Antibacterial activity of copper pyrazolate coordination polymers

Abstract

Novel copper(II) coordination polymers (CPs) [Cu(μ-4-NO₂pz)₂]_n and [Cu(μ-4-NO₂pz)₂·DMF H₂O]_n (4-NO₂pz⁻ = 4-nitropyrazolate; DMF = N,N′-dimethylformamide) were synthesized and characterized in the solid state and their thermal behaviour and structural features were investigated. Together with the known CPs [Cu(μ-pz)(μ-OH)]_n, [Cu(μ-pz)₂(H₂O)]_n and [Cu(μ-4-Xpz)₂(DMF)]_n [pz⁻ = pyrazolate; 4-Xpz⁻ = 4-X-pyrazolate, with X = H, Cl, Br, I], they were isolated in the form of very small particles whose dimensions range within 20–300 nm and, as such, they were investigated as potential antibacterial agents. Their antibacterial activity was assessed against two Gram-negative bacteria, namely Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa), and the Gram-positive bacterium Staphylococcus aureus (S. aureus), by monitoring the bacterial growth curve and the antibacterial rate as a function of time. The bactericidal mechanism seems to be related to the ROS production, directly activated by the contact of the CP tiny particles with the bacterial membrane, without a significant release of Cu(II) ions.