ON N-ACETYLCYSTEINE .1. EXPERIMENTAL AND THEORETICAL APPROACHES OF THE N-ACETYLCYSTEINE H2O2 COMPLEXATION

The complexation of N-acetylcysteine (RSH) with hydrogen peroxide has been studied experimentally and theoretically. Experimentally we have measured the evolution of RSH, H2O2, and RSSR (N-acetylcystine) as a f unction of time. Surprisingly, H2O2 decays by a biphasic process, whic h is not the case for RSH and RSSR. In the first stage of the kinetics , H2O2 disappears without oxidizing the thiol function of RSH. By anal ogy with glutathione (GSH), the formation of a complex between RSH and H2O2 has been proposed. The thermodynamic equilibrium constant of com plex formation has been determined. Theoretical calculations were perf ormed within the SIBFA method to pinpoint the sites of complexation in isolated and hydrated states. A mixed ''discrete-continuum'' model wa s used to evaluate the solvent effect. The two stable complexes found in isolated state have different behaviour under the influence of the solvent. Comparison with complexed GSH is discussed.