration-corrected transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). Comparing Co:ZnO samples deposited by pulsed laser deposition and reactive magnetron sputtering, both exhibit extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3-4 Co:ZnO layers at the interface.. In addition, we have measured the local strain which reveals the lattice distortion around the stacking faults.

Thermodynamic and electron paramagnetic resonance characterization of flavin in succinate dehydrogenase.

PubMed

Ohnishi, T; King, T E; Salerno, J C; Blum, H; Bowyer, J R; Maida, T

1981-06-10

Thermodynamic parameters of succinate dehydrogenase flavin were determined potentiometrically from the analysis of free radical signal levels as a function of the oxidation-reduction potential. Midpoint redox potentials of consecutive 1-electron transfer steps are -127 and -31 mV at pH 7.0. This corresponds to a stability constant of intermediate stability, 2.5 x 10(-2), which suggests flavin itself may be a converter from n = 2 to n = 1 electron transfer steps. The pK values of the free radical (FlH . in equilibrium Fl . -) and the fully reduced form (FlH2 in equilibrium FlH-) were estimated as 8.0 +/- 0.2 and 7.7 +/- 0.2, respectively. Succinate dehydrogenase flavosemiquinone elicits an EPR spectrum at g = 2.00 with a peak to peak width of 1.2 mT even in the protonated form, suggesting the delocalization in the unpaired electron density. A close proximity of succinate dehydrogenase flavin and iron-sulfur cluster S-1 was demonstrated based on the enhancement of flavin spin relaxation by Center S-1.

Quantitative estimation of magnetic nanoparticle distributions in one dimension using low-frequency continuous wave electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Coene, A.; Crevecoeur, G.; Dupré, L.; Vaes, P.

2013-06-01

In recent years, magnetic nanoparticles (MNPs) have gained increased attention due to their superparamagnetic properties. These properties allow the development of innovative biomedical applications such as targeted drug delivery and tumour heating. However, these modalities lack effective operation arising from the inaccurate quantification of the spatial MNP distribution. This paper proposes an approach for assessing the one-dimensional (1D) MNP distribution using electron paramagnetic resonance (EPR). EPR is able to accurately determine the MNP concentration in a single volume but not the MNP distribution throughout this volume. A new approach that exploits the solution of inverse problems for the correct interpretation of the measured EPR signals, is investigated. We achieve reconstruction of the 1D distribution of MNPs using EPR. Furthermore, the impact of temperature control on the reconstructed distributions is analysed by comparing two EPR setups where the latter setup is temperature controlled. Reconstruction quality for the temperature-controlled setup increases with an average of 5% and with a maximum increase of 13% for distributions with relatively lower iron concentrations and higher resolutions. However, these measurements are only a validation of our new method and form no hard limits.

Ultraviolet radiation and nanoparticle induced intracellular free radicals generation measured in human keratinocytes by electron paramagnetic resonance spectroscopy.

PubMed

Rancan, F; Nazemi, B; Rautenberg, S; Ryll, M; Hadam, S; Gao, Q; Hackbarth, S; Haag, S F; Graf, C; Rühl, E; Blume-Peytavi, U; Lademann, J; Vogt, A; Meinke, M C

2014-05-01

Several nanoparticle-based formulations used in cosmetics and dermatology are exposed to sunlight once applied to the skin. Therefore, it is important to study possible synergistic effects of nanoparticles and ultraviolet radiation. Electron paramagnetic resonance spectroscopy (EPR) was used to detect intracellular free radicals induced by ultraviolet B (UVB) radiation and amorphous silica nanoparticle and to evaluate the influence of nanoparticle surface chemistry on particle cytotoxicity toward HaCaT cells. Uncoated titanium dioxide nanoparticles served as positive control. In addition, particle intracellular uptake, viability, and induction of interleukin-6 were measured. We found that photo-activated titanium dioxide particles induced a significant amount of intracellular free radicals. On the contrary, no intracellular free radicals were generated by the investigated silica nanoparticles in the dark as well as under UVB radiation. However, under UVB exposure, the non-functionalized silica nanoparticles altered the release of IL-6. At the same concentrations, the amino-functionalized silica nanoparticles had no influence on UVB-induced IL-6 release. EPR spectroscopy is a useful technique to measure nanoparticle-induced intracellular free radicals. Non-toxic concentrations of silica particles enhanced the toxicity of UVB radiation. This synergistic effect was not mediated by particle-generated free radicals and correlated with particle surface charge and intracellular distribution. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Free radicals generated during oxidation of green tea polyphenols: electron paramagnetic resonance spectroscopy combined with density functional theory calculations.

PubMed

Severino, Joyce Ferreira; Goodman, Bernard A; Kay, Christopher W M; Stolze, Klaus; Tunega, Daniel; Reichenauer, Thomas G; Pirker, Katharina F

2009-04-15

Electron paramagnetic resonance spectroscopy and density functional theory calculations have been used to investigate the redox properties of the green tea polyphenols (GTPs) (-)-epigallocatechin gallate (EGCG), (-)-epigallocatechin (EGC), and (-)-epicatechin gallate (ECG). Aqueous extracts of green tea and these individual phenols were autoxidized at alkaline pH and oxidized by superoxide anion (O(2)(-)) radicals in dimethyl sulfoxide. Several new aspects of the free radical chemistry of GTPs were revealed. EGCG can be oxidized on both the B and the D ring. The B ring was the main oxidation site during autoxidation, but the D ring was the preferred site for O(2)(-) oxidation. Oxidation of the D ring was followed by structural degradation, leading to generation of a radical identical to that of oxidized gallic acid. Alkaline autoxidation of green tea extracts produced four radicals that were related to products of the oxidation of EGCG, EGC, ECG, and gallic acid, whereas the spectra from O(2)(-) oxidation could be explained solely by radicals generated from EGCG. Assignments of hyperfine coupling constants were made by DFT calculations, allowing the identities of the radicals observed to be confirmed.

Rapid and precise determination of zero-field splittings by terahertz time-domain electron paramagnetic resonance spectroscopy.

PubMed

Lu, Jian; Ozel, I Ozge; Belvin, Carina A; Li, Xian; Skorupskii, Grigorii; Sun, Lei; Ofori-Okai, Benjamin K; Dincă, Mircea; Gedik, Nuh; Nelson, Keith A

2017-11-01

Zero-field splitting (ZFS) parameters are fundamentally tied to the geometries of metal ion complexes. Despite their critical importance for understanding the magnetism and spectroscopy of metal complexes, they are not routinely available through general laboratory-based techniques, and are often inferred from magnetism data. Here we demonstrate a simple tabletop experimental approach that enables direct and reliable determination of ZFS parameters in the terahertz (THz) regime. We report time-domain measurements of electron paramagnetic resonance (EPR) signals associated with THz-frequency ZFSs in molecular complexes containing high-spin transition-metal ions. We measure the temporal profiles of the free-induction decays of spin resonances in the complexes at zero and nonzero external magnetic fields, and we derive the EPR spectra via numerical Fourier transformation of the time-domain signals. In most cases, absolute values of the ZFS parameters are extracted from the measured zero-field EPR frequencies, and the signs can be determined by zero-field measurements at two different temperatures. Field-dependent EPR measurements further allow refined determination of the ZFS parameters and access to the g -factor. The results show good agreement with those obtained by other methods. The simplicity of the method portends wide applicability in chemistry, biology and material science.

Electron Paramagnetic Resonance Oximetry as a Quantitative Method to Measure Cellular Respiration: A Consideration of Oxygen Diffusion Interference

PubMed Central

Presley, Tennille; Kuppusamy, Periannan; Zweier, Jay L.; Ilangovan, Govindasamy

2006-01-01

Electron paramagnetic resonance (EPR) oximetry is being widely used to measure the oxygen consumption of cells, mitochondria, and submitochondrial particles. However, further improvement of this technique, in terms of data analysis, is required to use it as a quantitative tool. Here, we present a new approach for quantitative analysis of cellular respiration using EPR oximetry. The course of oxygen consumption by cells in suspension has been observed to have three distinct zones: pO2-independent respiration at higher pO2 ranges, pO2-dependent respiration at low pO2 ranges, and a static equilibrium with no change in pO2 at very low pO2 values. The approach here enables one to comprehensively analyze all of the three zones together—where the progression of O2 diffusion zones around each cell, their overlap within time, and their potential impact on the measured pO2 data are considered. The obtained results agree with previously established methods such as high-resolution respirometry measurements. Additionally, it is also demonstrated how the diffusion limitations can depend on cell density and consumption rate. In conclusion, the new approach establishes a more accurate and meaningful model to evaluate the EPR oximetry data on cellular respiration to quantify related parameters using EPR oximetry. PMID:17012319

Clearance and Biodistribution of Liposomally Encapsulated Nitroxides: A Model for Targeted Delivery of Electron Paramagnetic Resonance Imaging Probes to Tumors

PubMed Central

Burks, Scott R.; Legenzov, Eric A.; Rosen, Gerald M.

2011-01-01

Electron paramagnetic resonance (EPR) imaging using nitroxides as molecular probes is potentially a powerful tool for the detection and physiological characterization of micrometastatic lesions. Encapsulating nitroxides in anti-HER2 immunoliposomes at high concentrations to take advantage of the “self-quenching” phenomenon of nitroxides allows generation of robust EPR signals in HER2-overexpressing breast tumor cells with minimal background from indifferent tissues or circulating liposomes. We investigated the in vivo pharmacological properties of nitroxides encapsulated in sterically stabilized liposomes designed for long circulation times. We show that circulation times of nitroxides can be extended from hours to days; this increases the proportion of liposomes in circulation to enhance tumor targeting. Furthermore, nitroxides encapsulated in sterically stabilized anti-HER2 immunoliposomes can be delivered to HER2-overexpressing tumors at micromolar concentrations, which should be imageable by EPR. Lastly, after in vivo administration, liposomally encapsulated nitroxide signal also appears in the liver, spleen, and kidneys. Although these organs are spatially distinct and would not hinder tumor imaging in our model, understanding nitroxide signal retention in these organs is essential for further improvements in EPR imaging contrast between tumors and other tissues. These results lay the foundation to use liposomally delivered nitroxides and EPR imaging to visualize tumor cells in vivo. PMID:21737567

Role of crystal field in mixed alkali metal effect: electron paramagnetic resonance study of mixed alkali metal oxyfluoro vanadate glasses.

PubMed

Honnavar, Gajanan V; Ramesh, K P; Bhat, S V

2014-01-23

The mixed alkali metal effect is a long-standing problem in glasses. Electron paramagnetic resonance (EPR) is used by several researchers to study the mixed alkali metal effect, but a detailed analysis of the nearest neighbor environment of the glass former using spin-Hamiltonian parameters was elusive. In this study we have prepared a series of vanadate glasses having general formula (mol %) 40 V2O5-30BaF2-(30 - x)LiF-xRbF with x = 5, 10, 15, 20, 25, and 30. Spin-Hamiltonian parameters of V(4+) ions were extracted by simulating and fitting to the experimental spectra using EasySpin. From the analysis of these parameters it is observed that the replacement of lithium ions by rubidium ions follows a "preferential substitution model". Using this proposed model, we were able to account for the observed variation in the ratio of the g parameter, which goes through a maximum. This reflects an asymmetric to symmetric changeover of the alkali metal ion environment around the vanadium site. Further, this model also accounts for the variation in oxidation state of vanadium ion, which was confirmed from the variation in signal intensity of EPR spectra.

Electron paramagnetic resonance oximetry as a quantitative method to measure cellular respiration: a consideration of oxygen diffusion interference.

PubMed

Presley, Tennille; Kuppusamy, Periannan; Zweier, Jay L; Ilangovan, Govindasamy

2006-12-15

Electron paramagnetic resonance (EPR) oximetry is being widely used to measure the oxygen consumption of cells, mitochondria, and submitochondrial particles. However, further improvement of this technique, in terms of data analysis, is required to use it as a quantitative tool. Here, we present a new approach for quantitative analysis of cellular respiration using EPR oximetry. The course of oxygen consumption by cells in suspension has been observed to have three distinct zones: pO(2)-independent respiration at higher pO(2) ranges, pO(2)-dependent respiration at low pO(2) ranges, and a static equilibrium with no change in pO(2) at very low pO(2) values. The approach here enables one to comprehensively analyze all of the three zones together-where the progression of O(2) diffusion zones around each cell, their overlap within time, and their potential impact on the measured pO(2) data are considered. The obtained results agree with previously established methods such as high-resolution respirometry measurements. Additionally, it is also demonstrated how the diffusion limitations can depend on cell density and consumption rate. In conclusion, the new approach establishes a more accurate and meaningful model to evaluate the EPR oximetry data on cellular respiration to quantify related parameters using EPR oximetry.

Electron paramagnetic resonance investigation on modulatory effect of benidipine on membrane fluidity of erythrocytes in essential hypertension.

PubMed

Tsuda, Kazushi

2008-03-01

It has been shown that benidipine, a long-lasting calcium (Ca) channel blocker, may exert its protective effect against vascular disorders by increasing nitric oxide (NO) production. The purpose of the present study was to investigate whether orally administered benidipine might influence the membrane function in patients with essential hypertension. We measured the membrane fluidity of erythrocytes by using an electron paramagnetic resonance (EPR) and spin-labeling method. In the preliminary study using erythrocytes obtained from healthy volunteers, benidipine decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS in the EPR spectra in vitro. The finding indicated that benidipine increased the membrane fluidity and improved the microviscosity of erythrocytes. In addition, it was demonstrated that the effect of benidipine on membrane fluidity of erythrocytes was significantly potentiated by the NO-substrate, L-arginine. In the separate series of the study, we observed that orally administered benidipine for 4 weeks significantly increased the membrane fluidity of erythrocytes with a concomitant increase in plasma NO metabolite levels in hypertensive subjects. The results of the present study demonstrated that benidipine might increase the membrane fluidity and improve the microviscosity of erythrocytes both in vitro and in vivo, to some extent, by the NO-dependent mechanism. Furthermore, it is strongly suggested that orally administered benidipine might have a beneficial effect on the rheologic behavior of erythrocytes and the improvement of the microcirculation in hypertensive subjects.

Estriol improves membrane fluidity of erythrocytes by the nitric oxide-dependent mechanism: an electron paramagnetic resonance study.

PubMed

Tsuda, K; Shimamoto, Y; Kimura, K; Nishio, I; Masuyama, Y

2001-05-01

The present in vitro study was performed to investigate the effects of estriol (E3) on membrane fluidity of erythrocytes by means of an electron paramagnetic resonance (EPR) and spin-labeling method. E3 was shown to significantly decrease the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes. This finding indicated that E3 might increase the membrane fluidity of erythrocytes. The effect of E3 was significantly potentiated by the nitric oxide (NO) donor, S-nitroso-N-acetylpenicillamine (SNAP), and a cyclic guanosine 3',5'-monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change in the membrane fluidity induced by E3 was antagonized by the NO synthase inhibitor, L-NG-nitroarginine-methyl-ester (L-NAME), and asymmetric dimethyl-L-arginine (ADMA). The results of the present study showed that E3 significantly increased the membrane fluidity and improved the microviscosity of erythrocyte membranes, partially mediated by an NO- and cGMP-dependent pathway. Furthermore, the data might be consistent with the hypothesis that E3 could have a beneficial effect on the rheological behavior of erythrocytes and may play a crucial role in the regulation of microcirculation.

Evaluation of synergistic antioxidant potential of complex mixtures using oxygen radical absorbance capacity (ORAC) and electron paramagnetic resonance (EPR).

PubMed

Parker, Tory L; Miller, Samantha A; Myers, Lauren E; Miguez, Fernando E; Engeseth, Nicki J

2010-01-13

Previous research has demonstrated that certain combinations of compounds result in a decrease in toxic or pro-oxidative effects, previously noted when compounds were administered singly. Thus, there is a need to study many complex interactions further. Two in vitro techniques [electron paramagnetic resonance (EPR) and oxygen radical absorbance capacity (ORAC) assays] were used in this study to assess pro- and antioxidant capacity and synergistic potential of various compounds. Rutin, p-coumaric acid, abscisic acid, ascorbic acid, and a sugar solution were evaluated individually at various concentrations and in all 26 possible combinations at concentrations found in certain foods (honey or papaya), both before and after simulated digestion. EPR results indicated sugar-containing combinations provided significantly higher antioxidant capacity; those combinations containing sugars and ascorbic acid demonstrated synergistic potential. The ORAC assay suggested additive effects, with some combinations having synergistic potential, although fewer combinations were significantly synergistic after digestion. Finally, ascorbic acid, caffeic acid, quercetin, and urate were evaluated at serum-achievable levels. EPR analysis did not demonstrate additive or synergistic potential, although ORAC analysis did, principally in combinations containing ascorbic acid.

Magnetization hysteresis electron paramagnetic resonance. A new null phase insensitive saturation transfer EPR technique with high sensitivity to slow motion.

PubMed Central

Vistnes, A I

1983-01-01

In electron paramagnetic resonance (EPR) nonlinear phenomena with respect to magnetic-field modulation are often studied by out-of-phase spectra recordings. The existence of a nonzero out-of-phase signal implies that the EPR signal is phase shifted relative to the modulation signal. This phase shift is called a magnetization hysteresis. The hysteresis angle varies during a sweep through the resonance conditions for a free radical. By recording this variation, a magnetization hysteresis (MH) spectrum results. In practice, a MH spectrum is computer calculated from two EPR spectra detected with a 90 degree difference in phase setting. There is no need for a careful null-phase calibration like that in traditional analysis of nonlinearities. The MH spectra calculated from second harmonic EPR spectra of spin labels were highly dependent on the rotational correlation time. The technique can therefore be used to study slow molecular motion. In the present work MH spectra and Hemminga and deJager's magnitude saturation transfer EPR spectra (Hemminga, M. A., and P. A. deJager, 1981, J. Magn. Reson., 43:324-327) have been analyzed to define parameters that can describe variations in the rotational correlation time. A novel modification of the sample holder and temperature regulation equipment is described. PMID:6309263

Assessing topology and surface orientation of an antimicrobial peptide magainin 2 using mechanically aligned bilayers and electron paramagnetic resonance spectroscopy.

PubMed

Mayo, Daniel J; Sahu, Indra D; Lorigan, Gary A

2018-07-01

Aligned CW-EPR membrane protein samples provide additional topology interactions that are absent from conventional randomly dispersed samples. These samples are aptly suited to studying antimicrobial peptides because of their dynamic peripheral topology. In this study, four consecutive substitutions of the model antimicrobial peptide magainin 2 were synthesized and labeled with the rigid TOAC spin label. The results revealed the helical tilts to be 66° ± 5°, 76° ± 5°, 70° ± 5°, and 72° ± 5° for the TOAC substitutions H7, S8, A9, and K10 respectively. These results are consistent with previously published literature. Using the EPR (electron paramagnetic resonance) mechanical alignment technique, these substitutions were used to critically assess the topology and surface orientation of the peptide with respect to the membrane. This methodology offers a rapid and simple approach to investigate the structural topology of antimicrobial peptides. Copyright © 2018 Elsevier B.V. All rights reserved.

A Quantitative Method to Monitor Reactive Oxygen Species Production by Electron Paramagnetic Resonance in Physiological and Pathological Conditions

PubMed Central

Mrakic-Sposta, Simona; Gussoni, Maristella; Montorsi, Michela; Porcelli, Simone; Vezzoli, Alessandra

2014-01-01

The growing interest in the role of Reactive Oxygen Species (ROS) and in the assessment of oxidative stress in health and disease clashes with the lack of consensus on reliable quantitative noninvasive methods applicable. The study aimed at demonstrating that a recently developed Electron Paramagnetic Resonance microinvasive method provides direct evidence of the “instantaneous” presence of ROS returning absolute concentration levels that correlate with “a posteriori” assays of ROS-induced damage by means of biomarkers. The reliability of the choice to measure ROS production rate in human capillary blood rather than in plasma was tested (step I). A significant (P < 0.01) linear relationship between EPR data collected on capillary blood versus venous blood (R 2 = 0.95), plasma (R 2 = 0.82), and erythrocytes (R 2 = 0.73) was found. Then (step II) ROS production changes of various subjects' categories, young versus old and healthy versus pathological at rest condition, were found significantly different (range 0.0001–0.05 P level). The comparison of the results with antioxidant capacity and oxidative damage biomarkers concentrations showed that all changes indicating increased oxidative stress are directly related to ROS production increase. Therefore, the adopted method may be an automated technique for a lot of routine in clinical trials. PMID:25374651

Redefining Nitric Oxide Production in Legume Nodules through Complementary Insights from Electron Paramagnetic Resonance Spectroscopy and Specific Fluorescent Probes.

PubMed

Calvo-Begueria, Laura; Rubio, Maria C; Martínez, Jesús I; Pérez-Rontomé, Carmen; Delgado, Maria J; Bedmar, Eulogio J; Becana, Manuel

2018-04-26

Nitric oxide (NO) is a signaling molecule with multiple functions in plants. Given its critical importance and reactivity as a gaseous free radical, we have examined NO production in legume nodules using electron paramagnetic resonance (EPR) spectroscopy and the specific fluorescent dye 4,5-diaminofluorescein diacetate. Also, in this context, we critically assess previous and current views of NO production and detection in nodules. EPR of intact nodules revealed that nitrosyl-leghemoglobin (Lb2+NO) was absent from bean or soybean nodules regardless of nitrate supply, but accumulated in soybean nodules treated with nitrate that were defective in nitrite or nitric oxide reductases or that were exposed to ambient temperature. Consequently, bacteroids are a major source of NO, denitrification enzymes are required for NO homeostasis, and Lb2+NO is not responsible for the inhibition of nitrogen fixation by nitrate. Further, we noted that Lb2+NO is artifactually generated in nodule extracts or in intact nodules not analyzed immediately after detachment. The fluorescent probe detected NO formation in bean and soybean nodule infected cells and in soybean nodule parenchyma. The NO signal was slightly decreased by inhibitors of nitrate reductase but not of nitric oxide synthase, which could indicate a minor contribution of plant nitrate reductase and supports the existence of nitrate- and arginine-independent pathways for NO production. Collectively, our data indicate that EPR and fluorometric methods are complementary to draw reliable conclusions about NO production in plants.

Identifying the Constituents of and Transformations in Diatomaceous Earth and Polysiloxane Foams Through the Use of Electron Paramagnetic Resonance Spectroscopy

NASA Astrophysics Data System (ADS)

Blair, Michael; Muenchausen, Ross; Bennett, Bryan; Smith, James; Stephens, Thomas; Cooke, Wayne

2007-03-01

The chemical aging of polymeric materials is largely governed by the characteristics of the storage environment. For polysiloxane foams, the diatomaceous earth (DE) filler is a small component of the foam, but it plays a large role in the handling of water in the system. The DE filler can act as either a ``source'' or a ``sink'' for water via both chemical hydroxylation/ dehydroxylation and physical adsorption/ desorption processes, depending on the processing history and storage conditions. We have used electron paramagnetic resonance (EPR) spectroscopy to examine composite foam material as well as the DE filler alone. Intense, broad (400 Gauss) resonances were recorded at room temperature as a function of the microwave power at X-band frequency. The observed spectra have been assigned to the iron oxide compounds goethite, lepidocrocite, hematite, and magnetite based upon the measured EPR spectra of these minerals. As the presence or absence of free H2O and the temperature of processing and storage also affects the interconversion of these various iron oxides, we indicate how this process can be followed by monitoring changes in the EPR spectra.

A combined positron emission tomography (PET)-electron paramagnetic resonance imaging (EPRI) system: initial evaluation of a prototype scanner

NASA Astrophysics Data System (ADS)

Tseytlin, Mark; Stolin, Alexander V.; Guggilapu, Priyaankadevi; Bobko, Andrey A.; Khramtsov, Valery V.; Tseytlin, Oxana; Raylman, Raymond R.

2018-05-01

The advent of hybrid scanners, combining complementary modalities, has revolutionized the application of advanced imaging technology to clinical practice and biomedical research. In this project, we investigated the melding of two complementary, functional imaging methods: positron emission tomography (PET) and electron paramagnetic resonance imaging (EPRI). PET radiotracers can provide important information about cellular parameters, such as glucose metabolism. While EPR probes can provide assessment of tissue microenvironment, measuring oxygenation and pH, for example. Therefore, a combined PET/EPRI scanner promises to provide new insights not attainable with current imagers by simultaneous acquisition of multiple components of tissue microenvironments. To explore the simultaneous acquisition of PET and EPR images, a prototype system was created by combining two existing scanners. Specifically, a silicon photomultiplier (SiPM)-based PET scanner ring designed as a portable scanner was combined with an EPRI scanner designed for the imaging of small animals. The ability of the system to obtain simultaneous images was assessed with a small phantom consisting of four cylinders containing both a PET tracer and EPR spin probe. The resulting images demonstrated the ability to obtain contemporaneous PET and EPR images without cross-modality interference. Given the promising results from this initial investigation, the next step in this project is the construction of the next generation pre-clinical PET/EPRI scanner for multi-parametric assessment of physiologically-important parameters of tissue microenvironments.

Electronic paramagnetic resonance investigation of the activity of Origanum vulgare L. essential oil on the Listeria monocytogenes membrane.

PubMed

Serio, A; Chiarini, M; Tettamanti, E; Paparella, A

2010-08-01

To evaluate the effect of oregano essential oil on Listeria monocytogenes cytoplasmic membrane. Nitroxide free-radical Electron Paramagnetic Resonance was applied on L. monocytogenes after 30 min exposure to oregano essential oil concentrations ranging from 0 to 1.25%. The impact of essential oil on the number of viable cells was evaluated by plate count. Growth dynamics of survivors in BHI and TSB were evaluated by turbidometry. After exposure to essential oil concentrations up to 0.50%, the membrane fluidity was changed and its order increased. When L. monocytogenes was exposed to higher concentrations, membrane order parameters slightly returned to the values of untreated cells. However, when the cells were exposed to EO in the presence of sodium azide, which impairs energy metabolism, the membrane fluidity was progressively enhanced, even at the lowest EO concentration (0.25%). Microbiological analyses confirmed a progressive reduction of viable count, at increasing essential oil concentrations. Both in BHI and TSB, the Lag phase length increased in treated cells with respect to controls, suggesting a cell damage recovery. The combined approach including microbiological and EPR analyses provided relevant information on membrane modification and cell response to essential oils. EPR approach was demonstrated to be an effective and helpful tool to comprehend the modifications exerted by essential oil on the bacterial membrane.

Investigation of Antioxidant Activity of Pomegranate Juices by Means of Electron Paramagnetic Resonance and UV-Vis Spectroscopy.

PubMed

Kozik, Violetta; Jarzembek, Krystyna; Jędrzejowska, Agnieszka; Bąk, Andrzej; Polak, Justyna; Bartoszek, Mariola; Pytlakowska, Katarzyna

2015-01-01

Pomegranate fruit (Punica granatum L.) is a source of numerous phenolic compounds, and it contains flavonoids such as anthocyanins, anthocyanidins, cyanidins, catechins and other complexes of flavonoids, ellagitannins, and hydrolyzed tannins. Pomegranate juice shows antioxidant, antiproliferative, and anti-atherosclerotic properties. The antioxidant capacity (TEAC) of the pomegranate juices was measured using electron paramagnetic resonance (EPR) spectroscopy and 1,1-diphenyl-2-picrylhydrazyl (DPPH•) as a source of free radicals, and the total phenolic (TP) content was measured using UV-Vis spectroscopy. All the examined pomegranate juices exhibited relatively high antioxidant properties. The TEAC values determined by means of EPR spectroscopy using Trolox (TE) as a free radical scavenger were in the range of 463.12 to 1911.91 μmol TE/100 mL juice. The TP content measured by the Folin-Ciocalteu method, using gallic acid (GA) as a free radical scavenger, widely varied in the investigated pomegranate juice samples and ranged from 1673.62 to 5263.87 mg GA/1 L juice. The strongest antioxidant properties were observed with the fresh pomegranate juices obtained from the fruits originating from Israel, Lebanon, and Azerbaijan. Correlation analysis of numerical data obtained by means of EPR spectroscopy (TEAC) and UV-Vis spectroscopy (TP) gave correlation coefficient (r)=0.90 and determination coefficient (r2)=0.81 (P<0.05).

Binding of manganese(II) to a tertiary stabilized hammerhead ribozyme as studied by electron paramagnetic resonance spectroscopy

PubMed Central

KISSELEVA, NATALIA; KHVOROVA, ANASTASIA; WESTHOF, ERIC; SCHIEMANN, OLAV

2005-01-01

Electron paramagnetic resonance (EPR) spectroscopy is used to study the binding of MnII ions to a tertiary stabilized hammer-head ribozyme (tsHHRz) and to compare it with the binding to the minimal hammerhead ribozyme (mHHRz). Continuous wave EPR measurements show that the tsHHRz possesses a single high-affinity MnII binding site with a KD of ≤10 nM at an NaCl concentration of 0.1 M. This dissociation constant is at least two orders of magnitude smaller than the KD determined previously for the single high-affinity MnII site in the mHHRz. In addition, whereas the high-affinity MnII is displaced from the mHHRz upon binding of the aminoglycoside antibiotic neomycin B, it is not from the tsHHRz. Despite these pronounced differences in binding, a comparison between the electron spin echo envelope modulation and hyperfine sublevel correlation spectra of the minimal and tertiary stabilized HHRz demonstrates that the structure of both binding sites is very similar. This suggests that the MnII is located in both ribozymes between the bases A9 and G10.1 of the sheared G · A tandem base pair, as shown previously and in detail for the mHHRz. Thus, the much stronger MnII binding in the tsHHRz is attributed to the interaction between the two external loops, which locks in the RNA fold, trapping the MnII in the tightly bound conformation, whereas the absence of long-range loop–loop interactions in the mHHRz leads to more dynamical and open conformations, decreasing MnII binding. PMID:15611296

Structural characterization of titania by X-ray diffraction, photoacoustic, Raman spectroscopy and electron paramagnetic resonance spectroscopy.

PubMed

Kadam, R M; Rajeswari, B; Sengupta, Arijit; Achary, S N; Kshirsagar, R J; Natarajan, V

2015-02-25

A titania mineral (obtained from East coast, Orissa, India) was investigated by X-ray diffraction (XRD), photoacoustic spectroscopy (PAS), Raman and Electron Paramagnetic Resonance (EPR) studies. XRD studies indicated the presence of rutile (91%) and anatase (9%) phases in the mineral. Raman investigation supported this information. Both rutile and anatase phases have tetragonal structure (rutile: space group P4(2)/mnm, a=4.5946(1) Å, c=2.9597(1) Å, V=62.48(1) (Å)(3), Z=2; anatase: space group I4(1)/amd, 3.7848(2) Å, 9.5098(11) Å, V=136.22(2) (Å)(3), Z=4). The deconvoluted PAS spectrum showed nine peaks around 335, 370, 415,485, 555, 605, 659, 690,730 and 785 nm and according to the ligand field theory, these peaks were attributed to the presence of V(4+), Cr(3+), Mn(4+) and Fe(3+) species. EPR studies revealed the presence of transition metal ions V(4+)(d(1)), Cr(3+)(d(3)), Mn(4+)(d(3)) and Fe(3+)(d(5)) at Ti(4+) sites. The EPR spectra are characterized by very large crystal filed splitting (D term) and orthorhombic distortion term (E term) for multiple electron system (s>1) suggesting that the transition metal ions substitute the Ti(4+) in the lattice which is situated in distorted octahedral coordination of oxygen. The possible reasons for observation of unusually large D and E term in the EPR spectra of transition metal ions (S=3/2 and 5/2) are discussed. Copyright © 2014 Elsevier B.V. All rights reserved.

Electron localization and optical absorption of polygonal quantum rings

NASA Astrophysics Data System (ADS)

Sitek, Anna; Serra, Llorenç; Gudmundsson, Vidar; Manolescu, Andrei

2015-06-01

We investigate theoretically polygonal quantum rings and focus mostly on the triangular geometry where the corner effects are maximal. Such rings can be seen as short core-shell nanowires, a generation of semiconductor heterostructures with multiple applications. We show how the geometry of the sample determines the electronic energy spectrum, and also the localization of electrons, with effects on the optical absorption. In particular, we show that irrespective of the ring shape low-energy electrons are always attracted by corners and are localized in their vicinity. The absorption spectrum in the presence of a magnetic field shows only two peaks within the corner-localized state domain, each associated with different circular polarization. This picture may be changed by an external electric field which allows previously forbidden transitions, and thus enables the number of corners to be determined. We show that polygonal quantum rings allow absorption of waves from distant ranges of the electromagnetic spectrum within one sample.

Application of Electron Paramagnetic Resonance Spectroscopy to Comparative Examination of Different Groups of Free Radicals in Thermal Injuries Treated with Propolis and Silver Sulphadiazine

PubMed Central

Olczyk, Pawel; Ramos, Pawel; Bernas, Marcin; Komosinska-Vassev, Katarzyna; Stojko, Jerzy; Pilawa, Barbara

2013-01-01

Different groups of free radicals expressed in burn wounds treated with propolis and silver sulphadiazine were examined. The thermal effect forms major types of free radicals in a wound because of the breaking of chemical bonds. Free radicals, located in the heated skin, were tested after 21 days of treating by these two substances. The aim of this work was to find the method for determination of types and concentrations of different groups of free radicals in wound after high temperature impact during burning. The effects of the therapy by propolis and silver sulphadiazine on free radicals were studied. Since the chemical methods of free radicals studies are destructive, the usefulness of the electron paramagnetic resonance spectroscopy was tested in this work. The electron paramagnetic resonance spectra measured with the microwave power of 2.2 mW were numerically fitted by theoretical curves of Gaussian and Lorentzian shapes. The experimental electron paramagnetic resonance spectra of tissue samples are best fitted by the sum of one Gauss and two Lorentz lines. An innovatory numerical procedure of spectroscopic skin analysis was presented. It is very useful in the alternative medicine studies. PMID:23762162

Electron paramagnetic resonance analysis of La(1-x)M(x)MnO(3+δ) (M = Ce, Sr) perovskite-like nanostructured catalysts.

PubMed

Oliva, Cesare; Allieta, Mattia; Scavini, Marco; Biffi, Cesare; Rossetti, Ilenia; Forni, Lucio

2012-08-06

The physical-chemical properties of some nanostructured perovskite-like catalysts of general formula La(1-x)M(x)MnO(3+δ) (M = Ce, Sr) have been investigated, in particular by using the electron paramagnetic resonance (EPR) technique. We show that the interplay between the -O-Mn(3+)-O-Mn(4+)-O- electron double-exchange and the electron mobility is strictly dependent on the dopant nature and the annealing conditions in air. A relationship between the observed properties of these samples and their activity in the methane flameless catalytic combustion is proposed.

Burn trauma in skeletal muscle results in oxidative stress as assessed by in vivo electron paramagnetic resonance

PubMed Central

KHAN, NADEEM; MUPPARAJU, SRIRAM P.; MINTZOPOULOS, DIONYSSIOS; KESARWANI, MEENU; RIGHI, VALERIA; RAHME, LAURENCE G.; SWARTZ, HAROLD M.; TZIKA, A. ARIA

2010-01-01

Using a mouse model, we tested the hypotheses that severe burn trauma causes metabolic disturbances in skeletal muscle, and that these can be measured and repeatedly followed by in vivo electron paramagnetic resonance (EPR). We used a 1.2-GHz (L-band) EPR spectrometer to measure partial pressure of oxygen (pO2) levels, redox status and oxidative stress following a non-lethal burn trauma model to the left hind limbs of mice. Results obtained in the burned mouse gastrocnemius muscle indicated a significant decrease in tissue pO2 immediately (P=0.032) and at 6 h post burn (P=0.004), compared to the gastrocnemius of the unburned hind limb. The redox status of the skeletal muscle also peaked at 6 h post burn (P=0.027) in burned mice. In addition, there was an increase in the EPR signal of the nitroxide produced by oxidation of the hydroxylamine (CP-H) probe at 12 h post burn injury, indicating a burn-induced increase in mitochondrial reactive oxygen species (ROS). The nitroxide signal continued to increase between 12 and 24 h, suggesting a further increase in ROS generation post burn. These results confirm genomic results, which indicate a downregulation of antioxidant genes and therefore strongly suggest the dysfunction of the mitochondrial oxidative system. We believe that the direct measurement of tissue parameters such as pO2, redox and ROS by EPR may be used to complement measurements by nuclear magnetic resonance (NMR) in order to assess tissue damage and the therapeutic effectiveness of antioxidant agents in severe burn trauma. PMID:21179378

Electron paramagnetic resonance (EPR) dosimetry using lithium formate in radiotherapy: comparison with thermoluminescence (TL) dosimetry using lithium fluoride rods.

PubMed

Vestad, Tor Arne; Malinen, Eirik; Olsen, Dag Rune; Hole, Eli Olaug; Sagstuen, Einar

2004-10-21

Solid-state radiation dosimetry by electron paramagnetic resonance (EPR) spectroscopy and thermoluminescence (TL) was utilized for the determination of absorbed doses in the range of 0.5-2.5 Gy. The dosimeter materials used were lithium formate and lithium fluoride (TLD-100 rods) for EPR dosimetry and TL dosimetry, respectively. 60Co gamma-rays and 4, 6, 10 and 15 MV x-rays were employed. The main objectives were to compare the variation in dosimeter reading of the respective dosimetry systems and to determine the photon energy dependence of the two dosimeter materials. The EPR dosimeter sensitivity was constant over the dose range in question, while the TL sensitivity increased by more than 5% from 0.5 to 2.5 Gy, thus displaying a supralinear dose response. The average relative standard deviation in the dosimeter reading per dose was 3.0% and 1.2% for the EPR and TL procedures, respectively. For EPR dosimeters, the relative standard deviation declined significantly from 4.3% to 1.1% over the dose range in question. The dose-to-water energy response for the megavoltage x-ray beams relative to 60Co gamma-rays was in the range of 0.990-0.979 and 0.984-0.962 for lithium formate and lithium fluoride, respectively. The results show that EPR dosimetry with lithium formate provides dose estimates with a precision comparable to that of TL dosimetry (using lithium fluoride) for doses above 2 Gy, and that lithium formate is slightly less dependent on megavoltage photon beam energy than lithium fluoride.

Electron paramagnetic resonance (EPR) dosimetry using lithium formate in radiotherapy: comparison with thermoluminescence (TL) dosimetry using lithium fluoride rods

NASA Astrophysics Data System (ADS)

Vestad, Tor Arne; Malinen, Eirik; Rune Olsen, Dag; Olaug Hole, Eli; Sagstuen, Einar

2004-10-01

Solid-state radiation dosimetry by electron paramagnetic resonance (EPR) spectroscopy and thermoluminescence (TL) was utilized for the determination of absorbed doses in the range of 0.5-2.5 Gy. The dosimeter materials used were lithium formate and lithium fluoride (TLD-100 rods) for EPR dosimetry and TL dosimetry, respectively. 60Co ggr-rays and 4, 6, 10 and 15 MV x-rays were employed. The main objectives were to compare the variation in dosimeter reading of the respective dosimetry systems and to determine the photon energy dependence of the two dosimeter materials. The EPR dosimeter sensitivity was constant over the dose range in question, while the TL sensitivity increased by more than 5% from 0.5 to 2.5 Gy, thus displaying a supralinear dose response. The average relative standard deviation in the dosimeter reading per dose was 3.0% and 1.2% for the EPR and TL procedures, respectively. For EPR dosimeters, the relative standard deviation declined significantly from 4.3% to 1.1% over the dose range in question. The dose-to-water energy response for the megavoltage x-ray beams relative to 60Co ggr-rays was in the range of 0.990-0.979 and 0.984-0.962 for lithium formate and lithium fluoride, respectively. The results show that EPR dosimetry with lithium formate provides dose estimates with a precision comparable to that of TL dosimetry (using lithium fluoride) for doses above 2 Gy, and that lithium formate is slightly less dependent on megavoltage photon beam energy than lithium fluoride.

Measuring “Free” Iron Levels in Caenorhabditis Elegans Using Low-Temperature Fe(III) Electron Paramagnetic Resonance Spectroscopy

PubMed Central

Pate, Kira T.; Rangel, Natalie A.; Fraser, Brian; Clement, Matthew H. S.; Srinivasan, Chandra

2007-01-01

Oxidative stress, caused by free radicals within the body, has been associated with the process of aging and many human diseases. As free radicals, in particular superoxide, are difficult to measure, an alternative indirect method for measuring oxidative stress levels has been successfully used in E. coli and yeast. This method is based on a proposed connection between elevated superoxide levels and release of iron from solvent exposed [4Fe-4S] enzyme clusters, which eventually leads to an increase in hydroxyl radical production. In past studies using bacteria and yeast, a positive correlation was found between superoxide production or oxidative stress due to superoxide within the organism and EPR (electron paramagnetic resonance) detectable “free” iron levels. In the present study, we have developed a reliable and an efficient method for measuring “free” iron levels in C. elegans using low temperature Fe(III) EPR at g = 4.3. This method utilizes synchronized worm cultures grown on plates, which are homogenized and treated with desferrioxamine, an Fe(III) chelator, prior to packing the EPR tube. Homogenization was found not to alter “free” iron levels, while desferrioxamine treatment significantly raised these levels, indicating presence of both Fe(II) and Fe(III) in the “free” iron pool. The correlation between free radical levels and the observed “free” iron levels was examined by using heat stress and paraquat treatment. The intensity of the Fe(III) EPR signal and thus, the concentration of the “free” iron pool, varied with the treatments that altered radical levels without changing the total iron levels. This study provides the groundwork needed to uncover the correlation between oxidative stress, “free” iron levels, and longevity in C. elegans. PMID:17010298

In Vivo Formation of Electron Paramagnetic Resonance-Detectable Nitric Oxide and of Nitrotyrosine Is Not Impaired during Murine Leishmaniasis

PubMed Central

Giorgio, Selma; Linares, Edlaine; Ischiropoulos, Harry; Von Zuben, Fernando José; Yamada, Aureo; Augusto, Ohara

1998-01-01

Recent studies have provided evidence for a dual role of nitric oxide (NO) during murine leishmaniasis. To explore this problem, we monitored the formation of NO and its derived oxidants during the course of Leishmania amazonensis infection in tissues of susceptible (BALB/c) and relatively resistant (C57BL/6) mice. NO production was detected directly by low-temperature electron paramagnetic resonance spectra of animal tissues. Both mouse strains presented detectable levels of hemoglobin nitrosyl (HbNO) complexes and of heme nitrosyl and iron-dithiol-dinitrosyl complexes in the blood and footpad lesions, respectively. Estimation of the nitrosyl complex levels demonstrated that most of the NO is synthesized in the footpad lesions. In agreement, immunohistochemical analysis of the lesions demonstrated the presence of nitrotyrosine in proteins of macrophage vacuoles and parasites. Since macrophages lack myeloperoxidase, peroxynitrite is likely to be the nitrating NO metabolite produced during the infection. The levels of HbNO complexes in the blood reflected changes occurring during the infection such as those in parasite burden and lesion size. The maximum levels of HbNO complexes detected in the blood of susceptible mice were higher than those of C57BL/6 mice but occurred at late stages of infection and were accompanied by the presence of bacteria in the cutaneous lesions. The results indicate that the local production of NO is an important mechanism for the elimination of parasites if it occurs before the parasite burden becomes too high. From then on, elevated production of NO and derived oxidants aggravates the inflammatory process with the occurrence of a hypoxic environment that may favor secondary infections. PMID:9453645

Electron-paramagnetic-resonance studies on nitrogenase of Klebsiella pneumoniae. Evidence for acetylene- and ethylene-nitrogenase transient complexes.

PubMed Central

Lowe, D J; Eady, R R; Thorneley, N F

1978-01-01

Klebsiella pneumoniae nitrogenase exhibited four new electron-paramagnetic-resonance signals during turnover at 10 degrees C, pH7.4, which were assigned to intermediates present in low concentrations in the steady state. 57Fe-substituted Mo--Fe protein showed that they arose from Fe--S clusters in the Mo--Fe protein of nitrogenase. The new signals are designated: Ic, g values at 4.67, 3.37 and approx. 2.0; VI, g values at 2.125, 2.000 and 2.000; VII, g values at 5.7 and 5.4; VIII, g values at 2.092, 1.974 and 1.933. The sharp axial signal VI arises from a Fe4S4 cluster at the --1 oxidation level. This signal was only detected in the presence of ethylene and provides the first evidence of an enzyme--product complex for nitrogenase. [13C]Acetylene and [13C]ethylene provided no evidence for direct binding of this substrate and product to the Fe--S clusters giving rise to these signals. The dependence of signal intensities on acetylene concentration indicated two types of binding site, with apparent dissociation constants K less than 16 micron and K approximately 13mM. A single binding site for ethylene (K=1.5mM) was detected. A scheme is proposed for the mechanism of reduction of acetylene to ethylene and inhibition of this reaction by CO. PMID:210766

A versatile and modular quasi optics-based 200 GHz dual dynamic nuclear polarization and electron paramagnetic resonance instrument

NASA Astrophysics Data System (ADS)

Siaw, Ting Ann; Leavesley, Alisa; Lund, Alicia; Kaminker, Ilia; Han, Songi

2016-03-01

Solid-state dynamic nuclear polarization (DNP) at higher magnetic fields (>3 T) and cryogenic temperatures (∼2-90 K) has gained enormous interest and seen major technological advances as an NMR signal enhancing technique. Still, the current state of the art DNP operation is not at a state at which sample and freezing conditions can be rationally chosen and the DNP performance predicted a priori, but relies on purely empirical approaches. An important step towards rational optimization of DNP conditions is to have access to DNP instrumental capabilities to diagnose DNP performance and elucidate DNP mechanisms. The desired diagnoses include the measurement of the "DNP power curve", i.e. the microwave (MW) power dependence of DNP enhancement, the "DNP spectrum", i.e. the MW frequency dependence of DNP enhancement, the electron paramagnetic resonance (EPR) spectrum, and the saturation and spectral diffusion properties of the EPR spectrum upon prolonged MW irradiation typical of continuous wave (CW) DNP, as well as various electron and nuclear spin relaxation parameters. Even basic measurements of these DNP parameters require versatile instrumentation at high magnetic fields not commercially available to date. In this article, we describe the detailed design of such a DNP instrument, powered by a solid-state MW source that is tunable between 193 and 201 GHz and outputs up to 140 mW of MW power. The quality and pathway of the transmitted and reflected MWs is controlled by a quasi-optics (QO) bridge and a corrugated waveguide, where the latter couples the MW from an open-space QO bridge to the sample located inside the superconducting magnet and vice versa. Crucially, the versatility of the solid-state MW source enables the automated acquisition of frequency swept DNP spectra, DNP power curves, the diagnosis of MW power and transmission, and frequency swept continuous wave (CW) and pulsed EPR experiments. The flexibility of the DNP instrument centered around the QO MW

A versatile and modular quasi optics-based 200 GHz dual dynamic nuclear polarization and electron paramagnetic resonance instrument

PubMed Central

Siaw, Ting Ann; Leavesley, Alisa; Lund, Alicia; Kaminker, Ilia; Han, Songi

2016-01-01

Solid-state dynamic nuclear polarization (DNP) at higher magnetic fields (>3 T) and cryogenic temperatures (~2–90 K) has gained enormous interest and seen major technological advances as an NMR signal enhancing technique. Still, the current state of the art DNP operation is not at a state at which sample and freezing conditions can be rationally chosen and the DNP performance predicted a priori, but relies on purely empirical approaches. An important step towards rational optimization of DNP conditions is to have access to DNP instrumental capabilities to diagnose DNP performance and elucidate DNP mechanisms. The desired diagnoses include the measurement of the “DNP power curve”, i.e. the microwave (MW) power dependence of DNP enhancement, the “DNP spectrum”, i.e. the MW frequency dependence of DNP enhancement, the electron paramagnetic resonance (EPR) spectrum and the saturation and spectral diffusion properties of the EPR spectrum upon prolonged MW irradiation typical of continuous wave (CW) DNP, as well as various electron and nuclear spin relaxation parameters. Even basic measurements of these DNP parameters require versatile instrumentation at high magnetic fields not commercially available to date. In this article, we describe the detailed design of such a DNP instrument, powered by a solid-state MW source that is tunable between 193 – 201 GHz and outputs up to 140 mW of MW power. The quality and pathway of the transmitted and reflected MWs is controlled by a quasi-optics (QO) bridge and a corrugated waveguide, where the latter couples the MW from an open-space QO bridge to the sample located inside the superconducting magnet and vice versa. Crucially, the versatility of the solid-state MW source enables the automated acquisition of frequency swept DNP spectra, DNP power curves, the diagnosis of MW power and transmission, and frequency swept continuous wave (CW) and pulsed EPR experiments. The flexibility of the DNP instrument centered around the

A versatile and modular quasi optics-based 200GHz dual dynamic nuclear polarization and electron paramagnetic resonance instrument.

PubMed

Siaw, Ting Ann; Leavesley, Alisa; Lund, Alicia; Kaminker, Ilia; Han, Songi

2016-03-01

Solid-state dynamic nuclear polarization (DNP) at higher magnetic fields (>3T) and cryogenic temperatures (∼ 2-90K) has gained enormous interest and seen major technological advances as an NMR signal enhancing technique. Still, the current state of the art DNP operation is not at a state at which sample and freezing conditions can be rationally chosen and the DNP performance predicted a priori, but relies on purely empirical approaches. An important step towards rational optimization of DNP conditions is to have access to DNP instrumental capabilities to diagnose DNP performance and elucidate DNP mechanisms. The desired diagnoses include the measurement of the "DNP power curve", i.e. the microwave (MW) power dependence of DNP enhancement, the "DNP spectrum", i.e. the MW frequency dependence of DNP enhancement, the electron paramagnetic resonance (EPR) spectrum, and the saturation and spectral diffusion properties of the EPR spectrum upon prolonged MW irradiation typical of continuous wave (CW) DNP, as well as various electron and nuclear spin relaxation parameters. Even basic measurements of these DNP parameters require versatile instrumentation at high magnetic fields not commercially available to date. In this article, we describe the detailed design of such a DNP instrument, powered by a solid-state MW source that is tunable between 193 and 201 GHz and outputs up to 140 mW of MW power. The quality and pathway of the transmitted and reflected MWs is controlled by a quasi-optics (QO) bridge and a corrugated waveguide, where the latter couples the MW from an open-space QO bridge to the sample located inside the superconducting magnet and vice versa. Crucially, the versatility of the solid-state MW source enables the automated acquisition of frequency swept DNP spectra, DNP power curves, the diagnosis of MW power and transmission, and frequency swept continuous wave (CW) and pulsed EPR experiments. The flexibility of the DNP instrument centered around the QO MW

Electron paramagnetic resonance, scanning electron microscopy with energy dispersion X-ray spectrometry, X-ray powder diffraction, and NMR characterization of iron-rich fired clays.

PubMed

Presciutti, Federica; Capitani, Donatella; Sgamellotti, Antonio; Brunetti, Brunetto Giovanni; Costantino, Ferdinando; Viel, Stéphane; Segre, Annalaura

2005-12-01

The aim of this study is to clarify the structure of an iron-rich clay and the structural changes involved in the firing process as a preliminary step to get information on ancient ceramic technology. To this purpose, illite-rich clay samples fired at different temperatures were characterized using a multitechnique approach, i.e., by electron paramagnetic resonance, scanning electron microscopy with electron dispersion X-ray spectrometry, X-ray powder diffraction, magic angle spinning and multiple quantum magic angle spinning NMR. During firing, four main reaction processes occur: dehydration, dehydroxylation, structural breakdown, and recrystallization. When the results are combined from all characterization methods, the following conclusions could be obtained. Interlayer H2O is located close to aluminum in octahedral sites and is driven off at temperatures lower than 600 degrees C. Between 600 and 700 degrees C dehydroxylation occurs whereas, between 800 and 900 degrees C, the aluminum in octahedral sites disappears, due to the breakdown of the illite structure, and all iron present is oxidized to Fe3+. In samples fired at 1000 and 1100 degrees C iron clustering was observed as well as large single crystals of iron with the occurrence of ferro- or ferrimagnetic effects. Below 900 degrees C the aluminum in octahedral sites presents a continuous distribution of chemical shift, suggesting the presence of slightly distorted sites. Finally, over the whole temperature range, the presence of at least two tetrahedral aluminum sites was revealed, characterized by different values of the quadrupolar coupling constant.

A photoluminescence, thermoluminescence and electron paramagnetic resonance study of EFG grown europium doped lithium fluoride (LiF) crystals

NASA Astrophysics Data System (ADS)

Seth, Pooja; Swati, G.; Haranath, D.; Rao, S. M. D.; Aggarwal, Shruti

2018-07-01

Europium (Eu) doped LiF crystals have been grown by the Edge-defined film fed growth (EFG) technique. The designing and installation of the furnace used for the growth of the crystals have been discussed in detail. In the present study, Eu (Eu2O3) has been doped in LiF in different concentration (0.02-0.2 wt %). X-ray diffractometry (XRD) and Energy Dispersive X-ray (EDX) spectroscopy confirms the incorporation of Eu in LiF. The influence of Eu on LiF has been investigated through photoluminescence (PL), thermoluminescence (TL) and electron paramagnetic resonance (EPR) in as-grown and annealed crystals. PL emission spectra shows the presence of both Eu3+ and Eu2+ form in the as-grown crystals which is confirmed by EPR results. Whereas, in annealed crystals, Eu is present predominantly as Eu2+ form. This suggests that growing crystals at high temperature (∼900 °C) in argon gas atmosphere through EFG technique favours the reduction of Eu3+ → Eu2+. This reduction phenomenon has been explained on the basis of charge compensation model. TL study of the LiF: Eu (0.02-0.2 wt %) crystals has been done after irradiation with Co60 gamma rays. In this study, it has been observed that the TL intensity as well as glow curve structure of LiF: Eu crystals are a strong function of Eu concentration. The maximum TL is observed at Eu concentration of 0.05 wt% at which a well defined glow curve structure with a prominent peak at 185 °C and a small peak at 253 °C. Beyond this concentration (0.05 wt %), TL intensity decreases due to aggregation of defects in the host. The peak at 185 °C in LiF: Eu (0.05 wt %) is certainly due to the presence of Eu2+ associated defects which is also supported by the PL spectra. It has been observed that Eu doping have a key role in creation of more defect levels which lead to the increased number of electron and hole traps. Further, trapping parameters are analysed using glow curve deconvolution method to have an insight study of TL phenomena

Using Hyperfine Electron Paramagnetic Resonance Spectroscopy to Define the Proton-Coupled Electron Transfer Reaction at Fe-S Cluster N2 in Respiratory Complex I.

PubMed

Le Breton, Nolwenn; Wright, John J; Jones, Andrew J Y; Salvadori, Enrico; Bridges, Hannah R; Hirst, Judy; Roessler, Maxie M

2017-11-15

Energy-transducing respiratory complex I (NADH:ubiquinone oxidoreductase) is one of the largest and most complicated enzymes in mammalian cells. Here, we used hyperfine electron paramagnetic resonance (EPR) spectroscopic methods, combined with site-directed mutagenesis, to determine the mechanism of a single proton-coupled electron transfer reaction at one of eight iron-sulfur clusters in complex I, [4Fe-4S] cluster N2. N2 is the terminal cluster of the enzyme's intramolecular electron-transfer chain and the electron donor to ubiquinone. Because of its position and pH-dependent reduction potential, N2 has long been considered a candidate for the elusive "energy-coupling" site in complex I at which energy generated by the redox reaction is used to initiate proton translocation. Here, we used hyperfine sublevel correlation (HYSCORE) spectroscopy, including relaxation-filtered hyperfine and single-matched resonance transfer (SMART) HYSCORE, to detect two weakly coupled exchangeable protons near N2. We assign the larger coupling with A( 1 H) = [-3.0, -3.0, 8.7] MHz to the exchangeable proton of a conserved histidine and conclude that the histidine is hydrogen-bonded to N2, tuning its reduction potential. The histidine protonation state responds to the cluster oxidation state, but the two are not coupled sufficiently strongly to catalyze a stoichiometric and efficient energy transduction reaction. We thus exclude cluster N2, despite its proton-coupled electron transfer chemistry, as the energy-coupling site in complex I. Our work demonstrates the capability of pulse EPR methods for providing detailed information on the properties of individual protons in even the most challenging of energy-converting enzymes.

Cerebral Oxygenation in Awake Rats during Acclimation and Deacclimation to Hypoxia: An In Vivo Electron Paramagnetic Resonance Study

PubMed Central

Khan, Mohammad N.; Hou, Huagang G.; Merlis, Jennifer; Abajian, Michelle A.; Demidenko, Eugene; Grinberg, Oleg Y.; Swartz, Harold M.

2011-01-01

Abstract Dunn, J. F., N. Khan, H. G. Hou, J. Merlis, M. A. Abajian, E. Demidenko, O.Y. Grinberg, and H. M. Swartz. Cerebral oxygenation in awake rats during acclimation and deacclimation to hypoxia: an in vivo EPR study. High Alt. Med. Biol. 12:71–77, 2011.— Exposure to high altitude or hypobaric hypoxia results in a series of metabolic, physiologic, and genetic changes that serve to acclimate the brain to hypoxia. Tissue Po2 (Pto2) is a sensitive index of the balance between oxygen delivery and utilization and can be considered to represent the summation of such factors as cerebral blood flow, capillary density, hematocrit, arterial Po2, and metabolic rate. As such, it can be used as a marker of the extent of acclimation. We developed a method using electron paramagnetic resonance (EPR) to measure Pto2 in unanesthetized subjects with a chronically implanted sensor. EPR was used to measure rat cortical tissue Pto2 in awake rats during acute hypoxia and over a time course of acclimation and deacclimation to hypobaric hypoxia. This was done to simulate the effects on brain Pto2 of traveling to altitude for a limited period. Acute reduction of inspired O2 to 10% caused a decline from 26.7 ± 2.2 to 13.0 ± 1.5 mmHg (mean ± SD). Addition of 10% CO2 to animals breathing 10% O2 returned Pto2 to values measured while breathing 21% O2, indicating that hypercapnia can reverse the effects of acute hypoxia. Pto2 in animals acclimated to 10% O2 was similar to that measured preacclimation when breathing 21% O2. Using a novel, individualized statistical model, it was shown that the T1/2 of the Pto2 response during exposure to chronic hypoxia was approximately 2 days. This indicates a capacity for rapid adaptation to hypoxia. When subjects were returned to normoxia, there was a transient hyperoxygenation, followed by a return to lower values with a T1/2 of deacclimation of 1.5 to 3 days. These data indicate that exposure to hypoxia results in significant

SU-C-BRD-05: Non-Invasive in Vivo Biodosimetry in Radiotherapy Patients Using Electron Paramagnetic Resonance (EPR) Spectroscopy

SciTech Connect

Bahar, N; Roberts, K; Stabile, F

Purpose: Medical intervention following a major, unplanned radiation event can elevate the human whole body exposure LD50 from 3 to 7 Gy. On a large scale, intervention cannot be achieved effectively without accurate and efficient triage. Current methods of retrospective biodosimetry are restricted in capability and applicability; published human data is limited. We aim to further develop, validate, and optimize an automated field-deployable in vivo electron paramagnetic resonance (EPR) instrument that can fill this need. Methods: Ionizing radiation creates highly-stable, carbonate-based free radicals within tooth enamel. Using a process similar to nuclear magnetic resonance, EPR directly measures the presence ofmore » radiation-induced free radicals. We performed baseline EPR measurements on one of the upper central incisors of total body irradiation (TBI) and head and neck (H&N) radiotherapy patients before their first treatment. Additional measurements were performed between subsequent fractions to examine the EPR response with increasing radiation dose. Independent dosimetry measurements were performed with optically-stimulated luminescent dosimeters (OSLDs) and diodes to more accurately establish the relationship between EPR signal and delivered radiation dose. Results: 36 EPR measurements were performed over the course of four months on two TBI and four H & N radiotherapy patients. We observe a linear increase in EPR signal with increasing dose across the entirety of the tested range. A linear least squares-weighted fit of delivered dose versus measured signal amplitude yields an adjusted R-square of 0.966. The standard error of inverse prediction (SEIP) is 1.77 Gy. For doses up to 7 Gy, the range most relevant to triage, we calculate an SEIP of 1.29 Gy. Conclusion: EPR spectroscopy provides a promising method of retrospective, non-invasive, in vivo biodosimetry. Our preliminary data show an excellent correlation between predicted signal amplitude and

Improved apparatus for trapped radical and other studies down to 1.5 K. [microwave cavity cryogenic equipment for electron paramagnetic resonance experiments

NASA Technical Reports Server (NTRS)

Woollam, J. A.; Sugawara, K.

1978-01-01

A Dewar system and associated equipment for electron paramagnetic resonance (EPR) studies of trapped free radicals and other optical or irradiation experiments are described. The apparatus is capable of reaching a temperature of 1.5 K and transporting on the order of 20 W per K temperature gradient; its principal advantages are for use at pumped cryogen temperatures and for experiments with large heat inputs. Two versions of the apparatus are discussed, one of which is designed for EPR in a rectangular cavity operating in a TE(102) mode and another in which EPR is performed in a cylindrical microwave cavity.

NASA three-laser airborne differential absorption lidar system electronics

NASA Technical Reports Server (NTRS)

Allen, R. J.; Copeland, G. D.

1984-01-01

The system control and signal conditioning electronics of the NASA three laser airborne differential absorption lidar (DIAL) system are described. The multipurpose DIAL system was developed for the remote measurement of gas and aerosol profiles in the troposphere and lower stratosphere. A brief description and photographs of the majority of electronics units developed under this contract are presented. The precision control system; which includes a master control unit, three combined NASA laser control interface/quantel control units, and three noise pulse discriminator/pockels cell pulser units; is described in detail. The need and design considerations for precision timing and control are discussed. Calibration procedures are included.

Electron Paramagnetic Resonance: Elementary Theory and Practical Applications, Second Edition (John A. Weil and James R. Bolton)

NASA Astrophysics Data System (ADS)

Williams, Ffrancon

2009-01-01

The detection of electron magnetic resonance by Zavoiskii in the mid 1940s (1) ushered in a golden age of physical and chemical applications. Perhaps no single book did more to stimulate this development of EPR spectroscopy than the classic text by Wertz and Bolton (2) , which appeared in 1972. A revised version, with John A. Weil added as a co-author, was published by Wiley in 1994. This 2007 text is formally described as the second edition of the 1994 version. Wertz died shortly after the publication of the 1994 edition leaving Weil and Bolton as authors. In noting that the senior author (JAW) takes most of the responsibility for the content of this 2007 version, the Preface refers to it at one point as the "third edition", which of course is precisely how older readers will regard it. The main thrust of the book is decidedly on the physical aspects of EPR, so that it nicely complements the more chemical emphasis provided in the recent comprehensive text by Gerson and Hüber (3) . As the authors remark, the 2007 edition does not differ dramatically from the 1994 version. The titles of the 13 chapters remain the same except for chapter 11, which now refers to the "Noncontinuous" instead of the "Time-Dependent" Excitation of Spins. Recent developments are generally accommodated by a few extra pages in each chapter. Thus, chapter 1 on Basic Principles of Paramagnetic Resonance has been expanded from 31 to 36 pages to introduce the topics of parallel-field EPR, time-resolved EPR, "computerology", and EPR imaging. Chapter 2 on Magnetic Interactions is essentially unchanged while chapter 3 on Isotropic Hyperfine Effects has been expanded to include new sections on Deviations from the Simple Multinomial Scheme (3.7) and Some Interesting π-Type Free Radicals (3.9). Section 3.9 provides a useful corrective to the notion that the EPR method can detect and characterize almost any type of radical species. This welcome touch of realism is nicely illustrated by mentioning

Hydride Conformers of the Nitrogenase FeMo-cofactor Two-Electron Reduced State E2(2H), Assigned Using Cryogenic Intra Electron Paramagnetic Resonance Cavity Photolysis.

PubMed

Lukoyanov, Dmitriy A; Khadka, Nimesh; Yang, Zhi-Yong; Dean, Dennis R; Seefeldt, Lance C; Hoffman, Brian M

2018-03-24

Early studies in which nitrogenase was freeze-trapped during enzymatic turnover revealed the presence of high-spin ( S = 3 / 2 ) electron paramagnetic resonance (EPR) signals from the active-site FeMo-cofactor (FeMo-co) in electron-reduced intermediates of the MoFe protein. Historically denoted as 1b and 1c, each of the signals is describable as a fictitious spin system, S' = 1 / 2 , with anisotropic g' tensor, 1b with g' = [4.21, 3.76, ?] and 1c with g' = [4.69, ∼3.20, ?]. A clear discrepancy between the magnetic properties of 1b and 1c and the kinetic analysis of their appearance during pre-steady-state turnover left their identities in doubt, however. We subsequently associated 1b with the state having accumulated 2[e - /H + ], denoted as E 2 (2H), and suggested that the reducing equivalents are stored on the catalytic FeMo-co cluster as an iron hydride, likely an [Fe-H-Fe] hydride bridge. Intra-EPR cavity photolysis (450 nm; temperature-independent from 4 to 12 K) of the E 2 (2H)/1b state now corroborates the identification of this state as storing two reducing equivalents as a hydride. Photolysis converts E 2 (2H)/1b to a state with the same EPR spectrum, and thus the same cofactor structure as pre-steady-state turnover 1c, but with a different active-site environment. Upon annealing of the photogenerated state at temperature T = 145 K, it relaxes back to E 2 (2H)/1b. This implies that the 1c signal comes from an E 2 (2H) hydride isomer of E 2 (2H)/1b that stores its two reducing equivalents either as a hydride bridge between a different pair of iron atoms or an Fe-H terminal hydride.

Application of electron paramagnetic resonance imaging to the characterization of the Ultem(R) exposed to 1 MeV electrons. Correlation of radical density data to tiger code calculations

SciTech Connect

Suleman, N.K.

1994-12-01

A major long-term goal of the Materials Division at the NASA Langley Research Center is the characterization of new high-performance materials that have potential applications in the aircraft industry, and in space. The materials used for space applications are often subjected to a harsh and potentially damaging radiation environment. The present study constitutes the application of a novel technique to obtain reliable data for ascertaining the molecular basis for the resilience and durability of materials that have been exposed to simulated space radiations. The radiations of greatest concern are energetic electrons and protons, as well as galactic cosmic rays. Presently,more » the effects of such radiation on matter are not understood in their entirety. It is clear however, that electron radiation causes ionization and homolytic bond rupture, resulting in the formation of paramagnetic spin centers in the polymer matrices of the structural materials. Since the detection and structure elucidation of paramagnetic species are most readily accomplished using Electron Paramagnetic Resonance (EPR) Spectroscopy, the NASA LaRC EPR system was brought back on-line during the 1991 ASEE term. The subsequent 1992 ASEE term was devoted to the adaptation of the EPR core system to meet the requirements for EPR Imaging (EPRI), which provides detailed information on the spatial distribution of paramagnetic species in bulk media. The present (1994) ASEE term was devoted to the calibration of this EPR Imaging system, as well as to the application of this technology to study the effects of electron irradiation on Ultem(exp R), a high performance polymer which is a candidate for applications in aerospace. The Ultem was exposed to a dose of 2.4 x 10(exp 9) Rads (1-MeV energy/electron) at the LaRC electron accelerator facility. Subsequently, the exposed specimens were stored in liquid nitrogen, until immediately prior to analyses by EPRI.« less

57Fe Mössbauer spectroscopy and electron paramagnetic resonance studies of human liver ferritin, Ferrum Lek and Maltofer®

NASA Astrophysics Data System (ADS)

Alenkina, I. V.; Oshtrakh, M. I.; Klencsár, Z.; Kuzmann, E.; Chukin, A. V.; Semionkin, V. A.

2014-09-01

A human liver ferritin, commercial Ferrum Lek and Maltofer® samples were studied using Mössbauer spectroscopy and electron paramagnetic resonance. Two Mössbauer spectrometers have been used: (i) a high velocity resolution (4096 channels) at 90 and 295 K, (ii) and a low velocity resolution (250 channels) at 20 and 40 K. It is shown that the three studied materials have different superparamagnetic features at various temperatures. This may be caused by different magnetic anisotropy energy barriers, sizes (volume), structures and compositions of the iron cores. The electron paramagnetic resonance spectra of the ferritin, Ferrum Lek and Maltofer® were decomposed into multiple spectral components demonstrating the presence of minor ferro- or ferrimagnetic phases along with revealing marked differences among the studied substances. Mössbauer spectroscopy provides evidences on several components in the measured spectra which could be related to different regions, layers, nanocrystallites, etc. in the iron cores that coincides with heterogeneous and multiphase models for the ferritin iron cores.

Spatially resolved nuclear spin relaxation, electron spin relaxation and light absorption in swift heavy ion irradiated LiF crystals.

PubMed

Stork, H; Dinse, K-P; Ditter, M; Fujara, F; Masierak, W; Neumann, R; Schuster, B; Schwartz, K; Trautmann, C

2010-05-12

Spatially resolved (19)F and (7)Li spin-lattice relaxation rates are measured for LiF single crystals after irradiation with two kinds of swift heavy ions ((12)C of 133 MeV and (208)Pb of 1.78 GeV incident energy). Like in earlier studies on (130)Xe and (238)U irradiated LiF crystals, we found a strong enhancement of the nuclear spin-lattice relaxation rate within the ion penetration depth and a slight--but still significant--enhancement beyond. By evaluating the nuclear relaxation rate enhancement within the ion range after irradiation with different projectiles, a universal relationship between the spin-lattice relaxation rate and the dose is deduced. The results of accompanying X-band electron paramagnetic resonance relaxation measurements and optical absorption spectroscopy are included in a physical interpretation of this relationship. Also the reason for the enhanced relaxation rate beyond the ion range is further discussed.

Effects of thermal annealing on the radiation produced electron paramagnetic resonance spectra of bovine and equine tooth enamel: Fossil and modern

NASA Astrophysics Data System (ADS)

Weeks, Robert A.; Bogard, James S.; Elam, J. Michael; Weinand, Daniel C.; Kramer, Andrew

2003-06-01

The concentration of stable radiation-induced paramagnetic states in fossil teeth can be used as a measure of sample age. Temperature excursions >100 °C, however, can cause the paramagnetic state clock to differ from the actual postmortem time. We have heated irradiated enamel from both fossilized bovid and modern equine (MEQ) teeth for 30 min in 50 °C increments from 100 to 300 °C, measuring the electron paramagnetic resonance (EPR) spectrum after each anneal, to investigate such effects. Samples were irradiated again after the last anneal, with doses of 300-1200 Gy from 60Co photons, and measured. Two unirradiated MEQ samples were also annealed for 30 min at 300 °C, one in an evacuated EPR tube and the other in a tube open to the atmosphere, and subsequently irradiated. The data showed that hyperfine components attributed to the alanine radical were not detected in the irradiated MEQ sample until after the anneals. The spectrum of the MEQ sample heated in air and then irradiated was similar to that of the heat treated fossil sample. We conclude that the hyperfine components are due to sample heating to temperatures/times >100 °C/30 min and that similarities between fossil and MEQ spectra after the 300 °C/30 min MEQ anneal are also due to sample heating. We conclude that the presence of the hyperfine components in spectra of fossil tooth enamel indicate that such thermal events occurred either at the time of death, or during the postmortem history.

Absorption effects in electron-sulfur-dioxide collisions

SciTech Connect

Machado, L. E.; Sugohara, R. T.; Santos, A. S. dos

2011-09-15

A joint experimental-theoretical study on electron-SO{sub 2} collisions in the low and intermediate energy range is reported. More specifically, experimental elastic differential, integral, and momentum transfer cross sections in absolute scale are measured in the 100-1000 eV energy range using the relative-flow technique. Calculated elastic differential, integral, and momentum transfer cross sections as well as grand-total and total absorption cross sections are also presented in the 1-1000 eV energy range. A complex optical potential is used to represent the electron-molecule interaction dynamics, whereas the Schwinger variational iterative method combined with the distorted-wave approximation is used to solve the scattering equations.more » Comparison of the present results is made with the theoretical and experimental results available in the literature.« less

A Paramagnetic Molecular Voltmeter

PubMed Central

Surek, Jack T.; Thomas, David D.

2008-01-01

We have developed a general electron paramagnetic resonance (EPR) method to measure electrostatic potential at spin labels on proteins to millivolt accuracy. Electrostatic potential is fundamental to energy-transducing proteins like myosin, because molecular energy storage and retrieval is primarily electrostatic. Quantitative analysis of protein electrostatics demands a site-specific spectroscopic method sensitive to millivolt changes. Previous electrostatic potential studies on macromolecules fell short in sensitivity, accuracy and/or specificity. Our approach uses fast-relaxing charged and neutral paramagnetic relaxation agents (PRAs) to increase nitroxide spin label relaxation rate solely through collisional spin exchange. These PRAs were calibrated in experiments on small nitroxides of known structure and charge to account for differences in their relaxation efficiency. Nitroxide longitudinal (R1) and transverse (R2) relaxation rates were separated by applying lineshape analysis to progressive saturation spectra. The ratio of measured R1 increases for each pair of charged and neutral PRAs measures the shift in local PRA concentration due to electrostatic potential. Voltage at the spin label is then calculated using the Boltzmann equation. Measured voltages for two small charged nitroxides agree with Debye-Hückel calculations. Voltage for spin-labeled myosin fragment S1 also agrees with calculation based on the pK shift of the reacted cysteine. PMID:17964835

Production and aging of paramagnetic point defects in P-doped floating zone silicon irradiated with high fluence 27 MeV electrons

NASA Astrophysics Data System (ADS)

Joita, A. C.; Nistor, S. V.

2018-04-01

Enhancing the long term stable performance of silicon detectors used for monitoring the position and flux of the particle beams in high energy physics experiments requires a better knowledge of the nature, stability, and transformation properties of the radiation defects created over the operation time. We report the results of an electron spin resonance investigation in the nature, transformation, and long term stability of the irradiation paramagnetic point defects (IPPDs) produced by high fluence (2 × 1016 cm-2), high energy (27 MeV) electrons in n-type, P-doped standard floating zone silicon. We found out that both freshly irradiated and aged (i.e., stored after irradiation for 3.5 years at 250 K) samples mainly contain negatively charged tetravacancy and pentavacancy defects in the first case and tetravacancy defects in the second one. The fact that such small cluster vacancy defects have not been observed by irradiation with low energy (below 5 MeV) electrons, but were abundantly produced by irradiation with neutrons, strongly suggests the presence of the same mechanism of direct formation of small vacancy clusters by irradiation with neutrons and high energy, high fluence electrons, in agreement with theoretical predictions. Differences in the nature and annealing properties of the IPPDs observed between the 27 MeV electrons freshly irradiated, and irradiated and aged samples were attributed to the presence of a high concentration of divacancies in the freshly irradiated samples, defects which transform during storage at 250 K through diffusion and recombination processes.

Effects of the Electronic Spin-Orbit Interaction on the Anomalous Asymmetric Scattering of the Spin-Polarized He+ Beam with Paramagnetic Target Materials II. Partial Wave Representation

NASA Astrophysics Data System (ADS)

Sakai, Osamu; Suzuki, Taku T.

2018-05-01

The scattering of an electron-spin-polarized 4He+ beam on paramagnetic materials has an anomalously large asymmetric scattering component (ASC) around 10%, which is 104 times that expected from the spin-orbit coupling for the potential of the target nucleus. The scattering angle (θ) dependence of the ASC has been measured. It changes sign near 90° for some materials (for example, Au and Pt), while it does not change sign for other materials (for example, Pb and Bi). It has been noted that the spin-orbit interaction of electrons on the target in the electron-transfer intermediate state causes the ASC of He nucleus motion, and it has also been predicted that the sign change in the θ dependence occurs when the d electron transfer is dominant. This seems to correspond to the cases of Au and Pt, but not to the cases of Pb and Bi. The previous approach is refined on the basis of the partial wave representation, which can give a more correct estimation of the ASC. It is shown that the sign change appears in the weak-resonance domain in the case of d electron excitation, whereas the sign change disappears in the strong-resonance domain. Our calculated results qualitatively agree with the material dependence of the ASC observed experimentally.

Parallel image-acquisition in continuous-wave electron paramagnetic resonance imaging with a surface coil array: Proof-of-concept experiments

NASA Astrophysics Data System (ADS)

Enomoto, Ayano; Hirata, Hiroshi

2014-02-01

This article describes a feasibility study of parallel image-acquisition using a two-channel surface coil array in continuous-wave electron paramagnetic resonance (CW-EPR) imaging. Parallel EPR imaging was performed by multiplexing of EPR detection in the frequency domain. The parallel acquisition system consists of two surface coil resonators and radiofrequency (RF) bridges for EPR detection. To demonstrate the feasibility of this method of parallel image-acquisition with a surface coil array, three-dimensional EPR imaging was carried out using a tube phantom. Technical issues in the multiplexing method of EPR detection were also clarified. We found that degradation in the signal-to-noise ratio due to the interference of RF carriers is a key problem to be solved.

Electron paramagnetic resonance spectral study of [Mn(acs){sub 2}(2–pic){sub 2}(H{sub 2}O){sub 2}] single crystals

SciTech Connect

Kocakoç, Mehpeyker, E-mail: mkocakoc@cu.edu.tr; Tapramaz, Recep, E-mail: recept@omu.edu.tr

Acesulfame potassium salt is a synthetic and non-caloric sweetener. It is also important chemically for its capability of being ligand in coordination compounds, because it can bind over Nitrogen and Oxygen atoms of carbonyl and sulfonyl groups and ring oxygen. Some acesulfame containing transition metal ion complexes with mixed ligands exhibit solvato and thermo chromic properties and these properties make them physically important. In this work single crystals of Mn{sup +2} ion complex with mixed ligand, [Mn(acs){sub 2}(2-pic){sub 2}(H{sub 2}O){sub 2}], was studied with electron paramagnetic resonance (EPR) spectroscopy. EPR parameters were determined. Zero field splitting parameters indicated that themore » complex was highly symmetric. Variable temperature studies showed no detectable chance in spectra.« less

Application of electron paramagnetic resonance imaging to the characterization of the Ultem(R) exposed to 1 MeV electrons. Correlation of radical density data to tiger code calculations

NASA Technical Reports Server (NTRS)

Suleman, Naushadalli K.

1994-01-01

A major long-term goal of the Materials Division at the NASA Langley Research Center is the characterization of new high-performance materials that have potential applications in the aircraft industry, and in space. The materials used for space applications are often subjected to a harsh and potentially damaging radiation environment. The present study constitutes the application of a novel technique to obtain reliable data for ascertaining the molecular basis for the resilience and durability of materials that have been exposed to simulated space radiations. The radiations of greatest concern are energetic electrons and protons, as well as galactic cosmic rays. Presently, the effects of such radiation on matter are not understood in their entirety. It is clear however, that electron radiation causes ionization and homolytic bond rupture, resulting in the formation of paramagnetic spin centers in the polymer matrices of the structural materials. Since the detection and structure elucidation of paramagnetic species are most readily accomplished using Electron Paramagnetic Resonance (EPR) Spectroscopy, the NASA LaRC EPR system was brought back on-line during the 1991 ASEE term. The subsequent 1992 ASEE term was devoted to the adaptation of the EPR core system to meet the requirements for EPR Imaging (EPRI), which provides detailed information on the spatial distribution of paramagnetic species in bulk media. The present (1994) ASEE term was devoted to the calibration of this EPR Imaging system, as well as to the application of this technology to study the effects of electron irradiation on Ultem(exp R), a high performance polymer which is a candidate for applications in aerospace. The Ultem was exposed to a dose of 2.4 x 10(exp 9) Rads (1-MeV energy/electron) at the LaRC electron accelerator facility. Subsequently, the exposed specimens were stored in liquid nitrogen, until immediately prior to analyses by EPRI. The intensity and dimensions of the EPR Images that

Silicon displacement threshold energy determined by electron paramagnetic resonance and positron annihilation spectroscopy in cubic and hexagonal polytypes of silicon carbide

NASA Astrophysics Data System (ADS)

Kerbiriou, X.; Barthe, M.-F.; Esnouf, S.; Desgardin, P.; Blondiaux, G.; Petite, G.

2007-05-01

Both for electronic and nuclear applications, it is of major interest to understand the properties of point defects into silicon carbide (SiC). Low energy electron irradiations are supposed to create primary defects into materials. SiC single crystals have been irradiated with electrons at two beam energies in order to investigate the silicon displacement threshold energy into SiC. This paper presents the characterization of the electron irradiation-induced point defects into both polytypes hexagonal (6H) and cubic (3C) SiC single crystals by using both positron annihilation spectroscopy (PAS) and electron paramagnetic resonance (EPR). The nature and the concentration of the generated point defects depend on the energy of the electron beam and the polytype. After an electron irradiation at an energy of 800 keV vSi mono-vacancies and vSi-vC di-vacancies are detected in both 3C and 6H-SiC polytypes. On the contrary, the nature of point defects detected after an electron irradiation at 190 keV strongly depends on the polytype. Into 6H-SiC crystals, silicon Frenkel pairs vSi-Si are detected whereas only carbon vacancy related defects are detected into 3C-SiC crystals. The difference observed in the distribution of defects detected into the two polytypes can be explained by the different values of the silicon displacement threshold energies for 3C and 6H-SiC. By comparing the calculated theoretical numbers of displaced atoms with the defects numbers measured using EPR, the silicon displacement threshold energy has been estimated to be slightly lower than 20 eV in the 6H polytype and close to 25 eV in the 3C polytype.

Anti-HER2 immunoliposomes for selective delivery of electron paramagnetic resonance imaging probes to HER2-overexpressing breast tumor cells

PubMed Central

Burks, Scott R.; Macedo, Luciana F.; Barth, Eugene D.; Tkaczuk, Katherine H.; Martin, Stuart S.; Rosen, Gerald M.; Halpern, Howard J.; Brodie, Angela M.

2014-01-01

Electron paramagnetic resonance (EPR) imaging is an emerging modality that can detect and localize paramagnetic molecular probes (so-called spin probes) in vivo. We previously demonstrated that nitroxide spin probes can be encapsulated in liposomes at concentrations exceeding 100 mM, at which nitroxides exhibit a concentration-dependent quenching of their EPR signal that is analogous to the self-quenching of fluorescent molecules. Therefore, intact liposomes encapsulating high concentrations of nitroxides exhibit greatly attenuated EPR spectral signals, and endocytosis of such liposomes represents a cell-activated contrast-generating mechanism. After endocytosis, the encapsulated nitroxide is liberated and becomes greatly diluted in the intracellular milieu. This dequenches the nitroxides to generate a robust intracellular EPR signal. It is therefore possible to deliver a high concentration of nitroxides to cells while minimizing background signal from unendocytosed liposomes. We report here that intracellular EPR signal can be selectively generated in a specific cell type by exploiting its expression of Human Epidermal Growth Factor Receptor 2 (HER2). When targeted by anti-HER2 immunoliposomes encapsulating quenched nitroxides, Hc7 cells, which are novel HER2-overexpressing cells derived from the MCF7 breast tumor cell line, endocytose the liposomes copiously, in contrast to the parent MCF7 cells or control CV1 cells, which do not express HER2. HER2-dependent liposomal delivery enables Hc7 cells to accumulate 750 μM nitroxide intracellularly. Through the use of phantom models, we verify that this concentration of nitroxides is more than sufficient for EPR imaging, thus laying the foundation for using EPR imaging to visualize HER2-overexpressing Hc7 tumors in animals. PMID:20066490

The impact of adsorption on the localization of spins in graphene oxide and reduced graphene oxide, observed with electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Kempiński, Mateusz; Florczak, Patryk; Jurga, Stefan; Śliwińska-Bartkowiak, Małgorzata; Kempiński, Wojciech

2017-08-01

We report the observations of electronic properties of graphene oxide and reduced graphene oxide, performed with electron paramagnetic resonance technique in a broad temperature range. Both materials were examined in pure form and saturated with air, helium, and heavy water molecules. We show that spin localization strongly depends on the type and amount of molecules adsorbed at the graphene layer edges (and possible in-plane defects). Physical and chemical states of edges play crucial role in electrical transport within graphene-based materials, with hopping as the leading mechanism of charge carrier transport. Presented results are a good basis to understand the electronic properties of other carbon structures made of graphene-like building blocks. Most active carbons show some degree of functionalization and are known of having good adsorptive properties; thus, controlling both phenomena is important for many applications. Sample treatment with temperature, vacuum, and various adsorbents allowed for the observation of a possible metal-insulator transition and sorption pumping effects. The influence of adsorption on the localization phenomena in graphene would be very important if to consider the graphene-based material as possible candidates for the future spintronics that works in ambient conditions.

Electron paramagnetic resonance spectra of CdO-Al2O3-Bi2O3-B2O3 quaternary glasses containing VO2+ ions

NASA Astrophysics Data System (ADS)

Lalithaphani, A. V.; Srinivas, B.; Hameed, Abdul; Chary, M. Narasimha; Shareefuddin, Md.

2018-04-01

Borate glasses containing different concentrations of heavy metal oxide (CdO) with 2mol% of V2O5 as the paramagnetic probe were prepared by the conventional melt quenching technique. The prepared glasses were characterized by XRD to confirm the amorphous nature. EPR and Optical absorption studies were carried out at room temperature. EPR spectra of these glass samples were recorded at X-band frequency with 100 kHz field modulation at room temperature. From the EPR spectra the spin-Hamiltonian parameters were evaluated. The spin-Hamiltonian parameter values indicated that g|| < g┴ < ge [=2.0023] and A∥︀ > A┴. This suggests that VO2+ ions are present in octahedral sites with tetragonal compression and belong to C4v symmetry with dxy being the ground state. The measure of tetragonal distortion (Δg∥︀/Δg┴)varies non-linearly with glass composition indicating change in tetragonal distortion. The covalency rates were estimated. The number of spins participating in the resonance [N] and susceptibility (χ) values were also evaluated.

Synthesis, structural and electron paramagnetic resonance studies on Pb0.9Bi0.1Fe0.7W0.3O3 ceramic

NASA Astrophysics Data System (ADS)

Shivaraja, I.; Matteppanvar, Shidaling; Dadami, Sunanda T.; Rayaprol, Sudhindra; Angadi, Basavaraj

2018-04-01

A single phase Pb0.9Bi0.1Fe0.7W0.3O3 (0.9Pb(Fe2/3W1/3)O3 - 0.1BiFeO3 or PBFW) polycrystalline ceramic was synthesized by the two step solid state reaction method, with low-temperature sintering at 800°C for 30 mins and slow cooling to room temperature (RT). Detailed studies of RT X-ray diffraction (XRD) and Raman spectroscopy measurements confirm the formation of high symmetry cubic structure with Pm-3m space group. The Rietveld refinement was carried out on RT XRD data and the obtained structural parameters are a = b = c = 3.97563(6) Å and unit cell volume = 62.837 (2) Å3. Scanning Electron Microscopy (SEM) images show the uniform distribution of grains with some agglomerated nature. RT Raman spectroscopy reveals the main broad peak at 770 cm-1, related to the A1g mode, which confirms the formation of cubic (ABO3 perovskite) structure. The single symmetric electron paramagnetic resonance (EPR) line shape with g = 2.13985 observed in PBFW was identified to be due to Fe3+ ions.

Investigation of 3C-SiC/SiO2 interfacial point defects from ab initio g-tensor calculations and electron paramagnetic resonance measurements

NASA Astrophysics Data System (ADS)

Nugraha, T. A.; Rohrmueller, M.; Gerstmann, U.; Greulich-Weber, S.; Stellhorn, A.; Cantin, J. L.; von Bardeleben, J.; Schmidt, W. G.; Wippermann, S.

SiC is widely used in high-power, high-frequency electronic devices. Recently, it has also been employed as a building block in nanocomposites used as light absorbers in solar energy conversion devices. Analogous to Si, SiC features SiO2 as native oxide that can be used for passivation and insulating layers. However, a significant number of defect states are reported to form at SiC/SiO2 interfaces, limiting mobility and increasing recombination of free charge carriers. We investigated the growth of oxide on different 3C-SiC surfaces from first principles. Carbon antisite Csi defects are found to be strongly stabilized in particular at the interface, because carbon changes its hybridization from sp3 in the SiC-bulk to sp2 at the interface, creating a dangling bond inside a porous region of the SiO2 passivating layer. Combining ab initio g-tensor calculations and electron paramagnetic resonance (EPR) measurements, we show that Csi defects explain the measured EPR signatures, while the hyperfine structure allows to obtain local structural information of the oxide layer. Financial support from BMBF NanoMatFutur Grant 13N12972 and DFG priority program SPP-1601 is gratefully acknowledged.

Electron Paramagnetic Resonance Spectroscopic Study on Nonequilibrium Reaction Pathways in the Photolysis of Solid Nitromethane (CH3NO2) and D3-Nitromethane (CD3NO2).

PubMed

Tsegaw, Yetsedaw Andargie; Sander, Wolfram; Kaiser, Ralf I

2016-03-10

Thin films of nitromethane (CH3NO2) along with its isotopically labeled counterpart D3-nitromethane (CD3NO2) were photolyzed at discrete wavelength between 266 nm (4.7 eV) and 121 nm (10.2 eV) to explore the underlying mechanisms involved in the decomposition of model compounds of energetic materials in the condensed phase at 5 K. The chemical modifications of the ices were traced in situ via electron paramagnetic resonance, thus focusing on the detection of (hitherto elusive) reaction intermediates and products with unpaired electrons. These studies revealed the formation of two carbon-centered radicals [methyl (CH3), nitromethyl (CH2NO2)], one oxygen-centered radical [methoxy (CH3O)], two nitrogen-centered radicals [nitrogen monoxide (NO), nitrogen dioxide (NO2)], as well as atomic hydrogen (H). The decomposition products of these channels and the carbon-centered nitromethyl (CH2NO2) radical in particular represent crucial reaction intermediates leading via sequential molecular mass growth processes in the exposed nitromethane samples to complex organic molecules as predicted previously by dynamics calculations. The detection of the nitromethyl (CH2NO2) radical along with atomic hydrogen (H) demonstrated the existence of a high-energy decomposition pathway, which is closed under collisionless conditions in the gas phase.

Electronic properties and optical absorption of a phosphorene quantum dot

NASA Astrophysics Data System (ADS)

Liang, F. X.; Ren, Y. H.; Zhang, X. D.; Jiang, Z. T.

2018-03-01

Using the tight-binding Hamiltonian approach, we theoretically study the electronic and optical properties of a triangular phosphorene quantum dot (PQD) including one normal zigzag edge and two skewed armchair edges (ZAA-PQD). It is shown that the energy spectrum can be classified into the filled band (FB), the zero-energy band (ZB), and the unfilled band (UB). Numerical calculations of the FB, ZB, and UB probability distributions show that the FB and the UB correspond to the bulk states, while the ZB corresponds to the edge states, which appear on all of the three edges of the ZAA-PQD sharply different from the other PQDs. We also find that the strains and the electric fields can affect the energy levels inhomogeneously. Then the optical properties of the ZAA-PQD are investigated. There appear some strong low-energy optical absorption peaks indicating its sensitive low-energy optical response that is absent in other PQDs. Moreover, the strains and the electric fields can make inhomogeneous influences on the optical spectrum of the ZAA-PQD. This work may provide a useful reference for designing the electrical, mechanical, and optical PQD devices.

Inter-spin distance determination using L-band (1-2 GHz) non-adiabatic rapid sweep electron paramagnetic resonance (NARS EPR)

PubMed Central

Kittell, Aaron W.; Hustedt, Eric J.; Hyde, James S.

2014-01-01

Site-directed spin-labeling electron paramagnetic resonance (SDSL EPR) provides insight into the local structure and motion of a spin probe strategically attached to a molecule. When a second spin is introduced to the system, macromolecular information can be obtained through measurement of inter-spin distances either by continuous wave (CW) or pulsed electron double resonance (ELDOR) techniques. If both methodologies are considered, inter-spin distances of 8 to 80 Å can be experimentally determined. However, there exists a region at the upper limit of the conventional X-band (9.5 GHz) CW technique and the lower limit of the four-pulse double electron-electron resonance (DEER) experiment where neither method is particularly reliable. The work presented here utilizes L-band (1.9 GHz) in combination with non-adiabatic rapid sweep (NARS) EPR to address this opportunity by increasing the upper limit of the CW technique. Because L-band linewidths are three to seven times narrower than those at X-band, dipolar broadenings that are small relative to the X-band inhomogeneous linewidth become observable, but the signal loss due to the frequency dependence of the Boltzmann factor, has made L-band especially challenging. NARS has been shown to increase sensitivity by a factor of five, and overcomes much of this loss, making L-band distance determination more feasible [1]. Two different systems are presented and distances of 18–30 Å have been experimentally determined at physiologically relevant temperatures. Measurements are in excellent agreement with a helical model and values determined by DEER. PMID:22750251

Electron and proton absorption calculations for a graphite/epoxy composite model. [large space structures

NASA Technical Reports Server (NTRS)

Long, E. R., Jr.

1979-01-01

The Bethe-Bloch stopping power relations for inelastic collisions were used to determine the absorption of electron and proton energy in cured neat epoxy resin and the absorption of electron energy in a graphite/epoxy composite. Absorption of electron energy due to bremsstrahlung was determined. Electron energies from 0.2 to 4.0 MeV and proton energies from 0.3 to 1.75 MeV were used. Monoenergetic electron energy absorption profiles for models of pure graphite, cured neat epoxy resin, and graphite/epoxy composites are reported. A relation is determined for depth of uniform energy absorption in a composite as a function of fiber volume fraction and initial electron energy. Monoenergetic proton energy absorption profiles are reported for the neat resin model. A relation for total proton penetration in the epoxy resin as a function of initial proton energy is determined. Electron energy absorption in the composite due to bremsstrahlung is reported. Electron and proton energy absorption profiles in cured neat epoxy resin are reported for environments approximating geosynchronous earth orbit.

Transition from a paramagnetic metallic to a cluster glass metallic state in electron-doped perovskite manganites

NASA Astrophysics Data System (ADS)

Maignan, A.; Martin, C.; Damay, F.; Raveau, B.; Hejtmanek, J.

1998-08-01

The study of Mn(IV)-rich manganites Ca1-xSmxMnO3 with low electron content corresponding to 0<=x<=0.12 demonstrates the large difference of their electronic and magnetic properties with that of Mn(III)-rich manganites. In particular, a metalliclike temperature dependence of the resistivity (ρ) is observed above TC, the smallest room-temperature ρ=10-3 Ω cm being reached for x=0.12. However increasing hopping energy with x suggests the creation of small polarons as eg electrons are injected into the Mn(IV) matrix. The thermopower (S) measurements confirm the increase of carriers with x and can be described within a single-band metal model. The ρ(T) and S(T) curves exhibit also a transition at a fixed temperature Tp~110 K for 0.075<=x<=0.12. Tp is related to the appearance of a ferromagnetic component as shown from T-dependent magnetization. Nevertheless, the ac-χ measurements reveal a complex behavior. CaMnO3 exhibits a weak ferromagnetic component (TC=122 K) whereas for Ca1-xSmxMnO3 (0electron-doped manganites.

The pH-dependent Structures of the Manganese Binding Sites in Oxalate Decarboxylase as Revealed by High-Field Electron Paramagnetic Resonance

PubMed Central

Tabares, Leandro C.; Gätjens, Jessica; Hureau, Christelle; Burrell, Matthew R.; Bowater, Laura; Pecoraro, Vincent L.; Bornemann, Stephen; Un, Sun

2009-01-01

A high-field electron paramagnetic resonance (HFEPR) study of oxalate decarboxylase (OxdC) is reported. OxdC breaks down oxalate to carbon dioxide and formate and possesses two distinct manganese(II) binding sites, referred to as site-1 and -2. The Mn(II) zero-field interaction was used to probe the electronic state of the metal ion and to examine chemical/mechanistic roles of each of the Mn(II) centers. High magnetic-fields were exploited not only to resolve the two sites, but also to measure accurately the Mn(II) zero-field parameters of each of the sites. The spectra exhibited surprisingly complex behavior as a function of pH. Six different species were identified based on their zero-field interactions, two corresponding to site-1 and four states to site-2. The assignments were verified using a mutant that only affected site-1. The speciation data determined from the HFEPR spectra for site -2 was consistent with a simple triprotic equilibrium model, while the pH dependence of site-1 could be described by a single pKa. This pH dependence was independent of the presence of the His-tag and of whether the preparations contained 1.2 or 1.6 Mn per subunit. Possible structures of the six species are proposed based on spectroscopic data from model complexes and existing protein crystallographic structures obtained at pH 8 are discussed. Although site-1 has been identified as the active site and no role has been assigned to site-2, the pronounced changes in the electronic structure of the latter and its pH behavior, which also matches the pH-dependent activity of this enzyme, suggests that even if the conversion of oxalate to formate is carried out at site-1, site-2 likely plays a catalytically relevant role. PMID:19505123

In vitro electron paramagnetic resonance characterization of free radicals: relevance to exercise-induced lipid peroxidation and implications of ascorbate prophylaxis.

PubMed

Davison, Gareth W; Ashton, Tony; Davies, Bruce; Bailey, Damian M

2008-04-01

This study tested the hypothesis that exercise-induced oxidative stress is caused by free radical-mediated damage to polyunsaturated fatty acids (PUFA) which can be prevented following ascorbate prophylaxis. Hyperfine coupling constants (HCC) of alpha-phenyl-tert-butylnitrone (PBN)-adducts were measured via room temperature electron paramagnetic resonance (EPR) spectroscopy in the venous blood of 12 subjects at rest and following maximal exercise during a randomized double-blind placebo-controlled trial and compared to those observed following room-air incubation (2 h at 37 degrees C) of L-alpha-phosphatidycholine, linoleic acid, alpha-linolenic acid and arachidonic acid. All adducts exhibited similar HCC [a(N) 13.6 Gauss (G) and a beta(H) 1.8 G] with the exception of L-alpha-phosphatidycholine [a(N1)=13.4 G, a beta(H1)=1.6 G (37%) and a(N2)=14.9 G, a beta(H2)=0.3 G (63%)] consistent with the trapping of lipid-derived alkoxyl and oleate radicals, respectively. Ascorbate pre-treatment ablated radical formation in both systems. These findings identify circulating PUFA as a potential source of secondary radicals that are capable of initiating oxidative stress in the exercising human.

Localization of dexamethasone within dendritic core-multishell (CMS) nanoparticles and skin penetration properties studied by multi-frequency electron paramagnetic resonance (EPR) spectroscopy.

PubMed

Saeidpour, S; Lohan, S B; Anske, M; Unbehauen, M; Fleige, E; Haag, R; Meinke, M C; Bittl, R; Teutloff, C

2017-07-01

The skin and especially the stratum corneum (SC) act as a barrier and protect epidermal cells and thus the whole body against xenobiotica of the external environment. Topical skin treatment requires an efficient drug delivery system (DDS). Polymer-based nanocarriers represent novel transport vehicles for dermal application of drugs. In this study dendritic core-multishell (CMS) nanoparticles were investigated as promising candidates. CMS nanoparticles were loaded with a drug (analogue) and were applied to penetration studies of skin. We determined by dual-frequency electron paramagnetic resonance (EPR) how dexamethasone (Dx) labelled with 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PCA) is associated with the CMS. The micro-environment of the drug loaded to CMS nanoparticles was investigated by pulsed high-field EPR at cryogenic temperature, making use of the fact that magnetic parameters (g-, A-matrices, and spin-lattice relaxation time) represent specific probes for the micro-environment. Additionally, the rotational correlation time of spin-labelled Dx was probed by continuous wave EPR at ambient temperature, which provides independent information on the drug environment. Furthermore, the penetration depth of Dx into the stratum corneum of porcine skin after different topical applications was investigated. The location of Dx in the CMS nanoparticles is revealed and the function of CMS as penetration enhancers for topical application is shown. Copyright © 2016 Elsevier B.V. All rights reserved.

Temperature-dependent electron paramagnetic resonance detect oxygen vacancy defects and Cr valence of tetragonal Ba(Ti1-xCrx)O3 ceramics

NASA Astrophysics Data System (ADS)

Han, Dan-Dan; Lu, Da-Yong; Meng, Fan-Ling; Yu, Xin-Yu

2018-03-01

Temperature-dependent electron paramagnetic resonance (EPR) study was employed to detect oxygen vacancy defects in the tetragonal Ba(Ti1-xCrx)O3 (x = 5%) ceramic for the first time. In the rhombohedral phase below -150 °C, an EPR signal at g = 1.955 appeared in the insulating Ba(Ti1-xCrx)O3 (x = 5%) ceramic with an electrical resistivity of 108 Ω cm and was assigned to ionized oxygen vacancy defects. Ba(Ti1-xCrx)O3 ceramics exhibited a tetragonal structure except Ba(Ti1-xCrx)O3 (x = 10%) with a tetragonal-hexagonal mixed phase and a first-order phase transition dielectric behavior (ε‧m > 11,000). Mixed valence Cr ions could coexist in ceramics, form CrTi‧-VOrad rad or CrTirad-TiTi‧ defect complexes and make no contribution to a dielectric peak shift towards low temperature.

The “Beta-Clasp” model of apolipoprotein A-I - a lipid-free solution structure determined by electron paramagnetic resonance spectroscopy

PubMed Central

Lagerstedt, Jens O.; Budamagunta, Madhu S.; Liu, Grace S.; DeValle, Nicole C.; Voss, John C.; Oda, Michael N.

2012-01-01

Apolipoprotein A-I (apoA-I) is the major protein component of high density lipoproteins (HDL) and plays a central role in cholesterol metabolism. The lipid-free / lipid-poor form of apoA-I is the preferred substrate for the ATP-binding cassette transporter A1 (ABCA1). The interaction of apoA-I with ABCA1 leads to the formation of cholesterol laden high density lipoprotein (HDL) particles, a key step in reverse cholesterol transport and the maintenance of cholesterol homeostasis. Knowledge of the structure of lipid-free apoA-I is essential to understanding its critical interaction with ABCA1 and the molecular mechanisms underlying HDL biogenesis. We therefore examined the structure of lipid-free apoA-I by electron paramagnetic resonance spectroscopy (EPR). Through site directed spin label EPR, we mapped the secondary structure of apoA-I and identified sites of spin coupling as residues 26, 44, 64, 167, 217 and 226. We capitalize on the fact that lipid-free apoA-I self-associates in an anti-parallel manner in solution. We employed these sites of spin coupling to define the central plane in the dimeric apoA-I complex. Applying both the constraints of dipolar coupling with the EPR-derived pattern of solvent accessibility, we assembled the secondary structure into a tertiary context, providing a solution structure for lipid-free apoA-I. PMID:22245143

New opportunities of the application of natural herb and spice extracts in plant oils: application of electron paramagnetic resonance in examining the oxidative stability.

PubMed

Kozłowska, Mariola; Szterk, Arkadiusz; Zawada, Katarzyna; Ząbkowski, Tomasz

2012-09-01

The aim of this study was to establish the applicability of natural water-ethanol extracts of herbs and spices in increasing the oxidative stability of plant oils and in the production of novel food. Different concentrations (0, 100, 300, 500, and 700 ppm) of spice extracts and butylated hydroxyanisole (BHA) (100 ppm) were added to the studied oils. The antioxidant activity of spice extracts was determined with electron paramagnetic resonance (EPR) spectroscopy using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical assay. The study showed that the extracts significantly increased the oxidative stability of the examined oils when compared to one of the strongest synthetic antioxidants--BHA. The applied simple production technology and addition of herb and spice extracts to plant oils enabled enhancement of their oxidative stability. The extracts are an alternative to the oils aromatized with an addition of fresh herbs, spices, and vegetables because it did not generate additional flavors thus enabling the maintenance of the characteristic ones. Moreover, it will increase the intake of natural substances in human diet, which are known to possess anticarcinogenic properties. © 2012 Institute of Food Technologists®

Measurement of differences in pO2 in response to perfluorocarbon/carbogen in FSa and NFSa murine fibrosarcomas with low-frequency electron paramagnetic resonance oximetry.

PubMed

Halpern, H J; Yu, C; Peric, M; Barth, E D; Karczmar, G S; River, J N; Grdina, D J; Teicher, B A

1996-05-01

We have used very low-frequency electron paramagnetic resonance (EPR) oximetry to measure the change in oxygen concentration (delta pO2) due to change in breathing atmosphere in FSa and NFSa fibrosarcomas implanted in the legs of C3H mice infused with perfluoro-octylbromine (PFOB). Measurements in each tumor were made before and after the administration of the high-density (47% v/v) perfluorocarbon PFOB, perflubron (Alliance Pharmaceutical Corporation, San Diego, CA). Measurements in each tumor were also made, after the administration of the PFOB, both before (PFOB/air) and after the administration of carbogen (95% O2 + 5% CO2, PFOB/carbogen). Large changes (delta p02) relative to PFOB/air oxygenation were seen with the administration of PFOB/carbogen. No significant difference in oxygen concentration was seen between air-breathing mice with and without PFOB. The mean delta pO2 for FSa tumors was 13 +/- 6 torr, while the mean for NFSa fibrosarcomas was 28 +/- 7 torr. There were such large intertumor differences that the trend toward a smaller change in the more hypoxic FSa tumors was not significant (P = 0.13). This paper describes a novel method of measuring differences in oxygenation in tumor tissues. The results of such measurements indicate large differences in pO2 response to different breathing atmospheres in PFOB-infused tumors of similar histology. The intertumor delta pO2 differences may correlate with differences in radiation response.

H6+ in irradiated solid para-hydrogen and its decay dynamics: reinvestigation of quartet electron paramagnetic resonance lines assigned to H2-.

PubMed

Kumada, Takayuki; Tachikawa, Hiroto; Takayanagi, Toshiyuki

2005-03-07

The quartet electron paramagnetic resonance (EPR) lines observed in gamma- and X-ray irradiated solid para-H2, which have previously been assigned to H2-, are reinvestigated. We have reassigned the quartet lines to H6 rather than H2- mainly due to comparison of experimentally obtained EPR parameters to theoretical results. Based on the new assignment, trapping site, rotation, ortho-para conversion, quantum diffusion and isotope effect of H+ have been reinterpreted by the precise reanalysis as follows. The H6+ ion is composed of the collinearly aligned H2+ core at the center and two H2 rotors at both ends, occupies a single substitutional site, and has a precession motion around a crystalline axis with the angle of approximately 57 degrees. The ortho-para conversion of H2+ core of H6+ is completed within the time-scale of hours, whereas ortho-H2 molecules near H6+ convert much faster. H6+ diffuses quantum mechanically by the repetition of H6+ + H2 --> H2 + H6+ reaction. The diffusion terminates by the reaction, H6(+) + HD --> H5D(+) + H2, with a HD impurity contained in the para-H2 sample at natural abundance. Finally, we will propose a possible reason why H6+ is produced instead of H3+ in the irradiated solid H2.

A calcium channel blocker, benidipine, improves cell membrane fluidity in human subjects via a nitric oxide-dependent mechanism. An electron paramagnetic resonance investigation.

PubMed

Tsuda, Kazushi; Nishio, Ichiro

2004-12-01

Recent studies have revealed that benidipine, a long-acting dihydropyridine-type of calcium (Ca) channel blocker, may exert its protective effect against vascular disorders by increasing nitric oxide (NO) production. The purpose of the present study was to investigate the effects of benidipine and NO on the membrane function in human subjects. We measured the membrane fluidity of erythrocytes by using an electron paramagnetic resonance (EPR) and spin-labeling method. Benidipine decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (h(o)/h(-1)) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner in normotensive volunteers. The finding indicated that benidipine increased the membrane fluidity and improved the microviscosity of erythrocytes. The effect of benidipine was significantly potentiated by the NO donor, S-nitroso-n-acetylpenicillamine, and by the cyclic guanosine 3', 5'-monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change evoked by benidipine was counteracted by the NO synthase inhibitors, N(G)-nitro-L-arginine-methyl-ester and asymmetric dimethyl-L-arginine. These results demonstrated that benidipine increased the membrane fluidity of erythrocytes, at least in part, via the NO- and cGMP-dependent mechanism. Furthermore, the data strongly suggest that benidipine might have a beneficial effect on the rheologic behavior of erythrocytes and the improvement of the microcirculation in humans.

Rapid determination of environmentally persistent free radicals (EPFRs) in atmospheric particles with a quartz sheet-based approach using electron paramagnetic resonance (EPR) spectroscopy

NASA Astrophysics Data System (ADS)

Chen, Qingcai; Wang, Mamin; Wang, Yuqin; Zhang, Lixin; Xue, Jian; Sun, Haoyao; Mu, Zhen

2018-07-01

Environmentally persistent free radicals (EPFRs) are present within atmospheric fine particles, and they are assumed to be a potential factor responsible for human pneumonia and lung cancer. This study presents a new method for the rapid quantification of EPFRs in atmospheric particles with a quartz sheet-based approach using electron paramagnetic resonance (EPR) spectroscopy. The three-dimensional distributions of the relative response factors in a cavity resonator were simulated and utilized for an accurate quantitative determination of EPFRs in samples. Comparisons between the proposed method and conventional quantitative methods were also performed to illustrate the advantages of the proposed method. The results suggest that the reproducibility and accuracy of the proposed method are superior to those of the quartz tube-based method. Although the solvent extraction method is capable of extracting specific EPFR species, the developed method can be used to determine the total EPFR content; moreover, the analysis process of the proposed approach is substantially quicker than that of the solvent extraction method. The proposed method has been applied in this study to determine the EPFRs in ambient PM2.5 samples collected over Xi'an, the results of which will be useful for extensive research on the sources, concentrations, and physical-chemical characteristics of EPFRs in the atmosphere.

Non-invasive imaging of the levels and effects of glutathione on the redox status of mouse brain using electron paramagnetic resonance imaging.

PubMed

Emoto, Miho C; Matsuoka, Yuta; Yamada, Ken-Ichi; Sato-Akaba, Hideo; Fujii, Hirotada G

2017-04-15

Glutathione (GSH) is the most abundant non-protein thiol that buffers reactive oxygen species in the brain. GSH does not reduce nitroxides directly, but in the presence of ascorbates, addition of GSH increases ascorbate-induced reduction of nitroxides. In this study, we used electron paramagnetic resonance (EPR) imaging and the nitroxide imaging probe, 3-methoxycarbonyl-2,2,5,5-tetramethyl-piperidine-1-oxyl (MCP), to non-invasively obtain spatially resolved redox data from mouse brains depleted of GSH with diethyl maleate compared to control. Based on the pharmacokinetics of the reduction reaction of MCP in the mouse heads, the pixel-based rate constant of its reduction reaction was calculated as an index of the redox status in vivo and mapped as a "redox map". The obtained redox maps from control and GSH-depleted mouse brains showed a clear change in the brain redox status, which was due to the decreased levels of GSH in brains as measured by a biochemical assay. We observed a linear relationship between the reduction rate constant of MCP and the level of GSH for both control and GSH-depleted mouse brains. Using this relationship, the GSH level in the brain can be estimated from the redox map obtained with EPR imaging. Copyright © 2017 Elsevier Inc. All rights reserved.

Analysis of gamma-irradiated melon, pumpkin, and sunflower seeds by electron paramagnetic resonance spectroscopy and gas chromatography-mass spectrometry.

PubMed

Sin, Della W M; Wong, Yiu Chung; Yao, Wai Yin

2006-09-20

Seeds of melon (Citrullus lanatus var. sp.), pumpkin (Cucurbita moschata), and sunflower (Heliantus annus) were gamma-irradiated at 1, 3, 5, and 10 kGy and analyzed by electron paramagnetic resonance (EPR) and gas chromatography-mass spectrometry (GC-MS) according to EN1787:2000 and EN1785:2003, respectively. Distinguishable triplet signals due to the presence of induced cellulose radicals were found at 2.0010-2.0047 g in the EPR spectra. The gamma-irradiated radiolytic markers of 2-dodecylcyclobutanone (2-DCB) and 2-tetradecylcyclobutanone (2-TCB) were identified in all irradiated seed samples. Both the free radicals and the alkylcyclobutanones were found to increase with irradiation dose. In general, linear relationships between the amount of radicals and irradiation dosage could be established. Studies at an ambient temperature (20-25 degrees C) in a humidity-controlled environment showed a complete disappearance of the cellulosic peaks for irradiated samples upon 60 days of storage. Such instability behavior was considered to render the usefulness of using EPR alone in the determination of irradiated seed samples. On the other hand, 2-DCB and 2-TCB were also found to decompose rapidly (>85% loss after 120 days of storage), but the radiolytic markers remained quantifiable after 120 days of postirradiation storage. These results suggest that GC-MS is a versatile and complimentary technique for the confirmation of irradiation treatment to seeds.

Hydrodynamic interpretation on the rotational diffusion of peroxylamine disulfonate solute dissolved in room temperature ionic liquids as studied by electron paramagnetic resonance spectroscopy.

PubMed

Miyake, Yusuke; Akai, Nobuyuki; Kawai, Akio; Shibuya, Kazuhiko

2011-06-23

Rotational motion of a nitroxide radical, peroxylamine disulfonate (PADS), dissolved in room temperature ionic liquids (RTILs) was studied by analyzing electron paramagnetic resonance spectra of PADS in various RTILs. We determined physical properties of PADS such as the hyperfine coupling constant (A), the temperature dependence of anisotropic rotational correlation times (τ(∥) and τ(⊥)), and rotational anisotropy (N). We observed that the A values remain unchanged for various RTILs, which indicates negligible interaction between the N-O PADS group and the cation of RTIL. Large N values suggest strong interaction of the negative sulfonyl parts of PADS with the cations of RTILs. Most of the τ(∥), τ(⊥), and (τ(∥)τ(⊥))(1/2) values are within the range calculated on the basis of a hydrodynamic theory with stick and slip boundary conditions. It was deduced that this theory could not adequately explain the measured results in some RTILs with smaller BF(4) and PF(6) anions.

Purification and properties of formate dehydrogenase from Pseudomonas aeruginosa. Electron-paramagnetic-resonance studies on the molybdenum centre.

PubMed Central

Gadsby, P M; Greenwood, C; Coddington, A; Thomson, A J; Godfrey, C

1987-01-01

Formate dehydrogenase from Pseudomonas aeruginosa contains molybdenum, a [4Fe-4S] cluster and cytochrome b. This paper reports the detection of molybdenum as Mo(V) by e.p.r. spectroscopy. In order to generate Mo(V) signals, addition of amounts of excess formate varying between 10- and 50-fold over enzyme, followed by 200-fold excess of sodium dithionite, were used. Two Mo(V) species were observed. One, the major component, has g1 = 2.012, g2 = 1.985 and g3 = 1.968, appeared at low concentrations of formate and increased linearly in intensity with increasing concentrations of formate up to 25-fold excess over the enzyme. At higher formate concentration this signal disappeared. The appearance and disappearance of this Mo(V) signal seems to parallel the state of reduction of the [4Fe-4S] clusters. A second, minor, Mo(V) species with g-values g1 = 1.996, g2 = 1.981 and g3 = 1.941 appears at a constant level during the formate-dithionite titration. No evidence has been obtained for nuclear hyperfine coupling to protons. The major Mo(V) species has unusual e.p.r. signals compared with other molybdenum-containing enzymes, except for that observed in the formate dehydrogenase from Methanobacterium formicicum [Barber, Siegel, Schauer, May & Ferry (1983) J. Biol. Chem. 258, 10839-10845]. The present work suggests that the enzyme is acting as a CO2 reductase, with dithionite as an electron donor to a [4Fe-4S] cluster, which in turn donates electrons to molybdenum, producing a Mo(V) species with CO2 bound to the metal. PMID:3038082

Investigation of Phenols Activity in Early Stage Oxidation of Edible Oils by Electron Paramagnetic Resonance and 19F NMR Spectroscopies Using Novel Lipid Vanadium Complexes As Radical Initiators.

PubMed

Drouza, Chryssoula; Dieronitou, Anthi; Hadjiadamou, Ioanna; Stylianou, Marios

2017-06-21

A novel dynamic method for the investigation of the phenols activity in early stage oxidation of edible oils based on the formation of α-tocopheryl radicals initiated by oil-soluble vanadium complexes is developed. Two new vanadium complexes in oxidation states V and IV were synthesized by reacting 2,2'-((2-hydroxyoctadecyl)azanediyl)bis(ethan-1-ol) (C18DEA) with [VO(acac) 2 ] and 1-(bis(pyridin-2-ylmethyl)amino)octadecan-2-ol (C18DPA) with VOCl 2 . Addition of a solution of either complex in edible oils resulted in the formation of α-tocopheryl radical, which was monitored by electron paramagnetic resonance (EPR) spectroscopy. The intensity of the α-tocopheryl signal in the EPR spectra was measured versus time. It was found that the profile of the intensity of the α-tocopheryl signal versus time depends on the type of oil, the phenolic content, and the storage time of the oil. The time interval until the occurrence of maximum peak intensity be reached (t m ), the height of the maximum intensity, and the rate of the quenching of the α-tocopheryl radical were used for the investigation of the mechanism of the edible oils oxidation. 19 F NMR of the 19 F labeled phenolic compounds (through trifluoroacetate esters) and radical trap experiments showed that the vanadium complexes in edible oil activate the one electron reduction of dioxygen to superperoxide radical. Superperoxide reacts with the lipids to form alkoperoxyl and alkoxyl lipid radicals, and all these radicals react with the phenols contained in oils.

CHARGE-TRANSFER ASSOCIATION AND PARAMAGNETISM OF SOME ORGANIC SYSTEMS

SciTech Connect

Eastman, J W

When p-xylene was combined with chloranil in n-heptane, charge-transfer optical absorption was observed. The magnitude of this absorption was used to calculate an equilibrium constant for the formation of a donor-acceptor complex containing one p-xylene was combined with carbon tetrabromide and with carbon tetrachloride in n-heptane, no charge-transfer absorption was observed. Reactions of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) with chloranil (pQCl/ sub 4/) were observed in ethylene dichloride and acetonitrile. In both solvents adduct formation occurred initially, as observed by its charge-transfer absorption. In acetonitrile time-dependent electron spin resonance (ESR) absorption was observed, and it was identified with the positive and negative radicalmore » ions of TMPD and pQCl/sub 4/, respectively. In this case a completely ionized electron transfer had occurred. Chloranil and other quinones were found to react with N,N-dimethylaniline forming a crystal violet salt. The diamagnetic donor-acceptor complexes and also semiquinone radicals are intermediates which were observed. Some physical measurements of the kinetics of this reaction are described and correlated. When fluoranil was allowed to react with dimethylaniline, the hyperfine splitting by the fluorine atoms of the fluoranil radical was not resolved. Characteristics of the ESR absorption by this radical in dimethylaniline are discussed in terms of an electron transfer between the semiquinone and quinone, and between the semiquinone and hydroquinone ion. Paramagnetism was discovered in hydrocarbon-quinone solids. ESR absorption was assigned to imperfections in the solid which was normally diamagnetic. The preparation of these solids and some of their physical characteristics are described. (auth)« less

Blood free Radicals Concentration Determined by Electron Paramagnetic Resonance Spectroscopy and Delayed Cerebral Ischemia Occurrence in Patients with Aneurysmal Subarachnoid Hemorrhage.

PubMed

Ewelina, Grzywna; Krzysztof, Stachura; Marek, Moskala; Krzysztof, Kruczala

2017-12-01

Pathophysiology of delayed cerebral ischemia and cerebral vasospasm following aneurysmal subarachnoid hemorrhage is still poorly recognized, however free radicals are postulated as one of the crucial players. This study was designed to scrutinize whether the concentration of free radicals in the peripheral venous blood is related to the occurrence of delayed cerebral ischemia associated with cerebral vasospasm. Twenty-four aneurysmal subarachnoid hemorrhage patients and seven patients with unruptured intracranial aneurysm (control group) have been studied. Free radicals in patients' blood have been detected by the electron paramagnetic resonance (CMH.HCl spin probe, 150 K, ELEXSYS E500 spectrometer) on admission and at least 72 h from disease onset. Delayed cerebral ischemia monitoring was performed by daily neurological follow-up and transcranial color coded Doppler. Delayed cerebral ischemia observed in six aneurysmal subarachnoid hemorrhage patients was accompanied by cerebral vasospasm in all six cases. No statistically significant difference in average free radicals concentration between controls and study subgroups was noticed on admission (p = .3; Kruskal-Wallis test). After 72 h free radicals concentration in delayed cerebral ischemia patients (3.19 ± 1.52 mmol/l) differed significantly from the concentration in aneurysmal subarachnoid hemorrhage patients without delayed cerebral ischemia (0.65 ± 0.37 mmol/l) (p = .012; Mann-Whitney test). These findings are consistent with our assumptions and seem to confirm the role of free radicals in delayed cerebral ischemia development. Preliminary results presented above are promising and we need perform further investigation to establish whether blood free radicals concentration may serve as the biomarker of delayed cerebral ischemia associated with cerebral vasospasm.

Electron Paramagnetic Resonance Studies of Spin-Labeled Hemoglobins and Their Implications to the Nature of Cooperative Oxygen Binding to Hemoglobin*

PubMed Central

Ho, Chien; Baldassare, Joseph J.; Charache, Samuel

1970-01-01

The spin label technique has been used to study human hemoglobins A, F, Zürich, and Chesapeake as a function of carbon monoxide saturation. The experimental results suggest that the changes in the electron paramagnetic resonance spectra of hemoglobin labeled with N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)iodoacetamide depend on the state of ligation of more than one heme group. For those hemoglobins with full or large cooperative ligand binding (such as A, F, and Zürich), there is a lack of isosbestic points in the spectra as a function of CO saturation. However, for those hemoglobins with little or no cooperative ligand binding (such as Chesapeake and methemoglobins), there is a sharp set of isosbestic points. These findings confirm and extend the early work of McConnell and co-workers. The absence of a set of isosbestic points in those hemoglobins with full cooperative ligand binding is consistent with the sequential model of Koshland, Némethy, and Filmer for cooperative oxygen binding to hemoglobin. The present results, with hemoglobin variants having known amino acid substitutions, also focus on the importance of the interactions among the amino acid residues located at α1-β2 or α2-β1 subunit contacts for the functioning of hemoglobin as an oxygen carrier. In addition, the resonance spectra of the spin label are very sensitive to small structural variations around the heme groups in the β- or γ-chains where the labels are attached. The results of the spin label experiment are discussed in relation to recent findings on the mechanism of oxygenation of hemoglobin from the nuclear magnetic resonance studies of this laboratory and the x-ray crystallographic analysis of Perutz and co-workers. PMID:4316679

Effect of TiO2 on electron paramagnetic resonance, optical transmission and dc conductivity of vanadyl doped sodium borate glasses.

PubMed

Agarwal, A; Seth, V P; Gahlot, P; Goyal, D R; Arora, M; Gupta, S K

2004-11-01

Glass systems with composition xTiO2.(30 - x)Na2O.70B2O3 (series I) and xTiO2.(70 - x)B2O3.30Na2O (series II) containing 2 mol% V2O5 have been prepared (0 < or = x < or = 7, mol%) by normal melt-quenching. The electron paramagnetic resonance (EPR) spectra of VO2+ ions have been recorded in the X-band (approximately 9.13 GHz) at room temperature. Spin Hamiltonian parameters, gparallel, gperpendicular, Aparallel, Aperpendicular, the dipolar hyperfine coupling parameter (P) and the Fermi contact interaction parameter (K) have been calculated. The increase in Deltagparallel/Deltagperpendicular with increase in TiO2 content in series I shows that the octahedral symmetry of V4+O6 complex is reduced, whereas in series II the octahedral symmetry is improved with increase in x. The decrease in P, in both the series, indicates that the 3dxy orbit expands with increase in mol% of TiO2. The molecular orbital coefficients, alpha2 and gamma2 have been calculated by recording the optical transmission spectra in the range 500-850 nm. alpha2 and gamma2 increase with increase in x in both the series, which indicates that, the covalency of the vanadium oxygen bonds decreases. The dc conductivity sigma, decreases and activation energy, W increases with increase in TiO2:Na2O ratio whereas with increase in TiO2:B2O3 ratio the variation in sigma and W is within experimental error.

Leptin improves membrane fluidity of erythrocytes in humans via a nitric oxide-dependent mechanism--an electron paramagnetic resonance investigation.

PubMed

Tsuda, Kazushi; Kimura, Keizo; Nishio, Ichiro

2002-09-27

Abnormalities in physical properties of the cell membranes may underlie the defects that are strongly linked to hypertension, stroke, and other cardiovascular diseases. Recently, there has been an indication that leptin, the product of the human obesity gene, actively participates not only in the metabolic regulations but also in the control of cardiovascular functions. In the present study, to assess the role of leptin in the regulation of membrane properties, the effects of leptin on membrane fluidity of erythrocytes in humans are examined. The membrane fluidity of erythrocytes in healthy volunteers by means of an electron paramagnetic resonance (EPR) and spin-labeling method is determined. In an in vitro study, leptin decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner in healthy volunteers. The finding indicated that leptin increased the membrane fluidity and improved the microviscosity of erythrocytes. The effect of leptin on the membrane fluidity was significantly potentiated by the nitric oxide (NO) donors, L-arginine and S-nitroso-N-acetylpenicillamine (SNAP), and a cyclic guanosine monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change evoked by leptin was significantly attenuated in the presence of the NO synthase inhibitors, N(G)-nitro-L-arginine-methyl-ester (L-NAME) and asymmetric dimethyl-L-arginine (ADMA). The results of the present study showed that leptin increased the membrane fluidity and improved the rigidity of cell membranes to some extent via an NO- and cGMP-dependent mechanism. Furthermore, the data also suggest that leptin might have a crucial role in the regulation of rheological behavior of erythrocytes and microcirculation in humans.

Fluorescence and electron paramagnetic resonance studies of norfloxacin and N-donor mixed-ligand ternary copper(II) complexes: Stability and interaction with SDS micelles

NASA Astrophysics Data System (ADS)

Vignoli Muniz, Gabriel S.; Incio, Jimmy Llontop; Alves, Odivaldo C.; Krambrock, Klaus; Teixeira, Letícia R.; Louro, Sonia R. W.

2018-01-01

The stability of ternary copper(II) complexes of a heterocyclic ligand, L (L being 2,2‧-bipyridine (bipy) or 1,10-phenanthroline (phen)) and the fluorescent antibacterial agent norfloxacin (NFX) as the second ligand was studied at pH 7.4 and different ionic strengths. Fluorescence quenching upon titration of NFX with the binary complexes allowed to obtain stability constants for NFX binding, Kb, as a function of ionic strength. The Kb values vary by more than two orders of magnitude when buffer concentration varies from 0.5 to 100 mM. It was observed that previously synthesized ternary complexes dissociate in buffer according with the obtained stability constants. This shows that equimolar solutions of NFX and binary complexes are equivalent to solutions of synthesized ternary complexes. The interaction of the ternary copper complexes with anionic SDS (sodium dodecyl sulfate) micelles was studied by fluorescence and electron paramagnetic resonance (EPR). Titration of NFX-loaded SDS micelles with the complexes Cu:L allowed to determine the stability constants inside the micelles. Fluorescence quenching demonstrated that SDS micelles increase the stability constants by factors around 50. EPR spectra gave details of the copper(II) local environment, and demonstrated that the structure of the ternary complexes inside SDS micelles is different from that in buffer. Mononuclear ternary complexes formed inside the micelles, while in buffer most ternary complexes are binuclear. The results show that anionic membrane interfaces increase formation of copper fluoroquinolone complexes, which can influence bioavailability, membrane diffusion, and mechanism of action of the antibiotics.

Membrane Disruption Mechanism of a Prion Peptide (106-126) Investigated by Atomic Force Microscopy, Raman and Electron Paramagnetic Resonance Spectroscopy.

PubMed

Pan, Jianjun; Sahoo, Prasana K; Dalzini, Annalisa; Hayati, Zahra; Aryal, Chinta M; Teng, Peng; Cai, Jianfeng; Rodriguez Gutierrez, Humberto; Song, Likai

2017-05-18

A fragment of the human prion protein spanning residues 106-126 (PrP106-126) recapitulates many essential properties of the disease-causing protein such as amyloidogenicity and cytotoxicity. PrP106-126 has an amphipathic characteristic that resembles many antimicrobial peptides (AMPs). Therefore, the toxic effect of PrP106-126 could arise from a direct association of monomeric peptides with the membrane matrix. Several experimental approaches are employed to scrutinize the impacts of monomeric PrP106-126 on model lipid membranes. Porous defects in planar bilayers are observed by using solution atomic force microscopy. Adding cholesterol does not impede defect formation. A force spectroscopy experiment shows that PrP106-126 reduces Young's modulus of planar lipid bilayers. We use Raman microspectroscopy to study the effect of PrP106-126 on lipid atomic vibrational dynamics. For phosphatidylcholine lipids, PrP106-126 disorders the intrachain conformation, while the interchain interaction is not altered; for phosphatidylethanolamine lipids, PrP106-126 increases the interchain interaction, while the intrachain conformational order remains similar. We explain the observed differences by considering different modes of peptide insertion. Finally, electron paramagnetic resonance spectroscopy shows that PrP106-126 progressively decreases the orientational order of lipid acyl chains in magnetically aligned bicelles. Together, our experimental data support the proposition that monomeric PrP106-126 can disrupt lipid membranes by using similar mechanisms found in AMPs.

Membrane Disruption Mechanism of a Prion Peptide (106-126) Investigated by Atomic Force Microscopy, Raman and Electron Paramagnetic Resonance Spectroscopy

PubMed Central

Pan, Jianjun; Sahoo, Prasana K.; Dalzini, Annalisa; Hayati, Zahra; Aryal, Chinta M.; Teng, Peng; Cai, Jianfeng; Gutierrez, Humberto Rodriguez; Song, Likai

2018-01-01

A fragment of the human prion protein spanning residues 106-126 (PrP106-126) recapitulates many essential properties of the disease-causing protein such as amyloidogenicity and cytotoxicity. PrP106-126 has an amphipathic characteristic that resembles many antimicrobial peptides (AMPs). Therefore, the toxic effect of PrP106-126 could arise from a direct association of monomeric peptides with membrane matrix. Several experimental approaches are employed to scrutinize the impacts of monomeric PrP106-126 on model lipid membranes. Porous defects in planar bilayers are observed by using solution atomic force microscopy. Adding cholesterol does not impede defect formation. Force spectroscopy experiment shows that PrP106-126 reduces Young’s modulus of planar lipid bilayers. We use Raman microspectroscopy to study the effect of PrP106-126 on lipid vibrational dynamics. For phosphatidylcholine lipids, PrP106-126 disorders the intra-chain conformation, while the inter-chain interaction is not altered; for phosphatidylethanolamine lipids, PrP106-126 increases the inter-chain interaction, while the intra-chain conformational order remains similar. We explain the observed differences by considering different modes of peptide insertion. Finally, electron paramagnetic resonance spectroscopy shows that PrP106-126 progressively decreases the orientational order of lipid acyl chains in magnetically aligned bicelles. Together, our experimental data support the proposition that monomeric PrP106-126 can disrupt lipid membranes by using similar mechanisms found in AMPs. PMID:28459565

Non-invasive imaging of the levels and effects of glutathione on the redox status of mouse brain using electron paramagnetic resonance imaging

SciTech Connect

Emoto, Miho C.; Department of Neurology, Sapporo Medical University School of Medicine, Sapporo, Hokkaido 060-8556; Matsuoka, Yuta

Glutathione (GSH) is the most abundant non-protein thiol that buffers reactive oxygen species in the brain. GSH does not reduce nitroxides directly, but in the presence of ascorbates, addition of GSH increases ascorbate-induced reduction of nitroxides. In this study, we used electron paramagnetic resonance (EPR) imaging and the nitroxide imaging probe, 3-methoxycarbonyl-2,2,5,5-tetramethyl-piperidine-1-oxyl (MCP), to non-invasively obtain spatially resolved redox data from mouse brains depleted of GSH with diethyl maleate compared to control. Based on the pharmacokinetics of the reduction reaction of MCP in the mouse heads, the pixel-based rate constant of its reduction reaction was calculated as an index ofmore » the redox status in vivo and mapped as a “redox map”. The obtained redox maps from control and GSH-depleted mouse brains showed a clear change in the brain redox status, which was due to the decreased levels of GSH in brains as measured by a biochemical assay. We observed a linear relationship between the reduction rate constant of MCP and the level of GSH for both control and GSH-depleted mouse brains. Using this relationship, the GSH level in the brain can be estimated from the redox map obtained with EPR imaging. - Highlights: • Redox status of glutathione-depleted mouse brain was examined with EPR imaging. • Redox status of mouse brain changed depending on glutathione (GSH) levels in brains. • Linear relationship between GSH levels and redox status in brains was found. • Using this relation, estimation of GSH levels in brains is possible from EPR images.« less

Copper doping of ZnO crystals by transmutation of 64Zn to 65Cu: An electron paramagnetic resonance and gamma spectroscopy study

NASA Astrophysics Data System (ADS)

Recker, M. C.; McClory, J. W.; Holston, M. S.; Golden, E. M.; Giles, N. C.; Halliburton, L. E.

2014-06-01

Transmutation of 64Zn to 65Cu has been observed in a ZnO crystal irradiated with neutrons. The crystal was characterized with electron paramagnetic resonance (EPR) before and after the irradiation and with gamma spectroscopy after the irradiation. Major features in the gamma spectrum of the neutron-irradiated crystal included the primary 1115.5 keV gamma ray from the 65Zn decay and the positron annihilation peak at 511 keV. Their presence confirmed the successful transmutation of 64Zn nuclei to 65Cu. Additional direct evidence for transmutation was obtained from the EPR of Cu2+ ions (where 63Cu and 65Cu hyperfine lines are easily resolved). A spectrum from isolated Cu2+ (3d9) ions acquired after the neutron irradiation showed only hyperfine lines from 65Cu nuclei. The absence of 63Cu lines in this Cu2+ spectrum left no doubt that the observed 65Cu signals were due to transmuted 65Cu nuclei created as a result of the neutron irradiation. Small concentrations of copper, in the form of Cu+-H complexes, were inadvertently present in our as-grown ZnO crystal. These Cu+-H complexes are not affected by the neutron irradiation, but they dissociate when a crystal is heated to 900 °C. This behavior allowed EPR to distinguish between the copper initially in the crystal and the copper subsequently produced by the neutron irradiation. In addition to transmutation, a second major effect of the neutron irradiation was the formation of zinc and oxygen vacancies by displacement. These vacancies were observed with EPR.

Brain redox imaging in the pentylenetetrazole (PTZ)-induced kindling model of epilepsy by using in vivo electron paramagnetic resonance and a nitroxide imaging probe.

PubMed

Emoto, Miho C; Yamato, Mayumi; Sato-Akaba, Hideo; Yamada, Ken-ichi; Fujii, Hirotada G

2015-11-03

Much evidence supports the idea that oxidative stress is involved in the pathogenesis of epilepsy, and therapeutic interventions with antioxidants are expected as adjunct antiepileptic therapy. The aims of this study were to non-invasively obtain spatially resolved redox data from control and pentylenetetrazole (PTZ)-induced kindled mouse brains by electron paramagnetic resonance (EPR) imaging and to visualize the brain regions that are sensitive to oxidative damage. After infusion of the redox-sensitive imaging probe 3-methoxycarbonyl-2,2,5,5-tetramethyl-piperidine-1-oxyl (MCP), a series of EPR images of PTZ-induced mouse heads were measured. Based on the pharmacokinetics of the reduction reaction of MCP in the mouse heads, the pixel-based rate constant of its reduction reaction was calculated as an index of redox status in vivo and mapped as a redox map. The obtained redox map showed heterogeneity in the redox status in PTZ-induced mouse brains compared with control. The co-registered image of the redox map and magnetic resonance imaging (MRI) for both control and PTZ-induced mice showed a clear change in the redox status around the hippocampus after PTZ. To examine the role of antioxidants on the brain redox status, the levels of antioxidants were measured in brain tissues of control and PTZ-induced mice. Significantly lower concentrations of glutathione in the hippocampus of PTZ-kindled mice were detected compared with control. From the results of both EPR imaging and the biochemical assay, the hippocampus was found to be susceptible to oxidative damage in the PTZ-induced animal model of epilepsy. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

The effect of lipophilicity of spin-labeled compounds on their distribution in solid lipid nanoparticle dispersions studied by electron paramagnetic resonance.

PubMed

Pegi, Ahlin; Julijana, Kristl; Slavko, Pecar; Janez, Strancar; Marjeta, Sentjurc

2003-01-01

Solid lipid nanoparticles (SLN) constitute an attractive drug carrier system. The aim of this study was to investigate the influence of lipophilicity and structure of different model molecules on their distribution in SLN dispersions. SLN composed of glyceryl tripalmitate as lipid and soybean lecithin and poloxamer 188 as stabilizers were prepared by a melt-emulsification process. PC(10,3), MeFASL(10,3), C(14)-Tempo, and Tempol were incorporated into SLN as spin-labeled compounds. The partition of SP between triglyceride and water was determined experimentally by electron paramagnetic resonance (EPR) and compared with calculated partition coefficients. The distribution of molecules in SLN dispersions was determined from the parameters of EPR spectra, from the reduction kinetics of the spin-labeled compounds with sodium ascorbate, and by computer simulation of EPR spectral line shapes. The experimentally obtained partition coefficients increase in the order Tempol < MeFASL(10,3) < C(14)-Tempo, showing the same trend as the partition coefficients calculated according to Rekker. In SLN dispersions, it was estimated that the ratio of SP between solid lipid core, phospholipid layers (deeper in SLN layer or in liposomes and closer to the surface of SLN), and water is for Tempol 0:0:100, for C(14)-Tempo 46:54(20:34):0, for MeFASL(10,3) 34:65(38:27):1, and for PC(10,3) 10:89(26:3:60):1. Copyright 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association

Manganese binding properties of human calprotectin under conditions of high and low calcium: X-ray crystallographic and advanced electron paramagnetic resonance spectroscopic analysis.

PubMed

Gagnon, Derek M; Brophy, Megan Brunjes; Bowman, Sarah E J; Stich, Troy A; Drennan, Catherine L; Britt, R David; Nolan, Elizabeth M

2015-03-04

The antimicrobial protein calprotectin (CP), a hetero-oligomer of the S100 family members S100A8 and S100A9, is the only identified mammalian Mn(II)-sequestering protein. Human CP uses Ca(II) ions to tune its Mn(II) affinity at a biologically unprecedented hexahistidine site that forms at the S100A8/S100A9 interface, and the molecular basis for this phenomenon requires elucidation. Herein, we investigate the remarkable Mn(II) coordination chemistry of human CP using X-ray crystallography as well as continuous-wave (CW) and pulse electron paramagnetic resonance (EPR) spectroscopies. An X-ray crystallographic structure of Mn(II)-CP containing one Mn(II), two Ca(II), and two Na(I) ions per CP heterodimer is reported. The CW EPR spectrum of Ca(II)- and Mn(II)-bound CP prepared with a 10:0.9:1 Ca(II):Mn(II):CP ratio is characterized by an unusually low zero-field splitting of 485 MHz (E/D = 0.30) for the S = 5/2 Mn(II) ion, consistent with the high symmetry of the His6 binding site observed crystallographically. Results from electron spin-echo envelope modulation and electron-nuclear double resonance experiments reveal that the six Mn(II)-coordinating histidine residues of Ca(II)- and Mn(II)-bound CP are spectroscopically equivalent. The observed (15)N (I = 1/2) hyperfine couplings (A) arise from two distinct classes of nitrogen atoms: the coordinating ε-nitrogen of the imidazole ring of each histidine ligand (A = [3.45, 3.71, 5.91] MHz) and the distal δ-nitrogen (A = [0.11, 0.18, 0.42] MHz). In the absence of Ca(II), the binding affinity of CP for Mn(II) drops by two to three orders of magnitude and coincides with Mn(II) binding at the His6 site as well as other sites. This study demonstrates the role of Ca(II) in enabling high-affinity and specific binding of Mn(II) to the His6 site of human calprotectin.

Paramagnetic Spin Seebeck Effect

SciTech Connect

Wu, Stephen M.; Pearson, John E.; Bhattacharya, Anand

2015-05-01

We report the observation of the longitudinal spin Seebeck effect in paramagnetic insulators. By using a microscale on-chip local heater, we generate a large thermal gradient confined to the chip surface without a large increase in the total sample temperature. Using this technique at low temperatures (< 20 K), we resolve the paramagnetic spin Seebeck effect in the insulating paramagnets Gd3Ga5O12 (gadolinium gallium garnet) and DyScO3 (DSO), using either W or Pt as the spin detector layer. By taking advantage of the strong magnetocrystalline anisotropy of DSO, we eliminate contributions from the Nernst effect in W or Pt, which producesmore » a phenomenologically similar signal.« less

The electronic states of cyclopropane studied by VUV absorption and electron energy-loss spectroscopies

NASA Astrophysics Data System (ADS)

Gingell, M.; Mason, N. J.; Walker, I. C.; Marston, G.; Zhao, H.; Siggel, M. R. F.

1999-06-01

Absolute optical (VUV) absorption cross sections for cyclopropane have been measured from 5.0 to 11.2 and 20-40 eV using synchrotron radiation. Also, electron energy-loss (EEL) spectra have been obtained using incident electrons of (a) 150 eV energy scattered through small angles (energy loss 5.0-15 eV) and (b) near-threshold energies scattered through large angles (energy loss 0-10.5 eV). Taken together these confirm that the low-lying excited electronic states of cyclopropane are of Rydberg type and, although spectral bands are diffuse, a known Rydberg series has been extended. Recent computations (Galasso V 1996 Chem. Phys. 206 289) appear to give a good account of the experimental spectrum from threshold to about 11 eV, but these must be extended if valence-excited states are to be characterized. Particular attention has been directed at the evaluation of absolute optical cross sections. These are now believed to be established over the energy ranges 5-15 and 20-40 eV. In the gap region (15-20 eV) second-order radiation may affect the optical measurements. From consideration of second-order effects, and comparison of the present studies with earlier measurements, we propose a best-estimate cross section in this energy region also.

Effect of MoO3 on electron paramagnetic resonance spectra, optical spectra and dc conductivity of vanadyl ion doped alkali molybdo-borate glasses

NASA Astrophysics Data System (ADS)

Agarwal, A.; Khasa, S.; Seth, V. P.; Sanghi, S.; Arora, M.

2014-02-01

Alkali molybdo-borate glasses having composition xMoO3·(30 - x)M2O·70B2O3 and xMoO3·(70 - x)B2O3·30M2O (M = Li, Na, K) with 0 ⩽ x ⩽ 15 (mol%) doped with 2.0 mol% of V2O5 have been prepared in order to study the influence of MoO3 on electrical conductivity, electron paramagnetic resonance (EPR) and optical spectra. From EPR studies it is observed that V4+ ions in these samples exist as VO2+ ions in octahedral coordination with a tetragonal compression and belong to C4V symmetry. The tetragonal nature and octahedral symmetry of V4+O6 complex increase as well as decrease depending upon the composition of glasses with increase in MoO3 but 3dxy orbit of unpaired electron in the VO2+ ion expands in all the glasses. The decrease in optical band gap suggests that there is an increase in the concentration of non-bridging oxygen's. From the study of optical transmission spectra it is observed that for all the glasses the degree of covalency of the σ-bonding decreases with increase in MoO3 content and the degree of covalency of the π-bonding also varies. These results based on optical spectroscopy are in agreement with EPR findings. It is found that dc conductivity decreases and activation energy increases with increase in MoO3:M2O (M = Li, Na, K) ratio in MoO3·M2O·B2O3 glasses, whereas the conductivity increases and activation energy decreases with increase in MoO3:B2O3 ratio in xMoO3·B2O3·M2O glasses, which is governed by the increase in nonbridging oxygen's. The variation in theoretical optical basicity, Λth is also studied.

Manganese Binding Properties of Human Calprotectin under Conditions of High and Low Calcium: X-ray Crystallographic and Advanced Electron Paramagnetic Resonance Spectroscopic Analysis

DOE PAGES

Gagnon, Derek M.; Brophy, Megan Brunjes; Bowman, Sarah E. J.; ...

2015-01-18

The antimicrobial protein calprotectin (CP), a hetero-oligomer of the S100 family members S100A8 and S100A9, is the only identified mammalian Mn(II)-sequestering protein. Human CP uses Ca(II) ions to tune its Mn(II) affinity at a biologically unprecedented hexahistidine site that forms at the S100A8/S100A9 interface, and the molecular basis for this phenomenon requires elucidation. Here in this paper, we investigate the remarkable Mn(II) coordination chemistry of human CP using X-ray crystallography as well as continuous-wave (CW) and pulse electron paramagnetic resonance (EPR) spectroscopies. An X-ray crystallographic structure of Mn(II)-CP containing one Mn(II), two Ca(II), and two Na(I) ions per CP heterodimermore » is reported. The CW EPR spectrum of Ca(II)- and Mn(II)-bound CP prepared with a 10:0.9:1 Ca(II):Mn(II):CP ratio is characterized by an unusually low zero-field splitting of 485 MHz (E/D = 0.30) for the S = 5/2 Mn(II) ion, consistent with the high symmetry of the His6 binding site observed crystallographically. Results from electron spin–echo envelope modulation and electron–nuclear double resonance experiments reveal that the six Mn(II)-coordinating histidine residues of Ca(II)- and Mn(II)-bound CP are spectroscopically equivalent. The observed 15N (I = 1/2) hyperfine couplings (A) arise from two distinct classes of nitrogen atoms: the coordinating ε-nitrogen of the imidazole ring of each histidine ligand (A = [3.45, 3.71, 5.91] MHz) and the distal δ-nitrogen (A = [0.11, 0.18, 0.42] MHz). In the absence of Ca(II), the binding affinity of CP for Mn(II) drops by two to three orders of magnitude and coincides with Mn(II) binding at the His6 site as well as other sites. This study demonstrates the role of Ca(II) in enabling high-affinity and specific binding of Mn(II) to the His 6 site of human calprotectin.« less

Manganese Binding Properties of Human Calprotectin under Conditions of High and Low Calcium: X-ray Crystallographic and Advanced Electron Paramagnetic Resonance Spectroscopic Analysis

SciTech Connect

Gagnon, Derek M.; Brophy, Megan Brunjes; Bowman, Sarah E. J.

The antimicrobial protein calprotectin (CP), a hetero-oligomer of the S100 family members S100A8 and S100A9, is the only identified mammalian Mn(II)-sequestering protein. Human CP uses Ca(II) ions to tune its Mn(II) affinity at a biologically unprecedented hexahistidine site that forms at the S100A8/S100A9 interface, and the molecular basis for this phenomenon requires elucidation. Here in this paper, we investigate the remarkable Mn(II) coordination chemistry of human CP using X-ray crystallography as well as continuous-wave (CW) and pulse electron paramagnetic resonance (EPR) spectroscopies. An X-ray crystallographic structure of Mn(II)-CP containing one Mn(II), two Ca(II), and two Na(I) ions per CP heterodimermore » is reported. The CW EPR spectrum of Ca(II)- and Mn(II)-bound CP prepared with a 10:0.9:1 Ca(II):Mn(II):CP ratio is characterized by an unusually low zero-field splitting of 485 MHz (E/D = 0.30) for the S = 5/2 Mn(II) ion, consistent with the high symmetry of the His6 binding site observed crystallographically. Results from electron spin–echo envelope modulation and electron–nuclear double resonance experiments reveal that the six Mn(II)-coordinating histidine residues of Ca(II)- and Mn(II)-bound CP are spectroscopically equivalent. The observed 15N (I = 1/2) hyperfine couplings (A) arise from two distinct classes of nitrogen atoms: the coordinating ε-nitrogen of the imidazole ring of each histidine ligand (A = [3.45, 3.71, 5.91] MHz) and the distal δ-nitrogen (A = [0.11, 0.18, 0.42] MHz). In the absence of Ca(II), the binding affinity of CP for Mn(II) drops by two to three orders of magnitude and coincides with Mn(II) binding at the His6 site as well as other sites. This study demonstrates the role of Ca(II) in enabling high-affinity and specific binding of Mn(II) to the His 6 site of human calprotectin.« less

Absorption of infrared radiation by electrons in the field of a neutral hydrogen atom

NASA Technical Reports Server (NTRS)

Stallcop, J. R.

1974-01-01

An analytical expression for the absorption coefficient is developed from a relationship between the cross-section for inverse bremsstrahlung absorption and the cross-section for electron-atom momentum transfer; it is accurate for those photon frequencies v and temperatures such that hv/kT is small. The determination of the absorption of infrared radiation by free-free transitions of the negative hydrogen ion has been extended to higher temperatures. A simple analytical expression for the absorption coefficient has been derived.

Paramagnetic and Diamagnetic Materials

ERIC Educational Resources Information Center

Thompson, Frank

2011-01-01

Paramagnetic and diamagnetic materials are now generally known as the "Cinderella" materials of the magnetic world. However, susceptibility measurements made on these materials in the past have revealed many details about the molecular bonding and the atomic structure of the so-called "transition" elements. Indeed, the magnetic moment of neodymium…

Demonstrating Paramagnetism Using Liquid Nitrogen.

ERIC Educational Resources Information Center

Simmonds, Ray; And Others

1994-01-01

Describes how liquid nitrogen is attracted to the poles of neodymium magnets. Nitrogen is not paramagnetic, so the attraction suggests that the liquid nitrogen contains a small amount of oxygen, which causes the paramagnetism. (MVL)

The absorption of energetic electrons by molecular hydrogen gas

NASA Technical Reports Server (NTRS)

Cravens, T. E.; Victor, G. A.; Dalgarno, A.

1975-01-01

The processes by which energetic electrons lose energy in a weakly ionized gas of molecular hydrogen are analyzed, and calculations are carried out taking into account the discrete nature of the excitation processes. The excitation, ionization, and heating efficiencies are computed for electrons with energies up to 100 eV absorbed in a gas with fractional ionizations up to 0.01, and the mean energy per pair of neutral hydrogen atoms is calculated.

A selective estrogen receptor modulator, tamoxifen, and membrane fluidity of erythrocytes in normotensive and hypertensive postmenopausal women: an electron paramagnetic resonance investigation.

PubMed

Tsuda, Kazushi; Nishio, Ichiro

2005-08-01

Recent studies have shown that tamoxifen, which belongs to a group called selective estrogen receptor modulators (SERM), may exert protective effects against cardiovascular diseases and stroke in postmenopausal women. On the other hand, abnormalities in physical properties of the cell membranes may underlie the defects that are strongly linked to hypertension, stroke, and other cardiovascular diseases. The present study was performed to investigate the effects of tamoxifen on cell membrane fluidity (a reciprocal value of membrane microviscosity) in normotensive and hypertensive postmenopausal women. We used an electron paramagnetic resonance (EPR) and spin-labeling method. Tamoxifen significantly decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (h(o)/h(-1)) for 16-NS obtained from EPR spectra of erythrocyte membranes in normotensive postmenopausal women (mean +/- SEM, order parameter value; control 0.719 +/- 0.002, n = 41; tamoxifen 1 x 10(-7) mol/L 0.704 +/- 0.002, n = 41, P < .0001; tamoxifen 1 x 10(-6) mol/L 0.696 +/- 0.002, n = 41, P < .0001; tamoxifen 1 x 10(-5) mol/L 0.692 +/- 0.002, n = 41, P < .0001). The finding indicated that tamoxifen increased the membrane fluidity and improved the membrane microviscosity of erythrocytes. The membrane action of tamoxifen was antagonized by the estrogen receptor antagonist ICI 182,780. The effect of tamoxifen was significantly potentiated by the nitric oxide (NO) donors, l-arginine and S-nitroso-N-acetylpenicillamine, and a cGMP analog 8-bromo-cGMP. In contrast, the change evoked by tamoxifen was counteracted by the NO synthase inhibitors N(G)-nitro-l-arginine-methyl-ester and asymmetric dimethyl-l-arginine. In hypertensive postmenopausal women, the membrane fluidity of erythrocytes was significantly lower than in normotensive postmenopausal women. The effect of tamoxifen on the membrane fluidity was more pronounced in hypertensive postmenopausal women than in normotensive

Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy. II. Broadband characterization

SciTech Connect

Sidabras, Jason W.; Anderson, James R.; Mainali, Laxman

Experimental results have been reported on an oversize rectangular waveguide assembly operating nominally at 94 GHz. It was formed using commercially available WR28 waveguide as well as a pair of specially designed tapers with a hyperbolic-cosine shape from WR28 to WR10 waveguide [R. R. Mett et al., Rev. Sci. Instrum. 82, 074704 (2011)]. The oversize section reduces broadband insertion loss for an Electron Paramagnetic Resonance (EPR) probe placed in a 3.36 T magnet. Hyperbolic-cosine tapers minimize reflection of the main mode and the excitation of unwanted propagating waveguide modes. Oversize waveguide is distinguished from corrugated waveguide, overmoded waveguide, or quasi-opticmore » techniques by minimal coupling to higher-order modes. Only the TE{sub 10} mode of the parent WR10 waveguide is propagated. In the present work, a new oversize assembly with a gradual 90° twist was implemented. Microwave power measurements show that the twisted oversize waveguide assembly reduces the power loss in the observe and pump arms of a W-band bridge by an average of 2.35 dB and 2.41 dB, respectively, over a measured 1.25 GHz bandwidth relative to a straight length of WR10 waveguide. Network analyzer measurements confirm a decrease in insertion loss of 2.37 dB over a 4 GHz bandwidth and show minimal amplitude distortion of approximately 0.15 dB. Continuous wave EPR experiments confirm these results. The measured phase variations of the twisted oversize waveguide assembly, relative to an ideal distortionless transmission line, are reduced by a factor of two compared to a straight length of WR10 waveguide. Oversize waveguide with proper transitions is demonstrated as an effective way to increase incident power and the return signal for broadband EPR experiments. Detailed performance characteristics, including continuous wave experiment using 1 μM 2,2,6,6-tetramethylpiperidine-1-oxyl in aqueous solution, provided here serve as a benchmark for other broadband low

In vivo visualization and ex vivo quantification of murine breast cancer cells in the mouse brain using MRI cell tracking and electron paramagnetic resonance.

PubMed

Danhier, Pierre; Magat, Julie; Levêque, Philippe; De Preter, Géraldine; Porporato, Paolo E; Bouzin, Caroline; Jordan, Bénédicte F; Demeur, Gladys; Haufroid, Vincent; Feron, Olivier; Sonveaux, Pierre; Gallez, Bernard

2015-03-01

Cell tracking could be useful to elucidate fundamental processes of cancer biology such as metastasis. The aim of this study was to visualize, using MRI, and to quantify, using electron paramagnetic resonance (EPR), the entrapment of murine breast cancer cells labeled with superparamagnetic iron oxide particles (SPIOs) in the mouse brain after intracardiac injection. For this purpose, luciferase-expressing murine 4 T1-luc breast cancer cells were labeled with fluorescent Molday ION Rhodamine B SPIOs. Following intracardiac injection, SPIO-labeled 4 T1-luc cells were imaged using multiple gradient-echo sequences. Ex vivo iron oxide quantification in the mouse brain was performed using EPR (9 GHz). The long-term fate of 4 T1-luc cells after injection was characterized using bioluminescence imaging (BLI), brain MRI and immunofluorescence. We observed hypointense spots due to SPIO-labeled cells in the mouse brain 4 h after injection on T2 *-weighted images. Histology studies showed that SPIO-labeled cancer cells were localized within blood vessels shortly after delivery. Ex vivo quantification of SPIOs showed that less than 1% of the injected cells were taken up by the mouse brain after injection. MRI experiments did not reveal the development of macrometastases in the mouse brain several days after injection, but immunofluorescence studies demonstrated that these cells found in the brain established micrometastases. Concerning the metastatic patterns of 4 T1-luc cells, an EPR biodistribution study demonstrated that SPIO-labeled 4 T1-luc cells were also entrapped in the lungs of mice after intracardiac injection. BLI performed 6 days after injection of 4 T1-luc cells showed that this cell line formed macrometastases in the lungs and in the bones. Conclusively, EPR and MRI were found to be complementary for cell tracking applications. MRI cell tracking at 11.7 T allowed sensitive detection of isolated SPIO-labeled cells in the mouse brain, whereas EPR

Acoustic paramagnetic logging tool

DOEpatents

Vail, III, William B.

1988-01-01

New methods and apparatus are disclosed which allow measurement of the presence of oil and water in geological formations using a new physical effect called the Acoustic Paramagnetic Logging Effect (APLE). The presence of petroleum in formation causes a slight increase in the earth's magnetic field in the vicinity of the reservoir. This is the phenomena of paramagnetism. Application of an acoustic source to a geological formation at the Larmor frequency of the nucleons present causes the paramagnetism of the formation to disappear. This results in a decrease in the earth3 s magnetic field in the vicinity of the oil bearing formation. Repetitively frequency sweeping the acoustic source through the Larmor frequency of the nucleons present (approx. 2 kHz) causes an amplitude modulation of the earth's magnetic field which is a consequence of the APLE. The amplitude modulation of the earth's magnetic field is measured with an induction coil gradiometer and provides a direct measure of the amount of oil and water in the excitation zone of the formation . The phase of the signal is used to infer the longitudinal relaxation times of the fluids present, which results in the ability in general to separate oil and water and to measure the viscosity of the oil present. Such measurements may be preformed in open boreholes and in cased well bores.

Electron Spin Polarization Transfer to ortho-H2 by Interaction of para-H2 with Paramagnetic Species: A Key to a Novel para → ortho Conversion Mechanism.

PubMed

Terenzi, Camilla; Bouguet-Bonnet, Sabine; Canet, Daniel

2015-05-07

We report that at ambient temperature and with 100% enriched para-hydrogen (p-H2) dissolved in organic solvents, paramagnetic spin catalysis of para → ortho hydrogen conversion is accompanied at the onset by a negative ortho-hydrogen (o-H2) proton NMR signal. This novel finding indicates an electron spin polarization transfer, and we show here that this can only occur if the H2 molecule is dissociated upon its transient adsorption by the paramagnetic catalyst. Following desorption, o-H2 is created until the thermodynamic equilibrium is reached. A simple theory confirms that in the presence of a static magnetic field, the hyperfine coupling between unpaired electrons and nuclear spins is responsible for the observed polarization transfer. Owing to the negative electron gyromagnetic ratio, this explains the experimental results and ascertains an as yet unexplored mechanism for para → ortho conversion. Finally, we show that the recovery of o-H2 magnetization toward equilibrium can be simply modeled, leading to the para → ortho conversion rate.

Multifrequency electron paramagnetic resonance and electron-nuclear double-resonance studies of photo-hole processes in AgBr and AgCl emulsion grains

NASA Astrophysics Data System (ADS)

Eachus, R. S.; Pawlik, Th D.; Baetzold, R. C.

2000-10-01

By using a combination of multifrequency EPR spectroscopy, ENDOR spectroscopy and calculations of structure and energy, the reactivities of photo-generated holes in microcrystalline AgBr and AgCl dispersions (photographic emulsions) have been followed in detail. Progress has been facilitated by the use of both gelatin and polyvinyl alcohol (PVA) as peptizers. The initial trapped hole centres produced by band-gap excitation have been identified. In AgBr, this species is [(Br4)3-.V], a neutral complex formed from hole trapping by the four nearest neighbours of a surface Ag+ vacancy (=V). [(Br4)3-.V] reacts with gelatin to produce a transient organic radical at the grain's surface. It does not, however, react with PVA. The formation of the oxidized gelatin radical might involve atomic bromine as an intermediate. In AgCl, the well-known self-trapped hole centre (AgCl6)4- is the initial hole species. The hole diffuses by an electron exchange process until it is trapped by a silver ion on the grain's surface or within its penultimate layer of lattice ions. It is subsequently released from this Ag2+ site to be retrapped at a centre containing four equivalent Cl- ions. The precise identity of this defect has yet to be determined, but its decay also results in the oxidation of gelatin.

Electronic absorption spectra of chromium-bearing sapphirine

NASA Astrophysics Data System (ADS)

Langer, K.; Platonov, A. N.; Matsuk, S. S.; Andrut, M.

1994-05-01

Violet, non-pleochroic and greenish-blue, pleochroic chromium-substituted sapphirines were found in corundum-bearing spinel-websterite xenolites from the Yakutian kimberlite pipes Noyabrskaya (N) and Sludyanka (Sl), respectively. The crystallochemical formulae of sapphirine crystals from such xenolites were determined by EMP to be (Mg3.40Fe0.23Al3.25Cr0.16)[6] Al{1.00/[6]}[O2/Al4.53Si1.47O18] (N) and (Mg2.53Fe0.55 Mn0.04Ti{0.03/4+}Al3.55Cr{0.08/3+})[6]Al{1.00/[16]}[O2/Al4.28Si1.73O18] (Sl). Single crystal spectra in the range 35000 6000 cm1- showed a slightly polarization dependent absorption edge near 3200 cm1- (N) or 30000 cm1- (Sl) and unpolarized bands at 25300 and 17300 cm1-, typical of spin-allowed transitions, derived from 4A2g→4T1g and 4A2g→4T2g, of Cr3+ in octahedral sites, with point symmetry C1, of the structure. Another weak band at 23000 cm-1 in the sapphirine-N spectra is attributed to low symmetry splitting of the excited 4T1 (F)-State of Cr3+. These assignments lead to crystal field parameters Dq=1730cm-1 and B= 685cm-1 of Cr3+ in sapphirine. Crystallochemical and spectroscopic arguments suggest that Cr3+ subsitutes for Al in the M(1) or M(8) sites of the sapphirine structure. In addition to Cr3+-transitions, spectra of Sl exhibit weak dd-bands of Fe2+ at 10000 and 7700 cm1-, which are unpolarized in consistency with the C1 site symmetry of the octahedra in the structure. Spectra of Sl show also prominent, broad bands (Δv1/2˜-5000 cm1-) at 15000 and 11000 cm1-, which occur in E//Y(//b) and E//Z(//c=12°) only and exhibit an intensity ratio αY∶αz close to 1∶3. This result, the large half width, as well as band energy — MM distance considerations suggest that these bands originate from Fe2+[6]-Fe3+[6] charge-transfer transitions in wall octahedra M(1)M(2), M(6)M(7) etc., forming MM vectors of 30° with the c-axis. The lack of Fe2+-Fe3+ charge-transfer bands in sapphirine N might indicate a lower oxygen fugacity during the formation of

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.

Ab initio calculation of the electronic absorption spectrum of liquid water

SciTech Connect

Martiniano, Hugo F. M. C.; Galamba, Nuno; Cabral, Benedito J. Costa, E-mail: ben@cii.fc.ul.pt

2014-04-28

The electronic absorption spectrum of liquid water was investigated by coupling a one-body energy decomposition scheme to configurations generated by classical and Born-Oppenheimer Molecular Dynamics (BOMD). A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies in the liquid phase were calculated with the equation of motion coupled cluster with single and double excitations method. Molecular dynamics configurations were generated by different approaches. Classical MD were carried out with the TIP4P-Ew and AMOEBA force fields. The BLYP and BLYP-D3 exchange-correlation functionals were used in BOMD. Theoretical and experimental results for the electronic absorption spectrum of liquid water are inmore » good agreement. Emphasis is placed on the relationship between the structure of liquid water predicted by the different models and the electronic absorption spectrum. The theoretical gas to liquid phase blue-shift of the peak positions of the electronic absorption spectrum is in good agreement with experiment. The overall shift is determined by a competition between the O–H stretching of the water monomer in liquid water that leads to a red-shift and polarization effects that induce a blue-shift. The results illustrate the importance of coupling many-body energy decomposition schemes to molecular dynamics configurations to carry out ab initio calculations of the electronic properties in liquid phase.« less

Ab initio calculation of the electronic absorption spectrum of liquid water

NASA Astrophysics Data System (ADS)

Martiniano, Hugo F. M. C.; Galamba, Nuno; Cabral, Benedito J. Costa

2014-04-01

The electronic absorption spectrum of liquid water was investigated by coupling a one-body energy decomposition scheme to configurations generated by classical and Born-Oppenheimer Molecular Dynamics (BOMD). A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies in the liquid phase were calculated with the equation of motion coupled cluster with single and double excitations method. Molecular dynamics configurations were generated by different approaches. Classical MD were carried out with the TIP4P-Ew and AMOEBA force fields. The BLYP and BLYP-D3 exchange-correlation functionals were used in BOMD. Theoretical and experimental results for the electronic absorption spectrum of liquid water are in good agreement. Emphasis is placed on the relationship between the structure of liquid water predicted by the different models and the electronic absorption spectrum. The theoretical gas to liquid phase blue-shift of the peak positions of the electronic absorption spectrum is in good agreement with experiment. The overall shift is determined by a competition between the O-H stretching of the water monomer in liquid water that leads to a red-shift and polarization effects that induce a blue-shift. The results illustrate the importance of coupling many-body energy decomposition schemes to molecular dynamics configurations to carry out ab initio calculations of the electronic properties in liquid phase.

Effect of ultraviolet irradiation on free radical scavenging activity of immunosuppressants used in lung transplantation and comparative electron paramagnetic resonance study of kinetics of their interactions with model free radicals.

PubMed

Stanjek-Cichoracka, A; Żegleń, S; Ramos, P; Pilawa, B; Wojarski, J

2018-06-01

The immunosuppressive drugs used in solid organ transplantation or autoimmunological processes were studied by electron paramagnetic resonance (EPR) spectroscopy to estimate their free radical scavenging activity. The interactions of immunosuppressants with free radicals were examined by an X-band (9.3 GHz) EPR spectroscopy and a model of DPPH free radicals. The EPR spectra of DPPH and DPPH interacting with individual drugs were compared. Kinetic studies were performed, and the effect of ultraviolet (UV) irradiation on the free radical scavenging activity of the tested drugs was determined. The free radical scavenging activity of non-irradiated drugs decreased in the order: rapamycin > mycophenolate mofetil > ciclosporin > tacrolimus. UV irradiation increased the free radical scavenging activity of all the tested immunosuppressive drugs, and the effect was highest for tacrolimus. For the non-irradiated samples, the speed of free radical interactions decreased in the order: ciclosporin > tacrolimus > mycophenolate mofetil > rapamycin. UV irradiation only slightly affected the speed of interactions of the immunosuppressive drugs with the model DPPH free radicals. Electron paramagnetic resonance spectroscopy is useful for obtaining information on interactions of immunosuppressive drugs with free radicals. We hypothesized that the long-term immunosuppressive effects of these drugs after transplantation or during autoimmune disorders may be mediated by anti-inflammatory action in addition to the known receptor/cell cycle inhibition. © 2018 John Wiley & Sons Ltd.

Electron photodetachment from gas phase peptide dianions. Relation with optical absorption properties.

PubMed

Joly, Laure; Antoine, Rodolphe; Broyer, Michel; Lemoine, Jérôme; Dugourd, Philippe

2008-02-07

Electron detachment from peptide dianions is studied as a function of the laser wavelength. The first step for the detachment is a resonant electronic excitation of the dianions. Electronic excitation spectra are reported for three peptides, including gramicidin. A comparative study of the detachment yield for 13 peptides was performed at 260 nm and at 220 nm. At 260 nm, the detachment yield is mainly driven by the sum of the absorption coefficients of the aromatic amino acids that are contained in the peptide. At 220 nm, no direct relation is observed between the electron photodetachement yields and the sum of absorption efficiencies. At this wavelength, the sequence and the structure of the peptide may have an influence on the photodetachment process.

Tuning of few-electron states and optical absorption anisotropy in GaAs quantum rings.

PubMed

Wu, Zhenhua; Li, Jian; Li, Jun; Yin, Huaxiang; Liu, Yu

2017-11-15

The electronic and optical properties of a GaAs quantum ring (QR) with few electrons in the presence of the Rashba spin-orbit interaction (RSOI) and the Dresselhaus spin-orbit interaction (DSOI) have been investigated theoretically. The configuration interaction (CI) method is employed to calculate the eigenvalues and eigenstates of the multiple-electron QR accurately. Our numerical results demonstrate that the symmetry breaking induced by the RSOI and DSOI leads to an anisotropic distribution of multi-electron states. The Coulomb interaction offers additional modulation of the electron distribution and thus the optical absorption indices in the quantum rings. By tuning the magnetic/electric fields and/or electron numbers in a quantum ring, one can change its optical properties significantly. Our theory provides a new way to control the multi-electron states and optical properties of a QR by hybrid modulations or by electrical means only.

X-ray absorption spectroscopy to determine originating depth of electrons that form an inelastic background of Auger electron spectrum

NASA Astrophysics Data System (ADS)

Isomura, Noritake; Cui, Yi-Tao; Murai, Takaaki; Oji, Hiroshi; Kimoto, Yasuji

2017-07-01

In Auger electron spectroscopy (AES), the spectral background is mainly due to inelastic scattering of Auger electrons that lose their kinetic energy in a sample bulk. To investigate the spectral components within this background for SiO2(19.3 nm)/Si(100) with known layer thickness, X-ray absorption spectroscopy (XAS) was used in the partial-electron-yield (PEY) mode at several electron kinetic energies to probe the background of the Si KLL Auger peak. The Si K-edge PEY-XAS spectra constituted of both Si and SiO2 components at each kinetic energy, and their component fractions were approximately the same as those derived from the simulated AES background for the same sample structure. The contributions of Auger electrons originating from layers at different depths to the inelastic background could thus be identified experimentally.

Imaging Plasmon Hybridization of Fano Resonances via Hot-Electron-Mediated Absorption Mapping.

PubMed

Simoncelli, Sabrina; Li, Yi; Cortés, Emiliano; Maier, Stefan A

2018-06-13

The inhibition of radiative losses in dark plasmon modes allows storing electromagnetic energy more efficiently than in far-field excitable bright-plasmon modes. As such, processes benefiting from the enhanced absorption of light in plasmonic materials could also take profit of dark plasmon modes to boost and control nanoscale energy collection, storage, and transfer. We experimentally probe this process by imaging with nanoscale precision the hot-electron driven desorption of thiolated molecules from the surface of gold Fano nanostructures, investigating the effect of wavelength and polarization of the incident light. Spatially resolved absorption maps allow us to show the contribution of each element of the nanoantenna in the hot-electron driven process and their interplay in exciting a dark plasmon mode. Plasmon-mode engineering allows control of nanoscale reactivity and offers a route to further enhance and manipulate hot-electron driven chemical reactions and energy-conversion and transfer at the nanoscale.

Electron paramagnetic resonance study of alinement induced by magnetic fields in two smectic-A liquid crystals not exhibiting nematic phases

NASA Technical Reports Server (NTRS)

Fryburg, G. C.; Gelerinter, E.

1972-01-01

Using vanadyl acetylacetonate (VAAC) as a paramagnetic probe, the molecular ordering in two smectic-A liquid crystals that do not display nematic phases were studied. Reproducible alinement was attained by slow cooling throughout the isotropic smectic-A transition in dc magnetic fields of 1.1 and 2.15 teslas. The degree of order attained is small for a smectic-A liquid crystal. Measurements were made of the variation of the average hyperfine splitting of the alined samples as a function of orientation relative to the dc magnetic field of the spectrometer. This functional dependence is in agreement with the theoretical prediction except where the viscosity of the liquid crystal becomes large enough to slow the tumbling of the VAAC, as indicated by asymmetry in the end lines of the spectrum.

Disentangling atomic-layer-specific x-ray absorption spectra by Auger electron diffraction spectroscopy

NASA Astrophysics Data System (ADS)

Matsui, Fumihiko; Matsushita, Tomohiro; Kato, Yukako; Hashimoto, Mie; Daimon, Hiroshi

2009-11-01

In order to investigate the electronic and magnetic structures of each atomic layer at subsurface, we have proposed a new method, Auger electron diffraction spectroscopy, which is the combination of x-ray absorption spectroscopy (XAS) and Auger electron diffraction (AED) techniques. We have measured a series of Ni LMM AED patterns of the Ni film grown on Cu(001) surface for various thicknesses. Then we deduced a set of atomic-layer-specific AED patterns in a numerical way. Furthermore, we developed an algorithm to disentangle XANES spectra from different atomic layers using these atomic-layer-specific AED patterns. Surface and subsurface core level shift were determined for each atomic layer.

Classical topological paramagnetism

NASA Astrophysics Data System (ADS)

Bondesan, R.; Ringel, Z.

2017-05-01

Topological phases of matter are one of the hallmarks of quantum condensed matter physics. One of their striking features is a bulk-boundary correspondence wherein the topological nature of the bulk manifests itself on boundaries via exotic massless phases. In classical wave phenomena, analogous effects may arise; however, these cannot be viewed as equilibrium phases of matter. Here, we identify a set of rules under which robust equilibrium classical topological phenomena exist. We write simple and analytically tractable classical lattice models of spins and rotors in two and three dimensions which, at suitable parameter ranges, are paramagnetic in the bulk but nonetheless exhibit some unusual long-range or critical order on their boundaries. We point out the role of simplicial cohomology as a means of classifying, writing, and analyzing such models. This opens an experimental route for studying strongly interacting topological phases of spins.

Potential benefits of triethylamine as n-electron donor in the estimation of forskolin by electronic absorption and emission spectroscopy

NASA Astrophysics Data System (ADS)

Raju, Gajula; Ram Reddy, A.

2016-02-01

Diterpenoid forskolin was isolated from Coleus forskolii. The electronic absorption and emission studies of forskolin were investigated in various solvents with an aim to improve its detection limits. The two chromophores present in the diterpenoid are not conjugated leading to the poor absorption and emission of UV light. The absorption and fluorescence spectra were solvent specific. In the presence of a monodentate ligand, triethylamine the detection of forskolin is improved by 3.63 times in ethanol with the fluorescence method and 3.36 times in DMSO by the absorption spectral method. The longer wavelength absorption maximum is blue shifted while the lower energy fluorescence maximum is red shifted in the presence of triethylamine. From the wavelength of fluorescence maxima of the exciplex formed between excited forskolin and triethylamine it is concluded that the order of reactivity of hydroxyl groups in the excited state forskolin is in the reverse order to that of the order of the reactivity of hydroxyl groups in its ground state.

Potential benefits of triethylamine as n-electron donor in the estimation of forskolin by electronic absorption and emission spectroscopy.

PubMed

Raju, Gajula; Ram Reddy, A

2016-02-05

Diterpenoid forskolin was isolated from Coleus forskolii. The electronic absorption and emission studies of forskolin were investigated in various solvents with an aim to improve its detection limits. The two chromophores present in the diterpenoid are not conjugated leading to the poor absorption and emission of UV light. The absorption and fluorescence spectra were solvent specific. In the presence of a monodentate ligand, triethylamine the detection of forskolin is improved by 3.63 times in ethanol with the fluorescence method and 3.36 times in DMSO by the absorption spectral method. The longer wavelength absorption maximum is blue shifted while the lower energy fluorescence maximum is red shifted in the presence of triethylamine. From the wavelength of fluorescence maxima of the exciplex formed between excited forskolin and triethylamine it is concluded that the order of reactivity of hydroxyl groups in the excited state forskolin is in the reverse order to that of the order of the reactivity of hydroxyl groups in its ground state. Copyright © 2015. Published by Elsevier B.V.

Collisionless absorption, hot electron generation, and energy scaling in intense laser-target interaction

SciTech Connect

Liseykina, T., E-mail: tatyana.tiseykina@uni-rostock.de; Institute of Computational Technologies SD RAS, Acad. Lavrentjev Ave. 6, 630090 Novosibirsk; Mulser, P.

2015-03-15

Among the various attempts to understand collisionless absorption of intense and superintense ultrashort laser pulses, a whole variety of models and hypotheses has been invented to describe the laser beam target interaction. In terms of basic physics, collisionless absorption is understood now as the interplay of the oscillating laser field with the space charge field produced by it in the plasma. A first approach to this idea is realized in Brunel's model the essence of which consists in the formation of an oscillating charge cloud in the vacuum in front of the target, therefore frequently addressed by the vague termmore » “vacuum heating.” The investigation of statistical ensembles of orbits shows that the absorption process is localized at the ion-vacuum interface and in the skin layer: Single electrons enter into resonance with the laser field thereby undergoing a phase shift which causes orbit crossing and braking of Brunel's laminar flow. This anharmonic resonance acts like an attractor for the electrons and leads to the formation of a Maxwellian tail in the electron energy spectrum. Most remarkable results of our investigations are the Brunel like spectral hot electron distribution at the relativistic threshold, the minimum of absorption at Iλ{sup 2}≅(0.3−1.2)×10{sup 21} Wcm{sup −2}μm{sup 2} in the plasma target with the electron density of n{sub e}λ{sup 2}∼10{sup 23}cm{sup −3}μm{sup 2}, the drastic reduction of the number of hot electrons in this domain and their reappearance in the highly relativistic domain, and strong coupling, beyond expectation, of the fast electron jets with the return current through Cherenkov emission of plasmons. The hot electron energy scaling shows a strong dependence on intensity in the moderately relativistic domain Iλ{sup 2}≅(10{sup 18}−10{sup 20}) Wcm{sup −2}μm{sup 2}, a scaling in vague accordance with current published estimates in the range Iλ{sup 2}≅(0.14−3.5)×10{sup 21} Wcm{sup �

Electron Paramagnetic Resonance (EPR) Spectroscopy in Studies of the Protective Effects of 24-Epibrasinoide and Selenium against Zearalenone-Stimulation of the Oxidative Stress in Germinating Grains of Wheat.

PubMed

Filek, Maria; Łabanowska, Maria; Kurdziel, Magdalena; Sieprawska, Apolonia

2017-05-27

These studies concentrate on the possibility of using selenium ions and/or 24-epibrassinolide at non-toxic levels as protectors of wheat plants against zearalenone, which is a common and widespread mycotoxin. Analysis using the UHPLC-MS technique allowed for identification of grains having the stress-tolerant and stress-sensitive wheat genotype. When germinating in the presence of 30 µM of zearalenone, this mycotoxin can accumulate in both grains and hypocotyls germinating from these grains. Selenium ions (10 µM) and 24-epibrassinolide (0.1 µM) introduced together with zearalenone decreased the uptake of zearalenone from about 295 to 200 ng/g and from about 350 to 300 ng/g in the grains of tolerant and sensitive genotypes, respectively. As a consequence, this also resulted in a reduction in the uptake of zearalenone from about 100 to 80 ng/g and from about 155 to 128 ng/g in the hypocotyls from the germinated grains of tolerant and sensitive wheat, respectively. In the mechanism of protection against the zearalenone-induced oxidative stress, the antioxidative enzymes-mainly superoxide dismutase (SOD) and catalase (CAT)-were engaged, especially in the sensitive genotype. Electron paramagnetic resonance (EPR) studies allowed for a description of the chemical character of the long-lived organic radicals formed in biomolecular structures which are able to stabilize electrons released from reactive oxygen species as well as the changes in the status of transition paramagnetic metal ions. The presence of zearalenone drastically decreased the amount of paramagnetic metal ions-mainly Mn(II) and Fe(III)-bonded in the organic matrix. This effect was particularly found in the sensitive genotype, in which these species were found at a smaller level. The protective effect of selenium ions and 24-epibrassinolide originated from their ability to inhibit the destruction of biomolecules by reactive oxygen species. An increased ability to defend biomolecules against zearalenone

UV-Vis absorption spectra and electronic structure of merocyanines in the gas phase

NASA Astrophysics Data System (ADS)

Ishchenko, Alexander A.; Kulinich, Andrii V.; Bondarev, Stanislav L.; Raichenok, Tamara F.

2018-02-01

Gas-phase absorption spectra of a merocyanine vinylogous series have been studied for the first time. In vapour, their long-wavelength absorption bands were found to be considerably shifted hypsochromically, broader, more symmetrical, less intense, and their vinylene shift much smaller than even in low-polarity n-hexane. This indicates that in the gas phase their electronic structure closely approaches the nonpolar polyene limiting structure. The TDDFT calculations of the long-wavelength electronic transitions in the studied merocyanines in vacuo demonstrated good-to-excellent correlation - depending on the functional used - with the obtained experimental data. For comparison, the solvent effects was accounted for using the polarizable continuum model (PCM) with n-hexane and ethanol as low-polarity and high-polarity media, and compared with the UV-Vis spectral data in these solvents. In this case, the discrepancy between theory and experiment was much greater, increasing at that with the polymethine chain length.

Imaging electronic trap states in perovskite thin films with combined fluorescence and femtosecond transient absorption microscopy

DOE PAGES

Xiao, Kai; Ma, Ying -Zhong; Simpson, Mary Jane; ...

2016-04-22

Charge carrier trapping degrades the performance of organometallic halide perovskite solar cells. To characterize the locations of electronic trap states in a heterogeneous photoactive layer, a spatially resolved approach is essential. Here, we report a comparative study on methylammonium lead tri-iodide perovskite thin films subject to different thermal annealing times using a combined photoluminescence (PL) and femtosecond transient absorption microscopy (TAM) approach to spatially map trap states. This approach coregisters the initially populated electronic excited states with the regions that recombine radiatively. Although the TAM images are relatively homogeneous for both samples, the corresponding PL images are highly structured. Themore » remarkable variation in the PL intensities as compared to transient absorption signal amplitude suggests spatially dependent PL quantum efficiency, indicative of trapping events. Furthermore, detailed analysis enables identification of two trapping regimes: a densely packed trapping region and a sparse trapping area that appear as unique spatial features in scaled PL maps.« less

Convenient determination of luminescence quantum yield using a combined electronic absorption and emission spectrometer

SciTech Connect

Prakash, John; Mishra, Ashok Kumar

2016-01-15

It is possible to measure luminescence quantum yield in a facile way, by designing an optical spectrometer capable of obtaining electronic absorption as well as luminescence spectra, with a setup that uses the same light source and detector for both the spectral measurements. Employment of a single light source and single detector enables use of the same correction factor profile for spectral corrections. A suitable instrumental scaling factor is used for adjusting spectral losses.

Excited state X-ray absorption spectroscopy: Probing both electronic and structural dynamics

NASA Astrophysics Data System (ADS)

Neville, Simon P.; Averbukh, Vitali; Ruberti, Marco; Yun, Renjie; Patchkovskii, Serguei; Chergui, Majed; Stolow, Albert; Schuurman, Michael S.

2016-10-01

We investigate the sensitivity of X-ray absorption spectra, simulated using a general method, to properties of molecular excited states. Recently, Averbukh and co-workers [M. Ruberti et al., J. Chem. Phys. 140, 184107 (2014)] introduced an efficient and accurate L 2 method for the calculation of excited state valence photoionization cross-sections based on the application of Stieltjes imaging to the Lanczos pseudo-spectrum of the algebraic diagrammatic construction (ADC) representation of the electronic Hamiltonian. In this paper, we report an extension of this method to the calculation of excited state core photoionization cross-sections. We demonstrate that, at the ADC(2)x level of theory, ground state X-ray absorption spectra may be accurately reproduced, validating the method. Significantly, the calculated X-ray absorption spectra of the excited states are found to be sensitive to both geometric distortions (structural dynamics) and the electronic character (electronic dynamics) of the initial state, suggesting that core excitation spectroscopies will be useful probes of excited state non-adiabatic dynamics. We anticipate that the method presented here can be combined with ab initio molecular dynamics calculations to simulate the time-resolved X-ray spectroscopy of excited state molecular wavepacket dynamics.

The origin of absorptive features in the two-dimensional electronic spectra of rhodopsin.

PubMed

Farag, Marwa H; Jansen, Thomas L C; Knoester, Jasper

2018-05-09

In rhodopsin, the absorption of a photon causes the isomerization of the 11-cis isomer of the retinal chromophore to its all-trans isomer. This isomerization is known to occur through a conical intersection (CI) and the internal conversion through the CI is known to be vibrationally coherent. Recently measured two-dimensional electronic spectra (2DES) showed dramatic absorptive spectral features at early waiting times associated with the transition through the CI. The common two-state two-mode model Hamiltonian was unable to elucidate the origin of these features. To rationalize the source of these features, we employ a three-state three-mode model Hamiltonian where the hydrogen out-of plane (HOOP) mode and a higher-lying electronic state are included. The 2DES of the retinal chromophore in rhodopsin are calculated and compared with the experiment. Our analysis shows that the source of the observed features in the measured 2DES is the excited state absorption to a higher-lying electronic state and not the HOOP mode.

Nuclear quantum effects in electronically adiabatic quantum time correlation functions: Application to the absorption spectrum of a hydrated electron

NASA Astrophysics Data System (ADS)

Turi, László; Hantal, György; Rossky, Peter J.; Borgis, Daniel

2009-07-01

A general formalism for introducing nuclear quantum effects in the expression of the quantum time correlation function of an operator in a multilevel electronic system is presented in the adiabatic limit. The final formula includes the nuclear quantum time correlation functions of the operator matrix elements, of the energy gap, and their cross terms. These quantities can be inferred and evaluated from their classical analogs obtained by mixed quantum-classical molecular dynamics simulations. The formalism is applied to the absorption spectrum of a hydrated electron, expressed in terms of the time correlation function of the dipole operator in the ground electronic state. We find that both static and dynamic nuclear quantum effects distinctly influence the shape of the absorption spectrum, especially its high energy tail related to transitions to delocalized electron states. Their inclusion does improve significantly the agreement between theory and experiment for both the low and high frequency edges of the spectrum. It does not appear sufficient, however, to resolve persistent deviations in the slow Lorentzian-like decay part of the spectrum in the intermediate 2-3 eV region.

Theoretical modeling of low-energy electronic absorption bands in reduced cobaloximes

DOE PAGES

Bhattacharjee, Anirban; Chavarot-Kerlidou, Murielle; Dempsey, Jillian L.; ...

2014-08-11

Here, we report that the reduced Co(I) states of cobaloximes are powerful nucleophiles that play an important role in the hydrogen-evolving catalytic activity of these species. In this work we have analyzed the low energy electronic absorption bands of two cobaloxime systems experimentally and using a variety of density functional theory and molecular orbital ab initio quantum chemical approaches. Overall we find a reasonable qualitative understanding of the electronic excitation spectra of these compounds but show that obtaining quantitative results remains a challenging task.

Calculation of Vibrational and Electronic Excited-State Absorption Spectra of Arsenic-Water Complexes Using Density Functional Theory

DTIC Science & Technology

2016-06-03

Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/6390--16-9681 Calculation of Vibrational and Electronic Excited-State Absorption Spectra...NUMBER OF PAGES 17. LIMITATION OF ABSTRACT Calculation of Vibrational and Electronic Excited-State Absorption Spectra of Arsenic-Water Complexes Using...Unclassified Unlimited Unclassified Unlimited 59 Samuel G. Lambrakos (202) 767-2601 Calculations are presented of vibrational and electronic excited-state

Elucidating ultrafast electron dynamics at surfaces using extreme ultraviolet (XUV) reflection-absorption spectroscopy.

PubMed

Biswas, Somnath; Husek, Jakub; Baker, L Robert

2018-04-24

Here we review the recent development of extreme ultraviolet reflection-absorption (XUV-RA) spectroscopy. This method combines the benefits of X-ray absorption spectroscopy, such as element, oxidation, and spin state specificity, with surface sensitivity and ultrafast time resolution, having a probe depth of only a few nm and an instrument response less than 100 fs. Using this technique we investigated the ultrafast electron dynamics at a hematite (α-Fe2O3) surface. Surface electron trapping and small polaron formation both occur in 660 fs following photoexcitation. These kinetics are independent of surface morphology indicating that electron trapping is not mediated by defects. Instead, small polaron formation is proposed as the likely driving force for surface electron trapping. We also show that in Fe2O3, Co3O4, and NiO, band gap excitation promotes electron transfer from O 2p valence band states to metal 3d conduction band states. In addition to detecting the photoexcited electron at the metal M2,3-edge, the valence band hole is directly observed as transient signal at the O L1-edge. The size of the resulting charge transfer exciton is on the order of a single metal-oxygen bond length. Spectral shifts at the O L1-edge correlate with metal-oxygen bond covalency, confirming the relationship between valence band hybridization and the overpotential for water oxidation. These examples demonstrate the unique ability to measure ultrafast electron dynamics with element and chemical state resolution using XUV-RA spectroscopy. Accordingly, this method is poised to play an important role to reveal chemical details of previously unseen surface electron dynamics.

X-ray Crystallographic, Multifrequency Electron Paramagnetic Resonance, and Density Functional Theory Characterization of the Ni(P(Cy)2N(tBu)2)2(n+) Hydrogen Oxidation Catalyst in the Ni(I) Oxidation State.

PubMed

Niklas, Jens; Westwood, Mark; Mardis, Kristy L; Brown, Tiara L; Pitts-McCoy, Anthony M; Hopkins, Michael D; Poluektov, Oleg G

2015-07-06

The Ni(I) hydrogen oxidation catalyst [Ni(P(Cy)2N(tBu)2)2](+) (1(+); P(Cy)2N(tBu)2 = 1,5-di(tert-butyl)-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane) has been studied using a combination of electron paramagnetic resonance (EPR) techniques (X-, Q-, and D-band, electron-nuclear double resonance, hyperfine sublevel correlation spectroscopy), X-ray crystallography, and density functional theory (DFT) calculations. Crystallographic and DFT studies indicate that the molecular structure of 1(+) is highly symmetrical. EPR spectroscopy has allowed determination of the electronic g tensor and the spin density distribution on the ligands, and revealed that the Ni(I) center does not interact strongly with the potentially coordinating solvents acetonitrile and butyronitrile. The EPR spectra and magnetic parameters of 1(+) are found to be distinctly different from those for the related compound [Ni(P(Ph)2N(Ph)2)2](+) (4(+)). One significant contributor to these differences is that the molecular structure of 4(+) is unsymmetrical, unlike that of 1(+). DFT calculations on derivatives in which the R and R' groups are systematically varied have allowed elucidation of structure/substituent relationships and their corresponding influence on the magnetic resonance parameters.

Two-Photon Absorption of Soft X-Ray Free Electron Laser Radiation by Graphite Near the Carbon K-Absorption Edge

SciTech Connect

Christensen, Steven T; Lam, Royce K.; Raj, Sumana L.

We have examined the transmission of soft X-ray pulses from the FERMI free electron laser through carbon films of varying thickness, quantifying nonlinear effects of pulses above and below the carbon K-edge. At typical of soft X-ray free electron laser intensities, pulses exhibit linear absorption at photon energies above and below the K-edge, ~308 and ~260 eV, respectively; whereas two-photon absorption becomes significant slightly below the K-edge, ~284.2 eV. The measured two-photon absorption cross section at 284.18 eV (~6 x 10-48 cm4 s) is 7 orders of magnitude above what is expected from a simple theory based on hydrogen-like atomsmore » - a result of resonance effects.« less

Two-photon absorption of soft X-ray free electron laser radiation by graphite near the carbon K-absorption edge

NASA Astrophysics Data System (ADS)

Lam, Royce K.; Raj, Sumana L.; Pascal, Tod A.; Pemmaraju, C. D.; Foglia, Laura; Simoncig, Alberto; Fabris, Nicola; Miotti, Paolo; Hull, Christopher J.; Rizzuto, Anthony M.; Smith, Jacob W.; Mincigrucci, Riccardo; Masciovecchio, Claudio; Gessini, Alessandro; De Ninno, Giovanni; Diviacco, Bruno; Roussel, Eleonore; Spampinati, Simone; Penco, Giuseppe; Di Mitri, Simone; Trovò, Mauro; Danailov, Miltcho B.; Christensen, Steven T.; Sokaras, Dimosthenis; Weng, Tsu-Chien; Coreno, Marcello; Poletto, Luca; Drisdell, Walter S.; Prendergast, David; Giannessi, Luca; Principi, Emiliano; Nordlund, Dennis; Saykally, Richard J.; Schwartz, Craig P.

2018-07-01

We have examined the transmission of soft X-ray pulses from the FERMI free electron laser through carbon films of varying thickness, quantifying nonlinear effects of pulses above and below the carbon K-edge. At typical of soft X-ray free electron laser intensities, pulses exhibit linear absorption at photon energies above and below the K-edge, ∼308 and ∼260 eV, respectively; whereas two-photon absorption becomes significant slightly below the K-edge, ∼284.2 eV. The measured two-photon absorption cross section at 284.18 eV (∼6 × 10-48 cm4 s) is 7 orders of magnitude above what is expected from a simple theory based on hydrogen-like atoms - a result of resonance effects.

Electronic structure of some adenosine receptor antagonists. III. Quantitative investigation of the electronic absorption spectra of alkyl xanthines

NASA Astrophysics Data System (ADS)

Moustafa, H.; Shalaby, Samia H.; El-sawy, K. M.; Hilal, Rifaat

2002-07-01

Quantitative and comparative investigation of the electronic absorption spectra of theophylline, caffeine and their derivatives is reported. The spectra of theophylline, caffeine and theobromine were compared to establish the predominant tautomeric species in solution. This comparison, analysis of solvent effects and assignments of the observed transitions via MO computations indicate the exits of only one tautomeric species in solution that is the N7 form. A low-lying triplet state was identified which corresponds to a HOMO-LUMO transition. This relatively long-lived T 1 state is always less polar than the ground state and may very well underlie the photochemical reactivity of alkyl xanthines. Substituents of different electron donating or withdrawing strengths and solvent effects are investigated and analyzed. The present analysis is facilitated via computer deconvolution of the observed spectra and MO computation.

Electronic structure of barium strontium titanate by soft-x-ray absorption spectroscopy

SciTech Connect

Uehara, Y.; Underwood, J.H.; Gullikson, E.M.

1997-04-01

Perovskite-type titanates, such as Strontium Titanate (STO), Barium Titanate (BTO), and Lead Titanate (PTO) have been widely studied because they show good electric and optical properties. In recent years, thin films of Barium Strontium Titanate (BST) have been paid much attention as dielectrics of dynamic random access memory (DRAM) capacitors. BST is a better insulator with a higher dielectric constant than STO and can be controlled in a paraelectric phase with an appropriate ratio of Ba/Sr composition, however, few studies have been done on the electronic structure of the material. Studies of the electronic structure of such materials can bemore » beneficial, both for fundamental physics research and for improving technological applications. BTO is a famous ferroelectric material with a tetragonal structure, in which Ti and Ba atoms are slightly displaced from the lattice points. On the other hand, BST keeps a paraelectric phase, which means that the atoms are still at the cubic lattice points. It should be of great interest to see how this difference of the local structure around Ti atoms between BTO and BST effects the electronic structure of these two materials. In this report, the authors present the Ti L{sub 2,3} absorption spectra of STO, BTO, and BST measured with very high accuracy in energy of the absorption features.« less

The effect of PVP on morphology, optical properties and electron paramagnetic resonance of Zn0.5Co0.5Fe2-xPrxO4 nanoparticles

NASA Astrophysics Data System (ADS)

Bitar, Z.; El-Said Bakeer, D.; Awad, R.

2017-07-01

Zinc Cobalt nano ferrite doped with Praseodymium, Zn0.5Co0.5Fe2-xPrxO4 (0 ≤ x ≤ 0.2), were prepared by co-precipitation method from an aqueous solution containing metal chlorides and two concentrations of poly(vinylpyrrolidone) (PVP) 0 and 30g/L as capping agent. The samples were characterized using X-ray powder diffraction (XRD), Transmission Electron Microscope (TEM), UV-visible optical spectroscopy, Fourier transform infrared (FTIR) and Electron Paramagnetic Resonance (EPR). XRD results display the formation of cubic spinel structure with space group Fd3m and the lattice parameter (a) is slightly decreased for PVP capping samples. The particle size that determined by TEM, decreases for PVP capping samples. The optical band energy Eg increases for PVP capping samples, confirming the variation of energy gap with the particle size. The FTIR results indicate that the metal oxide bands were shifted for the PVP capping samples. EPR data shows that the PVP addition increases the magnetic resonance field and hence decreases the g-factor.

Black Box Real-Time Transient Absorption Spectroscopy and Electron Correlation

NASA Astrophysics Data System (ADS)

Parkhill, John

2017-06-01

We introduce an atomistic, all-electron, black-box electronic structure code to simulate transient absorption (TA) spectra and apply it to simulate pyrazole and a GFP- chromophore derivative1. The method is an application of OSCF2, our dissipative exten- sion of time-dependent density-functional theory. We compare our simulated spectra directly with recent ultra-fast spectroscopic experiments. We identify features in the TA spectra to Pauli-blocking which may be missed without a first-principles model. An important ingredient in this method is the stationary-TDDFT correction scheme recently put forwards by Fischer, Govind, and Cramer which allows us to overcome a limitation of adiabatic TDDFT. We demonstrate that OSCF2 is able to reproduce the energies of bleaches and induced absorptions, as well as the decay of the transient spectrum, with only the molecular structure as input. We show that the treatment of electron correlation is the biggest hurdle for TA simulations, which motivates the second half of the talk a new method for realtime electron correlation. We continue to derive and propagate self-consistent electronic dynamics. Extending our derivation of OSCF2 to include electron correlation we obtain a non-linear correlated one-body equation of motion which corrects TDHF. Similar equations are known in quantum kinetic theory, but rare in electronic structure. We introduce approximations that stabilize the theory and reduce its computational cost. We compare the resulting dynamics with well-known exact and approximate theories showing improvements over TDHF. When propagated EE2 changes occupation numbers like exact theory, an important feature missing from TDHF or TDDFT. We introduce a rotating wave approximation to reduce the scaling of the model to O(N^4), and enable propagation on realistically large systems. The equation-of-motion does not rely on a pure-state model for the electronic state, and could be used to study the relationship between electron

Electronic absorption band broadening and surface roughening of phthalocyanine double layers by saturated solvent vapor treatment

SciTech Connect

Kim, Jinhyun; Yim, Sanggyu, E-mail: sgyim@kookmin.ac.kr

2012-10-15

Variations in the electronic absorption (EA) and surface morphology of three types of phthalocyanine (Pc) thin film systems, i.e. copper phthalocyanine (CuPc) single layer, zinc phthalocyanine (ZnPc) single layer, and ZnPc on CuPc (CuPc/ZnPc) double layer film, treated with saturated acetone vapor were investigated. For the treated CuPc single layer film, the surface roughness slightly increased and bundles of nanorods were formed, while the EA varied little. In contrast, for the ZnPc single layer film, the relatively high solubility of ZnPc led to a considerable shift in the absorption bands as well as a large increase in the surface roughnessmore » and formation of long and wide nano-beams, indicating a part of the ZnPc molecules dissolved in acetone, which altered their molecular stacking. For the CuPc/ZnPc film, the saturated acetone vapor treatment resulted in morphological changes in mainly the upper ZnPc layer due to the significantly low solubility of the underlying CuPc layer. The treatment also broadened the EA band, which involved a combination of unchanged CuPc and changed ZnPc absorption.« less

Electron Spin Resonance and optical absorption spectroscopic studies of manganese centers in aluminium lead borate glasses.

PubMed

SivaRamaiah, G; LakshmanaRao, J

2012-12-01

Electron Spin Resonance (ESR) and optical absorption studies of 5Al(2)O(3)+75H(3)BO(3)+(20-x)PbO+xMnSO(4) (where x=0.5, 1,1.5 and 2 mol% of MnSO(4)) glasses at room temperature have been studied. The ESR spectrum of all the glasses exhibits resonance signals with effective isotropic g values at ≈2.0, 3.3 and 4.3. The ESR resonance signal at isotropic g≈2.0 has been attributed to Mn(2+) centers in an octahedral symmetry. The ESR resonance signals at isotropic g≈3.3 and 4.3 have been attributed to the rhombic symmetry of the Mn(2+) ions. The zero-field splitting parameter (zfs) has been calculated from the intensities of the allowed hyperfine lines. The optical absorption spectrum exhibits an intense band in the visible region and it has been attributed to (5)E(g)→(5)T(2g) transition of Mn(3+)centers in an octahedral environment. The optical band gap and the Urbach energies have been calculated from the ultraviolet absorption edges. Copyright © 2012 Elsevier B.V. All rights reserved.

Electronic structure measurements of metal-organic solar cell dyes using x-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Johnson, Phillip S.

The focus of this thesis is twofold: to report the results of X-ray absorption studies of metal-organic dye molecules for dye-sensitized solar cells and to provide a basic training manual on X-ray absorption spectroscopy techniques and data analysis. The purpose of our research on solar cell dyes is to work toward an understanding of the factors influencing the electronic structure of the dye: the choice of the metal, its oxidation state, ligands, and cage structure. First we study the effect of replacing Ru in several common dye structures by Fe. First-principles calculations and X-ray absorption spectroscopy at the C 1s and N 1s edges are combined to investigate transition metal dyes in octahedral and square planar N cages. Octahedral molecules are found to have a downward shift in the N 1s-to-pi* transition energy and an upward shift in C 1s-to-pi* transition energy when Ru is replaced by Fe, explained by an extra transfer of negative charge from Fe to the N ligands compared to Ru. For the square planar molecules, the behavior is more complex because of the influence of axial ligands and oxidation state. Next the crystal field parameters for a series of phthalocyanine and porphyrins dyes are systematically determined using density functional calculations and atomic multiplet calculations with polarization-dependent X-ray absorption spectra. The polarization dependence of the spectra provides information on orbital symmetries which ensures the determination of the crystal field parameters is unique. A uniform downward scaling of the calculated crystal field parameters by 5-30% is found to be necessary to best fit the spectra. This work is a part of the ongoing effort to design and test new solar cell dyes. Replacing the rare metal Ru with abundant metals like Fe would be a significant advance for dye-sensitized solar cells. Understanding the effects of changing the metal centers in these dyes in terms of optical absorption, charge transfer, and electronic

Time-dependent broken-symmetry density functional theory simulation of the optical response of entangled paramagnetic defects: Color centers in lithium fluoride

NASA Astrophysics Data System (ADS)

Janesko, Benjamin G.

2018-02-01

Parameter-free atomistic simulations of entangled solid-state paramagnetic defects may aid in the rational design of devices for quantum information science. This work applies time-dependent density functional theory (TDDFT) embedded-cluster simulations to a prototype entangled-defect system, namely two adjacent singlet-coupled F color centers in lithium fluoride. TDDFT calculations accurately reproduce the experimental visible absorption of both isolated and coupled F centers. The most accurate results are obtained by combining spin symmetry breaking to simulate strong correlation, a large fraction of exact (Hartree-Fock-like) exchange to minimize the defect electrons' self-interaction error, and a standard semilocal approximation for dynamical correlations between the defect electrons and the surrounding ionic lattice. These results motivate application of two-reference correlated ab initio approximations to the M-center, and application of TDDFT in parameter-free simulations of more complex entangled paramagnetic defect architectures.

Time-resolved X-ray Absorption Spectroscopy for Electron Transport Study in Warm Dense Gold

NASA Astrophysics Data System (ADS)

Lee, Jong-Won; Bae, Leejin; Engelhorn, Kyle; Heimann, Philip; Ping, Yuan; Barbrel, Ben; Fernandez, Amalia; Beckwith, Martha Anne; Cho, Byoung-Ick; GIST Team; IBS Team; LBNL Collaboration; SLAC Collaboration; LLNL Collaboration

2015-11-01

The warm dense Matter represents states of which the temperature is comparable to Fermi energy and ions are strongly coupled. One of the experimental techniques to create such state in the laboratory condition is the isochoric heating of thin metal foil with femtosecond laser pulses. This concept largely relies on the ballistic transport of electrons near the Fermi-level, which were mainly studied for the metals in ambient conditions. However, they were barely investigated in warm dense conditions. We present a time-resolved x-ray absorption spectroscopy measured for the Au/Cu dual layered sample. The front Au layer was isochorically heated with a femtosecond laser pulse, and the x-ray absorption changes around L-edge of Cu, which was attached on the backside of Au, was measured with a picosecond resolution. Time delays between the heating of the `front surface' of Au layer and the alternation of x-ray spectrum of Cu attached on the `rear surface' of Au indicate the energetic electron transport mechanism through Au in the warm dense conditions. IBS (IBS-R012-D1) and the NRF (No. 2013R1A1A1007084) of Korea.

X-ray absorption investigation of the electronic structure of the CuI@SWCNT nanocomposite

NASA Astrophysics Data System (ADS)

Generalov, A. V.; Brzhezinskaya, M. M.; Vinogradov, A. S.; Püttner, R.; Chernysheva, M. V.; Lukashin, A. V.; Eliseev, A. A.

2011-03-01

The Cu 2 p, I 3 d, and C 1 sX-ray absorption spectra of the CuI@SWCNT nanocomposite prepared by filling single-walled carbon nanotubes (SWCNTs) with the CuI melt by the capillary technique have been measured with a high-energy resolution using the equipment of the Russian-German beamline at the BESSY electron storage ring. In order to characterize the electronic structure of the nanocomposite and possible changes in the atomic and electronic structures of CuI and SWCNTs in the CuI@SWCNT nanocomposite, the spectra obtained have been analyzed in the framework of the quasi-molecular approach by comparing with the spectra of the pristine (CuI and SWCNT) and reference (CuO) systems. It has been revealed that the encapsulation of the CuI compound inside SWCNTs is accompanied by changes in the electronic structure of CuI and SWCNTs due to the chemical interaction between the filler and carbon nanotubes and the change in the atomic structure of CuI.

Understanding the magnetic behavior of heat treated CaO-P2O5-Na2O-Fe2O3-SiO2 bioactive glass using electron paramagnetic resonance studies

NASA Astrophysics Data System (ADS)

Shankhwar, Nisha; Kothiyal, G. P.; Srinivasan, A.

2014-09-01

Bioactive glass of composition 41CaO-44SiO2-4P2O5-8Fe2O3-3Na2O has been heat treated in the temperature (TA) range of 750-1150 °C for time periods (tA) ranging from 1 h to 3 h to yield magnetic bioactive glass ceramics (MBCs). X-ray diffraction studies indicate the presence of bone mineral (hydroxyapatite and wollastonite) and magnetic (magnetite and α-hematite) phases in nanocrystalline form in the MBCs. Electron paramagnetic resonance (EPR) study was carried out to understand the variation in saturation magnetization and coercivity of the MBCs with TA and tA. These studies reveal the nature and amount of iron ions present in the MBCs and their interaction in the glassy oxide matrix as a function of annealing parameters. The deterioration in the magnetic properties of the glass heat treated above 1050 °C is attributed to the crystallization of the non-magnetic α-hematite phase. These results are expected to be useful in the application of these MBCs as thermoseeds in hyperthermia treatment of cancer.

Charge order suppression, emergence of ferromagnetism and absence of exchange bias effect in Bi0.25Ca0.75MnO3 nanoparticles: Electron paramagnetic resonance and magnetization studies

NASA Astrophysics Data System (ADS)

Singh, Geetanjali; Bhat, S. V.

2012-06-01

We report the results of magnetization and electron paramagnetic resonance (EPR) studies on nanoparticles (average diameter ˜ 30 nm) of Bi0.25Ca0.75MnO3 (BCMO) and compare them with the results on bulk BCMO. The nanoparticles were prepared using the nonaqueous sol-gel technique and characterized by XRD and TEM analysis. Magnetization measurements were carried out with a commercial physical property measurement system (PPMS). While the bulk BCMO exhibits a charge ordering transition at ˜230 K and an antiferromagnetic (AFM) transition at ˜130 K, in the nanoparticles, the CO phase is seen to have disappeared and a transition to a ferromagnetic (FM) state is observed at Tc ˜ 120 K. However, interestingly, the exchange bias effect observed in other nanomanganite ferromagnets is absent in BCMO nanoparticles. EPR measurements were carried out in the X-band between 8 and 300 K. Lineshape fitting to a Lorentzian with two terms (accounting for both the clockwise and anticlockwise rotations of the microwave field) was employed to obtain the relevant EPR parameters as functions of temperature. The results confirm the occurrence of ferromagnetism in the nanoparticles of BCMO.

Low-lying singlet states of carotenoids having 8-13 conjugated double bonds as determined by electronic absorption spectroscopy

NASA Astrophysics Data System (ADS)

Wang, Peng; Nakamura, Ryosuke; Kanematsu, Yasuo; Koyama, Yasushi; Nagae, Hiroyoshi; Nishio, Tomohiro; Hashimoto, Hideki; Zhang, Jian-Ping

2005-07-01

Electronic absorption spectra were recorded at room temperature in solutions of carotenoids having different numbers of conjugated double bonds, n = 8-13, including a spheroidene derivatives, neurosporene, spheroidene, lycopene, anhydrorhodovibrin and spirilloxanthin. The vibronic states of 1Bu+(v=0-4), 2Ag-(v=0-3), 3Ag- (0) and 1Bu- (0) were clearly identified. The arrangement of the four electronic states determined by electronic absorption spectroscopy was identical to that determined by measurement of resonance Raman excitation profiles [K. Furuichi et al., Chem. Phys. Lett. 356 (2002) 547] for carotenoids in crystals.

Trispyrazolylborate Complexes: An Advanced Synthesis Experiment Using Paramagnetic NMR, Variable-Temperature NMR, and EPR Spectroscopies

ERIC Educational Resources Information Center

Abell, Timothy N.; McCarrick, Robert M.; Bretz, Stacey Lowery; Tierney, David L.

2017-01-01

A structured inquiry experiment for inorganic synthesis has been developed to introduce undergraduate students to advanced spectroscopic techniques including paramagnetic nuclear magnetic resonance and electron paramagnetic resonance. Students synthesize multiple complexes with unknown first row transition metals and identify the unknown metals by…

Localized magnetoplasmons in quantum dots: Magneto-optical absorption, Raman scattering, and inelastic electron scattering

NASA Astrophysics Data System (ADS)

Kushwaha, M. S.

We investigate a one-component, quasi-zero dimensional, quantum plasma exposed to a parabolic potential and an applied magnetic field in the symmetric gauge. If the size of such a system as can be realized in the semiconducting quantum dots is on the order of the de-Broglie wavelength, the electronic and optical properties become highly tunable. Then the quantum size effects challenge the observation of many-particle phenomena such as the magneto-optical absorption, Raman intensity, and electron-energy-loss spectrum. An exact analytical solution of the problem leads us to infer that these many-particle phenomena are, in fact, dictated by the generalized Kohn's theorem in the long-wavelength limit. Maneuvering the confinement and/or the magnetic field furnishes the resonance energy capable of being explored with the FIR, Raman, or electron-energy-loss spectroscopy. This implies that either of these probes should be competent in observing the localized magnetoplasmons in the system. A deeper insight into the physics of quantum dots is paving the way for their implementation in such diverse fields as quantum computing and medical imaging.

Floquet theory of microwave absorption by an impurity in the two-dimensional electron gas

NASA Astrophysics Data System (ADS)

Chepelianskii, Alexei D.; Shepelyansky, Dima L.

2018-03-01

We investigate the dynamics of a two-dimensional electron gas (2DEG) under circular polarized microwave radiation in the presence of dilute localized impurities. Inspired by recent developments on Floquet topological insulators we obtain the Floquet wave functions of this system which allow us to predict the microwave absorption and charge density responses of the electron gas; we demonstrate how these properties can be understood from the underlying semiclassical dynamics even for impurities with a size of around a magnetic length. The charge density response takes the form of a rotating charge density vortex around the impurity that can lead to a significant renormalization of the external microwave field which becomes strongly inhomogeneous on the scale of a cyclotron radius around the impurity. We show that this inhomogeneity can suppress the circular polarization dependence which is theoretically expected for microwave induced resistance oscillations but which was not observed in experiments on semiconducting 2DEGs. Our explanation for this so far unexplained polarization independence has close similarities with the Azbel'-Kaner effect in metals where the interaction length between the microwave field and conduction electrons is much smaller than the cyclotron radius due to skin effect generating harmonics of the cyclotron resonance.

Change In The Electronic Structure And Optical Absorption Of Cuprate Delafossites Via B-site Alloying

NASA Astrophysics Data System (ADS)

Beesley, Ramon; Panapitiya, Gihan; Lewis, James; Lewis Group Team

Delafossite oxides are a family of materials with the form ABO2 , where the A-site is a monovalent cation (Cu , Ag , Au) and the B-site is a trivalent cation (Ga , Al , In). Delafossites typically have a wide optical band gap, this band gap may be tuned by adding a second B-site element forming an AB(1- x) 1B(x)2O2 alloy. We investigate changes in the electronic structure of CuAlO2 , CuGaO2 , and CuInO2 when alloyed with CuFeO2 . Using the FIREBALL program to optimize the atomic structure, calculate the total and partial density of states, calculate the valence band edge for each alloy level, and investigate the clustering factor of the second B-site atom, it is found that alloying with Fe creates midgap states caused by Fe - O interactions. From the partial density of state, each type of atoms contribution to the change in the valence band edge can be seen. Observed changes to the materials include increased optical absorption in the visible range, and symmetry breaking because of the deformation in the crystal structure. The CuFeO2 alloying percentages range from 0-5%. We are synthesizing these alloys to experimentally verify the changes in the optical absorption spectra.

Electron-cyclotron wave propagation, absorption and current drive in the presence of neoclassical tearing modes

NASA Astrophysics Data System (ADS)

Isliker, Heinz; Chatziantonaki, Ioanna; Tsironis, Christos; Vlahos, Loukas

2012-09-01

We analyze the propagation of electron-cyclotron waves, their absorption and current drive when neoclassical tearing modes (NTMs), in the form of magnetic islands, are present in a tokamak plasma. So far, the analysis of the wave propagation and power deposition in the presence of NTMs has been performed mainly in the frame of an axisymmetric magnetic field, ignoring any effects from the island topology. Our analysis starts from an axisymmetric magnetic equilibrium, which is perturbed such as to exhibit magnetic islands. In this geometry, we compute the wave evolution with a ray-tracing code, focusing on the effect of the island topology on the efficiency of the absorption and current drive. To increase the precision in the calculation of the power deposition, the standard analytical flux-surface labeling for the island region has been adjusted from the usual cylindrical to toroidal geometry. The propagation up to the O-point is found to be little affected by the island topology, whereas the power absorbed and the driven current are significantly enhanced, because the resonant particles are bound to the small volumes in between the flux surfaces of the island. The consequences of these effects on the NTM evolution are investigated in terms of the modified Rutherford equation.

ELECTRON MICROSCOPY OF ABSORPTION OF TRACER MATERIALS BY TOAD URINARY BLADDER EPITHELIUM

PubMed Central

Choi, Jae Kwon

1965-01-01

The absorption of Thorotrast and saccharated iron oxide by the epithelium of the toad urinary bladder was studied by electron microscopy. Whether the toads were hydrated, dehydrated, or given Pitressin, no significant differences in transport of colloidal particles by epithelial cells were observed. This implies that these physiological factors had little effect on the transport of the tracer particles. Tracer particles were encountered in three types of epithelial cells which line the bladder lumen, but most frequently in the mitochondria-rich cells. Tracer materials were incorporated into the cytoplasm of epithelial cells after being adsorbed to the coating layer covering the luminal surface of the cells. In the intermediate stage (1 to 3 hours after introducing tracer) particles were present in small vesicles, tubules, and multivesicular bodies. In the later stages (up to 65 hours), the particles were more commonly seen to be densely packed within large membrane-bounded bodies which were often found near the Golgi region. These large bodies probably were formed by the fusion of small vesicles. Irrespective of the stages of absorption, no particles were found in the intercellular spaces or in the submucosa. Particles apparently did not penetrate the intercellular spaces of the epithelium beyond the level of the tight junction. PMID:14287173

Visible light induction of an electron paramagnetic resonance split signal in Photosystem II in the S(2) state reveals the importance of charges in the oxygen-evolving center during catalysis: a unifying model.

PubMed

Sjöholm, Johannes; Styring, Stenbjörn; Havelius, Kajsa G V; Ho, Felix M

2012-03-13

Cryogenic illumination of Photosystem II (PSII) can lead to the trapping of the metastable radical Y(Z)(•), the radical form of the redox-active tyrosine residue D1-Tyr161 (known as Y(Z)). Magnetic interaction between this radical and the CaMn(4) cluster of PSII gives rise to so-called split electron paramagnetic resonance (EPR) signals with characteristics that are dependent on the S state. We report here the observation and characterization of a split EPR signal that can be directly induced from PSII centers in the S(2) state through visible light illumination at 10 K. We further show that the induction of this split signal takes place via a Mn-centered mechanism, in the same way as when using near-infrared light illumination [Koulougliotis, D., et al. (2003) Biochemistry 42, 3045-3053]. On the basis of interpretations of these results, and in combination with literature data for other split signals induced under a variety of conditions (temperature and light quality), we propose a unified model for the mechanisms of split signal induction across the four S states (S(0), S(1), S(2), and S(3)). At the heart of this model is the stability or instability of the Y(Z)(•)(D1-His190)(+) pair that would be formed during cryogenic oxidation of Y(Z). Furthermore, the model is closely related to the sequence of transfers of protons and electrons from the CaMn(4) cluster during the S cycle and further demonstrates the utility of the split signals in probing the immediate environment of the oxygen-evolving center in PSII.

Electronic structure of transition metal-cysteine complexes from X-ray absorption spectroscopy.

PubMed

Leung, Bonnie O; Jalilehvand, Farideh; Szilagyi, Robert K

2008-04-17

The electronic structures of HgII, NiII, CrIII, and MoV complexes with cysteine were investigated by sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy and density functional theory. The covalency in the metal-sulfur bond was determined by analyzing the intensities of the electric-dipole allowed pre-edge features appearing in the XANES spectra below the ionization threshold. Because of the well-defined structures of the selected cysteine complexes, the current work provides a reference set for further sulfur K-edge XAS studies of bioinorganic active sites with transition metal-sulfur bonds from cysteine residues as well as more complex coordination compounds with thiolate ligands.

Liquid-crystalline dendrimer Cu(II) complexes and Cu(0) nanoclusters based on the Cu(II) complexes: An electron paramagnetic resonance investigation

NASA Astrophysics Data System (ADS)

Domracheva, N. E.; Mirea, A.; Schwoerer, M.; Torre-Lorente, L.; Lattermann, G.

2007-07-01

New nanostructured materials, namely, the liquid-crystalline copper(II) complexes that contain poly(propylene imine) dendrimer ligands of the first (ligand 1) and second (ligand 2) generations and which have a columnar mesophase and different copper contents (x = Cu/L), are investigated by EPR spectroscopy. The influence of water molecules and nitrate counterions on the magnetic properties of complex 2 (x = 7.3) is studied. It is demonstrated that water molecules can extract some of the copper ions from dendrimer complexes and form hexaaqua copper complexes with free ions. The dimer spectra of fully hydrated complex 2 (x = 7.3) are observed at temperatures T < 10 K. For this complex, the structure is identified and the distance between the copper ions is determined. It is shown that the nitrate counterion plays the role of a bridge between the hexaaqua copper(II) complex and the dendrimer copper(II) complex. The temperature-induced valence tautomerism attended by electron transport is revealed for the first time in blue dendrimer complexes 1 (x = 1.9) with a dimer structure. The activation energy for electron transport is estimated to be 0.35 meV. The coordination of the copper ion site (NO4) and the structural arrangement of green complexes 1 (x = 1.9) in the columnar mesophase are determined. Complexes of this type form linear chains in which nitrate counterions serve as bridges between copper centers. It is revealed that green complexes 1 (x = 1.9) dissolved in isotropic inert solvents can be oriented in the magnetic field (B 0 = 8000 G). The degree of orientation of these complexes is rather high (S z = 0.76) and close to that of systems with a complete ordering (S z = 1) in the magnetic field. Copper(0) nanoclusters prepared by reduction of complex 2 (x = 7.3) in two reducing agents (NaBH4, N2H4 · H2O) are examined. A model is proposed for a possible location of Cu(0) nanoclusters in a dendrimer matrix.

Optical detection of paramagnetic centres: From crystals to glass-ceramics

NASA Astrophysics Data System (ADS)

Rogulis, Uldis

2016-07-01

An unambiguous attribution of the absorption spectra to definite paramagnetic centres identified by the EPR techniques in the most cases is problematic. This problem may be solved by applying of a direct measurement techniques—the EPR detected via the magnetic circular dichroism, or briefly MCD-EPR. The present survey reports on the advantages and disadvantages applying the MCD-EPR techniques to simple and complex paramagnetic centres in crystals as well as glasses and glass-ceramics.

Electron phonon couplings in 2D perovskite probed by ultrafast photoinduced absorption spectroscopy

NASA Astrophysics Data System (ADS)

Huynh, Uyen; Ni, Limeng; Rao, Akshay

We use the time-resolved photoinduced absorption (PIA) spectroscopy with 20fs time resolution to investigate the electron phonon coupling in the self-assembled hybrid organic layered perovskite, the hexyl ammonium lead iodide compound (C6H13NH3)2 (PbI4) . The coupling results in the broadening and asymmetry of its temperature-dependence photoluminescence spectra. The exact time scale of this coupling, however, wasn't reported experimentally. Here we show that using an ultrashort excitation pulse allows us to resolve from PIA kinetics the oscillation of coherent longitudinal optical phonons that relaxes and self-traps electrons to lower energy states within 200 fs. The 200fs relaxation time is equivalent to a coupling strength of 40meV. Two coupled phonon modes are also identified as about 100 cm-1 and 300 cm-1 from the FFT spectrum of the PIA kinetics. The lower energy mode is consistent with previous reports and Raman spectrum but the higher energy one hasn't been observed before.

Paramagnetic or diamagnetic persistent currents? A topological point of view

NASA Astrophysics Data System (ADS)

Waintal, Xavier

2009-03-01

A persistent current flows at low temperatures in small conducting rings when they are threaded by a magnetic flux. I will discuss the sign of this persistent current (diamagnetic or paramagnetic response) in the special case of N electrons in a one dimensional ring [1]. One dimension is very special in the sense that the sign of the persistent current is entirely controlled by the topology of the system. I will establish lower bounds for the free energy in the presence of arbitrary electron-electron interactions and external potentials. Those bounds are the counterparts of upper bounds derived by Leggett using another topological argument. Rings with odd (even) numbers of polarized electrons are always diamagnetic (paramagnetic). The situation is more interesting with unpolarized electrons where Leggett upper bound breaks down: rings with N=4n exhibit either paramagnetic behavior or a superconductor-like current-phase relation. The topological argument provides a rigorous justification for the phenomenological Huckel rule which states that cyclic molecules with 4n + 2 electrons like benzene are aromatic while those with 4n electrons are not. [4pt] [1] Xavier Waintal, Geneviève Fleury, Kyryl Kazymyrenko, Manuel Houzet, Peter Schmitteckert, and Dietmar Weinmann Phys. Rev. Lett.101, 106804 (2008).

Syntheses, X-ray structures, solid state high-field electron paramagnetic resonance, and density-functional theory investigations on chloro and aqua Mn(II) mononuclear complexes with amino-pyridine pentadentate ligands.

PubMed

Hureau, Christelle; Groni, Sihem; Guillot, Régis; Blondin, Geneviève; Duboc, Carole; Anxolabéhère-Mallart, Elodie

2008-10-20

The two pentadentate amino-pyridine ligands L5(2) and L5(3) (L5(2) and L5(3) stand for the N-methyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine and the N-methyl-N,N',N'-tris(2-pyridylmethyl)propane-1,3-diamine, respectively) were used to synthesize four mononuclear Mn(II) complexes, namely [(L5(2))MnCl](PF6) (1(PF6)), [(L5(3))MnCl](PF6) (2(PF6)), [(L5(2))Mn(OH2)](BPh4)2 (3(BPh4)2), and [(L5(3))Mn(OH2)](BPh4)2 (4(BPh4)2). The X-ray diffraction studies revealed different configurations for the ligand L5(n) (n = 2, 3) depending on the sixth exogenous ligand and/or the counterion. Solid state high-field electron paramagnetic resonance spectra were recorded on complexes 1-4 as on previously described mononuclear Mn(II) systems with tetra- or hexadentate amino-pyridine ligands. Positive and negative axial zero-field splitting (ZFS) parameters D were determined whose absolute values ranged from 0.090 to 0.180 cm(-1). Density-functional theory calculations were performed unraveling that, in contrast with chloro systems, the spin-spin and spin-orbit coupling contributions to the D-parameter are comparable for mixed N,O-coordination sphere complexes.

In vivo high-resolution magic angle spinning magnetic and electron paramagnetic resonance spectroscopic analysis of mitochondria-targeted peptide in Drosophila melanogaster with trauma-induced thoracic injury.

PubMed

Constantinou, Caterina; Apidianakis, Yiorgos; Psychogios, Nikolaos; Righi, Valeria; Mindrinos, Michael N; Khan, Nadeem; Swartz, Harold M; Szeto, Hazel H; Tompkins, Ronald G; Rahme, Laurence G; Tzika, A Aria

2016-02-01

Trauma is the most common cause of mortality among individuals aged between 1 and 44 years and the third leading cause of mortality overall in the US. In this study, we examined the effects of trauma on the expression of genes in Drosophila melanogaster, a useful model for investigating genetics and physiology. After trauma was induced by a non-lethal needle puncture of the thorax, we observed the differential expression of genes encoding for mitochondrial uncoupling proteins, as well as those encoding for apoptosis-related and insulin signaling-related proteins, thus indicating muscle functional dysregulation. These results prompted us to examine the link between insulin signaling and mitochondrial dysfunction using in vivo nuclear magnetic resonance (NMR) with complementary electron paramagnetic resonance (EPR) spectroscopy. Trauma significantly increased insulin resistance biomarkers, and the NMR spectral profile of the aged flies with trauma-induced thoracic injury resembled that of insulin-resistant chico mutant flies. In addition, the mitochondrial redox status, as measured by EPR, was significantly altered following trauma, indicating mitochondrial uncoupling. A mitochondria-targeted compound, Szeto-Schiller (SS)-31 that promotes adenosine triphosphate (ATP) synthesis normalized the NMR spectral profile, as well as the mitochondrial redox status of the flies with trauma-induced thoracic injury, as assessed by EPR. Based on these findings, we propose a molecular mechanism responsible for trauma-related mortality and also propose that trauma sequelae in aging are linked to insulin signaling and mitochondrial dysfunction. Our findings further suggest that SS-31 attenuates trauma-associated pathological changes.

Polarized electronic absorption spectra of Cr2SiO4 single crystals

NASA Astrophysics Data System (ADS)

Furche, A.; Langer, K.

Polarized electronic absorption spectra, E∥a(∥X), E∥b(∥Y) and E∥c(∥Z), in the energy range 3000-5000 cm-1 were obtained for the orthorhombic thenardite-type phase Cr2SiO4, unique in its Cr2+-allocation suggesting some metal-metal bonding in Cr2+Cr2+ pairs with Cr-Cr distance 2.75 Å along [001]. The spectra were scanned at 273 and 120 K on single crystal platelets ∥(100), containing optical Y and Z, and ∥(010), containing optical X and Z, with thicknesses 12.3 and 15.6 μm, respectively. Microscope-spectrometric techniques with a spatial resolution of 20 μm and 1 nm spectral resolution were used. The orientations were obtained by means of X-ray precession photographs. The xenomorphic, strongly pleochroic crystal fragments (X deeply greenish-blue, Y faint blue almost colourless, Z deeply purple almost opaque) were extracted from polycrystalline Cr2SiO4, synthesized at 35 kbar, above 1440 °C from high purity Cr2O3, Cr (10% excess) and SiO2 in chromium capsules. The Cr2SiO4-phase was identified by X-ray diffraction (XRD). Four strongly polarized bands, at about 13500 (I), 15700 (II), 18700 (III) and 19700 (IV) cm-1, in the absorption spectra of Cr2SiO4 single crystals show properties (temperature behaviour of linear and integral absorption coefficients, polarization behaviour, molar absorptivities) which are compatible with an assignment to localized spin-allowed transitions of Cr2+ in a distorted square planar coordination of point symmetry C2. The crystal field parameter of Cr2+ is estimated to be 10 Dq =10700 cm-1. A relatively intense, sharp band at 18400 cm-1 and three other minor features can, from their small half widths, be assigned to spin-forbidden dd-transitions of Cr2+. The intensity of such bands strongly decreases on decreasing temperature. The large half widths, near 5000 cm-1 of band III are indicative of some Cr-Cr interactions, i.e. δ-δ* transitions of Cr24+, whereas the latter alone would be in conflict with the strong

Substituent and solvent effects on electronic absorption spectra of some N-(substitutedphenyl)benzene sulphonamides

NASA Astrophysics Data System (ADS)

Suganya, Krishnasamy; Kabilan, Senthamaraikannan

2004-04-01

The effects of substituents and solvents have been studied through the absorption spectra of nearly 23 ortho- and para-N-(substitutedphenyl)benzene sulphonamides in the range of 200-400 nm. The effects of substituents on the absorption spectra of compounds under present investigation are interpreted by correlation of absorption frequencies with simple and extended Hammett equations. Effect of solvent polarity and hydrogen bonding on the absorption spectra are interpreted by means of Kamlet equation and the results are discussed.

Dependence of the electronic absorption spectra of aqueous solutions of iodine monochloride on the conditions of dilution and storage time

NASA Astrophysics Data System (ADS)

Klyubin, V. V.; Klyubina, K. A.; Makovetskaya, K. N.

2017-04-01

The electronic absorption spectra of aqueous solutions of iodine monochloride ICl are studied. The spectra of as-prepared solutions display the absorption band associated with hydrated ICl molecules. An additional band indicating that molecular iodine was formed in the solution emerges in the spectrum as dissolution takes place. Only the band belonging to iodine monochloride remains in the absorption spectra, and no additional bands appear after chloride anions Cl- are added to the solution. The absorption spectrum becomes more complex when ICl is dissolved in an alkaline medium. The band belonging to molecular iodine emerges in the spectra at low alkali concentrations, while being transformed to other shorter-wavelength bands at high alkali concentrations (pH ≥ 12).

Synthesis and evaluation of changes induced by solvent and substituent in electronic absorption spectra of some azo disperse dyes

NASA Astrophysics Data System (ADS)

Mohammadi, Asadollah; Yazdanbakhsh, Mohammad Reza; Farahnak, Lahya

2012-04-01

Five azo disperse dyes were prepared by diazotizing 4'-aminoacetophenone and p-anisidine and coupling with varies N-alkylated aromatic amines. Characterization of the dyes was carried out by using UV-vis, FTIR and 1H NMR spectroscopic techniques. The electronic absorption spectra of dyes are determined at room temperature in fifteen solvents with different polarities. The solvent dependent maximum absorption band shifts, were investigated using dielectric constant (ɛ), refractive index (n) and Kamlet-Taft polarity parameters (hydrogen bond donating ability (α), hydrogen bond accepting ability (β) and dipolarity/polarizability polarity scale (π*)). Acceptable agreement was found between the maximum absorption band of dyes and solvent polarity parameters especially with π*. The effect of substituents of coupler and/or diazo component on the color of dyes was investigated. The effects of acid and base on the visible absorption maxima of the dyes are also reported.

Paramagnetic resonance and susceptibility of ilmenite, FeTiO3 crystal

NASA Technical Reports Server (NTRS)

Mcdonald, P. F.; Parasiris, A.; Pandey, R. K.; Gries, B. L.; Kirk, W. P.

1991-01-01

Large high-purity single crystals of FeTiO3 with ilmenite structure have been grown from a stoichiometric melt of Fe2O3 and TiO2 under an inert atmosphere using the modified Czochralski technique. Susceptibility and X-band paramagnetic resonance studies have been performed. Susceptibility measurements indicate a Neel temperature of about 59 K. The paramagnetic resonance spectrum for magnetic field perpendicular to the crystal c axis consists of a portion of a single, very intense approximately Lorentzian absorption line with its peak at about 600 G and half width at half maximum almost 1200 G. The absorption extends to zero magnetic field. For magnetic field approximately parallel to the c axis, the paramagnetic absorption is much smaller and may be considered a superposition of two approximately Lorentzian line shapes. The magnetic resonance measurements indicate a weak temperature dependence and large angular anisotropy.

Revealing electronic structure changes in Chevrel phase cathodes upon Mg insertion using X-ray absorption spectroscopy

SciTech Connect

Wan, Liwen F.; Wright, Joshua; Perdue, Brian R.

Following previous work predicting the electronic response of the Chevrel phase Mo6S8 upon Mg insertion (Thole et al., Phys. Chem. Chem. Phys., 2015, 17, 22548), we provide the experimental proof, evident in X-ray absorption spectroscopy, to illustrate the charge compensation mechanism of the Chevrel phase compound during Mg insertion and de-insertion processes.

First principles electron-correlated calculations of optical absorption in magnesium clusters★

NASA Astrophysics Data System (ADS)

Shinde, Ravindra; Shukla, Alok

2017-11-01

In this paper, we report large-scale configuration interaction (CI) calculations of linear optical absorption spectra of various isomers of magnesium clusters Mgn (n = 2-5), corresponding to valence transitions. Geometry optimization of several low-lying isomers of each cluster was carried out using coupled-cluster singles doubles (CCSD) approach, and these geometries were subsequently employed to perform ground and excited state calculations using either the full-CI (FCI) or the multi-reference singles-doubles configuration interaction (MRSDCI) approach, within the frozen-core approximation. Our calculated photoabsorption spectrum of magnesium dimer (Mg2) is in excellent agreement with the experiments both for peak positions, and intensities. Owing to the sufficiently inclusive electron-correlation effects, these results can serve as benchmarks against which future experiments, as well as calculations performed using other theoretical approaches, can be tested. Supplementary material in the form of one pdf fille available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-80356-6.

Attosecond transient absorption probing of electronic superpositions of bound states in neon. Detection of quantum beats

DOE PAGES

Beck, Annelise R; Bernhardt, Birgitta; Warrick, Erika R.; ...

2014-11-07

Electronic wavepackets composed of multiple bound excited states of atomic neon lying between 19.6 and 21.5 eV are launched using an isolated attosecond pulse. Individual quantum beats of the wavepacket are detected by perturbing the induced polarization of the medium with a time-delayed few-femtosecond near-infrared (NIR) pulse via coupling the individual states to multiple neighboring levels. All of the initially excited states are monitored simultaneously in the attosecond transient absorption spectrum, revealing Lorentzian to Fano lineshape spectral changes as well as quantum beats. The most prominent beating of the several that were observed was in the spin–orbit split 3d absorptionmore » features, which has a 40 femtosecond period that corresponds to the spin–orbit splitting of 0.1 eV. The few-level models and multilevel calculations confirm that the observed magnitude of oscillation depends strongly on the spectral bandwidth and tuning of the NIR pulse and on the location of possible coupling states.« less

Substituent and solvent effects on electronic absorption spectra of some N-(substitutedphenyl)benzene sulphonamides.

PubMed

Suganya, Krishnasamy; Kabilan, Senthamaraikannan

2004-04-01

The effects of substituents and solvents have been studied through the absorption spectra of nearly 23 ortho- and para-N-(substitutedphenyl)benzene sulphonamides in the range of 200-400 nm. The effects of substituents on the absorption spectra of compounds under present investigation are interpreted by correlation of absorption frequencies with simple and extended Hammett equations. Effect of solvent polarity and hydrogen bonding on the absorption spectra are interpreted by means of Kamlet equation and the results are discussed. Copyright 2003 Elsevier B.V.

Effect of interdiffusion and external magnetic field on electronic states and light absorption in Gaussian-shaped double quantum ring

NASA Astrophysics Data System (ADS)

Aziz-Aghchegala, V. L.; Mughnetsyan, V. N.; Kirakosyan, A. A.

2018-02-01

The effect of interdiffusion and magnetic field on confined states of electron and heavy hole as well as on interband absorption spectrum in a Ga1-xAlxAs/GaAs Gaussian-shaped double quantum ring are investigated. It is shown that both interdiffusion and magnetic field lead to the change of the charge carriers' quantum states arrangement by their energies. The oscillating behavior of the electron ground state energy as a function of magnetic field induction gradually disappears with the increase of diffusion parameter due to the enhanced tunneling of electron to the central region of the ring. For the heavy hole the ground state energy oscillations are not observable in the region of the values of magnetic field induction B = 0 - 10 T . For considered transitions both the magnetic field and the interdiffusion lead to a blue-shift of the absorption spectrum and to decreasing of the absorption intensity. The obtained results indicate on the opportunity of purposeful manipulation of energy states and absorption spectrum of a Gaussian-shaped double quantum ring by means of the post growth annealing and the external magnetic field.

Ionic species produced on gamma radiolysis: Studies by matrix isolation technique—I. Electronic absorption spectra of perfluorosubstituted aromatic radical anions

NASA Astrophysics Data System (ADS)

Shou-te, Lian C. T.; Mittal, Jai P.

The absorption spectra of several perfluorosubstituted aromatic radical anions are compared with the corresponding perhydro compounds in which the various transitions involved have been assigned to those predicted theoretically. The electronic absorption spectra were obtained for pentafluorostyrene, pentafluorobenzaldehyde, pentafluorobenzoic acid, pentafluorobenzonitride, tetrafluorophthalic acid and pentafluoroaniline, by gamma radiolysis in 2-methyltetrahydrofuran at 77 K. A general similarity in the absorption spectra between the perfluorinated and the corresponding perhydro radical anion is observed except for a shift in the absorption band.

Electronic absorption spectrum of copper-doped magnesium potassium phosphate hexahydrate

NASA Astrophysics Data System (ADS)

Rao, S. N.; Sivaprasad, P.; Reddy, Y. P.; Rao, P. S.

1992-04-01

The optical absorption and EPR spectra of magnesium potassium phosphate hexahydrate (MPPH) doped with copper ions are recorded both at room and liquid nitrogen temperatures. The spectrum is characteristic of Cu2+ in tetragonal symmetry. The spin-Hamiltonian parameters and molecular orbital coefficients are evaluated. A correlation between EPR and optical absorption studies is drawn.

Comparison between POES energetic electron precipitation observations and riometer absorptions: Implications for determining true precipitation fluxes

NASA Astrophysics Data System (ADS)

Rodger, Craig J.; Kavanagh, Andrew J.; Clilverd, Mark A.; Marple, Steve R.

2013-12-01

electron precipitation (EEP) impacts the chemistry of the middle atmosphere with growing evidence of coupling to surface temperatures at high latitudes. To better understand this link, it is essential to have realistic observations to properly characterize precipitation and which can be incorporated into chemistry-climate models. The Polar-orbiting Operational Environmental Satellite (POES) detectors measure precipitating particles but only integral fluxes and only in a fraction of the bounce loss cone. Ground-based riometers respond to precipitation from the whole bounce loss cone; they measure the cosmic radio noise absorption (CNA), a qualitative proxy with scant direct information on the energy flux of EEP. POES observations should have a direct relationship with ΔCNA and comparing the two will clarify their utility in studies of atmospheric change. We determined ionospheric changes produced by the EEP measured by the POES spacecraft in ~250 overpasses of an imaging riometer in northern Finland. The ΔCNA modeled from the POES data is 10-15 times less than the observed ΔCNA when the >30 keV flux is reported as <106 cm-2 s-1 sr-1. Above this level, there is relatively good agreement between the space-based and ground-based measurements. The discrepancy occurs mostly during periods of low geomagnetic activity, and we contend that weak diffusion is dominating the pitch angle scattering into the bounce loss cone at these times. A correction to the calculation using measurements of the trapped flux considerably reduces the discrepancy and provides further support to our hypothesis that weak diffusion leads to underestimates of the EEP.

Electron-cyclotron absorption in high-temperature plasmas: quasi-exact analytical evaluation and comparative numerical analysis

NASA Astrophysics Data System (ADS)

Albajar, F.; Bertelli, N.; Bornatici, M.; Engelmann, F.

2007-01-01

On the basis of the electromagnetic energy balance equation, a quasi-exact analytical evaluation of the electron-cyclotron (EC) absorption coefficient is performed for arbitrary propagation (with respect to the magnetic field) in a (Maxwellian) magneto-plasma for the temperature range of interest for fusion reactors (in which EC radiation losses tend to be important in the plasma power balance). The calculation makes use of Bateman's expansion for the product of two Bessel functions, retaining the lowest-order contribution. The integration over electron momentum can then be carried out analytically, fully accounting for finite Larmor radius effects in this approximation. On the basis of the analytical expressions for the EC absorption coefficients of both the extraordinary and ordinary modes thus obtained, (i) for the case of perpendicular propagation simple formulae are derived for both modes and (ii) a numerical analysis of the angular distribution of EC absorption is carried out. An assessment of the accuracy of asymptotic expressions that have been given earlier is also performed, showing that these approximations can be usefully applied for calculating EC power losses from reactor-grade plasmas. Presented in part at the 14th Joint Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating, Santorini, Greece, 9-12 May 2006.

Time-Resolved IR-Absorption Spectroscopy of Hot-Electron Dynamics in Satellite and Upper Conduction Bands in GaP

NASA Technical Reports Server (NTRS)

Cavicchia, M. A.; Alfano, R. R.

1995-01-01

The relaxation dynamics of hot electrons in the X6 and X7 satellite and upper conduction bands in GaP was directly measured by femtosecond UV-pump-IR-probe absorption spectroscopy. From a fit to the induced IR-absorption spectra the dominant scattering mechanism giving rise to the absorption at early delay times was determined to be intervalley scattering of electrons out of the X7 upper conduction-band valley. For long delay times the dominant scattering mechanism is electron-hole scattering. Electron transport dynamics of the upper conduction band of GaP has been time resolved.

Towards simultaneous measurements of electronic and structural properties in ultra-fast x-ray free electron laser absorption spectroscopy experiments

PubMed Central

Gaudin, J.; Fourment, C.; Cho, B. I.; Engelhorn, K.; Galtier, E.; Harmand, M.; Leguay, P. M.; Lee, H. J.; Nagler, B.; Nakatsutsumi, M.; Ozkan, C.; Störmer, M.; Toleikis, S.; Tschentscher, Th; Heimann, P. A.; Dorchies, F.

2014-01-01

The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called “molecular movie” within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level of the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes. PMID:24740172

Towards simultaneous measurements of electronic and structural properties in ultra-fast x-ray free electron laser absorption spectroscopy experiments

NASA Astrophysics Data System (ADS)

Gaudin, J.; Fourment, C.; Cho, B. I.; Engelhorn, K.; Galtier, E.; Harmand, M.; Leguay, P. M.; Lee, H. J.; Nagler, B.; Nakatsutsumi, M.; Ozkan, C.; Störmer, M.; Toleikis, S.; Tschentscher, Th; Heimann, P. A.; Dorchies, F.

2014-04-01

The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called ``molecular movie'' within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level of the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.

Towards simultaneous measurements of electronic and structural properties in ultra-fast x-ray free electron laser absorption spectroscopy experiments

DOE PAGES

Gaudin, J.; Fourment, C.; Cho, B. I.; ...

2014-04-17

The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called “molecular movie” within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level ofmore » the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.« less

Dependency of magnetic microwave absorption on surface architecture of Co20Ni80 hierarchical structures studied by electron holography

NASA Astrophysics Data System (ADS)

Liu, Qinhe; Xu, Xianhui; Xia, Weixing; Che, Renchao; Chen, Chen; Cao, Qi; He, Jingang

2015-01-01

To design and fabricate rational surface architecture of individual particles is one of the key factors that affect their magnetic properties and microwave absorption capability, which is still a great challenge. Herein, a series of Co20Ni80 hierarchical structures with different surface morphologies, including flower-, urchin-, ball-, and chain-like morphologies, were obtained using structure-directing templates via a facile one-step solvothermal treatment. The microwave reflection loss (RL) of urchin-like Co20Ni80 hierarchical structures reaches as high as -33.5 dB at 3 GHz, with almost twice the RL intensity of the ball- and chain-like structures, and the absorption bandwidth (<-10 dB) is about 5.5 GHz for the flower-like morphology, indicating that the surface nanospikes and nanoflakes on the Co20Ni80 microsphere surfaces have great influences on their magnetic microwave absorption properties. Electron holography analysis reveals that the surface nanospikes and nanoflakes could generate a high density of stray magnetic flux lines and contribute a large saturation magnetization (105.62 emu g-1 for urchin-like and 96.41 emu g-1 for flower-like morphology), leading the urchin-like and flower-like Co20Ni80 to possess stronger microwave RL compared with the ball-like and chain-like Co20Ni80 alloys. The eddy-current absorption mechanism μ''(μ')-2(f)-1 is dominant in the frequency region above 8 GHz, implying that eddy-current loss is a vital factor for microwave RL in the high frequency range. It can be supposed from our findings that different surface morphologies of magnetic hierarchical structures might become an effective path to achieve high-performance microwave absorption for electromagnetic shielding and stealth camouflage applications.To design and fabricate rational surface architecture of individual particles is one of the key factors that affect their magnetic properties and microwave absorption capability, which is still a great challenge. Herein, a

Optical absorption, electron spin resonance, and electron spin echo studies of the photoionization of tetramethylbenzidine in cationic and anionic synthetic vesicles: comparison with analogous micellar systems

SciTech Connect

Li, A.S.W.; Kevan, L.

1983-09-07

The photoionization of N,N,N',N'-tetramethylbenzidine (TMB) in dihexadecylphosphate anionic vesicles and in dioctadecyldimethylammonium chloride cationic vesicles has been studied by optical absorption and electron spin resonance in liquid and frozen solutions. The TMB cation has been observed to be stabilized in both types of vesicles. The photoionization efficiency is about twofold greater in the cationic vesicles compared to the anionic vesicles. Shifts in the optical absorption maximum between micellar and vesicle solutions indicate that TMB is in a less polar environment in the vesicle systems. Electron spin echo modulation spectrometry has been used to detect TMB cation-water interactions that are foundmore » to be weaker than in previously studied micellar solutions. This is consistent with the optical absorption results and with an asymmetric solubilization site for TMB and TMB/sup +/ within the vesicular structure. A new absorption in the photoionized vesicles is assigned to a nonparamagnetic diamine-diimine charge-transfer complex between two TMB cations in the same vesicle. This complex is not formed in micellar systems. 5 figures.« less

Biocompatible Collagen Paramagnetic Scaffold for Controlled Drug Release.

PubMed

Bettini, Simona; Bonfrate, Valentina; Syrgiannis, Zois; Sannino, Alessandro; Salvatore, Luca; Madaghiele, Marta; Valli, Ludovico; Giancane, Gabriele

2015-09-14

A porous collagen-based hydrogel scaffold was prepared in the presence of iron oxide nanoparticles (NPs) and was characterized by means of infrared spectroscopy and scanning electron microscopy. The hybrid scaffold was then loaded with fluorescein sodium salt as a model compound. The release of the hydrosoluble species was triggered and accurately controlled by the application of an external magnetic field, as monitored by fluorescence spectroscopy. The biocompatibility of the proposed matrix was also tested by the MTT assay performed on 3T3 cells. Cell viability was only slightly reduced when the cells were incubated in the presence of the collagen-NP hydrogel, compared to controls. The economicity of the chemical protocol used to obtain the paramagnetic scaffolds as well as their biocompatibility and the safety of the external trigger needed to induce the drug release suggest the proposed collagen paramagnetic matrices for a number of applications including tissue engeneering and drug delivery.

Optical absorption in fused silica at elevated temperatures during 1.5-MeV electron irradiation

NASA Technical Reports Server (NTRS)

Smith, A. B.

1972-01-01

An experimental determination of the optical transmission of Corning 7940 UV and Suprasil 1 and 2 fused silica has been made during 1.5-MeV electron bombardment. The fused silica reached temperatures ranging from 150 to 1000 C. The Lewis Research Center dynamitron provided electron current densities which corresponded to a dose rate of 2.6 to 20 Mrad/sec. The irradiation induced absorption was measured at 215.0, 270.0, and 450.0 nm (2150, 2700, 4500 A). The length of each irradiation was sufficient so that an equilibrium between radiation induced coloration and high temperature annealing was reached. The experimental results indicate a significant optical absorption, with values of the induced absorption coefficient at 215.0 nm (2150 A) of 14.5 to 2.2/cm, at 270.0 nm (2700 A) of 9.7 to 3.0/cm and at 450.0 nm (4500 A) of 3.7 to 0.5/cm. This would make the use of fused silica as the separating wall material in the nuclear light bulb propulsion concept questionable.

Observation of ultrahigh-energy electrons by resonance absorption of high-power microwaves in a pulsed plasma.

PubMed

Rajyaguru, C; Fuji, T; Ito, H; Yugami, N; Nishida, Y

2001-07-01

The interaction of high power microwave with collisionless unmagnetized plasma is studied. Investigation on the generation of superthermal electrons near the critical layer, by the resonance absorption phenomenon, is extended to very high microwave power levels (eta=E(2)(0)/4 pi n(e)kT(e) approximately 0.3). Here E0, n(e), and T(e) are the vacuum electric field, electron density, and electron temperature, respectively. Successive generation of electron bunches having maximum energy of about 2 keV, due to nonlinear wave breaking, is observed. The electron energy epsilon scales as a function of the incident microwave power P, according to epsilon proportional to P0.5 up to 250 kW. The two-dimensional spatial distribution of high energy electrons reveals that they are generated near the critical layer. However, the lower energy component is again produced in the subcritical density region indicating the possibility of other electron heating mechanisms.

Operando X-ray absorption and EPR evidence for a single electron redox process in copper catalysis

DOE PAGES

Lu, Qingquan; Zhang, Jian; Peng, Pan; ...

2015-05-26

An unprecedented single electron redox process in copper catalysis is confirmed using operando X-ray absorption and EPR spectroscopies. The oxidation state of the copper species in the interaction between Cu(II) and a sulfinic acid at room temperature, and the accurate characterization of the formed Cu(I) are clearly shown using operando X-ray absorption and EPR evidence. Further investigation of anion effects on Cu(II) discloses that bromine ions can dramatically increase the rate of the redox process. Moreover, it is proven that the sulfinic acids are converted into sulfonyl radicals, which can be trapped by 2-arylacrylic acids and various valuable β-keto sulfonesmore » are synthesized with good to excellent yields under mild conditions.« less

Paramagnetism of cobalt-doped ZnO nanoparticles obtained by microwave solvothermal synthesis.

PubMed

Wojnarowicz, Jacek; Kusnieruk, Sylwia; Chudoba, Tadeusz; Gierlotka, Stanislaw; Lojkowski, Witold; Knoff, Wojciech; Lukasiewicz, Malgorzata I; Witkowski, Bartlomiej S; Wolska, Anna; Klepka, Marcin T; Story, Tomasz; Godlewski, Marek

2015-01-01

Zinc oxide nanopowders doped with 1-15 mol % cobalt were produced by the microwave solvothermal synthesis (MSS) technique. The obtained nanoparticles were annealed at 800 °C in nitrogen (99.999%) and in synthetic air. The material nanostructure was investigated by means of the following techniques: X-ray diffraction (XRD), helium pycnometry density, specific surface area (SSA), inductively coupled plasma optical emission spectrometry (ICP-OES), extended X-ray absorption fine structure (EXAFS) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and with magnetometry using superconducting quantum interference device (SQUID). Irrespective of the Co content, nanoparticles in their initial state present a similar morphology. They are composed of loosely agglomerated spherical particles with wurtzite-type crystal structure with crystallites of a mean size of 30 nm. Annealing to temperatures of up to 800 °C induced the growth of crystallites up to a maximum of 2 μm in diameter. For samples annealed in high purity nitrogen, the precipitation of metallic α-Co was detected for a Co content of 5 mol % or more. For samples annealed in synthetic air, no change of phase structure was detected, except for precipitation of Co3O4 for a Co content of 15 mol %. The results of the magentometry investigation indicated that all as-synthesized samples displayed paramagnetic properties with a contribution of anti-ferromagnetic coupling of Co-Co pairs. After annealing in synthetic air, the samples remained paramagnetic and samples annealed under nitrogen flow showed a magnetic response under the influences of a magnetic field, likely related to the precipitation of metallic Co in nanoparticles.

RETRACTED: Theoretical study of electronic properties and isotope effects in the UV absorption spectrum of disulfur

NASA Astrophysics Data System (ADS)

Sarka, Karolis; Danielache, Sebastian O.; Kondorskiy, Alexey; Nanbu, Shinkoh

2017-05-01

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy) This article has been retracted at the request of the Authors because of a large amount of errors caused by incorrect interpretation of the potential energy curve boundaries by the data processing functions in their close-coupling algorithm, producing incorrect wavefunctions for the continuum region in the absorption spectrum. The spectrum calculated using the incorrect wavefunctions introduced periodic fluctuation in the absorption cross-section seen in the original article, which results in erroneous isotopic fractionation values. The updated spectra calculated after fixing the issues features a smooth continuum band, removing all false artifacts from isotopic effect analysis, producing significantly different results from the ones in this original article. The authors will submit the corrected data in a new article.

Theoretical infrared and electronic absorption spectra of C16H10 isomers, their ions and doubly ions

NASA Astrophysics Data System (ADS)

Naganathappa, Mahadevappa; Chaudhari, Ajay

2012-09-01

Polycyclic aromatic hydrocarbons (PAHs) or PAH-related molecules are considered to be responsible for the unidentified infrared (UIR) emission features at 3.3, 6.2, 7.7, 8.6 and 11.2 μm. However, the exact identification of PAH or PAH-related molecules is difficult. There have been several investigations on the spectroscopic characterization of PAH molecules. But none of them compared the spectra of isomers of PAHs, which might have help in the identification of the UIR emission features. This work presents the infrared and electronic absorption spectra of isomers of C16H10. The aim of the present work is to compare infrared and electronic absorption spectra of four isomers of C16H10 PAH viz. pyrene, aceanthrylene, acephenanthrylene and fluoranthene, their ions and doubly ions. We also compare the spectra of pyrene in the gas-phase and in H2O ice. We have used the density functional theory with B3LYP exchange and correlation functional and 6-311++g** basis set to study the infrared spectra. The time-dependent density functional theory (TDDFT) has been used to obtain the electronic absorption spectra. Significant difference in the CC stretching, CH in-plane bending and CH out-of-plane bending vibration modes is observed for the isomers of C16H10 whereas there is no large difference in the CH stretching vibration band. A significant change in the vibrational band is observed for pyrene in H2O ice compared to gas-phase pyrene. Though isomers of C16H10 PAH have the same number of carbon and hydrogen atoms, their spectroscopic characteristics are different. This study should help in identifying the isomers of C16H10, their ions and doubly cation in the interstellar medium.

Studies of the differential absorption rocket experiment. [to measure atmospheric electron density

NASA Technical Reports Server (NTRS)

Ginther, J. C.; Smith, L. G.

1975-01-01

Investigations of the ionosphere, in the rocket program of the Aeronomy Laboratory, include a propagation experiment, the data from which may be analyzed in several modes. This report considers in detail the differential absorption experiment. The sources of error and limitations of sensitivity are discussed. Methods of enhancing the performance of the experiment are described. Some changes have been made in the system and the improvement demonstrated. Suggestions are made for further development of the experiment.

Ab Initio Modeling of the Electronic Absorption Spectrum of Previtamin D in Solution

NASA Astrophysics Data System (ADS)

Zhu, Tianyang

To study the solvent effects of water on the previtamin D absorption spectrum, we use the quantum mechanics (QM)/molecular mechanics (MM) method combined with replica-exchange molecular dynamics (REMD). The QM method is applied for the previtamin D molecule and the MM method is used for the water molecules. To enhance conformational sampling of the flexible previtamin D molecule we apply REMD. Based on the REMD structures, we calculate the macroscopic ensemble of the absorption spectrum in solution by time-dependent density functional theory (TDDFT). Comparison between the calculated spectrum in the gas phase and in the solution reveals minor influences of the solvent on the absorption spectrum. In the conventional molecule dynamics simulation, the previtamin D molecule can be trapped by local minimum and cannot overcome energetics barriers when it is calculated at the room temperature. In addition, the higher temperature calculation for the molecule in REMD allows to overcome energetics barriers and to change the structure to other rotational isomers, then switch to the lower temperature and gives a more complete result in the configuration space for the lower temperature.

Comment on "Hydrogen Balmer beta: The separation between line peaks for plasma electron density diagnostics and self-absorption test"

NASA Astrophysics Data System (ADS)

Gautam, Ghaneshwar; Surmick, David M.; Parigger, Christian G.

2015-07-01

In this letter, we present a brief comment regarding the recently published paper by Ivković et al., J Quant Spectrosc Radiat Transf 2015;154:1-8. Reference is made to previous experimental results to indicate that self absorption must have occurred; however, when carefully considering error propagation, both widths and peak-separation predict electron densities within the error margins. Yet the diagnosis method and the presented details on the use of the hydrogen beta peak separation are viewed as a welcomed contribution in studies of laser-induced plasma.

Comparative absorption, electroabsorption and electrochemical studies of intervalence electron transfer and electronic coupling in cyanide-bridged bimetallic systems: ancillary ligand effects

NASA Astrophysics Data System (ADS)

Vance, Fredrick W.; Slone, Robert V.; Stern, Charlotte L.; Hupp, Joseph T.

2000-03-01

Electroabsorption or Stark spectroscopy has been used to evaluate the systems (NC) 5M II-CN-Ru III(NH 3) 51- and (NC) 5M II-CN-Ru III(NH 3) 4py 1-, where M II=Fe II or Ru II. When a pyridine ligand is present in the axial position on the Ru III acceptor, the effective optical electron transfer distance - as measured by the change in dipole moment, |Δ μ| - is increased by more than 35% relative to the ammine substituted counterpart. Comparison of the charge transfer distances to the crystal structure of Na[(CN) 5Fe-CN-Ru(NH 3) 4py] · 6H 2O reveals that the Stark derived distances are ˜50% to ˜90% of the geometric separation of the metal centers. The differences result in an upward revision in the Hush delocalization parameter, c b2, and of the electronic coupling matrix element, H ab, relative to those parameters obtained exclusively from electronic absorption measurements. The revised parameters are compared to those, which are obtained via electrochemical techniques and found to be in only fair agreement. We conclude that the absorption/electroabsorption analysis likely yields a more reliable set of mixing and coupling parameters.

Rapid and precise determination of zero-field splittings by terahertz time-domain electron paramagnetic resonance spectroscopy† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc00830a Click here for additional data file.

PubMed Central

Lu, Jian; Ozel, I. Ozge; Belvin, Carina A.; Li, Xian; Skorupskii, Grigorii; Sun, Lei; Ofori-Okai, Benjamin K.; Dincă, Mircea; Gedik, Nuh

2017-01-01

Zero-field splitting (ZFS) parameters are fundamentally tied to the geometries of metal ion complexes. Despite their critical importance for understanding the magnetism and spectroscopy of metal complexes, they are not routinely available through general laboratory-based techniques, and are often inferred from magnetism data. Here we demonstrate a simple tabletop experimental approach that enables direct and reliable determination of ZFS parameters in the terahertz (THz) regime. We report time-domain measurements of electron paramagnetic resonance (EPR) signals associated with THz-frequency ZFSs in molecular complexes containing high-spin transition-metal ions. We measure the temporal profiles of the free-induction decays of spin resonances in the complexes at zero and nonzero external magnetic fields, and we derive the EPR spectra via numerical Fourier transformation of the time-domain signals. In most cases, absolute values of the ZFS parameters are extracted from the measured zero-field EPR frequencies, and the signs can be determined by zero-field measurements at two different temperatures. Field-dependent EPR measurements further allow refined determination of the ZFS parameters and access to the g-factor. The results show good agreement with those obtained by other methods. The simplicity of the method portends wide applicability in chemistry, biology and material science. PMID:29163882

Where Is the Electronic Oscillator Strength? Mapping Oscillator Strength across Molecular Absorption Spectra.

PubMed

Zheng, Lianjun; Polizzi, Nicholas F; Dave, Adarsh R; Migliore, Agostino; Beratan, David N

2016-03-24

The effectiveness of solar energy capture and conversion materials derives from their ability to absorb light and to transform the excitation energy into energy stored in free carriers or chemical bonds. The Thomas-Reiche-Kuhn (TRK) sum rule mandates that the integrated (electronic) oscillator strength of an absorber equals the total number of electrons in the structure. Typical molecular chromophores place only about 1% of their oscillator strength in the UV-vis window, so individual chromophores operate at about 1% of their theoretical limit. We explore the distribution of oscillator strength as a function of excitation energy to understand this circumstance. To this aim, we use familiar independent-electron model Hamiltonians as well as first-principles electronic structure methods. While model Hamiltonians capture the qualitative electronic spectra associated with π electron chromophores, these Hamiltonians mistakenly focus the oscillator strength in the fewest low-energy transitions. Advanced electronic structure methods, in contrast, spread the oscillator strength over a very wide excitation energy range, including transitions to Rydberg and continuum states, consistent with experiment. Our analysis rationalizes the low oscillator strength in the UV-vis spectral region in molecules, a step toward the goal of oscillator strength manipulation and focusing.

Local 3d Electronic Structures of Co-Based Complexes with Medicinal Molecules Probed by Soft X-ray Absorption

NASA Astrophysics Data System (ADS)

Yamagami, Kohei; Fujiwara, Hidenori; Imada, Shin; Kadono, Toshiharu; Yamanaka, Keisuke; Muro, Takayuki; Tanaka, Arata; Itai, Takuma; Yoshinari, Nobuto; Konno, Takumi; Sekiyama, Akira

2017-07-01

We have examined the local 3d electronic structures of Co-Au multinuclear complexes with the medicinal molecules d-penicillaminate (d-pen) [Co{Au(PPh3)(d-pen)}2]ClO4 and [Co3{Au3(tdme)(d-pen)3}2] by Co L2,3-edge soft X-ray absorption (XAS) spectroscopy, where PPh3 denotes triphenylphosphine and tdme stands for 1,1,1-tris[(diphenylphosphino)methyl]ethane. The Co L2,3-edge XAS spectra indicate the localized ionic 3d electronic states in both materials. The experimental spectra are well explained by spectral simulation for a localized Co ion under ligand fields with the full multiplet theory, which verifies that the ions are in the low-spin Co3+ state in the former compound and in the high-spin Co2+ state in the latter.

The Martian Dust Devil Electron Avalanche: Laboratory Measurements of the E-Field Fortifying Effects of Dust-Electron Absorption

NASA Technical Reports Server (NTRS)

Farrell, W. M.; McLain, J. L.; Collier, M. R.; Keller, J. W.

2017-01-01

Analogous to terrestrial dust devils, charged dust in Mars dust devils should become vertically stratified in the convective features, creating large scale E-fields. This E-field in a Martian-like atmosphere has been shown to stimulate the development of a Townsend discharge (electron avalanche) that acts to dissipate charge in regions where charge build-up occurs. While the stratification of the charged dust is a source of the electrical energy, the uncharged particulates in the dust population may absorb a portion of these avalanching electrons, thereby inhibiting dissipation and leading to the development of anomalously large E-field values. We performed a laboratory study that does indeed show the presence of enhanced E-field strengths between an anode and cathode when dust-absorbing filaments (acting as particulates) are placed in the avalanching electron flow. Further, the E-field threshold condition to create an impulsive spark discharge increases to larger values as more filaments are placed between the anode and cathode. We conclude that the spatially separated charged dust creates the charge centers and E-fields in a dust devil, but the under-charged portion of the population acts to reduce Townsend electron dissipation currents, further fortifying the development of larger-than-expected E-fields.

X-ray absorption spectroscopy using a self-seeded soft X-ray free-electron laser

PubMed Central

Kroll, Thomas; Kern, Jan; Kubin, Markus; Ratner, Daniel; Gul, Sheraz; Fuller, Franklin D.; Löchel, Heike; Krzywinski, Jacek; Lutman, Alberto; Ding, Yuantao; Dakovski, Georgi L.; Moeller, Stefan; Turner, Joshua J.; Alonso-Mori, Roberto; Nordlund, Dennis L.; Rehanek, Jens; Weniger, Christian; Firsov, Alexander; Brzhezinskaya, Maria; Chatterjee, Ruchira; Lassalle-Kaiser, Benedikt; Sierra, Raymond G.; Laksmono, Hartawan; Hill, Ethan; Borovik, Andrew; Erko, Alexei; Föhlisch, Alexander; Mitzner, Rolf; Yachandra, Vittal K.; Yano, Junko; Wernet, Philippe; Bergmann, Uwe

2016-01-01

X-ray free electron lasers (XFELs) enable unprecedented new ways to study the electronic structure and dynamics of transition metal systems. L-edge absorption spectroscopy is a powerful technique for such studies and the feasibility of this method at XFELs for solutions and solids has been demonstrated. However, the required x-ray bandwidth is an order of magnitude narrower than that of self-amplified spontaneous emission (SASE), and additional monochromatization is needed. Here we compare L-edge x-ray absorption spectroscopy (XAS) of a prototypical transition metal system based on monochromatizing the SASE radiation of the linac coherent light source (LCLS) with a new technique based on self-seeding of LCLS. We demonstrate how L-edge XAS can be performed using the self-seeding scheme without the need of an additional beam line monochromator. We show how the spectral shape and pulse energy depend on the undulator setup and how this affects the x-ray spectroscopy measurements. PMID:27828320

X-ray absorption spectroscopy using a self-seeded soft X-ray free-electron laser

DOE PAGES

Kroll, Thomas; Kern, Jan; Kubin, Markus; ...

2016-09-19

X-ray free electron lasers (XFELs) enable unprecedented new ways to study the electronic structure and dynamics of transition metal systems. L-edge absorption spectroscopy is a powerful technique for such studies and the feasibility of this method at XFELs for solutions and solids has been demonstrated. But, the required x-ray bandwidth is an order of magnitude narrower than that of self-amplified spontaneous emission (SASE), and additional monochromatization is needed. We compare L-edge x-ray absorption spectroscopy (XAS) of a prototypical transition metal system based on monochromatizing the SASE radiation of the linac coherent light source (LCLS) with a new technique based onmore » self-seeding of LCLS. We demonstrate how L-edge XAS can be performed using the self-seeding scheme without the need of an additional beam line monochromator. Lastly, we show how the spectral shape and pulse energy depend on the undulator setup and how this affects the x-ray spectroscopy measurements.« less

Binding of anti-prion agents to glycosaminoglycans: Evidence from electronic absorption and circular dichroism spectroscopy

SciTech Connect

Zsila, Ferenc; Gedeon, Gabor

2006-08-11

The polyanionic glycosaminoglycans (GAGs) are intimately involved in the pathogenesis of protein conformational disorders such as amyloidosis and prion diseases. Several cationic agents are known to exhibit anti-prion activity but their mechanism of action is poorly understood. In this study, UV absorption and circular dichroism (CD) spectroscopic techniques were used to investigate the interaction between heparin and chondroitin-6-sulfate and anti-prion drugs including acridine, quinoline, and phenothiazine derivatives. UV band hypochromism of ({+-})-quinacrine, ({+-})-primaquine, tacrine, quinidine, chlorpromazine, and induced CD spectra of ({+-})-quinacrine upon addition of GAGs provided evidence for the GAG binding of these compounds. The association constants ({approx}10{sup 6}-10{supmore » 7} M{sup -1}) estimated from the UV titration curves show high-affinity drug-heparin interactions. Ionic strength-dependence of the absorption spectra suggested that the interaction between GAGs and the cationic drugs is principally electrostatic in nature. Drug binding differences of heparin and chondroitin-6-sulfate were attributed to their different negative charge density. These results call the attention to the alteration of GAG-prion/GAG-amyloid interactions by which these compounds might exert their anti-prion/anti-amyloidogenic activities.« less

Photoluminescence and gain/absorption spectra of a driven-dissipative electron-hole-photon condensate

NASA Astrophysics Data System (ADS)

Hanai, Ryo; Littlewood, Peter B.; Ohashi, Yoji

2018-06-01

We investigate theoretically nonequilibrium effects on photoluminescence and gain/absorption spectra of a driven-dissipative exciton-polariton condensate, by employing the combined Hartree-Fock-Bogoliubov theory with the generalized random phase approximation extended to the Keldysh formalism. Our calculated photoluminescence spectra is in semiquantitative agreement with experiments, where features such as a blue shift of the emission from the condensate, the appearance of the dispersionless feature of a diffusive Goldstone mode, and the suppression of the dispersive profile of the mode are obtained. We show that the nonequilibrium nature of the exciton-polariton condensate strongly suppresses the visibility of the Bogoliubov dispersion in the negative energy branch (ghost branch) in photoluminescence spectra. We also show that the trace of this branch can be captured as a hole burning effect in gain/absorption spectra. Our results indicate that the nonequilibrium nature of the exciton-polariton condensate strongly reduces quantum depletion, while a scattering channel to the ghost branch is still present.

Electronically excited states of vitamin B12 and methylcobalamin: theoretical analysis of absorption, CD, and MCD data.

PubMed

Solheim, Harald; Kornobis, Karina; Ruud, Kenneth; Kozlowski, Pawel M

2011-02-03

Linear and quadratic response time-dependent density functional theory (TD-DFT) has been applied to investigate absorption (Abs), circular dichroism (CD), and magnetic CD (MCD) spectra of cyanocobalamin (CNCbl) and methylcobalamin (MeCbl). Although electronically excited states of both cobalamins have been probed by applying different experimental techniques, their exact nature remains poorly understood from an electronic structure point of view. Recent theoretical studies have revealed a lot of relevant information about their properties but also left some unresolved issues related to the nature of individual transitions. In this contribution, not only Abs but also CD and MCD spectra of both cobalamins were computed for direct comparison with experiment. The results were evaluated with respect to the choice of exchange-correlation functional, basis set, and the environment (gas phase or solvent) used in the calculation. Taking into account the complexity of the CNCbl and MeCbl systems, reliable agreement between theory and experiment was achieved based on calculations employing the BP86 functional, particularly for the low-energy α/β bands. This spectral range has been traditionally interpreted as a vibrational progression associated with a single electronic excitation, but according to the present analysis for both cobalamins, these bands are best interpreted as consisting of multiple electronic transitions.

Multi-photon Rabi oscillations in high spin paramagnetic impurity

NASA Astrophysics Data System (ADS)

Bertaina, S.; Groll, N.; Chen, L.; Chiorescu, I.

2011-10-01

We report on multiple photon monochromatic quantum oscillations (Rabi oscillations) observed by pulsed EPR (Electron Paramagnetic Resonance) of Mn2+ (S = 5/2) impurities in MgO. We find that when the microwave magnetic field is similar or large than the anisotropy splitting, the Rabi oscillations have a spectrum made of many frequencies not predicted by the S = l/2 Rabi model. We show that these new frequencies come from multiple photon coherent manipulation of the multi-level spin impurity. We develop a model based on the crystal field theory and the rotating frame approximation, describing the observed phenomenon with a very good agreement.

Temperature-Induced Large Broadening and Blue Shift in the Electronic Band Structure and Optical Absorption of Methylammonium Lead Iodide Perovskite.

PubMed

Yang, Jia-Yue; Hu, Ming

2017-08-17

The power conversion efficiency of hybrid halide perovskite solar cells is profoundly influenced by the operating temperature. Here we investigate the temperature influence on the electronic band structure and optical absorption of cubic CH 3 NH 3 PbI 3 from first-principles by accounting for both the electron-phonon interaction and thermal expansion. Within the framework of density functional perturbation theory, the electron-phonon coupling induces slightly enlarged band gap and strongly broadened electronic relaxation time as temperature increases. The large broadening effect is mainly due to the presence of cation organic atoms. Consequently, the temperature-dependent absorption peak exhibits blue-shift position, decreased amplitude, and broadened width. This work uncovers the atomistic origin of temperature influence on the optical absorption of cubic CH 3 NH 3 PbI 3 and can provide guidance to design high-performance hybrid halide perovskite solar cells at different operating temperatures.

Buckling of paramagnetic chains in soft gels

NASA Astrophysics Data System (ADS)

Huang, Shilin; Pessot, Giorgio; Cremer, Peet; Weeber, Rudolf; Holm, Christian; Nowak, Johannes; Odenbach, Stefan; Menzel, Andreas M.; Auernhammer, Günter K.

We study the magneto-elastic coupling behavior of paramagnetic chains in soft polymer gels exposed to external magnetic fields. To this end, a laser scanning confocal microscope is used to observe the morphology of the paramagnetic chains together with the deformation field of the surrounding gel network. The paramagnetic chains in soft polymer gels show rich morphological shape changes under oblique magnetic fields, in particular a pronounced buckling deformation. The details of the resulting morphological shapes depend on the length of the chain, the strength of the external magnetic field, and the modulus of the gel. Based on the observation that the magnetic chains are strongly coupled to the surrounding polymer network, a simplified model is developed to describe their buckling behavior. A coarse-grained molecular dynamics simulation model featuring an increased matrix stiffness on the surfaces of the particles leads to morphologies in agreement with the experimentally observed buckling effects.

Molecular design of photovoltaic materials for polymer solar cells: toward suitable electronic energy levels and broad absorption.

PubMed

Li, Yongfang

2012-05-15

Bulk heterojunction (BHJ) polymer solar cells (PSCs) sandwich a blend layer of conjugated polymer donor and fullerene derivative acceptor between a transparent ITO positive electrode and a low work function metal negative electrode. In comparison with traditional inorganic semiconductor solar cells, PSCs offer a simpler device structure, easier fabrication, lower cost, and lighter weight, and these structures can be fabricated into flexible devices. But currently the power conversion efficiency (PCE) of the PSCs is not sufficient for future commercialization. The polymer donors and fullerene derivative acceptors are the key photovoltaic materials that will need to be optimized for high-performance PSCs. In this Account, I discuss the basic requirements and scientific issues in the molecular design of high efficiency photovoltaic molecules. I also summarize recent progress in electronic energy level engineering and absorption spectral broadening of the donor and acceptor photovoltaic materials by my research group and others. For high-efficiency conjugated polymer donors, key requirements are a narrower energy bandgap (E(g)) and broad absorption, relatively lower-lying HOMO (the highest occupied molecular orbital) level, and higher hole mobility. There are three strategies to meet these requirements: D-A copolymerization for narrower E(g) and lower-lying HOMO, substitution with electron-withdrawing groups for lower-lying HOMO, and two-dimensional conjugation for broad absorption and higher hole mobility. Moreover, better main chain planarity and less side chain steric hindrance could strengthen π-π stacking and increase hole mobility. Furthermore, the molecular weight of the polymers also influences their photovoltaic performance. To produce high efficiency photovoltaic polymers, researchers should attempt to increase molecular weight while maintaining solubility. High-efficiency D-A copolymers have been obtained by using benzodithiophene (BDT), dithienosilole

Spatio-temporal analysis of the electron power absorption in electropositive capacitive RF plasmas based on moments of the Boltzmann equation

NASA Astrophysics Data System (ADS)

Schulze, J.; Donkó, Z.; Lafleur, T.; Wilczek, S.; Brinkmann, R. P.

2018-05-01

Power absorption by electrons from the space- and time-dependent electric field represents the basic sustaining mechanism of all radio-frequency driven plasmas. This complex phenomenon has attracted significant attention. However, most theories and models are, so far, only able to account for part of the relevant mechanisms. The aim of this work is to present an in-depth analysis of the power absorption by electrons, via the use of a moment analysis of the Boltzmann equation without any ad-hoc assumptions. This analysis, for which the input quantities are taken from kinetic, particle based simulations, allows the identification of all physical mechanisms involved and an accurate quantification of their contributions. The perfect agreement between the sum of these contributions and the simulation results verifies the completeness of the model. We study the relative importance of these mechanisms as a function of pressure, with high spatial and temporal resolution, in an electropositive argon discharge. In contrast to some widely accepted previous models we find that high space- and time-dependent ambipolar electric fields outside the sheaths play a key role for electron power absorption. This ambipolar field is time-dependent within the RF period and temporally asymmetric, i.e., the sheath expansion is not a ‘mirror image’ of the sheath collapse. We demonstrate that this time-dependence is mainly caused by a time modulation of the electron temperature resulting from the energy transfer to electrons by the ambipolar field itself during sheath expansion. We provide a theoretical proof that this ambipolar electron power absorption would vanish completely, if the electron temperature was constant in time. This mechanism of electron power absorption is based on a time modulated electron temperature, markedly different from the Hard Wall Model, of key importance for energy transfer to electrons on time average and, thus, essential for the generation of capacitively

Bimodal Exciplex Formation in Bimolecular Photoinduced Electron Transfer Revealed by Ultrafast Time-Resolved Infrared Absorption.

PubMed

Koch, Marius; Licari, Giuseppe; Vauthey, Eric

2015-09-03

The dynamics of a moderately exergonic photoinduced charge separation has been investigated by ultrafast time-resolved infrared absorption with the dimethylanthracene/phthalonitrile donor/acceptor pair in solvents covering a broad range of polarity. A distinct spectral signature of an exciplex could be identified in the -C≡N stretching region. On the basis of quantum chemistry calculations, the 4-5 times larger width of this band compared to those of the ions and of the locally excited donor bands is explained by a dynamic distribution of exciplex geometry with different mutual orientations and distances of the constituents and, thus, with varying charge-transfer character. Although spectrally similar, two types of exciplexes could be distinguished by their dynamics: short-lived, "tight", exciplexes generated upon static quenching and longer-lived, "loose", exciplexes formed upon dynamic quenching in parallel with ion pairs. Tight exciplexes were observed in all solvents, except in the least polar diethyl ether where quenching is slower than diffusion. The product distribution of the dynamic quenching depends strongly on the solvent polarity: whereas no significant loose exciplex population could be detected in acetonitrile, both exciplex and ion pair are generated in less polar solvents, with the relative population of exciplex increasing with decreasing solvent polarity. These results are compared with those reported previously with donor/acceptor pairs in different driving force regimes to obtain a comprehensive picture of the role of the exciplexes in bimolecular photoinduced charge separation.

Dynamics of intramolecular electron transfer reaction of FAD studied by magnetic field effects on transient absorption spectra.

PubMed

Murakami, Masaaki; Maeda, Kiminori; Arai, Tatsuo

2005-07-07

The kinetics of intermediates generated from intramolecular electron-transfer reaction by photo irradiation of the flavin adenine dinucleotide (FAD) molecule was studied by a magnetic field effect (MFE) on transient absorption (TA) spectra. Existence time of MFE and MFE action spectra have a strong dependence on the pH of solutions. The MFE action spectra have indicated the existence of interconversion between the radical pair and the cation form of the triplet excited state of flavin part. All rate constants of the triplet and the radical pair were determined by analysis of the MFE action spectra and decay kinetics of TA. The obtained values for the interconversion indicate that the formation of cation radical promotes the back electron-transfer reaction to the triplet excited state. Further, rate constants of spin relaxation and recombination have been studied by the time profiles of MFE at various pH. The drastic change of those two factors has been obtained and can be explained by SOC (spin-orbit coupling) induced back electron-transfer promoted by the formation of a stacking conformation at pH > 2.5.

Structure and electronic absorption spectra of nematogenic alkoxycinnamic acids - a comparative study based on semiempirical and DFT methods.

PubMed

Praveen, Pogula Lakshmi; Ojha, Durga Prasad

2012-04-01

Structure of nematogenic p-n-Alkoxy cinnamic acids (nOCAC) with various alkyl chain carbon atoms (n = 2, 4, 6, 8) has been optimized using density functional B3LYP with 6-31+G (d) basis set using crystallographic geometry as input. Using the optimized geometry, electronic structure of the molecules has been evaluated using the semiempirical methods and DFT calculations. Molecular charge distribution and phase stability of these systems have been analyzed based on Mulliken and Löwdin population analysis. The electronic absorption spectra of nOCAC molecules have been simulated by employing DFT method, semiempirical CNDO/S and INDO/S parameterizations. Two types of calculations have been performed for model systems containing single and double molecules of nOCAC. UV-Visible spectra have been calculated for all single molecules. The UV stability of the molecules has been discussed in light of the electronic transition oscillator strength (f). The dimer complexes of higher homologues (n = 6, 8) have also been reported to enable the comparison between single and double molecules.

Occupied and unoccupied electronic structures of an L-cysteine film studied by core-absorption and resonant photoelectron spectroscopies

NASA Astrophysics Data System (ADS)

Kamada, M.; Hideshima, T.; Azuma, J.; Yamamoto, I.; Imamura, M.; Takahashi, K.

2016-04-01

Unoccupied and occupied electronic structures of an L-cysteine film have been studied by absorption and resonant photoelectron spectroscopies. Core absorptions at S-L, C-K, N-K, and O-K levels indicate that the lower unoccupied states are predominantly composed of oxygen-2p, carbon-2p, and sulfur-4s+3d orbitals, while higher unoccupied states may be attributed dominantly to nitrogen-np (n ≥ 3), oxygen-np (n ≥ 3), and sulfur-ns+md (n ≥ 4, m ≥ 3) orbitals. Resonant photoelectron spectra at S-L23 and O-K levels indicate that the highest occupied state is originated from sulfur-3sp orbitals, while oxygen-2sp orbitals contribute to the deeper valence states. The delocalization lifetimes of the oxygen-1s and sulfur-2p excited states are estimated from a core-hole clock method to be about 9 ± 1 and 125 ± 25 fs, respectively.

Occupied and unoccupied electronic structures of an L-cysteine film studied by core-absorption and resonant photoelectron spectroscopies

SciTech Connect

Kamada, M., E-mail: kamada@cc.saga-u.ac.jp; Hideshima, T.; Azuma, J.

2016-04-15

Unoccupied and occupied electronic structures of an L-cysteine film have been studied by absorption and resonant photoelectron spectroscopies. Core absorptions at S-L, C-K, N-K, and O-K levels indicate that the lower unoccupied states are predominantly composed of oxygen-2p, carbon-2p, and sulfur-4s+3d orbitals, while higher unoccupied states may be attributed dominantly to nitrogen-np (n ≥ 3), oxygen-np (n ≥ 3), and sulfur-ns+md (n ≥ 4,  m ≥ 3) orbitals. Resonant photoelectron spectra at S-L{sub 23} and O-K levels indicate that the highest occupied state is originated from sulfur-3sp orbitals, while oxygen-2sp orbitals contribute to the deeper valence states. The delocalization lifetimesmore » of the oxygen-1s and sulfur-2p excited states are estimated from a core-hole clock method to be about 9 ± 1 and 125 ± 25 fs, respectively.« less

Novel carbazole derivatives with quinoline ring: synthesis, electronic transition, and two-photon absorption three-dimensional optical data storage.

PubMed

Li, Liang; Wang, Ping; Hu, Yanlei; Lin, Geng; Wu, Yiqun; Huang, Wenhao; Zhao, Quanzhong

2015-03-15

We designed carbazole unit with an extended π conjugation by employing Vilsmeier formylation reaction and Knoevenagel condensation to facilitate the functional groups of quinoline from 3- or 3,6-position of carbazole. Two compounds doped with poly(methyl methacrylate) (PMMA) films were prepared. To explore the electronic transition properties of these compounds, one-photon absorption properties were experimentally measured and theoretically calculated by using the time-dependent density functional theory. We surveyed these films by using an 800 nm Ti:sapphire 120-fs laser with two-photon absorption (TPA) fluorescence emission properties and TPA coefficients to obtain the TPA cross sections. A three-dimensional optical data storage experiment was conducted by using a TPA photoreaction with an 800 nm-fs laser on the film to obtain a seven-layer optical data storage. The experiment proves that these carbazole derivatives are well suited for two-photon 3D optical storage, thus laying the foundation for the research of multilayer high-density and ultra-high-density optical information storage materials. Copyright © 2014 Elsevier B.V. All rights reserved.

Purification of electron-transferring flavoprotein from Megasphaera elsdenii and binding of additional FAD with an unusual absorption spectrum.

PubMed

Sato, Kyosuke; Nishina, Yasuzo; Shiga, Kiyoshi

2003-11-01

Electron-transferring flavoprotein (ETF), its redox partner flavoproteins, i.e., D-lactate dehydrogenase and butyryl-CoA dehydrogenase, and another well-known flavoprotein, flavodoxin, were purified from the same starting cell paste of an anaerobic bacterium, Megasphaera elsdenii. The purified ETF contained one mol FAD/mol ETF as the sole non-protein component and bound almost one mol of additional FAD. This preparation is a better subject for investigations of M. elsdenii ETF than the previously isolated ETF, which contains varying amounts of FAD and varying percentages of modified flavins such as 6-OH-FAD and 8-OH-FAD. The additionally bound FAD shows an anomalous absorption spectrum with strong absorption around 400 nm. This spectral change is not due to a chemical modification of the flavin ring because the flavin released by KBr or guanidine hydrochloride is normal FAD. It is also not due to unknown small molecules because the same spectrum appears when ETF is reconstituted from its guanidine-denatured subunits and FAD. A similar anomalous spectrum was observed for AMP-free pig ETF under acidic conditions, suggesting a common flavin environment between pig and M. elsdenii ETFs.

Probing the Electronic Structure of - and Electron-Doped High-Temperature Superconductors with Photoemission and X-Ray Absorption Spectroscopies

NASA Astrophysics Data System (ADS)

Lederman, Eli R.

1990-01-01

The electronic structures of hole- and electron -doped high temperature superconductors have been probed using x-ray absorption near-edge spectroscopy (XANES) and photoelectron emission spectroscopy (PES). These measurements have been performed on RBa_2Cu _3O_{rm 7-y} , La_{rm 2-x}Sr _{rm x}CuO _4 and Ln_{rm 2 -x}Ce_{rm x} CuO_{rm 4} for R = Y, Eu and Ln = Nd, Pr and Sm. The parameters x and y have been varied to include a range of hole and electron carrier densities and the undoped parent compounds. Previous XANES and PES results have indicated that unoccupied states of O 2p character can be associated with the carriers in the materials RBa_2 Cu_3O_{ rm 7-y} and La_{ rm 2-x}Sr_{rm x}CuO_4 and that the density of holes increases with O and Sr content, respectively. Conduction was hole-based in all known high-T_{ rm c} cuprates until the recent discovery of superconductivity in Ln_{rm 2-x}Ce_{rm x} CuO_4. Hall coefficient measurements have suggested that the carriers in this system are electrons added with Ce doping. It has been anticipated that these electron-doped materials will provide an important test for models of high temperature superconductivity. PES measurements are presented that show significant Cu 3d character in the valence band of these electron-based materials, but that the Cu^{2+} /Cu^{1+} ratio is unchanged by the level of Ce doping, indicating that doped electrons are itinerant rather than highly correlated. Resonant photoemission from the valence band indicates the presence of unoccupied O 2p states, but these holes are less abundant than in the hole-doped materials. Measurements of XANES at the O 1s edge suggest that unoccupied states of O 2p character in the electron -doped materials are not related to conduction in a simple way. The density of these holes is shown to decrease upon Ce doping and the process of reduction, despite the fact that both are necessary of superconductivity. Furthermore, whereas the O 2p holes are at E_{rm F} in the

Photoinduced electron-transfer in perylenediimide triphenylamine-based dendrimers: single photon timing and femtosecond transient absorption spectroscopy.

PubMed

Fron, Eduard; Pilot, Roberto; Schweitzer, Gerd; Qu, Jianqiang; Herrmann, Andreas; Müllen, Klaus; Hofkens, Johan; Van der Auweraer, Mark; De Schryver, Frans C

2008-05-01

The excited state dynamics of two generations perylenediimide chromophores substituted in the bay area with dendritic branches bearing triphenylamine units as well as those of the respective reference compounds are investigated. Using single photon timing and multi-pulse femtosecond transient absorption experiments a direct proof of a reversible charge transfer occurring from the peripheral triphenylamine to the electron acceptor perylenediimide core is revealed. Femtosecond pump-dump-probe experiments provide evidence for the ground state dynamics by populating excited vibronic levels. It is found by the means of both techniques that the rotational isomerization of the dendritic branches occurs on a time scale that ranges up to 1 ns. This time scale of the isomerization depends on the size of the dendritic arms and is similar both in the ground and excited state.

Selective Two-Photon Absorptive Resonance Femtosecond-Laser Electronic-Excitation Tagging (STARFLEET) Velocimetry in Flow and Combustion Diagnostics

NASA Technical Reports Server (NTRS)

Jiang, Naibo; Halls, Benjamin R.; Stauffer, Hans U.; Roy, Sukesh; Danehy, Paul M.; Gord, James R.

2016-01-01

Selective Two-Photon Absorptive Resonance Femtosecond-Laser Electronic-Excitation Tagging (STARFLEET), a non-seeded ultrafast-laser-based velocimetry technique, is demonstrated in reactive and non-reactive flows. STARFLEET is pumped via a two-photon resonance in N2 using 202.25-nm 100-fs light. STARFLEET greatly reduces the per-pulse energy required (30 µJ/pulse) to generate the signature FLEET emission compared to the conventional FLEET technique (1.1 mJ/pulse). This reduction in laser energy results in less energy deposited in the flow, which allows for reduced flow perturbations (reactive and non-reactive), increased thermometric accuracy, and less severe damage to materials. Velocity measurements conducted in a free jet of N2 and in a premixed flame show good agreement with theoretical velocities and further demonstrate the significantly less-intrusive nature of STARFLEET.

UV-Visible Absorption Spectroscopy Enhanced X-ray Crystallography at Synchrotron and X-ray Free Electron Laser Sources.

PubMed

Cohen, Aina E; Doukov, Tzanko; Soltis, Michael S

2016-01-01

This review describes the use of single crystal UV-Visible Absorption micro-Spectrophotometry (UV-Vis AS) to enhance the design and execution of X-ray crystallography experiments for structural investigations of reaction intermediates of redox active and photosensitive proteins. Considerations for UV-Vis AS measurements at the synchrotron and associated instrumentation are described. UV-Vis AS is useful to verify the intermediate state of an enzyme and to monitor the progression of reactions within crystals. Radiation induced redox changes within protein crystals may be monitored to devise effective diffraction data collection strategies. An overview of the specific effects of radiation damage on macromolecular crystals is presented along with data collection strategies that minimize these effects by combining data from multiple crystals used at the synchrotron and with the X-ray free electron laser.

Search for exotic short-range interactions using paramagnetic insulators

DOE PAGES

Chu, Pinghan; Weisman, E.; Liu, C. -Y.; ...

2015-05-26

We describe a proposed experimental search for exotic spin-coupled interactions using a solid-state paramagnetic insulator. The experiment is sensitive to the net magnetization induced by the exotic interaction between the unpaired insulator electrons with a dense, nonmagnetic mass in close proximity. An existing experiment has been used to set limits on the electric dipole moment of the electron by probing the magnetization induced in a cryogenic gadolinium gallium garnet sample on application of a strong electric field. With suitable additions, including a movable source mass, this experiment can be used to explore “monopole-dipole” forces on polarized electrons with unique ormore » unprecedented sensitivity. As a result, the solid-state, nonmagnetic construction, combined with the low-noise conditions and extremely sensitive magnetometry available at cryogenic temperatures could lead to a sensitivity over 10 orders of magnitude greater than exiting limits in the range below 1 mm.« less

Paramagnetic defects in KH{sub 2}PO{sub 4} crystals with high concentration of embedded TiO{sub 2} nanoparticles

SciTech Connect

Grachev, Valentin G., E-mail: grachev@physics.montana.edu; Tse, Romand; Malovichko, Galina I.

2016-01-21

Qualitative transformations of spectra of Electron Paramagnetic Resonance, EPR, were found in KH{sub 2}PO{sub 4} crystals grown from liquor with 10{sup −5}–10{sup −1 }wt. % of anatase TiO{sub 2} nanoparticles in comparison with nominally pure KH{sub 2}PO{sub 4}. The nanoparticles have larger segregation coefficient for prismatic parts of the crystals than for pyramidal ones. Significant decrease in resonance absorption, complete disappearance of EPR lines of Fe{sup 3+} and Cr{sup 3+} centers, and appearance of four weak lines of equal intensities together with broad asymmetric lines with g-factors about 2.07–2.5 was observed in pyramidal parts grown with concentration of TiO{sub 2} nanoparticlesmore » larger than the threshold value 10{sup −2 }wt. %. The four lines were attributed to non-controlled impurity As substituted for P. In the presence of TiO{sub 2} nanoparticles, non-paramagnetic AsO{sub 4}{sup 3−} clusters trap electrons becoming AsO{sub 4}{sup 4−}. Disappearance of Fe{sup 3+} and Cr{sup 3+} centers was explained by their recharge to “EPR-silent” states and/or pairing at the surface of TiO{sub 2} nanoparticles.« less

Nicotine absorption from electronic cigarette use: comparison between first and new-generation devices.

PubMed

Farsalinos, Konstantinos E; Spyrou, Alketa; Tsimopoulou, Kalliroi; Stefopoulos, Christos; Romagna, Giorgio; Voudris, Vassilis

2014-02-26

A wide range of electronic cigarette (EC) devices, from small cigarette-like (first-generation) to new-generation high-capacity batteries with electronic circuits that provide high energy to a refillable atomizer, are available for smokers to substitute smoking. Nicotine delivery to the bloodstream is important in determining the addictiveness of ECs, but also their efficacy as smoking substitutes. In this study, plasma nicotine levels were measured in experienced users using a first- vs. new-generation EC device for 1 hour with an 18 mg/ml nicotine-containing liquid. Plasma nicotine levels were higher by 35-72% when using the new- compared to the first-generation device. Compared to smoking one tobacco cigarette, the EC devices and liquid used in this study delivered one-third to one-fourth the amount of nicotine after 5 minutes of use. New-generation EC devices were more efficient in nicotine delivery, but still delivered nicotine much slower compared to tobacco cigarettes. The use of 18 mg/ml nicotine-concentration liquid probably compromises ECs' effectiveness as smoking substitutes; this study supports the need for higher levels of nicotine-containing liquids (approximately 50 mg/ml) in order to deliver nicotine more effectively and approach the nicotine-delivery profile of tobacco cigarettes.

Dual excitation acoustic paramagnetic logging tool

DOEpatents

Vail, III, William B.

1989-01-01

New methods and apparatus are disclosed which allow measurement of the presence of oil and water in gelogical formations using a new physical effect called the Acoustic Paramagnetic Logging Effect (APLE). The presence of petroleum in formation causes a slight increase in the earth's magnetic field in the vicinity of the reservoir. This is the phenomena of paramagnetism. Application of an acoustic source to a geological formation at the Larmor frequency of the nucleous present causes the paramagnetism of the formation to disappear. This results in a decrease in the earth's magnetic field in the vicinity of the oil bearing formation. Repetitively frequency sweeping the acoustic source through the Larmor frequency of the nucleons present (approx. 2 kHz) causes an amplitude modulation of the earth's magnetic field which is a consequence of the APLE. The amplitude modulation of the earth's magnetic field is measured with an induction coil gradiometer and provides a direct measure of the amount of oil and water in the excitation zone of the formation. The phase of the signal is used to infer the longitudinal relaxation times of the fluids present, which results in the ability in general to separate oil and water and to measure the viscosity of the oil present. Such measurements may be preformed in open boreholes and in cased well bores. The Dual Excitation Acoustic Paramagnetic Logging Tool employing two acoustic sources is also described.

Dual excitation acoustic paramagnetic logging tool

DOEpatents

Vail, W.B. III.

1989-02-14

New methods and apparatus are disclosed which allow measurement of the presence of oil and water in geological formations using a new physical effect called the Acoustic Paramagnetic Logging Effect (APLE). The presence of petroleum in formation causes a slight increase in the earth's magnetic field in the vicinity of the reservoir. This is the phenomena of paramagnetism. Application of an acoustic source to a geological formation at the Larmor frequency of the nucleons present causes the paramagnetism of the formation to disappear. This results in a decrease in the earth's magnetic field in the vicinity of the oil bearing formation. Repetitively frequency sweeping the acoustic source through the Larmor frequency of the nucleons present (approx. 2 kHz) causes an amplitude modulation of the earth's magnetic field which is a consequence of the APLE. The amplitude modulation of the earth's magnetic field is measured with an induction coil gradiometer and provides a direct measure of the amount of oil and water in the excitation zone of the formation. The phase of the signal is used to infer the longitudinal relaxation times of the fluids present, which results in the ability in general to separate oil and water and to measure the viscosity of the oil present. Such measurements may be performed in open boreholes and in cased well bores. The Dual Excitation Acoustic Paramagnetic Logging Tool employing two acoustic sources is also described. 6 figs.

Red shift of the SF6 vibration spectrum induced by the electron absorption: An ab initio study

NASA Astrophysics Data System (ADS)

Tang, Bin; Zhang, Long-Fei; Han, Fang-Yuan; Luo, Zong-Chang; Liang, Qin-Qin; Liu, Chen-Yao; Zhu, Li-Ping; Zhang, Jie-Ming

2018-01-01

As a widely used gas insulator, sulfur hexafluoride (SF6) has a large cross section for electron absorption, which may make the molecule ionized to the -1 charge state in the high-voltage environment. Using ab initio calculations, we show that the absorbed electron is located averagely on the six F atoms, occupying the antibonding level of the s-p σ bonds and increasing the S-F bond length. The ionized SF6- molecule decreases its decomposition energy to only 1.5 eV, much lower than that of the neutral molecule (4.8 eV), which can be understood according to the occupying of the antibonding orbital and thus weakening of the s-p σ bonds. The weakening of the bonds results in an obvious red shift in the vibrational modes of the ionized SF6- molecule by 120-270 cm-1, compared to those of the neutral molecule. The detailed origin of these vibrational modes is analyzed. Since the appearance of the ionized SF6- molecules is before the decomposition reaction of the SF6- molecule into low-fluoride sulfides, this method may improve the sensitivity of the defection of the partial discharge and save more time for the prevention of the insulation failure in advance.

Backscattering and absorption coefficients for electrons: Solutions of invariant embedding transport equations using a method of convergence

SciTech Connect

Figueroa, C.; Brizuela, H.; Heluani, S. P.

2014-05-21

The backscattering coefficient is a magnitude whose measurement is fundamental for the characterization of materials with techniques that make use of particle beams and particularly when performing microanalysis. In this work, we report the results of an analytic method to calculate the backscattering and absorption coefficients of electrons in similar conditions to those of electron probe microanalysis. Starting on a five level states ladder model in 3D, we deduced a set of integro-differential coupled equations of the coefficients with a method know as invariant embedding. By means of a procedure proposed by authors, called method of convergence, two types ofmore » approximate solutions for the set of equations, namely complete and simple solutions, can be obtained. Although the simple solutions were initially proposed as auxiliary forms to solve higher rank equations, they turned out to be also useful for the estimation of the aforementioned coefficients. In previous reports, we have presented results obtained with the complete solutions. In this paper, we present results obtained with the simple solutions of the coefficients, which exhibit a good degree of fit with the experimental data. Both the model and the calculation method presented here can be generalized to other techniques that make use of different sorts of particle beams.« less

The effect of realistic heavy particle induced secondary electron emission coefficients on the electron power absorption dynamics in single- and dual-frequency capacitively coupled plasmas

NASA Astrophysics Data System (ADS)

Daksha, M.; Derzsi, A.; Wilczek, S.; Trieschmann, J.; Mussenbrock, T.; Awakowicz, P.; Donkó, Z.; Schulze, J.

2017-08-01

In particle-in-cell/Monte Carlo collisions (PIC/MCC) simulations of capacitively coupled plasmas (CCPs), the plasma-surface interaction is generally described by a simple model in which a constant secondary electron emission coefficient (SEEC) is assumed for ions bombarding the electrodes. In most PIC/MCC studies of CCPs, this coefficient is set to γ = 0.1, independent of the energy of the incident particle, the electrode material, and the surface conditions. Here, the effects of implementing energy-dependent secondary electron yields for ions, fast neutrals, and taking surface conditions into account in PIC/MCC simulations is investigated. Simulations are performed using self-consistently calculated effective SEECs, {γ }* , for ‘clean’ (e.g., heavily sputtered) and ‘dirty’ (e.g., oxidized) metal surfaces in single- and dual-frequency discharges in argon and the results are compared to those obtained by assuming a constant secondary electron yield of γ =0.1 for ions. In single-frequency (13.56 MHz) discharges operated under conditions of low heavy particle energies at the electrodes, the pressure and voltage at which the transition between the α- and γ-mode electron power absorption occurs are found to strongly depend on the surface conditions. For ‘dirty’ surfaces, the discharge operates in α-mode for all conditions investigated due to a low effective SEEC. In classical dual-frequency (1.937 MHz + 27.12 MHz) discharges {γ }* significantly increases with increasing low-frequency voltage amplitude, {V}{LF}, for dirty surfaces. This is due to the effect of {V}{LF} on the heavy particle energies at the electrodes, which negatively influences the quality of the separate control of ion properties at the electrodes. The new results on the separate control of ion properties in such discharges indicate significant differences compared to previous results obtained with different constant values of γ.

Plasmon inducing effects for enhanced photoelectrochemical water splitting: X-ray absorption approach to electronic structures.

PubMed

Chen, Hao Ming; Chen, Chih Kai; Chen, Chih-Jung; Cheng, Liang-Chien; Wu, Pin Chieh; Cheng, Bo Han; Ho, You Zhe; Tseng, Ming Lun; Hsu, Ying-Ya; Chan, Ting-Shan; Lee, Jyh-Fu; Liu, Ru-Shi; Tsai, Din Ping

2012-08-28

Artificial photosynthesis using semiconductors has been investigated for more than three decades for the purpose of transferring solar energy into chemical fuels. Numerous studies have revealed that the introduction of plasmonic materials into photochemical reaction can substantially enhance the photo response to the solar splitting of water. Until recently, few systematic studies have provided clear evidence concerning how plasmon excitation and which factor dominates the solar splitting of water in photovoltaic devices. This work demonstrates the effects of plasmons upon an Au nanostructure-ZnO nanorods array as a photoanode. Several strategies have been successfully adopted to reveal the mutually independent contributions of various plasmonic effects under solar irradiation. These have clarified that the coupling of hot electrons that are formed by plasmons and the electromagnetic field can effectively increase the probability of a photochemical reaction in the splitting of water. These findings support a new approach to investigating localized plasmon-induced effects and charge separation in photoelectrochemical processes, and solar water splitting was used herein as platform to explore mechanisms of enhancement of surface plasmon resonance.

THE INTERACTION OF PARAMAGNETIC RELAXATION REAGENTS WITH INTRA- AND INTERMOLECULAR HYDROGEN BONDED PHENOLS

EPA Science Inventory

Intermolecular electron-nuclear 13-C relaxation times (T(1)sup e's) from solutions containing the paramagnetic relaxation reagent (PARR), Cr(acac)3, used in conjunction with 13-C T(1)'s in diamagnetic solutions (intramolecular 13-C - (1)H dipolar T(1)'s) provide a significant inc...

Investigation of nanoparticulate silicon as printed layers using scanning electron microscopy, transmission electron microscopy, X-ray absorption spectroscopy and X-ray photoelectron spectroscopy

DOE PAGES

Unuigbe, David M.; Harting, Margit; Jonah, Emmanuel O.; ...

2017-08-21

The presence of native oxide on the surface of silicon nanoparticles is known to inhibit charge transport on the surfaces. Scanning electron microscopy (SEM) studies reveal that the particles in the printed silicon network have a wide range of sizes and shapes. High-resolution transmission electron microscopy reveals that the particle surfaces have mainly the (111)- and (100)-oriented planes which stabilizes against further oxidation of the particles. X-ray absorption spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS) measurements at the O 1s-edge have been utilized to study the oxidation and local atomic structure of printed layers of silicon nanoparticles which were milledmore » for different times. XANES results reveal the presence of the +4 (SiO 2) oxidation state which tends towards the +2 (SiO) state for higher milling times. Si 2pXPS results indicate that the surfaces of the silicon nanoparticles in the printed layers are only partially oxidized and that all three sub-oxide, +1 (Si 2O), +2 (SiO) and +3 (Si 2O 3), states are present. The analysis of the change in the sub-oxide peaks of the silicon nanoparticles shows the dominance of the +4 state only for lower milling times.« less

Effect of solvent on the electronic absorption spectral properties of some mixed β-octasubstituted Zn(II)-tetraphenylporphyrins

NASA Astrophysics Data System (ADS)

Bhyrappa, P.; Sankar, M.

2018-01-01

A series of mixed β-octasubstituted Zn(II)-porphyrins, 2,3,12,13-tetra(chloro/cyano/methyl)-5,7,8,10,15,17,18,20-octaphenylporphinato zinc(II), ZnTPP(Ph)4X4 (X = CN, Cl and CH3) have been examined by electronic absorption spectroscopy in various solvents. These Zn(II)-porphyrins exhibited varying degree of red-shift of absorption bands as high as 20-30 nm in 'B' band and 50-60 nm in longest wavelength band, 'Q(0,0)' band in polar solvents relative to that found in nonpolar solvents. The red-shift of B and Q(0,0) bands showed an unusual trend, ZnTPP(Ph)4(CN)4 > ZnTPP(Ph)4(CH3)4 > ZnTPP(Ph)4Cl4 but fails to follow an anticipated anodic shift in first porphyrin ring oxidation (vs Ag/AgCl) potential: ZnTPP(Ph)4(CN)4 (1.02 V) > ZnTPP(Ph)4Cl4 (0.74 V) > ZnTPP(Ph)4(CH3)4 (0.38 V). Such a trend suggests the combined effect of non-planarity of the macrocycle and electronic effect of the peripheral substituents. The equilibrium constants for the binding of nitrogenous bases with the Zn(II)-porphyrins showed as high as twenty fold increase for ZnTPP(Ph)4X4 (X = Br and CN) relative to ZnTPP(Ph)4(CH3)4 and follow the order: ZnTPP(Ph)4(CN)4 > ZnTPP(Ph)4Br4 > ZnTPP(Ph)4(CH3)4 ≤ ZnTPP which is approximately in line with an increase in anodic shift of their first ring redox potentials (ZnTPP(Ph)4(CN)4 (1.02 V) > ZnTPP(Ph)4Br4 (0.72 V) > ZnTPP (0.84 V) > ZnTPP(Ph)4(CH3)4) (0.38 V).

Electronic Structure and Absorption Spectra of Sodium 2-Hydroxy-5-({2-Methoxy-4[(4-Sulfophenyl)Diazenyl]Phenyl}Diazenyl)Benzoate

NASA Astrophysics Data System (ADS)

Almodarresiyeh, H. A.; Shahab, S. N.; Zelenkovsky, V. M.; Agabekov, V. E.

2014-03-01

The electronic structure and geometry of the synthesized azodye sodium 2-hydroxy-5-({2-methoxy-4[(4-sulfophenyl) diazenyl]phenyl}diazenyl)benzoate (M12) were calculated theoretically by an ab initio Hartree-Fock method in basis set 6-31G. The nature of absorption bands in the visible and near-UV spectral regions was interpreted.

Ionic liquids and solids with paramagnetic anions.

PubMed

Krieger, Brenna M; Lee, Heather Y; Emge, Thomas J; Wishart, James F; Castner, Edward W

2010-08-21

Four paramagnetic ionic compounds have been prepared and their magnetic, structural and thermal properties have been investigated. The four compounds are methylbutylpyrrolidinium tetrachloroferrate(III) ([Pyrr(14)](+)/[FeCl(4)](-)), methyltributylammonium tetrachloroferrate(III) ([N(1444)](+)/[FeCl(4)](-)), butylmethylimidazolium tetrachloroferrate(III) ([bmim](+)/[FeCl(4)](-)) and tetrabutylammonium bromotrichloroferrate(III) ([N(4444)](+)/[FeBrCl(3)](-)). Temperature-dependent studies of their magnetic behaviors show that all four compounds are paramagnetic at ambient temperatures. Glass transitions are observed for only two of the four compounds, [Pyrr(14)](+)/[FeCl(4)](-) and [bmim](+)/[FeCl(4)](-). Crystal structures for [Pyrr(14)](+)/[FeCl(4)](-) and [N(1444)](+)/[FeCl(4)](-) are compared with the previously reported [N(4444)](+)/[FeBrCl(3)](-).

Analysis of molecular hydrogen absorption toward QSO B0642–5038 for a varying proton-to-electron mass ratio

SciTech Connect

Bagdonaite, J.; Ubachs, W.; Murphy, M. T.

2014-02-10

Rovibronic molecular hydrogen (H{sub 2}) transitions at redshift z {sub abs} ≅ 2.659 toward the background quasar B0642–5038 are examined for a possible cosmological variation in the proton-to-electron mass ratio μ. We utilize an archival spectrum from the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph (UVES) with a signal-to-noise ratio of ∼35 per 2.5 km s{sup –1} pixel at the observed H{sub 2} wavelengths (335-410 nm). Some 111 H{sub 2} transitions in the Lyman and Werner bands have been identified in the damped Lyα system for which a kinetic gas temperature of ∼84 K and a molecular fraction log fmore » = –2.18 ± 0.08 are determined. The H{sub 2} absorption lines are included in a comprehensive fitting method, which allows us to extract a constraint on a variation of the proton-electron mass ratio Δμ/μ from all transitions at once. We obtain Δμ/μ = (17.1 ± 4.5{sub stat} ± 3.7{sub sys}) × 10{sup –6}. However, we find evidence that this measurement has been affected by wavelength miscalibration errors recently identified in UVES. A correction based on observations of objects with solar-like spectra gives a smaller Δμ/μ value and contributes to a larger systematic uncertainty: Δμ/μ = (12.7 ± 4.5{sub stat} ± 4.2{sub sys}) × 10{sup –6}.« less

Minerals discovered in paleolithic black pigments by transmission electron microscopy and micro-X-ray absorption near-edge structure

NASA Astrophysics Data System (ADS)

Chalmin, E.; Vignaud, C.; Salomon, H.; Farges, F.; Susini, J.; Menu, M.

2006-05-01

Analysis of archeological materials aims to rediscover the know-how of prehistoric men by determining the nature of the painting matter, its preparation mode, and the geographic origin of its raw materials. The preparation mode of the painting matter of the paleolithic rock art apparently consisted of mixing, grinding, and also heat-treatment. In this study, we focus on black pigments and more particularly manganese oxides. Using the combined approach of transmission electron microscopy (TEM) and Mn K-edge X-ray absorption near-edge structure (XANES) spectroscopy, we analyzed a variety of archeological black painted samples. The studied pigments arise from the caves of Ekain (Basque country, Spain), Labastide and Gargas (Hautes-Pyrénées, France). In addition, a black “crayon” (i.e., a “pen”) from the cave of Combe Saunière (Dordogne, France) was also investigated. From the analysis of these painting matters, several unusual minerals have been identified as black pigment, such as manganite, groutite, todorokite and birnessite. These conclusions enable us to estimate the technical level of paleolithic artists: they didn’t use heat-treatment to prepare black painting matter. Consequently, the unusual mineralogy found in some of these pigments suggests that some of the manganese ores are coming from geological settings that are sometimes relatively far away from the Dordogne and Basque region such as in Ariège (central-oriental Pyrénées).

Optical, Structural and Paramagnetic Properties of Eu-Doped Ternary Sulfides ALnS2 (A = Na, K, Rb; Ln = La, Gd, Lu, Y)

PubMed Central

Jarý, Vítězslav; Havlák, Lubomír; Bárta, Jan; Buryi, Maksym; Mihóková, Eva; Rejman, Martin; Laguta, Valentin; Nikl, Martin

2015-01-01

Eu-doped ternary sulfides of general formula ALnS2 (A = Na, K, Rb; Ln = La, Gd, Lu, Y) are presented as a novel interesting material family which may find usage as X-ray phosphors or solid state white light emitting diode (LED) lighting. Samples were synthesized in the form of transparent crystalline hexagonal platelets by chemical reaction under the flow of hydrogen sulfide. Their physical properties were investigated by means of X-ray diffraction, time-resolved photoluminescence spectroscopy, electron paramagnetic resonance, and X-ray excited fluorescence. Corresponding characteristics, including absorption, radioluminescence, photoluminescence excitation and emission spectra, and decay kinetics curves, were measured and evaluated in a broad temperature range (8–800 K). Calculations including quantum local crystal field potential and spin-Hamiltonian for a paramagnetic particle in D3d local symmetry and phenomenological model dealing with excited state dynamics were performed to explain the experimentally observed features. Based on the results, an energy diagram of lanthanide energy levels in KLuS2 is proposed. Color model xy-coordinates are used to compare effects of dopants on the resulting spectrum. The application potential of the mentioned compounds in the field of white LED solid state lighting or X-ray phosphors is thoroughly discussed. PMID:28793612

Evolution of dielectric function of Al-doped ZnO thin films with thermal annealing: effect of band gap expansion and free-electron absorption.

PubMed

Li, X D; Chen, T P; Liu, Y; Leong, K C

2014-09-22

Evolution of dielectric function of Al-doped ZnO (AZO) thin films with annealing temperature is observed. It is shown that the evolution is due to the changes in both the band gap and the free-electron absorption as a result of the change of free-electron concentration of the AZO thin films. The change of the electron concentration could be attributed to the activation of Al dopant and the creation/annihilation of the donor-like defects like oxygen vacancy in the thin films caused by annealing.

Full-potential theoretical investigations of electron inelastic mean free paths and extended x-ray absorption fine structure in molybdenum.

PubMed

Chantler, C T; Bourke, J D

2014-04-09

X-ray absorption fine structure (XAFS) spectroscopy is one of the most robust, adaptable, and widely used structural analysis tools available for a range of material classes from bulk solids to aqueous solutions and active catalytic structures. Recent developments in XAFS theory have enabled high-accuracy calculations of spectra over an extended energy range using full-potential cluster modelling, and have demonstrated particular sensitivity in XAFS to a fundamental electron transport property-the electron inelastic mean free path (IMFP). We develop electron IMFP theory using a unique hybrid model that simultaneously incorporates second-order excitation losses, while precisely accounting for optical transitions dictated by the complex band structure of the solid. These advances are coupled with improved XAFS modelling to determine wide energy-range absorption spectra for molybdenum. This represents a critical test case of the theory, as measurements of molybdenum K-edge XAFS represent the most accurate determinations of XAFS spectra for any material. We find that we are able to reproduce an extended range of oscillatory structure in the absorption spectrum, and demonstrate a first-time theoretical determination of the absorption coefficient of molybdenum over the entire extended XAFS range utilizing a full-potential cluster model.

Electronic structure study of wide band gap magnetic semiconductor (La0.6Pr0.4)0.65Ca0.35MnO3 nanocrystals in paramagnetic and ferromagnetic phases

NASA Astrophysics Data System (ADS)

Dwivedi, G. D.; Joshi, Amish G.; Kumar, Shiv; Chou, H.; Yang, K. S.; Jhong, D. J.; Chan, W. L.; Ghosh, A. K.; Chatterjee, Sandip

2016-04-01

X-ray circular magnetic dichroism (XMCD), X-ray photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) techniques were used to study the electronic structure of nanocrystalline (La0.6Pr0.4)0.65Ca0.35MnO3 near Fermi-level. XMCD results indicate that Mn3+ and Mn4+ spins are aligned parallel to each other at 20 K. The low M-H hysteresis curve measured at 5 K confirms ferromagnetic ordering in the (La0.6Pr0.4)0.65Ca0.35MnO3 system. The low temperature valence band XPS indicates that coupling between Mn3d and O2p is enhanced and the electronic states near Fermi-level have been suppressed below TC. The valence band UPS also confirms the suppression of electronic states near Fermi-level below Curie temperature. UPS near Fermi-edge shows that the electronic states are almost absent below 0.5 eV (at 300 K) and 1 eV (at 115 K). This absence clearly demonstrates the existence of a wide band-gap in the system since, for hole-doped semiconductors, the Fermi-level resides just above the valence band maximum.

Giant Paramagnetism of Copper Nanoparticles in Nanocomposites Cu@C

NASA Astrophysics Data System (ADS)

Sharoyan, Eduard; Mirzakhanyan, Armen; Gyulasaryan, Harutyun; Manukyan, Aram; Estiphanos, Medhanie; Goff, Michael; Bernal, Oscar; Kocharian, Armen

The copper nanoparticles in nanocomposites Cu@C, encapsulated in graphitized carbon shell was obtained by the solid-phase pyrolysis method of polycrystalline phthalocyanine (CuPc, Pc =C32N8H16) . The average sizes of the nanoparticles are in the range of 2-6 nm. Magnetic measurements were carried out by vibrational magnetometer in the temperature range 10-300 K. At low temperatures (<70K) we observed a giant paramagnetism, apparently due to the (ballistic) conduction electron (large orbital magnetism). The values of the specific susceptibility at T = 10K with magnetic specific susceptibility of 510-5 emu/gOe order. This work was supported by the RA MES State Committee of Science, in the frames of the research project SCS-13-1C090. The work at California State University was supported by the National Science Foundation-Partnerships for Research and Education in Materials under Grant DMR-1523588.

Benign Synthesis of Black Microspheres of Anatase TiO2 with Paramagnetic Oxygen Vacancies through NH3 Treatment.

PubMed

Maqbool, Qysar; Srivastava, Aasheesh

2017-10-09

Coloured TiO 2 is coveted for its ability to extract energy from the visible region of electromagnetic spectrum. Here a facile synthesis of black anatase titania microspheres (B-TiO 2 ) through a two-step process is reported. In the first step, amorphous white TiO 2 microspheres (W-TiO 2 ) are obtained by hydrolysing titanium tetraisopropoxide by ammonia vapours in ethanol. In the second step, the W-TiO 2 is thermally annealed at 500 °C to obtain B-TiO 2 . The diffuse reflectance analysis showed that B-TiO 2 absorbs across visible spectrum with absorption extending well into NIR region. Raman scattering together with EPR analysis showed compelling evidence of the existence of oxygen deficiency within the crystal in B-TiO 2 that induces black colouration in the sample. The defects present in the black anatase sample were confirmed to be single-electron-trapped (or paramagnetic) oxygen vacancies (V o ⋅) by XPS and EPR studies. The magnetic susceptibility studies showed existence of antiferromagnetic interactions between these unpaired electron spins. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

An experimental study of the electronic absorption and fluorescence spectral properties of new p-substituted-N-phenylpyrroles and their electrosynthesized polymers.

PubMed

Diaw, A K D; Gningue-Sall, D; Yassar, A; Brochon, J-C; Henry, E; Aaron, J-J

2015-01-25

Electronic absorption and fluorescence spectral properties of new p-substituted-N-phenylpyrroles (N-PhPys), including HOPhPy, MeOPhPy, ThPhPy, PhDPy, DPhDPy, PyPhThThPhPy, and their available, electrosynthesized polymers were investigated. Electronic absorption spectra, fluorescence excitation and emission spectra, fluorescence quantum yields (ΦF) and lifetimes (τF), and other photophysical parameters of these N-PhPy derivatives and their polymers were measured in DMF, DMSO diluted solutions and/or solid state at room temperature. The electronic absorption spectra of N-PhPy derivatives and their polymers included one to several bands, located in the 270-395 nm region, according to the p-phenyl substituent electron-donating effect and conjugated heteroaromatic system length. The fluorescence excitation spectra were characterized by one broad main peak, with, in most cases, one (or more) poorly resolved shoulder (s), appearing in the 270-405 nm region, and their emission spectra were generally constituted of several bands located in the 330-480 nm region. No significant shift of the absorption, fluorescence excitation and emission spectra wavelengths was found upon going from the monomers to the corresponding polymers. ΦF values were high, varying between 0.11 and 0.63, according to the nature of substituents(s) and to the conjugated system extension. Fluorescence decays were mono-exponential for the monomers and poly-exponential for PyPhThThPhPy and for polymers. τF values were relatively short (0.35-5.17 ns), and markedly decreased with the electron-donor character of the phenyl group p-substituent and the conjugated system extension. Copyright © 2014 Elsevier B.V. All rights reserved.

Temperature dependence of the hydrated electron's excited-state relaxation. II. Elucidating the relaxation mechanism through ultrafast transient absorption and stimulated emission spectroscopy

NASA Astrophysics Data System (ADS)

Farr, Erik P.; Zho, Chen-Chen; Challa, Jagannadha R.; Schwartz, Benjamin J.

2017-08-01

The structure of the hydrated electron, particularly whether it exists primarily within a cavity or encompasses interior water molecules, has been the subject of much recent debate. In Paper I [C.-C. Zho et al., J. Chem. Phys. 147, 074503 (2017)], we found that mixed quantum/classical simulations with cavity and non-cavity pseudopotentials gave different predictions for the temperature dependence of the rate of the photoexcited hydrated electron's relaxation back to the ground state. In this paper, we measure the ultrafast transient absorption spectroscopy of the photoexcited hydrated electron as a function of temperature to confront the predictions of our simulations. The ultrafast spectroscopy clearly shows faster relaxation dynamics at higher temperatures. In particular, the transient absorption data show a clear excess bleach beyond that of the equilibrium hydrated electron's ground-state absorption that can only be explained by stimulated emission. This stimulated emission component, which is consistent with the experimentally known fluorescence spectrum of the hydrated electron, decreases in both amplitude and lifetime as the temperature is increased. We use a kinetic model to globally fit the temperature-dependent transient absorption data at multiple temperatures ranging from 0 to 45 °C. We find the room-temperature lifetime of the excited-state hydrated electron to be 137 ±40 fs, in close agreement with recent time-resolved photoelectron spectroscopy (TRPES) experiments and in strong support of the "non-adiabatic" picture of the hydrated electron's excited-state relaxation. Moreover, we find that the excited-state lifetime is strongly temperature dependent, changing by slightly more than a factor of two over the 45 °C temperature range explored. This temperature dependence of the lifetime, along with a faster rate of ground-state cooling with increasing bulk temperature, should be directly observable by future TRPES experiments. Our data also suggest

Optical activity and electronic absorption spectra of some simple nucleosides related to cytidine and uridine: all-valence-shell molecular orbital calculations.

PubMed Central

Miles, D W; Redington, P K; Miles, D L; Eyring, H

1981-01-01

The circular dichroism and electronic absorption of three simple model systems for cytidine and uridine have been measured to 190 nm. The molecular spectral properties (excitation wavelengths, oscillator strengths, rotational strengths, and polarization directions) and electronic transitional patterns were investigated by using wave functions of the entire nucleoside with the goal of establishing the reliability of the theoretical method. The computed electronic absorption quantities were shown to be in satisfactory agreement with experimental data. It was found that the computed optical rotatory strengths of the B2u and E1u electronic transitions and lowest observed n-pi transition are in good agreement with experimental values. Electronic transitions were characterized by their electronic transitional patterns derived from population analysis of the transition density matrix. The theoretical rotational strengths associated with the B2u and E1u transitions stabilize after the use of just a few singly excited configurations in the configuration interaction basis and, hypothetically, are more reliable as indicators of conformation in pyrimidine nucleosides related to cytidine. PMID:6950393

Electronic transitions and heterogeneity of the bacteriophytochrome Pr absorption band: An angle balanced polarization resolved femtosecond VIS pump–IR probe study

PubMed Central

Linke, Martin; Yang, Yang; Zienicke, Benjamin; Hammam, Mostafa A.S.; von Haimberger, Theodore; Zacarias, Angelica; Inomata, Katsuhiko; Lamparter, Tilman; Heyne, Karsten

2013-01-01

Photoisomerization of biliverdin (BV) chromophore triggers the photoresponse in native Agp1 bacteriophytochrome. We discuss heterogeneity in phytochrome Pr form to account for the shape of the absorption profile. We investigated different regions of the absorption profile by angle balanced polarization resolved femtosecond VIS pump–IR probe spectroscopy. We studied the Pr form of Agp1 with its natural chromophore and with a sterically locked 18Et-BV (locked Agp1). We followed the dynamics and orientations of the carbonyl stretching vibrations of ring D and ring A in their ground and electronically excited states. Photoisomerization of ring D is reflected by strong signals of the ring D carbonyl vibration. In contrast, orientational data on ring A show no rotation of ring A upon photoexcitation. Orientational data allow excluding a ZZZasa geometry and corroborates a nontwisted ZZZssa geometry of the chromophore. We found no proof for heterogeneity but identified a new, to our knowledge, electronic transition in the absorption profile at 644 nm (S0→S2). Excitation of the S0→S2 transition will introduce a more complex photodynamics compared with S0→S1 transition. Our approach provides fundamental information on disentanglement of absorption profiles, identification of chromophore structures, and determination of molecular groups involved in the photoisomerization process of photoreceptors. PMID:24138851

Specimen charging in X-ray absorption spectroscopy: correction of total electron yield data from stabilized zirconia in the energy range 250-915 eV.

PubMed

Vlachos, Dimitrios; Craven, Alan J; McComb, David W

2005-03-01

The effects of specimen charging on X-ray absorption spectroscopy using total electron yield have been investigated using powder samples of zirconia stabilized by a range of oxides. The stabilized zirconia powder was mixed with graphite to minimize the charging but significant modifications of the intensities of features in the X-ray absorption near-edge fine structure (XANES) still occurred. The time dependence of the charging was measured experimentally using a time scan, and an algorithm was developed to use this measured time dependence to correct the effects of the charging. The algorithm assumes that the system approaches the equilibrium state by an exponential decay. The corrected XANES show improved agreement with the electron energy-loss near-edge fine structure obtained from the same samples.

VO2+ ions in zinc lead borate glasses studied by EPR and optical absorption techniques.

PubMed

Prakash, P Giri; Rao, J Lakshmana

2005-09-01

Electron paramagnetic resonance (EPR) and optical absorption spectra of vanadyl ions in zinc lead borate (ZnO-PbO-B2O3) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO2+ ions. The values of spin-Hamiltonian parameters indicate that the VO2+ ions in zinc lead borate glasses were present in octahedral sites with tetragonal compression and belong to C4V symmetry. The spin-Hamiltonian parameters g and A are found to be independent of V2O5 content and temperature but changing with ZnO content. The decrease in Deltag( parallel)/Deltag( perpendicular) value with increase in ZnO content indicates that the symmetry around VO2+ ions is more octahedral. The decrease in intensity of EPR signal above 10 mol% of V2O5 is attributed to a fall in the ratio of the number of V4+ ions (N4) to the number of V5+ ions (N5). The number of spins (N) participating in resonance was calculated as a function of temperature for VO2+ doped zinc lead borate glass sample and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility was calculated at various temperatures and the Curie constant was evaluated from the 1/chi-T graph. The optical absorption spectra show single absorption band due to VO2+ ions in tetragonally distorted octahedral sites.

Ionic Liquids and Solids with Paramagnetic Anions

SciTech Connect

Castner, Jr., E.W.; Wishart, J.; Krieger, B.M.

2010-06-18

Four paramagnetic ionic compounds have been prepared and their magnetic, structural and thermal properties have been investigated. The four compounds are methylbutylpyrrolidinium tetrachloroferrate(III) ([Pyrr{sub 14}]{sup +}/[FeCl{sub 4}]{sup -}), methyltributylammonium tetrachloroferrate(III) ([N{sub 1444}]{sup +}/[FeCl{sub 4}]{sup -}), butylmethylimidazolium tetrachloroferrate(III) ([bmim]{sup +}/[FeCl{sub 4}]{sup -}) and tetrabutylammonium bromotrichloroferrate(III) ([N{sub 4444}]{sup +}/[FeBrCl{sub 3}]{sup -}). Temperature-dependent studies of their magnetic behaviors show that all four compounds are paramagnetic at ambient temperatures. Glass transitions are observed for only two of the four compounds, [Pyrr{sub 14}]{sup +}/[FeCl{sub 4}]{sup -} and [bmim]{sup +}/[FeCl{sub 4}]{sup -}. Crystal structures for [Pyrr{sub 14}]{sup +}/[FeCl{sub 4}]{sup -} and [N{sub 1444}]{sup +}/[FeCl{sub 4}]{sup -}more » are compared with the previously reported [N{sub 4444}]{sup +}/[FeBrCl{sub 3}]{sup -}.« less

An EPR study on tea: Identification of paramagnetic species, effect of heat and sweeteners

NASA Astrophysics Data System (ADS)

Bıyık, Recep; Tapramaz, Recep

2009-10-01

Tea ( Camellia Sinensis) is the most widely consumed beverage in the world, and is known to be having therapeutic, antioxidant and nutritional effects. Electron paramagnetic resonance (EPR) spectral studies made on the tea cultivated along the shore of Black Sea, Turkey, show Mn 2+ and Fe 3+ centers in green tea leaves and in black tea extract. Dry black tea flakes and dry extract show additional sharp line attributed to semiquinone radical. The origins of the paramagnetic species in black tea are defined and discussed. Effect of humidity and heat are investigated. It is observed that dry extract of black tea melts at 100 °C and the semiquinone radical lives up to 140 °C while Mn 2+ sextet disappears just above 100 °C in tea extract. Natural and synthetics sweeteners have different effects on the paramagnetic centers. White sugar (sucrose) quenches the Mn 2+ and semiquinone lines in black tea EPR spectrum, and glucose, fructose, lactose and maltose quench Fe 3+ line while synthetic sweeteners acesulfam potassium, aspartame and sodium saccharine do not have any effect on paramagnetic species in tea.

An EPR study on tea: identification of paramagnetic species, effect of heat and sweeteners.

PubMed

Biyik, Recep; Tapramaz, Recep

2009-10-15

Tea (Camellia Sinensis) is the most widely consumed beverage in the world, and is known to be having therapeutic, antioxidant and nutritional effects. Electron paramagnetic resonance (EPR) spectral studies made on the tea cultivated along the shore of Black Sea, Turkey, show Mn(2+) and Fe(3+) centers in green tea leaves and in black tea extract. Dry black tea flakes and dry extract show additional sharp line attributed to semiquinone radical. The origins of the paramagnetic species in black tea are defined and discussed. Effect of humidity and heat are investigated. It is observed that dry extract of black tea melts at 100 degrees C and the semiquinone radical lives up to 140 degrees C while Mn(2+) sextet disappears just above 100 degrees C in tea extract. Natural and synthetics sweeteners have different effects on the paramagnetic centers. White sugar (sucrose) quenches the Mn(2+) and semiquinone lines in black tea EPR spectrum, and glucose, fructose, lactose and maltose quench Fe(3+) line while synthetic sweeteners acesulfam potassium, aspartame and sodium saccharine do not have any effect on paramagnetic species in tea.

Ultrafast saturable absorption in TiS2 induced by non-equilibrium electrons and the generation of a femtosecond mode-locked laser.

PubMed

Tian, Xiangling; Wei, Rongfei; Liu, Meng; Zhu, Chunhui; Luo, Zhichao; Wang, Fengqiu; Qiu, Jianrong

2018-05-24

Non-equilibrium electrons induced by ultrafast laser excitation in a correlated electron material can disturb the Fermi energy as well as optical nonlinearity. Here, non-equilibrium electrons translate a semiconductor TiS2 material into a plasma to generate broad band nonlinear optical saturable absorption with a sub-picosecond recovery time of ∼768 fs (corresponding to modulation frequencies over 1.3 THz) and a modulation response up to ∼145%. Based on this optical nonlinear modulator, a stable femtosecond mode-locked pulse with a pulse duration of ∼402 fs and a pulse train with a period of ∼175.5 ns is observed in the all-optical system. The findings indicate that non-equilibrium electrons can promote a TiS2-based saturable absorber to be an ultrafast switch for a femtosecond pulse output.

Thermophysical properties of paramagnetic Fe from first principles

NASA Astrophysics Data System (ADS)

Ehteshami, Hossein; Korzhavyi, Pavel A.

2017-12-01

A computationally efficient, yet general, free-energy modeling scheme is developed based on first-principles calculations. Finite-temperature disorder associated with the fast (electronic and magnetic) degrees of freedom is directly included in the electronic structure calculations, whereas the vibrational free energy is evaluated by a proposed model that uses elastic constants to calculate average sound velocity of the quasiharmonic Debye model. The proposed scheme is tested by calculating the lattice parameter, heat capacity, and single-crystal elastic constants of α -, γ -, and δ -iron as functions of temperature in the range 1000-1800 K. The calculations accurately reproduce the well-established experimental data on thermal expansion and heat capacity of γ - and δ -iron. Electronic and magnetic excitations are shown to account for about 20% of the heat capacity for the two phases. Nonphonon contributions to thermal expansion are 12% and 10% for α - and δ -Fe and about 30% for γ -Fe. The elastic properties predicted by the model are in good agreement with those obtained in previous theoretical treatments of paramagnetic phases of iron, as well as with the bulk moduli derived from isothermal compressibility measurements [N. Tsujino et al., Earth Planet. Sci. Lett. 375, 244 (2013), 10.1016/j.epsl.2013.05.040]. Less agreement is found between theoretically calculated and experimentally derived single-crystal elastic constants of γ - and δ -iron.

Chemometric analysis of correlations between electronic absorption characteristics and structural and/or physicochemical parameters for ampholytic substances of biological and pharmaceutical relevance.

PubMed

Judycka-Proma, U; Bober, L; Gajewicz, A; Puzyn, T; Błażejowski, J

2015-03-05

Forty ampholytic compounds of biological and pharmaceutical relevance were subjected to chemometric analysis based on unsupervised and supervised learning algorithms. This enabled relations to be found between empirical spectral characteristics derived from electronic absorption data and structural and physicochemical parameters predicted by quantum chemistry methods or phenomenological relationships based on additivity rules. It was found that the energies of long wavelength absorption bands are correlated through multiparametric linear relationships with parameters reflecting the bulkiness features of the absorbing molecules as well as their nucleophilicity and electrophilicity. These dependences enable the quantitative analysis of spectral features of the compounds, as well as a comparison of their similarities and certain pharmaceutical and biological features. Three QSPR models to predict the energies of long-wavelength absorption in buffers with pH=2.5 and pH=7.0, as well as in methanol, were developed and validated in this study. These models can be further used to predict the long-wavelength absorption energies of untested substances (if they are structurally similar to the training compounds). Copyright © 2014 Elsevier B.V. All rights reserved.

Electronic Interactions of n-Doped Perylene Diimide Groups Appended to Polynorbornene Chains: Implications for Electron Transport in Organic Electronics.

PubMed

Nguyen, Minh T; Biberdorf, Joshua D; Holliday, Bradley J; Jones, Richard A

2017-11-01

A polymer consisting of a polynorbornene backbone with perylene diimide (PDI) pendant groups on each monomeric unit is synthesized via ring opening metathesis polymerization. The PDI pendant groups along the polymer backbone, studied by UV-vis absorption, fluorescence emission, and electron paramagnetic resonance spectroscopy in addition to electrochemical methods, show evidence of molecular aggregation and corresponding electronic coupling with neighboring groups, which forms pathways for efficient electron transport from one group to another in a specific reduced form. When n-doped, the title polymer shows redox conductivity of 5.4 × 10 -3 S cm -1 , comparable with crystalline PDI materials, and is therefore a promising material for use in organic electronics. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electronic absorption spectroscopy of matrix-isolated polycyclic aromatic hydrocarbon cations. I - The naphthalene cation (C10H8/+/)

NASA Technical Reports Server (NTRS)

Salama, F.; Allamandola, L. J.

1991-01-01

The ultraviolet, visible, and near-infrared absorption spectra of naphthalene (C10H8) and its radical ion (C10H8/+/), formed by vacuum ultraviolet irradiation, were measured in argon and neon matrices at 4.2 K. The associated vibronic band systems and their spectroscopic assignments are discussed together with the physical and chemical conditions governing ion production in the solid phase. The absorption coefficients were calculated for the ion and found lower than previous values, presumably due to the low polarizability of the neon matrix.

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Study of photoinduced absorption by the method of modified laser photothermal radiometry

NASA Astrophysics Data System (ADS)

Skvortsov, L. A.; Maksimov, E. M.; Tuchkov, A. A.

2008-10-01

The application of the method of modified laser photothermal radiometry for studying the photoinduced absorption in thin films is considered. The sensitivity of the method is estimated. The mechanism of induced near-IR absorption in titanium dioxide films is proposed and the nature of surface defects responsible for this process is explained. It is shown that kinetic equations describing monomolecular recombination are consistent with the experimental dependences for the thermal activation energy of defects equal to 0.17±0.04 eV.

Paramagnetic and glass transitions in sudoku

NASA Astrophysics Data System (ADS)

Williams, A.; Ackland, G. J.

2012-09-01

We study the statistical mechanics of a model glassy system based on sudoku, a familiar and popular mathematical puzzle. Sudoku puzzles provide a very rare example of a class of frustrated systems with a unique ground state without symmetry. Here, the puzzle is recast as a thermodynamic system where the number of violated rules defines the energy. We use Monte Carlo simulation to show that the “sudoku Hamiltonian” exhibits two transitions as a function of temperature, a paramagnetic, and a glass transition. Of these, the intermediate condensed phase is the only one that visits the ground state (i.e., it solves the puzzle, though this is not the purpose of the study). Both transitions are associated with an entropy change, paramagnetism measured from the dynamics of the Monte Carlo run, showing a peak in specific heat, while the residual glass entropy is determined by finding multiple instances of the glass by repeated annealing. There are relatively few such simple models for frustrated or glassy systems that exhibit both ordering and glass transitions; sudoku puzzles are unique for the ease with which they can be obtained, with the proof of the existence of a unique ground state via the satisfiability of all constraints. Simulations suggest that in the glass phase there is an increase in information entropy with lowering temperature. In fact, we have shown that sudoku puzzles have the type of rugged energy landscape with multiple minima that typifies glasses in many physical systems. This puzzling result is a manifestation of the paradox of the residual glass entropy. These readily available puzzles can now be used as solvable model Hamiltonian systems for studying the glass transition.

One- and two-photon absorption spectra of the yellow fluorescent protein citrine: effects of intramolecular electron-vibrational coupling and intermolecular interactions

NASA Astrophysics Data System (ADS)

Chen, Fasheng; Zhao, Xinyi; Liang, WanZhen

2018-04-01

Both the vibrationally resolved and statistically averaged one-photon absorption (OPA) and two-photon absorption (TPA) spectra of the anionic form of chromophore (AC) in its micro-environment of yellow fluorescent protein (YFP) Citrine have been calculated. The result comparison has been made with those of the AC model compounds in vacuo and methanol solution, which allows us to allocate the individual contribution of the intramolecular electron-vibrational coupling, the electrostatic π-stacking interaction between Tyr203 and AC, and the interaction between AC and its micro-environment to the spectra. The results reveal that the non-Condon vibronic coupling effect is responsible for the blue shift of TPA absorption maximum compared with its OPA counterpart corresponding to S0 → S1, and that the π-stacking interaction between Tyr203 and AC alters the relative intensities of TPA maxima, which further enhances the higher-energy vibronic peaks and weakens the lowest-energy peak. The statically averaged OPA and TPA spectra calculated by quantum mechanics/molecular mechanics (QM/MM) methods based on Born-Oppenheimer molecular dynamics simulation largely deviate the experimental spectral lineshapes, which further verifies the significant contribution of non-Condon vibronic coupling effect on the spectra. The interaction of individual amino acid residue or water close to AC+Tyr203 has different effects on the spectra, which may increase/decrease the excitation energy depending on its position and electronic property.

Measurement of Electronic States of PbS Nanocrystal Quantum Dots Using Scanning Tunneling Spectroscopy: The Role of Parity Selection Rules in Optical Absorption

NASA Astrophysics Data System (ADS)

Diaconescu, Bogdan; Padilha, Lazaro A.; Nagpal, Prashant; Swartzentruber, Brian S.; Klimov, Victor I.

2013-03-01

We study the structure of electronic states in individual PbS nanocrystal quantum dots by scanning tunneling spectroscopy (STS) using one-to-two monolayer nanocrystal films treated with 1, 2-ethanedithiols (EDT). Up to six individual valence and conduction band states are resolved for a range of quantum dot sizes. The measured states’ energies are in good agreement with calculations using the k·p four-band envelope function formalism. A comparison of STS and optical absorption spectra indicates that some of the absorption features can only be explained by asymmetric transitions involving the states of different symmetries (e.g., S and P or P and D), which points towards the relaxation of the parity selection rules in these nanostructures. STS measurements also reveal a midgap feature, which is likely similar to one observed in previous charge transport studies of EDT-treated quantum dot films.

Mechanism for the occurrence of paramagnetic planes within magnetically ordered cerium systems

NASA Astrophysics Data System (ADS)

Kioussis, Nicholas; Cooper, Bernard R.; Banerjea, Amitava

1988-11-01

Hybridization of moderately delocalized f electrons with band electrons gives rise to a highly anisotropic two-ion interaction. Previously it has been shown that such an interaction explains the experimentally observed unusual magnetic behavior of CeBi, yielding a phase transition from a higher-temperature type-I (↑↓) to a lower-temperature type-IA (↑↑↓↓) antiferromagnetic structure. If the hybridization-mediated interaction is the key to understanding the magnetic behavior of such moderately delocalized f-electron systems, we should expect to be able to understand on this basis the even more unusual magnetic behavior of CeSb. In CeSb, there is a sequence of magnetic structures in which the higher-temperature structures involve a periodic stacking of paramagnetic \\{001\\} planes alternating with magnetically ordered \\{001\\} planes of [001]-moment alignment. In this paper we show that such a coexistence of paramagnetic and magnetically ordered Ce3+ sites can be understood on the basis of the hybridization-mediated interionic interaction when there are cubic crystal-field (CF) interactions of comparable strength. The tendency to form paramagnetic planes is found to increase with increasing CF strength (Γ7 ground state); and the stability of the up-down paramagnetic plane arrangement at high temperatures is shown to arise from the reconciliation of the magnetic ordering with the CF interactions. We also find that for a certain range of parameters a different novel situation occurs, with a fully nonmagnetic (singlet) ground state for the Ce3+ ion. This singlet state is not Kondo-like, and occurs in such a way that the system would be expected to fluctuate between two differently polarized states, one of which is the singlet state.

Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc00880e

PubMed Central

Prasad, Saumya; Mandal, Imon; Singh, Shubham; Paul, Ashim; Mandal, Bhubaneswar

2017-01-01

Electronic absorption spectra of proteins are primarily characterized over the ultraviolet region (185–320 nm) of the electromagnetic spectrum. While recent studies on peptide aggregates have revealed absorption beyond 350 nm, monomeric proteins lacking aromatic amino acids, disulphide bonds, and active site prosthetic groups are expected to remain optically silent beyond 250 nm. Here, in a joint theoretical and experimental investigation, we report the distinctive UV-Vis absorption spectrum between 250 nm [ε = 7338 M–1 cm–1] and 800 nm [ε = 501 M–1 cm–1] in a synthetic 67 residue protein (α3C), in monomeric form, devoid of aromatic amino acids. Systematic control studies with high concentration non-aromatic amino acid solutions revealed significant absorption beyond 250 nm for charged amino acids which constitute over 50% of the sequence composition in α3C. Classical atomistic molecular dynamics (MD) simulations of α3C reveal dynamic interactions between multiple charged sidechains of Lys and Glu residues present in α3C. Time-dependent density functional theory calculations on charged amino acid residues sampled from the MD trajectories of α3C reveal that the distinctive absorption features of α3C may arise from two different types of charge transfer (CT) transitions involving spatially proximal Lys/Glu amino acids. Specifically, we show that the charged amino (NH3+)/carboxylate (COO–) groups of Lys/Glu sidechains act as electronic charge acceptors/donors for photoinduced electron transfer either from/to the polypeptide backbone or to each other. Further, the sensitivity of the CT spectra to close/far/intermediate range of encounters between sidechains of Lys/Glu owing to the three dimensional protein fold can create the long tail in the α3C absorption profile between 300 and 800 nm. Finally, we experimentally demonstrate the sensitivity of α3C absorption spectrum to temperature and pH-induced changes in protein structure. Taken together, our

Probing Lewis Acid-Base Interactions with Born-Oppenheimer Molecular Dynamics: The Electronic Absorption Spectrum of p-Nitroaniline in Supercritical CO2.

PubMed

Cabral, Benedito J Costa; Rivelino, Roberto; Coutinho, Kaline; Canuto, Sylvio

2015-07-02

The structure and dynamics of p-nitroaniline (PNA) in supercritical CO2 (scCO2) at T = 315 K and ρ = 0.81 g cm(-3) are investigated by carrying out Born-Oppenheimer molecular dynamics, and the electronic absorption spectrum in scCO2 is determined by time dependent density functional theory. The structure of the PNA-scCO2 solution illustrates the role played by Lewis acid-base (LA-LB) interactions. In comparison with isolated PNA, the ν(N-O) symmetric and asymmetric stretching modes of PNA in scCO2 are red-shifted by -17 and -29 cm(-1), respectively. The maximum of the charge transfer (CT) absorption band of PNA in scSCO2 is at 3.9 eV, and the predicted red-shift of the π → π* electronic transition relative to the isolated gas-phase PNA molecule reproduces the experimental value of -0.35 eV. An analysis of the relationship between geometry distortions and excitation energies of PNA in scCO2 shows that the π → π* CT transition is very sensitive to changes of the N-O bond distance, strongly indicating a correlation between vibrational and electronic solvatochromism driven by LA-LB interactions. Despite the importance of LA-LB interactions to explain the solvation of PNA in scCO2, the red-shift of the CT band is mainly determined by electrostatic interactions.

Investigating the Distribution of Stable Paramagnetic Species in an Apple Seed Using X-Band EPR and EPR Imaging.

PubMed

Nakagawa, Kouichi; Epel, Boris

2017-03-01

This study investigated the location and distribution of paramagnetic species in apple seeds using electron paramagnetic resonance (EPR) and X-band (9 GHz) EPR imaging (EPRI). EPR primarily detected two paramagnetic species per measured seed. These two different radical species were assigned as stable radicals and Mn 2+ species based on the g values and hyperfine components. The signal from the stable radical was noted at g ≈ 2.00 and was strong and relatively stable. The subsequent noninvasive EPRI of the radical present in each seed revealed that the stable radicals were located primarily in the seed coat, with very few radicals observed in the cotyledon of the seed. These results indicate that the stable radical species were only found within the seed coat, and few radical species were found in other seed parts.

Structural, optical, electron paramagnetic, thermal and dielectric characterization of chalcopyrite.

PubMed

Prameena, B; Anbalagan, G; Gunasekaran, S; Ramkumaar, G R; Gowtham, B

2014-03-25

Chalcopyrite (CuFeS2) a variety of pyrite minerals was investigated through spectroscopic techniques and thermal analysis. The morphology and elemental analysis of the chalcopyrite have been done by high resolution SEM with EDAX. The lattice parameters were from the powder diffraction data (a=5.3003±0.0089 Å, c=10.3679±0.0289 Å; the volume of the unit cell=291.266 Å(3) with space group I42d (122)). The thermal decomposition behavior of chalcopyrite was studied by means of thermogravimetric analysis at three different heating rates 10, 15 and 20 °C/min. The values of effective activation energy (Ea), pre-exponential factor (ln A) for thermal decomposition have been measured at three different heating rates by employing Kissinger, Kim-Park and Flynn-Wall methods. Dielectric studies at different temperatures have also been carried out and it was found that both dielectric constant and dielectric loss decreases with the increase of frequency. Copyright © 2013 Elsevier B.V. All rights reserved.

Electron paramagnetic resonance of deep boron in silicon carbide

NASA Astrophysics Data System (ADS)

Baranov, P. G.; Mokhov, E. N.

1996-04-01

In this article we report the first EPR observation of deep boron centres in silicon carbide. A direct identification of the boron atom involved in the defect centre, considered as deep boron, has been established by the presence of a hyperfine interaction with 0268-1242/11/4/005/img1 and 0268-1242/11/4/005/img2 nuclei in isotope-enriched 6H-SiC:B crystals. Deep boron centres were shown from EPR spectra to have axial symmetry along the hexagonal axis. A correspondence between the EPR spectra and the luminescence, ODMR and DLTS spectra of deep boron centres has been indicated. The structural model for a deep boron centre as a boron - vacancy pair is presented and the evidence for bistable behaviour of deep boron centres is discussed.

Low field electron paramagnetic resonance imaging with SQUID detection

NASA Technical Reports Server (NTRS)

Hahn, Inseob (Inventor); Day, Peter K. (Inventor); Penanen, Konstantin I. (Inventor); Eom, Byeong H. (Inventor); Cohen, Mark S. (Inventor)

2012-01-01

In one embodiment, a flux transformer with a gradiometer pickup coil is magnetically coupled to a SQUID, and a SQUID array amplifier comprising a plurality of SQUIDs, connected in series, is magnetically coupled to the output of the SQUID. Other embodiments are described and claimed.

Paramagnet induced signal quenching in MAS-DNP experiments in frozen homogeneous solutions

NASA Astrophysics Data System (ADS)

Corzilius, Björn; Andreas, Loren B.; Smith, Albert A.; Ni, Qing Zhe; Griffin, Robert G.

2014-03-01

The effects of nuclear signal quenching induced by the presence of a paramagnetic polarizing agent are documented for conditions used in magic angle spinning (MAS)-dynamic nuclear polarization (DNP) experiments on homogeneous solutions. In particular, we present a detailed analysis of three time constants: (1) the longitudinal build-up time constant TB for 1H; (2) the rotating frame relaxation time constant T1ρ for 1H and 13C and (3) T2 of 13C, the transverse relaxation time constant in the laboratory frame. These relaxation times were measured during microwave irradiation at a magnetic field of 5 T (140 GHz) as a function of the concentration of four polarizing agents: TOTAPOL, 4-amino-TEMPO, trityl (OX063), and Gd-DOTA and are compared to those obtained for a sample lacking paramagnetic doping. We also report the EPR relaxation time constants T1S and T2S, the DNP enhancements, ε, and the parameter E, defined below, which measures the sensitivity enhancement for the four polarizing agents as a function of the electron concentration. We observe substantial intensity losses (paramagnetic quenching) with all of the polarizing agents due to broadening mechanisms and cross relaxation during MAS. In particular, the monoradical trityl and biradical TOTAPOL induce ∼40% and 50% loss of signal intensity. In contrast there is little suppression of signal intensity in static samples containing these paramagnetic species. Despite the losses due to quenching, we find that all of the polarizing agents provide substantial gains in signal intensity with DNP, and in particular that the net enhancement is optimal for biradicals that operate with the cross effect. We discuss the possibility that much of this polarization loss can be regained with the development of instrumentation and methods to perform electron decoupling.

Soft x-ray absorption spectroscopy of metalloproteins and high-valent metal-complexes at room temperature using free-electron lasers

PubMed Central

Kubin, Markus; Kern, Jan; Gul, Sheraz; Kroll, Thomas; Chatterjee, Ruchira; Löchel, Heike; Fuller, Franklin D.; Sierra, Raymond G.; Quevedo, Wilson; Weniger, Christian; Rehanek, Jens; Firsov, Anatoly; Laksmono, Hartawan; Weninger, Clemens; Alonso-Mori, Roberto; Nordlund, Dennis L.; Lassalle-Kaiser, Benedikt; Glownia, James M.; Krzywinski, Jacek; Moeller, Stefan; Turner, Joshua J.; Minitti, Michael P.; Dakovski, Georgi L.; Koroidov, Sergey; Kawde, Anurag; Kanady, Jacob S.; Tsui, Emily Y.; Suseno, Sandy; Han, Zhiji; Hill, Ethan; Taguchi, Taketo; Borovik, Andrew S.; Agapie, Theodor; Messinger, Johannes; Erko, Alexei; Föhlisch, Alexander; Bergmann, Uwe; Mitzner, Rolf; Yachandra, Vittal K.; Yano, Junko; Wernet, Philippe

2017-01-01

X-ray absorption spectroscopy at the L-edge of 3d transition metals provides unique information on the local metal charge and spin states by directly probing 3d-derived molecular orbitals through 2p-3d transitions. However, this soft x-ray technique has been rarely used at synchrotron facilities for mechanistic studies of metalloenzymes due to the difficulties of x-ray-induced sample damage and strong background signals from light elements that can dominate the low metal signal. Here, we combine femtosecond soft x-ray pulses from a free-electron laser with a novel x-ray fluorescence-yield spectrometer to overcome these difficulties. We present L-edge absorption spectra of inorganic high-valent Mn complexes (Mn ∼ 6–15 mmol/l) with no visible effects of radiation damage. We also present the first L-edge absorption spectra of the oxygen evolving complex (Mn4CaO5) in Photosystem II (Mn < 1 mmol/l) at room temperature, measured under similar conditions. Our approach opens new ways to study metalloenzymes under functional conditions. PMID:28944255

Soft x-ray absorption spectroscopy of metalloproteins and high-valent metal-complexes at room temperature using free-electron lasers

DOE PAGES

Kubin, Markus; Kern, Jan; Gul, Sheraz; ...

2017-09-01

X-ray absorption spectroscopy at the L-edge of 3d transition metals provides unique information on the local metal charge and spin states by directly probing 3d-derived molecular orbitals through 2p-3d transitions. But, this soft x-ray technique has been rarely used at synchrotron facilities for mechanistic studies of metalloenzymes due to the difficulties of x-ray-induced sample damage and strong background signals from light elements that can dominate the low metal signal. Here, we combine femtosecond soft x-ray pulses from a free-electron laser with a novel x-ray fluorescence-yield spectrometer to overcome these difficulties. We present L-edge absorption spectra of inorganic high-valent Mn complexesmore » (Mn ~ 6-15 mmol/l) with no visible effects of radiation damage. We then present the first L-edge absorption spectra of the oxygen evolving complex (Mn 4 CaO 5 ) in Photosystem II (Mn < 1 mmol/l) at room temperature, measured under similar conditions. Our approach opens new ways to study metalloenzymes under functional conditions.« less

Absorption spectra of 4f electron transitions of neodymium and erbium with 8-hydroxyquinoline-5-sulphonic acid and diethylamine systems and its analytical application

SciTech Connect

Wang Naixing; Qi Ping

1992-06-01

In this paper the absorption spectra of 4f electron transitions of the systems of neodymium and erbium with 8-hydroxyquinoline-5-sulphonic acid and diethylamine have been studied by normal and third-derivative spectrophotometry. Their molar absorptivities are 80 1.mol{sup {minus}1}.cm{sup {minus}1} for neodymium and 65 1.mol{sup {minus}1}.cm{sup {minus}1} for erbium. Use of the third-derivative spectra, eliminates the interference by other rare earths and increases the sensitivity for Nd and Er. The derivative molar absorptivities are 390 1.mol{sup {minus}1}.cm{sup {minus}1} for Nd and 367 1.mol{sup {minus}1}.cm{sup {minus}1} for Er. The calibration graphs were linear up to 11.8 {mu}g/ml of Nd and 12.3 {mu}g/ml ofmore » Er, respectively. The relative standard deviations evaluated from eleven independent determinations of 7.2 {mu}g/ml (for Nd) and 8.3 {mu}g/ml (for Er) are 1.3% and 1.4%, respectively. The detection limits are 0.2 {mu}g/ml for Nd and 0.3 {mu}g/ml for Er. The method has been developed for determining those two elements in mixture of lanthanides by means of the third-derivative spectra and the analytical results obtained are satisfactory.« less

Paramagnetic oxotungsten(V) complexes containing the hydrotris(3,5-dimethylpyrazol-1-yl)borate ligand.

PubMed

Sproules, Stephen; Eagle, Aston A; Taylor, Michelle K; Gable, Robert W; White, Jonathan M; Young, Charles G

2011-05-16

Sky-blue Tp*WOCl(2) has been synthesized from the high-yielding reaction of Tp*WO(2)Cl with boron trichloride in refluxing toluene. Dark-red Tp*WOI(2) was prepared via thermal decarbonylation followed by aerial oxidation of Tp*WI(CO)(3) in acetonitrile. From these precursors, an extensive series of mononuclear tungstenyl complexes, Tp*WOXY [X = Cl(-), Y = OPh(-), SPh(-); X = Y = OPh(-), 2-(n-propyl)phenolate (PP(-)), SPh(-), SePh(-); XY = toluene-3,4-dithiolate (tdt(2-)), quinoxaline-2,3-dithiolate (qdt(2-)), benzene-1,2-diselenolate (bds(2-)); Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate], was prepared by metathesis with the respective alkali-metal salt of X(-)/XY(2-) or (NHEt(3))(2)(qdt). The complexes were characterized by microanalysis, mass spectrometry, electrochemistry, IR, electron paramagnetic resonance (EPR), and electronic absorption spectroscopies, and X-ray crystallography (for X = Y = OPh(-), PP(-), SPh(-); XY = bds(2-)). The six-coordinate, distorted-octahedral tungsten centers are coordinated by terminal oxo [W≡O = 1.689(6)-1.704(3) Å], tridentate Tp*, and monodentate or bidentate O/S/Se-donor ligands. Spin Hamiltonian parameters derived from the simulation of fluid-solution X-band EPR spectra revealed that the soft-donor S/Se ligand complexes had larger g values and smaller (183)W hyperfine coupling constants than the less covalent hard-donor O/Cl species. The former showed low-energy ligand-to-metal charge-transfer bands in the near-IR region of their electronic absorption spectra. These oxotungsten(V) complexes display lower reduction potentials than their molybdenum counterparts, underscoring the preference of tungsten for higher oxidation states. Furthermore, the protonation of the pyrazine nitrogen atoms of the qdt(2-) ligand has been examined by spectroelectrochemistry; the product of the one-electron reduction of [Tp*WO(qdtH)](+) revealed usually intense low-energy bands.

On the Electronic Structure of Cu Chlorophyllin and Its Breakdown Products: A Carbon K-Edge X-ray Absorption Spectroscopy Study.

PubMed

Witte, Katharina; Mantouvalou, Ioanna; Sánchez-de-Armas, Rocío; Lokstein, Heiko; Lebendig-Kuhla, Janina; Jonas, Adrian; Roth, Friedrich; Kanngießer, Birgit; Stiel, Holger

2018-02-15

Using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, the carbon backbone of sodium copper chlorophyllin (SCC), a widely used chlorophyll derivative, and its breakdown products are analyzed to elucidate their electronic structure and physicochemical properties. Using various sample preparation methods and complementary spectroscopic methods (including UV/Vis, X-ray photoelectron spectroscopy), a comprehensive insight into the SCC breakdown process is presented. The experimental results are supported by density functional theory calculations, allowing a detailed assignment of characteristic NEXAFS features to specific C bonds. SCC can be seen as a model system for the large group of porphyrins; thus, this work provides a novel and detailed description of the electronic structure of the carbon backbone of those molecules and their breakdown products. The achieved results also promise prospective optical pump/X-ray probe investigations of dynamic processes in chlorophyll-containing photosynthetic complexes to be analyzed more precisely.

Watching adsorption and electron beam induced decomposition on the model system Mo(CO)6/Cu(1 1 1) by X-ray absorption and photoemission spectroscopies

NASA Astrophysics Data System (ADS)

Paufert, Pierre; Fonda, Emiliano; Li, Zheshen; Domenichini, Bruno; Bourgeois, Sylvie

2013-11-01

An in-depth study of the first steps of electron beam assisted growth of Mo from molybdenum hexacarbonyl on Cu(1 1 1) has been carried out exploiting the complementarity of X-ray photoemission and X-ray absorption spectroscopies. Frank van der Merwe (2D) growth mode has been observed for the completion of the two first monolayers of adsorbed molecules through a simple physisorption process. Irradiation of the Mo(CO)6 deposit by 1 keV electron beam induces a modification of molybdenum coordination, the average number of C-neighbors decreasing from 6 to 3. Decomposed molecules remain on the surface after annealing at 520 K and organize themselves, the molybdenum atoms moving in Cu(1 1 1) surface fcc hollow sites. After annealing at 670 K, metallic molybdenum growth begins, if the total amount of adsorbed Mo atoms exceeds 1.2 monolayers.

Realization of a Cascaded Quantum System: Heralded Absorption of a Single Photon Qubit by a Single-Electron Charged Quantum Dot.

PubMed

Delteil, Aymeric; Sun, Zhe; Fält, Stefan; Imamoğlu, Atac

2017-04-28

Photonic losses pose a major limitation for the implementation of a quantum state transfer between nodes of a quantum network. A measurement that heralds a successful transfer without revealing any information about the qubit may alleviate this limitation. Here, we demonstrate the heralded absorption of a single photonic qubit, generated by a single neutral quantum dot, by a single-electron charged quantum dot that is located 5 m away. The transfer of quantum information to the spin degree of freedom takes place upon the emission of a photon; for a properly chosen or prepared quantum dot, the detection of this photon yields no information about the qubit. We show that this process can be combined with local operations optically performed on the destination node by measuring classical correlations between the absorbed photon color and the final state of the electron spin. Our work suggests alternative avenues for the realization of quantum information protocols based on cascaded quantum systems.

Electronic structure of Cr doped Fe3O4 thin films by X-ray absorption near-edge structure spectroscopy

NASA Astrophysics Data System (ADS)

Chen, Chi-Liang; Dong, Chung-Li; Asokan, Kandasami; Chern, G.; Chang, C. L.

2018-04-01

Present study reports the electronic structures of Cr doped Fe3O4 (Fe3-xCrxO4 (0 ≤ x ≤ 3) grown on MgO (100) substrates in the form of thin films fabricated by a plasma-oxygen assisted Molecular Beam Epitaxy (MBE). X-ray absorption near-edge structure (XANES) spectra at Cr & Fe L-, and O K-edges were used to understand the electronic structure: changes in the bonding nature, valence states, and site occupancies. Cr doping in Fe3O4 results in the change of charge transfer, crystal structure, and selective occupation of ions in octahedral and tetrahedral sites. Such change modifies the electrical and magnetic properties due to the covalency of Cr ions. The physical and chemical properties of ferrites are strongly dependent on the lattice site, ion size of dopant, and magnetic nature present at different structural symmetry of the spinel structure.

Hydrogen-Mediated Electron Doping of Gold Clusters As Revealed by In Situ X-ray and UV-vis Absorption Spectroscopy.

PubMed

Ishida, Ryo; Hayashi, Shun; Yamazoe, Seiji; Kato, Kazuo; Tsukuda, Tatsuya

2017-06-01

We previously reported that small (∼1.2 nm) gold clusters stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP) exhibited a localized surface plasmon resonance (LSPR) band at ∼520 nm in the presence of NaBH 4 . To reveal the mechanism of this phenomenon, the electronic structure of Au:PVP during the reaction with NaBH 4 in air was examined by means of in situ X-ray absorption spectroscopy at Au L 3 -edge and UV-vis spectroscopy. These measurements indicated that the appearance of the LSPR band is not associated with the growth in size but is ascribed to electron doping to the Au sp band by the adsorbed H atoms.

Paramagnetic Manganese in the Atherosclerotic Plaque of Carotid Arteries

PubMed Central

Chelyshev, Yury; Ignatyev, Igor; Zanochkin, Alexey; Mamin, Georgy; Sorokin, Boris; Sorokina, Alexandra; Lyapkalo, Natalya; Gizatullina, Nazima; Orlinskii, Sergei

2016-01-01

The search for adequate markers of atherosclerotic plaque (AP) instability in the context of assessment of the ischemic stroke risk in patients with atherosclerosis of the carotid arteries as well as for solid physical and chemical factors that are connected with the AP stability is extremely important. We investigate the inner lining of the carotid artery specimens from the male patients with atherosclerosis (27 patients, 42–64 years old) obtained during carotid endarterectomy by using different analytical tools including ultrasound angiography, X-ray analysis, immunological, histochemical analyses, and high-field (3.4 T) pulse electron paramagnetic resonance (EPR) at 94 GHz. No correlation between the stable and unstable APs in the sense of the calcification is revealed. In all of the investigated samples, the EPR spectra of manganese, namely, Mn2+ ions, are registered. Spectral and relaxation characteristics of Mn2+ ions are close to those obtained for the synthetic (nano) hydroxyapatite species but differ from each other for stable and unstable APs. This demonstrates that AP stability could be specified by the molecular organization of their hydroxyapatite components. The origin of the obtained differences and the possibility of using EPR of Mn2+ as an AP stability marker are discussed. PMID:28078287

Functionalization of paramagnetic nanoparticles for protein immobilization and purification.

PubMed

Carneiro, Lara A B C; Ward, Richard J

2018-01-01

A paramagnetic nanocomposite coated with chitosan and N-(5-Amino-1-carboxy-pentyl) iminodiacetic acid (NTA) that is suitable for protein immobilization applications has been prepared and characterized. The nanoparticle core was synthesized by controlled aggregation of Fe 3 O 4 under alkaline conditions, and Transmission Electron Microscopy revealed a size distribution of 10-50 nm. The nanoparticle core was coated with chitosan and derivatized with glutaraldehyde and NTA, as confirmed by Fourier Transform Infrared Spectroscopy. The final nanoparticles were used as a metal affinity matrix to separate a recombinant polyhistidine-tagged β-galactosidase from Bacillus subtilis directly from E. coli cell lysates with high purity (>95%). After loading with Ni 2+ , nanoparticles demonstrated a binding capacity of 250 μg of a polyhistidine-tagged β-galactosidase per milligram of support. The immobilized enzyme retained 80% activity after 9 cycles of washing, and the immobilized recombinant protein could be eluted with high purity with imidazole. The applications for these nanomagnetic composites extend beyond protein purification, and can also be used for immobilizing enzymes, where the β-galactosidase immobilized on the nanomagnetic support was used in multiple cycles of catalytic reactions with no significant loss of catalytic activity. Copyright © 2017. Published by Elsevier Inc.

Electronic and nuclear contributions to time-resolved optical and X-ray absorption spectra of hematite and insights into photoelectrochemical performance

DOE PAGES

Hayes, Dugan; Hadt, Ryan G.; Emery, Jonathan D.; ...

2016-11-02

Ultrafast time-resolved studies of photocatalytic thin films can provide a wealth of information crucial for understanding and thereby improving the performance of these materials by directly probing electronic structure, reaction intermediates, and charge carrier dynamics. The interpretation of transient spectra, however, can be complicated by thermally induced structural distortions, which appear within the first few picoseconds following excitation due to carrier–phonon scattering. Here we present a comparison of ex situ steady-state thermal difference spectra and transient absorption spectra spanning from NIR to hard X-ray energies of hematite thin films grown by atomic layer deposition. We find that beyond the firstmore » 100 picoseconds, the transient spectra measured for all excitation wavelengths and probe energies are almost entirely due to thermal effects as the lattice expands in response to the ultrafast temperature jump and then cools to room temperature on the microsecond timescale. At earlier times, a broad excited state absorption band that is assigned to free carriers appears at 675 nm, and the lifetime and shape of this feature also appear to be mostly independent of excitation wavelength. The combined spectroscopic data, which are modeled with density functional theory and full multiple scattering calculations, support an assignment of the optical absorption spectrum of hematite that involves two LMCT bands that nearly span the visible spectrum. Lastly, our results also suggest a framework for shifting the ligand-to-metal charge transfer absorption bands of ferric oxide films from the near-UV further into the visible part of the solar spectrum to improve solar conversion efficiency.« less

Nickel complexes of o-amidochalcogenophenolate(2-)/o-iminochalcogenobenzosemiquinonate(1-) pi-radical: synthesis, structures, electron spin resonance, and x-ray absorption spectroscopic evidence.

PubMed

Hsieh, Chung-Hung; Hsu, I-Jui; Lee, Chien-Ming; Ke, Shyue-Chu; Wang, Tze-Yuan; Lee, Gene-Hsiang; Wang, Yu; Chen, Jin-Ming; Lee, Jyh-Fu; Liaw, Wen-Feng

2003-06-16

The preparation of complexes trans-[Ni(-SeC(6)H(4)-o-NH-)(2)](-) (1), cis-[Ni(-TeC(6)H(4)-o-NH-)(2)](-) (2), trans-[Ni(-SC(6)H(4)-o-NH-)(2)](-) (3), and [Ni(-SC(6)H(4)-o-S-)(2)](-) (4) by oxidative addition of 2-aminophenyl dichalcogenides to anionic [Ni(CO)(SePh)(3)](-) proves to be a successful approach in this direction. The cis arrangement of the two tellurium atoms in complex 2 is attributed to the intramolecular Te.Te contact interaction (Te.Te contact distance of 3.455 A). The UV-vis electronic spectra of complexes 1 and 2 exhibit an intense absorption at 936 and 942 nm, respectively, with extinction coefficient epsilon > 10000 L mol(-)(1) cm(-)(1). The observed small g anisotropy, the principal g values at g(1) = 2.036, g(2) = 2.062, and g(3) = 2.120 for 1 and g(1) = 2.021, g(2) = 2.119, and g(3) = 2.250 for 2, respectively, indicates the ligand radical character accompanied by the contribution of the singly occupied d orbital of Ni(III). The X-ray absorption spectra of all four complexes show L(III) peaks at approximately 854.5 and approximately 853.5 eV. This may indicate a variation of contribution of the Ni(II)-Ni(III) valence state. According to the DFT calculation, the unpaired electron of complex 1 and 2 is mainly distributed on the 3d(xz)() orbital of the nickel ion and on the 4p(z)() orbital of selenium (tellurium, 5p(z)()) as well as the 2p(z)() orbital of nitrogen of the ligand. On the basis of X-ray structural data, UV-vis absorption, electron spin resonance, magnetic properties, DFT computation, and X-ray absorption (K- and L-edge) spectroscopy, the monoanionic trans-[Ni(-SeC(6)H(4)-o-NH-)(2)](-) and cis-[Ni(-TeC(6)H(4)-o-NH-)(2)](-) complexes are appositely described as a resonance hybrid form of Ni(III)-bis(o-amidochalcogenophenolato(2-)) and Ni(II)-(o-amidochalcogenophenolato(2-))-(o-iminochalcogenobenzosemiquinonato(1-) pi-radical; i.e., complexes 1 and 2 contain delocalized oxidation levels of the nickel ion and ligands.

Role of defects in BiFeO₃ multiferroic films and their local electronic structure by x-ray absorption spectroscopy

SciTech Connect

Ravalia, Ashish; Vagadia, Megha; Solanki, P. S.

2014-10-21

Present study reports the role of defects in the electrical transport in BiFeO₃ (BFO) multiferroic films and its local electronic structure investigated by near-edge X-ray absorption fine structure. Defects created by high energy 200 MeV Ag⁺¹⁵ ion irradiation with a fluence of ∼5 × 10¹¹ ions/cm² results in the increase in structural strain and reduction in the mobility of charge carriers and enhancement in resistive (I-V) and polarization (P-E) switching behaviour. At higher fluence of ∼5 × 10¹² ions/cm², there is a release in the structural strain due to local annealing effect, resulting in an increase in the mobility of charge carriers, which are releasedmore » from oxygen vacancies and hence suppression in resistive and polarization switching. Near-edge X-ray absorption fine structure studies at Fe L₃,₂- and O K-edges show a significant change in the spectral features suggesting the modifications in the local electronic structure responsible for changes in the intrinsic magnetic moment and electrical transport properties of BFO.« less

DFT study of electron absorption and emission spectra of pyramidal LnPc(OAc) complexes of some lanthanide ions in the solid state

NASA Astrophysics Data System (ADS)

Hanuza, J.; Godlewska, P.; Lisiecki, R.; Ryba-Romanowski, W.; Kadłubański, P.; Lorenc, J.; Łukowiak, A.; Macalik, L.; Gerasymchuk, Yu.; Legendziewicz, J.

2018-05-01

The electron absorption and emission spectra were measured for the pyramidal LnPc(OAc) complexes in the solid state and co-doped in silica glass, where Ln = Er, Eu and Ho. The theoretical electron spectra were determined from the quantum chemical DFT calculation using four approximations CAM-B3LYP/LANL2DZ, CAM-B3LYP/CC-PVDZ, B3LYP/LANL2DZ and B3LYP/CC-PVDZ. It was shown that the best agreement between the calculated and experimental structural parameters and spectroscopic data was reached for the CAM-B3LYP/LANL2DZ model. The emission spectra were measured using the excitations both in the ligand and lanthanide absorption ranges. The possibility of energy transfer between the phthalocyanine ligand and excited states of lanthanide ions was discussed. It was shown that the back energy transfer from metal states to phthalocyanine state is responsible for the observed emission of the studied complexes both in the polycrystalline state and silica glass.

Excited state electron and energy relays in supramolecular dinuclear complexes revealed by ultrafast optical and X-ray transient absorption spectroscopy

SciTech Connect

Hayes, Dugan; Kohler, Lars; Hadt, Ryan G.

Here, the kinetics of photoinduced electron and energy transfer in a family of tetrapyridophenazine-bridged heteroleptic homo- and heterodinuclear copper(I) bis(phenanthroline)/ruthenium(II) polypyridyl complexes were studied using ultrafast optical and multi-edge X-ray transient absorption spectroscopies. This work combines the synthesis of heterodinuclear Cu(I)–Ru(II) analogs of the homodinuclear Cu(I)–Cu(I) targets with spectroscopic analysis and electronic structure calculations to first disentangle the dynamics at individual metal sites by taking advantage of the element and site specificity of X-ray absorption and theoretical methods. The excited state dynamical models developed for the heterodinuclear complexes are then applied to model the more challenging homodinuclear complexes. These resultsmore » suggest that both intermetallic charge and energy transfer can be observed in an asymmetric dinuclear copper complex in which the ground state redox potentials of the copper sites are offset by only 310 meV. We also demonstrate the ability of several of these complexes to effectively and unidirectionally shuttle energy between different metal centers, a property that could be of great use in the design of broadly absorbing and multifunctional multimetallic photocatalysts. This work provides an important step toward developing both a fundamental conceptual picture and a practical experimental handle with which synthetic chemists, spectroscopists, and theoreticians may collaborate to engineer cheap and efficient photocatalytic materials capable of performing coulombically demanding chemical transformations.« less

DFT study of electron absorption and emission spectra of pyramidal LnPc(OAc) complexes of some lanthanide ions in the solid state.

PubMed

Hanuza, J; Godlewska, P; Lisiecki, R; Ryba-Romanowski, W; Kadłubański, P; Lorenc, J; Łukowiak, A; Macalik, L; Gerasymchuk, Yu; Legendziewicz, J

2018-05-05

The electron absorption and emission spectra were measured for the pyramidal LnPc(OAc) complexes in the solid state and co-doped in silica glass, where Ln=Er, Eu and Ho. The theoretical electron spectra were determined from the quantum chemical DFT calculation using four approximations CAM-B3LYP/LANL2DZ, CAM-B3LYP/CC-PVDZ, B3LYP/LANL2DZ and B3LYP/CC-PVDZ. It was shown that the best agreement between the calculated and experimental structural parameters and spectroscopic data was reached for the CAM-B3LYP/LANL2DZ model. The emission spectra were measured using the excitations both in the ligand and lanthanide absorption ranges. The possibility of energy transfer between the phthalocyanine ligand and excited states of lanthanide ions was discussed. It was shown that the back energy transfer from metal states to phthalocyanine state is responsible for the observed emission of the studied complexes both in the polycrystalline state and silica glass. Copyright © 2018. Published by Elsevier B.V.

Excited state electron and energy relays in supramolecular dinuclear complexes revealed by ultrafast optical and X-ray transient absorption spectroscopy

DOE PAGES

Hayes, Dugan; Kohler, Lars; Hadt, Ryan G.; ...

2017-11-28

Here, the kinetics of photoinduced electron and energy transfer in a family of tetrapyridophenazine-bridged heteroleptic homo- and heterodinuclear copper(I) bis(phenanthroline)/ruthenium(II) polypyridyl complexes were studied using ultrafast optical and multi-edge X-ray transient absorption spectroscopies. This work combines the synthesis of heterodinuclear Cu(I)–Ru(II) analogs of the homodinuclear Cu(I)–Cu(I) targets with spectroscopic analysis and electronic structure calculations to first disentangle the dynamics at individual metal sites by taking advantage of the element and site specificity of X-ray absorption and theoretical methods. The excited state dynamical models developed for the heterodinuclear complexes are then applied to model the more challenging homodinuclear complexes. These resultsmore » suggest that both intermetallic charge and energy transfer can be observed in an asymmetric dinuclear copper complex in which the ground state redox potentials of the copper sites are offset by only 310 meV. We also demonstrate the ability of several of these complexes to effectively and unidirectionally shuttle energy between different metal centers, a property that could be of great use in the design of broadly absorbing and multifunctional multimetallic photocatalysts. This work provides an important step toward developing both a fundamental conceptual picture and a practical experimental handle with which synthetic chemists, spectroscopists, and theoreticians may collaborate to engineer cheap and efficient photocatalytic materials capable of performing coulombically demanding chemical transformations.« less

Excited state electron and energy relays in supramolecular dinuclear complexes revealed by ultrafast optical and X-ray transient absorption spectroscopy.

PubMed

Hayes, Dugan; Kohler, Lars; Hadt, Ryan G; Zhang, Xiaoyi; Liu, Cunming; Mulfort, Karen L; Chen, Lin X

2018-01-28

The kinetics of photoinduced electron and energy transfer in a family of tetrapyridophenazine-bridged heteroleptic homo- and heterodinuclear copper(i) bis(phenanthroline)/ruthenium(ii) polypyridyl complexes were studied using ultrafast optical and multi-edge X-ray transient absorption spectroscopies. This work combines the synthesis of heterodinuclear Cu(i)-Ru(ii) analogs of the homodinuclear Cu(i)-Cu(i) targets with spectroscopic analysis and electronic structure calculations to first disentangle the dynamics at individual metal sites by taking advantage of the element and site specificity of X-ray absorption and theoretical methods. The excited state dynamical models developed for the heterodinuclear complexes are then applied to model the more challenging homodinuclear complexes. These results suggest that both intermetallic charge and energy transfer can be observed in an asymmetric dinuclear copper complex in which the ground state redox potentials of the copper sites are offset by only 310 meV. We also demonstrate the ability of several of these complexes to effectively and unidirectionally shuttle energy between different metal centers, a property that could be of great use in the design of broadly absorbing and multifunctional multimetallic photocatalysts. This work provides an important step toward developing both a fundamental conceptual picture and a practical experimental handle with which synthetic chemists, spectroscopists, and theoreticians may collaborate to engineer cheap and efficient photocatalytic materials capable of performing coulombically demanding chemical transformations.

Intersubband optical absorption between multi energy levels of electrons in InGaN/GaN spherical core-shell quantum dots

NASA Astrophysics Data System (ADS)

Liu, W. H.; Qu, Y.; Ban, S. L.

2017-02-01

The intersubband optical absorption between multi energy levels of electrons in InxGa1-xN/GaN spherical core-shell quantum dots (CSQDs) and ternary mixed crystal and size effects have been investigated by using the principle of density matrix. Electronic eigenstates under the effect of built-in electric field (BEF) have been calculated by a finite element method. The results show that optical absorption between intersubbands with main quantum numbers n = 1 and n = 2 are as important as that between ones with n = 1 and different angular quantum numbers when the BEF is taken into account. In consideration of BEF, the saturation of total optical absorption coefficients (ACs) and secondary peaks of refractive index changes (RICs) appear when incident light intensity I surpasses a certain value. For a given I, the maximum ACs and zero RICs positions in InxGa1-xN/GaN CSQDs with a fixed shell size have a blue-shift when x increases or the core InxGa1-xN radius R1 decreases from 5 nm. However, when R1 > 5 nm, ACs and RICs tend to be stable. The results indicate that effective adjustment of ACs and RICs in CSQDs with BEFs by size is in a limited scale range. The saturation of ACs or secondary peaks of RICs appear more likely in CSQDs with smaller x or larger R1. These results are expected to be helpful both in the further theoretical and experimental study on optic devices consisting of CSQDs.

Spectroscopic and DFT study of solvent effects on the electronic absorption spectra of sulfamethoxazole in neat and binary solvent mixtures

NASA Astrophysics Data System (ADS)

Almandoz, M. C.; Sancho, M. I.; Blanco, S. E.

2014-01-01

The solvatochromic behavior of sulfamethoxazole (SMX) was investigated using UV-vis spectroscopy and DFT methods in neat and binary solvent mixtures. The spectral shifts of this solute were correlated with the Kamlet and Taft parameters (α, β and π*). Multiple lineal regression analysis indicates that both specific hydrogen-bond interaction and non specific dipolar interaction play an important role in the position of the absorption maxima in neat solvents. The simulated absorption spectra using TD-DFT methods were in good agreement with the experimental ones. Binary mixtures consist of cyclohexane (Cy)-ethanol (EtOH), acetonitrile (ACN)-dimethylsulfoxide (DMSO), ACN-dimethylformamide (DMF), and aqueous mixtures containing as co-solvents DMSO, ACN, EtOH and MeOH. Index of preferential solvation was calculated as a function of solvent composition and non-ideal characteristics are observed in all binary mixtures. In ACN-DMSO and ACN-DMF mixtures, the results show that the solvents with higher polarity and hydrogen bond donor ability interact preferentially with the solute. In binary mixtures containing water, the SMX molecules are solvated by the organic co-solvent (DMSO or EtOH) over the whole composition range. Synergistic effect is observed in the case of ACN-H2O and MeOH-H2O, indicating that at certain concentrations solvents interact to form association complexes, which should be more polar than the individual solvents of the mixture.

BASIC STUDIES IN PERCUTANEOUS ABSORPTION.

DTIC Science & Technology

FATTY ACIDS, *SKIN(ANATOMY), ABSORPTION, ALKYL RADICALS, AMIDES, DIFFUSION, ELECTRON MICROSCOPY, HUMIDITY, LABORATORY ANIMALS, LIPIDS, ORGANIC SOLVENTS, PENETRATION, PRIVATION, PROTEINS, RATS, TEMPERATURE, WATER

Microwave absorption enhancement, magnetic coupling and ab initio electronic structure of monodispersed (Mn1-xCox)3O4 nanoparticles

NASA Astrophysics Data System (ADS)

Zhao, Pengfei; Liang, Chongyun; Gong, Xiwen; Gao, Ran; Liu, Jiwei; Wang, Min; Che, Renchao

2013-08-01

Monodispersed manganese oxide (Mn1-xCox)3O4 (0 <= x <= 0.5) nanoparticles, less than 10 nm size, are respectively synthesized via a facile thermolysis method at a rather low temperature, ranging from 90 to 100 °C, without any inertia gas for protection. The influences of the Co dopant content on the critical reaction temperature required for the nanoparticle formation, electronic band structures, magnetic properties, and the microwave absorption capability of (Mn1-xCox)3O4 are comprehensively investigated by means of both experimental and theoretical approaches including powder X-ray diffraction (XRD), electron energy loss spectroscopy (EELS), super conductivity quantum interference device (SQUID) examination, and first-principle simulations. Co is successfully doped into the Mn atomic sites of the (Mn1-xCox)3O4 lattice, which is further confirmed by EELS data acquired from one individual nanoparticle. Therefore, continuous solid solutions of well-crystallized (Mn1-xCox)3O4 products are achieved without any impurity phase or phase separation. With increases in the Co dopant concentration x from 0 to 0.5, the lattice parameters change systemically, where the overall saturation magnetization at 30 K increases due to the more intense coupling of the 3d electrons between Mn and Co, as revealed by simulations. The microwave absorption properties of the (Mn1-xCox)3O4 nanoparticles are examined between 2 and 18 GHz. The maximum absorption peak -11.0 dB of the x = 0 sample is enhanced to -11.5 dB for x = 0.2, -12.7 dB for x = 0.25, -15.6 dB for x = 0.33, and -24.0 dB for x = 0.5 respectively, suggesting the Co doping effects. Our results might provide novel insights into the understanding of the influences of metallic ion doping on the electromagnetic properties of metallic oxide nanomaterials.Monodispersed manganese oxide (Mn1-xCox)3O4 (0 <= x <= 0.5) nanoparticles, less than 10 nm size, are respectively synthesized via a facile thermolysis method at a rather low

The absorption- and luminescence spectra of Mn3+ in beryl and vesuvianite

NASA Astrophysics Data System (ADS)

Czaja, Maria; Lisiecki, Radosław; Chrobak, Artur; Sitko, Rafał; Mazurak, Zbigniew

2018-05-01

The electron absorption-, photoluminescence- and electron paramagnetic-resonance spectra of Mn3+ in red beryl from Wah Wah Mountains (Utah USA) and of pink- and purple vesuvianite from Jeffrey Mine (Asbestos, Canada) were measured at room- and low temperatures. The crystal field stabilization energies are equal to 130.9 kJ/mol for the red beryl, and 151.5-158.0 and 168.0 kJ/mol for for the pink- and the purple vesuvianite, respectively. The red photoluminescence of Mn3+ was not intensive either at room- or at low temperatures. The high Mn content in the crystals caused the emergence of an additional emission band and short photoluminescence-decay lifetimes. The latter are only 183 μs for beryl and 17 μs for vesuvianite.

The absorption- and luminescence spectra of Mn3+ in beryl and vesuvianite

NASA Astrophysics Data System (ADS)

Czaja, Maria; Lisiecki, Radosław; Chrobak, Artur; Sitko, Rafał; Mazurak, Zbigniew

2017-12-01

The electron absorption-, photoluminescence- and electron paramagnetic-resonance spectra of Mn3+ in red beryl from Wah Wah Mountains (Utah USA) and of pink- and purple vesuvianite from Jeffrey Mine (Asbestos, Canada) were measured at room- and low temperatures. The crystal field stabilization energies are equal to 130.9 kJ/mol for the red beryl, and 151.5-158.0 and 168.0 kJ/mol for for the pink- and the purple vesuvianite, respectively. The red photoluminescence of Mn3+ was not intensive either at room- or at low temperatures. The high Mn content in the crystals caused the emergence of an additional emission band and short photoluminescence-decay lifetimes. The latter are only 183 μs for beryl and 17 μs for vesuvianite.

Upcycling: converting waste plastics into paramagnetic, conducting, solid, pure carbon microspheres.

PubMed

Pol, Vilas Ganpat

2010-06-15

The recent tremendous increase in the volume of waste plastics (WP) will have a harmful environmental impact on the health of living beings. Hundreds of years are required to degrade WP in atmospheric conditions. Hence, in coming years, in addition to traditional recycling services, innovative "upcycling" processes are necessary. This article presents an environmentally benign, solvent-free autogenic process that converts various WP [low density polyethylene (LDPE), high density polyethylene (HDPE), polyethylene terephthalate (PET), polystyrene (PS), or their mixtures] into carbon microspheres (CMSs), an industrially significant, value-added product. The thermal dissociation of these individual or mixed WP in a closed reactor under autogenic pressure ( approximately 1000 psi) produced dry, pure powder of CMSs. In this paper, the optimization of process parameters such as the effect of mixing of WP with other materials, and the role of reaction temperature and time are reported. Employing advanced analytical techniques, the atomic structure, composition, and morphology of as-obtained CMSs were analyzed. The room-temperature paramagnetism in CMSs prepared from waste LDPE, HDPE, and PS was further studied by electron paramagnetic resonance (EPR). The conducting and paramagnetic nature of CMSs holds promise for their potential applications in toners, printers, paints, batteries, lubricants, and tires.

Upcycling : converting waste plastics into paramagnetic, conducting, solid, pure carbon microspheres.

SciTech Connect

Pol, V.

2010-06-15

The recent tremendous increase in the volume of waste plastics (WP) will have a harmful environmental impact on the health of living beings. Hundreds of years are required to degrade WP in atmospheric conditions. Hence, in coming years, in addition to traditional recycling services, innovative 'upcycling' processes are necessary. This article presents an environmentally benign, solvent-free autogenic process that converts various WP [low density polyethylene (LDPE), high density polyethylene (HDPE), polyethylene terephthalate (PET), polystyrene (PS), or their mixtures] into carbon microspheres (CMSs), an industrially significant, value-added product. The thermal dissociation of these individual or mixed WP in a closed reactormore » under autogenic pressure (1000 psi) produced dry, pure powder of CMSs. In this paper, the optimization of process parameters such as the effect of mixing of WP with other materials, and the role of reaction temperature and time are reported. Employing advanced analytical techniques, the atomic structure, composition, and morphology of as-obtained CMSs were analyzed. The room-temperature paramagnetism in CMSs prepared from waste LDPE, HDPE, and PS was further studied by electron paramagnetic resonance (EPR). The conducting and paramagnetic nature of CMSs holds promise for their potential applications in toners, printers, paints, batteries, lubricants, and tires.« less

Absorption and backscatter of internal conversion electrons in the measurements of surface contamination of ¹³⁷Cs.

PubMed

Yunoki, A; Kawada, Y; Yamada, T; Unno, Y; Sato, Y; Hino, Y

2013-11-01

We measured 4π and 2π counting efficiencies for internal conversion electrons (ICEs), gross β-particles and also β-rays alone with various source conditions regarding absorber and backing foil thickness using e-X coincidence technique. Dominant differences regarding the penetration, attenuation and backscattering properties among ICEs and β-rays were revealed. Although the abundance of internal conversion electrons of (137)Cs-(137)Ba is only 9.35%, 60% of gross counts may be attributed to ICEs in worse source conditions. This information will be useful for radionuclide metrology and for surface contamination monitoring. © 2013 Elsevier Ltd. All rights reserved.

Potential-dependent recombination kinetics of photogenerated electrons in n- and p-type GaN photoelectrodes studied by time-resolved IR absorption spectroscopy.

PubMed

Yamakata, Akira; Yoshida, Masaaki; Kubota, Jun; Osawa, Masatoshi; Domen, Kazunari

2011-07-27

Recombination kinetics of photogenerated electrons in n-type and p-type GaN photoelectrodes active for H(2) and O(2) evolution, respectively, from water was examined by time-resolved IR absorption (TR-IR) spectroscopy. Illumination of a GaN film with UV pulse (355 nm and 6 ns in duration) gives transient interference spectra in both transmittance and reflection modes. Simulation shows that the interference spectra are caused by photogenerated electrons. We observed that recombination in the microsecond region is greatly affected by the applied potentials, the lifetime becoming longer at negative and positive potentials for n- and p-type GaN electrodes, respectively. There is a good correlation between potential dependence of the steady-state reaction efficiency and that of the number of surviving electrons in the millisecond region. We also performed potential jump measurement to examine the shift in Fermi level by photogenerated charge carriers. In the case of n-type GaN, the electrode potential jumps to the negative side by accumulation of electrons in the bulk. However, in the case of p-type GaN, the electrode potential first jumps to the negative side within 20 μs and gradually shifts to the positive side in a few milliseconds, while the number of charge carriers is constant at >0.2 ms. This two-step process is ascribed to electron transport from the bulk to the surface of GaN, because the electrode potential is sensitive to the number of electrons in the bulk. The results confirm that TR-IR combined with potential jump measurement provides useful information for understanding the behavior of charge carriers in photoelectrochemical systems.

Imaging ultrafast excited state pathways in transition metal complexes by X-ray transient absorption and scattering using X-ray free electron laser source

SciTech Connect

Chen, Lin X.; Shelby, Megan L.; Lestrange, Patrick J.

2016-01-01

This report will describe our recent studies of transition metal complex structural dynamics on the fs and ps time scales using an X-ray free electron laser source, Linac Coherent Light Source (LCLS). Ultrafast XANES spectra at the Ni K-edge of nickel(II) tetramesitylporphyrin (NiTMP) were successfully measured for optically excited state at a timescale from 100 fs to 50 ps, providing insight into its sub-ps electronic and structural relaxation processes. Importantly, a transient reduced state Ni(I) (π, 3dx2-y2) electronic state is captured through the interpretation of a short-lived excited state absorption on the low-energy shoulder of the edge, which is aidedmore » by the computation of X-ray transitions for postulated excited electronic states. The observed and computed inner shell to valence orbital transition energies demonstrate and quantify the influence of electronic configuration on specific metal orbital energies. A strong influence of the valence orbital occupation on the inner shell orbital energies indicates that one should not use the transition energy from 1s to other orbitals to draw conclusions about the d-orbital energies. For photocatalysis, a transient electronic configuration could influence d-orbital energies up to a few eV and any attempt to steer the reaction pathway should account for this to ensure that external energies can be used optimally in driving desirable processes. NiTMP structural evolution and the influence of the porphyrin macrocycle conformation on relaxation kinetics can be likewise inferred from this study.« less

Paramagnetic resonance studies of bistrispyrazolylborate cobalt(II) and related derivatives

NASA Astrophysics Data System (ADS)

Myers, William K.

Herein, a systematic frozen solution electron-nuclear double resonance (ENDOR) study of high-spin Co(II) complexes is reported to demonstrate the efficacy of methyl substitutions as a means of separating dipolar and contact coupling, and further, to increase the utility of high-spin Co(II) as a spectroscopic probe for the ubiquitous, but spectroscopically-silent Zn(II) metalloenzymes. High-spin (hs) Co(II) has been subject of paramagnetic resonance studies for over 50 years and has been used as a spectroscopic probe for Zn metalloenzymes for over 35 years. However, as will be seen, the inherent complexity of the electronic properties of the cobaltous ion remains to be exploited to offer a wealth of information on Zn(II) enzymatic environments. Specifically, ENDOR measurements on bistrispyrazolylborate cobalt(II) confirm the utility of the novel method of methyl substitution to differentiate dipolar and Fermi contact couplings. An extensive set of electron paramagnetic resonance (EPR) simulations were performed. Software was developed to implement an ENDOR control interface. Finally, proton relaxation measurements were made in the range of 12-42 MHz, which were accounted for with the large g-value anisotropy of the Co(II) compounds. Taken as a whole, these studies point to the rich complexity of the electronic structure of high-spin cobalt(II) and, when sufficiently well-characterized, the great utility it has as a surrogate of biological Zn(II).

Probability and shape of the spectral line of a single bulk characteristic energy loss of a fast electron in a medium with electron absorption and strong spatial dispersion

SciTech Connect

Libenson, B. N., E-mail: libenson-b@yandex.ru

2011-10-15

The probability of single characteristic energy loss of a fast electron in a reflection experiment has been calculated. Unlike many works concerning this subject, the bremsstrahlung of bulk plasmons in the non- Cherenkov ranges of frequencies and wavevectors of a plasmon has been taken into account. The contributions to the probability of single loss and to the shape of the spectral line from a quantum correction that is due to the interference of elastic and inelastic electron scattering events have been determined. The probability has been calculated in the kinetic approximation for the relative permittivity, where the short-wavelength range ofmore » the plasmon spectrum is correctly taken into account. In view of these circumstances, the expression for the mean free path of the electron with respect to the emission of a bulk plasmon that was obtained by Pines [D. Pines, Elementary Excitations in Solids (Benjamin, New York, 1963)] has been refined. The coherence length of the fast electron in the medium-energy range under consideration has been estimated. The shape of the spectral line of energy losses in the non-Cherenkov frequency range has been determined. It has been shown that the probability of the single emission of the bulk plasmon incompletely corresponds to the Poisson statistics.« less

Observation of microwave absorption and emission from incoherent electron tunneling through a normal-metal-insulator-superconductor junction.

PubMed

Masuda, Shumpei; Tan, Kuan Y; Partanen, Matti; Lake, Russell E; Govenius, Joonas; Silveri, Matti; Grabert, Hermann; Möttönen, Mikko

2018-03-02

We experimentally study nanoscale normal-metal-insulator-superconductor junctions coupled to a superconducting microwave resonator. We observe that bias-voltage-controllable single-electron tunneling through the junctions gives rise to a direct conversion between the electrostatic energy and that of microwave photons. The measured power spectral density of the microwave radiation emitted by the resonator exceeds at high bias voltages that of an equivalent single-mode radiation source at 2.5 K although the phonon and electron reservoirs are at subkelvin temperatures. Measurements of the generated power quantitatively agree with a theoretical model in a wide range of bias voltages. Thus, we have developed a microwave source which is compatible with low-temperature electronics and offers convenient in-situ electrical control of the incoherent photon emission rate with a predetermined frequency, without relying on intrinsic voltage fluctuations of heated normal-metal components or suffering from unwanted losses in room temperature cables. Importantly, our observation of negative generated power at relatively low bias voltages provides a novel type of verification of the working principles of the recently discovered quantum-circuit refrigerator.

Constraint on a varying proton-to-electron mass ratio from molecular hydrogen absorption towards quasar SDSS J123714.60+064759.5

NASA Astrophysics Data System (ADS)

Daprà, M.; Bagdonaite, J.; Murphy, M. T.; Ubachs, W.

2015-11-01

Molecular hydrogen transitions in the sub-damped Lyman α absorber at redshift zabs ≃ 2.69, towards the background quasar SDSS J123714.60+064759.5, were analysed in order to search for a possible variation of the proton-to-electron mass ratio μ over a cosmological time-scale. The system is composed of three absorbing clouds where 137 H2 and HD absorption features were detected. The observations were taken with the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph with a signal-to-noise ratio of 32 per 2.5 km s-1 pixel, covering the wavelengths from 356.6 to 409.5 nm. A comprehensive fitting method was used to fit all the absorption features at once. Systematic effects of distortions to the wavelength calibrations were analysed in detail from measurements of asteroid and `solar twin' spectra, and were corrected for. The final constraint on the relative variation in μ between the absorber and the current laboratory value is Δμ/μ = (-5.4 ± 6.3stat ± 4.0syst) × 10-6, consistent with no variation over a look-back time of 11.4 Gyr.

Revealing the electronic ground state of ReNiO3 combining Ni-L3 x-ray absorption and resonant inelastic x-ray scattering

NASA Astrophysics Data System (ADS)

Bisogni, Valentina; Catalano, Sara; Green, Robert; Gibert, Marta; Scherwitzl, Raoul; Huang, Yaobo; Balandesh, Shadi; Strocov, Vladimir N.; Zubko, Pavlo; Sawatzky, George; Triscone, Jean-Marc; Schmitt, Thorsten

Rare-earth nickelates ReNiO3 attract a lot of interest thanks to their intriguing physical properties like sharp metal to insulator transition, unusual magnetic order and expected superconductivity in nickelate-based heterostructures. Full understanding of these materials, however, is hampered by the difficulties in describing their electronic ground state (GS). Taking a NdNiO3 thin film as a representative example, we reveal with x-ray absorption and resonant inelastic x-ray scattering unusual coexistence of bound and continuum excitations, providing strong evidence for abundant O 2p holes in the GS of these materials. Using an Anderson impurity model interpretation, we show that these distinct spectral signatures arise from a Ni 3d8 configuration along with holes in the O 2p valence band, confirming suggestions that these materials exhibit a negative charge-transfer energy, with O 2p states extending across the Fermi level.

Studies on effective atomic numbers for photon energy absorption and electron density of some narcotic drugs in the energy range 1 keV-20 MeV

NASA Astrophysics Data System (ADS)

Gounhalli, Shivraj G.; Shantappa, Anil; Hanagodimath, S. M.

2013-04-01

Effective atomic numbers for photon energy absorption ZPEA,eff, photon interaction ZPI,eff and for electron density Nel, have been calculated by a direct method in the photon-energy region from 1 keV to 20 MeV for narcotic drugs, such as Heroin (H), Cocaine (CO), Caffeine (CA), Tetrahydrocannabinol (THC), Cannabinol (CBD), Tetrahydrocannabivarin (THCV). The ZPEA,eff, ZPI,eff and Nel values have been found to change with energy and composition of the narcotic drugs. The energy dependence ZPEA,eff, ZPI,eff and Nel is shown graphically. The maximum difference between the values of ZPEA,eff, and ZPI,eff occurs at 30 keV and the significant difference of 2 to 33% for the energy region 5-100 keV for all drugs. The reason for these differences is discussed.

Vibrational and electronic absorption spectral studies of 5-amino-1-(4-bromophenyl)-3-phenyl-1-H-pyrazole

NASA Astrophysics Data System (ADS)

Prasad, M. V. S.; Chaitanya, Kadali; Udaya Sri, N.; Veeraiah, V.

2012-12-01

The FT-IR and FT-Raman spectra of 5-amino-1-(4-bromophenyl)-3-phenyl-1-H-pyrazole have been measured in the regions 4000-400 cm-1 and 3500-100 cm-1, respectively. The equilibrium geometry, bonding features and harmonic vibrational frequencies have been carried out with the help of DFT method. The assignments of the vibrational spectra have been carried out with the normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The first-order hyperpolarizability (β0) and related properties (μ, α0, and Δα) of 5A4BP3PP are calculated by using HF/6-31G(d,p) method on the finite field approach. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bonding orbital (NBO) analysis. The results show that electron density (ED) in the σ* and π* antibonding orbitals and second order delocalization energies E(2) confirms the occurrence of the intramolecular charge transfer (ICT) within the molecule. UV-vis spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were performed by TDDFT using 6-31G(d,p). The HOMO-LUMO calculations indicating the charge transfer takes place within the molecule.

Electronic absorption and MCD spectra of M sub 2 (TMB) sub 4 sup 2+ , M = Rh and Ir. A valence-bond description of the upper electronic excited states

SciTech Connect

Smith, D.C.; Miskowski, V.M.; Gray, H.B.

1990-05-09

Electronic absorption and magnetic circular dichroism (MCD) spectra of Rh{sub 2}(TMB){sub 4}{sup 2+} and Ir{sub 2}(TMB){sub 4}{sup 2+} are reported along with polarized single-crystal absorption spectra of (Ir{sub 2}(TMB){sub 4})(B(C{sub 6}H{sub 5}){sub 4}){sub 2} {times} CH{sub 3}C{sub 6}H{sub 5} (TMB = 2,5-diisocyano-2,5-dimethylhexane). Interpretation of the spectra is based on a valence-bond model that accommodates highly perturbed dimer transitions as well as monomer-like dimer excitations. In this model, half of the dimer electronic excited states possess ionic character; these states involve metal-to-metal charge transfer (MMCT). The most prominent of the weak features ({approximately} 430 nm) is assigned to the transition tomore » {sup 1}A{sub 1g} (a single-center d{sub z{sup 2}} {yields} p{sub z} excitation). High-energy features ({lambda} < 300 nm) in the spectra of Rh{sub 2}(TMB){sub 4}{sup 2+} and Ir{sub 2}(TMB){sub 4}{sup 2+} are assigned to MMCT arising from d{sub xzyz} {yields} p{sub z} excitations.« less

Spectroscopic characterization of C7H3(+) and C7H3˙: electronic absorption and fluorescence in 6 K neon matrices.

PubMed

Chakraborty, Arghya; Fulara, Jan; Dietsche, Rainer; Maier, John P

2014-04-21

Mass selective deposition of C7H3(+) (m/z = 87) into solid neon reveals the 1(1)A1←X(1)A1 electronic absorption system of hepta-1,2,3,4,5,6-heptahexaenylium cation B(+) [H2CCCCCCCH](+) with an origin band at 441.3 nm, 1(1)A'←X(1)A' transition of 2,4-pentadiynylium,1-ethynyl cation C(+) [HCCCHCCCCH](+) starting at 414.6 nm and the 1(1)A1←X(1)A1 one of cyclopropenylium,1,3-butadiynyl cation A(+) [HCCCCC<(CH=CH)](+) with an onset at 322.2 nm. Vibrationally resolved fluorescence was observed for isomer B(+) upon laser excitation of the absorption bands in the 1(1)A1←X(1)A1 transition. After neutralization of the cations in the matrix five absorption systems of the C7H3 neutral radicals starting at 530.3, 479.4, 482.3, 325.0 and 302.5 nm were detected. These were identified as the 1(2)A'←X(2)A' and 2(2)A'←X(2)A' electronic transitions of 2-(buta-1,3-diynyl)cycloprop-2yl-1-1ylidene E˙ [HCCCCC<(C=CH2)]˙, 1(2)B1←X(2)B1 of 1,2,3,4,5,6-heptahexaenyl B˙ [H2CCCCCCCH]˙, 3(2)B1←X(2)B1 of 3-buta-1,3-diynyl-cyclopropenyl A˙ [HCCCCC<(CH=CH)]˙ and 2(2)B1←X(2)A2 transition of 1,2-divinylidene-cyclopropanyl radical F˙ [HCC-cyc-(CCHC)-CCH]˙, respectively. The assignment is based on calculated vertical excitation energies using the CASPT2 method. Comparison of the calculated harmonic vibrational frequencies with those inferred from the spectra supports the assignment.

Molecular and electronic structure, magnetotropicity and absorption spectra of benzene-trinuclear copper(I) and silver(I) trihalide columnar binary stacks.

PubMed

Tsipis, A C; Stalikas, A V

2012-02-20

The molecular and electronic structures, stabilities, bonding features, magnetotropicity and absorption spectra of benzene-trinuclear Cu(I) and Ag(I) trihalide columnar binary stacks with the general formula [c-M(3)(μ(2)-X)(3)](n)(C(6)H(6))(m) (M = Cu, Ag; X = halide; n, m ≤ 2) have been investigated by means of electronic structure calculation methods. The interaction of c-M(3)(μ(2)-X)(3) clusters with one and two benzene molecules yields 1:1 and 1:2 binary stacks, while benzene sandwiched 2:1 stacks are formed upon interaction of two c-M(3)(μ(2)-X)(3) clusters with one benzene molecule. In all binary stacks the plane of the alternating c-M(3)(μ(2)-X)(3) and benzene components adopts an almost parallel orientation. The separation distance between the centroids of the benzene and the proximal c-M(3)(μ(2)-X)(3) metallic cluster found in the range 2.97-3.33 Å at the B97D/Def2-TZVP level is indicative of a π···π stacking interaction mode, for the centroid separation distance is very close to the sum of the van der Waals radii of Cu···C (3.10 Å) and Ag···C (3.44 Å). Energy decomposition analysis (EDA) at the SSB-D/TZP level revealed that the dominant term in the c-M(3)(μ(2)-X)(3)···C(6)H(6) interaction arises from dispersion and electrostatic forces while the covalent interactions are predicted to be negligible. On the other hand, charge decomposition analysis (CDA) illustrated very small charge transfer from C(6)H(6) toward the c-M(3)(μ(2)-X)(3) clusters, thus reflecting weak π-base/π-acid interactions which are further corroborated by the respective electrostatic potentials and the fact that the total dipole moment vector points to the center of the metallic ring of the c-M(3)(μ(2)-X)(3) cluster. The absorption spectra of all aromatic columnar binary stacks simulated by means of TD-DFT calculations showed strong absorptions in the UV region. The main features of the simulated absorption spectra are thoroughly analyzed, and assignments of

Paramagnetic Europium Salen Complex and Sickle-Cell Anemia

NASA Astrophysics Data System (ADS)

Wynter, Clive I.; Ryan, D. H.; May, Leopold; Oliver, F. W.; Brown, Eugene; Hoffman, Eugene J.; Bernstein, David

2005-04-01

A new europium salen complex, Eu(salen)2NH4, was synthesized, and its composition was confirmed by chemical analysis and infrared spectroscopy. Further characterization was carried out by 151 Eu Mössbauer spectroscopy and magnetic susceptibility measurements. Mössbauer spectroscopic measurements were made at varying temperatures between 9 K and room temperature and a value of Debye temperature of 133 ±5 K was computed. Both Mössbauer and magnetic susceptibility measurements confirmed the paramagnetic behavior of this complex and the trivalent state of the europium ion. In view of the fact that the "odd" paramagnetic molecule NO has been shown to reverse sickling of red blood cells in sickle cell anemia, the interaction between the paramagnetic europium salen complex and sickle cells was examined after incubation with this europium complex and shown to have similar effects.

In Situ Industrial Bimetallic Catalyst Characterization using Scanning Transmission Electron Microscopy and X-ray Absorption Spectroscopy at One Atmosphere and Elevated Temperature.

PubMed

Prestat, Eric; Kulzick, Matthew A; Dietrich, Paul J; Smith, Mr Matthew; Tien, Mr Eu-Pin; Burke, M Grace; Haigh, Sarah J; Zaluzec, Nestor J

2017-08-18

We have developed a new experimental platform for in situ scanning transmission electron microscope (STEM) energy dispersive X-ray spectroscopy (EDS) which allows real time, nanoscale, elemental and structural changes to be studied at elevated temperature (up to 1000 °C) and pressure (up to 1 atm). Here we demonstrate the first application of this approach to understand complex structural changes occurring during reduction of a bimetallic catalyst, PdCu supported on TiO 2 , synthesized by wet impregnation. We reveal a heterogeneous evolution of nanoparticle size, distribution, and composition with large differences in reduction behavior for the two metals. We show that the data obtained is complementary to in situ STEM electron energy loss spectroscopy (EELS) and when combined with in situ X-ray absorption spectroscopy (XAS) allows correlation of bulk chemical state with nanoscale changes in elemental distribution during reduction, facilitating new understanding of the catalytic behavior for this important class of materials. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Microwave-induced resistance oscillations on a high-mobility two-dimensional electron gas: Exact waveform, absorption/reflection and temperature damping

NASA Astrophysics Data System (ADS)

Studenikin, S. A.; Potemski, M.; Sachrajda, A.; Hilke, M.; Pfeiffer, L. N.; West, K. W.

2005-06-01

In this work we address experimentally a number of unresolved issues related to microwave induced resistance oscillations (MIROs) leading to the zero-resistance states observed recently on 2D electron gases in GaAs/AlGaAs heterostructures. We stress the importance of the electrodynamic effects detected in both reflection and absorption experiments, although they are not revealed in transport experiments on very high mobility samples. We also study the exact waveform of MIROs and their damping due to temperature. A simple equation is given, which can be considered as phenomenological, which describes precisely the experimental MIROs waveform. The waveform depends only on a single parameter—the width of the Landau levels, which is related to the quantum lifetime. A very good correlation was found between the temperature dependencies of the quantum lifetime from MIROs and the transport scattering time from the electron mobility with a ratio τtr/τq≃20 . It is found that the prefactor in the equation for MIROs decays as 1/T2 with the temperature which can be explained within the distribution function model suggested by Dmitriev . The results are compared with measurements of the Shubnikov-de Haas oscillations down to 30mK on the same sample.

Determination of equilibrium structures of bromothymol blue revealed by using quantum chemistry with an aid of multivariate analysis of electronic absorption spectra.

PubMed

Shimada, Toru; Hasegawa, Takeshi

2017-10-05

The pH dependent chemical structures of bromothymol blue (BTB), which have long been under controversy, are determined by employing a combined technique of multivariate analysis of electronic absorption spectra and quantum chemistry. Principle component analysis (PCA) of the pH dependent spectra apparently reveals that only two chemical species are adequate to fully account for the color changes, with which the spectral decomposition is readily performed by using augmented alternative least-squares (ALS) regression analysis. The quantity variation by the ALS analysis also reveals the practical acid dissociation constant, pK a '. The determination of pK a ' is performed for various ionic strengths, which reveals the thermodynamic acid constant (pK a =7.5) and the number of charge on each chemical species; the yellow form is negatively charged species of -1 and the blue form that of -2. On this chemical information, the quantum chemical calculation is carried out to find that BTB molecules take the pure quinoid form in an acid solution and the quinoid-phenolate form in an alkaline solution. The time-dependent density functional theory (TD-DFT) calculations for the theoretically determined chemical structures account for the peak shift of the electronic spectra. In this manner, the structures of all the chemical species appeared in equilibrium have finally been confirmed. Copyright © 2017 Elsevier B.V. All rights reserved.

Electronic states in oxidized NaxCoO2 as revealed by X-ray absorption spectroscopy coupled with ab initio calculation

NASA Astrophysics Data System (ADS)

Niwa, Hideharu; Higashiyama, Kazuyuki; Amaha, Kaoru; Kobayashi, Wataru; Moritomo, Yutaka

2018-04-01

Layered cobalt oxides are promising cathode materials for sodium ion secondary batteries (SIBs). By combined study of the X-ray absorption spectroscopy (XAS) around the O K-edge and ab initio calculation, we investigated the electronic state of the NaxCoO2 with different oxidization state, i.e, in O3-Na0.91CoO2 (CoO2-0.91) and P2-Na0.66CoO2 (CoO2-0.66). The O K-edge spectra in the pre-edge (529-536 eV) region shows significant change with oxidization of NaxCoO2. In O3-Na0.91CoO2, the spectra shows an intense band (B band) at 531 eV. In P2-Na0.66CoO2, the spectral weight of the B band increases and a new band (A band) appears at 530 eV. These spectral changes are qualitatively reproduced by the calculated partial density of states (pDOSs) of O3-NaCoO2 and P2-Na1/2CoO2. These results indicate that the electrons are partially removed from the O 2p state with oxidization of NaxCoO2.

Determination of equilibrium structures of bromothymol blue revealed by using quantum chemistry with an aid of multivariate analysis of electronic absorption spectra

NASA Astrophysics Data System (ADS)

Shimada, Toru; Hasegawa, Takeshi

2017-10-01

The pH dependent chemical structures of bromothymol blue (BTB), which have long been under controversy, are determined by employing a combined technique of multivariate analysis of electronic absorption spectra and quantum chemistry. Principle component analysis (PCA) of the pH dependent spectra apparently reveals that only two chemical species are adequate to fully account for the color changes, with which the spectral decomposition is readily performed by using augmented alternative least-squares (ALS) regression analysis. The quantity variation by the ALS analysis also reveals the practical acid dissociation constant, pKa‧. The determination of pKa‧ is performed for various ionic strengths, which reveals the thermodynamic acid constant (pKa = 7.5) and the number of charge on each chemical species; the yellow form is negatively charged species of - 1 and the blue form that of - 2. On this chemical information, the quantum chemical calculation is carried out to find that BTB molecules take the pure quinoid form in an acid solution and the quinoid-phenolate form in an alkaline solution. The time-dependent density functional theory (TD-DFT) calculations for the theoretically determined chemical structures account for the peak shift of the electronic spectra. In this manner, the structures of all the chemical species appeared in equilibrium have finally been confirmed.

Magnetic resonance force microscopy with a paramagnetic probe

SciTech Connect

Berman, G. P.; Gorshkov, V. N.; Tsifrinovich, V. I.

Here, we consider theoretically extension of magnetic resonance force microscopy (MRFM) replacing a ferromagnetic probe on a cantilever tip (CT) with a paramagnetic one (PMRFM). The dynamics of the interaction between the paramagnetic probe and a local magnetic moment in a sample is analyzed, using a quasi-classical approach. We show that the application of a proper sequence of electromagnetic pulses provides a significant deflection of the CT from the initial equilibrium position. Periodic application of these sequences of pulses results in quasi-periodic CT deflections from the equilibrium, which can be used for detection of the magnetic moment in a sample.

Magnetic resonance force microscopy with a paramagnetic probe

NASA Astrophysics Data System (ADS)

Berman, G. P.; Gorshkov, V. N.; Tsifrinovich, V. I.

2017-04-01

We consider theoretically extension of magnetic resonance force microscopy (MRFM) replacing a ferromagnetic probe on a cantilever tip (CT) with a paramagnetic one (PMRFM). The dynamics of the interaction between the paramagnetic probe and a local magnetic moment in a sample is analyzed, using a quasi-classical approach. We show that the application of a proper sequence of electromagnetic pulses provides a significant deflection of the CT from the initial equilibrium position. Periodic application of these sequences of pulses results in quasi-periodic CT deflections from the equilibrium, which can be used for detection of the magnetic moment in a sample.

Dedicated Co-deposition System for Metallic Paramagnetic Films

DOE PAGES

Jaeckel, F.; Kotsubo, V.; Hall, J. A.; ...

2012-01-27

Here, we describe a dedicated co-sputtering/ion-mill system developed to study metallic paramagnetic films for use in magnetic microcalorimetry. Small-diameter sputtering guns allow study of several precious-metal-based paramagnetic alloy systems within a reasonable budget. We demonstrated safe operation of a 1" sputtering gun at >5x the rated maximum power, achieving deposition rates up to ~900 Å/min/gun (Cu) in our co-sputtering geometry. Demonstrated co-sputtering deposition ratios up to 100:1 allow accurate tuning of magnetic dopant concentration and eliminate the difficulty of preparing homogeneous alloy targets of extreme dilution.

Magnetic resonance force microscopy with a paramagnetic probe

DOE PAGES

Berman, G. P.; Gorshkov, V. N.; Tsifrinovich, V. I.

2017-04-01

Here, we consider theoretically extension of magnetic resonance force microscopy (MRFM) replacing a ferromagnetic probe on a cantilever tip (CT) with a paramagnetic one (PMRFM). The dynamics of the interaction between the paramagnetic probe and a local magnetic moment in a sample is analyzed, using a quasi-classical approach. We show that the application of a proper sequence of electromagnetic pulses provides a significant deflection of the CT from the initial equilibrium position. Periodic application of these sequences of pulses results in quasi-periodic CT deflections from the equilibrium, which can be used for detection of the magnetic moment in a sample.

Van vleck paramagnetism in orthorhombic TiO2 (Brookite)

USGS Publications Warehouse

Senftle, F.E.; Thorpe, A.N.

1968-01-01

The magnetic susceptibility of the orthorhombic form of titanium dioxide has been measured from 5 to 300??K. After deducting the temperature-dependent component, which is probably due to defects or impurities, and the free-ion diamagnetic component, the Van Vleck paramagnetism was estimated to be 33??10-6 emu/mole. Comparison is made between this value and the Van Vleck paramagnetism of strontium titanate and the two tetragonal forms of titanium dioxide: rutile and anatase. ?? 1968 The American Physical Society.

DFT/TD-semiempirical study on the structural and electronic properties and absorption spectra of supramolecular fullerene-porphyrine-metalloporphyrine triads based dye-sensitized solar cells.

PubMed

Rezvani, M; Darvish Ganji, M; Jameh-Bozorghi, S; Niazi, A

2018-04-05

In the present work density functional theory (DFT) and time-dependent semiempirical ZNIDO/S (TD-ZNIDO/S) methods have been used to investigate the ground state geometries, electronic structures and excited state properties of triad systems. The influences of the type of metal in the porphyrin ring, change in bridge position and porphyrine-ZnP duplicate on the energies of frontier molecular orbital and UV-Vis spectra has been studied. Geometry optimization, the energy levels and electron density of the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO), chemical hardness (η), electrophilicity index (ω), electron accepting power (ω + ) were calculated using ZINDO/S method to predict which molecule is the most efficient with a great capability to be used as a triad molecule in solar industry. Moreover the light harvesting efficiency (LHE) was calculated by means of the oscillator strengths which are obtained by TD-ZINDO/S calculation. Theoretical studies of the electronic spectra by ZINDO/S method were helpful in interpreting the observed electronic transitions. This aspect was systematically explored in a series of C 60 -Porphyrine-Metalloporphyrine (C 60 -P-Mp) triad system with M being Fe, Co, Ni, Ti, and Zn. Generally, transition metal coordination compounds are used as effective sensitizers, due to their intense charge-transfer absorption over the whole visible range and highly efficient metal-to-ligand charge transfer. We aim to optimize the performance of the title solar cells by altering the frontier orbital energy gaps. The results reveal that cell efficiency can be enhanced by metal functionalization of the free base porphyrin. Ti-porphyrin was found to be the most efficient dye sensitizer for dye sensitized solar cells (DSSCs) based on C 60 -P-Mptriad system due to C 60 -Por-TiP complex has lower chemical hardness, gap energy and chemical potential as well as higher electron accepting power among other complexes

DFT/TD-semiempirical study on the structural and electronic properties and absorption spectra of supramolecular fullerene-porphyrine-metalloporphyrine triads based dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Rezvani, M.; Darvish Ganji, M.; Jameh-Bozorghi, S.; Niazi, A.

2018-04-01

In the present work density functional theory (DFT) and time-dependent semiempirical ZNIDO/S (TD-ZNIDO/S) methods have been used to investigate the ground state geometries, electronic structures and excited state properties of triad systems. The influences of the type of metal in the porphyrin ring, change in bridge position and porphyrine-ZnP duplicate on the energies of frontier molecular orbital and UV-Vis spectra has been studied. Geometry optimization, the energy levels and electron density of the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO), chemical hardness (η), electrophilicity index (ω), electron accepting power (ω+) were calculated using ZINDO/S method to predict which molecule is the most efficient with a great capability to be used as a triad molecule in solar industry. Moreover the light harvesting efficiency (LHE) was calculated by means of the oscillator strengths which are obtained by TD-ZINDO/S calculation. Theoretical studies of the electronic spectra by ZINDO/S method were helpful in interpreting the observed electronic transitions. This aspect was systematically explored in a series of C60-Porphyrine-Metalloporphyrine (C60-P-Mp) triad system with M being Fe, Co, Ni, Ti, and Zn. Generally, transition metal coordination compounds are used as effective sensitizers, due to their intense charge-transfer absorption over the whole visible range and highly efficient metal-to-ligand charge transfer. We aim to optimize the performance of the title solar cells by altering the frontier orbital energy gaps. The results reveal that cell efficiency can be enhanced by metal functionalization of the free base porphyrin. Ti-porphyrin was found to be the most efficient dye sensitizer for dye sensitized solar cells (DSSCs) based on C60-P-Mptriad system due to C60-Por-TiP complex has lower chemical hardness, gap energy and chemical potential as well as higher electron accepting power among other complexes. In

Electronic structure, bonding, charge distribution, and x-ray absorption spectra of the (001) surfaces of fluorapatite and hydroxyapatite from first principles

NASA Astrophysics Data System (ADS)

Rulis, Paul; Yao, Hongzhi; Ouyang, Lizhi; Ching, W. Y.

2007-12-01

Fluorapatite (FAP) and hydroxyapatite (HAP) are two very important bioceramic crystals. The (001) surfaces of FAP and HAP crystals are studied by ab initio density functional calculations using a supercell slab geometry. It is shown that in both crystals, the O-terminated (001) surface is more stable with calculated surface energies of 0.865 and 0.871J/m2 for FAP and HAP, respectively. In FAP, the two surfaces are symmetric. In HAP, the orientation of the OH group along the c axis reduces the symmetry such that the top and bottom surfaces are no longer symmetric. It is revealed that the atoms near the surface and subsurface are significantly relaxed especially in the case of HAP. The largest relaxations occurred via the lateral movements of the O ions at the subsurface level. The electronic structures of the surface models in the form of layer-by-layer resolved partial density of states for all the atoms show systematic variation from the surface region toward the bulk region. The calculated Mulliken effective charge on each type of atom and the bond order values between cations (Ca, P) and anions (O, F) show different charge transfers and bond strength variations from the bulk crystal values. Electron charge density calculations show that the surfaces of both FAP and HAP crystals are mostly positively charged due to the presence of Ca ions at the surface. The positively charged surfaces have implications for the absorption on apatite surfaces of water and other organic molecules in an aqueous environment which are an important part of its bioactivity. The x-ray absorption near-edge structure (XANES) spectra ( Ca-K , O-K , F-K , P-K , and P-L3 edges) of both the surface models and the bulk crystals are calculated and compared. The calculations use a supercell approach which takes into account the electron-core-hole interaction. It is shown that the site-specific XANES spectra show significant differences between atoms near the surface and in the bulk and are very

Experimental observation of left polarized wave absorption near electron cyclotron resonance frequency in helicon antenna produced plasma

SciTech Connect

Barada, Kshitish K.; Chattopadhyay, P. K.; Ghosh, J.

2013-01-15

Asymmetry in density peaks on either side of an m = +1 half helical antenna is observed both in terms of peak position and its magnitude with respect to magnetic field variation in a linear helicon plasma device [Barada et al., Rev. Sci. Instrum. 83, 063501 (2012)]. The plasma is produced by powering the m = +1 half helical antenna with a 2.5 kW, 13.56 MHz radio frequency source. During low magnetic field (B < 100 G) operation, plasma density peaks are observed at critical magnetic fields on either side of the antenna. However, the density peaks occurred at differentmore » critical magnetic fields on both sides of antenna. Depending upon the direction of the magnetic field, in the m = +1 propagation side, the main density peak has been observed around 30 G of magnetic field. On this side, the density peak around 5 G corresponding to electron cyclotron resonance (ECR) is not very pronounced, whereas in the m = -1 propagation side, very pronounced ECR peak has been observed around 5 G. Another prominent density peak around 12 G has also been observed in m = -1 side. However, no peak has been observed around 30 G on this m = -1 side. This asymmetry in the results on both sides is explained on the basis of polarization reversal of left hand polarized waves to right hand polarized waves and vice versa in a bounded plasma system. The density peaking phenomena are likely to be caused by obliquely propagating helicon waves at the resonance cone boundary.« less

Effect of body temperature on the pharmacokinetics of a triarylmethyl-type paramagnetic contrast agent used in EPR oximetry.

PubMed

Matsumoto, Ken-Ichiro; Hyodo, Fuminori; Mitchell, James B; Krishna, Murali C

2018-02-01

Pharmacokinetics of the tri[8-carboxy-2,2,6,6-tetrakis(2-hydroxymethyl)benzo[1,2-d:4,5-d']bis(1,3)dithio-4-yl]methyl radical (Oxo63) after a single bolus and/or continuous intravenous infusion was investigated in tumor-bearing C3H mice with or without body temperature control while under anesthesia. The in vivo time course of Oxo63 in blood was measured using X-band electron paramagnetic resonance spectroscopy. Distribution of Oxo63 in normal muscle and tumor tissues was obtained using a surface coil resonator and a 700-MHz electron paramagnetic resonance spectrometer. The whole-body distribution of Oxo63 was obtained by 300-MHz continuous-wave electron paramagnetic resonance imaging. The high-resolution 300-MHz time-domain electron paramagnetic resonance imaging was also carried out to probe the distribution of Oxo63. Urination of mice was retarded at low body temperature, causing the concentration of Oxo63 in blood to attain high levels. However, the concentration of Oxo63 in tumor tissue was lower with no control of body temperature than active body temperature control. The nonsystemized blood flow in the tumor tissues may pool Oxo63 at lower body temperature. Pharmacokinetics of the contrast agent were found to be significantly affected by body temperature of the experimental animal, and can influence the probe distribution and the image patterns. Magn Reson Med 79:1212-1218, 2018. © Published 2017. This article is a U.S. Government work and is in the public domain in the USA. © Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Cob(I)alamin: insight into the nature of electronically excited states elucidated via quantum chemical computations and analysis of absorption, CD and MCD data.

PubMed

Kornobis, Karina; Ruud, Kenneth; Kozlowski, Pawel M

2013-02-07

The nature of electronically excited states of the super-reduced form of vitamin B(12) (i.e., cob(I)alamin or B(12s)), a ubiquitous B(12) intermediate, was investigated by performing quantum-chemical calculations within the time-dependent density functional theory (TD-DFT) framework and by establishing their correspondence to experimental data. Using response theory, the electronic absorption (Abs), circular dichroism (CD) and magnetic CD (MCD) spectra of cob(I)alamin were simulated and directly compared with experiment. Several issues have been taken into considerations while performing the TD-DFT calculations, such as strong dependence on the applied exchange-correlation (XC) functional or structural simplification imposed on the cob(I)alamin. In addition, the low-lying transitions were also validated by performing CASSCF/MC-XQDPT2 calculations. By comparing computational results with existing experimental data a new level of understanding of electronic excitations has been established at the molecular level. The present study extends and confirms conclusions reached for other cobalamins. In particular, the better performance of the BP86 functional, rather than hybrid-type, was observed in terms of the excitations associated with both Co d and corrin π localized transitions. In addition, the lowest energy band was associated with multiple metal-to-ligand charge transfer excitations as opposed to the commonly assumed view of a single π → π* transition followed by vibrational progression. Finally, the use of the full cob(I)alamin structure, instead of simplified molecular models, shed new light on the spectral analyses of cobalamin systems and revealed new challenges of this approach related to long-range charge transfer excitations involving side chains.

HIGH-ENERGY ELECTRON IRRADIATION OF INTERSTELLAR CARBONACEOUS DUST ANALOGS: COSMIC-RAY EFFECTS ON THE CARRIERS OF THE 3.4 μ m ABSORPTION BAND

SciTech Connect

Maté, Belén; Molpeceres, Germán; Jiménez-Redondo, Miguel

2016-11-01

The effects of cosmic rays on the carriers of the interstellar 3.4 μ m absorption band have been investigated in the laboratory. This band is attributed to stretching vibrations of CH{sub 3} and CH{sub 2} in carbonaceous dust. It is widely observed in the diffuse interstellar medium, but disappears in dense clouds. Destruction of CH{sub 3} and CH{sub 2} by cosmic rays could become relevant in dense clouds, shielded from the external ultraviolet field. For the simulations, samples of hydrogenated amorphous carbon (a-C:H) have been irradiated with 5 keV electrons. The decay of the band intensity versus electron fluence reflectsmore » a-C:H dehydrogenation, which is well described by a model assuming that H{sub 2} molecules, formed by the recombination of H atoms liberated through CH bond breaking, diffuse out of the sample. The CH bond destruction rates derived from the present experiments are in good accordance with those from previous ion irradiation experiments of HAC. The experimental simplicity of electron bombardment has allowed the use of higher-energy doses than in the ion experiments. The effects of cosmic rays on the aliphatic components of cosmic dust are found to be small. The estimated cosmic-ray destruction times for the 3.4 μ m band carriers lie in the 10{sup 8} yr range and cannot account for the disappearance of this band in dense clouds, which have characteristic lifetimes of 3 × 10{sup 7} yr. The results invite a more detailed investigation of the mechanisms of CH bond formation and breaking in the intermediate region between diffuse and dense clouds.« less

Cancer detection based on Raman spectra super-paramagnetic clustering

NASA Astrophysics Data System (ADS)

González-Solís, José Luis; Guizar-Ruiz, Juan Ignacio; Martínez-Espinosa, Juan Carlos; Martínez-Zerega, Brenda Esmeralda; Juárez-López, Héctor Alfonso; Vargas-Rodríguez, Héctor; Gallegos-Infante, Luis Armando; González-Silva, Ricardo Armando; Espinoza-Padilla, Pedro Basilio; Palomares-Anda, Pascual

2016-08-01

The clustering of Raman spectra of serum sample is analyzed using the super-paramagnetic clustering technique based in the Potts spin model. We investigated the clustering of biochemical networks by using Raman data that define edge lengths in the network, and where the interactions are functions of the Raman spectra's individual band intensities. For this study, we used two groups of 58 and 102 control Raman spectra and the intensities of 160, 150 and 42 Raman spectra of serum samples from breast and cervical cancer and leukemia patients, respectively. The spectra were collected from patients from different hospitals from Mexico. By using super-paramagnetic clustering technique, we identified the most natural and compact clusters allowing us to discriminate the control and cancer patients. A special interest was the leukemia case where its nearly hierarchical observed structure allowed the identification of the patients's leukemia type. The goal of this study is to apply a model of statistical physics, as the super-paramagnetic, to find these natural clusters that allow us to design a cancer detection method. To the best of our knowledge, this is the first report of preliminary results evaluating the usefulness of super-paramagnetic clustering in the discipline of spectroscopy where it is used for classification of spectra.

Apparatus for magnetic separation of paramagnetic and diamagnetic material

DOEpatents

Doctor, Richard D.

1988-01-01

The present invention relates to methods and apparatus for segregating paramagnetic from diamagnetic particles in particulate material and, in particular, to the open gradient magnetic separation of ash producing components and pyritic sulfur from coal. The apparatus includes a vertical cylinder and a rotatable vertical screw positioned within the cylinder, the screw having a helical blade angled downwardly and outwardly from the axis. Rotation of the vertical screw causes denser particles, which in the case of coal include pyritic sulfur and ash, which are paramagnetic, to migrate to the outside of the screw, and less dense particles, such as the low sulfur organic portion of the coal, which are diamagnetic, to migrate towards the center of the screw. A vibration mechanism attached to the screw causes the screw to vibrate during rotation, agitating and thereby accommodating further segregation of the particles. An open gradient magnetic field is applied circumferentially along the entire length of the screw by a superconducting quadropole magnet. The open gradient magnetic field further segregates the paramagnetic particles from the diamagnetic particles. The paramagnetic particles may then be directed from the cylinder into a first storage bin, and the diamagnetic particles, which are suitable for relatively clean combustion, may be directed into a second storage bin.

Apparatus for magnetic separation of paramagnetic and diamagnetic material

DOEpatents

Doctor, R.D.

1988-10-18

The present invention relates to methods and apparatus for segregating paramagnetic from diamagnetic particles in particulate material and, in particular, to the open gradient magnetic separation of ash producing components and pyritic sulfur from coal. The apparatus includes a vertical cylinder and a rotatable vertical screw positioned within the cylinder, the screw having a helical blade angled downwardly and outwardly from the axis. Rotation of the vertical screw causes denser particles, which in the case of coal include pyritic sulfur and ash, which are paramagnetic, to migrate to the outside of the screw, and less dense particles, such as the low sulfur organic portion of the coal, which are diamagnetic, to migrate towards the center of the screw. A vibration mechanism attached to the screw causes the screw to vibrate during rotation, agitating and thereby accommodating further segregation of the particles. An open gradient magnetic field is applied circumferentially along the entire length of the screw by a superconducting quadrupole magnet. The open gradient magnetic field further segregates the paramagnetic particles from the diamagnetic particles. The paramagnetic particles may then be directed from the cylinder into a first storage bin, and the diamagnetic particles, which are suitable for relatively clean combustion, may be directed into a second storage bin. 5 figs.

Apparatus for magnetic separation of paramagnetic and diamagnetic material

DOEpatents

Doctor, R.D.

1986-07-24

The present invention relates to methods and apparatus for segregating paramagnetic from diamagnetic particles in particulate material and, in particular, to the open gradient magnetic separation of ash producing components and pyritic sulfur from coal. The apparatus includes a vertical cylinder and a rotatable vertical screw positioned within the cylinder, the screw having a helical blade angled downwardly and outwardly from the axis. Rotation of the vertical screw causes denser particles, which in the case of coal include pyritic sulfur and ash, which are paramagnetic, to migrate to the outside of the screw, and less dense particles, such as the low sulfur organic portion of the coal, which are diamagnetic, to migrate towards the center of the screw. A vibration mechanism attached to the screw causes the screw to vibrate during rotation, agitating and thereby accommodating further segregation of the particles. An open gradient magnetic field is applied circumferentially along the entire length of the screw by a superconducting quadrupole magnet. The open gradient magnetic field further segregates the paramagnetic-particles from the diamagnetic particles. The paramagnetic particles may then be directed from the cylinder into a first storage bin, and the diamagnetic particles, which are suitable for relatively clean combustion, may be directed into a second storage bin. 5 figs.

Electronic structure and optical properties of CdSxSe1-x solid solution nanostructures from X-ray absorption near edge structure, X-ray excited optical luminescence, and density functional theory investigations

NASA Astrophysics Data System (ADS)

Murphy, M. W.; Yiu, Y. M.; Ward, M. J.; Liu, L.; Hu, Y.; Zapien, J. A.; Liu, Yingkai; Sham, T. K.

2014-11-01

The electronic structure and optical properties of a series of iso-electronic and iso-structural CdSxSe1-x solid solution nanostructures have been investigated using X-ray absorption near edge structure, extended X-ray absorption fine structure, and X-ray excited optical luminescence at various absorption edges of Cd, S, and Se. It is found that the system exhibits compositions, with variable local structure in-between that of CdS and CdSe accompanied by tunable optical band gap between that of CdS and CdSe. Theoretical calculation using density functional theory has been carried out to elucidate the observations. It is also found that luminescence induced by X-ray excitation shows new optical channels not observed previously with laser excitation. The implications of these observations are discussed.

Color centers of a borosilicate glass induced by 10 MeV proton, 1.85 MeV electron and 60Co-γ ray

NASA Astrophysics Data System (ADS)

Du, Jishi; Wu, Jiehua; Zhao, Lili; Song, Lixin

2013-05-01

Optical absorption spectra, electron paramagnetic resonance (EPR) spectra, Raman spectra of a borosilicate glass after irradiation by 10 MeV proton, 1.85 MeV electron and 60Co-γ ray were studied. The process of irradiation inducing color centers in the glass was discussed. The band gap of the glass before and after 60Co-γ ray irradiation was studied using Mott and Davis's theory, and it was found that calculated change of the band gap introduced a paradox, because Mott and Davis's theory on the band gap cannot be adopted in the study on the irradiated glass.

Simulating Ru L 3 -Edge X-ray Absorption Spectroscopy with Time-Dependent Density Functional Theory: Model Complexes and Electron Localization in Mixed-Valence Metal Dimers

SciTech Connect

Van Kuiken, Benjamin E.; Valiev, Marat; Daifuku, Stephanie L.

2013-05-30

Ruthenium L3-edge X-ray absorption (XA) spectroscopy probes unoccupied 4d orbitals of the metal atom and is increasingly being used to investigate the local electronic structure in ground and excited electronic states of Ru complexes. The simultaneous development of computational tools for simulating Ru L3-edge spectra is crucial for interpreting the spectral features at a molecular level. This study demonstrates that time-dependent density functional theory (TDDFT) is a viable and predictive tool for simulating ruthenium L3-edge XA spectroscopy. We systematically investigate the effects of exchange correlation functional and implicit and explicit solvent interactions on a series of RuII and RuIII complexesmore » in their ground and electronic excited states. The TDDFT simulations reproduce all of the experimentally observed features in Ru L3-edge XA spectra within the experimental resolution (0.4 eV). Our simulations identify ligand-specific charge transfer features in complicated Ru L3-edge spectra of [Ru(CN)6]4- and RuII polypyridyl complexes illustrating the advantage of using TDDFT in complex systems. We conclude that the B3LYP functional most accurately predicts the transition energies of charge transfer features in these systems. We use our TDDFT approach to simulate experimental Ru L3-edge XA spectra of transition metal mixed-valence dimers of the form [(NC)5MII-CN-RuIII(NH3)5] (where M = Fe or Ru) dissolved in water. Our study determines the spectral signatures of electron delocalization in Ru L3-edge XA spectra. We find that the inclusion of explicit solvent molecules is necessary for reproducing the spectral features and the experimentally determined valencies in these mixed-valence complexes. This study validates the use of TDDFT for simulating Ru 2p excitations using popular quantum chemistry codes and providing a powerful interpretive tool for equilibrium and ultrafast Ru L3-edge XA spectroscopy.« less

Curie-type paramagnetic NMR relaxation in the aqueous solution of Ni(II).

PubMed

Mareš, Jiří; Hanni, Matti; Lantto, Perttu; Lounila, Juhani; Vaara, Juha

2014-04-21

Ni(2+)(aq) has been used for many decades as a model system for paramagnetic nuclear magnetic resonance (pNMR) relaxation studies. More recently, its magnetic properties and also nuclear magnetic relaxation rates have been studied computationally. We have calculated electron paramagnetic resonance and NMR parameters using quantum-mechanical (QM) computation of molecular dynamics snapshots, obtained using a polarizable empirical force field. Statistical averages of hyperfine coupling, g- and zero-field splitting tensors, as well as the pNMR shielding terms, are compared to the available experimental and computational data. In accordance with our previous work, the isotropic hyperfine coupling as well as nuclear shielding values agree well with experimental measurements for the (17)O nuclei of water molecules in the first solvation shell of the nickel ion, whereas larger deviations are found for (1)H centers. We report, for the first time, the Curie-type contribution to the pNMR relaxation rate using QM calculations together with Redfield relaxation theory. The Curie relaxation mechanism is analogous to chemical shift anisotropy relaxation, well-known in diamagnetic NMR. Due to the predominance of other types of paramagnetic relaxation mechanisms for this system, it is possible to extract the Curie term only computationally. The Curie mechanism alone would result in around 16 and 20 s(-1) of relaxation rates (R1 and R2 respectively) for the (1)H nuclei of water molecules bonded to the Ni(2+) center, in a magnetic field of 11.7 T. The corresponding (17)O relaxation rates are around 33 and 38 s(-1). We also report the Curie contribution to the relaxation rate for molecules beyond the first solvation shell in a 1 M solution of Ni(2+) in water.

X-ray absorption spectroscopy study of annealing process on Sr1-xLaxCuO2 electron-doped cuprate thin films

NASA Astrophysics Data System (ADS)

Galdi, A.; Orgiani, P.; Sacco, C.; Gobaut, B.; Torelli, P.; Aruta, C.; Brookes, N. B.; Minola, M.; Harter, J. W.; Shen, K. M.; Schlom, D. G.; Maritato, L.

2018-03-01

The superconducting properties of Sr1-xLaxCuO2 thin films are strongly affected by sample preparation procedures, including the annealing step, which are not always well controlled. We have studied the evolution of Cu L2,3 and O K edge x-ray absorption spectra (XAS) of Sr1-xLaxCuO2 thin films as a function of reducing annealing, both qualitatively and quantitatively. By using linearly polarized radiation, we are able to identify the signatures of the presence of apical oxygen in the as-grown sample and its gradual removal as a function of duration of 350 °C Ar annealing performed on the same sample. Even though the as-grown sample appears to be hole doped, we cannot identify the signature of the Zhang-Rice singlet in the O K XAS, and it is extremely unlikely that the interstitial excess oxygen can give rise to a superconducting or even a metallic ground state. XAS and x-ray linear dichroism analyses are, therefore, shown to be valuable tools to improving the control over the annealing process of electron doped superconductors.

Absorption spectroscopic and FTIR studies on EDA complexes between TNT (2,4,6-trinitrotoluene) with amines in DMSO and determination of the vertical electron affinity of TNT.

PubMed

Sharma, S P; Lahiri, S C

2008-06-01

TNT (2,4,6-trinitrotoluene) formed deep red 1:1 CT complexes with chromogenic agents like isopropylamine, ethylenediamine, bis(3-aminopropyl)amine and tetraethylenepentamine in DMSO. The complexes were also observed in solvents like methanol, acetone, etc. when the amines were present in large excess. The isopropylamine, complex showed three absorption peaks (at 378, 532 and 629 nm) whereas higher amines showed four peaks (at 370, 463, 532 and 629 nm). The peak at 463 nm vanished rapidly. The peak of the complexes near 530 nm required about 8-10 min to develop and the complexes were stable for about an hour but the peak slowly shifted towards 500 nm and the complexes were found to be stable for more than 24 h. The evidence of complex formation was obtained from distinct spots in HPTLC plates and from the shifts in frequencies and formation of new peaks in FTIR spectra. The peaks near 460 nm (transient) and 530 nm may be due to Janovsky reaction but could not be established. The extinction coefficients of the complexes were determined directly which enabled the accurate determination of the association constants KDA with TNT and amines in stoichiometric ratios. The results were verified using iterative method. The quantification of TNT was made using epsilon value of the complex with ethylenediamine. The vertical electron affinity (EA) of TNT was calculated using the method suggested by Mulliken.

Magneto-thermoelectric effects in the two-dimensional electron gas of a HgTe quantum well due to THz laser heating by cyclotron resonance absorption

NASA Astrophysics Data System (ADS)

Pakmehr, Mehdi; Bruene, Christoph; Buhmann, Hartmut; Molenkamp, Laurens; McCombe, Bruce

2015-03-01

HgTe quantum wells (QWs) have shown a number of interesting phenomena over the past 20 years, most recently the first two-dimensional topological insulating state. We have studied thermoelectric photovoltages of 2D electrons in a 6.1 nm wide HgTe quantum well induced by cyclotron resonance absorption (B = 2 - 5 T) of a focused THz laser beam. We have estimated thermo-power coefficients by detailed analysis of the beam profile at the sample surface and the photovoltage signals developed across various contacts of a large Hall bar structure at a bath temperature of 1.6 K. We obtain reasonable values of the magneto-thermopower coefficients. Work at UB was supported by NSF DMR 1008138 and the Office of the Provost, and at the University of Wuerzburg by DARPA MESO Contract N6601-11-1-4105, by DFG Grant HA5893/4-1 within SPP 1666 and the Leibnitz Program, and the EU ERC-AG Program (Project 3-TOP.

Electronic structure change of NiS2- x Se x in the metal-insulator transition probed by X-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Jeong, Jinwon; Park, Kyung Ja; Cho, En-Jin; Noh, Han-Jin; Kim, Sung Baek; Kim, Hyeong-Do

2018-01-01

The electronic structure change of NiS2- x Se x as a function of Se concentration x has been studied by Ni L-edge X-ray absorption spectroscopy (XAS). The XAS spectra show distinct features in Ni L 3 edge, indicating whether the system is insulating or metallic. These features can be semi-quantitatively explained within the framework of the configurational interaction cluster model (CICM). In the S-rich region, relatively large charge-transfer energy (Δ 5 eV) from ligand p to Ni 3 d states and a little small p- d hybridization strength ( V pdσ 1.1 eV) can reproduce the experimental spectra in the CICM calculation, and vice versa in the Se-rich region. Our analysis result is consistent with the Zaanen-Sawatzky-Allen scheme that the systems in S-rich side ( x ≤ 0.5) are a charge transfer insulator. However, it also requires that the Δ value must change abruptly in spite of the small change of x near x = 0.5. As a possible microscopic origin, we propose a percolation scenario where a long range connection of Ni[(S,Se)2]6 octahedra with Se-Se dimers plays a key role to gap closure.

Frozen lattice and absorptive model for high angle annular dark field scanning transmission electron microscopy: A comparison study in terms of integrated intensity and atomic column position measurement.

PubMed

Alania, M; Lobato, I; Van Aert, S

2018-01-01

In this paper, both the frozen lattice (FL) and the absorptive potential (AP) approximation models are compared in terms of the integrated intensity and the precision with which atomic columns can be located from an image acquired using high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). The comparison is made for atoms of Cu, Ag, and Au. The integrated intensity is computed for both an isolated atomic column and an atomic column inside an FCC structure. The precision has been computed using the so-called Cramér-Rao Lower Bound (CRLB), which provides a theoretical lower bound on the variance with which parameters can be estimated. It is shown that the AP model results into accurate measurements for the integrated intensity only for small detector ranges under relatively low angles and for small thicknesses. In terms of the attainable precision, both methods show similar results indicating picometer range precision under realistic experimental conditions. Copyright © 2017 Elsevier B.V. All rights reserved.

Quantitative treatment of the solvent effects on the electronic absorption and fluorescence spectra of acridines and phenazines. The ground and first excited singlet-state dipole moments

NASA Astrophysics Data System (ADS)

Aaron, Jean Jacques; Maafi, Mounir; Párkányi, Cyril; Boniface, Christian

1995-04-01

Electronic absorption and fluorescence excitation and emission spectra of four acridines (acridine, Acridine Yellow, 9-aminoacridine and proflavine) and three phenazines (phenazine, neutral Red and safranine) are determined at room temperature (298 K) in several solvents of various polarities (dioxane, chloroform, ethyl ether, ethyl acetate, 1-butanol, 2-propanol, ethanol, methanol, dimethylformamide, acetonitrile and dimethyl sulfoxide). The effect of the solvent upon the spectral characteristics of the above compounds, is studied. In combination with the ground-state dipole moments of these compounds, the spectral data are used to evaluate their first excited singlet-state dipole moments by means of the solvatochromic shift method (Bakhshiev's and Kawski-Chamma-Viallet's correlations). The theoretical ground and excited singlet-state dipole moments for acridines and phenazines are also calculated as a vector sum of the π-component (obtained by the PPP method) and the σ-component (obtained from σ-bond moments). For most acridines and phenazines under study, the experimental excited singlet-state dipole moments are found to be higher than their ground state counterpart. The application of the Kamlet-Abboud-Taft solvatochromic parameters to the solvent effect on spectral properties of acridine and phenazine derivatives is discussed.

Investigation of electronic and local structural changes during lithium uptake and release of nano-crystalline NiFe2O4 by X-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Zhou, Dong; Permien, Stefan; Rana, Jatinkumar; Krengel, Markus; Sun, Fu; Schumacher, Gerhard; Bensch, Wolfgang; Banhart, John

2017-02-01

Nano-crystalline NiFe2O4 particles were synthesized and used as active electrode material for a lithium ion battery that showed a high discharge capacity of 1534 mAh g-1 and charge capacity of 1170 mAh g-1 during the 1st cycle. X-ray absorption spectroscopy including XANES and EXAFS were used to investigate electronic and local structural changes of NiFe2O4 during the 1st lithiation and de-lithiation process. As lithium is inserted into the structure, tetrahedral site Fe3+ ions are reduced to Fe2+ and moved from tetrahedral sites to empty octahedral sites, while Ni2+ ions are unaffected. As a consequence, the matrix spinel structure collapses and transforms to an intermediate rock-salt monoxide phase. Meanwhile, the inserted Li is partially consumed by the formation of SEI and other side reactions during the conversion reaction. With further lithiation, the monoxide phase is reduced to highly disordered metallic Fe/Ni nanoparticles with a number of nearest neighbors of 6.0(8) and 8.1(4) for Fe and Ni, respectively. During subsequent de-lithiation, the metal particles are individually re-oxidized to Fe2O3 and NiO phases instead to the original NiFe2O4 spinel phase.

Electronic Absorption Spectra of Mass-Selected Hydrocarbon Cations in Solid Neon: C_nH_4+ (n=5-8,10,12)

NASA Astrophysics Data System (ADS)

Nagy, A.; Fulara, J.; Garkusha, I.; Maier, J. P.

2011-05-01

Small, unsaturated hydrocarbons, C_nH_m (n,m≤6), play an important role in astrochemical models as they have been detected in various space objects such as the interstellar medium or envelopes of carbon-rich stars. Although identification of most of these species was based on rotational studies, they are candidate carriers of the infamous diffuse interstellar bands. It has been proposed that corresponding cationic species formed upon UV radiation may also be of astrophysical relevance; therefore, their optical spectra need to be determined. In this contribution, electronic absorption spectra of mass-selected C_nH_4+ (n=5-8,10,12) ions trapped in neon matrices are presented. The cations were produced in a hot-cathode discharge source, guided through a series of electrostatic lenses, mass filtered and co-deposited with excess of neon onto a rhodium-coated sapphire plate held at 6 K. In the same experiments, neutral species were generated from the cations by a photobleaching procedure.

Single crystal EPR and optical studies of paramagnetic ions doped zinc potassium phosphate hexahydrate—Part I: Cu(II)—a case of orthorhombic symmetry

NASA Astrophysics Data System (ADS)

Sambasiva Rao, P.; Rajendiran, T. M.; Venkatesan, R.; Madhu, N.; Chandrasekhar, A. V.; Reddy, B. J.; Reddy, Y. P.; Ravikumar, R. V. S. S. N.

2001-12-01

Single crystal electron paramagnetic resonance (EPR) studies on Cu(II) doped zinc potassium phosphate hexahydrate (ZPPH) were carried out at room temperature. The angular variation spectra in the three orthogonal planes indicate that the paramagnetic impurity has entered the lattice substitutionally in place of Zn(II) and the spin Hamiltonian parameters calculated from these spectra are gxx=2.188, gyy=2.032, gzz=2.373, Axx=50 G, Ayy=65.0 G and Azz=80 G. The g and A tensors were coincident and these values matched fairly well with the values obtained from powder spectrum. The bonding parameters have also been calculated.

Paramagnetic Ce3 + optical emitters in garnets: Optically detected magnetic resonance study and evidence of Gd-Ce cross-relaxation effects

NASA Astrophysics Data System (ADS)

Tolmachev, D. O.; Gurin, A. S.; Uspenskaya, Yu. A.; Asatryan, G. R.; Badalyan, A. G.; Romanov, N. G.; Petrosyan, A. G.; Baranov, P. G.; Wieczorek, H.; Ronda, C.

2017-06-01

Paramagnetic Ce3 +optical emitters have been studied by means of optically detected magnetic resonance (ODMR) via Ce3 + spin-dependent emission in cerium-doped garnet crystals which were both gadolinium free and contain gadolinium in a concentration from the lowest (0.1%) to 100%, i.e., to the superparamagnetic state. It has been shown that the intensity of photoluminescence excited by circularly polarized light into Ce3 + absorption bands can be used for selective monitoring the population of the Ce3 + ground-state spin sublevels. Direct evidence of the cross-relaxation effects in garnet crystals containing two electron spin systems, i.e., the simplest one of Ce3 + ions with the effective spin S =1/2 and the system of Gd3 + ions with the maximum spin S =7/2 , has been demonstrated. Magnetic resonance of Gd3 + has been found by monitoring Ce3 + emission in cerium-doped garnet crystals with gadolinium concentrations of 0.1 at. %, 4%-8%, and 100%, which implies the impact of the Gd3 + spin polarization on the optical properties of Ce3 +. Strong internal magnetic fields in superparamagnetic crystals were shown to modify the processes of recombination between UV-radiation-induced electron and hole centers that lead to the recombination-induced Ce3 + emission. Observation of spikes and subsequent decay in the cross-relaxation-induced ODMR signals under pulsed microwave excitation is suggested to be an informative method to investigate transient processes in the many-spin system of Ce3 +, Gd3 +, and electron and hole radiation-induced centers.

A Paramagnetic Copper(III) Complex Containing an Octahedral CuIII S6 Coordination Polyhedron.

PubMed

Krebs, Carsten; Glaser, Thorsten; Bill, Eckhard; Weyhermüller, Thomas; Meyer-Klaucke, Wolfram; Wieghardt, Karl

1999-02-01

Only the second octahedral, paramagnetic copper(III) complex (S=1) has now been synthesized and characterized. Six thiolato bridging ligands in the heterotrinuclear species [LCo III Cu III Co III L](ClO 4 ) 3 ⋅2 Me 2 CO (L=1,4,7-tris(4-tert-butyl-2-sulfidobenzyl)-1,4,7-triazacyclononane) stabilize this rare electron configuration. A section of the structure of the reduced form (Cu II , S=½) is shown. XAS, EXAFS, and EPR spectroscopy prove unambiguously that the one-electron oxidation to the copper(III) is metal- rather than ligand-centered. © 1999 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.

CW EPR and 9 GHz EPR imaging investigation of stable paramagnetic species and their antioxidant activities in dry shiitake mushroom (Lentinus edodes).

PubMed

Nakagawa, Kouichi; Hara, Hideyuki

2016-01-01

We investigated the antioxidant activities and locations of stable paramagnetic species in dry (or drying) shiitake mushroom (Lentinus edodes) using continuous wave (CW) electron paramagnetic resonance (EPR) and 9 GHz EPR imaging. CW 9 GHz EPR detected paramagnetic species (peak-to-peak linewidth (ΔHpp) = 0.57 mT) in the mushroom. Two-dimensional imaging of the sharp line using a 9 GHz EPR imager showed that the species were located in the cap and shortened stem portions of the mushroom. No other location of the species was found in the mushroom. However, radical locations and concentrations varied along the cap of the mushroom. The 9 GHz EPR imaging determined the exact location of stable paramagnetic species in the shiitake mushroom. Distilled water extracts of the pigmented cap surface and the inner cap of the mushroom showed similar antioxidant activities that reduced an aqueous solution of 0.1 mM 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl. The present results suggest that the antioxidant activities of the edible mushroom extracts are much weaker than those of ascorbic acid. Thus, CW EPR and EPR imaging revealed the location and distribution of stable paramagnetic species and the antioxidant activities in the shiitake mushroom for the first time.

Research program in nuclear and solid state physics. [including pion absorption spectra and muon spin precession

NASA Technical Reports Server (NTRS)

1974-01-01

The survey of negative pion absorption reactions on light and medium nuclei was continued. Muon spin precession was studied using an iron target. An impulse approximation model of the pion absorption process implied that the ion will absorb almost exclusively on nucleon pairs, single nucleon absorption being suppressed by energy and momentum conservation requirements. For measurements on both paramagnetic and ferromagnetic iron, the external magnetic field was supplied by a large C-type electromagnet carrying a current of about 100 amperes.

Isolation of EPR spectra and estimation of spin-states in two-component mixtures of paramagnets.

PubMed

Chabbra, Sonia; Smith, David M; Bode, Bela E

2018-04-26

The presence of multiple paramagnetic species can lead to overlapping electron paramagnetic resonance (EPR) signals. This complication can be a critical obstacle for the use of EPR to unravel mechanisms and aid the understanding of earth abundant metal catalysis. Furthermore, redox or spin-crossover processes can result in the simultaneous presence of metal centres in different oxidation or spin states. In this contribution, pulse EPR experiments on model systems containing discrete mixtures of Cr(i) and Cr(iii) or Cu(ii) and Mn(ii) complexes demonstrate the feasibility of the separation of the EPR spectra of these species by inversion recovery filters and the identification of the relevant spin states by transient nutation experiments. We demonstrate the isolation of component spectra and identification of spin states in a mixture of catalyst precursors. The usefulness of the approach is emphasised by monitoring the fate of the chromium species upon activation of an industrially used precatalyst system.

Models for aerobic carbon monoxide dehydrogenase: synthesis, characterization and reactivity of paramagnetic MoVO(μ-S)CuI complexes† †Electronic supplementary information (ESI) available: Synthetic yields and microanalytical, mass spectrometric and IR spectroscopic data for all new compounds. CCDC 1576257–1576260. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc04239f

PubMed Central

Gourlay, Craig; Nielsen, David J.; Evans, David J.; White, Jonathan M.

2017-01-01

Reaction of [CoCp2][TpiPrMoOS(OAr)] [Cp = η5-cyclopentadienyl; TpiPr = hydrotris(3-isopropylpyrazol-1-yl)borate; OAr = phenolate or derivative thereof] with [Cu(NCMe)(Me3tcn)]BF4 (Me3tcn = 1,4,7-trimethyl-1,4,7-triazacyclononane) in MeCN at –30 °C results in the formation of red-brown/black, paramagnetic, μ-sulfido-Mo(v)/Cu(i) complexes, TpiPrMoO(OAr)(μ-S)Cu(Me3tcn). The complexes possess the MoO(μ-S)Cu core found in aerobic carbon monoxide dehydrogenases (CODHs) and exhibit X-band EPR spectra closely related to those of semi-reduced CODH, with giso ∼ 1.937, hyperfine coupling to 95,97Mo (aiso = 39–42 × 10–4 cm–1) and strong superhyperfine coupling to 63,65Cu (aiso = 34–63 × 10–4 cm–1). Anisotropic spectra exhibit monoclinic symmetry with g1 ∼ 1.996, g2 ∼ 1.944 and g3 ∼ 1.882, and nearly isotropic ACu values (75–90 × 10–4 cm–1). The X-ray structures of four derivatives (Ar = Ph, C6H4tBu-2, C6H4sBu-2, C6H4Ph-4) are reported and discussed along with that of the Ar = C6H3tBu2-3,5 derivative (communicated in C. Gourlay, D. J. Nielsen, J. M. White, S. Z. Knottenbelt, M. L. Kirk and C. G. Young, J. Am. Chem. Soc., 2006, 128, 2164). The complexes exhibit distorted octahedral oxo-Mo(v) and distorted tetrahedral Cu(i) centres bridged by a single bent μ-sulfido ligand, with Mo–S and Cu–S distances and Mo–S–Cu angles in the ranges 2.262–2.300 Å, 2.111–2.134 Å and 115.87–134.27°, respectively. The 2 t-butyl derivative adopts a unique phenolate conformation with O 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000

A clinical case-based hypothesis: secretory IgA operates as an electronic transistor controlling the selection or rejection of molecules in the absorption process in the lumen of gastrointestinal tract

PubMed Central

Zamm, Alfred V

2013-01-01

There is a clinical correlation between (1) an allergic patient’s ability to resist the development of symptoms that would have resulted from an allergenic challenge, (2) the magnitude of geomagnetism at a geographic site, and (3) the amount of solar energy falling on that site. It is suggested that the digestive membrane has an electronic gatekeeper that “decides” electronically which molecules to allow or not allow to pass on to the absorptive surface. The unique bipolar structure of secretory immunoglobulin A (IgA), having a central secretory piece and the resultant unique electronic function of this polarized molecule, allows it to function as an electronic transistor, producing an electronic gatekeeper in the form of an electronic sieve. PMID:24068871

A clinical case-based hypothesis: secretory IgA operates as an electronic transistor controlling the selection or rejection of molecules in the absorption process in the lumen of gastrointestinal tract.

PubMed

Zamm, Alfred V

2013-01-01

There is a clinical correlation between (1) an allergic patient's ability to resist the development of symptoms that would have resulted from an allergenic challenge, (2) the magnitude of geomagnetism at a geographic site, and (3) the amount of solar energy falling on that site. It is suggested that the digestive membrane has an electronic gatekeeper that "decides" electronically which molecules to allow or not allow to pass on to the absorptive surface. The unique bipolar structure of secretory immunoglobulin A (IgA), having a central secretory piece and the resultant unique electronic function of this polarized molecule, allows it to function as an electronic transistor, producing an electronic gatekeeper in the form of an electronic sieve.

Alfven seismic vibrations of crustal solid-state plasma in quaking paramagnetic neutron star

SciTech Connect

Bastrukov, S.; Xu, R.-X.; Molodtsova, I.

2010-11-15

Magneto-solid-mechanical model of two-component, core-crust, paramagnetic neutron star responding to quake-induced perturbation by differentially rotational, torsional, oscillations of crustal electron-nuclear solid-state plasma about axis of magnetic field frozen in the immobile paramagnetic core is developed. Particular attention is given to the node-free torsional crust-against-core vibrations under combined action of Lorentz magnetic and Hooke's elastic forces; the damping is attributed to Newtonian force of shear viscose stresses in crustal solid-state plasma. The spectral formulas for the frequency and lifetime of this toroidal mode are derived in analytic form and discussed in the context of quasiperiodic oscillations of the x-ray outburst fluxmore » from quaking magnetars. The application of obtained theoretical spectra to modal analysis of available data on frequencies of oscillating outburst emission suggests that detected variability is the manifestation of crustal Alfven's seismic vibrations restored by Lorentz force of magnetic field stresses.« less

Improved paramagnetic chelate for molecular imaging with MRI

NASA Astrophysics Data System (ADS)

Winter, Patrick; Athey, Phillip; Kiefer, Garry; Gulyas, Gyongyi; Frank, Keith; Fuhrhop, Ralph; Robertson, David; Wickline, Samuel; Lanza, Gregory

2005-05-01

The relaxivity and transmetallation of two lipophilic paramagnetic chelates incorporated onto perfluorocarbon nanoparticles, i.e., gadolinium-methoxy-tetraazacyclododecane-tetraacetic acid phosphatidylethanolamine (Gd-MeO-DOTA-PE) and gadolinium-methoxy-tetraazacyclododecane-tetraacetic acid triglycine phosphatidylethanolamine (Gd-MeO-DOTA-triglycine-PE (Gd-MeO-DOTA-triglycine-PE)), were compared to a prototypic gadolinium-diethylene-triamine-pentaacetic acid bis-oleate (Gd-DTPA-BOA) paramagnetic formulation. Nanoparticles with MeO-DOTA-based chelates demonstrated higher relaxivity (40% higher for Gd-MeO-DOTA-PE and 55% higher for Gd-MeO-DOTA-triglycine-PE) and less transmetallation than the original Gd-DTPA-BOA-based agent.

Paramagnetic particles and mixing in micro-scale flows.

PubMed

Calhoun, R; Yadav, A; Phelan, P; Vuppu, A; Garcia, A; Hayes, M

2006-02-01

Mixing in microscale flows with rotating chains of paramagnetic particles can be enhanced by adjusting the ratio of viscous to magnetic forces so that chains dynamically break and reform. Lattice Boltzmann (LB) simulations were used to calculate the interaction between the fluid and suspended paramagnetic particles under the influence of a rotating magnetic field. Fluid velocities obtained from the LB simulations are used to solve the advection diffusion equation for massless tracer particles. At relatively high Mason numbers, small chains result in low edge velocities, and hence mixing is slower than at other Mason numbers. At low Mason numbers, long, stable chains form and produce little mixing toward the center of the chains. A peak in mixing rate is observed when chains break and reform. The uniformity of mixing is greater at higher Mason numbers because more small chains result in a larger number of small mixing areas.

Spin injection and spin transport in paramagnetic insulators

DOE PAGES

Okamoto, Satoshi

2016-02-22

We investigate the spin injection and the spin transport in paramagnetic insulators described by simple Heisenberg interactions using auxiliary particle methods. Some of these methods allow access to both paramagnetic states above magnetic transition temperatures and magnetic states at low temperatures. It is predicted that the spin injection at an interface with a normal metal is rather insensitive to temperatures above the magnetic transition temperature. On the other hand below the transition temperature, it decreases monotonically and disappears at zero temperature. We also analyze the bulk spin conductance. We show that the conductance becomes zero at zero temperature as predictedmore » by linear spin wave theory but increases with temperature and is maximized around the magnetic transition temperature. These findings suggest that the compromise between the two effects determines the optimal temperature for spintronics applications utilizing magnetic insulators.« less

X-ray absorption near edge structure/electron energy loss near edge structure calculation using the supercell orthogonalized linear combination of atomic orbitals method