Stabilities and thermodynamic parameters of 1:2 metalxanthosine complexes in solution

Abstract

Potentiometric equilibrium measurements were made at 5, 25, 35 and 45°C to determine the stability constants of Cu(II), Ni(II), Zn(II), Co(II), Mn(II), Mg(II) and Ca(II) with xanthosine in a 1:2 ratio (μ = 0.10 M KNO 3). The enthalpy and entropy changes associated with the above interactions were also calculated using temperature coefficient data. The stability constants of these 1:2 metalxanthosine complexes are higher than the corresponding complexes of 1:1 systems (Δ log K positive). This enhanced stability is measured in terms of ΔΔH° f (ΔH 2 − ΔH 1), a quantity which directly measures the extent of extra interaction. This enhanced interaction in the 1:2 system is attributed to a favourable ‘stacking’ interaction between two xanthosine moieties in solution.