Electropolymerization of Pyrrole-Tailed Imidazolium Ionic Liquid for the Elaboration of Antibacterial Surfaces.

A strategy was developed to prepare antibacterial surfaces by electropolymerization of a pyrrole-functionalized imidazolium ionic liquid bearing an halometallate anion. The objective was to combine the antibacterial efficiency of polypyrrole (PPy) with those of the ionic liquid's components (cation and anion). For this, -(1-methyl-3-octylimidazolium)pyrrole bromide monomer [PyCMIm]Br was synthesized and coordinated to ZnCl affording [PyCMIm]Br-ZnCl. The antibacterial properties of [PyCMIm]Br-ZnCl monomer were evaluated against and by measurement of the minimum inhibitory concentration (MIC) values. This monomer presents higher activity against (MIC = 0.098 μmol·mL) than against (MIC = 2.10 μmol·mL). Mixtures of pyrrole and the pyrrole-functionalized ionic liquid [PyCMIm]Br-ZnCl were then used for the electrodeposition of PPy films on Fluorine-doped tin oxide (FTO) substrates. The concentration of pyrrole was fixed to 50 mM, while the concentration of [PyCMIm]Br-ZnCl was varied from 5 to 100 mM. The efficient incorporation of the imidazolium cation and zinc halometallate anion into the films was confirmed by X-ray photoelectron spectroscopy (XPS) measurements. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements confirmed the homogeneity of the different films with structures that depend on the [PyCMIm]Br-ZnCl concentration. The films' thickness determined by profilometry varies only slightly with the [PyCMIm]Br-ZnCl concentration from 7.4 μm at 5 mM to 8.9 μM at 100 mM. The films become more hydrophilic with an increase of [PyCMIm]Br-ZnCl concentration with water contact angles varying from 47° at the lowest concentration to 32° at the highest concentration. The antibacterial activities of the different PPy films were determined both by the halo inhibition method and by the colony forming units (CFUs) counting method over time against Gram-positive and Gram-negative bacteria. Films obtained by incorporation of [PyCMIm]Br-ZnCl showed excellent antibacterial properties, at least two times higher than those of neat PPy, validating our strategy. Furthermore, a comparison of the antibacterial properties of the films obtained using the same [PyCMIm]Br-ZnCl concentration (50 mM) evidenced much better activity against Gram-positive (no bacterial survival within 5 min) than against Gram-negative bacteria (no bacterial survival within 3 h). Finally, the antibacterial performances over time could be tuned by the concentration of the employed pyrrole-functionalized ionic liquid monomer. Against , using 100 mM of [PyCMIm]Br-ZnCl, the bacteria were totally killed within a few minutes, using 50 mM, they were killed after 2 h while using 10 mM, about 20% of bacteria survived even after 6 h.