Studies on reaction of amino acids and triplet thioxanthone derivatives by laser flash photolysis.

Excitation of the thioxanthone derivatives (TXs), 2, 4-diethylthioxanthone (DETX) and 2-(2,3-epoxypropyloxy) thioxanthone (ETX) in acetonitrile/water mixture solution (1:1, v/v) upon 355 nm laser flash produced the triplet of TXs ((3)TXs(*)). Characteristic absorption spectra of (3)TXs(*)(590 nm) were recorded and rate constants of (3)TXs(*) quenched by O(2) and by its ground state were determined (9.8 x 10(9) M(-1) s(-1), 7.3 x 10(9) M(-1) s(-1) and 2.6 x 10(8) M(-1) s(-1), 2.2 x 10(8) M(-1) s(-1) respectively). The reactions of some amino acids oxidized by (3)TXs(*) were carried out. It has been found that tryptophan (Trp) and tyrosine (Tyr) can quench (3)TXs(*) via electron transfer process and related quenching rate constants were obtained. (3)TXs(*) induced protein damage was investigated using electrophoresis and significant levels of dimerisation were observed under aerobic and anaerobic conditions. The influence of photo-sensitizer's structure on photo-oxidation of amino acid and protein has been discussed.