Substitution kinetics of platinum N,N,N’,N’-Tetrakis (2-pyridyl methyl) octane diamine aqua complex with thiourea, glutathione and L-cysteine nucleophiles

Abstract

The ligand substitution kinetics of the platinum(II) complex, [Pt2(L)(OH2)2](ClO4)4 (L = N, N,N’,N’-tetrakis (2-pyridylmethyl) octane diamine) by a series of nucleophiles, viz. thiourea (TU), L-cystein (L-CYST), and glutathione (GLT) were investigated in 0.2 M NaClO4 ionic strength. The reactions were studied under pseudo-first order conditions at different temperatures and nucleophile concentrations. Reactions involving glutathione and L-cysteine were investigated using UV-Vis spectrophotomer while the faster reactions of thiourea were monitored on the stopped-flow spectrofluorimeter. Second order rate constants (M-1s-1) at 298 K are 0.194, 0.567, and 1.505 for GLT, L-CYST, and TU, respectively. The activation parameters obtained for the three nucleophiles in the same order of GLT, L-CYST, and TU, are ΔH≠ (kJ mol-1): 58.0, 13.0, 41.6 and ΔS≠ (J K-1 mol-1): -63.6, -206.1 and -101.8, respectively.