The potential antimicrobial properties of a tridentate polypyridyl ligand 4-butoxy-N,N-bis(pyridin-2-ylmethyl)aniline (BUT) 1 and its corresponding mixed ligand ruthenium complexes were investigated on drug-resistant and non-drug-resistant bacterial species. The ligand and its complexes were synthesized and successfully characterized by 1H NMR, UV/Vis, and FTIR spectra; ESI-MS; and magnetic susceptibility. Electronic spectra and magnetic susceptibility of these Ru(II)/(III) complexes suggest that they are of a low spin crystal field split, where the Ru(III) is a d5 and Ru(II) d6 low spin. These compounds were tested for antibacterial activity on two bacterial species: Staphylococcus aureus (S. aureus) and Klebsiella pneumoniae (K. pneumoniae), as well as their drug-resistant strains methicillin-resistant Staphylococcus aureus (MRSA) and multidrug resistant Klebsiella pneumoniae (MDR K. pneumoniae). All the compounds inhibited growth of the two non-drug-resistant bacteria and only one drug-resistant strain MRSA. However, only the ligands BUT and 2,2-dipyridylamine showed activity against MRSA, while all complexes did not show any antibacterial activity on MRSA. We observed large zones of inhibition for the Gram-positive S. aureus and MRSA bacteria, compared to the Gram-negative K. pneumoniae bacteria. DNA cleavage studies with gel electrophoresis showed denatured bacterial DNA on the gel from all the complexes, with the exception of the ligand, suggesting DNA nuclease activity of the complexes in the bacterial DNA.
Formation constants of copper(ii), zinc(ii) and calcium(ii) with 3,5-diaminodiamido-4-oxahexacyclododecane (cageL) has been studied by glass electrode potentiometry at 25 degrees C and an ionic strength of 0.15 mol dm(-3). Copper(ii) forms more stable complexes with cageL than zinc(ii) and calcium(ii). Metal ion complexation promotes deprotonation and coordination of the amide nitrogens resulting in overall tetragonal coordination of Cu(2+) suggested by the UV-visible electronic spectra. Speciation calculations using a blood plasma model suggest that zinc(ii) and calcium(ii) are good competitors of copper(ii) in vivo. Bio-distribution experiments using (64)Cu-labelled Cu(ii)-cageL show that about 50% dose of the complex is retained in the body after 24 h.
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