Synthesis, characterization and antimicrobial studies of Schiff base derived from 2’-hydroxyacetophenone and 4,5-diaminopyrimidine and its Mn(II) and Ni(II) complexes

Abstract

A novel Schiff base ligand was synthesized by condensing 2’-hydroxyacetophenone with 4,5- diaminopyrimidine. This Schiff base was utilized to prepare transition metal complexes of Mn(II) and Ni(II). Characterization of the ligand and its metal complexes was carried out based on solubility test, thermal stability (melting/decomposition temperatures), Fourier Transformed Infrared (FTIR) spectroscopy, conductivity measurements, magnetic susceptibility measurements, UV-Vis spectroscopy, and Job’s method of continuous variation for determination of the average number of coordinated ligand to the metal ion. The compounds were soluble in DMF and DMSO, sparingly soluble in polar solvents, but insoluble in non-polar solvents. The azomethine peak in the FTIR spectra of the Schiff base was observed at 1603 cm^-1, which as a result of complexation shifted to the lower frequencies of 1581 and 1594cm^-1 in the Mn and Ni complex respectively. UV spectra revealed absorption at 246nm for the ligand while those of Mn and Ni complex shifted to 247 and 253nm respectively for π-π* transition in the aromatic ring, also n-π* transitions of the azomethine group in the ligand was observed at 328nm while that of the complexes shifted to 352 and 305nm for Mn and Ni complexes respectively. The metal to ligand ratio was found to be 1:2 by Job's method of continuous variation. The antimicrobial activities of the Schiff base and its metal complexes were evaluated against Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli, and Klebsiella pneumoniae, as well as two fungal isolates, Aspergillus flavus and Aspergillus nigar. The results showed that the metal complexes exhibited higher antimicrobial activity than the Schiff base, which might be due to complexation or metal ion toxicity. However, their activity was lower than that of the standard drugs ciprofloxacin (antibacterial) and ketoconazole (antifungal).