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

Summary 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 (³TXs^*). Characteristic absorption spectra of ³TXs^*(590 nm) were recorded and rate constants of ³TXs^* quenched by O₂ and by its ground state were determined (9.8 × 10⁹ M⁻¹ s⁻¹, 7.3 × 10⁹ M⁻¹ s⁻¹ and 2.6 × 10⁸ M⁻¹ s⁻¹, 2.2 × 10⁸ M⁻¹ s⁻¹ respectively). The reactions of some amino acids oxidized by ³TXs^* were carried out. It has been found that tryptophan (Trp) and tyrosine (Tyr) can quench ³TXs^* via electron transfer process and related quenching rate constants were obtained. ³TXs^* 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.