Kinetic and mechanistic investigations of [Zn (II)‐Trp]+ and ninhydrin in aqueous and cationic CTAB surfactant

Abstract

AbstractKinetic and mechanistic investigations of [Zn (II)‐Trp]+ and ninhydrin in aqueous and cationic cetyltrimethylammonium bromide (CTAB) surfactant have been executed in CH3COOH‐CH3COONa buffers of pH 5.0. Spectrophotometric as well as conductometric techniques were employed to carry out the study at experimental temperature. The values of rate constant (kobs in aqueous and kψ in CTAB surfactant) and binding parameters (KB for [Zn (II)‐Trp]+ and KN for ninhydrin) have been determined by the means of a computer program referred to as linear least squares technique. Fractional‐ and first‐order kinetics were found in ninhydrin and [Zn (II)‐Trp]+, respectively, in aqueous and cationic CTAB. Study was catalyzed and accelerated by CTAB surfactant. An increase in CTAB surfactant concentration from 0 to 45 mmol kg−1 resulted to an increase in kψ from 2.5 × 10−5 s−1 to 22.7 × 10−5 s−1. Surfactant concentration beyond 45 mmol kg−1 had a slow decreasing effect in kψ. In order to elucidate CTAB effect on kψ, a pseudo‐phase model of micelles was applied.