Kinetics and mechanism of interaction of dipeptide (glycyl-glycine) with ninhydrin in aqueous micellar media

Influence of twin-headed gemini micellar system on the study of methionine amino acid with ninhydrin in buffer solution

The influence of double-headed gemini was examined in the present study by studying the amino acid methionine mixed with ninhydrin in CH₃COOH-CH₃COONa buffer solvent. The absorbance was monitored at fixed time intervals with UV-vis spectroscopy. An impact typical of surfactants was observed on the ninhydrin-methionine reaction and explained by a pseudo-phase model of micelles. The effect of different temperatures (343 to 363 K) was also determined. Based on data showing the impact of temperature on k_ψ , several relevant thermodynamic quantities, ΔH ^#, ΔS ^#, and E _a, were calculated using linear least-squares regression. In addition, the influence of the other reaction ingredients on the reaction, that is, pH and the concentration of ninhydrin and methionine, was studied. The CMC (critical micelle concentration) of pure geminis and the surfactant system with methionine and ninhydrin was evaluated at two temperatures, i.e. at 303 K and 353 K by conductivity measurements. The CMC values of pure gemini surfactants evaluated in the existing case at 303 K are concordant with the results stated before. Moreover, other parameters, including rates and binding constants, were calculated.

A Kinetic Investigation of Metal-Dipeptide Complex with Ninhydrin in the Absence and Presence of CTAB Micelles

This paper presents the results of a kinetic study performed between ninhydrin and a Ni(II) dipeptide complex under various conditions. The rate of formation of the imine adduct was measured spectrophotometrically both in plain aqueous media and in aqueous micellar media in which CTAB (cetyltrimethylammonium bromide) is used as the surfactant. These studies were carried out at pH 5 and over a temperature a range of 50 to 70°C. Studies were also conducted to elucidate the effect of some organic sodium salts on the rate of this reaction. In these studies, it was found that the formation of imine adduct followed a first-order kinetics with respect to [Ni(II)-Gly-Leu]⁺ in both aqueous and micellar medium. A fractional-order kinetics was observed with respect to ninhydrin, again in both aqueous and micellar media. Increase in the total concentration of CTAB from 0 to 40×10^-3 mol dm^-3 resulted in approximately two folds increase in the pseudo-first-order rate constant (k_ψ). The rate constant (k_Ψ) in micellar medium first increased with increase in CTAB concentration, reached a maximum value, and finally, with further increase in CTAB concentration, a decreasing effect was observed. Quantitative kinetic analysis of k_ψ-[CTAB] data was performed on the basis of the pseudo-phase model of the micelles. The rate profile in presence of CTAB suggests a cooperative effect in the enhanced formation of the imine adduct as is commonly found in enzyme catalyzed reactions. Addition of organic sodium salts (such as benzoate, salicylate and tosylate) enhanced the rate at lower concentrations but rates start to decrease at higher concentrations. This suggests that tightly binding organic counter-anions were the most effective. Viscosity of the reaction media seems to affect the kinetic behavior in micellar media.

Synthesis and characterization of geminis and implications of their micellar solution on ninhydrin and metal amino acid complex

In our study, three gemini dicationic surfactants with different methylene group spacer (16-6-16, 16-5-16 and 16-4-16) have been synthesized and characterized in solution by 1H NMR spectroscopic technique. The implications of gemini micellar solution on ninhydrin and metal amino acid complex ([Cu(II)-Trp]+) were performed by the means of single-beam UV-visible spectroscopy. The absorbance was noted at regular time intervals and values of rate constant (kψ ) were determined by using a computer-based program. Synthesized surfactants proved as an efficient catalyst on the interaction of ninhydrin with metal amino acid complex as compared with conventional surfactant and aqueous systems. The required description regarding the implications of gemini dicationic surfactants are provided in the text in detail. The conductivity technique was applied in order to get critical micelle concentration (cmc) of geminis in the presence and absence of reactants. Catalytic results developed in gemini dicationic surfactant system were explained effectively by pseudo-phase model. Various thermodynamic quantities, viz., activation energy, E a, activation enthalpy, ΔH #, and activation entropy, ΔS #, were obtained on interaction of ninhydrin with [Cu(II)-Trp]+ in gemini systems by applying Eyring equation. A detailed explanation about these evaluated parameters was also made.

Synthesis and Characterization of Dicationic Gemini Surfactant Micelles and their Effect on the Rate of Ninhydrin–Copper-Peptide Complex Reaction

Herein, we have synthesized and characterized dicationic Gemini surfactants. The effect of their micelles on the rate constant of ninhydrin with [Cu(II)-Gly-Gly]+ complex reaction was investigated under pseudo-first-order-conditions. Experiments were carried out by means of spectrophotometry. First- and fractional-order dependencies on [Cu(II)-Gly-Gly]+ and ninhydrin, respectively, were found. The results indicated that the efficiency of micellar catalysis by Gemini surfactants was significantly higher as compared to single-chained surfactant cetyltrimethylammonium bromide, CTAB. The Gemini surfactant produces a catalytic effect and leveling-off regions (just like CTAB) on the reaction rate. Later, Gemini with higher concentrations gives a third region of increasing k ψ. The effect of surfactants was rationalized by hydrophobic and electrostatic interactions. The observed kinetic effects are explained by applying the Menger-Portnoy model.

Dipeptide Glycyl-Glycine (Gly-Gly)–Ninhydrin Reaction: Effect of Alkanediyl-α,ω-bis(dimethylcetylammonium bromide) (16-s-16, s = 4, 5, 6) Gemini Surfactants on the Reaction Rate

The present work concerns with the effect of alkanediyl-α,ω-bis(dimethylcetylammonium bromide) gemini surfactants on the reaction rate of ninhydrin with glycyl-glycine. The spectra showed peaks at 400 nm and 570 nm in aqueous and aqueous–micellar media indicating the formation of the same product. Under pseudo-first-order conditions of excess ninhydrin, the reaction followed an irreversible first- and fractional-order kinetics with respect to [Gly-Gly] and [ninhydrin]. Also, the rate constants (kψ) increases and leveling-off regions are found with [geminis] (akin to conventional cetyltrimethylammonium bromide, CTAB), a third-region of increasing kψ is observed at higher [geminis]. The kinetic data in gemini micellar medium have been examined with the pseudo-phase model.

Kinetic Study of the Formation of Ruhemann's Purple in Micellar and Microemulsion Phases

The reaction kinetics of ninhydrine (Nin) with glycine–glycine dipeptide (Gly) was studied in aqueous solution. The same reaction was studied in micellar solutions of different surfactants such as sodium dioctylsulfosuccinate (AOT) and sodium dodecyl sulfate (SDS). The reaction was also studied in the L2 microemulsion phase of the three systems AOT/heptane/water, SDS/pentanol/heptane/water, CTAB/pentanol/heptane/water. Spectrophotometric measurements were perfomed at 570 nm. The data show that the reaction is first-order with respect to Nin and Gly in all cases. Values of the observed rate constants (k obs) increase with increasing concentration of the surfactant in micellar media. AOT was more promotional than SDS. The reaction rate in the presence of different micelles could be explained using a pseudo-phase kinetic model. Association constants of Nin and Gly with surfactant micelles are reported. Values of k obs for the reaction rates in the microemulsion phases are reported. AOT/heptane L2 microemulsion system has been clearly found as the most promotional among all the other studied systems. Association constants of Nin and Gly with surfactant in microemulsion were obtained. The rate was increased with the temperature in aqueous, micellar and microemulsion phases. The activation parameters ΔH*, ΔS* and ΔG* have also been obtained. The reaction rate in different microemulsion media is slightly increased with the change of oil (heptane > hexane > pentane), while co-surfactants (butanol, pentanol and hexanol) have no effect on k obs values in AOT, CTAB or SDS microemulsion.

Effect of gemini (alkanediyl-α,ω-bis(dimethylcetylammonium bromide)) (16-s-16, s=4, 5, 6) surfactants on the interaction of ninhydrin with chromium-glycylphenylalanine

The effect of gemini (alkanediyl-α,ω-bis(dimethylcetylammonium bromide)) (16-s-16, s=4, 5, 6) surfactants on the interaction of ninhydrin with chromium(III) complex of glycylphenylalanine ([Cr(III)-Gly-Phe]2+) has been investigated using UV-visible spectrophotometer at different temperatures. The order of reaction with respect to [Cr(III)-Gly-Phe]2+ is unity while it is fractional with respect to ninhydrin. Whereas, the values of rate constant (kψ) increase and leveling-off regions, like conventional single chain cetyltrimethylammonium bromide (CTAB) surfactant, were observed with geminis, later produces a third region of increasing kψ at higher gemini surfactant concentrations. This unusual third-region effect of the gemini micelles is assigned to changes in their micellar morphologies. The results obtained in micellar media were treated in terms of pseudo-phase model. The values of thermodynamic parameters (Ea, ΔH# and ΔS#) and binding constants (KA and KNin) have been evaluated.

Interaction of Chromium(III) Complex of Glycylphenylalanine with Ninhydrin in Aqueous and Cetyltrimethylammonium Bromide (CTAB) Micellar Media

In this paper, we are reporting the influence of cationic CTAB surfactant on the interaction of chromium(III) complex of glycylphenylalanine [Cr(III)-Gly-Phe]2+ with ninhydrin under varying experimental conditions. The reaction follows irreversible first-order reaction kinetics with respect to [complex] and fractional-order with respect to [ninhydrin]. With progressive increase in [CTAB], the rate constant (k Ψ) for condensation of ninhydrin into [Cr(III)-Gly-Phe]2+ complex increased, reached a maximum value, and then decreased. The results are best accounted for by the distribution of substrate into micellar and aqueous pseudo-phases as well as combination of substrate molecules with surfactant molecule. On the basis of above results, template mechanism has been discussed.