Influence of TTAB/14-S-14 Micelles on the Rate of the Condensation between Ninhydrin and Mercury-Dipeptide Complex in Absence and Presence of Salts and Organic Solvents: A Kinetic Approach

Abstract

The interaction of mercury(II)–glycyl-L-alanine [Hg(II)–Gly-L-Ala]⁺ complex with ninhydrin has been studied kinetically both in aqueous as well as micellar media (cationic conventional/gemini surfactants) using UV-vis spectrophotometer at 70 ºC and a particular pH 5.0. The study was carried out as functions of [Hg(II)–Gly-L-Ala]⁺, [ninhydrin], [surfactant] [salts], and solvents (%v/v). The first-order-rate is observed concerning [Hg(II)–Gly-L-Ala]⁺, whereas fractional-order-rate dependence for [ninhydrin]. It has been found that 14-s-14 geminis enhance the rate of reaction more effectively than related cationic conventional surfactant tetradecyltrimethylammonium bromide (TTAB). The effect of additives such as salts (inorganic/organic) and organic solvents on the rate was also investigated. The reaction rate was explained in terms of the modified pseudo phase model (considering the association/adsorption of both the reactants on the micellar surface) and changes in micellar morphology occurring at higher [geminis]. The Eyring equation is valid for the reaction over the range of temperatures used. Various thermodynamic parameters and binding constants between reactants with the micelles have been evaluated.