Silver(I) complexes with 1,10-phenanthroline-based ligands: The influence of epoxide function on the complex structure and biological activity

Abstract

In a continuing search for a novel metal-containing antimicrobial agents, the present study reports the synthesis, characterization and biological evaluation of two silver(I) complexes with 1,10-phenanthroline-based ligands, [Ag(1,10-phen)2]CF3COO·H2O (Ag1) and [Ag(CF3COO)(5,6-epoxy-1,10-phen)]2 (Ag2), 1,10-phen is 1,10-phenanthroline and 5,6-epoxy-1,10-phen is 5,6-epoxy-5,6-dihydro-1,10-phenanthroline. The complexes were characterized by different spectroscopic techniques (IR, 1H and 13C NMR and UV–Vis), while the crystal structure of Ag2 complex was determined by a single-crystal X-ray diffraction analysis. The spectroscopic data confirmed that the structure of Ag1 complex, with silver(I) ion tetrahedrally coordinated by two bidentate 1,10-phen ligands, is in accordance to the previous report (S.E. Paramonov et al., 2003). The crystallographic results showed that in dinuclear Ag2 complex, both Ag(I) ions are coordinated bidentately by 5,6-epoxy-1,10-phen and monodentately by trifluoroacetate, with presence of the short Ag∙∙∙Ag contact of 2.963 Å. Both silver(I) complexes were evaluated in vitro for antimicrobial activity against four bacterial and four Candida species, showing selectivity towards the investigated species of Candida with minimal inhibitory concentrations (MICs) between 0.9 and 12.5 µM. Moreover, Ag2 complex manifested significant antiproliferative properties in the case of a range of human cell lines, including human breast cancer (MDA-MB 231), which resulted from the presence of epoxy functional group in the ligand. The gel electrophoresis results obtained from the studies of Ag1 and Ag2 interactions with bacteriophage lambda DNA (λDNA) suggested that these complexes did not cause DNA degradation.