Kinetic and mechanistic studies on the interaction of uridine with hydroxopentaaquarhodium (III) ion

489-492Kinetics of interaction between uridine and [Rh(H2O)5OH]2+ has been studied spectrophotometrically as a function of [Rh(H2O)5OH]2+, [uridine], pH and temperature. The reaction has been monitored at 290 nm, the λmax of the substituted complex and where spectral difference between the reactant and product is maximum. The reaction rate increases with [uridine] 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 (ΔH≠= 46.5 ± 1.4 kJ mol-1, ΔS≠ =-181 ± 4 J K-1 mol-1) support the proposition. The negative ΔGo (-15.1 kJ mol-1) for the first equilibrium step also supports the spontaneous formation of an outersphere association complex