The role of substituents on the complexation of thiols with copper ion

Copper complex formation has been monitored along with thiols (RSH) in the non-enzymatic wine oxidation reactions [1]. The presence of different substituents can be effective in the stability of Cu2+···RS2 complexes. The effects of some substituents on the binding energy (ΔE) of Cu2+···RS2 complexes has been investigated in the present work. All calculations were carried out at the B3LYP/6-31G(d,p) level of theory and using the Gaussian09 program package [2]. The trend of –ΔE values is: OCH3 > CH3 > H > Cl > NO2. The Cu2+··· RS2 complexes become more stable in the presence of electron-donating substituents (OCH3 and CH3), because of increase in the negative charge density on the S atom. A linear relationship is observed between –ΔE and the total Hammett constant, σt, (σt = σmeta + σpara and R = 0.98).