STUDIES OF METAL IONS INTERACTION WITH PURINE PYRIMIDINE BASE PAIR

Abstract

The interaction of some divalent transition metal ions, viz. Co (II), Ni (II), Cu (II), Zn (II) and Cd (II) with adenine (A), uracil (U) and 5 bromouracil (5 BrU) separately in binary (1:1) and in presence of each other in ternary (1:1:1) metal-ligand systems has been studied pH-metrically at 25 ± 0.1°C temperature and a constant ionic strength of 0.1 M NaNO3 in aqueous medium. The stability constant of binary (MA / ML) and ternary (MAL) complexes formed in solution were determined by using Bjerrum-Calvin's method as adopted by Irving and Rossotti for binary, and Chidambaram and Bhattacharya for ternary systems respectively. For the studies of ternary complexes, adenine (A) has been taken as primary ligand and uracil (U) as well as 5 bromouracil (5 BrU) as secondary ligand. The Alog K values of the ternary systems are positive in comparison to binary metal-A systems and those with respect to binary metal-U or 5 BrU systems are mostly negative. This suggests that the ternary complexes of U or 5 BrU are more stable than the metal-A binary systems but are less stable than corresponding metal-U or 5 BrU binary complexes.