Kinetic study of cysteine oxidation by potassium hexacyanoferrate(III) in the presence of sodium dioctylsulfosuccinate

The kinetic oxidation of cysteine (Cyst) by 0.001 M hexacyanoferrate(III) (Fe(CN)(6)(3-)) in 0.06 M HCI at 25 degreesC in aqueous and/or in and 0.005 M sodium dioctylsulfosuccinate (AOT) has been studied using optical absorption at 420 nm. The present data show that the reaction is first-order with respect to [Cyst](T) and Fe(CN)(6)(3-). Also, k(obs) is constant within the 0.05-0.10 M HCI range and decreases with increasing concentration of AOT up to 0.003 M, and then increases above 0.005 M AOT. The rate of the reaction in the presence of micelles can be explained using a pseudo-phase model of the kinetics. Association constants of Cyst and Fe (CN)(6)(3-) with AOT micelles are reported. The activation parameters DeltaH(#) and DeltaS(#) have also been obtained. The variation of the reaction rate with the nature of the salt is discussed.