Effect of Alkanediyl-α,ω-Type Cationic Dimeric (Gemini) Surfactants on the Reaction Rate of Ninhydrin with [Cu(II)-Gly-Tyr]+ Complex

The effect of gemini (16-s-16, s = 4, 5, 6) surfactants on the reaction rate of ninhydrin with [Cu(II)-Gly-Tyr](+) complex was determined using a spectrophotometric technique. The ninhydrin concentration was kept in excess in order to maintain pseudo-first-order conditions. The reaction followed irreversible first- and fractional-order kinetics with respect to [Cu(II)-Gly-Tyr](+) and [ninhydrin], respectively. It is found that gemini surfactants effectively catalyze the reaction. The rate constants (k (psi)) first increase and then become relatively constant with increasing gemini surfactant concentration similar to conventional cetyltrimethylammonium bromide. At higher gemini surfactant concentration a third region of increasing k (psi) is observed. The unusual third region is ascribed to changes in micellar morphology. The kinetic data has been analyzed using a micellar pseudo-phase model.