Zinc dipeptide complex ([Zn(II)-Gly-Tyr]+)-ninhydrin reaction in the presence of gemini surfactants: A kinetic study

Kinetics of the title reaction has been carried out by studying the reaction spectrophotometrically at 353 K and pH 5.0 in the presence of cationic gemini (alkanediyl-α, ω-bis(dimethylhexadecylammonium bromide)) surfactants. The reaction followed first-order kinetics in [Zn(II)-Gly-Tyr]T+ complex and fractional-order kinetics in [ninhydrin]T. In addition to the rate constant (kΨ) increase and leveling-off regions, typically observed in case of conventional monomeric surfactant (e.g., CTAB) catalyzed reactions, a third region of increasing kΨ was seen at higher gemini surfactant concentrations. The data are interpreted in terms of pseudo-phase model (assuming the association/incorporation of both the reactants at the micellar surface) and changes in micellar morphology occurring at higher gemini concentrations.