No abstract

The intensive use of antibiotics has led to an increase of drug resistant bacteria against known antibiotics. To overcome the alarming problem of microbial resistance to antibiotics, the discovery of novel active compounds against new targets is a matter of urgency. Based on this, we report three new mixed ligand complexes of cobalt (II)viz. mononuclear ([Co(phen)2(Act)(H2O)]Cl2.H2O and [Co(phen)2(Act)(en)]Cl2), and binuclear [Co2(phen)4(Act)2(en)]Cl4 which were synthesized from CoCl2.6H2O, 1,10-phenanthroline monohydrate, acetamide and ethylenediamine. These complexes were characterized using spectroscopic (ESI-MS, ICP-OES, FT-IR, and UV-Vis), chloride determination as well as melting point and conductance measurement. Invitro antibacterial activity was also tested on two Gram positive (Staphylococcus aureus, Streptococcus pyogenes) and two Gram negative (Escherichia coli and Klebsiella pneumoniae) bacteria using disc diffusion method. The complexes performed well even against the Gram-negative bacteria. The antibacterial result was found comparable with the commercial drug Gentamicin even at lower concentration of complexes. Thus, the synthesized complexes may be considered as potential antibacterial agents after passing cytotoxicity testing.

New organic salts were synthesized by quaternizing 1,10-phenanthroline using 1-bromotetradecane. The first step yielded an organic salt of formula [C26H37N2]Br. Anion exchange reaction using Li[(CF3SO2)2N] resulted in a more stable salt of formula [C26H37N2][(CF3SO2)2N]. The organic salts were investigated by spectrometry (1H, 13C, 19F NMR, X-ray photoelectron spectroscopy (XPS), UV-Vis, and matrix-assisted laser desorption/ionization mass spectroscopy (MALDI MS), CHNSBr elemental analysis, and thermal analysis (TGA and DSC). The thermal characterization showed the melting and decomposition points of [C26H37N2][(CF3SO2)2N] to be 48°C and 290°C, respectively, which indicates it is an ionic liquid with large liquidus range. The biological activities of the salts were investigated against two Gram-positive (Staphylococcus aureus and Streptococcus pyogenes) and two Gram-negative (Escherichia coli and Klebsiella pneumoniae) bacteria, and they are found to be active against all of them. They were compared with [Cu(1,10-phenanthroline)2Cl]Cl. They are found more active against the Gram-negative bacteria. The salts demonstrated minimum inhibitory concentration as low as 50 µg/L. These results suggest the synthesized salts can be considered as a better alternative to certain transition metal complex drugs. This minimizes the concern of introducing metal ions into the organism.