For stirring and maintaining at an inert atmosphere, pure nitrogen gas (free from CO2 and O2) was bubbled through the reaction mixture. The reaction was started by adding a requisite volume of thermally equilibrated ninhydrin solution and the zero-time was taken when half of the ninhydrin solution had been added. The experiments were carried out under pseudo-first-order conditions by taking [ninhydrin] in excess over [Gly-Tyr].