Influence of dicationic quaternary ammonium gemini surfactant system on metal-amino acid complex-ninhydrin reaction

Abstract

In the current study, we have elucidated the influence of dicationic quaternary ammonium geminis system on metal-amino acid [Ni(II)-his]+ complex-ninhydrin reaction with the help of UV–vis spectrophometer at 343 K and pH 5.0. Under varying experimental conditions, rate constant values, kψ, were determined using a computer-based program. Quaternary ammonium gemini systems (rate constant values of 16-6-16, 16-5-16 and 16-4-16 at 30 × 10−5 mol dm−3 are 5.5 × 10−5 s−1, 6.5 × 10−5 s−1 and 7.5 × 10−5 s−1, respectively) are detected more superior compared to aqueous system (rate constant in aqueous is 1.7 × 10−5 s−1). Study was catalyzed and accelerated by gemini surfactants (even though at concentrations below than their cmc values) compared to aqueous medium. Rate constant increases progressively on increasing [gemini] (region I, where [gemini] is smaller than their cmc) and levelling-off regions attain (region II, at [gemini] up to 400 × 10−5 mol dm−3). Afterward, gemini provides a region III of increasing kψ at higher concentration (region III, beyond 400 × 10−5 mol dm−3). Experimental results acquired in dicationic quaternary ammonium gemini surfactant system are deduced quantitatively by kinetic pseudo-phase model. For determination of cmc of geminis having a different methylene spacer chain length (s = 4, 5, 6), the specific conductance at varied [16-6-16], [16-5-16] and [16-4-16] (i.e., water and water + ninhydrin + [Ni(II)-his]+) were 0.043 × 10−3 mol dm−3 at 303 K and 0.053 × 10−3 mol dm−3 at 343 K; 0.034 × 10−3 mol dm−3 at 303 K and 0.044 × 10−3 mol dm−3 at 343 K; 0.032 × 10−3 mol dm−3 at 303 K; 0.040 × 10−3 mol dm−3 at 343 K, respectively, recorded on a conductivity meter. Several activation parameters for 16-6-16, 16-5-16 and 16-4-16 (ΔH# = 45.0, 43.5 and 42.0 kJ mol−1; ΔS# 87.0, 87.6 and 88.3 JK-1; Ea = 47.8, 46.3 and 44.8 kJ mol−1) and binding parameters for 16-6-16, 16-5-16 and 16-4-16 (KX = 63.0, 58.0 and 54.0 mol−1 dm3; KY = 70.0, 66.0 and 62.0 mol−1 dm3) are also determined.