The kinetics and mechanism of the substitution reaction between [Cr(H 2 O) 6 ] 3? and L-Dopa in aqueous medium has been studied over the range 1.8 B pH B 2.6, 1.68 9 10 -2 mol dm -3 B [Dopa] B 5.04 9 10 -2 mol dm -3 , I = 0.1 mol dm -3 (KNO 3 ) at 50°C. The reaction takes place via an outer sphere association between Cr 3? and L-Dopa followed by chelation. The product was characterized by physicochemical and infrared spectroscopic methods. The antiparkinsonian activity of the product was found to be higher than that of L-Dopa.Electronic supplementary material The online version of this article (

The kinetics of the electron transfer reaction of NADH with 12-tungstocobaltate(III) has been studied over the range 5.07 ≤ 104[NADH] ≤ 15.22 mol dm-3, 7.0 ≤ pH ≤ 8.0 and 20 ≤ t ≤ 35oC in aqueous medium. The electron transfer reaction showed first-order dependence each in [NADH]Tand [12-tungstocobaltate(III)]T. The products of the reaction were found to be NAD+and 12-tungstocobaltate(II). The activation parameters ΔH#(kJ mol-1) and ΔS#(JK-1mol-1) of the electron transfer reactions were found to be 64.4±1.8 and -48.86±6.0. Negative value of ΔS#is an indicative of an ordered transition state for the electron transfer reaction.

The kinetics of the reactions of L-cysteine and N-acetylcysteine with cis-[Pt(en)(OH 2 ) 2 ] 2+ have been studied spectrophotometrically as a function of [Pt(en) (OH 2 ) 2 ] 2+ T , [L-cysteine] T /[N-acetylcysteine] T and temperature at pH (4.0) where the Pt(II) complex exists predominantly as a diaqua species and L-cysteine and N-acetylcysteine as zwitterions. The substitution reaction shows two consecutive processes; the first step is the ligand assisted anation and the second one is the chelation step. The anation rate constants for N-acetylcysteine were found to be greater than that for L-cysteine. H # 1 (61.6 ± 1.8 kJ mol −1 ) H # 2 (47.5 ± 2.0 kJ mol −1 ), S # 1 (−54.4 ± 5.3 J.K −1 mol −1 ) and S # 2 (−164.8 ± 6.5 J.K −1 mol −1 ) for L-cysteine and H # 1 (23.2 ± 0.8 kJ mol −1 ), H # 2 (61.5 ± 0.6 kJ mol −1 ) and S # 1 (−178.6 ± 2.6 J.K −1 mol −1 ), S # 2 (−115.6 ± 2.0 J.K −1 mol −1 ) for N-acetylcysteine indicate an associative mode of activation for both the ligand substitution processes in the two consecutive steps.