Abstract
Kinetics of the title reaction has been investigated spectrophotometrically in aqueous solution as well as in the presence of cetyltrimethylammonium bromide (CTAB) cationic micelles. The reaction rate is first- and fractional-order with respect to [substrate] and [ninhydrin], respectively, both in the absence and presence of cationic micelles. Whereas SDS addition shows formation of a different product, the reaction of copper(II)-tryptophan complex with ninhydrin is catalyzed by CTAB: the maximum rate enhancement being ca . 5-fold. The data are interpreted in terms of the pseudo-phase model (assuming the association/incorporation of both the reactants at the micellar surface). The binding constants of copper(II)-tryptophan ( K S ) and ninhydrin ( K N ) with CTAB micelles have been calculated. The presence of inorganic salts (NaCl, NaBr, NaNO 3 and Na 2 SO 4 ) leads to a decrease in the rate followed by an increase and it is found that tightly bound/incorporated anions are most effective.