Substitution on [(H₂O)(tap)₂RuORu(tap)₂(H₂O)]²⁺ ion with inosine at physiological <i>p</i>H<i> </i>in aqueous medium

Abstract

The interaction of inosine with the title complex has been studied spectrophotometrically in aqueous medium as a function of [substrate complex], [ligand], <i>p</i>H and temperature at constant ionic strength. At physiological <i>p</i>H (7.4) the interaction with inosine shows two distinct consecutive steps; both the processes are [ligand] dependent. An associative

interchange mechanism is proposed; the activation parameters calculated from Eyring plots are: Δ<i>H</i>₁^# = 12.5 ± 1.1 kJ mol^-1, Δ<i>S</i>₁^# = -259 ± 3 JK^-1 mol^-1, Δ<i>H</i>₂^#= 28.9 ± 1.1 kJ mol^-1 and Δ<i>S</i>₂^#= -230 ± 3 JK^-1 mol^-1 . From temperature dependence of the outer sphere association complex formation equilibrium constant, the thermodynamic parameters calculated are: Δ<i>H</i>₁° = 12. 1 ± 1.0 kJ mol^-1, Δ<i>S</i>₁° = 100 ± 3 JK^-1 mol^-1and Δ<i>H</i>₂° = 7.6 ± 0.3 kJ mol^-1, Δ<i>S</i>₂° = 70 ±1 JK^-1 mol^-1, which gives a negative Δ<i>G</i>° at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex.