Binary and ternary metal complexes of guanosine: stability and thermodynamic parameters
The stability constants of the binary and ternary complexes of CuII, NiII, ZnII, CoII, MnII, MgII, and CaII 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 ΔHf⊖, ΔSf⊖, and ΔGf⊖ are reported for all the systems.