Complexes de V(IV), Co(II), Ni(II) et Cu(II) avec les bases de Schiff hétérocycliques : synthèse, caractérisation et activités biologiques

Abstract

Two Schiff bases 4-((phenyl (pyridin-2-yl) methylene) amino) benzenesulfonamide (LI) and 1-phenyl-1- (pyridin-2-yl) -N- (pyrimidin-2-yl) methanimine dihydrate (LII) were synthesized by a condensation reaction between sulfanilamide, 2-aminopyrimidine and benzoylpyridine. The reactions of 4-((phenyl (pyridin-2-yl) methylene) amino) benzenesulfonamide (LI) and 1-phenyl-1- (pyridin-2-yl) -N- (pyrimidin-2-yl) methanimine dihydrate (LII) with V(IV), Co(II), Ni(II) and Cu(II) salts resulted in to the hydrolysis of LI to give sulfanilamido-metal complexes and of LII to give binuclear complexes of 2-benzoylpyridine (l1) and phenyl (pyridin-2-yl) methanediol (l2). The ligands and corresponding complexes obtained were characterized using 13C-NMR, 1H-NMR, DEPT-135, HSQC, HMBC, COZY, NOESY, microanalysis, spectroscopies methods (FT-IR, UV-vis) and TGA. The Schiff bases (LI) and (LII) were soluble in methanol, ethanol, DMSO, acetone and DMF and melted at temperatures of 216°C and 64°C respectively. Microanalysis and spectral studies indicated that binuclear metal complexes were obtained by the coordination of the metal ion to 2-benzoylpyridine (l1) and phenyl (pyridin-2-yl) methanediol (l2) from the hydrolysis of the Schiff base (LII). Visible spectroscopic analyses suggested an octahedral geometry for the Ni(L)2 complex, a pyramidal and tetrahedral geometries, each comprising two molecules of the monodentate amino ligand (L) proposed for the VO(L)2, Co(L)2 and Cu(L)2. Based on the visible spectra obtained, square-based pyramidal geometries are proposed for the binuclear Cu(II) and V(IV) complexes while a square planar geometry is proposed for the binuclear Co(II) complex. The single crystal x-ray structure determined for the copper(II) complex revealed a binuclear Cu(II) complex of l1 and l2 resulting from the hydrolysis of LII. The structure is non-centrosymmetric with a rectangular binuclear (Cu-O-R)2 nucleus and two ligands l1 and l2 in the unit cell. This compound crystallizes in monoclinic system with a space group P21/n (no. 14). In vitro antimicrobial screening in 10% DMSO against three bacterial strains (Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus) and three fungal strains (Candida albicans, Candida glabrata and Candida parapsilosis) showed that the ligand LI and the complexes VO(L)2, Co(L)2 and Cu(L)2 were found to be active on the bacterium Staphylococcus aureus with zone of inhibition ranging from 16 to 20 mm compared to zone of inhibition of diameter 22 mm for Rifampicin. The Co(L)2, Ni(L)2 and Cu(L)2 complexes were found to be moderately active on the yeast strain, Candida albicans with a zone of inhibition of 10 to 16 mm greater, than that of the 8 mm determined for the reference, Fluconazole. Only the binuclear complex [VO(l2)2] is active on all bacterial strains. Antioxidant studies reveal that the L1 ligand and VO(L)2, Co(L)2 complexes showed moderate activity against the free radical 1,1-diphenyl-2-picryl-hydrazyl (DPPH) for an antioxidant activity. On the other hand, only the binuclear complexes of cobalt(II) and oxovanadium (II) were found to be active in eliminate free radicals.