Oxidation of Some Sustainable Sulfated Natural Polymers: Kinetics and Mechanism of Oxidation of Water-Soluble Chondroitin-4-Sulfate Polysaccharide by Hexachloroiridate(IV) in Aqueous Solutions

Abstract

The kinetics and mechanism of hexachloroiridate(IV) oxidation of chondroitin-4-sulfate as a sustainable coordination biopolymer macromolecule (CS) in aqueous acidic solutions at a constant ionic strength of 0.1 mol dm-3 has been investigated spectrophotometrically. Pseudo first-order plots gave sigmoidal curves of S-shape nature, indicating that the kinetics is complex. Two distinct stages have been observed. The first stage was relatively fast corresponding to the autoacceleration period, followed by a slow stage which became linear at a longer time period called the induction period. First-order dependence with respect to the [OX] and fractional first order in [CS] was observed for both stages. Kinetic evidence for formation of the 1:1 intermediate complex within the two stages has been revealed. The influence of [H+] on the rate constants indicated that the oxidation was of acid inhibition nature. The kinetic parameters have been evaluated, and a suitable reaction mechanism is suggested and discussed in terms of the nature of the electron-transfer process.