Kinetic investigation on the oxidation of N -acetyl cysteine by dioxygen of μ-dioxytetrakis(histidinato)dicobalt(II) complex

Abstract

At neutral and alkaline pH cobalt(II)histidine complex binds with molecular oxygen reversibly to form μ-dioxytetrakis(histidinato)dicobalt(II), an oxygen adduct complex. The reaction proceeds in such a way that the addition of N-acetyl cysteine to μ-dioxytetrakis(histidinato)dicobalt(II) results in the fading away of brown color of μ-dioxytetrakis(histidinato)dicobalt(II) due to the oxidation of N-acetyl cysteine. Thus, kinetic measurement of this oxidation was exploited and studied spectrophotometrically at different concentration of N-acetyl cysteine, μ-dioxytetrakis(histidinato)dicobalt(II) and hydroxide ion. Effect of μ-dioxytetrakis(histidinato)dicobalt(II) was studied in the concentration range from 1.0 × 10− 3 mol dm− 3 to 5.0 × 10− 3 mol dm− 3 and it was found that rate constant was independent on [Co(II)histidine] with the average value of rate constant 1.11 × 10− 3 s− 1. It was observed that the values of rate constant were found to be independent of [N-acetyl cysteine] at higher concentrations, but, varied linearly with [N-acetyl cysteine] at lower concentrations (1–6 × 10− 3 mol dm− 3). The values of rate constant increased from 1.17 × 10− 3 s− 1 (at [NaOH] = 5.0 × 10− 4 mol dm− 3) to 2.55 × 10− 3 s− 1 when the concentration of NaOH is increased to 1.0 × 10− 2 mol dm− 3.