Pulse radiolysis study on the rutin and quercetin anions formation and their behaviours in N2-saturated ethanol solution

Abstract

pulse radiolysis and gamma-radiolysis. The results show that solvated electron can add to rutin and quercetin and produce corresponding radical anions which show a maximum UV absorbance band at 430 and 420 nm. The epsilon(max) of radical anions of rutin and quercetin are 3.5 x 10(3) mol(-1) dm(3) cm(-1) and 5.5 x 10(3) mol(-1) dm(3) cm(-1), respectively. The rate constants of build-up of radical anions of rutin and quercetin are 7.5(+/-0.9) x 10(9) mol(-1) dm(3) s(-1) and 7.7(+/-0.6) x 10(9) mol(-1) dm(3) s(-1), respectively. The decay of radical anions is induced by the protonation which contains a pseudo-first-order reaction and a second-order reaction. For the radical anion of rutin, the rate constants of decay are 1.1(+/-0.1) x 10(4) s(-1) and 2.7(+/-0.2) x 10(9) mol(-1) dm(3) s(-1), respectively. For the radical anion of quercetin, the rate constants of decay are 1.5(+/-0.1) x 10(4) s(-1) and 4.0(+/-0.5) x 10(9) mol(-1) dm(3) s(-1), respectively. The electron transfer between radical anions and acetaldehyde can occur at the rate constants of 8.9(+/-1.2) x 10(7) mol(-1) dm(3) s(-1) for radical anion of rutin and 1.2(+/-0.1) x 10(8) mol(-1) dm(3) s(-1) for radical anion of quercetin. The rate constants of their corresponding counter-reactions are 5.7(+/-0.8) x 10(7) mol(-1) dm(3) s(-1) and 2.0(+/-0.6) x 10(7) mol(-1) dm(3) s(-1), respectively. The equilibrium constants of electron transfer reactions are 1.6 and 6.0, respectively. The standard electrode potential of radical anions of rutin and quercetin are obtained to be -1.94 and -1.98 V. (C) 1999 Elsevier Science Ltd. All rights reserved.