[Quenching of singlet oxygen with chlorophylls and porphyrins]

The rate constants (kox) of irreversible oxidation of chlorophylls and porphyrins by 1 delta g state of oxygen (1O2) have been determined. It has been shown that kox values are 1-5 orders of magnitude lower than the values of rate constants of quenching 1O2 (kq) with the same pigments. The correlation between kox and kq has been found. Its analysis allowed to conclude that oxidation proceeds via intermediate formation of a charge transfer complex between the pigments and 1O2. A kinetic scheme of the processes leading to physical and chemical quenching 1O2 with chlorophylls and porphyrins is proposed, its mathematical analysis is carried out. The results of this analysis can be used for a search of substances capable of effective quenching 1O2 without destruction of the quenchers. It is concluded that chlorophylls protect photosynthetic membranes from the destruction by 1O2, and some synthetic metal-porphyrins can be used as good protectors of different systems against photooxidation.