Kaname Hashizaki

Freeze-fracture electron microscopic and calorimetric studies on microscopic states of surface-modified liposomes with poly(ethylene glycol) chains

Abstract The differential scanning calorimetry (DSC) and the freeze-fracture electron microscopy of dipalmitoyl phosphatidylcholine (DPPC) liposomes containing distearoyl-N-monomethoxy poly(ethylene glycol)-succinyl-phosphatidylethanolamines (PEG-DSPE) were carried out. The DSC peak of DPPC liposomes containing PEG-DSPE had a shoulder. The main phase transition temperature of DPPC bilayer membranes containing PEG-DSPE whose molecular weight of PEG is less than 3000 was slightly shifted to a higher temperature, while that containing PEG-DSPE whose molecular weight of PEG is more than 5000 was slightly shifted to a lower temperature. The electron micrographs of freeze-fracture replicas of DPPC liposomes containing PEG-DSPE quenched from 37±2°C exhibited banded and planar textures, suggesting the lateral phase separation in the bilayer membranes.

Emulsifying Ability of β-Cyclodextrins for Common Oils

Emulsification of various common oils was investigated using natural β-cyclodextrin (β-CD) and its derivatives as emulsifiers. An oil/water (O/W) emulsion was formed using β-CD, whereas a water/oil (W/O) emulsion was formed using tripropanoyl-β-CD and tributanoyl-β-CD derivatives. Triacetyl-β-CD gave rise to both O/W and W/O emulsions. The type of emulsion was governed by the contact angle (θow), which the precipitate of CD origin make with the oil-water interface.

A new reverse worm-like micellar system from a lecithin, multivalent carboxylic acid and oil mixture.

We developed new lecithin organogels composed of reverse worm-like micelles with lecithin/multivalent carboxylic acid/oil systems, and discussed their phase behavior and rheological properties. The most important findings in this study are the following. From a screening test of many carboxylic acids for gelation, it was found that the number and position of the carboxyl groups of the multivalent carboxylic acids are the determinants for the formation of reverse worm-like micelles, and appropriate carboxylic acids such as citric acid and 1,2,3-propanetricarboxylic acid can change the lecithin/oil solution into a gel. Furthermore, upon addition of these carboxylic acids, the zero-shear viscosity of solutions increased monotonically until phase separation or cloudiness occurred. For example, when citric acid was used, the maximum zero-shear viscosity of the solution was 70,000,000 times larger than that of n-decane. From studies on the scaling of rheological parameters, it was found that further addition of multivalent carboxylic acids not only induced the formation of linear reverse worm-like micelles but also brought about their branching.

Determination of Stability Constants for Alkanol/α-Cyclodextrin Inclusion Complexes using the Surface Tension Method

The stability constants for the inclusion of alkanols withα-cyclodextrin (α-CD) in aqueous solutionhave been determined using the surface tension method. Dataanalyses assuming 1 : 1 stoichiometry were appliedto estimate the stability constants of thesecomplexes. The stability constants obtained using this methodwere in reasonable agreement with the corresponding values inthe literature. Chemically modified α-CDs could not beused in this method because those CDs themselves have surfaceactivity. In addition, the relation between the stability constantsand the carbon number of alkanols is discussed.

Comparison of the Solubilizing Ability of Cyclodextrins and Surfactants for (+)-α-Pinene

A comparison of the solubilizing ability of cyclodextrins (CDs) and surfactants for (+)-α-pinene (αP, a fragrance) in aqueous solution was made using a static head-space gas chromatography technique. The findings show that the solubilizing ability of CDs for αP is competitive to that of surfactants.

Preparation and Characterization of Cycloalkanol/Water Emulsion Using α-Cyclodextrin as an Emulsifier

We examined the preparation and characterization of cycloalkanol/water emulsions using α-cyclodextrin (α-CD) as an emulsifier. Emulsions were prepared by mixing α-CD, cycloalkanol, and water using a vortex mixer. The mechanism of emulsification was investigated with some physicochemical techniques. From phase diagrams of cycloalkanol/α-CD/water systems, the emulsion phase extended as the carbon number of cycloalkanols increased. Furthermore, it was thought that the coexistence of precipitated cycloalkanol/α-CD complexes were necessary for formation of the emulsion. However, the precipitated complexes did not have surface activity. From observation using a polarized light microscope, it was suggested that the precipitated complexes were formed at the oil-water interface and supplied to the continuous phase. We concluded that cycloalkanol/water emulsions using α-CD were stabilized by precipitated complexes that exist on the droplet surface and the continuous phase, and these emulsions were a type of Pickering emulsion.

Effects of Inorganic Salts on Micellization and Solubilization in an Aqueous Solution of Poly(ethylene oxide)/Poly(propylene oxide)/Poly(ethylene oxide) Triblock Copolymer

The effects of inorganic salts on micellization and solubilization of prednisolone in aqueous solution of poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) triblock copolymer (Pluronic P85) were studied. The effect of inorganic salts on decrease in the cloud point and the critical micelle concentration (cmc) of Pluronic P85 was the order of Na2HPO4 > NaH2PO4 > NaCl > NaBr. Moreover, it was found that Pluronic P85 forms two kinds of micelles: monomolecular micelles and polymolecular micelles. The polymolecular micelle increased with increasing amount of added inorganic salts. Moreover, solubilization behavior is explained from the standpoint of salting out for prednisolone and association characteristics of Pluronic P85.

Solubilization of (+)-α-Pinene by Cyclodextrin/Surfactant Mixed Systems

The mixing effects of 6-O-α-D-glucosyl-β-cyclodextrin (G-β-CD) and surfactants on the solubilization of (+)-α-pinene (αP, a fragrance) in aqueous solution were studied using a head-space gas chromatography technique. The findings show that the mixing of G-β-CD and surfactant result in negative synergistic effects on the solubility of αP.

Solubilization of (+)-Limonene by Anionic/Cationic Mixed Surfactant Systems

Abstract The combined effects of sodium n-octyl sulfate (SOS) and cetyltrimethylammonium bromide (CTAB) on the solubilization of (+)-limonene in aqueous solution were studied using a headspace gas chromatography technique. The findings showed the mixing of SOS and CTAB resulted in positive synergistic effects on the solubility of (+)-limonene. The positive synergistic effects are explained from the perspective of the phase behavior of this mixed surfactant system.

Determination of the Stability Constants in Alkanol/α-Cyclodextrin Mixed System

The simultaneous determination of the stability constants for inclusion of alkanols with α-cyclodextrin (α-CD) was investigated in a mixed alkanol system using static head-space gas chromatography (SHSGC). The 1:1 stability constants obtained were in fair agreement with those obtained previously using other methods. The time required for determination of the stability constant was markedly reduced using this simultaneous SHSGC method.