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

The effect of gemini (16-s-16, s = 4, 5, 6) surfactants on the reaction rate of ninhydrin with [Cu(II)-Gly-Tyr]^sup +^ 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]^sup +^ and [ninhydrin], respectively. It is found that gemini surfactants effectively catalyze the reaction. The rate constants (k ^sub [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 ^sub [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.