Synthesis and Characterization of Cobalt(III) Complex of 1,5-bis(2-Hydroxybenzamido)-3-aza pentane and its Interaction with Glutathione: A Kinetic and Spectrophotometric Study

Abstract

A new octahedral cobalt(III) complex of 1,5-bis(2-hydroxybenzamido)-3-aza pentane was synthesized and characterized by elemental analysis, UV-visible, IR, mass spectrometry and thermal analysis methods. Oxidative behaviour of the complex towards the physiologically abundant tripeptide, glutathione(GSH) was studied by UV-visible and FT-NMR techniques. Kinetics of electron transfer between the complex and GSH was studied at 25.0 ≤ t/°C ≤ 45.0, 0.025 ≤ [H⁺]/mol dm^-3 ≤ 0.20 and I = 1.0 mol dm^-3 (NaClO₄). NMR spectra of the reaction mixture were taken as a function of time. Changes observed in the NMR-spectrum during the period of scanning are the initial disappearance of the fine structure and subsequent broadening of the signals of GSH protons. Peaks at (δ, ppm): 2.93 and 2.98, characteristics of Cys-CH₂ δ protons in GSH get disappear slowly and new peaks develop at (δ, ppm): 3.33 and 3.38, corresponding to resonating frequencies of Cys-CH₂ δ protons in GSSG. Likewise, the peak at (δ, ppm):2.93, characteristic of Cys-CH₂ δ proton in GSH is replaced by the resurgence of two peaks at (δ, ppm): 4.3 and 4.1 ppm, commensurate with the resonating frequencies of same set of protons as that of GSH but in a dimeric environment. The time dependent NMR simulation of the reaction reveals that GSH reduces the Co^III moiety successfully, while it gets converted into the dimer, GSSG. The relatively fast transformation of GSH to GSSG as evident from both electronic spectra and NMR studies together with the activation parameters obtained from the temperature dependence of reaction rate suggest that there is no involvement of any bridging group for electron transfer and the redox process may be taking place via outer sphere mechanism.