Modelling the natural photodegradation of water contaminants. Kinetics of the light-induced aerobic interactions between riboflavin and N-heteroaromatic derivates

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MODELLING THE NATURAL PHOTODEGRADATION OF WATER CONTAMINANTS. KINETICS OF THE LIGHT-INDUCED AEROBIC INTERACTIONS BETWEEN RIBOFLAVIN AND N-HETEROAROMATIC DERIVATIVES. Within our current studies on the natural photodegradation of representative aquatic environmental contaminants, the visible light irradiation of the three model compounds of pesticides, in air-equilibrated aqueous solutions and in the presence of the naturally-occurring pigment Riboflavin (Vitamin B2, Rf) was studied. The model contaminants were 3-hydroxypyridine (3-OHP), 4-hydroxypyridine (4-OHP) and 2-amino-4-hydroxy-6-methylpyrimidine (AHMPD). Employing stationary photolysis, polarographic detection of oxygen uptake, stationary and time resolved fluorescence spectroscopy, and laser flash photolysis, results support the existence of competitive oxidation processes, which can alternatively determine the degradation of both the pigment and the contaminants. As a global result, the photodecomposition of Rf -which proceeds from the excited triplet state of the pigment- stands on the concentration of the dissolved substrates. At relatively high substrate concentration (> 5 mM ) the singlet excited Rf is quenched and no further reaction occurs. On the other hand, when substrate concentration is in the range 0.1 – 0.01 mM, a non simple picture of competitive reactions operates, with the participation of singlet molecular oxygen and superoxide radical anion, that produce the oxidation of the contaminants and the concomitant delay in Rf degradation. Información suministrada por el agente en SIGEVA