Photoinduced Electron Tunneling in Biological Systems

The reaction centre (RC) of purple bacteria seems to be a suitable object for elucidating the mechanisms providing extremely high efficiency of electron transfer in photosynthetic systems. 

The electron localized on the particle QA is subsequently used, through a complicated chain of chemical reactions, to reduce C02 to the carbohydrates (CH20)6, while the hole is finally used to oxidize some certain substrate, say hydrogen sulphide to sulphur. This results in the regeneration of the active centre. 

Early experimental studies on the role of electron tunneling in biological systems were typically carried out on subchromatophore and subchloroplast fragments at low temperatures. The operation of photosynthetic organisms at low temperatures 

After [9], numerous papers were published related to the low-temperature photooxidation of P700 in the PS1 reaction centres of plants and the reverse process of recombination of P700+ and a reduced electron acceptor (see e.g. Refs. [208-211]). In these works controversial data on the kinetics of the dark decay of P700 + were obtained. Therefore in Ref. [212] the kinetics of charge recombination in the PS1 reaction centres was investigated in detail over a broad range of times and temperatures. 

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