Artificial photosynthetic assemblies

Table 1 summarizes several redox transformations that can be accomplished in artificial photosynthetic assemblies including the photolysis of water, carbon dioxide reduction, and nitrogen fixation processes. The endoergicities of these transformations, and the number of electrons involved in the reduction processes, are also indicated in the table. It is evident that the energy per electron to drive the various transformations are met by visible light quanta. 

A variety of transition-metal complexes have been applied as homogeneous catalysts for C02-fixation in artificial photosynthetic assemblies. Typical photo-... 

Rubpy is an often used shorthand for the well studied [Ru(bpy)3]2+ complex cation and is also used more loosely to refer to any Ru(D) polypyridyl complex with similar properties. As shown in Fig. 7, the three best studied members of the Rubpy family are the parent complex, [Ru(bpy)3]2+, the phenanthroline analogue, [Ru(phen)3]2+, and the bis terpy complex, [Ru(terpy)3]2+, which has less optimal photophysical properties but has a number of synthetic and stereochemical advantages. The synthe sis, stability and photophysics of Rubpy complexes has been reviewed many times17 54 57 and the highlights of these properties as related to artificial photosynthetic assemblies is summarized here. 

Some frontier research works on the artificial photosynthetic assemblies with zeolite membranes have been done by Kim and Dutta et al. from the Ohio State University [50]. 

Figures Ib-f show examples of molecular systems that feature essential functions that are required for a prospective artificial photosynthetic assembly. The examples are restricted to assemblies build from molecular units only and to abundant elements as far as catalysts are concerned.

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). 

Figure 1. Schematic representation of the artificial photosynthetic reaction center by a monolayer assembly by A-S-D triad and antenna molecules for light harvesting (H), lateral energy migration and energy transfer, and charge separation across the membrane via multistep electron transfer (a) Side view of mono-layer assembly, (b) top view of a triad surrounded by H molecules, and (c) energy diagram for photo-electric conversion in a monolayer assembly.

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... 

The objectives of this account are to review the problems involved in tailoring man-made photosynthetic systems and to highlight the scientific accomplishments in artificial photosynthesis. The chemical methodology of linking catalysts, biocatalysts and photosystems into integrated photosynthetic assemblies will be discussed. 

Although the thermodynamic feasibility to design artificial photosynthetic processes is obvious, practical assembly of such systems confronts substantial difficulties. Thermodynamic limitations accompanying artificial photosynthetic systems have been considered theoretically [40-42], and the recent progress in the subject has been reviewed [43, 44] in several articles and monographs [45, 46]. 

Mother nature has resolved the various limitations involved in multi-electron processes. Unique assemblies composed of cofactors and enzymes provide the microscopic catalytic environments capable of activating the substrates, acting as multi-electron relay systems and inducing selectivity and specificity. Artificially tailored heterogeneous and homogeneous catalysts as well as biocatalysts (enzymes and cofactors) are, thus, essential ingredients of artificial photosynthetic devices. 

Bioinspired Supramolecular Device and Self-Assembly for Artificial Photosynthetic Reaction Center... 

The structure and function of this bacterial photosystem reveals important principles for the design of artificial photosystems. First, the sensitizer needs to be posi tioned close to secondary acceptors and donors which themselves are spatially iso lated from each other such that photoexcitation leads to rapid spatial separation of the electron hole pair. Second, compartmentalization of the photosynthetic assembly is likely to be necessary so as to prevent wasteful back reactions. For water splitting, a system in which H2 and O2 are generated in separate compartments would have both safety and efficiency advantages. 

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