Study On The Reaction Of Singlet Oxygen With L-Tryptophan And L-Tyrosine

In this paper a heterogeneous photosensitization system was constructed with Methylene Blue(MB) immobilized on cationic resins(R) and 9,10-diphenylanthracene as a trapper. The oxidation of Tryptophan and Tyrosine by singlet oxygen (1O2) was investigated. The main results are shown as follows:(1) Oxygen resolved in photosensitive system is the premise condition of yielding 1O2. Methylene Blue and Rose Bengal performed the most efficacy on photosensitivity and the optimal concentration for Methylene Blue is 10-4mol/L.(2) Diffuse reflectance spectra of MB-R show that MB molecules adsorbed on resins in monomeric form. The chemiluminescence and the high performance liquid chromatography of 9,10-diphenylanthracene peroxide demonstrated that methylene blue(MB) immobilized on cationic resins(R) in the photosensitization system enhanced the transformation of ground oxygen into singlet oxygen.(3) The results indicated that the reaction kinetics of 1O2 and Tryptophan is of second-order in the system. Irradiation indensity accelerated the oxidation of Tryptophan, whereas the rate of oxidation decreased as the initial concentration of Tryptophan increased. The oxidation of Tryptophan was not affected significantly with pH. The rate of oxidation for Tryptophan in heterogeneous photosensitization system is higher than in homogeneous system.(4) The reaction kinetics of 1O2 and Tyrosine is of second-order as well. The oxidation rate of Tyrosine decreased as the initial concentration of Tyrosine increased and affected with pH. The oxidation rate constant is smaller in mild base solution whereas larger in alkali. Tryptophan enhanced the oxidation of Tyrosine. The reaction rate of oxidation for Tyrosine in heterogeneous photosensitization system is higher than in homogeneous system.Tryptophan and Tyrosine in presence of photosensitive agents heterogeneous can be oxided under the irradiation of visible-light. The results would be help for understanding the mechanism for food nutritional losing and undesirable flavor occurring etc..