Synthesis and Structure of Silver Complexes with Nicotinate-Type Ligands Having Antibacterial Activities against Clinically Isolated Antibiotic Resistant Pathogens

The synthesis and low-temperature X-ray crystal structures of five new silver complexes, [Ag₂-μ-O,O'(2-aminonicotinium)₂(NO₃)₂]_n (7), [Ag(isonicotinamide)₂-μ-O,O'(NO₃)]₂ (8), [Ag(ethyl nicotinate)₂](NO₃) (9), [Ag(ethyl isonicotinate)₂(NO₃)] (10), and [Ag(methyl isonicotinate)₂(H₂O)](NO₃) (11), are presented and fully characterized by spectral and elemental analysis. The antimicrobial activities of these complexes were screened using 12 different clinical isolates belonging to four pathogenic bacteria, S. aureus, S. pyogenes, P. mirabilis, and Ps. Aeruginosa, all obtained from diabetic foot ulcers. These tested bacteria were resistant for at least 10 antibiotics commonly used for treatment of diabetic foot ulcers. Compounds 7 and 8 had considerable activity against Ps. Aeruginosa (MIC values 2-8 µg/mL), compound 9 against S. aureus (MIC 4-16 µg/mL) and S. pyogenes (MIC 2-4 µg/mL), and also 9 and 11 against P. mirabilis (MIC 1-16 µg/mL). All complexes were non-toxic for daphnia at concentrations above 512 µg/mL overnight