Inhibition of {cysteine–surfactant} aggregation in cysteine–cystine transformation by alkaline hexacyanoferrate(III); A kinetic study

The kinetics of cysteine–cystine transformation by alkaline hexacyanoferrate(III) in presence of cationic (cetyltrimethyl ammonium bromide, CTAB), anionic (sodium lauryl sulphate, NaLS) and non-ionic (polyoxyethylene (10) octylphenol, Tx-100) surfactant has been studied in the temperature range 25–35 °C. An inhibition effect of CTAB and NaLS on the rate of reaction has been observed at even below the critical miceller concentration (CMC) of the surfactants indicating association/binding of the substrate with the surfactants. Non-ionic surfactant (Tx-100) also retards the rate of reaction but above the CMC of the surfactant. On the basis of the kinetic results, the mechanism of the reaction has been proposed. The kinetic data have also been rationalized in terms of Manger and Portnoy's model for micellar inhibition and binding parameters (viz. binding constants, partition coefficient, free energy transfer from water to micelle, etc.) as well as activation parameters have been evaluated and explained.