Add time:08/16/2019         Source:sciencedirect.com

A study of the effect of some divalent anions (carbonate, oxalate, phthalate, phosphate) on the kinetics of photodegradation reactions of riboflavin (RF) and its pathways, product composition and fluorescence quenching in the pH range 6.0–8.0 has been conducted. The photodegradation of RF in the presence of 0.2–1.0 M divalent anions on visible irradiation leads to the formation of cyclodehydroriboflavin (CDRF) by photoaddition pathway and lumichrome (LC) by photoreduction pathway as the major end products. These products are formed by simultaneous first–order reactions. The divalent anions deviate the photoreduction pathway of RF in favor of photoaddition pathway to yield CDRF. The extent of this variation depends on the strength of RF–divalent anion complex as indicated by an increase in the loss of RF fluorescence due to complex formation. The first– and second–order rate constants for the photodegradation of RF have been determined and the effect of pH on the rates of these reactions evaluated. The rate of divalent anion catalyzed formation of CDRF is maximum at pH 7 and occurs in the order: carbonate > phosphate > oxalate > phthalate. The catalytic activity of the divalent anions increases with the strength of RF–divalent anion complex resulting in an increase in the rate of formation of CDRF and a decrease in the rate of formation of LC by different pathways.

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