Electron-transfer reactions artificial photosynthetic systems

WiUner, I., and Willner, B. Artificial Photosynthetic Model Systems Using Light-Induced Electron Transfer Reactions in Catalytic and Biocatalytic Assemblies. 159,153-218 (1991). 

Warwel, S., Sojka, M., and Riisch, M. Synthesis of Dicarboxylic Acids by Transition-Metal Catalyzed Oxidative Cleavage of Terminal-Unsaturated Fatty Acids. 164, 79-98 (1993). Willner, I., and Willner, B. Artificial Photosynthetic Model Systems Using Light-Induced Electron Transfer Reactions in Catalytic and Biocatalytic Assemblies. 159, 153-218 (1991). 

The design of such artificial photosynthetic systems suffers from some basic limitations a) The recombination of the photoproducts A and S+ or D+ is a thermodynamically favoured process. These degra-dative pathways prevent effective utilization of the photoproducts in chemical routes, b) The processes outlined in eq. 2-4 are multi electron transfer reactions, while the photochemical reactions are single electron transformations. Thus, the design of catalysts acting as charge relays is crucial for the accomplishment of subsequent chemical fixation processes. 

Willner I, Willner B (1991) Artificial Photosynthetic Model Systems Using light-induced Electron Transfer Reactions in Catalytic and Biocatalytic Assemblies. 159 153-218 Woggon W-D (1997) Cytochrome P450 Significance, Reaction Mechanisms and Active Site Analogues. 184 39-96 Xia Y, see Qin D (1998) 194 1-20 Yamazaki T, see Kitazume T (1997) 193 91 -130... 

Artificial Photosynthetic Model Systems Using Light-Induced Electron Transfer Reactions in Catalytic and Biocatalytic Assemblies... 

Intrinsic limitations of an artificial photosynthetic system include the thermodynamically favoured back electron transfer reactions of the intermediate photoproducts [47, 48]. For an oxidative ET quenching process the destructive back electron reactions are given by Eq. (9) and (10). The fraction of usable photo-... 

As indicated in Figure I, wild-type bacterial reaction centers also contain a carotenoid polyene. This polyene is not involved as a donor or acceptor in the normal electron transfer sequence, although carotenoid radical cations have been observed spectroscopically in photosynthetic preparations under certain conditions [18,19]. In many of the artificial photosynthetic systems which will be discussed below, the carotenoid is used as a convenient secondary electron donor. Carotenoids do perform two important functions in photosynthesis. They provide photoprotection from singlet oxygen damage, and act as light-gathering antennas for the special pair (see Sections III and IV). 

C-P-Q-Q Tetrads. Electron transfer in the P-Q and C-P-Q species bears some resemblance to the tetrapyrrole to quinone Q electron transfer observed in photosynthetic reaction centers. Thus, a logical next step in the evolution of the artificial photosynthetic systems would be the construction of molecular devices containing two quinone moieties, as per the Qa-Qb system in reaction centers. Indeed, P-Qa-Qb triad 14 was reported some years ago by Sakata, Mataga and co-workers [31]. 

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