Kazuhiro Fukada

Characterization of swollen lamellar phase of dimyristoylphosphatidylcholine-gramicidin A mixed membranes by DSC, SAXS, and densimetry

For the fully hydrated multilamellar stack of dimyristoylphosphatidylcholine (DMPC) fluid membranes containing hydrophobic peptide gramicidin A (GrA), the membrane thickness and the bilayer-bilayer separation (i.e., water layer thickness) were determined by measuring small-angle X-ray scattering and the density of aqueous suspensions of DMPC-GrA mixtures. When the molar ratio of GrA to DMPC was 0.04, the membrane thickness decreased by 2-3 A by the incorporation of GrA molecules into DMPC bilayers, whereas the water layer thickness increased by 3-4 A. As the cause of the increment of water layer thickness, two possibilities were considered; (1) attractive van der Waals force acting between the bilayer membranes weakened by the decrease of membrane thickness, and (2) repulsive undulation force enhanced by the incorporation of GrA which may stabilize the gauche conformers of the lipid acyl chains.

Effect of pressure and temperature on adiabatic compressibility of aqueous solutions of amphiphiles with a perfluorocarbon chain

Abstract The apparent adiabatic compressibility and the apparent molar volume of sodium perfluoroheptanoate (C 6 F 13 COONa) were obtained from the experimental data of ultrasound velocity and density of its aqueous solutions at the concentration above and below CMC (critical micelle concentration) as functions of applied pressure (0–70xa0MPa) and temperature (5–35°C). Those were compared to the reported data for sodium decanoate (C 9 H 19 COONa) of Vikingstad et al. [J. Colloid Interface Sci. 72 (1979) 59]. It was found that the micelles of C 6 F 13 COONa were more easily compressible than C 9 H 19 COONa micelles under the condition studied. For the singly dispersed state below CMC, negative apparent compressibility of C 6 F 13 COONa was confirmed and it approached to zero with the increase of pressure or temperature suggesting the decreased electrostriction and hydrophobic hydration with pressure or temperature rise.

In situ AFM observation of heterogeneous growth of adsorbed film on cleaved mica surface

Abstract The dynamic process of cationic surfactant molecules to form adsorbed layer on cleaved mica surface was observed in situ for the first time by AFM. At the initial stage of adsorption, the adsorbed molecules are observed as the small island-like aggregates with the size of about 10–30 nm. These islands are replaced by larger patches as time lapses. After the continuous growth of the patches, a close-packed film with uniform appearance is approached. The driving force to increase the size of molecular aggregates may either be by line tension or by two dimensional Laplace pressure that induce coalescence of smaller aggregates into larger patches.

Solid state phase behaviors of dodecyldimethylamine oxide: protonation and counterion effects

Abstract Solid phase behaviors of dodecyldimethylamine oxide (C12DAO) studied by differential scanning calorimetry and X-ray scattering have shown clearly the effects of protonation. Besides the protonated (cationic) (C12DAO HCl) and the nonionic (C12DAO) species, 1:1 composition or hemihydrochloride (C12DAO 1/2 HCl) was shown to be a stable complex. The phase behavior of C12DAOHCl was similar to that of dodecylammonium chloride rather than dodecyltrimethylammonium chloride (C12TACl), although similar crystal structure was suggested for C12DAOCl and C12TABr. Solid phase behaviors changed dramatically by changing the counterion from Cl− to NO3− or SO42− for both the cationic and 1:1 species.

Phase behaviors and light scattering for dilute mixtures of C12E5 and lauric acid

Phase behaviors and light scattering patterns have been investigated for a water–C12E5–lauric acid system. Incorporation of small amount of lauric acid profoundly increases the existence region of the Lα phase. Light scattering pattern in the Lα phase shows diffraction peak much stronger than that for the sample without lauric acid. The spacing distance obtained from the peak position (∼250 nm) slightly decreases as the mole fraction of lauric acid in the total mixed solute (xa) increases from 0 to 0.175 where the total concentration of mixed solute (ctot) is kept constant (1.4 wt.%). The results are compared to the electrostatic theory of de Vries which takes into account the interplay between thermal undulations and electrostatic repulsion for salt-free lamellar phase. Addition of small amount of sodium chloride (0.1–1 mM) makes the diffraction peak broaden and increases the intensity of small angle scattering. Changes in phase behaviors and light scattering patterns along dilution line at a fixed mole fraction (xa=0.05) have been also investigated. In the concentration range 0.5

Hydration of the organized molecular assembly of ionic surfactants as studied by vapor pressure and x-ray diffraction

Equilibrium vapor pressure of water was measured for ionic surfactant-water binary systems as a function of water content over the temperature range 5–11°C. The measurement of x-ray powder diffraction has also been performed to characterize the microscopic structures of these two-component systems. Examined surfactants were the homologs of sodium alkyl sulfate and alkyltrimethylammonium bromide. It was found that dodecyl and decyl sulfate formed solid di-and trihydrate respectively, while octyl sulfate and the cationic surfactants formed lyotropic liquid crystal instead. The x-ray long spacing of the liquid crystals scarcely varied with water content.Enthalpy of vaporization was calculated for both solid hydrates and lyotropic liquid crystals.

Density and compressibility measurements of a highly viscous polyelectrolyte solution: a study on aqueous solutions of sodium hyaluronate

Abstract The density of a highly viscous polyelectrolyte solution was measured using both pycnometers and oscillating-tube densimeters in parallel to elucidate the difficulties inevitably involved when an oscillating tube is employed for density measurements of viscous liquids. It was confirmed that the oscillating-tube densimeter gives too high values for viscous liquids, and the deviation increases with the increase in the viscosity of liquids. The analysis of adiabatic compressibilities of sodium hyaluronate (NaHy) solutions, as estimated from density and ultrasound velocity data of the same solution, suggests that the disaccharide unit of the NaHy chain is less hydrated than the sum of its component monosaccharide residues.

Packing of Alkyl Group on Oxidized Silicon Wafer by Silylation, Studies by AFM and Ellipsometry

Oxidized surface of the silicon single crystal was silylized by octadecyltrichlorosilane (OTS) to give highly hydrophobic surface which shows contact angle larger than 110 ° against water. The optimal condition of OTS silylation was developed to plant alkyl chain as close as possible on oxidized silicon surface and to give well-qualified hydrophobic surface. The silylated surface was examined in water by AFM. The image shows that the methyl groups of octadecyl chains are arranged at the surface to have a cross sectional area of 0.43 ± 0.07 nm2. While, the thickness and the refractive indices of alkylated layers on silicon surface were estimated by Ellipsometric measurements, from which each octadecyl chain was found to occupy 0.6 ± 0.1 nm2, which is in good agreement with that estimated by AFM.