On N-acetylcysteine. Part I. Experimental and theoretical approaches of the N-acetylcysteine/H2O2 complexation

Article abstract of DOI:10.1139/v94-266

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 function of time. Surprisingly, H₂O₂ decays by a biphasic process, which 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 analogy with glutathione (GSH), the formation of a complex between RSH and H₂O₂ has been proposed. The thermodynamic equilibrium constant of complex formation has been determined. Theoretical calculations were performed within the SIBFA method to pinpoint the sites of complexation in isolated and hydrated states. A mixed 'discrete-continuum' model was 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.