Bactericidal activity of the layered cupric hydroxy-fluoride Cu(OH)F against pathogenic Escherichia coli strain

Micrometre-sized particles of layered cupric hydroxy-fluoride Cu(OH)F were prepared through hydrothermal route from CuO powder and diluted aqueous hydrofluoric acid. Thermogravimetric (TG) and Mass Spectrometric (MS) evolved gas analyses showed a deviation of 0.06% from the expected OH : F ratio of 1 : 1 in this heteroanionic material (HAM). The isoelectric hydroxide and fluoride anions occupy distinct crystallographic sites and are therefore perfectly ordered in the monoclinic structure of Cu(OH)_1.06F_0.94 determined from X-ray powder diffraction data. The bactericidal activity of the Cu(OH)_1.06F_0.94 particles was evaluated at 20 °C in sterile water against pathogenic Escherichia coli. The number of bacterial colonies falls by more than six orders of magnitude in the first hour alone, and the entire inoculum is eradicated after 3 hours of contact with the Cu(OH)_1.06F_0.94 particles. This fast bactericidal kinetics is attributed to fluoride ions which both promote the production of reactive oxygen species (ROS) by cupric ions released and located on the surface of particles, and prevent E. coli from detoxifying them.