Role of gemini surfactants (m-s-m type; m=16, s=4-6) on the reaction of [Zn(II)-Gly-Phe]+ with ninhydrin

In the present paper, reaction of zinc-glycylphenylalanine ([Zn(II)-Gly-Phe](+)) with ninhydrin has been investigated in gemini (m-s-m type; m = 16, s = 4-6) surfactants at temperature (70 degrees C) and pH (5.0). Monitoring the appearance of product at 400 nm was used to follow the kinetics, spectrophotometrically. The order of the reaction with respect to [Zn(II)-Gly-Phe](+) was unity while with respect to [ninhydrin] was fractional. The reaction constants involved in the mechanism were obtained. In addition to the rate constant (k(Psi)) increase and leveling-off regions are observed with the geminis, just like as seen with conventional surfactant hexadecyltrimethylammonium bromide (CTAB), the former produced a third region of increasing k(Psi) at higher concentrations. A close agreement between observed and calculated rate constants was found under varying experimental conditions. A suitable mechanism consistent with the experimental findings has been proposed. Copyright (C) 2014 John Wiley & Sons, Ltd.