Kinetics of oxidation of Cysteine and Captopril via [Mo(CN)8] and [W(CN)8]

Abstract

The kinetics of the oxidation of cysteine and captopril via octacyanomolybdate(V) and octacyanotungstate(V) in a buffered acidic media (pH range 2.20–4.80) have been studied spectrophotometrically. The rate law for the oxidation is: Rate = k [RSH] [Ox] [H+] 1 , where RSH is cysteine or captopril and Ox is Cs3[Mo(CN)8] or Cs3[W(CN)8]. The activation parameters (Ea, DH#, DG#, DS#) for the oxidation of cysteine and captopril via Cs3[Mo(CN)8] or Cs3[W(CN)8] have been determined. The results indicate that Cs3[Mo(CN)8] is more reactive than Cs3[W(CN)8] as an oxidizing agent. Effects of pH, ionic strength, temperature, dielectric constant of the reaction medium and copper(II) ions on the oxidation rate have been studied. Mechanisms for the oxidation of cysteine to cystine and captopril to the corresponding disulfide have been proposed.