Micro-level Estimation of Methionine Using Inhibitory Kinetic Spectrophotometric Method

Abstract

A large number of bioactive molecules and drugs contain sulfur as an important constituent. Organo-sulfur compounds form a stable complex with Hg2+, thereby inhibiting its catalytic activity. The Hg2+ catalyzed the exchange rate of cyanide with nitroso-R-salt [N-R-salt] from [Ru(CN)6]4- will be reduced by the addition of sulfur-containing amino acid, methionine (MET). This inhibitory property of MET can be employed for its micro-level kinetic determination. Optimum reaction condition viz. I=0.05 M (KNO3), pH = 7.0 ± 0.02, [Ru(CN)64] = 5.25 × 10-5 M, [N-R-salt] = 6.5 × 10-4 M, [Hg+2] = 5.5 × 10-5 M, and Temperature = 45.0 ± 0.1 o C were utilized to investigate the kinetic measurements at 525 nm (λmax of [Ru(CN)5 N-R-salt]3- complex). To explain the mechanism of inhibition caused by methionine on Hg2+ catalyzed exchange of cyanide with N-R-salt from [Ru(CN)6]4-, a modified mechanistic scheme has been proposed. MET can be quantitatively determined up to 2.5 × 10-6 M level by the proposed analytical method. The methodology can be economically and effectively employed for the quantitative estimation of MET in distinct samples.