Akihiko Kanazawa

Study on antibacterial dental resin using tri-n-butyl(4-vinylbenzyl) phosphonium chloride

The antibacterial properties of a polymeric phosphonium salt were studied to determine its suitability as an additive to develop an antibacterial dental resin. The phosphonium salt monomer studied was tri-n-butyl(4-vinylbenzyl)phosphonium chloride (VP), and acrylic acid (AC) and methacryloyloxyethyl trimethyl ammonium chloride (MA) were used as controls. The antibacterial activity of these monomers and their corresponding polymers (PVP, PAC, and PMA) against Streptococcus mutans (S. mutans) was examined. When incubating S. mutans in a medium containing 10 μmol/mL for 24 hours, the antibacterial activity of PVP against S. mutans was high, while the antibacterial activity of PMA and VP was lower. AC, PAC and PMA exhibited the lowest antibacterial activity. The mechanical properties of the copolymers of methyl methacrylate, 2-hydroxyethyl methacrylate, and VP decreased as VP content increased, and were lower than those of poly(methyl methacrylate).

Hydration-aggregation pretreatment for drastically improving esterification activity of commercial lipases in non-aqueous media

We investigated a novel, simple method for activating lipases in non-aqueous reaction media. Lipase powders were suspended in n-fatty alcohols and were then hydrated by adding a small amount of water. A paste-like aggregate was recovered from the mixture followed by lyophilization for obtaining activated lipases as dry powders. Lipase activity was evaluated for esterification between myristic acid and methanol in n-hexane. The activated lipases exhibited high esterification activity depending on the experiment conditions during hydration-aggregation pretreatment such as the amount of added water, the temperature, the pH of added buffer solutions, and the carbon chain length of the n-fatty alcohols used as pretreatment solvents. Various commercial lipases from different origins could be activated by this method. Changes in lipase conformation induced by the hydration-aggregation pretreatment were studied based on fluorescence and Fourier-transform infrared spectroscopy.

Freeze-dryable lipid vesicles with size tunability and high encapsulation efficiency prepared by the multiple emulsification-solvent evaporation method

We investigated the extent of potential applicability of our recently developed method for preparing lipid vesicles [T. Kuroiwa et al., J. Am. Oil Chem. Soc., 93 (2016) 421], designated as the multiple emulsification-solvent evaporation method, with the intention of controlling the vesicle diameter and achieving high entrapment efficiency for water-soluble compounds. Using this method, the diameter of lipid vesicles could be varied by selecting the methods for preparing the primary water-in-oil emulsion, which contained water droplets as templates for the internal water phases of lipid vesicles. We obtained lipid vesicles with mean diameters of 0.2-4.4μm from water-in-oil-in-water multiple emulsions after solvent evaporation. A high entrapment yield of calcein, a water-soluble fluorescent dye, into the lipid vesicles was obtained for each vesicle sample, depending on their diameter and the type of emulsifier added to the external water phase. The use of polymeric emulsifier was more effective in achieving a high entrapment yield. The obtained lipid vesicles were powderized via freeze-drying. Vesicles could be powderized while maintaining their original diameter, as confirmed by scanning electron microscopy. Furthermore, the powderized vesicles could be rehydrated and resuspended without significant change in their diameter. However, the entrapment yield of calcein decreased after freeze-drying and rehydration. The calcein leakage during the freeze-drying followed by rehydration could be suppressed by adding an appropriate amount of trehalose as a lyoprotectant.

Effect of Charge Transfer Complex on Electrical Properties of 4-Cyano-4'-pentylbiphenyl

The dielectric constant, threshold voltage, and response time were measured for a nematic binary mixture of 4-cyano-4-pentylbiphenyl (5CB) molecules and the doped electron acceptor tetracyanoethylene (TCNE). The doping of TCNE caused a large increase in the dielectric constant and dielectric anisotropy. However, no marked improvement was achieved for threshold voltage and response time. Considering that the large increase was due to mobile charges in the system, we proposed a theoretical model to discuss the singularity that appeared in experimental results obtained in an electric field.