Study of the interaction between ninhydrin and chromium(III)-amino acid in an aqueous-micellar system: Influence of gemini surfactant micelles

Chromium(III)-amino acid ([Cr(III)-His]2+) and ninhydrin in an aqueous-micellar system were combined in acetate buffer at 353 K and analyzed by UV–vis spectroscopy. Dimeric geminis (16-s-16, s, spacer, = 4 to 6) were chosen as a surfactant and their influence on the reaction rate was determined. To show this behavior of gemini surfactants on rate constant (kψ), kψ was plotted against different surfactant concentrations. kψ increases with increasing [16-s-16] (at concentrations lesser than their cmc values, segment I) and levelling-off regions attain (concentration upto 400 × 10−5 mol dm−3, segment II). Later, [16-s-16] generates a third region of increasing kψ at higher [16-s-16] ([16-s-16] > 400 × 10−5 mol dm−3, segment III). The uncommon plot behavior of kψ vs. [16-s-16] was revealed, effectively, by utilizing a pseudo-phase model of micellar activity. Critical micellar concentration of pure gemini surfactants, as well as their mixed solution with reactants, was determined by conductometry. Based on the data, various thermodynamic parameters and binding constants were calculated under different experimental reaction conditions.