Processes occurring during mechanochemical activation (MA) of {gamma}-Al{sub 2}O{sub 3} are studied by physicochemical methods. As a result of MA, the surface concentration of coordinatively unsaturated aluminum ions falls. The concentration of strong Lewis acid sites decreases by two orders of magnitude, and that of weak Lewis centers falls several times, whereas the bulk ...
Energy Citations Database
We present here new results together with an overview of the current knowledge on the coupled processes of electron and proton transfer in bacterial reaction centers. The importance of a multidisciplinary approach associating molecular genetics, structural biology, biochemistry and spectroscopy is underlined. We emphasize the electrostatic role of the protein to maintain a ...
The decomposition of dimethyl and diethyl disulfides on solid catalysts at elevated temperatures in a He or H{sub 2}S medium results mainly in the formation of alkanethiols. The reaction is supposed to involve the donor-acceptor interaction of the sulfur atom of the disulfide with the acid center of the catalyst with the subsequent ...
The formation of hydrogen (H)-related complexes was investigated in boron (B)-doped Si treated with high concentration of H. The isotope shifts of H-related Raman peaks by replacement of H to deuterium and 10B to 11B clearly showed the formation of the B H complexes in which H directly bonds to B in Si. The results of the resistivity measurements suggested ...
NASA Astrophysics Data System (ADS)
Ab initio supercell calculations of the binding energies predict complex formation between aluminum and carbon interstitials in SiC. In high-energy implanted SiC aluminum acceptor can form very stable complexes with two carbon interstitials. We also show that carbon vacancy can be attached to shallow aluminum acceptor. All of these ...
We used luminescent CdSe-ZnS core-shell quantum dots (QDs) as energy donors in fluorescent resonance energy transfer (FRET) assays. Engineered maltose binding protein (MBP) appended with an oligohistidine tail and labeled with an acceptor dye (Cy3) was immobilized on the nanocrystals via a noncovalent self-assembly scheme. This configuration allowed accurate control of the ...
PubMed
We have investigated the spatial distribution of different transitions identified in the emission spectra of CdTe thin films and solar cells by cathodoluminescence spectroscopic imaging (CLSI). Prior to back-contact deposition, the spectra are dominated by excitons (X) and donor-to-acceptor (DAP) transitions. After contacting, Cu acceptor states are ...
... Descriptors : (*COMPLEX COMPOUNDS, *HEAT OF FORMATION), (*SILICON COMPOUNDS, COMPLEX COMPOUNDS), (*GERMANIUM ...
DTIC Science & Technology
... Title : Radical Ion Formation in ... ELECTRON ACCEPTORS, TRANSFER, KINETICS, BEHAVIOR ... PHYSICAL CHEMISTRY POLYMER CHEMISTRY. ...
Several unknown, hydrogenic acceptors and donors were recently discovered in ultra-pure germanium by photoelectric spectroscopy. These centers are not created by elemental impurities. Comparative analysis of a large number of crystals grown under various conditions lead to the conclusion that copper, a fast diffusing multivalent ...
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The structure for the ground state of the AX deep acceptor center in II-VI semiconductors is identified and the sign of its formation energy is found to be a reliable indicator of p-type dopability. Results from ab initio total-energy calculations on ZnS, ZnSe, ZnTe, and CdTe doped with N, P, As, or Sb show that the tendency for deep ...
The formation of hydrogen (H) related complexes and their effect on boron (B) dopant were investigated in B-ion implanted and annealed silicon (Si) substrates treated with a high concentration of H. Isotope shifts by replacement of B10 with B11 were observed for some H-related Raman peaks, but not for other peaks. This shows proof of the formation of ...
We report on the results of a complex study of electrical (77-300 K) and luminescence (10-300 K) properties of n-ZnSe single crystals annealed in a Zn melt containing Al impurity at concentrations ranging from 0.1 to 80 at. %. It was established that Al atoms form donor centers only at a low impurity concentration (<=0.5 at. %). The increase of the amount of Al atoms in the ...
The donor-acceptor interactions of iodine chloride with uni- and multi-dentate linear and cyclic ethers are all of the same character. The enthalpies of formation of the corresponding complexes are close in value. Depending on the number of donor centers and the conformations of the polyfunctional ethers investigated, with ICI these ...
A comprehensive study of single native point defects in hexagonal silicon nitride (?-Si3N4) has been carried out based on density functional calculations of formation energies. Both nitrogen- and silicon-rich native defect centers form donor and acceptor states in the band gap of ?-Si3N4, confirming their amphoteric behavior. Silicon ...
When a negatively charged muon is captured by a silicon atom, the atom is transformed into a solitary acceptor center similar to an Al atom. An external electric field influences the formation process of the neutral acceptor center (A.C.). It is shown in this article that the behaviour of the ...
Proton implantation in GaN is found to reduce the free carrier density through two mechanisms - first, by creating electron and hole traps at around Ec-0.8eV and Ev+0.9eV that lead to compensation in both n- and p-type material, and second, by leading to formation of (AH)O complexes, where A is any acceptor (Mg, Ca, Zn, Be, Cd). The former mechanism is ...
It is shown by Hall measurements that quenching complexly doped Ge1 ? x Si x (0 ? x ? 0.20) crystals from 1050-1080 K leads to the formation of additional electroactive acceptor centers in them. The activation energy of these centers increases linearly with an increase in the silicon content in the ...
An analysis is made of some aspects of defect formation in laser semiconductor crystals under conditions of capture of nonequilibrium carriers by the resonance level of a deep center. Calculations are made of the resonance level width GAMMA/sub n/ with respect to electron autoionization for the cases of acceptor and donor ...
The purpose of this study was to explore how the mitochondrial AOX (alternative oxidase) pathway alleviates photoinhibition in Rumex K-1 leaves. Inhibition of the AOX pathway decreased the initial activity of NADP-malate dehydrogenase (EC 1.1.1.82, NADP-MDH) and the pool size of photosynthetic end electron acceptors, resulting in an over-reduction of the PSI ...
Using first-principles calculations we have studied the electronic and structural properties of cation vacancies and their complexes with hydrogen impurities in SnO(2), In(2)O(3) and ?-Ga(2)O(3). We find that cation vacancies have high formation energies in SnO(2) and In(2)O(3) even in the most favorable conditions. Their formation energies are ...
Using first-principles calculations we have studied the electronic and structural properties of cation vacancies and their complexes with hydrogen impurities in SnO2, In2O3 and ?-Ga2O3. We find that cation vacancies have high formation energies in SnO2 and In2O3 even in the most favorable conditions. Their formation energies are significantly lower in ...
The enzymatic transfer of activated mannose yields mannosides in glycoconjugates and oligo- and polysaccharides. Yet, despite its biological necessity, the mechanism by which glycosyltransferases recognize mannose and catalyze its transfer to acceptor molecules is poorly understood. Here, we report broad high-throughput screening and kinetic analyses of both natural and ...
Photoinduced, multistep charge separation in bacterial reaction centers proceeds from the lowest excited singlet state of the dimeric bacteriochlorophyll electron donor in two steps, to yield a weakly interacting dimer cation-quinone anion radical pair, P{sup +}-Q{sup {minus}}, separated by 28 {angstrom}. Recently, we developed criteria for achieving high quantum yield charge ...
The spinel cobalt aluminate has gained interest as a potential photoelectrochemical catalyst for the renewable production of hydrogen. Using band structure theory, we determine the energetics of possible intrinsic point defects in spinel CoAl{sub 2}O{sub 4} and analyze their effect on its electronic and chemical properties. Extrinsic Fe-doping is also examined. Cation vacancies are found to be ...
The phenomenon of recombination-induced formation of hydrogen-defect complexes in epitaxial silicon carbide (SiC) was further investigated on p-type samples treated in deuterium plasma. Qualitatively similar effects were observed for hydrogen and deuterium. The formation of hydrogen-related (deuterium-related) defects would depend on the temperature of the ...
Mg+ ions were implanted into highly pure InP grown by the liquid encapsulated Czochralski (LEC) method in which the Mg concentration [Mg] was varied between 1�1015 cm?3 and 3�1020 cm 3. Two annealing methods were used: furnace annealing (FA) up to 740� C and flash lamp annealing (rapid thermal annealing, RTA) up to 900� C. For characterization, photoluminescence (PL) spectra were measured ...
Abstract: ... polyaryl sulfone, chlorinated polyvinyl chloride ... as an organic amine and an electron acceptor compound such as nitroaromatic compound. ...
NASA Website
ESR has been used in studying the distribution of electron acceptor centers in mordenite in relation to the method of its decationization and dealuminizaion. Data from x-ray structure analysis have been compared with the ESR data. A relationship has been found between the decrease in number of electron acceptor ...
Though investigated for decades, interest in push-pull chromophores (D-pi-A), strong electron donors (D) connected by pi-conjugating spacers to strong electron acceptors (A), continues to grow. Such chromophores are of substantial interest for optoelectronic devices such as waveguides. Also, strong donors and acceptors form bimolecular charge-transfer (CT) ...
Donor-acceptor complexes of borazine (BZ) and its substituted derivatives with Lewis acids (A = MCl(3), MBr(3); M = B, Al, Ga) and Lewis bases (D = NH(3), Py) have been theoretically studied at the B3LYP/TZVP level of theory. The calculations showed that complexes with Lewis bases only are unstable with respect to dissociation into their components, while complexes with Lewis ...
EPR was used to study the influence of formate on the electron acceptor side of photosystem II (PSII) from Thermosynechococcus elongatus. Two new EPR signals were found and characterized. The first is assigned to the semiquinone form of Q(B) interacting magnetically with a high spin, non-heme-iron (Fe�(+), S=2) when the native bicarbonate/carbonate ...
We study from first principles the energetics, complex formation, and diffusion of Al in crystalline Si. We first consider the interaction of Al with self-interstitials Sii : at variance with B and In, the complex formed by substitutional AlSi and a self-interstitial Sii is metastable and trasforms into interstitial Ali in the tetrahedral site. Therefore in the ...
We present a study of the electronic properties of narrow zigzag and armchair nanoribbons substitutionally doped with a single boron, nitrogen, or phosphorus atom. Using density functional calculations, we analyze the formation energy, electronic band structures, magnetic, and quantum conductance properties of these nanoribbons with doping site positions ranging from the edge ...
In this letter we describe an unusual result in terms of regioselectivity with respect to copper-catalyzed conjugate additions of various Grignard reagents to cyclic enynones. The use of Cu(OTf)(2) and NHC ligand L1 as the catalyst combination in CH(2)Cl(2) led to the unique formation of the 1,4 adduct. This selectivity does not follow the general trend previously observed in ...
The effect of Fe2O3-doping on the defect structure and piezoelectric properties of [Bi0.5Na0.5]TiO3 ceramics is studied by means of electron paramagnetic resonance spectroscopy. The results show that the Fe3+ functional centers are incorporated at the perovskite B-site, and clearly can be attributed to the formation of (FeTi'-VO��)� defect complexes ...
Many of the physical phenomena surrounding Complex Oxide involve the creation and annihilation of charge carriers by cross --substitution of atoms or by the formation of vacancies and interstitials. We have used the machinery of First-Principles defect calculation, developed and tested over the years on semiconductors (where experimental data needed to test DFT corrections is ...
Pressure is shown to have a drastic effect an the annealing characteristics of p-type, nitrogen-doped ZnSe. Samples annealed in vacuum show decreased carrier concentrations and simultaneous formation of deep-donor-related luminescence, while samples annealed under pressure show suppression of this compensating donor. Results are interpreted as an increase in the ...
Luminescence lifetimes ([tau][sub m]) of the [sigma]-bond-to-ligand charge-transfer (SBLCT) excited states of two diastereomers of fac-tris[(8-quinolyl)phenylmethylsilyl]iridium(III) differ by about a factor of 2 and are strongly solvent dependent. The [tau][sub m] values of the more symmetric [Delta]RRR, [Lambda]SSS diastereomer (A) are generally longer than those of the less symmetric ...
Multi-frequency and pulsed electron paramagnetic resonance (EPR) provides a sensitive spectroscopic tool to elucidate the defect structure of transition-metal doped perovskite oxides, as well as to monitor dynamic processes of oxygen vacancies in these materials. In this regard, high-frequency EPR spectrometers and pulsed EPR techniques such as the hyperfine sublevel correlation experiment ...
Impurity clouds in germanium are formed by acceptor centers. This conclusion is important for the understanding of the mechanism of charge losses in germanium detectors of nuclear radiation.
The use of the univalent indium reagent [In([18]crown-6)][OTf] as a donor is investigated by its reactions with acceptors including InX(3) (X=Cl, Br, I). The donor-acceptor complexes of the form [X([18]crown-6)In-InX(3)] obtained in this manner represent the first new isomeric form of indium(II) halides identified for at least five decades. The ...
This research addressed electron transfer in photosynthetic reaction centers. Specifically, the nature of the medium that lies between the electron donors and acceptors in the reaction centers has been studied. The approach was to synthesize four fixed-distance porphyrin-quinone molecules in order to study the effects of changing the ...
Light induced damage of the photosynthetic apparatus is an important and highly complex phenomenon, which affects primarily the Photosystem II complex. Here the author summarizes the current state of understanding of the molecular mechanisms, which are involved in the light induced inactivation of Photosystem II electron transport together with the relevant mechanisms of photoprotection. Short ...
An all-inorganic heterobinuclear chromophore consisting of Ti(IV) oxo-bridged to a Mn(II) center has been assembled on the surface of silica pores of MCM-41 material. The key step of covalent attachment on the pore surface is the reaction of a Mn(II) precursor featuring weakly held CH3CN ligands with the OH group of a previously anchored titanol site. The optical diffuse ...
In reaction center proteins of photosynthetic bacteria, the amplitude of proton uptake induced by the one-electron reduction of either of the two quinone electron acceptors (Q{sub A} and Q{sub B}) is an intrinsic observable of the electrostatic interactions associated with the redox function of the complex. We report here that, in Rhodobacter capsulatus, ...
First-principles results are presented for various native defects in CdGeAs2 as function of the relevant elements� chemical potentials. The defect formation energies were calculated using fully relaxed 64 atom supercells by means of the full-potential linearized muffin-tin orbital implementation of the density-functional theory in the local-density approximation (LDA). The ...
The ratio between the stage equilibrium constants in the successive addition reactions of ICl molecules with the sulfides C/sub 4/H/sub 9/S(SC/sub 2/)/sub n/SC/sub 4/H/sub 9/ depends on the value of n. With n greater than or equal to 5, K/sub 1/:K/sub 2/ = 2, which agrees with the theoretically expected value for the case where there is no mutual influence of the reaction ...
Presented at the 2001 NCPV Program Review Meeting: A theoretical study of the doping limits of CdTe. First-principles total energy and band structure calculations are performed to understand the factors that limit doping in CdTe. We calculated systematically the formation energies and transition energy levels of intrinsic and extrinsic defects. We find that n-type doping in ...
The group-III nitrides have important commercial applications in optoelectronic devices. To achieve high-efficiency UV lasers and LEDs, AlN substrates and high Al-content AlGaN alloys will likely be required. A better understanding of the role of defects and impurities in AlN is crucial. One of the outstanding problems in the study of AlN and high-Al-content AlGaN is the ...
The intermediate products of the radiolysis of potassium 3-sulfolanyldithiocarbamate and sulfolane were studied by the method of pulsed radiolysis with optical recording. It was found that the hydrated electron adds to the sulfonyl and dithiocarbamate groups to form anion radicals A and B, which have maximal absorption at /lambda//sub max/ /equals/ 600 and 315 nm, respectively. The kinetic ...
Molecular complexes of substituted indoles with (pi) *-acceptors have been investigated by means of Fourier Transform Infrared Spectroscopy. The formation constants of the complexes, evaluated on characteristic vibrational modes of the acceptors, are in substantial agreement with those determined by optical spectroscopy and nuclear ...
In bacterial photosynthetic reaction centers, the protonation events associated with the different reduction states of the two quinone molecules constitute intrinsic probes of both the electrostatic interactions and the different kinetic events occurring within the protein in response to the light-generated introduction of a charge. The kinetics and stoichiometries of proton ...
... Abstract : Cellular d-graph languages are shown to be closed under set ... of arc end numbering, concatenation, closure, and formation of line graphs. ...
Experimental results on hole capture in germanium are reviewed; good agreement is found not only among various investigators for the same center, but among different acceptors regardless of charge state. For these acceptors, the capture cross section depends only on temperature (~T-1). Collision theory is used to transform temperature ...
Hybrid cells based on ZnO/P3HT heterojunctions have the advantage of better device stability, but suffer poor photovoltaic performance compared to all-organic cells which use PCBM as the electron acceptor. The photovoltaic effect in these hybrid systems is accomplished via photoinduced charge separation at the interface between the absorbing polymer (P3HT) and the electron ...
Carbon-doped InAs samples grown by organometallic vapor phase epitaxy were studied by Raman and IR spectroscopy. Local vibrational modes (LVMs) related to isolated substitutional carbon acceptors, carbon acceptor-hydrogen complexes, and dicarbon centers were detected in samples doped with two isotopes of carbon. Energies of the ...
In the bacterium R. sphaeroides, the polypeptide PufX is indispensable for photosynthetic growth. Its deletion is known to have important consequences on the organization of the photosynthetic apparatus. In the wild-type strain, complexes between the reaction center (RC) and the antenna (light-harvesting complex 1 (LH1)) are associated in dimers, and LH1 does not fully ...
... In this case the rate of F-center formation is dependent on the number of F centers bleached by the preceding optical bleaching but not on the kind ...
In studying thermodonors-II (TD-II) in oxygen-containing Si crystals with a high carbon content we detected an extensive set of centers with thermal ionization energy element of = 0.019-0.21 eV. This communication is devoted to a comprehensive study of the distinctive features of the formation, destruction, and properties of TD-II's in such ...
... Center PNR Point-of-No Return (duration after which thermal cookoff is inevitable) °R degrees Rankin sec or s seconds SCG Storage Comptibility ...
The introduction of boron on the arsenic site in gallium arsenide, as monitored by the strength of its local vibrational modes (LVM) at 601.7 and 628.3 cm/sup -1/, has been observed as a function of 2 MeV electron fluence. Simultaneous monitoring of the strength of the 1S-2P electronic transitions of the neutral shallow acceptors and of the neutral 78 meV ...
The electrical characteristics and persistent-conductivity effects in MgZnO:P alloys grown by the method of pulsed laser deposition on undoped n-ZnO substrates are systematically investigated. It is shown that the pronounced persistent conductivity and the persistent photocapacitance related to the presence of high-barrier electron traps for electron capture are observed in initial unannealed ...
We study the existence of Li-related shallow and deep acceptor levels in Li-doped ZnO nanocrystals using electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. ZnO nanocrystals with adjustable Li concentrations between 0% and 12% have been prepared using organometallic precursors and show a significant lowering of the Fermi energy upon doping. The deep ...
The charge transfer complexes of the donor p-toluidine with ?-acceptor picric acid have been studied spectrophotometrically in various solvents such as acetone, ethanol, and methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CTC in less polar solvent is high. The stoichiometry of the complex was found to ...
The interaction between substitutional and interstitial donors and single or double acceptors in Si, GaAs, InP, and InAs has been studied by perturbed angular correlation spectroscopy (PAC). For the case of Si, complex formation between substitutional donors (As, P) and different radioactive acceptors (111In, 111Cd, 117Cd) has been ...
Molybdenum is widely available to biological systems due to the solubility of its high-valent oxides in water and is found in two basic forms: as an integral component of the multinuclear M center of nitrogenases and as the mononuclear active sites of a much more diverse group of enzymes that in general function catalytically to transfer an oxygen atom either to or from a ...
To ascertain the nature of the transannular Si /l arrow/ N bond in molecules of the atrane type and the possibility of its description in semiempirical MO methods we calculated the 1-methylsilatrane (I), trimethylamine (II), triethylamine (III), triethanolamine (IV), trimethoxymethylsilane (V), triethoxymethylsilane (VI), and N,N-dimethylaminotrimethoxysilane (VII) molecules by the CNDO/2 and INDO ...
The highest equilibrium free-carrier doping concentration possible in a given material is limited by the ''pinning energy'' which shows a remarkable universal alignment in each class of semiconductors. Our first-principles total energy calculations reveal that equilibrium n -type doping is ultimately limited by the spontaneous formation of ...
The standard theory of the electron transfer between donor and acceptor molecules was used to describe oscillations in the reduction kinetics of the intermediate electron acceptor BA and the primary electron acceptor HA. The kinetics of the reduction of BA and HA were simulated on the basis of the model in which one and two accepting ...
We present a study of the electronic properties of narrow zigzag and armchair nanoribbons substitutionally doped with a single boron, nitrogen, or phosphorus atom. Using density-functional calculations, we analyze the formation energy, electronic band structure, magnetic, and quantum conductance properties of these nanoribbons with doping sites ranging from the edge to the ...
One of the main obstacles to the technical application of the wide-gap semiconductor ZnO represents the difficulty to achieve reliable and sufficient p-type doping. The theoretically proposed concepts of cluster-doping or codoping should lead to an enhanced and stable p-type conductivity of ZnO. We report on PAC results obtained by codoping experiments of ZnO by ion implantation using the donor ...
Electronic energy band structure of In-doped ZnO transparent conducting oxide was investigated by density functional calculations using local density approximation+Hubbard U (LDA+U) scheme. By systematically calculating the formation energies and transition energy levels of In atom and In-related complex in ZnO, it has been shown that the substitutional In atom has a low ...
The efficient use of luminescent semiconductor quantum dots (QDs) as F�rster Resonance Energy Transfer (FRET) acceptors can be accomplished with terbium complexes (TCs) as donors. TCs exhibit long excited state lifetimes (in the millisecond range) up to 105 times longer than typical QD lifetimes. When FRET occurs from TCs to QDs the measured TC luminescence decay times ...
Mild synthetic methods are demonstrated for the selective assembly of oxo-bridged heterobinuclear units of the type TiOCrIII, TiOCoII, and TiOCeIII on mesoporous silica support MCM-41. One method takes advantage of the higher acidity and, hence, higher reactivity of titanol compared to silanol OH groups towards CeIII or CoII precursor. The procedure avoids the customary use of strong base. The ...
Mild synthetic methods are demonstrated for the selective assembly of oxo-bridged heterobinuclear units of the type TiOCr{sup III}, TiOCO{sup II}, and TiOCe{sup III} on mesoporous silica support MCM-41. One method takes advantage of the higher acidity and, hence, higher reactivity of titanol compared to silanol OH groups toward Ce{sup III} or CO{sup II} precursors. The procedure avoids the ...
Photosystem II (PSII), the first supercomplex of the electron transport chain, governs the energy transfer using harvested light energy, which is transformed into biochemical energy. Phosphatidylglycerol and sulfoquinovosyl diacylglycerol, the anionic lipids of photosynthetic organisms, together with a neutral lipid, digalactosyldiacylglycerol, assist in the assembly of photosynthetic complexes. ...
A detailed study of as-grown Zn-doped GaN employing optically detected magnetic resonance (ODMR) spectroscopy is presented. Besides the well-known ODMR spectra of an effective-mass-like donor and Zn acceptor, a positive ODMR signal of an S=12 paramagnetic center was observed when monitoring the dominating blue luminescence band peaking at 2.8 eV. The ...
Recent progresses of the studies of isolated hydrogen center in ZnO and GaN by muon spin rotation methods are reported. Preliminary experimental results for shallow muonium hunting as an acceptor in InSb and GaSb are also discussed.
We investigate theoretically light- and bias-induced metastabilities in Cu(In,Ga)Se2 (CIGS) based solar cells, suggesting the Se-Cu divacancy complex (VSe-VCu) as the source of this hitherto puzzling phenomena. Due to its amphoteric nature, the (VSe-VCu) complex is able to convert by persistent carrier capture or emission from a shallow donor into a shallow acceptor ...
Ab initio supercell calculations have been carried out to investigate the complexes of boron acceptors with carbon self-interstitials in cubic silicon carbide. Based on the calculated binding energies, the complex formation of carbon interstitials with shallow boron acceptor and boron interstitial is energetically favored in silicon ...
Mid-infrared spectral changes associated with the photoreduction of the bacteriopheophytin electron acceptor H(A) in reaction centers (RCs) of the filamentous anoxygenic phototrophic bacterium Chloroflexus (Cfl.) aurantiacus are examined by light-induced Fourier transform infrared (FTIR) spectroscopy. The light-induced H(A)(-)/H(A) FTIR (1800-1200cm(-1)) ...
PubMed Central
An explosive plane-wave air lens which enables a spherical wave form to be converted to a planar wave without the need to specially machine or shape explosive materials is described. A disc-shaped impactor having a greater thickness at its center than around its periphery is used to convert the spherical wave into a plane wave. When the wave reaches the impactor, the ...
As a prelude to studies of 'externally facilitated' superexchange coupling in energy- and electron-transfer processes, a series of crown-linked donor-acceptor (D-A) complexes have been prepared. Photoexcitation at the rhenium-pyridyl center leads to intramolecular charge transfer across the crown spacer to the remote ...
Photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides capture solar energy by electron transfer from primary donor, D, to quinone acceptor, Q(B,) through the active A-branch of electron acceptors, but not the inactive B-branch. The light induced EPR spectrum from native RCs that had Fe(2+) replaced by Zn(2+) was ...
A new synthesis of 2-alkoxy-1,1-cyclobutane diesters and their first use in dipolar cycloadditions is reported. Both the formation of the donor-acceptor cyclobutanes and their subsequent annulation with in situ formed imines are catalyzed by Yb(OTf)(3). Cyclobutanes with carbon donor groups give piperidines with high trans stereoselectivity. PMID:20925412
on the structures of hydrogen bonded water patterns4 we did consider the question of a predictive rule, but could that water molecules in the CSD prefer to form the pattern of two donor hydrogen bonds and 1 acceptor as donor (D) and acceptor (A). We show the distribution of the total number of hydrogen bonds per water
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A process is described for producing halocarbons which comprises passing a halogen acceptor and a halocarbon reactant over an acidic, crystalline aluminosilicate zeolite catalyst having a constraint index of 1 to 12 and a silica:alumina ratio of at least 12:1 to form a halogenated product by halogenation of the halogen acceptor.
(ADP-ribose) polymerases (PARPs) (43). PARPs catalyze formation of long chains of poly(ADP-ribose) onto protein acceptors the properties of the protein acceptor. In addition to the PARP domain at the C terminus, tankyrase 1 contains-protein interactions (38). Tankyrase 1 uses its ankyrin domain to bind TRF1 and its PARP domain to ADP
Incubation of Fe(II) cations with Mn-depleted PSII membranes (PSII(-Mn)) under weak continuous light is accompanied by blocking of the high-affinity, Mn-binding (HAZ) site with ferric cations (Semin, B.K. et al. Biochemistry 2002, 41, 5854-5864). In this study we investigated the blocking yield under single-turnover flash conditions. The flash-probe fluorescence method was used to estimate the ...
The electron donor-acceptor (EDA) interactions were studied using p-phenylenediamine as donor and polyoxyethylene-sorbitan-monolaurate (Tween 20), polyoxyethylene-sorbitan-monopalmitate (Tween 40), polyoxyethylene-sorbitan-monostearate (Tween 60) and polyoxyethylene-sorbitan-monooleate (Tween 80) as acceptor in micellar and reverse micellar environments. A ...
Charge transfer complexes between colchicine as donor and pi acceptors such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), p-chloranil (p-CHL) have been studied spectrophotometrically in dichloromethane at 21 degrees C. The stoichiometry of the complexes was found to be 1:1 ratio by the Job method between donor and acceptors ...
We investigated optical properties of Sb-doped p-type ZnO films grown on n-Si (100) substrates by oxygen plasma-assisted pulsed laser deposition. Two acceptor states, with the acceptor levels of 161 and 336 meV, are identified by well-resolved photoluminescence spectra. Under oxygen-rich conditions, the deep acceptor in Sb-doped ZnO ...
There remains considerable interest in the behavior of acceptors in ZnO, the ultimate goal being the realization of device grade p-type material. Silver is a candidate acceptor, and, in this study, in situ doping of silver was performed during plasma-assisted molecular beam epitaxy. Silver concentrations, as determined by ion beam analysis, ranged between ...
The enthalpy of mixing is a reliable experimental characteristic of interactions in solution. However, no satisfactory correlation has yet been established between the donor-acceptor properties of solvents and the thermodynamic functions of mixing with hydrocarbons. In order to arrange hydrocarbons and solvents in series in accordance with their ...
Organic donor/acceptor bilayers form a two-dimensional charge sheet composed of electron-hole pairs at their heterointerfaces due to formation of charge-transfer (CT) complexes. The CT induces electron-hole pairs which are useful for carrier transport in both vertical and lateral direction, providing novel electronic device applications. Here, we ...
This work discusses the synthesis, photophysical behavior, and photoinduced electron-transfer reactivity of multichromophoric molecules having a visible-light-absorbing MLCT component coupled to a ligand with a localized excited state of the same spin multiplicity that serves to lengthen the excited-state lifetime of the complex significantly. The appropriate ligands were prepared by Wittig ...
Metalloradical EPR signals have been found in intact Photosystem II at cryogenic temperatures. They reflect the light-driven formation of the tyrosine Z radical (Y(Z)) in magnetic interaction with the CaMn(4) cluster in a particular S state. These so-called split EPR signals, induced at cryogenic temperatures, provide means to study the otherwise transient Y(Z) and to probe ...
Fluorescence of aromatic molecules in solid solutions at room temperature and low temperature is quenched by addition of strong electron donors. The efficiency of quenching correlates well with calculated energetics for electron transfer (ET) from the added donors to the excited molecules, D + A* ..-->.. D/sup +/ + A/sup -/. The quencher (D) always had a substantially higher-lying excited state ...
The effect of multivalency manganese doping on the defect structure and enhanced electrical resistivity is studied for the high-temperature piezoelectric (1?x)BiScO3�xPbTiO3 (BSPT) solid-solution system by means of multifrequency electron paramagnetic resonance spectroscopy combined with conductivity measurements. The results show that manganese is rather incorporated on a scandium than a ...
It is shown that vibrational coherence modulates the femtosecond kinetics of stimulated emission and absorption of reaction centers of purple bacteria. In the DLL mutant of Rhodobacter capsulatus, which lacks the bacteriopheophytin electron acceptor, oscillations with periods of approximately 500 fs and possibly also of approximately 2 ps were observed, ...
Donor-acceptor blends based on conjugated polymers are the heart of state-of-the-art polymer solar cells, and the control of the blend morphology is crucial for their efficiency. As the film morphology can inherit the polymer conformational state from solution, the approaches for probing and controlling the polymer conformational state in the blends are of high importance. In ...
In the maltose-acceptor reaction of Leuconostoc mesenteroides B-512FM dextransucrase, some of the D-glucose moieties of sucrose are diverted from the synthesis of dextran and are transferred to the nonreducing end of maltose to form panose. Glucose is also transferred to panose and to subsequent acceptor products to give a homologous series of isomaltosyl ...
The formation and decay of the optical hole (bleach) for 4 nm CdSe nanoparticles (NPs) with adsorbed electron acceptors (1,4-benzoquinone and 1,2-naphthoquinone) and the rise and decay of the reduced electron acceptors formed after interfacial electron transfer from the CdSe NPs were investigated by femtosecond laser spectroscopy. The ...
The role of the accessary bacteriochlorophyll bridging the gap between the primary donor and bacteriopheophytin acceptor is examined. Experimental data based on magnetic interactions in the radical pair formed between primary donor and primary acceptor is presented which is consistent with the bridging bacteriochlorophyll providing a site of superexchange. ...
The Medusa(TM) Sequencer consists of a DNA or RNA polymerase functionalized at each end with a pair of flexible, long chain groups. At the end of each group is a nonhydrolyzable nucleotide and a spectrally distinct Forster Resonance Energy Transfer (FRET) acceptor fluorophore. A FRET donor fluorophore is attached to the polymerase and can excite the ...
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resistivities. The density of centers has been taken as 1012 cm 3 . Curves for interstitial iron (FeiCapture cross sections of the acceptor level of iron�boron pairs in p-type silicon by injection of iron-diffused, boron-doped silicon wafers of different resistivities are used to determine the electron
State-of-the-art STM techniques have made it possible to substitute transition metal impurities for individual atoms in semiconductor crystals and have provided detailed information on the nature of the bound acceptor or donor states. Individual coupled acceptor (or donor)-impurity centers represent a new class of nanomagnets which we ...
In organic photovoltaics with a mixed donor and acceptor structure, the junction property is directly related to the morphology because charge transportation is determined by the formation of inter penetrating networks. Therefore, structural studies are very important to understand the fundamental problems in mixed donor and acceptor ...
Developing new acceptor materials as alternatives to fullerene acceptors remains a challenge in the field of organic photovoltaics. We report on the synthesis and optoelectronic properties of three acceptor polymers bearing diketopyrrolopyrrole units in the main chain (PA, PB and PC). Their performance as the ...
The introduction of chloranil into coal leads to the formation of stable donor acceptor complexes. The properties of adducts with chloranil of high-rank coal and of the residual coal after pyridine extraction were obtained. 2 refs., 4 figs., 2 tabs.
The photochemistry of valeraldehyde was examined in the presence of the electron acceptors paraquat(1,1'-dimethyl-4,4'-bipyridylium) ions and 4-carboxy-1-methylpyridynium. Kinetic data for the trapping of biradicals by the compounds are shown in a graph.
... above were simply divided by the free HFIP remaining (Taft et al. ... Acceptor K e log K eq Ref. Dimethyl ethyl phosphonate 1680 3.23 t 0.10 Taft et al. ...
Jan 22, 2011 ... Donor-acceptor polyenes displaying a wide BLA range were synthesized. en_US. dc. format.extent, 388536 bytes, - ...
A photosystem I (PS I) particle has been prepared by lithium dodecyl sulfate digestion which lacks the acceptor X, and iron-sulfur centers B and A. Illumination of these particles at liquid helium temperature results in the appearance of a light-induced spin-polarized triplet signal observed by EPR. This signal is attributed to the triplet state of P-700, ...
The origins and properties of deep-level defects associated with native disorder and transition-metal impurities in LEC and VPE InP were studied. Native defects and related complexes were examined in 1- 2-MeV electron-irradiated n and p-type crystals. Primary native defects were found to be unstable at 298 K. The dependence of total defect introduction rates on acceptor ...
The one-electron reduction of Co(III) complexes containing nitrophenyl ligands possessing differing lead-in and bridging groups by radiolytically generated CO/sub 2//sup -/ and C(CH/sub 3/)/sub 2/OH radicals in neutral and acidic aqueous solution results in the formation of coordinated nitrophenyl ligand radicals. The uv-visible absorption spectra, the acid-base properties, ...
Besides the resonance lines attributable to tetrahedrally (Al[sup IV]) and octahedrally (Al[sup VI]) coordinated aluminum, the MAS NMR[sup 27]Al spectra of transition aluminas obtained from finely divided precursors gibbsite and boehmite have a line which can be assigned to pentacoordinated Al(Al[sup v]). This line which is very intense en ex-boehmite aluminas, as compared to ex-gibbsite aluminas, ...
2,4,6-Trihydroxybenzoic acid (FA) is the carboxylic acid of phloroglucinol and, in turn, the parent compound of many biologically active compounds. The biological activities of FA are "extreme" among trihydroxybenzoic acids (e.g., lowest antioxidant activity, highest toxicity toward crustaceans). A complete MP2/6-31++G(d,p) conformational study in vacuo shows that the lowest energy conformers ...
[(ttpy)Os(tpy-ph-TPH(3)(+))](3+) (2), [(ttpy)Os(tpy-xy-TPH(3)(+))](3+) (3), [(ttpy)Os(tpy-ph-TPH(2)(NO(2))(+))](3+) (4), and [(ttpy)Os(tpy-xy-TPH(2)(NO(2))(+))](3+) (5) are a series of dyads made of an Os(II) bis-tpy complex (tpy = 2,2':6',2"-terpyridine) as the photosensitizer (P) and 2,4,6-triarylpyridinium group (TP(+)) as the electron acceptor (A). These dyads were ...
This paper studies the effect of substituents at the tin atom and triple bond on the comp exing capacity of acetylenylstannanes relative to iodine. The action of iodine on trialkylacetylenylstannanes with one, two and three tert-butyl groups at the tin atom containing alkyl or heteroorganic groups (with a silicon subgroup element) were studied as were halogens or hydrogen at the opposite end of ...
2,3-Di-O-benzyl-4,6-O-benzylidene-thiohexopyranosides, on activation with 1-benzenesulfinyl piperidine and triflic anhydride, react with allyl silanes and stannanes, and with silyl enolethers to give C-glycosides. In mannose the ?-isomers are formed selectively whereas the glucose series provides the ?-anomers. This selectivity pattern parallels that of O-glycoside formation ...
Low temperature (77-90 K) measurements of absorption spectral changes induced by red light illumination in isolated photosystem II (PSII) reaction centers (RCs, D1/D2/Cyt b559 complex) with different external acceptors and in PSII core complexes have shown that two different electron donors can alternatively function in PSII: chlorophyll (Chl) dimer P(680) ...
The tendency of asphaltenes to associate, accompanied by the formation of stable supermolecular formations, to a great degree determines the methods of processing and using residual petroleum fractions. For this reason, investigators have been continuously interested in establishing the nature of binding of asphaltene molecules in these primary ...
Intron A of the human growth hormone gene does not contain an A residue within 56 nucleotides preceding the 3' splice site. The analysis of the excised intron lariat revealed a C residue 28 nucleotides upstream from the 3' splice site as the major branch acceptor nucleotide. Two additional minor branched nucleotides were identified as U residues at positions ...
Rate constants for both radical ion pair formation and recombination in porphyrin - quinone donor-acceptor molecules are reported. The ion pair formation and recombination depend on the exothermicity of the respective electron-transfer reaction in a manner previously reported. The question as to what fraction of energy change is due to ...
This paper presents new data regarding the formation rate of iron�boron (Fei�B) pairs in p-type crystalline silicon. Improvements in the temperature control of the sample, a reduction in measurement error of the effective lifetime of the sample after all Fei�B pairs have reformed, and improved statistical analysis have led to a revision of the value of the pre-factor in ...
Organic photochemists began to recognize in the 1970s that a new mechanistic pathway involving excited-state single-electron transfer (SET) could be used to drive unique photochemical reactions. Arnold's seminal studies demonstrated that SET photochemical reactions proceed by way of ion radical intermediates, the properties of which govern the nature of the ensuing reaction pathways. Thus, in ...
After an ''incubation'' period in the 1970's and early 80's, during which the first hydrogen related centers were discovered and characterized in ultra-pure germanium, a sharp increase of research activity occurred after the discovery of shallow acceptor ...
National Technical Information Service (NTIS)
The Naval Facilities Engineering Service Center is developing a new ordnance storage magazine that will reduce encumbered land and improve operational efficiency. Non propagation walls are used to prevent sympathetic detonation between munitions stored in...
... [1]. Detailed measure- ments of PhC glass semiconductors ... glass semiconductor a-As2Se 3, levels of ... by measuring optical absorption [5], levels of ...
identified such a mechanism as the origin of the mild to asymptomatic phenotype observed in cystic fibrosis membrane of epithelial cells, cause cystic fibrosis (CF). CF is the most common severe autosomal recessive for the centers that contributed the data to the French Cystic Fibrosis registry and particularly Prof. Yves
Formate is known to cause significant inhibition in the electron and proton transfers in photosystem II (PSII); this inhibition is uniquely reversed by bicarbonate. It has been suggested that bicarbonate functions by providing ligands to the non-heme iron and by facilitating protonation of the secondary plastoquinone QB. Numerous lines of evidence indicate an intimate ...
Bicarbonate anions have a strong positive influence on the electron and proton transfers in photosystem II (PS II). It has been suggested that bicarbonate binds to the non-heme iron and the QB binding niche of the PS II reaction center. To investigate the potential amino acid binding environment of bicarbonate, an arginine residue (R269) of the D1 protein of PS II of ...
This paper makes a more accurate determination of the depth at which the acceptors created by manganese lie, measures the cross section for trapping of holes in its centers, and obtains additional information on hopping conductivity in Mn-doped InP. In addition, the optical chracteristics of Mn centers and the kinetics of the ...
The charge transfer complexes of the donor p-toluidine with pi-acceptor picric acid have been studied spectrophotometrically in various solvents such as carbon tetrachloride, chloroform, dichloromethane acetone, ethanol, and methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CTC in non-polar solvent is ...
Interaction of 2-aminopyrimidine (AP) with iodine as a typical ?-type acceptor and with a typical ?-type acceptor, 2,3,5,6-tetrachloro-1,4-benzoquinone, p-chloranil (CHL) have been studied spectrophotometrically. Electronic absorption spectra of the system AP-I2 in several organic solvents of different polarities have performed clear charge transfer (CT) ...
Calculation of the spectra of intermolecular complexes of 3-aminophthalimide is used as an example to show that when hydrogen bonds are present, the resonance integrals for the proton donor and acceptor atoms are different from zero. Theoretical analysis of strained 3-aminophthalimide complexes allowed us to establish the determining role of hydrogen bonds in their ...
The charge-transfer (CT) complexes of methamphetamine (MPA) as a n-donor with several acceptors including bromocresolgreen (BCG), bromocresolpurple (BCP), chlorophenolred (CPR), picric acid (PIC), and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) have been studied spectrophotometrically in chloroform solutions in order to obtain some information about their stoichiometry and ...
The charge recombination dynamics of excited donor-acceptor complexes in polar solvents has been investigated within the framework of the stochastic approach. The model involves the excited state formation by the pump pulse and accounts for the reorganization of a number of intramolecular high-frequency vibrational modes, for their relaxation as well as ...
This paper reports on scanning transmission electron microscopy (STEM) of positive-temperature-coefficient (PTC) BaTiO{sub 3} thermistors that shows that the grain-boundary oxygen content in as-received (oxidatively cooled) materials, is slightly enriched compared to quenched samples, and the acceptor-rich space-charge present at high temperatures is retained upon cooling. The ...
We report the neutralization of the shallow acceptors boron and gallium in p-type silicon to a depth >1 ..mu..m after exposure to a H/sub 2/O plasma for 3 h at temperatures as low as 80 /sup 0/C. The fact that uncompensated n-type silicon is unaffected by the plasma treatment means that donor formation is excluded. Exposure to either O/sub 2/ or H/sub ...
Electrically active defects introduced into Ge crystals co-doped with tin and phosphorus atoms by irradiation with 6 MeV electrons have been studied by means of transient capacitance techniques and ab-initio density functional modeling. It is shown that Sn atoms are effective traps for vacancies (V) in the irradiated Ge:Sn+P crystals. The electronic structure of Sn-V is unraveled on the basis of ...
The carrier transport through heterojunctions is influenced by the interconnection between the bands of the two semiconductors, by space charge effects near this interconnection and by interface recombination. The estimation of the discontinuity of the conduction bands using the difference in electron affinities is insufficient. A modified model takes the chemical and crystallographical nature of ...
It is known that the ease of the 1,5 migration of groups in cyclopentadienes is associated with their acceptor power. On the basis of this and in view of the tendency of phosphonoacetic acid triester to react at the C=O group of ..cap alpha..-enols (Wittig-Horner reaction), the authors studied the reactions of phosphonoacetic acid trimethyl ester with cyclones. ...
The influence of irradiation by {alpha} particles and subsequent isochronal annealing on n-GaAs doped with silicon, was investigated. Photoluminescence (PL) studies revealed the formation of an induced radiation center at 1.486 eV. In addition to the PL investigation we also employed capacitance{endash}voltage (C{endash}V) measurements and deep level ...
The conversion of solar light into usable chemical energy by plants and photosynthetic bacteria comprises light gathering by antenna pigment-protein complexes, photochemical charge separation in a special pigment-protein complex called reaction center, and stabilization of the charges by dark electron transport. The charged electron transport cofactors form ...
The report provides the reader with a detailed background of the technologies available for the bioremediation of contaminated soil and ground water. The document has been prepared for scientists, consultants, regulatory personnel, and others who are associated in some way with the restoration of soil and ground water at hazardous waste sites. It provides the most recent scientific understanding ...
The gas phase reactivity of 1,3,5-triazine with several oxyanions and carbanions, as well as amide, was evaluated using a flowing afterglow-selected ion flow tube mass spectrometer. Isotopic labeling, H/D exchange, and collision induced dissociation experiments were conducted to facilitate the interpretation of structures and fragmentation processes. A multi-step (? HCN + HC2N{2/-} ? CN- + 2 HCN) ...
The luminescence from SmI(2) in THF can be readily quenched by a variety of electron acceptors. In the case of organohalides, the reaction is quite fast; for example, for dichloromethane the rate constant is 2.7 x 10(8) M(-)(1) s(-)(1). Electron transfer leads to halide loss and formation of the carbon-centered radical. In the case of ...
The ultrafast (<100 fs) conversion of delocalized exciton into charge-separated state between the primary donor P700 (bleaching at 705 nm) and the primary acceptor A0 (bleaching at 690 nm) in photosystem I (PS I) complexes from Synechocystis sp. PCC 6803 was observed. The data were obtained by application of pump-probe technique with 20-fs low-energy pump pulses ...
The bacterial reaction center (RC) is a membrane protein complex that performs photosynthetic electron transfer from a bacteriochlorophyll dimer to quinone acceptors Q(A) and Q(B). Q(B) accepts electrons from the primary quinone, Q(A), in two sequential electron transfer reactions coupled to uptake of a proton from solution. It has been suggested that ...
The reaction of hydroxyl radicals with ?-glutamyl-methionine and ?-glutamyl-glycyl-methionyl-glycine at neutral pH results in similar N-terminal decarboxylation efficiency. The underlying mechanism involves an intramolecular proton transfer from the protonated N-terminal amino group of the glutamyl moiety to an initially formed hydroxy sulphuranyl radical at the methionine residue. This process ...
An understanding of the role of the medium that lies between electron donors and acceptors is particularly important for the study of photosynthetic reaction centers where the medium is thought to have a large influence on the observed rates of electron transfer. In the bacterial photosynthetic reaction center a bacteriochlorophyll ...
xHigh resolution photoluminescence (PL) and infrared optical quenching measurements were performed to study the recombination mechanisms in CdTe:I epilayers grown by molecular beam epitaxy and in bulk CdTe and Cd_{1-x}Zn_{x}Te. Sample measurements were performed over the temperature range from 4.8 K to 300 K. The PL technique is a sensitive, non-contact, and non-destructive method to investigate ...
In the reaction center (RC) of the photosynthetic bacterium Rhodobacter sphaeroides, two ubiquinone molecules, QA and QB, play a pivotal role in the conversion of light energy into chemical free energy by coupling electron transfer to proton uptake. In native RCs, the transfer of an electron from QA to QB takes place in the time range of 5-200 micros. On the basis of ...
Experimental evidence for the existence of two new lanthanide-metalloligand adducts (CpSiMe(3))(3)Ce-ECp* (E = Al, Ga) is presented. Paramagnetic (1)H NMR titration experiments were employed to derive thermodynamic parameters for Ce-Ga dative bond formation, and competition experiments with the U analogue were performed. Density functional theory calculations were undertaken ...
Cyclic ozone (O3) has not been isolated so far, despite its computed kinetic persistence. Possibilities of "trapping" this molecule (or the valence-isoelectronic cyclic thiozone, S3) in transition metal complexes are investigated in this paper. Candidates were constructed, first using the 18-electron rule as a guide and then optimizing the structures with the DFT-B3LYP method. A variety of ...
Recent experimental and theoretical information regarding the states of hydrogen in crystalline semiconductors is reviewed. The abundance of results illustrates that hydrogen does not preferentially occupy a few specific lattice sites but that it binds to native defects and impurities, forming a large variety of neutral and electrically active complexes. The study of hydrogen passivated shallow ...
The systematics of the V/double bond/O stretching frequency in vanadyl porphyrins are investigated with resonance Raman (RR) spectroscopy. For a series of solvents the frequency decreases with increasing solvent acceptor number consistent with solvent-induced polarization of the V-O bond. Variations in the solvent dependence are seen for different porphyrins, reflecting ...
Thermal emission rates of electrons and holes at the gold acceptor center (E(c)-E(Au-) = 550 mV) and of holes at the gold-donor center (E(Au+)-E(y) = 350 mV) are measured using the dark current, dark capacitance, and photocapacitance transient methods. Ab...
In photosynthetic reaction centers, a quinone molecule, Q(sub B), is the terminal acceptor in light-induced electron transfer. The crystal structure of the reaction center implicates the protonatable amino acid residues L212Glu and L213Asp in the binding ...
Lifetime predictions for CdTe photovoltaic modules represent a complex problem, partly due to the fact that a fundamental understanding of the CdTe material properties and device operation is far from being complete. One of the stability issues actively investigated is the use of Cu for the formation of a back contact. Cu is one of the few good p-dopants for CdTe, which, by ...
Assimilatory NADH:nitrate reductase catalyzes the transfer of reducing equivalents from NADH to molecular oxygen. Initial rate studies performed under conditions of optimal pH (8.0) and constant ionic strength (mu = 0.2) revealed that the maximal rate of activity with molecular oxygen was 0.5% (0.44 mumol NADH consumed/min/nmol heme) with a Km for O2 of 586 microM. NADH:molecular oxygen reductase ...
The nicotinamide adenine dinucleotide phosphate (NADP)-dependent formate dehydrogenase in Clostridium thermoaceticum used, in addition to its natural electron acceptor, methyl and benzyl viologen. The enzyme was purified to a specific activity of 34 (micromoles per minute per milligram of protein) with NADP as electron acceptor. Disc ...
It has been found that the formation of an intermolecular charge transfer complex in the ground electronic state between the model conjugated polymer (poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and the low-molecular-weight organic acceptor (2,4,7-trinitrofluorenone, TNF) occurs stepwise with an increase in the ...
Experimental results are reported from measurements of the temperature dependence of the absorption and photoconductivity spectra and the absorption spectra within a magnetic field of high-purity Ge semiconductors into which were introduced quenched-in shallow acceptors. Specifically, the study examined the far-IR absorption properties of the crystals impregnated with B, Al, ...
The rapid interaction between o-tolidine and p-toluidine (pi-donors) with the pi-acceptors, e.g., 3,5-dinitrobenzoic acid (DNB) and 2,6-dichloroquinone-4-chloroimide (DCQ) results in the formation of 1:1 charge-transfer complexes as the final products, [(o-tolidine) (acceptor)] and [(p-toluidine) (acceptor)]. The ...
Planet Formation Processes and the Formation of Prebiotic Conditions -- 17-21 March 2008, Sponsored by the Center for Exoplanet Science ...
Formation estimation methodologies for distributed spacecraft systems are formulated and analyzed. A
NASA Technical Reports Server (NTRS)
... Title : Alternative Fuel Deposit Formation,. Corporate Author : UNITED TECHNOLOGIES RESEARCH CENTER EAST HARTFORD CT. ...
It has generally been recognized that Mg gives rise to an interstitial donor level in Si although the possibility of the existence of a Mg substitutional acceptor in Si has been suggested. In this work, we explore the synthetic conditions required to obtain substitutional Mg acceptor in Si. We have diffused Mg into Si wafers under the Mg vapor environment ...
Several very stable imine derivatives were synthesized by the reaction of aromatic aldehydes with diaminomaleonitrile. These compounds include different donor groups connected to the acceptor by conjugated chains of different lengths. Another group of compounds that have been synthesized is chiral pyrrolidine derivatives with varying acceptor substituents. ...
Newly proton or charge transfer complex [(OPDH)(+)(PA)(-)] was synthesized by the reaction of the donor, o-phenylenediamine (OPD) with acceptor, 2,4,6-trinitrophenol (PAH). The chemical reaction has occurred via strong hydrogen bonding followed by migration of proton from acceptor to donor. UV-vis, (1)H NMR and FTIR spectra, in addition to the thermal and ...
Donor-acceptor bonding between group 13 elements seems counter-intuitive because one normally thinks of e.g. boron and aluminium compounds as classical Lewis acids. Indeed, many such compounds have achieved industrial prominence in this regard. Recently, however, it has become possible to stabilize these and other group 13 elements in the +1 oxidation state as opposed to the ...
This work aims at describing the water structure characteristics that influence the electron transfer superexchange mechanism by explicitly calculating the solvent mediated conductance between the donor and acceptor in a generic pair. The method employed here is based on the non-equilibrium Green function formalism for calculating the conductance over solvent trajectories ...
... Title : Formation of Face-Centered Cubic Titanium on a Ni Single Crystal and in Ni/Ti Multilayers. Descriptive Note : Journal article,. ...
Aminoacyl (Phe, Gly) derivatives of nucleoside aliphatic analogues bearing a hydroxyalkyl chain have been prepared by the condensation of the alcohols with N-benzyloxycarbonyl-amino acid in the presence of DCC followed by hydrogenolysis in methanol. These compounds inhibit peptidyl transferase activity and binding of acceptor substrate to E. coli ribosomes. The inhibitory ...
Means for studying the catalytic activity of hydrogenase in biophotolytic hydrogen-production systems are described. Attention is given to the reduction of an acceptor by hydrogen, measurement of the enzymatic catalysis of the exchange reaction between hydrogen and deuterated or tritiated water, the assessment of hydride formation, and the heterolytic ...
We propose a method for calculating the Gibbs energies of hydrogen bonding of solutes with associated solvents via the thermodynamic analysis of experimental values of solvation Gibbs energies. The method is applied to solutions of different proton acceptors in methanol. It is shown that the contribution of hydrogen bonding processes to the solvation Gibbs energy in methanol ...
Flexible donor ligands like 1,2-bis(3-pyridyl)ethyne or 1,4-bis(3-pyridyl)-1,3-butadiyne self-assemble into discrete supramolecules instead of infinite networks upon combination with organoplatinum 90, 120, and 180 degree acceptor units. These systems are unique examples of versatile pyridine donors adjusting their bonding directionality to accommodate rigid platinum ...
Planar lipid bilayers containing reaction centers from Rhodopseudomonas sphaeroides R-26 were formed by apposing two reaction center�lipid monolayers formed from a reaction center�lipid complex in hexane. Secondary donors (cytochrome c) and acceptors (ubiquinone-0) were added on opposite sides of the membrane. ...
Lab scale mulch-biofilm biowall barriers were constructed and tested to monitor the effect of biofilm formation on the performance of the biobarrier. Naphthalene, a two-ring polycyclic aromatic hydrocarbon (PAH), was used as the model compound. With column reactors, the amounts of viable naphthalene degraders and biofilm formation were monitored, as was ...
The formation of carbamate from CO/sub 2/ and the various amine solutions has been investigated for the purpose of elucidating the structure of the species generated in the reaction. The amine solutions used were 1 and 2 molar solutions of di-n-butylamine (DNBA) in triethylamine (TEA), pure DNBA and pure TEA. It has been found that the nonaqueous solvent participates in the ...
... Agency (DARPA) Rapid Knowledge Formation (RKF ... permit scientific, technical, and military experts, such ... center and intelligence-center personnel ...
A multi-method research design consisting of in-depth interviews with program officials and builders, field-level observation, and field surveys with randomly chosen acceptors was used to provide a unique set of insights into the process of diffusion and acceptance of improved smokeless wood stoves in Rajasthan, India. Over 450 village women were interviewed about their energy ...
Hydrogen has been shown to activate the neutral impurities carbon, silicon and oxygen in ultra-pure germanium and form shallow level complexes. The double acceptors beryllium and zinc in silicon and germanium, as well as the triple acceptor copper in germanium, can be partially passivated, leading to single hole acceptors. The study of ...
The formation of complexes of sterols with different compounds determines the biological properties of both sterols and various natural substances such as saponins and polyene antibiotics. Complex formation by sterols with phospholipids, steroid saponins, and polyene antibiotics is determined by the same characteristic features of the structure of the ...
The effect of solvents on electron-donor-acceptor complex formation reactions has been studied thermodynamically. The nonpolar analog model (NPA) is examined theoretically and methods are developed for using it to predict thermodynamic properties of the t...
formation energies for substitu- Fig. 1. Schematic diagram of (a) wurtzite and (b) zinc-blende struc- tures are the solubility (equilibrium concentration, as determined by the formation energy), the depth of the acceptor concentration when the Al content of the AlGaN alloy is increased [8,9]. We have addressed these doping issues
Pore Formation and Mobility Investigation (PFMI) ... Flight in Huntsville, Ala., examines the furnace used to conduct his Pore Formation and Mobility Investigation ...
The adoption of the RDF format by both data centers means that the format of data ... In addition, since the RDF format is also being utilized by other ...
Single electron transfer (SET) via ion/neutral complex (INC) was proposed and confirmed to be the key step in the formation of N-centered odd-electron ions from fragmentation of protonated even-electron ions in the present study. Upon collisional activation, the model compounds, protonated N,N'-dibenzylpiperazine and protonated N-benzylpiperazines ...
In the reaction centers from the purple photosynthetic bacterium Rhodobacter capsulatus, we have determined that residue L212Glu, situated near the secondary quinone acceptor Q{sub B}, modulates the free energy level of the reduced primary quinone molecule A{sub A}{sup -} at high pH. Even though the distance between L212Glu and Q{sub A} is 17 {angstrom}, ...
