Interaction between dipeptide (glycyl-phenylalanine) and ninhydrin: role of CTAB and gemini (16-s-16, s=4, 5, 6) surfactant micelles.

The kinetics of interaction of dipeptide glycylphenylalanine (Gly-Phe) with ninhydrin have been studied by following the reaction spectrophotometrically at 70 °C and a particular pH 5.0 in the absence and presence of conventional cetyltrimethylammonium bromide (CTAB) and gemini (alkanediyl-α,ω-bis(dimethylhexadecylammonium bromide)) surfactants. The rate shows first- and fractional-order dependence on [Gly-Phe] and [ninhydrin], respectively. The surfactants were found to catalyse the reaction. Furthermore, whereas the typical rate constant (kΨ) increase and leveling-off regions are observed with geminis, just like as seen with conventional surfactants, the former produced a third region of increasing kΨ at higher concentrations. A kinetic rate law consistent with experimental results has been derived on the basis of the proposed mechanism.