Thermodynamic quantities associated with the interaction of guanosine triphosphate and inosine triphosphate with bivalent metal ions

Potentiometric equilibrium measurements have been made at 25, 35 and 45° for the combination of tetranegative anions of GTP and ITP with 7 bivalent metal ions in a 1:1 ratio of ligand to metal ion. At all the temperatures studied, the constants decrease in the order Cu(II) > Ni(II) > Zn(II) > Co(II) > Mn(II) > Mg(II) > Ca(II) for GTP chelates and for the ITP chelates in the order Cu(II) > Ni(II) > Co(II) > Zn(II) > Mn(II) > Mg(II) > Ca(II). The enthalpy and entropy changes for the formation of normal chelates of GTP and ITP are calculated from temperature coefficient data. The relatively small values of ΔHf° coupled with a large positive values of ΔSf° offers an evidence for the role of entropy as the primary factor favouring the formation of the normal 1:1 metal chelate species of GTP and ITP in solution