EQUILIBRIUM STUDIES ON TERNARY CU(II) COMPLEXES CONTAINING ADENOSINE-5'-TRIPHOSPHATE

Interaction of adenosine-5'-triphosphate (ATP) with a series of binary Cu(II) complexes (ML) (where L=o-phenanthroline (Phen), 5-nitrophenan throline (NPhen), 5-methyl phenanthroline (MPhen), 2,9-dimethylphenant hroline (DPhen), 2,9-dimethyl-4,7-diphenylphenanthroline (DPhPhen), 2, 2'-bipyridyl (Bipy), bis(imidazol-2-yl) methane (BIM), oxalic acid (Ox ), glycine (Gly), alanine (Ala), valine (Val), phenylalanine (Phe), tr yptophan (Trp), methionine (Met), histidine (His) or aspartic acid (As p) to form ternary complexes (MLA) was investigated by a pH-metric tec hnique and the formation constants were evaluated at 35.0 degrees C an d mu = 0.2 M (KNO3). The influence exerted by ligand L on the binding of ATP to Cu(II) was quantitatively assessed and ATP was found to bind more strongly when L = bidentate nitrogen donors, relatively less str ongly when L = amino acids and least strongly when L = a bidentate oxy gen donor. With respect to the nitrogen donor ligands the stability of the ternary complexes decreases in the order NPhen > Phen > Bipy > MP hen > DPhen > BIM approximate to DPhPhen, whereas in ternary complexes containing amino acids the stability decreases in the order: Phe appr oximate to Trp > Ala > Gly approximate to Val approximate to Met > His > Asp. The trends in the stability of the various complexes are discu ssed in terms of the nature of the metal ion and the two ligands in it s coordination sphere.