Photosynthetic electron transfer

Photosynthetic Electron Transfer in the R. viridis Reaction Center... 

Fullerenes linked with one or two porphyrin residues as novel acceptors in photosynthetic electron transfer 99EJ02445. 

M. Antolovich, P. J. Keyte, A M. Oliver, M. N. Paddon-Row, J. Kroon, J. W. Verhoeven, S. A Jonker, J. M. War-man, Modelling Long-Range Photosynthetic Electron Transfer in Rigidly Bridged Porphyrin-Quinone Systems ,/. Phys. Chem. 1991, 95,1933-1941. 

In this system, oxygen is produced by photosystem II, as in green plants and cyanobacteria. The photosynthetic electron transfer, via photosystem I, is linked by low-potential electron carriers to hydrogenase, which produces H2 (Fig. 10.3). Benemann and Weare (1974) then went on to investigate H2 evolution by N2-fixing cyanobacterial cultures as a whole-cell source of hydrogen energy. 

Theories for photosynthetic electron transfer normally begin with the premise that the electron transfer is nonadiabatic (40-48). The... 

The 2Fe2S (S, acid-labile sulfur) ferredoxins have a redox active binuclear center, with each of the two iron atoms attached to the protein by two cysteinyl sulfur ligands and connected by two inorganic acid-labile sulfur ligands. At cty-ogenic temperatures these clusters are EPR detectable, with characteristic features in the vicinity of g = 1.94. Spinach ferredoxin has principal g values of 2.03, 1.96, and 1.88 and a broad absorbance spectrum with a weak maximum around 420 nm, giving these proteins a reddish brown color which bleaches on reduction. Ferredoxins are low potential electron carriers chloroplast ferredoxins function in photosynthetic electron transfer, but related proteins such as adrenal ferredoxin are involved in steroidogenic electron transfer in mitochondria in tissues which produce steroid hormones. 

The extent to which an electron carrier is oxidized or reduced during photosynthetic electron transfer can sometimes be observed directly with a spectrophotometer. When chloroplasts are illuminated with 700 nm light, cytochrome/, plastocyanin, and plastoquinone are oxidized. When chloroplasts are illuminated with 680 nm light, however, these electron carriers are reduced. Explain. 

Many kinetic studies have been carried out on the reactions of cytochrome c. This work, as is the case for other electron-transfer proteins, has followed two general courses. One approach involves the study of reactions of cytochrome c with inorganic and organic reagents and with isolated electron-transfer proteins. The second approach has involved the use of intact or partially disrupted mitochondrial or photosynthetic electron-transfer systems. 

This review highlights recent studies of synthetic, covalently linked multicomponent molecular devices which mimic aspects of photosynthetic electron transfer. After an introduction to the topic, some of the salient features of natural bacterial photosynthetic reaction centers are described. Elementary electron transfer theory is briefly discussed in order to provide a framework for the discussion which follows. Early work with covalently linked photosynthetic models is then mentioned, with references to recent reviews. The bulk of the discussion concerns current progress with various triad (three-part) molecules. Finally, some even more complex multicomponent molecules are examined. The discussion will endeavor to point out aspects of photoinitiated electron transfer which are unique to the multicomponent species, and some of the considerations important to the design, synthesis and photochemical study of such molecules. 

The simplest covalently linked models for photosynthetic electron transfer must consist of a chromophore covalently linked to a donor or acceptor. The following reactions are then observable, in principle. 

The vast majority of the dyad models for photosynthetic electron transfer have consisted of synthetic porphyrins covalently linked to quinones. The first such models were reported in the late 1970 s. Kong and Loach prepared the ester-linked dyad 2 in 1978 [38], and the amide 3 was reported by Tabushi and coworkers in 1979 [39]. A large number of these P-Q systems have now appeared in the literature. The reader is referred to several reviews [13, 34, 40], including the recent review by Connolly and Bolton [41] for a complete compilation of these results. 

The second article also deals with PET in arranged media, however, this time by discussing comprehensively the various types of heterogeneous devices which may control supramolecular interactions and consequently chemical reactions. Before turning to such applications, photosynthetic model systems, mainly of the triad type, are dealt with in the third contribution. Here, the natural photosynthetic electron transfer process is briefly discussed as far as it is needed as a basis for the main part, namely the description of artificial multicomponent molecules for mimicking photosynthesis. In addition to the goal to learn more about natural photosynthetic energy conversion, these model systems may also have applications, which, for example, lie in the construction of electronic devices at the molecular level. 

Imahori H,Tamaki K, Yamada H, et al. Photosynthetic electron transfer using fullerenes as novel acceptors. Carbon 2000 38 1599-605. 

Imahori, H. and Sakata, Y. 1999. Fullerenes as novel acceptors in photosynthetic electron transfer. Eur. J. Org. Chem 1999, 2445-2457. 

Interference by Herbicides with Photosynthetic Electron Transfer... 

Nagarajan, V., Parson, W. W., Gaul, D., and Schenck, C., 1990, Effect of specific mutations of tyrosine-(M)210 on the primary photosynthetic electron-transfer process in Rhodobacter sphaeroides. Proc. Natl. Acad. Set USA, 87 788897892. 

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