New metal compounds and their reactivity towards bovine milk casein

Abstract

The l,2-bis(sulphapyridyl)oxamide ligand [L] and its complexes with FeIII, CoII, CuII and ZnII chloride were synthesized and characterized by elemental analyses, i.r., n.m.r., e.p.r. and u.v.–vis. spectroscopy and molar conductance measurements. Spectroscopic studies show that all the complexes are octahedral and covalent. The electrochemical behaviour of the CoII complex was monitored by cyclic voltammetry in a buffer/DMF solution (95:5). The E0 values −0.622 and −0.502 V reveal a reversible one electron redox wave attributed to a CoII/CoI redox couple at a scan rate of 0.1 V s−1. The interaction of the CoII complex with bovine milk casein (BMC) was studied at the same scan rate, which reveals a strong binding as the E0 values shift to more negative potential (E0 = −0.908 and −0.703 V). The cyclic voltammograms of the CoII complex bound by BMC were recorded at different pH's. The plot of E0versus pH showed that E0 values are maximal at pH 7.4 indicating good interaction between the BMC and the CoII complex which is further confirmed by kinetic data. The kinetic studies of the CoII complex bound to BMC was monitored in phosphate buffer solution at different pH's by spectrophotometry. The absorbance changes were monitored at 278 nm (λmax for BMC) with respect to time and pseudo-first-order rate constants, Kobs, were obtained from the slope and intercept of the straight line using the least squares regression method. The plot of absorbance versus time at different pH's was linear up to 80% completion of the reaction. The pH-rate profile data reveals that the reactions are pH dependent.