Kinetic study of the metal-dipeptide complex with ninhydrin facilitated by gemini (m-s-m) surfactant micelles

Abstract

The three Gemini (m-s-m; m (head group) = 16 and s (spacer) = 4, 5, 6) surfactants have been synthesized and their impact on reaction of zinc(II)-glycylleucine complex ([Zn(II)-Gly-Leu]+) and ninhydrin were studied at temperature (343 K) and pH (5.0) using spectroscopic method. Influence of several factors, viz., [Zn(II)-Gly-Leu]+, [ninhydrin], temperature and pH were also carried out on title reaction in geminis. Rates of reaction are the first-order path in concentration of [Zn(II)-Gly-Leu]+ complex and fractional order path in concentration of ninhydrin. The catalysis of gemini 16-s-16 surfactant micelles was investigated below and above their critical micelle concentration (cmc) value and detailed elaboration were provided in the text. In the present case, rate constants, kψ, increased on increasing geminis ([gemini] are below their cmc, region I) and stayed nearly constant (region II). The shape of (region I and II) surfactants ([gemini] = 0 to 400 × 10−5 mol dm−3) are similar to a cetyltrimethylammonium bromide, CTAB (single hydrophilic head group and hydrophobic part). Later, a sharp increment in rate was observed with higher [gemini] (region III, (Fig. 5). The study was catalyzed and accelerated quite enough by geminis (at concentrations below their cmc) compared to aqueous. An appropriate mechanism has been proposed for accounting for the distribution of reactants between aqueous and micellar pseudo phases. Resulting kinetic data were used to determine the binding constants of micelle-substrate (KB) and micelle-ninhydrin (KNin).