Kyohei Yamashita

Water adsorption–desorption isotherms of two-dimensional hexagonal mesoporous silica around freezing point

Zr-doped mesoporous silica with a diameter of approximately 3.8 nm was synthesized via an evaporation-induced self-assembly process, and the adsorption-desorption isotherms of water vapor were measured in the temperature range of 263-298 K. The measured adsorption-desorption isotherms below 273 K indicated that water confined in the mesopores did not freeze at any relative pressure. All isotherms had a steep curve, resulting from capillary condensation/evaporation, and a pronounced hysteresis. The hysteresis loop, which is associated with a delayed adsorption process, increased with a decrease in temperature. Furthermore, the curvature radius where capillary evaporation/condensation occurs was evaluated by the combined Kelvin and Gibbs-Tolman-Koening-Buff (GTKB) equations for the modification of the interfacial tension due to the interfacial curvature. The thickness of the water adsorption layer for capillary condensation was slightly larger, whereas that for capillary evaporation was slightly smaller than 0.7 nm.

Coarse-grained molecular dynamics simulations of capillary evaporation of water confined in hydrophilic mesopores

ABSTRACT Non-equilibrium molecular dynamics (MD) simulations were performed to investigate the capillary evaporation of water confined in hydrophilic mesopores. The electrostatics-based (ELBA) coarse-grained water model was employed to calculate the duration of the time-consuming capillary evaporation process. To evaluate the effect of hydrophilicity of mesopores on the capillary evaporation of water, three types of thin films with a cylindrical mesopore were modelled by tuning the interactions between water and wall atoms. Initially, the cylindrical mesopore was filled with water, and evaporation of the water into vacuum was simulated. The calculation results showed that when capillary evaporation occurred, the desorption rate of water was almost constant in a highly hydrophilic mesopore where a stable water layer was formed on the pore surface, whereas the rate decreased with time in a weakly hydrophilic mesopore where the water layer did not remain stable. As time progressed, the water column shortened and then broke up. The number of water molecules in the mesopores decreased exponentially with time. The difference in the hydrophilicity of the mesopores resulted in different relaxation curves of water desorption from the mesopores.

Grand canonical Monte Carlo and molecular dynamics simulations of capillary condensation and evaporation of water in hydrophilic mesopores

ABSTRACT A combination of grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations (GCMD simulations) was performed to investigate the effect of the difference in chemical potential between the pore surface and gas phase on the adsorption and desorption kinetics of water in a hydrophilic mesopore. The chemical potential of water vapour was controlled by the GCMC method and the adsorption/desorption of water to/from a hydrophilic mesopore was simulated by the MD method. The calculation results showed that when the stepwise change in chemical potential of the gas phase was small, the initial rate of adsorption or desorption of water could be well predicted by the kinetic theory of gases. However, the rate greatly varied depending on the transport mechanisms of water in mesopores such as film flow and column flow. On the other hand, when the stepwise change in chemical potential was large, the initial rate was overestimated by the kinetic theory of gases; however, it did not change greatly with time.

Studies on Phenolic Lactones:Part VI. Synergistic Activities of Phenolic Lactones

The synergistic action of phenolic lactones on allethrin and pyrethrin were investigated from the mortality of synergized pyrethroids against rice-weevil by petri-dish method.In the series of α-benzylidene-γ-butyrolactones, (±) hibalactone and α-piperonylidenebutyrolactone were appreciably sy~ergistic on allethrin although less effective than piperonyl butoxide. (±) Hinokinin, 2-piperonylidene-3-piperonyl-l,4-butanediol also showed week activation, but α-benzylidene-, α-anisylidene-, α-veratrylidene-butyrolactone, α-piperonylidenea-α’-piperonyl-tetrahydrofuran, α-trirnethoxybenzylidene-β-trimethoxybenzyl-butyrolactone were not synergistic on the insecticidal action.In the series of synergized pyrethrin, (±) hibalactone and α-piperonylidene-butyrolactone showed week synergism but the other test compounds showed no appreciable synergism.

A New Synthetic Method of 6-Hydroxypurines

Synthesis of hypoxanthine via some new pyrimidine derivatives is described. Convenient methods for syntheses of hypoxanthine, guanine, xanthine, 3-methylxanthine via 5-isonitroso-pyrimidine compounds in two steps and some new routine synthesis of 6-hydroxy-N-alkyl-purines are also described.

Molecular Simulation of Adsorbed Water on Mesoporous Silica Thin Films

Grand canonical Monte Carlo (GCMC) and canonical ensemble molecular dynamics (NVT-MD) simulations were performed to investigate water adsorption properties in mesoporous silica thin films. The effect of pore radius on the adsorption properties was assessed using two models of mesoporous silica thin films having different pore radius and film thickness (1.38 and 5.66 nm in Model 1, respectively, and 1.81 and 7.30 nm in Model 2, respectively). In the simulations, a water adsorption layer or water menisci were formed in a mesopore accompanying the growth or shrinkage of stable adsorption layers on the upper and lower surfaces. The stable two water adsorption layers were formed on the pore surface in both models. The curvature radius of a water meniscus decreased monotonically and approached a constant value. In addition, NVT-MD simulations were performed to investigate the kinetics of water uptake into a model of mesoporous silica thin film having a radius and thickness of 1.38 and 7.93 nm (Model 3). The calculation results showed that the kinetics of water uptake depended on the number of water molecules and there were two different transport mechanisms in the pore. One was diffusion of water along the pore surface, and the other was capillary rise of liquid water.Copyright

Studies on Phenolic Lactones:Part III. Synthesis of (±) Hibalactone

(±) Hibalactone, α-piperonylidene-β-piperonyl-butyrolactone, was synthesized by the following method. α-Piperonylidene-β-piperonyl-succinic acid dimethylester was reduced with lithium aluminum hydride to 2-piperonylidene-3-piperonyl-1, 4-butanediol, m. p. 117°C. Oxidation of the glycol with manganese dioxide in acetone yielded α-piperonylidene-β-piperonyl-γ-hydroxy-butyraldehyde, which afforded racemic hibalactone, m.p. 154~5°, after oxidation with silver oxide and lactonization.

Studies on Phenolic Lactones: Part II. A New Synthetic Method of Isohibalactone

Isohibalactone, the geometric isomer of hibalactone, was synthesized by the following route. Piperonylsuccinic acid anhydride was converted into thioethyl methyl ester ans was reduced to piperonylbutyrolactone by Raney nickel catalyst. Piperonylbutyrolactone was also prepared from piperonylsuccinic anhydride by the reduction with amalgamated aluminum. Condensation of piperdnal with the lactone in the presence of potassium amide afforded α-(3,4-methyIenedioxy-phenyl-hydroxymethyl)-β-(3,4-methylenedioxybenzyl)-butyrolactone, m.p. 151~2°C. Dehydration of the hydroxylactone with p-toluenesulfonic acid gave isohibalactone, m.p. 156~6.5°C.

Studies on Chrysanthemic Acid: Part III. Oxidation and Reduction Products of Chrysanthemic Acid

Starting from (±)-cis- and (±)-trans-chrysanthemic acid several oxidation and reduction products were obtained: These are shown in the figure.

The Syntheses of Peptides by the Phthaloyl Method

We modified the phthaloyl method for the syntheses of peptides. In the presence of sodium acetate or potassium acetate, phthalimidoacyl chlorides readily reacted with variousamino acids in glacial acetic acid to give corresponding phthaloyl peptides. By this method we synih-esized following phthaloyl-derivatives; phthaloy l-glycylanilide, -glycylglycine, -glycyl-DL-ala nine, -glycyl-L-leucine, -glycyl-DL-phenylalanine, -glycyl-L-phenylalanine, -glycyl-DL-valine, glycylglycylglycine, -DL-alanyl-DL-alanine, -DL-alanyl-DL-phenylalanine, -DL-phenylalanylglycine, -DL-phenylalanyl-DL-alanine and -DL-phenylalanyl-DL-phenylalanine. By the hydrazinolysis of these phthaloyl peptides we readily obtained corresponding peptides in moderate yield.