Kinetic studies on the reactions of [Pd(dach)(X–Y)] complexes with some DNA constituents

Abstract

The kinetics of complex-formation reactions of six Pd(dach) complexes, dach = 1,2-trans-R,R-diaminocyclohexane, viz. [Pd(dach)Cl₂], [Pd(dach)(H₂O)₂]²⁺, and four complexes with different chelating leaving groups X–Y, viz. [Pd(dach)(O,O-cyclobutane-1,1-dicarboxylate)], [Pd(dach)(N,O-glycine)]⁺, [Pd(dach)(N,S-methionine)]⁺ and [Pd(dach)(O,O-oxalate)], were studied. The effect of the leaving group on the lability of the resulting Pd(II) complexes was studied for the nucleophiles inosine, inosine-5′-monophosphate and guanosine-5′-monophosphate under pseudo-first-order conditions as a function of nucleophile concentration, temperature and pressure using stopped-flow techniques. Two consecutive reaction steps, which both depend on the nucleophile concentration, were observed. The rate constants for all reactions indicate a direct substitution of the X–Y chelate by the selected nucleophiles, thereby showing that the nature of the chelate, viz. O–O (cbdca), (ox), N–O (gly) or S–N (L-met), plays an important role in the kinetic and mechanistic behavior of the Pd(II) complexes. The mechanism of the substitution reactions is associative in nature as supported by the large and negative values of ΔS^‡ and ΔV^‡.