Abstract

Badar T. Khan and Ch. Abraham Lincoln

The stability constants of the binary and ternary complexes of Cu(II), Ni(II), Co(II), Zn(II), Mg(II) and Ca(II) with adenosine as a primary ligand and cytidine, uridine and thymidine as secondary ligands were determined by potentiometric titrations at 15°, 25°, 35°, and 45°C and 0.10M (KNO3) ionic strength. The stability of 1:2 metal-adenosine and ternary metal complexes was characterized by the D 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 adenosine and ternary systems, this is attributed to stacking interactions. The thermodynamic parameters DH°f, DS°f and DG°f, are reported for all the systems. The enhanced stabilities of ternary systems have been measured in terms of their DDH, = DH2 - DH, where DH2, is DH°f of 1:1:1 system and DH1 is DH°f for 1:1 systems and DDS = DS2 - DS1 where DS2 and DS1 are the DS°f for 1:1:1 and 1:1 systems respectively. The DDH values are highly negative and DDS values are negative for their systems. The exothermic enthalpy in the formation of 1:1:1 ternary complexes may be attributed to the energy of stacking in these systems.

Binary; ternary metal complexes; adenosine; thermodynamic parameters

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