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331.
Shevela D Koroidov S Najafpour MM Messinger J Kurz P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(19):5415-5423
Oxygen evolution catalysed by calcium manganese and manganese-only oxides was studied in (18)O-enriched water. Using membrane-inlet mass spectrometry, we monitored the formation of the different O(2) isotopologues (16)O(2), (16)O(18)O and (18)O(2) in such reactions simultaneously with good time resolution. From the analysis of the data, we conclude that entirely different pathways of dioxygen formation catalysis exist for reactions involving hydrogen peroxide (H(2)O(2)), hydrogen persulfate (HSO(5)(-)) or single-electron oxidants such as Ce(IV) and [Ru(III) (bipy)(3)](3+) . Like the studied oxide catalysts, the active sites of manganese catalase and the oxygen-evolving complex (OEC) of photosystem II (PSII) consist of μ-oxido manganese or μ-oxido calcium manganese sites. The studied processes show very similar (18)O-labelling behaviour to the natural enzymes and are therefore interesting model systems for in vivo oxygen formation by manganese metalloenzymes such as PSII. 相似文献
332.
Lukoyanov D Dikanov SA Yang ZY Barney BM Samoilova RI Narasimhulu KV Dean DR Seefeldt LC Hoffman BM 《Journal of the American Chemical Society》2011,133(30):11655-11664
Enzymatic N(2) reduction proceeds along a reaction pathway composed of a sequence of intermediate states generated as a dinitrogen bound to the active-site iron-molybdenum cofactor (FeMo-co) of the nitrogenase MoFe protein undergoes six steps of hydrogenation (e(-)/H(+) delivery). There are two competing proposals for the reaction pathway, and they invoke different intermediates. In the 'Distal' (D) pathway, a single N of N(2) is hydrogenated in three steps until the first NH(3) is liberated, and then the remaining nitrido-N is hydrogenated three more times to yield the second NH(3). In the 'Alternating' (A) pathway, the two N's instead are hydrogenated alternately, with a hydrazine-bound intermediate formed after four steps of hydrogenation and the first NH(3) liberated only during the fifth step. A recent combination of X/Q-band EPR and (15)N, (1,2)H ENDOR measurements suggested that states trapped during turnover of the α-70(Ala)/α-195(Gln) MoFe protein with diazene or hydrazine as substrate correspond to a common intermediate (here denoted I) in which FeMo-co binds a substrate-derived [N(x)H(y)] moiety, and measurements reported here show that turnover with methyldiazene generates the same intermediate. In the present report we describe X/Q-band EPR and (14/15)N, (1,2)H ENDOR/HYSCORE/ESEEM measurements that characterize the N-atom(s) and proton(s) associated with this moiety. The experiments establish that turnover with N(2)H(2), CH(3)N(2)H, and N(2)H(4) in fact generates a common intermediate, I, and show that the N-N bond of substrate has been cleaved in I. Analysis of this finding leads us to conclude that nitrogenase reduces N(2)H(2), CH(3)N(2)H, and N(2)H(4) via a common A reaction pathway, and that the same is true for N(2) itself, with Fe ion(s) providing the site of reaction. 相似文献
333.
The mechanism of nanobump formation in femtosecond pulse laser nanostructuring of thin metal films 总被引:1,自引:0,他引:1
Dmitriy S. Ivanov Baerbel Rethfeld Gerard M. O’Connor Thomas J. Glynn Alexey N. Volkov Leonid V. Zhigilei 《Applied Physics A: Materials Science & Processing》2008,92(4):791-796
The physical mechanisms responsible for the formation of nanobump structures on a surface of a thin metal film irradiated
by a tightly focused femtosecond laser pulse are investigated in a large-scale molecular dynamics simulation. The simulation
is performed with a combined atomistic-continuum model adapted for an adequate representation of laser-induced processes at
the length-scale of the entire laser spot. The relaxation of the compressive stresses generated by the fast laser heating
is identified as the main driving force responsible for the separation of the metal film from the substrate and formation
of the nanobump. The kinetics of the transient melting and resolidification, occurring under conditions of the fast cooling
due to the two-dimensional electron heat conduction, defines the shape of the nanobump. The predictions of the simulation
are related to the surface structures observed in femtosecond laser nanostructuring. 相似文献
334.
Nonlinear interaction of two femtosecond laser pulses in a filament, induced by one of them inside a fused silica plate, leads to generation of the new spectral components. These spectral components reach hundreds of nanometers bandwidth. Their spatial and spectral properties can be explained by four-wave parametric coupling in the filament. The energy measurements indicate the high efficiency of this process. 相似文献
335.
Nikolay O. Mchedlov‐Petrossyan Dmitriy Yu. Filatov Sergey T. Goga Alexander V. Lebed 《Journal of Physical Organic Chemistry》2010,23(5):418-430
Properties of a protophobic polar non‐HBD solvent can be strongly modified by introduction of a small amount of a protophilic polar non‐HBD solvent. In this paper, acetone (AC) with 5 mol% additive of DMSO, a solvent with , was considered as a media for acid–base reactions. Conductance was used for determination of dissociation constants of a set of salts, hydrogen chloride, and picric acid. The last‐named was also studied by UV‐vis spectroscopy. The introduction of 5 mol% of DMSO results in suppressing, to some extent, the homoconjugation processes in AC media as well as of proton hydration by (possible) traces of water. The dissociation of salicylic acid and 2,4‐dinitrophenol was examined utilizing quinhydrone electrodes in a cell with liquid junction. The pKa values of buffer acids and values of buffer solutions were calculated by taking into account the incomplete dissociation of salts. The response of the glass electrode appeared to be satisfactory, which allowed the estimation of the pKa value of benzoic acid. The apparent ionization constants of 22 acid–base indicators in buffer mixtures and perchloric acid solutions were determined in (AC + 5 mol% DMSO) using the spectrophotometric procedure. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
336.
Bobko AA Kirilyuk IA Gritsan NP Polovyanenko DN Grigor'ev IA Khramtsov VV Bagryanskaya EG 《Applied magnetic resonance》2010,39(4):437-451
The X- and W-band electron paramagnetic resonance (EPR) spectroscopies were employed to investigate a series of imidazolidine
nitroxide radicals with different number of ethyl and methyl substituents at positions 2 and 5 of a heterocycle in liquid
and frozen solutions. The influence of the substituents on the line shape and width was studied experimentally and analyzed
using quantum chemical calculations. Each pair of the geminal ethyl groups in the positions 2 or 5 of the imidazolidine ring
was found to produce an additional hyperfine splitting (hfs) of about 0.2 mT in the EPR spectra of the nitroxides. The effect
was attributed to the hfs constant of only one of four methylene hydrogen atoms of two geminal ethyl substituents not fully
averaged by ethyl group rotation and ring puckering. In accordance with this assumption, the substitution of hydrogen atoms
of CH2 groups in 2,2,5,5-tetraethyl-substituted imidazolidine nitroxides by deuterium leads to the substantial narrowing of EPR
lines which could be useful for many biochemical and biomedical applications, including pH-monitoring. W-band EPR spectra
of 2,2,5,5-tetraethyl-substituted imidazolidine nitroxide and its 2,2,5,5-tetraethyl–d8 deuterium-substituted analog measured at low temperatures demonstrated high sensitivity of their g-factors to pH, which indicates their applicability as spin labels possessing high stability. 相似文献
337.
Alzhan Z. Baimenov Ildar R. Fakhradiyev Dmitriy A. Berillo Timur Saliev Sergey V. Mikhalovsky Talgat S. Nurgozhin Vassilis J. Inglezakis 《Molecules (Basel, Switzerland)》2021,26(24)
The effectiveness of an amphoteric cryogel (AAC) as an oral sorbent (enerosorbent) for the treatment of acute poisoning of small animals (rats) with heavy metals (HMs) was studied in in vivo experiments. The morphological structure of the cryogel was examined using scanning electron microscopy/energy-dispersive X-ray analysis and confocal microscopy. The use of the cryogel in the treatment of rats administered an LD50 dose of Cd(NO3)2, CsNO3, Sr(NO3)2, or HgCl2 in aqueous solution showed their high survival rate compared to the control group, which did not receive such treatment. The histological and chemical analysis of internal tissues and the biochemical analysis of the blood of the experimental animals showed the effectiveness of the cryogel in protecting the animals against the damaging effect of HMs on the organism comparable with unithiol, a chelating agent based on 2,3-dimercapto-1-propane sulfonic acid sodium salt (DMPS) approved for the treatment of acute poisoning with some heavy metals. 相似文献
338.