Pulse radiolysis studies of mangiferin: A C-glycosyl xanthone isolated from Mangifera indica

Pulse radiolysis technique has been employed to study the reaction of different oxidizing and reducing radicals with mangiferin. The reaction of (OH)-O-center dot radical showed the formation of transient species absorbing in 380-390 and 470-480 nm region. The reaction with specific one-electron oxidants (N-3(center dot), CCl3O2 center dot) also showed the formation of similar transient absorption bands and is assigned to phenoxyl radicals. The pK(a) values of the transient species have been determined to be 6.3 and 11.9. One-electron oxidation potential of mangiferin at pH 9 has been found to be 0.62 V vs. NHE. The reaction of e(aq)(-) showed the formation of transient species with lambda(max) at 340 nm, which is assigned to the ketyl anion radical formed on addition of e(aq)(-) at carbonyl site. Reactions of one-electron oxidised mangiferin radicals with ascorbic acid have also been studied. (C) 2005 Elsevier Ltd. All rights reserved.