Role of cationic gemini surfactants toward enhanced ninhydrin-tryptophan reaction

In this paper we report the effect of dicationic 'gemini' surfactants (CH3)(2)C16H33N+-(CH2)(m)-N+C16H33(CH3)(2), 2B(-) (where m = 4, 5, 6) on the reaction of ninhydrin with DL-tryptophan. The gemini surfactant micellar media are comparatively more effective than their conventional monomeric counterpart cetyltrimethylammonium bromide (CTAB) micelles. Also, whereas typical rate constant (k(psi)) increase and leveling-off regions, just like CTAB, are observed with geminis, the latter produce a third region of increasing k(psi) at higher concentrations. These subsequent increases are ascribed to changes in micellar morphologies, consistent with changes in H-1 NMR line widths. Quantitative kinetic analysis of the rate constant-[surfactant] data has been performed on the basis of modified pseudophase model. Copyright (c) 2007 John Wiley & Sons, Ltd.