RADIOLYSIS OF GLYCYRRHIZIC ACID MONOAMMONIUM IN N2O SATURATED AQUEOUS-SOLUTION - A PRODUCT AND PULSE-RADIOLYSIS STUDY

The mechanism and kinetics of glycyrrhizic acid monoamonium (GAM) reac ting with hydroxyl radical generated by gamma-ray irradiated N2O-satur ated aqueous solution were studied. The radiolytic products were separ ated with HPLC and the molecular structures were determined by UV, IR, MS and elementary analysis methods. The major product was formed by t he attack of hydroxyl radical to the C=C double bond of GAM. The other s resulted from the release of one and two glucuronic acid molecules i n GAM respectively. The rate constant of GAM reacting with the hydroxy l radical was measured using a competition method by pulse radiolysis technique to be of 3.0 x 10(9) dm(3) mol(-1) s(-1). The transient spec ies generated by pulse radiolysis of GAM aqueous solution saturated wi th N2O at pH 10 exhibited an absorption maximum at about 325 nm with e xtinction coefficient 260 dm(3) mol(-1) cm(-1). The rate constant of s econd-order decay of transient species was 5.8 x 10(8) dm(3) mol(-1) s (-1). The transient species was formed by the attack of hydroxyl radic al to the CC double bond of GAM. The G values of GAM and its radiolyti c products of 4.0 x 10(-4) mol dm(-3) aqueous solution saturated with N2O at absorbed dose of 500 Gy are: G(-GAM) = 2.4, G(RP1) = 2.2, G(RP2 ) = 0.3, G(RP3) = 0.1. (C) 1998 Elsevier Science Ltd. All rights reser ved.