Kinetic and Mechanistic Studies on the Interaction of Inosine with Hydroxopentaaquarhodium(III) Ion

Kinetics of interacti on between uridine and [Rh(H10 )sOHf+ has been studied spectrophotometrically as a functi o n of [Rh(HzO)sOH 2 +] , [uridine] , pH and temperature. The reacti on has been monitored at 290 nm, the Amax of the substituted complex and where spectral difference between the reactant and product is maximum. The reaction rate increases with [uri ­ dine] and reaches limiting value at higher ligand concentration. From the experimental findings an associative interchange mechanism for the substitution process is suggested. The activation parameters (t<.f{' = 46.5 ± 1.4 kJ mort, t<.S ~ =-181 ± 4 J K-'mor') support the proposition. The negative t<.C" (-15.1 kJ mort) for the first equilibrium step al so supports the sponta­ neous formation of an outersphere association complex. Platinum complexes, particularly cis-platin, a pure inorganic compound, exhibit powerful anticancer properties l . 2 . Because of it's toxicity the search for other alternatives continued in other 3d, 4d and 5d metal ions 3 - 6 . It is now established 7 that cis-platin is first hydro­ lysed in biological conditions and the aqua variety is the active species. Some of the products of hydrolysis are responsible for toxicity. Thus it is expected that the aqua complexes, if used directly, will be less toxic. ]n order to examine the bioactivity of rho­ dium(IIl) complexes we have already reported studies on the interaction of rhodium(lII) with pyridine-2Id . 8 dl h" 9 I . 10 d . II a oxtme, -met 10nIne, -cysteme , a enosme and cytidine l2 . Tn this paper the interaction of uridine with hydroxopentaaquarhodium(1J1) ion in aqueous medium is reported.