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41.
Dong Jin Qian 《中国化学快报》2008,(5)
Hydrogen evolution was detected in an artificial system composed of light-harvesting unit of purified photosystem I,catalyst of hydrogenase,methyl viologen and electron donor under radiation.Absorption spectral features confirmed that electron transfer from electron donors to proton was via a photoinduced reductive process of methyl viologen. 相似文献
42.
Fluorescence induction curves (F(t)) in low intensity 1s light pulses have been measured in leaf discs in the presence and absence of valinomycin (VMC). Addition of VMC causes: (i) no effect on the initial fluorescence level Fo and the initial (O-J) phase of F(t) in the 0.01-1 ms time range. (ii) An approximately 10% decrease in the maximal fluorescence Fm in the light reached at the P level in the O-J-I-P induction curve. (iii) Nearly twofold increase in the rate and extent of the F(t) rise in the J-I phase in the 1-50 ms time range. (iv) A 60-70% decrease in the rise (I-P phase) in the 50-1000 ms time range with no appreciable effect, if at all, on the rate. System analysis of F(t) in terms of rate constants of electron transfer at donor and acceptor sides have been done using the Three State Trapping Model (TSTM). This reveals that VMC causes: (i) no, or very little effect on rate constants of e-transfer reactions powered by PSII. (ii) A manifold lower rate constant of radical pair recombination (k(-1)) in the light as compared to that in the control. The low rate constant of radical pair recombination in the reaction center (RC) in the presence of VMC is reflected by a substantial increase in the nonzero trapping efficiency in RCs in which the primary quinone acceptor (Q(A)) is reduced (semi-open centers). This causes an increase in their rate of closure and in the overall trapping efficiency. Data suggest evidence that membrane chaotropic agents like VMC abolish the stimulation of the rate constant of radical pair recombination by light. This light stimulation that becomes apparent as an increase in Fo has been documented before [Biophys. J. 79 (2000) 26]. It has been ascribed to effects of (changes in) local electric fields in the vicinity of the RC. The decrease of the I-P phase is attributed to a decrease in the photoelectric trans-thylakoid potential in the presence of VMC. Such effects have been hypothesized and illustrated. 相似文献
43.
Results of Density Functional Theory (DFT) theoretical investigations, which use a model tyrosyl (Tyr) radical and tyrosyl-histidine
(Tyr-His) complex to mimick the Y
D
·
radical in Photosystem II (PSII) are presented and compared to experimental results from 15N Electron-Nuclear Double Resonance spectroscopy (ENDOR) studies of the τ nitrogen coupling from His-189 in the PSII Tyr-His complex. The DFT calculations are performed using an optimized geometry
of the tyrosine radical and Tyr-His complex. The conformational space of the Tyr-His tandem is explored by varying the relative
geometry of the two components; relevant parameters, such as the spin distribution on the phenoxy-ring carbons of the Tyr
radical and the EPR hyperfine tensors, are calculated at each geometry and compared with the available experimental data.
The isotropic 15N-ENDOR signal arising from spin delocalization on the His hydrogen-bonded to the PSII tyrosine radical is analyzed in terms
of the DFT obtained parameters. The calculations of the g tensor using the Gauge Independent Atomic Orbital (GIAO) approach are presented and the influence of the geometry of the
Tyr-His complex on the deviation of the g-tensor elements from the free electron values is discussed. 相似文献
44.
Yulia N. Pushkar Dietmar Stehlik Maurice van Gastel Wolfgang Lubitz 《Journal of Molecular Structure》2004,700(1-3):233-241
Hydrogen bonding to the photoaccumulated secondary acceptor radical anion A1√− in photosystem (PS) I has been studied using pulsed Q-band ENDOR spectroscopy. With deuterated quinone in protonated PS I particles it is demonstrated that the observed radical anion has only one hydrogen-bond hyperfine coupling (hfc) tensor with tensor components above the 2 MHz range. Below 2 MHz the protein matrix protons dominate and a second weak H-bond could not be detected. The spectral resolution of pulsed Q-band ENDOR is critically required to separate the signals of the H-bond proton from those of the primary chlorophyll acceptor, A0√−, which cannot be avoided to be formed to some extent in the photoaccumulation procedure. The determined H-bond hfc tensor of A1√− is found to be close to axial symmetry with a small isotropic component, as expected from a predominantly dipolar electron–proton spin interaction in a hydrogen-bond. The principal tensor components are A=(+)7.7, MHz A=(−)4.9 MHz, Aiso=(−)0.7 MHz. The magnitude of the dipolar tensor corresponds to an unusually short H-bond which can be estimated from the point-dipole approximation (1.5±0.1 Å). Based on previous studies with A- and B-branch specific site-directed mutants of the A1 site of PS I and the chosen photoaccumulation protocol, the observed A1√− radical anion can be assigned to the QK–A site of the A-branch. The observed H-bond hfc tensor is compared to those determined for related quinone radical anions observed in frozen protic solution as well as in the QA site of type II bacterial reaction centers. 相似文献
45.
Photosystem II (PSII) complex activity is known to decrease under strong white light illumination, and this photoinhibition phenomenon is connected to the photobleaching of the PSII photosynthetic pigments. In this work the pigment photobleaching has been studied on PSII core complexes, by observing the effects of different factors such as the aggregation state (PSII monomers and dimers were used), temperature (20 degrees C and 10 degrees C temperatures were tested) and the presence of the exogenous phospholipids (cardiolipin and phosphatidylglycerol). In particular, PSII resistance against white light stress was studied by means of UV/VIS Absorption and Fluorescence Emission measurements. It was found that PSII dimers resulted more resistant against photobleaching and that lower temperature reduces the pigment photodestruction. Moreover, the presence of phosphatidylglycerol or cardiolipin enhanced the PSII resistance to the photobleaching phenomenon, mainly at lower temperatures. 相似文献
46.
Two manganese(II) bipyridine carboxylate complexes, [(bipy)2MnII(μ‐C2H5CO2)2MnII(bipy)2}2](ClO4)2 ( 1 ), and [MnII(ClCH2CO2)(H2O)(bipy)2]ClO4 · H2O ( 2 ) were prepared. 1 crystallizes in the triclinic space group P 1 with a = 8.604(3), b = 12.062(3), c = 13.471(3) Å, α = 112.47(2), β = 93.86(2), γ = 92.87(3)°, V = 1211.1(6) Å3 and Z = 1. In the dimeric, cationic complex with a crystallographic center of symmetry two 2,2′‐bipyridine molecules chelate each manganese atom. These two metal fragments are then bridged by two propionato groups in a syn‐anti conformation. The Mn…Mn distance is 4.653 Å. 2 crystallizes in the monoclinic space group P21/c with a = 9.042(1), b = 13.891(1), c = 21.022(3) Å, β = 102.00(1)°, V = 2569.3(5) Å3 and Z = 4. 2 is a monomeric cationic complex in which two bipyridine ligands chelate the manganese atom in a cis fashion. A chloroacetato and an aqua ligand complete the six‐coordination. Only in 2 is the intermolecular packing controlled by weak π‐stacking besides C–H…π contacts between the bipyridine ligands. 相似文献
47.
48.
对高等植物类囊体膜的研究表明,易于损伤生物体的超氧阴离子自由基(O2- )可以在其光系统Ⅱ(PSⅡ)中大量生成,并且可能是导致光系统的光抑制和光破坏现象的主要根源之一[1-3].然而,由于超氧阴离子自由基化学性质活泼,而且生物体中含量很低,因此受物理检测手段的局限,对于PSⅡ中O2-的生成机制所知甚少. 相似文献
49.
Silvia Mauthe Irene Fleischer Thorsten M. Bernhardt Sandra M. Lang Robert N. Barnett Uzi Landman 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(25):8592-8597
One of the fundamental processes in nature, the oxidation of water, is catalyzed by a small CaMn3O4?MnO cluster located in photosystem II (PS II). Now, the first successful preparation of a series of isolated ligand‐free tetrameric CanMn4?nO4+ (n=0–4) cluster ions is reported, which are employed as structural models for the catalytically active site of PS II. Gas‐phase reactivity experiments with D2O and H218O in an ion trap reveal the facile deprotonation of multiple water molecules via hydroxylation of the cluster oxo bridges for all investigated clusters. However, only the mono‐calcium cluster CaMn3O4+ is observed to oxidize water via elimination of hydrogen peroxide. First‐principles density functional theory (DFT) calculations elucidate mechanistic details of the deprotonation and oxidation reactions mediated by CaMn3O4+ as well as the role of calcium. 相似文献
50.
Zhen Li Yu Qi Wangyin Wang Deng Li Zheng Li Yanan Xiao Guangye Han Jian-Ren Shen Can Li 《催化学报》2019,40(4):486-494
Photocatalytic Z-scheme water splitting is considered as a promising approach to produce solar hydrogen. However, the forward hydrogen production reaction is often impeded by backward reactions. In the present study, in a photosystem II-integrated hybrid Z-scheme water splitting system, the backward hydrogen oxidation reaction was significantly suppressed by loading a PtCrOx cocatalyst on a ZrO2/TaON photocatalyst. Due to the weak chemisorption and activation of molecular hydrogen on PtCrOx, where Pt is stabilized in the oxidized forms, PtII and PtIV, hydrogen oxidation is inhibited. However, it is remarkably well-catalyzed by the metallic Pt cocatalyst, thereby rapidly consuming the produced hydrogen. This work describes an approach to inhibit the backward reaction in the photosystem II-integrated hybrid Z-scheme water splitting system using Fe(CN)63?/Fe(CN)64? redox couple as an electron shuttle. 相似文献