Amino Acid–Furfural Schiff Bases and their Co(II)/Cu(II) Complexes: Synthesis, Characterization and Antimicrobial Activity
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Abstract
Schiff bases carrying the azomethine (–CH=N–) linkage and their metal complexes continue to attract attention, as they find use in medicinal chemistry, in catalysis and as thermally stable materials. In the present work, three Schiff bases (SB1–SB3) were prepared by condensing furfural with L-phenylalanine, L-tyrosine and L-histidine. These ligands were then reacted with Co2+ and Cu2+ chlorides, which gave the metal complexes SB1M1–SB3M2. All the compounds were characterised by FTIR, ¹H NMR, ¹³C NMR, ESI-MS and DSC. In the IR spectra of the complexes, the azomethine and carboxylate stretching bands were shifted with respect to the free ligands, and new bands due to metal–nitrogen and metal–oxygen bonds were seen, pointing towards coordination of the ligand with Co(II) and Cu(II). Formation of the Schiff bases and their proposed compositions were supported by NMR and ESI-MS data, while DSC gave information on the melting and decomposition behaviour. UV–Vis spectra and XRD patterns showed that the optical response and the crystallinity of the compounds changed after binding with the metal ion. All compounds showed antibacterial activity at 15.625 μg/disc. Inhibition zones ranged from 18–25 mm against E. coli and 12–21.67 mm against S. aureus, comparable to ciprofloxacin. SB2M2 showed the strongest activity against E. coli, whereas SB2M1 was most effective against S. aureus.
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