Yoko Imai

Surface activities of ferrocene surfactants

Abstract Surface-chemical properties of ferrocene surfactants were investigated in the reduced and oxidized states of their ferrocene moiety at the air-water and oil-water interfaces. N,N -dimethylferrocenylmethylalkylammonium bromides. F(II)C n AB, were synthesized by the reaction of N,N -dimethylaminomethylferrocene with 1-alkylbromides: C n Br ( n = 8, 10, 12, 14 and 18), N,N -dimethylferroceniummethylalkylammonium nitrates, F(III)C n AN, which corresponded to the oxidized states of F(II)C n AB, were prepared in aqueous solution by oxidizing F(II)C n AB with AgNO 3 . The redox states of these ferrocene surfactants were confirmed by visible and Mo¨ssbauer spectra. Solubility, surface tension lowering, surface activity, foaming and emulsion stabilities were measured in the reduced and oxidized states of ferrocene surfactants. As a result, it was found that when the ferrocene surfactants had been oxidized, their ferrocene moieties were converted from a hydrophobic to a hydrophilic character, and then became less surface active at the oil water interface as well as at the air-water interface. The difference between ferrocenyl and ferrocenium moieties in surface activity corresponds to a difference of about two carbon atoms in the long alkyl chain. Remarkably different features of the redox states were observed in studies of foaming height and emulsion stability. These phenomena of the ferrocene surfactants were explained by conformational differences in the ferrocene moieties of the surfactants at the interface.

Thermal transitions in the bilayer assembly of dimyristoylphosphatidylglycerol sodium salt dispersion in water: a new phase transition through an intermediate state

The thermal properties of the dispersion of sodium salt of dimyristoylphosphatidylglycerol (NaDMPG) in water have been investigated as functions of incubation temperature and aging time by DSC, XRD, sodium ion activity, pH, zeta-potential, and IR measurements. The DSC charts for NaDMPG dispersions incubated below 30 degrees C showed an endothermic peak at 31.7 degrees C with a small shoulder peak at Tm (gel-liquid crystal transition temperature: 23.5 degrees C). The temperature of 31.7 degrees C coincides with the T* temperature at which a high-order transition in the NaDMPG bilayer assembly has been found to occur in our previous studies. However, no peak was observed for the dispersions incubated above 32 degrees C. These results indicate that thermal properties of NaDMPG bilayers definitely differ below and above the T* temperature. The dispersion which had been once incubated at 40 degrees C for 24 h never showed the endothermic peak at T* even after the further aging at 3 degrees C for 12-day. Namely, the NaDMPG bilayer assembly exhibits an intensive thermohysteresis. The XRD charts for the NaDMPG dispersions incubated at 25 degrees C showed a sharp X-ray diffraction pattern corresponding to the repeat distance of d = 4.75 nm regardless of their aging time, while the dispersions incubated at 40 degrees C had no diffraction peak until 9-day elapsed. After 10-day aging at 40 degrees C, however, a diffraction peak corresponding to d = 5.55 nm clearly appeared. In the DSC measurements for the dispersion incubated at 40 degrees C, a few endothermic peaks began to appear between Tm and T* after approximately 7-day aging. Then, they shifted toward higher temperatures and finally converged into a single peak at 40-42 degrees C after 14-day aging. These XRD and DSC peaks observed after a long period of aging time above T* suggest that conformations of the hydrophilic groups and the hydrocarbon chains in the NaDMPG bilayers take a more tight and closer arrangement very slowly via an intermediate state above T*, and a new gel phase of the bilayers is consequently formed, the transition temperature (T(I) temperature) of which is 40-42 degrees C. A molecular interpretation for such transition processes in the bilayer assembly of NaDMPG dispersions has been proposed on the basis of pH, sodium ion activity, zeta-potential, IR data, etc.

Solubilization of hydrocarbons into a bilayer assembly of dimyristoylphosphatidylcholine in water

Abstract Solubilization of octane, hexadecane and perfluorononane into a bilayer assembly of dimyristoylphosphatidylcholine (DMPC) in water has been studied at 25 and 35°C as a function of mole fraction ( X ) of these solubilizates. In order to determine the occurrence of solubilization, a change of the gel–liquid crystal transition temperature ( T m ) of the DMPC bilayer assembly was monitored by differential scanning calorimetry measurement. Solubilization of octane into the DMPC bilayer assembly was observed both at 25 and 35°C. On the other hand, solubilization of hexadecane took place above X =0.40 at 25°C, while at 35°C solubilization did not occur at any mole fraction. Solubilization of perfluorononane into the DMPC bilayer assembly was not observed either at 25 or 35°C. Saturated solubilization of octane or hexadecane into the DMPC bilayer assembly was achieved at X =0.67, where the mole ratio is 1(DMPC):2(oil), i.e. the ratio of the number of hydrocarbon chains of DMPC to that of oil is 1:1. The heat of gel–liquid crystal transition (Δ H m ) of the DMPC bilayers saturated with octane at 25°C is 16.5 J g −1 at T m =14.8°C, and that of the DMPC bilayers saturated with hexadecane at 25°C is 22.0 J g −1 at T m =31.4°C; whereas the Δ H m value for the pure DMPC bilayers is 27.0 J g −1 at T m =23.7°C. X-ray diffraction data indicate that the hydrocarbon solubilizates are located in the palisade layers of the DMPC bilayers. It has been also revealed that the surface of emulsion droplets of octane or hexadecane are covered with multibilayers of DMPC at 25°C, and with a monolayer of DMPC at 35°C. Such differences in solubilization and emulsion stabilization mechanisms between 25 and 35°C are attributable to the higher order transition of the DMPC bilayers at T * (29.0°C).

Radical isomerization of 9,10-dihydro-9,10-disilaanthracene derivatives: stabilization factor of silyl radicals

Abstract In order to examine the nature of the silyl radical in the disilaanthracene framework, separation and radical isomerization of the cis and trans isomers of the disilaanthracene derivatives were investigated. When a pentane solution of the disilaanthracene derivative was irradiated with a 400 W mercury lamp in the presence of DTBP for 4 h, both isomers readily isomerized to give a mixture of cis and trans isomers in a ratio of ca. 50:50. However, no such isomerization reaction of 9,10-dihydro-9-silaanthracene derivatives occurred under similar conditions.

A Preferable Method for the Formation of Vesicles from Lamellar Liquid Crystals Using Chemical Additives

We present a method for vesicle formation from lamellar liquid crystals (LCs) using a cationic amphiphilic substance, namely 2-hydroxyethyl di(alkanol)oxyethyl methylammonium methylsulfate (DEAE). Vesicle formation from the DEAE lamellar dispersion occurred via a two-step chemical addition. This method required neither additional mechanical energy nor the use of special solvents. The transition was solubilized using an organic substance (e.g., limonene) in the lamellar DEAE LC, after which, a small amount of inorganic salt was added to the solubilized lamellar LC dispersion with gentle stirring. The viscosity of the DEAE dispersion following salt addition decreased sharply from 105 mPa·s to 102 mPa·s, and the DEAE dispersion was converted into a high fluidity liquid. Several organic substances were examined as potential solubilizates to initiate the lamellar-vesicle transition. Inorganic salts were also examined as transition triggers using various types of electrolytes; only neutral salts were effective as trigger additives. Dissociation of inorganic salts yielded anions, which inserted between the DEAE bilayer membranes and induced OH- ion exchange. In addition, a number of cations simultaneously formed ion pairs with the DEAE counter ions (CH3SO4- ions). However, as the amount of solubilized organic substances in the DEAE bilayer membrane decreased over time, the vesicles were transformed into lamellar LCs once again. The DEAE states in each step were measured by monitoring the zeta potential, pH, viscosity, and by examination of scanning electron microscopy and atomic force microscopy images. A possible molecular mechanism for the lamellar-vesicle transition of DEAE was proposed.

Thermodynamic Analysis of the Transition of Liquid Crystals from Lamellar to Vesicular Phase

Here, we report the results of thermodynamic analyses on the lamellar-vesicular transition for a cationic amphiphilic species, namely 2-hydroxyethyl di(alkanol)oxyethyl methylammonium methylsulfate (DEAE). Previously, we have shown that spontaneous vesicle formation from a Lα-lamellar liquid crystal (LC) phase only occurs on the addition of a quantitative amount of additives to the DEAE LC at certain temperatures and that this change occurs without the input of any extra mechanical energy. These lamellar-vesicular transitions occur in two steps: the first step is the formation of an excited state, caused by the solubilization of organic substances in the bilayer structure. The second step, induced by the addition of a small amount of inorganic salt to the excited LC state, is the transition from lamellar to vesicular phase. From our experimental data, the change in the Gibbs free energy was estimated by assuming an ideal electrical chemical potential. As a result, the thermodynamic parameters at 303 K for the lamellar-vesicular transition from the initial state (lamellar) to the final state (vesicle) were found to be approximately -2.7 kJ/mol for the Gibbs free energy, -14.6 kJ/mol for the enthalpy change, and -11.9 kJ/mol for the entropy change. Each state change was due to structural changes not only in the LC bilayers but also in the hydration structure of the surrounding water. Moreover, the most significant finding is that the free energy change in lamellar-vesicular transition is negative, which may be explained based on the stabilization of solubilized vesicles with respect to the unsolubilized lamellar phases.

Adsorption of the Three-phase Emulsion on Various Solid Surfaces

The present study investigates the adsorption of the three-phase emulsion on various solid/water interfaces. Vesicles can be used as emulsifiers in the three-phase emulsions and act as an independent phase unlike the surfactant used in conventional emulsions; therefore, it is expected that the three-phase emulsion formed by the adhesion of vesicles to the oil/water interface will adsorb on various solid/water interfaces. The cationic three-phase emulsion was prepared to encourage emulsion adsorption on negatively charged solid substrates in water. The emulsifier polyoxyethylene-(10) hydrogenated castor oil was rendered cationic by mixing with the surfactant cetyltrimethylammonium bromide and then used to prepare the cationic three-phase emulsion of hexadecane-in-water. Three solid substrates (silicon, glass, and copper) were dipped in the cationic emulsion and the emulsion was found to adsorb on the solid substrates while maintaining its structure. The amount of hexadecane adsorbed on the various surfaces was investigated by gas chromatography and found to increase with increasing hexadecane concentration in the emulsion and eventually plateaued just like molecular adsorption. The maximum surface coverage of the emulsion on the substrates was approximately 80%. However, even the equivalent nonionic three-phase emulsion was found to adsorb on the three solid surfaces. This was attributed to a novel mechanism of irreversible adhesion via the van der Waals attractive force.