Antimicrobial and antiprotozoal activities of silver coordination polymers derived from the asymmetric halogenated Schiff base ligands

A series of polymeric silver(I) complexes with Schiff base ligands containing pyridine and 3,5-halogen substituted phenol moieties were synthesized and characterized by spectroscopic methods and in the case of Ag6 also by X-ray crystallography. All silver(I) complexes (Ag1–Ag8) were evaluated for their biological activity against a panel of pathogens including the protozoa Trypanosoma cruzi, T. brucei, T. rhodesiense and Leishmania infantum; the bacteria Staphylococcus aureus, Escherichia coli, Mycobacterium tuberculosis H37Ra and the yeast Candida albicans. Cytotoxicity evaluation was carried out on human lung fibroblasts (MRC-5) and on primary peritoneal mouse macrophages. The most relevant result reveals antileishmanial activity potential with all complexes demonstrating higher potency than the reference drug miltefosine. Complexes with the best antiprotozoal profile (i.e., Ag2 and Ag7) were selected for incorporation into poly (lactic acid) nanoparticles (PLA NPs) with the aim to enhance selectivity. PLA/Ag2 NPs and PLA/Ag7 NPs exhibited adequate physicochemical properties, that is, average size of 263 ± 60 nm and 225 ± 6 nm, respectively, good entrapment efficiency (69% and 63%), loading content (6.2% and 5.7%) and stability. The cytotoxicity of PLA/Ag2 NPs and PLA/Ag7 NPs on MRC-5 cells was reduced with respect to the “free” metal complexes by 2-fold and 6-fold, respectively.