Polynuclear silver(I) complex with thianthrene: structural characterization, antimicrobial activity and interaction with biomolecules

Silver(I) complexes showed a wide range of applications in medicine as effective antiseptic, antibacterial and anti-inflammatory agents. Antimicrobial properties of silver(I) complexes have been well known since the successful use of cream containing silver(I) sulfadiazine for the treatment of burn wounds. The critical factor in determining the antimicrobial activity of silver(I) complexes is the type of the ligand donor atom bound to the Ag(I) ion. In this respect, in the last few decades, research has been focusing on the synthesis of silver(I) complexes with sulfur-donor ligands, including mercaptan, thioamide and thione ligands. Herein, new silver(I) complex with thianthrene (tia), [Ag(NO₃)(tia)(H₂O)]_n, was synthesized by the reaction of AgNO₃ with an equimolar amount of tia in ethanol/dichlormethane (v/v 1:1) at room temperature, and characterized by NMR, IR and UV-Vis spectroscopy and single-crystal X-ray diffraction analysis. The antimicrobial activity of the synthesized complex was evaluated against the broad panel of Gram-positive and Gram-negative bacteria and Candida spp. This complex showed significant activity toward important human pathogens Gram-positive Staphylococcus aureus and Candida parapsilosis with minimal inhibitory concentrations (MICs) being 3.91 µg/mL. The interaction of [Ag(NO₃)(tia)(H₂O)]_n with calf thymus DNA (ctDNA) and bovine serum albumin (BSA) was studied to evaluate the binding affinity towards these biomolecules for possible insights on the mode of antimicrobial activity. The binding affinity of the investigated complex to BSA is higher than that for DNA, indicating that proteins could be more favorable binding sites for this complex in comparison to the nucleic acids.