VERSATILE COMPLEX-FORMATION KINETICS OBSERVED FOR THE REACTIONS OF A MODEL CIS-BIS(AMINE)PALLADIUM(II) COMPLEX WITH DNA NUCLEOSIDES AND NUCLEOTIDES

The complex-formation reactions of Pd(Et4en)Cl2 (Et4en = N,N,N',N'-tetraethylethylenediamine) with inosine and inosine 5'-monophosphate were studied as a function of nucleophile and chloride concentration. Two consecutive reaction steps could be observed under all experimental conditions. A detailed kinetic analysis revealed that [Pd(Et4en)(Cl)H2O]+ is the reactive species in the first complex-formation step, for which a steady-state approximation can be used. In the case of the second step, a rapid preequilibrium [Pd(Et4en)(Nu)Cl]+ + H2O half arrow right over half arrow left [Pd(Et4en)(Nu)H2O]2+ + Cl- is followed by rate-determining substitution of the aqua complex to produce the 1:2 product species. The complex-formation reaction of [Pd(Et4en)(H2O)2]2+ with the dinucleotide d(GpG) was studied as a function of nucleophile concentration, temperature and pressure. Two consecutive reaction steps were observed in which the first exhibits a dependence on the d(GpG) concentration and the second is concentration independent. The negative DELTAS(double dagger) and DELTAV(double dagger) values for the first reaction step support an associative complex-formation reaction, which is followed by the slower ring-closure reaction.