The emergence of
multidrug-resistant microbes is a significant
health concern posing a constant need for new antimicrobials. Membrane-targeting
antibiotics are promising candidates with reduced ability of microbes
to develop resistance. In the present investigation, the principal
reason behind choosing cholic acid as the crucial scaffold lies in
the fact that it has a facially amphiphilic nature, which provides
ample opportunity to refine the amphiphilicity by linking the amino
acid lysine. A total of 16 novel amphipathic cholic acid derivatives
were synthesized by sequentially linking lysine to C3-β-amino
cholic acid methyl ester to maintain the hydrophobic/hydrophilic balance,
which could be the essential requirement for the antimicrobial activity.
Among the synthesized conjugates, a series with fluorenyl-9-methoxycarbonyl
moiety attached to cholic acid via lysine linker showed promising
antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans. A pronounced effect of increase
in lysine residues was noted on the observed activity. The lead compounds
were found to be active against drug-resistant bacterial and fungal
clinical isolates and also improved the efficacy of antifungal agents
amphotericin B and voriconazole. Membrane-permeability studies demonstrated
the ability of these compounds to induce membrane damage in the tested
microbes. The active conjugates did not show any hemolytic activity
and were also found to be nontoxic to the normal cells as well as
the examined cancer cell lines. The observed antimicrobial activity
was attributed to the facial amphiphilic conformations, hydrophobic/hydrophilic
balance, and the overall charge on the molecules.
Stoichiometric polycrystalline tin oxide thin films were deposited by the reactive evaporation of tin and the SnO 2 formation was found to be strongly dependent on the deposition parameters. The preferred orientation of the SnO z films deposited on different substrates was varying due to the dislocation defects arising during the thin film formation. The X-ray diffraction (XRD) studies identified a tetragonal structure while the scanning electron microscopic (SEM) studies revealed a polycrystalline surface for the SnO 2 films reactively deposited.
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