Kinetic and mechanistic studies on the reaction of thiosemicarbazide with [(H2O)(tap)2RuORu(tap)2(H2O)]2+ {tap = 2-(m-tolylazo)pyridine}

Abstract

The interaction of thiosemicarbazide with the title complex has been studied spectrophotometrically in aqueous medium as a function of [complex], [thiosemicarbazide], pH and temperature at constant ionic strength. At pH 7.4, the reaction shows two distinct paths; both of which are [thiosemicarbazide] dependent. A parallel reaction scheme fits well with the experimental findings. An associative interchange mechanism is proposed for both the paths; the activation parameters calculated from Eyring plots are DH 1 = = 14.2 ± 0.8 kJ mol -1 , DS 1 = = -241 ± 2 JK -1 mol -1 , DH 2 = = 30.8 ± 1.4 kJ mol -1 and DS 2 = = -236 ± 4 JK -1 mol -1 . From the temperature dependence of the outer sphere association complex equilibrium constants, the thermodynamic parameters calculated are DH 1°= 34.25 ± 1.9 kJ mol -1 , DS 1°= 146 ± 6 J K -1 mol -1 and DH 2°= 9.4 ± 1.1 kJ mol -1 , DS 2°= 71 ± 3 JK -1 mol -1 , which gives a negative DG°at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex.

Kinetics and Mechanism of the Interaction of Glycyl-L-Leucine with [(H2O)(Tap)2Ruoru(Tap)2(H2O)]2+ Ion at Physiological Ph

“…In our earlier work [31] we reported such a study with thiosemicarbazide, a (S, N) donor system. We report here the interaction of glycyl-L-leucine, a dipeptide with a different set of donor atoms.…”