THE AEROBIC RIBOFLAVIN-SENSITIZED PHOTODECOMPOSITION OF TRYPTOPHAN, TRYPTAMINE AND INDOLE ACETIC-ACID - GROUND-STATE AND PHOTOPROMOTED FLAVIN-INDOLE INTERACTIONS

The interaction between riboflavin (RF) and the indole derivatives try ptophan, tryptamine and indole-3-acetic acid at visible light irradiat ion was studied in water and water/ethanol mixed solvent. Besides a da rk indole-RF association, important only at indole concentration highe r than 10(-3) mol dm-3, a complex picture of competitive reactions ope rate. Triplet excited RF is quenched by the indoles in concentrations ca 10(-4) mol dm-3 (rate constants of the order of 10(9) mol-1 dm3 s-1 ) and by dissolved oxygen. Both, singlet molecular oxygen and superoxi de anion (in a further reaction step) are produced. As a consequence t he rate of indole photodecomposition decreases in order: indole-3-acet ic acid > tryptophan >> tryptamine, and the rate of RF autofading suff ers an important delay compared with that in the absence of the indole s.