The kinetics of interaction between ninhydrin and zinc-dipeptide (glycyl-tyrosine), [Zn(II)-Gly-Tyr]+
complex have been studied in
aqueous and in micelles formed by the cationic surface active material, cetyltrimethylammonium bromide (CTAB) at 80 C and pH 5.0.
The reaction follows first- and fractional- order kinetics with respect to [Zn(II)-Gly-Tyr]+
and [ninhydrin], respectively, both in the absence
and presence of cationic CTAB micelles. The catalytic role of [CTAB] can be related to the extent of incorporation or association of the
[Zn(II)-Gly-Tyr]+
complex and ninhydrin into the micelles. CTAB micelles decrease the activation enthalpy and make the activation
entropy less negative. The micellar catalysis is explained in terms of the pseudo-phase model of the micelles. Binding constants KS for
[Zn(II)-Gly-Tyr]+
and KN for ninhydrin with micelles are calculated with the help of observed kinetic data.
Key words: glycyl tyrosine dipeptide, ninhydrin, micelle, [Zn(II)-Gly-Tyr]+
, cetyltrimethylammonium bromide, CTAB
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