Interaction of Nickel-Dipeptide complex with Ninhydrin in Aqueous and Micellar Media

Ninhydrin reactions using manual and automated techniques as well as ninhydrin spray reagents are widely used to analyze and characterize amino acids, peptides, and proteins as well as numerous other ninhydrin positive compounds in biomedical, clinical, food, forensic, histochemical, microbiological, and nutritional and plant studies. Ninhydrin in aqueous solution reacts with α-amino acids to give a compound known as Ruhemann’s purple (diketohydrindylidenediketohydrindamine, DYDA). In order to elucidate the mechanism of the reactions of ninhydrin with [Ni(II)-Gly-Leu] complexes, systematic kinetic studies were performed by following appearance of the respective colored condensation products at different [surfactant], [reactant], [salt] and temperature. The rates of the reaction were determined in both water and surfactant micelles in the absence and presence of various organic and inorganic salts at 70 °C and pH 5.0. The result shows that the reaction follows the same first-order and fractional-order kinetics with respect to [Ni(II)-Gly-Leu] and [ninhydrin], respectively, in both aqueous and micellar medium. Quantitative kinetic analysis of kψ−[CTAB] data was performed on the basis of the pseudo-phase model of the micelles.