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NEW PHOTOSYSTEM I ELECTRON ACCEPTORS: IMPROVEMENT OF HYDROGEN PHOTOPRODUCTION BY CHLOROPLASTS *
Author(s) -
Cuendet Pierre,
Grätzel Michael
Publication year - 1982
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1982.tb04365.x
Subject(s) - electron transfer , chemistry , electron transport chain , photosystem i , photochemistry , photosynthetic reaction centre , electron acceptor , photosystem ii , membrane , hydrogenase , photosynthesis , redox , chloroplast , catalysis , inorganic chemistry , biochemistry , gene
Four novel electron carriers (two zwitterionic bipyridyls, dicarboxyl colbalticinium and sodium metatungstate), which are negatively charged in their reduced form, have been tested as photo‐system I acceptors and as mediators of H 2 evolution. Measurements of O 2 uptake, anaerobic photoreduction rates and stationary concentrations of reduced species under continuous illumination indicate that Coulombic interactions control the electron transfer between the photosynthetic membrane and the mediators. Both rates of forward transfer and back reaction (electron cycling) seem to depend on the charge of the electron carrier. The low concentration of anionic species in the diffuse layer associated with the membrane could explain our results. Hydrogen evolution rates obtained with these four mediators used as electron relays between the photosynthetic membrane and colloidal platinum catalyst are higher than with methylviologen. This improvement of the conversion efficiency parallels the high steady state accumulation of reduced carriers favoured by their negative charge. It is also shown that these synthetic mediators, except metatungstate, are able to evolve hydrogen with an hydrogenase isolated from Desulfovibrio desulfuricans .