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Photosensitized Oxidation of Oxopurines by Rose Bengal†

Daniel Horacio Murgida, Pedro Francisco Aramendía, Rosa Erra Balsells

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Abstract

Abstract Photosensitized oxidations of oxopurines (OP) as caffeine, theophylline, theobromine and 1,3,7‐trimethyluric acid (TMU) by Rose Bengal were investigated. In all cases photooxidations occur by a type II mechanism. Reactive and nonreactive 1O2 quenching rate constants by OP were determined in different solvents. Based on the correlations of the rate constants with different solvent parameters (α, β, ET[30], AN, DN, *,), the initial formation of an exciplex between 1O2 and OP is proposed that evolves to a zwitterionic transition state. Some reaction products were characterized, among them 3‐mefh‐yl‐5‐(methylamine)‐1,5‐dehydrohydantoin was obtained as the main photooxidation product of TMU. A reaction mechanism is proposed for the formation of this and other reaction products.

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What this paper is about

Abstract Photosensitized oxidations of oxopurines (OP) as caffeine, theophylline, theobromine and 1,3,7‐trimethyluric acid (TMU) by Rose Bengal were investigated. In all cases photooxidations occur by a type II mechanism. Reactive and nonreactive 1O2 quenching rate constants by OP were determined in different solvents. Based on the correlations of the rate constants with different solvent parameters (α, β, ET[30], AN, DN, *,), the initial formation of an exciplex between 1O2 and OP is proposed that evolves to a zwitterionic transition state. Some reaction products were characterized, among them 3‐mefh‐yl‐5‐(methylamine)‐1,5‐dehydrohydantoin was obtained as the main photooxidation product of TMU. A reaction mechanism is proposed for the formation of this and other reaction products.

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Available abstract

Abstract Photosensitized oxidations of oxopurines (OP) as caffeine, theophylline, theobromine and 1,3,7‐trimethyluric acid (TMU) by Rose Bengal were investigated. In all cases photooxidations occur by a type II mechanism. Reactive and nonreactive 1O2 quenching rate constants by OP were determined in different solvents. Based on the correlations of the rate constants with different solvent parameters (α, β, ET[30], AN, DN, *,), the initial formation of an exciplex between 1O2 and OP is proposed that evolves to a zwitterionic transition state. Some reaction products were characterized, among them 3‐mefh‐yl‐5‐(methylamine)‐1,5‐dehydrohydantoin was obtained as the main photooxidation product of TMU. A reaction mechanism is proposed for the formation of this and other reaction products.

Key concepts: Rose bengal, Chemistry, Theobromine, Reaction rate constant, Theophylline, Photochemistry, Quenching (fluorescence), Solvent

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