THE PHOTOLYSIS OF TRYPTOPHAN IN THE PRESENCE OF OXYGEN

Abstract— Quantum yields for the destruction of tryptophan by a single 500 J flash in aqueous solution have been determined over the pH range 1–13 in both air-equilibrated and nitrogen-saturated conditions. When these quantum yields are compared with the quantum yields for radical formation and photoejection of electrons, it is found that there is good agreement only for the nitrogen-saturated case. In air-equilibrated solutions of tryptophan, there is a large disparity between the measured degradation quantum yields and those for photoejection of electrons and radical formation. Oxygen, therefore, is playing a major role in the photochemical decomposition and it is proposed that the major reaction which occurs, under normal atmospheric conditions, is the reaction of the lowest triplet excited state of tryptophan with oxygen.
Preliminary photolysis-product distributions against pH are discussed, and indicate that a total of nine major products are formed in the presence of oxygen.