PHOTOCHEMISTRY AND SPECTROSCOPY OF CHLOROPHYLL, BACTERIOCHLOROPHYLL AND BACTERIOVIRIDIN IN MODEL SYSTEMS AND PHOTOSYNTHETIZING ORGANISMS

Abstract— In the system (electron donor—pigment—electron acceptor), the photosensitising pigment transfers an electron (hydrogen) from the donor to the acceptor by converting light energy, absorbed by the pigment, into the potential chemical energy of the products. The dependence of the reaction of excited pigments with electron donors or acceptors on the magnitude of the electron affinity of the reacting molecules, the nature of the medium, and the experimental conditions was observed. The initial photo-process was seen to involve the formation of free radicals, with the subsequent formation of compounds with saturated valencies. The reverse reaction of the photoproducts was accompanied by chemiluminescence. The study of systems containing pyridinenucleotides showed the possibility of photosensitised oxidation—reduction of these compounds by a pigment, and of direct photooxidation of reduced pyridinenucleotides by an electron acceptor of a different kind. In order to understand the specific photo-transfer of an electron in organisms, the spectral properties of pigments in organisms were compared with the properties of model pigments in monomeric and aggregated forms. It was established that the main role in the spectroscopic properties shown by bacteriochlorophyll, bacterioviridin and chloropyll in organisms is played by various types of intermolecular interactions (aggregations). Different forms of pigment may be involved in different stages of the phototransfer of an electron.