KINETICS AND MECHANISM OF COMPLEXATION OF TRANS-[PTCL(NH3)(2)(H2O)](-METHYLINOSINE IN AQUEOUS-SOLUTION AT DIFFERENT PH VALUES() WITH INOSINE AND 1)

The kinetics of complexation of trans-[PtCl(NH3)(2)(H2O)](+) with inos ine and its 1-methyl derivative has been studied at 298.2 K in aqueous solution (pH 2.8-8.4) by employing HPLC as an analytical tool. Under these conditions trans-[PtCl(NH3)(2)(H2O)](+) behaves like a monofunct ional platinum(II) species. Throughout the pH range studied the comple x formation can be explained by substitution of the aqua ligand by the incoming nucleoside, the OH group appearing to be inert toward substi tution. 1-Methylinosine forms only a N-7-bound 1:1 complex. This bindi ng mode is favoured also with inosine when pH <6, whereas above this p H N-1 becomes an additional binding site which facilitates the formati on of a N-1, N-7-bonded diplatinum species, too. Rate parameters obtai ned for the formation of the inosine 1:1 complexes show that the N-7 s ite is preferred over the N-1 site, whereas in the binding of the seco nd platinum(II) unit to the different 1:1 complexes the N-1 site is sl ightly more favourable than the N-7 site. Co-ordination of trans-[PtCl (NH3)(2)(H2O)](+) to the inosine N-7 site lowers the basicity-of (NH)- H-1 site by about 1.3 log units.