VIVO and CuII complexation by ligands based on pyridine nitrogen donors

Abstract

The binary and ternary systems formed by V(IV)O and Cu(II) ions with ligands (L) based on the pyridine ring (1,10-phenanthroline (phen), 2,2'-bipyridine (bpy), 2,2':6',2''-terpyridine (terpy), 2,2'-bipyrimidine (bpm) and 2,3-bis(2-pyridyl)pyrazine (bpp)) were studied, combining spectroscopic (EPR and UV-vis), pH-potentiometric and computational (DFT calculations) methods. In the systems with V(IV)O, the formation of mono-chelated complexes with equatorial-equatorial and equatorial-axial (phen, bpy, bpm and bpp) or equatorial-equatorial-equatorial and equatorial-axial-equatorial coordination (terpy) and bis-chelated species with cis-octahedral geometry, with a water or a hydroxido ion in the fourth equatorial position, is demonstrated. Phen, bpy, bpm and bpp form also a dinuclear [(VO)(2)L(2)(H(2)O)(2)(OH)(2)](2+) complex with an anti-coplanar arrangement of the two V(IV)O ions and a ferromagnetic coupling between the metal ions. Due to the low basicity of the nitrogen donors, the potentially tetradentate 2,2'-bipyrimidine and 2,3-bis(2-pyridyl)pyrazine behave like simple bidentate ligands, and in the ternary systems with 2,2'-bipyridine the expected dinuclear species, in which the former ligands would act as a bridge between the two metal ions using all four nitrogen donors, are not formed. The interaction of phen and Cu(II)-phen complexes with human serum albumin (HSA) was also studied at pH 7.4 by circular dichroism and EPR spectroscopy, the formation of several HSA-Cu(II)-phen containing species being confirmed and their binding constants determined.