In the ground (unexcited) state of molecules (atoms) all electrons usually are located on the orbitals, next to a kernel, in pairs, and in each couple of electrons of the direction of their rotation around an axis (i.e. spins) are opposite. Such condition of a molecule is called the ground singlet state. At excitement (absorption of quantum of energy) one of electrons passes to an overlying orbital without change of spin. At the same time there is an excited singlet state of a molecule. In wild spirits electrons buy identical spins from a part of molecules, i.e. there is an address of spin. This condition of a molecule is called triplet. The return transition of molecules from the excited singlet or triplet states in the ground singlet state often is followed luminescence (see). Transition of molecules of a number of dyes (methylene blue, toluidine blue, tetraethyl-diamino-triphenyl-carbohydride sulfate, etc.) in excited state represents the first link of their bactericidal photodynamic action.
The most studied and important in biol. the relation S. of page of oxygen is. Contrary to the majority of other connections of a molecule of oxygen usually are in a triplet state and possess rather low biol. activity. Transition them in S. the village demands energy consumption not less than 94,2 cd (22,5 kcal/mol). High biol. activity of singlet oxygen is caused by its high reactivity concerning many biomolecules possessing unsaturated chemical bonds (in particular, nucleinic to - t, lipids, aromatic amino acids). Assume that bactericidal effect of nek-ry dyes and polymorphonuclear leukocytes, and also cytotoxic effect of nek-ry herbicides (metilviologen), pollutants of the atmosphere (ozone, nitric oxide, acetyl-peroxynitrates), the separate reactions proceeding at x-ray and UF-radiation, are caused by transition of molecular oxygen to S. of page. Hypotheses of a role of a singlet form of oxygen in an etiology of malignant new growths, aging and in the mechanism of the damaging action of nek-ry toxic agents are formulated (see. Carcinogenesis , Radicals free ).
Bibliography: Introduction to photochemistry of organic compounds, under the editorship of G. O. Becker, the lane with it., L., 1976; Merzlyak M. H. ii the Sable in A. S. A role superoxidic radical anion and singlet oxygen in pathology of membranes, in book: Molek. patol. membrane structures, under the editorship of Yu. A. Vladimirov, page 118, M., 1975; Foot of X. Photosensitized oxidation and singlet oxygen, the Biological investigations, in book: Free radicals in biol., under the editorship of U. Pryor, the lane with English, t. 2, page 96, M., 1979, bibliogr.
M. N. Merzlyak, A.S. Sobolev.