Kinetics and mechanism of the ninhydrin reaction with nikel (II)-tryptophan complex in aqueous and aqueous-micellar solutions

摘要

The kinetics of the coloured reaction between ninhydrin and nickel (II)-tryptophan complex have been investigated spectrophotometrically in aqueous as well as in micellar solutions. The reaction follows first-and fractional-order kinetics with respect to [Ni(II)-trp] and [ninhydrin], respectively, both in the absence and in the presence of cationic micelles. The results are discussed in terms of pseudo-phase model. The values of k_m, K_S, K_N, E_a, #DELTA#H~# and #DELTA#S~# have been calculated. Presence of NaCl, NaBr, NaNO_3 and Na_2SO_4 respectively shows a decrease (except with Na_2SO_4) in the rate followed by an increase in the rate and it is found that tightly bound/incorporated cations are most effective.