Template mechanism kinetics for the complexation of ninhydrin with copper(II) complexes of asparagine and serin

Abstract

Ninhydrin has been found to form a 1 : 1 complex with Cu(II) complexes of asparagine and serine. The kinetics of the complexation reaction has been studied spectrophotometrically in acetate buffer. The effect of the [ninhydrin], pH, and temperature on the reaction rate of the reaction was studied. The reaction follows fractional-order kinetics with respect to ninhydrin and first-order with respect to asparagine-Cu(II) and serine-Cu(II), respectively. The reaction proceeds through the coordination of ninhydrin with the same Cu(II) of asparagine and serine complexes. The results are best accounted by the "Template mechanism" for the inner sphere complexation. The values for the inner sphere complex formation constant were also calculated from the kinetic data. The role of Cu(II) in this reaction is to inhibit the breaking of C - C (evolution of CO2) as well as stabilize the C = N of Schiff base. On the basis of observed results, probable mechanism has been proposed. © 1996 John Wiley & Sons, Inc.