A potentiometric investigation of complex formation between some metal ions and biologically active quinazoline-4-3(H)-one Schiff’s base

The proton dissociation constant of the ligand and the stability of the complexes of Co(II), Ni(II), Zn(II), Cd(II), Hg(II), Pb(II), Cu(II), Ba(II), Mg(II), Mn(II), Th(IV), and UO₂(II) ions with 2-phenyl-3-(2′-hydroxy-5′-benzylidine)-quinazoline-4-(3H)-one PBQ] were determined potentiometrically at 30 ± 0.1°C and ionic strengths of 0.025, 0.05, 0.10, 0.15 and 0.20 M NaNO₃ in a 60:40 (v/v) ethanol-water medium. The proton-ligand and metal-ligand stability constants of the complexes were determined pH metrically by the Calvin-Bjerrum titration technique. The order of stability constants obeys the Irving-Rossotti rule. The negative values of ΔG° suggest that the reactions are spontaneous. The article is published in the original.