Assessment of antimicrobial activity of 6-APA conjugated Zn coordination polymers

Antimicrobial resistance is among the top ten global health threats. One way to overcome this problem is to design new antibiotics; with this aim, zinc (Zn) coordination polymers were synthesized by conjugation with 6-aminopenicilanic acid (6-APA) and benzene-1,3,5-tricarboxylic acid (BTC). The crystalline structure of Zn coordination polymers was analyzed by X-Ray Diffraction (XRD), the appropriate chemical coordination was studied by Attenuated Total Reflectance Fourier Transformed Infrared (ATR-FTIR), and their thermal stability was characterized by Thermogravimetric Analysis and Differential Thermal Analysis (TGA-DTA). The Zn coordination polymers were solubilized in water, obtaining different concentrations (25,000, 20,000, 15,000, 10,000, and 5,000 ppm (mg/L)) to emulate the concentration of commercial antibiotics. Then, these solutions were biologically characterized by testing the cell viability of human monocytes and porcine dermis fibroblasts, and a hemolysis assay to prove their biocompatibility. Their antimicrobial activity was tested against the E. Coli and S. Aureus strains in a liquid and solid medium (antibiograms). The results of ATR-FTIR indicated the suitable chemical coordination between Zn and its ligands, but the 6-APA loses its high crystallinity when it is conjugated with Zn; this effect is more evident when BTC is also added. However, the TGA-DTA analysis indicates that chemical conjugation increases the thermal stability of Zn conjugated polymers, especially when BTC is added in the synthesis process. The hemolysis test shows that Zn coordination polymers are slightly cytotoxic, but the cell viability assays indicate that 6-APA Zn conjugated polymers exhibits the highest cell viability and thus better biocompatibility. However, when the antimicrobial properties of Zn coordination polymers were tested, the ligand 6-APA shows the highest bactericidal properties in liquid and solid medium for both E. Coli and S. Aureus strains.