Kinetics and Mechanism of the Complexation of trans-Diamminediaquaplatinum(II) with the 6-Oxopurine Nucleosides Inosine and 1-Methylinosine in Aqueous Solution as a Function of the pH

Kinetics of complexation of trans-[Pt(NH3)2(H2O)2]2+ with the model nucleobases inosine and 1-methylinosine has been studied in aqueous solution at 298.2 K in the pH range 2.8−9.6 (I = 0.1 M) by using HPLC as an analytical tool. The complexation of aquated trans-PtII(NH3)2 with the nucleobases employed can be quantitatively explained by replacement of the aqua ligand with the nucleobase, while the hydroxo group bound to Pt(II) is inert to substitution reaction relative to the coordinated water molecule. The stepwise acidity constants of trans-[Pt(NH3)2(H2O)2]2+ obtained from kinetic measurements were in excellent agreement with those found potentiometrically (pKa1 = 4.48 ± 0.02, pKa2 = 7.20 ± 0.05). The reactivity of the Pt(II) dication is 7−8 times higher than that of the monocation despite the moderate trans effect OH- > H2O. In excess of the nucleobase, stepwise formation of 1:1 and 1:2 complexes is observed. 1-Methylinosine forms only N7-bound species, as does inosine when pH < 5.5. Although deprotona...