USE OF DEOXYRIBOSE AS A PROBE FOR THE DETERMINATION OF RATE CONSTANTSFOR REACTIONS OF HYDROXYL RADICALS ON MERCURY-ELECTRODES

A voltammetric procedure is described which allows determination of ra te constants for reactions of hydroxyl radicals. Hydroxyl radicals, ge nerated by reaction of an iron-EDTA complex with H2O2 in the presence of ascorbic acid, attack deoxyribose to form products that, upon heati ng with thiobarbituric acid under acid conditions, yield a pink chromo gen with second order derivative cathodic wave at -0.88 V vs SCE. Adde d hydroxyl radical 'scavengers' compete with deoxyribose for the hydro xyl radicals produced and diminish chromogen formation. The electroche mical behavior of the chromogen has been determined using voltammetry and cyclic voltammetric techniques. A rate constant for reaction of th e scavenger with hydroxyl radical can be deduced from the inhibition o f chromogen formation. For a wide range of compounds, the results fit well with rate constants previously obtained with other methods. It is suggested that voltammetric deoxyribose assay is a simple and cheap a lternative for determination of rate constants for reaction of most bi ological molecules with hydroxyl radicals. Rate constants for reaction s of six kinds of active compounds extracted from rheum, a traditional Chinese herb, have been determined by this method. Reaction mechanism has also been discussed. (C) 1998 Elsevier Science S.A.