Abstract
A novel tridentate Schiff base, 1-((E)-(2-mercaptophenylimino) methyl) naphthalen-2-ol (H2L1), was synthesized by the condensation reaction of 2-hydroxy-1-naphthaldehyde with 2-aminothiophenol in absolute ethanol. The resulting ligand was reacted with Co(II), Ni(II), and Cu(II) ions to obtain tetrahedral CoL1, NiL1, and square planar CuL1 complexes. The Schiff base and its metal complexes were characterized using 1H-NMR, microanalysis, FT-IR, UV-visible, and mass spectroscopy (ESI-MS). All the compounds are soluble in DMSO and DMF. Spectroscopic studies show that the ligand coordinates to the metal center through the azomethine nitrogen, naphthoxide oxygen, and thiophenoxide sulfur to form a tridentate chelate system. Conductance measurements show that these compounds are molecular in solution. Cyclic voltammetry studies show Co(III)/Co(II) and Cu(II)/Cu(I) redox systems to be quasi-reversible involving a monoelectronic transfer while Ni(III)/Ni(II) was irreversible. In vitro antibacterial and antifungal activity against five bacterial strains (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus faecalis, and Proteus mirabilis) and five fungal strains (Candida albicans, Candida glabrata, Candida tropicalis, Candida krusei, and Candida parapsilosis) showed no antifungal activity but moderate antibacterial activity on E. coli, S. aureus, P. aeruginosa, and P. mirabilis bacterial strains. Antioxidant studies reveal that the ligand and its Cu(II) complex are more potent than Co(II) and Ni(II) complexes to eliminate free radicals.
Highlights
Maurice Kuate,1,2 Mariam Asseng Conde,2 Evans Ngandung Mainsah,3 Awawou G
In continuation of our studies on metal complexes of aromatic Schiff base ligands, we report, the synthesis and electrochemical studies of Co(II), Ni(II), and Cu(II) complexes of a tridentate Schiff base derived from 2-aminothiophenol and 2-hydroxy-1-naphthaldehyde and the evaluation their antioxidant and antimicrobial properties
A 1 : 1 reaction ratio for metal ion and the ligand during the formation of the complexes was proposed. us, the complexes were of the form [ML], which may dimerize [33, 34], to form a neutral dimeric four-coordinate complex [ML]2. e dimerization is presumed to occur as a result of bridging between the two M(II) centers through the deprotonated thiophenolic sulfur atoms. e very low molar conductivities of the synthesized compounds in DMSO indicated that all complexes are molecular in nature
Summary
Maurice Kuate ,1,2 Mariam Asseng Conde ,2 Evans Ngandung Mainsah,3 Awawou G. Our group has recently embarked on studies on the biological activities of complexes of heterocyclic Schiff base ligands [15, 22].
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