Binary and ternary metal complexes of guanosine: stability and thermodynamic parameters

Abstract

The stability constants of the binary and ternary complexes of Cu^II, Ni^II, Zn^II, Co^II, Mn^II, Mg^II, and Ca^II with guanosine as a primary ligand and 2,2′-bipyridyl, 1,10-phenanthroline, and 5-sulphosalicylic acid as secondary ligands were determined from potentiometric titrations at 45, 35, 25, and 15 °C at I= 0.10 mol dm^–3(KNO₃). The stability of 1 : 2 metal–guanosine and ternary metal complexes was characterized by the Δ log K values (difference in stabilities of the 1 : 2 and 1 : 1 complexes and difference between the 1 : 1 : 1 and the corresponding binary systems). These values are positive for the 1 : 2 metal–guanosine and 1 : 1 : 1 metal–bipyridyl–guanosine systems. This is attributed to stacking of guanosine. The Δ log K values are negative for the ternary phenanthroline and 5-sulphosalicylic acid systems. The thermodynamic parameters ΔH_f^⊖, ΔS_f^⊖, and ΔG_f^⊖ are reported for all the systems.