AQUATION OF THE ANTICANCER COMPLEX TRANS-[RUCL4(HIM)2]- (HIM=IMIDAZOLE)

Aquation of the anticancer complex trans-[H2im][RuCl4(Him)2] 1 (Him = imidazole) has been studied in D2O at a range of pH (meter reading) v alues between 2.4 and 10 by observation of paramagnetically shifted H- 1 NMR resonances. At 310 K, pH 5.6, the half-life was 3.4 h and three products were detected, assigned as mono- and di-aqua species. The ra te was similar at low pH, but the reaction followed a different cours e at high pH. Aquation was also studied by separation of the products on a reversed-phase column using HPLC, by conductivity measurements, and by EPR spectroscopy. Slow oxidation of the complex to Ru(IV) appea red to take place in perchlorate, phosphate or acetate solutions. Cycl ic voltammetric studies showed that reduction of 1 to Ru(II) (E(m) - 0 .14 V versus the normal hydrogen electrode, pH 7) was accompanied by t he uptake of two protons with associated pK(a) values of 6.26 and 3.87 . Both aquation and the more favourable reduction of 1 at low pH may p lay a role in the biological activity of the complex.