Alina Khodosovskaya

Schiff bases bearing a sterically hindered phenolic moiety and their Bi(III) complexes were synthesized and characterized by physicochemical, quantum chemical, and biological methods. The compounds were screened in vitro against bacterial and yeast strains. It was found that Bi(III) complexes demonstrate higher antimicrobial activity compared to the parent ligands as well as to the commonly used drug (De-Nol®). Moreover, the antibacterial activity of investigated compounds did not directly correlate with their hemolytic activity, indicating that the antimicrobial effect of Bi(III) complexes cannot be explained solely by their membranolytic properties. Spectrofluorometric studies of the interaction of the Bi(III) complexes with plasma proteins indicate their moderate to high affinity toward BSA and hemoglobin, which is crucial for the determination of their pharmacological profile as well as toxicity assessment. Additionally, molecular docking was performed to predict the possible interaction modes and binding energies of the tested compounds at the molecular level. The results obtained may provide the basis for the design and development of novel Bi(III)-based antimicrobial agents.

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Novel Ag(I) complexes (2a–2c) with phenolic Schiff bases were synthesized using 4,6-di-tert-butyl-3-(((5-mercapto-1,3,4-thiadiazol-2-yl)imino)methyl)benzene-1,2-diol (1a), 4,6-di-tert-butyl-3-(((4-mercaptophe­nyl­)­imino)­methyl)benzene-1,2-diol (1b), and 4,6-di-tert-butyl-3-(((3-mercaptophenyl)imino)methyl)­benzene-1,2-diol (1c). They were examined by elemental analysis, FT-IR, UV-Vis, 1H-NMR spectroscopy, XRD, cyclic voltammetry, conductivity measurements, and biological methods. The complexes are characterized by distorted geometry of the coordination cores AgN2S2 (2c), AgNS (2b) and AgS2 (2a). These stable complexes were not typified by the intramolecular redox reaction in organic solvents resulting in the formation of silver nanoparticles (AgNPs). Antibacterial activity of 1a–1c and 2a–2c was evaluated in comparison with AgNPs and commonly used antibiotics. All the complexes were more active than the ligands against the bacteria tested (14), but they were less active than AgNPs and commonly used antibiotics. Both 1a–1c and their complexes 2a–2c exhibited the capability for the bovine heart Fe(III)-Cyt c reduction. The ligands 1b and 1c were characterized by the highest reduction rate among the compounds under study, and they showed a higher reducing ability (determined by cyclic voltammetry) as compared with that of their Ag(I) complexes 2b and 2c.