Ru(III)-catalyzed oxidation of N-acetyl-L-cysteine by methylene blue in absence and in presence of Cu(II) in acidic medium: influence of solvent and morphology

N-acetyl l-cysteine (NAC), the substrate used presently has got diverse medicinal applications and is widely used as a mucolytic agent. The oxidation of bioactive molecules, in general, involves metal ion catalysis facilitated by the participation of metal nanoparticles. In view of this, the oxidation of NAC by a phenothiazine dye methylene blue (MB), a model electron receptor, catalyzed by Ru(III) in the absence and in the presence of Cu(II) has been investigated in acidic medium. The concentration order in MB is zero, while the order in NAC is one and two in Ru(III)-catalyzed and Ru(III)-Cu(II)-catalyzed reactions, respectively. Hydrogen ions retard the rate in Ru(III)-Cu(II)-catalyzed reaction, whereas the rate increases linearly with increasing Ru(III)] in both the systems. The rate increases with increasing Cu(II)] and attains a limiting value. The addition of the reaction products does not affect the rate of reaction. The reaction is characterized by a large negative entropy of activation. The kinetic deviations of the reaction, explained by presuming the participation of a reactive form of the NAC molecule or its new conformational polymorph reported recently, indicate the regulatory influence of the morphology of nanoparticles.