The synthesis, characterization and antimicrobial activity determination of some aminopyridine-and (aminomethyl)pyridine-salicylaldimine copper(II) complexes were realized. The ligands, L 1-L 6 , were prepared by condensing salicylaldehyde and o-vanillin with 2-and 3-amino-and (aminomethyl)pyridine, respectively. The complexes were characterized by micro-analytical, electronic, infrared and conductivity data. The structures of the Schiff base ligands were further confirmed from 1 Hand 13 C-NMR spectral data. This study established that salicylaldimine ligands could coordinate as neutral species via the imine-N and the undeprotonated phenolic-O. The complexes have the molecular formula: [CuLCl], [Cu(LH) 2 Cl 2 ]•xH 2 O or [Cu(LH)Cl(H 2 O)]Cl. The X-ray crystal structure of [CuL 6 Cl] indicated a square planar geometry with the Schiff base ligand coordinated to the Cu(II) ion as a tridentate monobasic, N 2 O, ligand. The crystals crystallized in a monoclinic system with P2 1 /c space group. All the ligands and their Cu(II) complexes were screened for their antimicrobial activity against Staphylococcus aureus subsp. aureus ATCC ® 6538™  , Bacillus subtillis subsp. spizizenii ATCC ® 6633™  , Escherichia coli ATCC ® 8739™  and Candida albicans ATCC ® 2091™  using agar diffusion and broth dilution techniques. The presence of the methoxyl group enhanced the antimicrobial activity of the salicylaldimine Schiff base ligands.

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The synthesis, characterization and antimicrobial activity of Cu(II) complexes of some p-substituted aniline Schiff base ligands have been carried out. The Schiff bases were obtained from salicylaldehyde and o-vanillin. The Cu(II) complexes have been characterized by elemental analysis, conductivity measurement, infrared and electronic spectral data. The complexes were obtained either as metal chelates [Cu(L)2] or Schiff base adducts (CuCl2.2LH).xH2O. The metal chelates were non-electrolytes while the Schiff base adducts exhibited 1:1 or 2:1 electrolytes in methanol. The Cu(II) complexes exhibited slight antimicrobial activity against Escherichia coli ATCC® 8739™*, Staphylococcus aureus subsp. aureus ATCC® 6538™*, Bacillus subtilis subsp. spizizenii ATCC® 6633™* and Candida albicans ATCC® 2091™*. The complexes exhibited significant antifungal activity.                     KEY WORDS: Metal Chelates, Schiff bases, Adducts, Cu(II) complexes, Salicylaldimines   Bull. Chem. Soc. Ethiop. 2021, 35(1), 33-42. DOI: https://dx.doi.org/10.4314/bcse.v35i1.3

Introduction: The unending interest in the study of Schiff base ligands arise from the ease of their preparation and their versatility in several fields of Chemistry and Biochemistry. Some of the major biochemical processes such as trans-amination and glycosylation involve the formation of Schiff base intermediates. In addition, compounds containing the azomethine group have been found to often possess different biological activity such as anti-microbial, anti-viral and anti-inflammatory activity. In most cases, the extent of the potency depends on the nature of the constituent amino and or aldehyde moiety. Aims: The aim of this study was to synthesize, characterize and evaluate the antimicrobial activity of Schiff base ligands derived from p-vanillin and vanillin. Materials and Methods: The Schiff base ligands were prepared by condensing p-vanillin and vanillin with substituted aniline, aminonaphthalene and 3-aminopyridine respectively. The ligands have been characterized by elemental analysis, 1H- & 13C-NMR, infrared, Raman and electronic spectral data. The antimicrobial study was carried out by screening the prepared ligands against Staphylococcus aureus subsp. aureus ATCC® 6538™, Bacillus substillis subsp. spizizenii ATCC® 6633™*, Escherichia coli ATCC® 8739™* and Candida albicans ATCC® 2091™* using agar diffusion technique. Results: The azomethine, HC=N, 1H- & 13C-NMR signals were observed at 8.66-8.30 ppm and 164.42-157.99 ppm respectively. The infrared band appeared at 1622-1607 cm-1. The p-vanillin ligands exhibited higher activity than the vanillin based ligands. The p-hydroxyl and 3-aminopyridine ligands possess significant antimicrobial activity especially, antifungal activity. Conclusion: The spectroscopic spectral data of the compounds confirmed the formation of the Schiff base ligands. The antimicrobial activity of the compounds depends largely on the nature of the aldehyde moiety.

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The aim of this study was to synthesize and evaluate the antimicrobial activity of Cu(II) complexes of some substituted salicylaldimines with benzimidazole nucleus. The salicylaldimine ligands were prepared by condensing 2-aminobenzimidazole with salicylaldehyde, o-vanillin and p-vanillin. All the compounds and the Cu(II) complexes were characterized by elemental , electronic, infrared and molar conductivity data. In addition, the structures of the ligands were confirmed with 1H-NMR and 13C-NMR spectral data. Both the ligands and the Cu(II) complexes have been screened for their in vitro antimicrobial activity against Staphylococcus aureus subsp. aureus ATCC® 6538™, Bacillus substillis subsp. spizizenii ATCC® 6633™*, Escherichia coli ATCC® 8739™* and Candida albicans ATCC® 2091™* using agar diffusion and broth dilution techniques. The ligands coordinated to the Cu(II) ion in a 1:2 (M:L) ratio as tridentate monobasic species via the imine-N, the imidazole-N and the phenolic–O to give six-coordinated Cu(II) complexes. The free ligands exhibited varying antimicrobial activity on the tested organisms from low activity to significant potency. Candida albicans was specifically susceptible to the o-vanillin Schiff base ligand. The presence of Cu(II) ion, however, did not have a regular effect on the activity of the compounds.