Yoshihiro Takebayashi

A formulation method using D, L-lactic acid oligomer for protein release with reduced initial burst

Abstract This paper describes a preparation method of D,L -lactic acid oligomer formulations capable of sustained release of proteins without any large initial burst in release. The oligomer formulations containing various proteins were prepared by a W/O emulsion method to examine the protein release. Briefly, the W/O emulsion of protein aqueous solution and oligomer/chloroform solution was prepared by probe sonication. Then, the powders obtained by freeze-drying the W/O emulsion were compression molded at 60°C into rods. As another method (mixing method), the protein was mixed with the oligomer at 45–60°C and the mixture was molded into rods similarly. Moreover, the resulting rods were ground into granules. The recovery of the oligomer formulation was about 95% and the formulation incorporated about 90% of the theoretical amount of proteins, irrespective of the type of proteins and oligomers used. Both the W/O and mixing methods permitted sustained release of proteins from the oligomer rods without any large initial burst when the protein loading was less than 20%. However, the release profile was different between the granules prepared by the two methods. For granules of sizes less than 200μm prepared by the mixing method, greater than 50% of protein was released during the first day of the release test, irrespective of the oligomer molecular weight, the type of proteins, and their loading. On the contrary, the granules obtained by the emulsion method significantly reduced the extent of large initial burst in protein release. Light microscopic observations demonstrated a high homogeneity of protein dispersion through the oligomer formulation prepared by the W/O emulsion method, which led to the sustained release of proteins with a reduced initial burst. However, the emulsion method was associated with a loss in protein activity during preparation of the oligomer formulation. The emulsion method caused 45% and 63% loss in the biological activity of trypsin and insulin while about 10% of the activity was lost for the mixing method.

Preparation of titania-impregnated silicaaerogels and their application to removal of benzene in air

Silica–titania aerogels were prepared by impregnating titanium ntetraisopropoxide modified with acetylacetone into a silica alcogel followed nby supercritical drying. The effects of the impregnation conditions, the supercritical ndrying medium (ethanol, 2-propanol or CO2) and the calcination ntemperature on the homogeneity of the aerogel and the nature of the impregnated ntitania were investigated. Aerogels prepared in this way had large specific nsurface areas and maximum titanium contents of ca. 32xa0at%. nEthanol and CO2 dried samples were homogeneous, but 2-propanol ndried samples were inhomogeneous because of the extraction of impregnated ntitania. Ethanol and 2-propanol dried samples contained anatase particles nof <10xa0nm agglomerated into clusters of 100–300xa0nm nsize, whereas CO2 dried samples contained amorphous titania. Their napplication to the removal of benzene from air was attempted. Ethanol dried nsamples possessed excellent benzene adsorption capacities and the adsorbate ncould be decomposed to CO2 by photocatalytic reaction.

Water/Supercritical CO2 Microemulsions with Mixed Surfactant Systems

Phase behavior was investigated for water/supercritical CO 2 (W/scCO2) microemulsions stabilized with sodium bis(1H,1H,2H,2H-heptadecafluorodecyl)-2-sulfosuccinate (8FS(EO) 2) mixed with various guest surfactants. Only for the mixtures with fluorocarbon-hydrocarbon hybrid anionic surfactants (FC6-HC n), the maximum water-to-surfactant molar ratio (W0(c)) was larger than that estimated from linear interpolation of the W0(c) values for pure 8FS(EO) 2 and pure guest surfactant. Fourier transform infrared (FT-IR) measurement for the microemulsion revealed that the mixing of 8FS(EO) 2 with FC6-HC n can prevent a phase transition from the microemulsion to the liquid crystal even in the presence of excess water. It was also found from the measurement of water/scCO 2 interfacial tension that the area occupied per surfactant molecule was markedly increased by the mixing with FC6-HC n. The loose molecular packing, probably due to a microsegregation of 8FS(EO) 2 and FC6-HC n, is consistent with the enhanced stability of the microemulsion upon surfactant mixing.

Fourier transform infrared spectroscopic study of water-in-supercritical CO2 microemulsion as a function of water content.

Fourier transform infrared (FT-IR) spectrum of water-in-supercritical CO(2) microemulsion was measured at 60 degrees C and 30.0 MPa over a wide range of water/CO(2) ratio from 0.0 to 1.2 wt % to study the distribution of water into CO(2), interfacial area around surfactant headgroup, and core water pool. The microemulsion was stabilized by sodium bis(1H,1H,2H, 2H-heptadecafluorodecyl)-2-sulfosuccinate [8FS(EO)(2)] equimolarly mixed with sodium 1-oxo-1-[4-(tridecafluorohexyl)phenyl]-2-hexanesulfonate [FC6HC4] or with poly(ethylene glycol) 2,6,8-trimethyl-4-nonyl ether [TMN-6]. The signal area of the O-H stretching band of water suggested that the number of water molecules in the microemulsion increases linearly with the water/CO(2) ratio, except for a slow initial increase below 0.4 wt % due to a part of water dissolved in CO(2). The amount of water in CO(2) was evaluated by decomposing the bending band of water into two components, one at lower frequency ascribed to water in CO(2) and the other at higher frequency to water in the microemulsion. The decomposition confirmed that CO(2) is saturated with water at the water content of 0.4 wt %. It was also revealed, from the symmetric SO stretching frequency of the surfactant, that the sulfonate headgroup is completely hydrated at the water/CO(2) ratio of 0.4-0.5 wt %. The results demonstrated that water is introduced preferentially into CO(2) and the interfacial area at small water content, and then is loaded into the micelle core after the saturation of CO(2) with water and the full hydration of the surfactant headgroup.

Microscopic solvent structure of subcritical and supercritical methanol from ultraviolet/visible absorption and fluorescence spectroscopies

Ultraviolet/visible absorption and fluorescence spectroscopies at different temperatures and pressures were applied to investigate the microscopic solvent structures of subcritical and supercritical methanol using 4-nitroanisole, ethyl-(4-dimethylamino)benzoate, Reichardt’s dye, and anthracene as the probe molecules. It was found that at temperatures higher than 150u200a°C the long winding chains of sequentially hydrogen-bonded methanol molecules were probably broken, but the small hydrogen-bonded aggregates possibly existed in methanol even at higher temperature. It was also found that the solvation process of the anthracene molecule in the S0-ground state obeyed the Langmuir adsorption model. However, in the case of fluorescence measurements in supercritical methanol, we detected deviations from the simple Langmuir adsorption model. These deviations were explained in terms of preferential solvation of the solvent molecules around photoexcited anthracene. Judging from the experimental results, it was conclud...

Near-infrared spectroscopic study of a water-in-supercritical CO2 microemulsion as a function of the water content.

A water-in-supercritical CO(2) microemulsion is a reverse micelle encapsulating a nanometer-size water droplet dispersed in supercritical CO(2). In the microemulsion solution, water exists not only in the reverse micelle but also in the solvent CO(2). For quantitative analysis of the water distribution, near-infrared spectra of water + CO(2) and water + surfactant + CO(2) mixtures were measured over a wide range of water/CO(2) ratios from 0.1 to 1.0 wt% at 60 °C and 30.0 MPa. The stretching combination band of water was decomposed into two components, a sharp one peaked at 7194 cm(-1) assigned to monomeric water dissolved in CO(2) and a broad one around 7000 cm(-1) corresponding to aggregated water in the microemulsion. Integrated molar absorptivities of these types of water were negligibly different from each other, despite the different hydrogen-bonding environments. The spectral decomposition revealed that water is distributed mainly into CO(2) at water contents smaller than 0.5 wt% and then is introduced into the microemulsion after saturation of water in CO(2) and full hydration of the surfactant headgroup.

Preparation of SiO2-TiO2 Aerogels Using Supercritical Impregnation

The preparation of SiO2-TiO2 aerogels by supercritical impregnation of titanium alkoxides into silica alcogels was investigated. A mixture of CO2 and 2-propanol with dissolved titanium tetraisopropoxide modified with acetylacetone was used as the impregnation medium. Prior to the experiments, the supercritical behaviour of the impregnation solution was investigated. The microstructure and properties of aerogels prepared by the supercritical impregnation method were almost identical to those generated by the liquid impregnation. However, the time for impregnation was substantially decreased and the homogeneity of the impregnated titanium distribution on the aerogel increased.

Effect of the solvent density and species on the back-electron transfer rate in the hexamethylbenzene/tetracyanoethylene charge-transfer complex

The back-electron transfer (b-ET) process in the hexamethylbenzene/tetracyanoethylene charge-transfer complex was studied by the transient absorption spectroscopy in several fluids (ethane, nitrous oxide, carbon dioxide, and trifluoromethane) from the critical density to twice that of it at 323.2 K. The b-ET rate was determined by the decay rate of the excited state absorption. The b-ET rate increased with the increase of solvent density in carbon dioxide and nitrous oxide. The b-ET rate also increased in the order of ethane, nitrous oxide, carbon dioxide, and trifluoromethane, compared at the similar reduced density divided by the solvent critical density. Based on the formulation by Marcus and Jortner, the reaction free energy and the solvent reorganization energy were estimated from the change of the absorption spectrum relative to the gaseous phase spectrum, simply by assuming that the intramolecular reorganization energy does not depend on the solvent density and the species. The reaction free energy...

Electron-transfer rate in the hexamethylbenzene-tetracyanoethylene charge-transfer complex in carbon dioxide

Abstract An electron-transfer (ET) rate in the hexamethylbenzene-tetracyanoethylene complex has been measured in supercritical carbon dioxide at various solvent densities. The ET rate increases by almost a factor of two on increasing the solvent density from the critical density to twice it. The density dependence of the ET rate is well simulated by the theory based on that of Marcus and Jortner, although the theory predicts a somewhat smaller density effect in the higher density region.

Density dependence of the optical Kerr effect of linear molecules

We investigated the density dependence of the optical Kerr effect of two linear molecules, CO2 and N2O, by the optical Kerr effect experiment for a wide range of densities higher than the critical density. We also performed molecular dynamics simulation for CO2 in order to analyze the mechanism of the optical response. The density was controlled from the critical density ρc=0.467 g/cm3 to 2.8 times ρc at a supercritical temperature of 323 K. We found good agreement between the experimental and simulation results. The relative importance of orientational dynamics of molecules and the collision-induced polarizability to the optical Kerr effect was studied at the molecular level. In particular, the collective orientational dynamics of the molecules as compared to that of the single molecule and the effect of the dipole-induced-dipole on the optical response function were analyzed in detail. Furthermore, the correspondence between the transition of the response function and the transition of the static struct...