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

Abstract

Ninhydrin reactions using manual and automated techniques as well as ninhydrin spray reagents are wide ly used to analyze and characterize amino acids, peptides, and proteins as well as numerous other ninhydrin po sitive compounds in biomedical, clinical, food, forensic, histochemical , microbiological, and nutritional and plant studie s. 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 o f ninhydrin with (Ni(II)-Gly-Leu) + complexes, systematic kinetic studies were perform ed by following appearance of the respective colore d condensation products at different (surfactant), (r eactant), (salt) and temperature. The rates of the reaction were determined in both water and surfactant micelles in the absence and presence of various org anic and inorganic salts at 70 °C and pH 5.0. The result shows that the reaction follows the same fir st-order and fractional-order kinetics with respect to (Ni(II)-Gly-Leu) + and (ninhydrin), respectively, in both aqueous and mice llar medium. Quantitative kinetic analysis of k ψ(CTAB) data was performed on the basis of the pseudo-phase model of the micelles. + , CTAB