Synthesis, Characterization, And Antioxidant Activities Of Some Transition Metal (â…¡) Complexes With Schiff Bases

In this paper, we synthesized and characterized six kinds of Schiff bases and theirtransition metal complexes with Mn(Ⅱ), Co(Ⅱ), Ni(Ⅱ), Cu(Ⅱ) and Zn(Ⅱ). Theantioxidant activities of these compounds were tested against O2.-,·OH and H2O2.(1) We have synthesized six Schiff bases, which were4-(4-hydroxyphenyl)but-3-en-2-one thiosemicarbazone (HL1),4-(4-hydroxy-3-methoxyphenyl)but-3-en-2-onethiosemicarbazone (HL2),4-hydroxybenzaldehyde Isonicotinoyl hydrazone (HL3),4-hydroxy-3-methoxy-benzaldehyde Isonicotinoyl hydrazone (HL4),4-(4-hydroxyphenyl)but-3-en-2-one Isonicotinoyl hydrazone (HL5) and4-(4-hydroxy-3-methoxy-phenyl)but-3-en-2-one Isonicotinoyl hydrazone (HL6), respectively.(2) We have synthesized21complexes of transition metal with these Schiff bases.These complexes were characterized by IR, UV, elemental analysis, TG-DTG analysisand molar conductivity. The most probable structures of the complexes weresuggested.(3) Scavenging activity of the compounds against·OH was tested. The activitiesof these complexes are higher than their own ligands. The scavenging ratios of thecompounds depend on the value of concentrations, and the concentrantion has asignificant effect on the activity. The activities of complexes of thiosemicarbazone are3to17times higher than those of the ligands. The complexes of isonicotinoylhydrazone show high scavenging activity. The scavenging ratios of Cu(L4)2Cl2,Zn(L4)2·3H2O and Co(L5)2are more than90%when the concentration is100μg·mL-1.(4) Scavenging activity of the compounds against O2·-was determined. Theactivities of complexes with HL5are close to the ligand’s. Compared with the ligands,activities of the other metal complexes significantly increase, the activities of nickel(Ⅱ)complexes are maximum.(5) Scavenging activity of the compounds against H2O2was determined. Theactivities of complexes with thiosemicarbazones increase except Cu(L2)2. In additionto Ni(L3)2and Zn(L6)2, the activities of the complexes with isonicotinoyl hydrazonedecline.