Oxidative degradation of l-histidine by manganese dioxide (MnO2) nano-colloid in HClO4 medium with/without using TX-100 catalyst: a kinetic approach

Abstract

The kinetics of the oxidative degradation of L-histidine (His) in perchloric acid medium by freshly prepared manganese dioxide (MnO₂) nano-colloid have been investigated with and without using TX-100 catalyst at a constant temperature of 35 °C. The progress of the oxidation reaction was checked by monitoring the decrease in absorbance of MnO₂ spectrophotometrically at 360 nm. The reaction was observed to be first order with respect to [MnO₂] and fractional with respect to [His] and [HClO₄] in both uncatalysed and TX-100-catalysed paths. The catalytic effect of TX-100 on the oxidation reaction has been explained by the Tuncay model. Protonated L-histidine is bound to TX-100 and forms a [TX-100–His] intermediate complex which further reacts with MnO₂ and decomposes into the oxidation products: 2-imidazole acetaldehyde, Mn(II), NH₄⁺ and CO₂. On the basis of the kinetics results, a possible reaction mechanism is proposed.