Periodic charge matching driven immobilization of gentamicin in nanoclays for stable and long-term antibacterial coating.

Matching of charge periodicity between a guest and a host enabled effective immobilization of highly water-soluble antibiotic drug, gentamicin C, in a bentonite clay by cation exchange. X-ray diffraction, infrared spectroscopy and CHNS analysis revealed the immobilization manner of gentamicin C, which was immobilized between bentonite layers via periodic charge-charge interaction with tilted arrangement, as a trication. Both gentamicin alone and a gentamicin/bentonite hybrid were coated onto a polyurethane substrate using water-borne polyurethane binder. The antibiotic character of both films was investigated as prepared or after immersion in phosphate-buffered saline till 5 days against E. coli and B. subtilis bacteria. It was clearly shown that the gentamicin/bentonite hybrid-coated film showed sustained antibacterial efficacy even after exposure to phosphate-buffered saline, while gentamicin only-coated film gradually lost its performance under the same condition.

Systematic utilization of layered double hydroxide nanosheets for effective removal of methyl orange from an aqueous system by π-π stacking-induced nanoconfinement.

Systematic utilization of carbonated Mg-Al layered double hydroxide (LDH) nanosheets for methyl orange removal was investigated with respect to particle dimensions. LDHs with the smallest dimensions were carefully synthesized to have a small lateral size as well as high dispersibility. The other particles, with medium and large sizes, were prepared by hydrothermal treatment and urea hydrolysis to have larger sizes and higher crystallinity. According to kinetics and isotherm analyses, the smallest LDH showed efficient adsorption of methyl orange (1250 mg/g-LDH), which was remarkably higher than the adsorption by the other LDHs with larger lateral sizes. Unlike the larger lateral-sized LDHs, the small ones were shown to utilize all accessible adsorption sites on the nanosheets, generating nanoconfinement of methyl orange molecules. Transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD) patterns indicated that the LDHs with lateral dimensions of ~40 nm fully utilized interlayer nanospace. Monte Carlo simulation suggested that the intercalated methyl orange was stabilized not only through electrostatic interactions with the LDH layer but also by π-π stacking between the methyl orange molecules, which is thought to be the driving force for replacement of carbonate anions.

Hierarchical Ag Nanostructures Fabricated from Silver Coordination Polymers for Antibacterial Surface.

A hierarchical silver nanostructure with improved antibacterial property was fabricated utilizing silver coordination polymer. Octadecanethiolate⁻silver polymer was synthesized to have a layered structure and was coated on silicon wafer by drop-casting method utilizing hydrophobic⁻hydrophobic interaction. Thus, the silver coordination polymer was calcined under reductive condition to produce zero-valent silver with a hierarchical nanostructure. X-ray diffraction patterns revealed that layered silver coordination polymer successfully transformed to hexagonal silver upon calcination. According to scanning electron and atomic force microscopy, silver coordination polymer with ~145.5 nm size was homogeneously coated on the surface before calcination, and it evolved micrometer-sized lumps and grooves which were composed of ~58.8 nm sized Ag nanoparticles. The hierarchical structure-micrometer lump/groove consisting of Ag nanoparticles-would be advantageous to kill bacteria; micrometer-grooves provide physical condition (pocket for bacteria capture) and the Ag nanoparticles from the neighboring lump endow chemical condition (antibacterial property of released Ag⁺). The antibacterial activity test on Escherichia coli via colony forming inhibitory assay indeed exhibited an improved antibacterial activity of hierarchical Ag nanostructure compared with the surface simply coated with Ag nanoparticles. From the line profile of atomic force microscopy, the bacterium trapped in the hierarchical Ag nanostructure was shown to interact intimately with Ag surface.