Synthesis, Spectroscopic Characterization and Antimicrobial Assessment of 4-Acetyl Pyrazolone Schiff Base and Its Cobalt (II) Complex
Ogbuagu, O. E. *
Department of Chemistry, Alvan Ikoku Federal University of Education Owerri, Imo State, Nigeria.
Ezenweke, L. O.
Department of Pure & Industrial Chemistry, Chukwuemeka Odumegwu Ojukwu University Uli, Anambra State, Nigeria.
Ojiako, E. N.
Department of Pure & Industrial Chemistry, Chukwuemeka Odumegwu Ojukwu University Uli, Anambra State, Nigeria.
Achonye, C.C.
Department of Science Laboratory Technology, Anambra State Polytechnic, Mgbakwu, Anambra State Nigeria.
Okolo, A. J.
Department of Pure & Industrial Chemistry, Chukwuemeka Odumegwu Ojukwu University Uli, Anambra State, Nigeria.
Silas, C.U.
Department of Chemistry, Kingsley Ozumba Mbadiwe University, Ideato, Imo State, Nigeria.
Ndupu, R. O.
Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056 USA.
*Author to whom correspondence should be addressed.
Abstract
This study is focused on the synthesis, characterization, and evaluation of the antimicrobial activities of a novel Schiff base ligand derived from 4-acyl pyrazolone and its cobalt (II) complex. This work aims to compare structural variations arising from metal coordination with changes in biological activity. The research adopted an experimental design involving chemical synthesis, spectroscopic characterization, and antimicrobial screening. The Schiff base ligand was synthesized by condensing 4-acyl pyrazolone with diaminobenzene, followed by coordination with cobalt (II) chloride hexahydrate (CoCl2.H2O) to obtain the Co (II) complex. Characterization was done using melting point, elemental analysis, molar conductivity, infrared (IR), UV–Vis, 1H NMR, and GC–MS spectroscopy. Antimicrobial testing against Gram positive bacteria, Gram negative bacterial and fungal strains were conducted using the agar well diffusion method in accordance with CLSI guidelines. Spectral analyses confirmed Schiff base formation through the appearance of an azomethine (C=N) band at 1636 cm⁻¹ and coordination to Co(II) via nitrogen, nitrogen and oxygen (N, N and O) donor atoms, confirmed by M–L bands at 760 cm⁻¹and 677 cm⁻¹. The Co(II) complex exhibited higher melting point and lower molar conductivity, indicating greater stability and non-electrolytic nature. Antimicrobial screening indicated that the Co(II) complex showed enhanced activity (zones of inhibition: 30–42 mm) compared to the free ligand (14–32 mm), particularly against C. albicans and S. typhi. MIC and MBC/MFC data confirmed enhanced efficacy upon complexation. Coordination of the Schiff base ligand with Co (II) significantly increased antimicrobial activity due to increased lipophilicity and membrane permeability, consistent with Tweedy’s chelation theory. The synthesized Co(II) complex shows greater potential for further development as an effective antibacterial and antifungal agent.
Keywords: Schiff base ligand, cobalt (II) complex, pyrazolone derivative, antimicrobial activity