Antimicrobial activity of novel synthesized coumarin based transitional metal complexes

Sahoo, Jyotirmaya; Paidesetty, Sudhir K.

The FT/IR spectra of synthesized ligands 3a and 3b showed vibrations at 1619e1603 cm À1 , 1726e1745 cm À1 , 1298e1246 cm À1 and 1529e1505 cm À1 corresponding to C]C str., C]O str., CeO str. and N]N str., respectively, which were also observed in the synthesized complexes (4ae 4h). The only exception is the bands due to OH str. at 3479e 3445 cm À1 exhibited in the ligands that are not observable in the complexes. In metal Cu(II), Ni(II) Co(II) and Zn(II) complexes of 3a and 3b, the FT/IR absorption band due to the hydroxyl group at 4-HC has been diminished and indicates the metal co-ordination of the OH group via deprotonation due to liberation of hydrochloric acid. In addition to these FT/IR spectral data, stretching of the MÀN and MÀO bonds of the complexes, which appear in the higher frequency wavenumber region in the range 451e441 and 538e531 cm À1 , also indicates that complexation occurred through nitrogen and oxygen atoms from the azo-enolic ligands. 22, 23 The 1 H NMR spectra of ligands 3a and 3b showed the enolic OH peak at 16.81 and 16.86 ppm. The disappearance of the enolic OH group in all the complexes (4ae4h) may be due to the interaction of metal chlorides Scheme 1: Synthesis of coumarin based transitional metal complexes. with the hydroxyl group of the ligands resulting in deprotonation and complexation of the ligands to the metal ions. Ligand 3b shows three identical, similarenvironment protons at 3.83 ppm, which indicates the presence of an eOCH 3 functional group. The good bathochromic shift at 463 and 450 nm exhibited by complexes 4a and 4e may be due to the attachment of transition metal ion Co þþ to the respective ligands 3a and 3b. Most of the compounds showed good antimicrobial activity in comparison to ampicillin. The enhanced antimicrobial activity exhibited by complexes 4a, 4b, 4e and 4f relative to their ligands against E. coli may be due to coordination of Co þþ and Ni þþ ions to the respective ligands 3a and 3b. However, complexes 4a and 4e showed considerably enhanced antimicrobial activity against most of the pathogenic strains relative to their ligands. Complexation reduces the polarity of the metal ion by coordinating with ligands and increases the lipophilicity of the metals. 24 Thus, it facilitates the penetration of the novel synthesized complexes into the lipoid cell membrane of microorganisms and inhibits their growth. The limitations of our study include only the investigation of antimicrobial activity of the novel synthesized complexes against a few bacterial and fungal strains. Furthermore, it is necessary to investigate the antimicrobial activities of the novel complexes against multidrug-resistant microorganisms.