Mutsuo Matsumoto

Significance of β-sheet formation for micellization and surface adsorption of surfactin

Abstract It was found that surfactin, an anionic lipopeptide biosurfactant, forms large rod-shaped micelles (micellar weight, 179 000, aggregation number n = 173) having a critical CMC of 9.4 × 10−6 M and a surface tension at the CMC γCMC of 30 mN m−1 in 0.1 M NaHCO3 (pH 8.7). This excellent surface-active behaviour was attributed to the ease of piling of surfactin molecules organized by β-sheet formation. Surfactin also showed a possible organization between molecules due to β-sheet structure at the air-water interface under forced experimental conditions.

Structural studies of poly-γ-benzyl-l-glutamate monolayers by infrared ATR and transmission spectra

Abstract An apparent plateau region was observed in the surface pressure (F)-area (A) isotherm of poly-γ-benzyl- l -glutamate (PBG) monolayers spread on the water surface from methylene chloride solution. Polarized infrared ATR and transmission studies were made of built-up films of PBG transferred onto a germanium plate from the monolayers compressed at 10 and 5 dyne/cm, which are above and below the plateau surface pressure (8 dyne/cm), respectively. The molecular orientation and relative thickness of the films were quantitatively examined. It was found for the thin layers compressed at both surface pressures that the PBG molecules were in the α-helical conformation and lay flat on the water surface. It was also likely that the molecular chains on the water surface were packed in parallel with each other making a certain angle with the direction of compression. On the preparation of built-up films, the thin layers were transferred onto the germanium plate so that the helix axes formed an angle of ca. 35° with the direction of withdrawal. The built-up films prepared above the plateau surface pressure were found to be almost twice as thick as those prepared below the plateau surface pressure. This result supports Malcolms proposal that the plateau region can be ascribed to a transition process from monolayer to bilayer.

Studies of poly-γ-methyl-l-glutamate monolayers by infrared ATR and transmission spectroscopy and electron microscopy

Abstract Polarized infrared ATR and transmission spectra were studied of built-up films of poly-γ-methyl- l -glutamate (PMLG) transferred onto a germanium plate at 15 and 22 mN·m−1, which are below and above an apparent plateau region, respectively, in the surface pressure (π)-area (A) isotherm. Electron photomicrographs of these films were also obtained by using the folding method, and the film thickness was measured. It was concluded from results of these experiments that the PMLG molecules were in the α-helical conformation and helix axes lay flat on the water surface as condensed ordered arrays forming a certain angle with the compressing direction. The plateau region in the π-A isotherm was ascribed to a transition process from monolayer to bilayer, the molecular conformation as well as orientation being left unchanged.

Interaction of fusogenic synthetic peptide with phospholipid bilayers: orientation of the peptide alpha-helix and binding isotherm.

We studied the binding characteristics of a synthetic 20-residue peptide to supported single planar bilayers of phosphatidylcholine, and the orientation of the peptide by Fourier-transform infrared spectroscopy with an attenuated total reflection method. This peptide, designed to resemble a putative fusion peptide of influenza virus hemagglutinin, assumes an amphiphilic alpha-helix and induces fusion of liposomes in an acidic solution (pH approximately 5). At neutral pH, the peptides were bound to lipid bilayers in the manner of a Langmuirs adsorption isotherm, and their orientation was nearly random or oblique. On the other hand, at acidic pH, the peptides were bound, making their helix axis parallel to the membrane surface, and the binding was cooperative. This cooperativity suggested dimerization of the peptides. These characteristics are expected to be important for the synthetic fusogenic peptide or the fusion peptide in hemagglutinin to induce membrane fusion.

CONTACT ANGLE MEASUREMENTS WITH SESSILE DROPS AND BUBBLES

Abstract In this note a simple and precise method for measurement of contact angles in the range 0°–180° on solid surfaces is proposed. In the case when the three-phase contact line is irregular due to surface roughness and inhomogeneity, the method provides an effective averaged value of the contact angle. The method is based on a numerical solution of the Laplace equation for the interfacial profile. The input parameters used are the liquid-gas surface tension and a pair of the following parameters of the drop (bubble) shape: volume, height, contact radius, and equatorial radius. Depending on the magnitude of the contact angle different pairs of parameters are to be measured for the purpose of best accuracy.

Surface pressure dependence of monolayer structure of poly-ϵ-benzyloxycarbonyl-l-lysine

The surface pressure dependence of the monolayer structure of PBCL was studied by means of infrared spectroscopy and electron microscopy, and discussed in connection with the characteristic feature of the π-A isotherm. The main conclusion is as follows. The PBCL molecules are in the α-helical conformation in the monolayer on the water surface and helix axes lie flat on the surface as condensed ordered arrays forming a certain angle with the compressing direction. The series of transitions observed in the π-A isotherm is ascribed to the consecutive formation of additional layers of molecules. During these processes, the molecular conformation is left unchanged. This conclusion is consistent with Malcolms proposal on PBCL (11, 12).

Electron cryo-microscopic studies on micellar shape and size of surfactin, an anionic lipopeptide

Abstract Micelles of surfactin, a biosurfactant, in water, were visualized by an ice-embedding technique and transmission electron cryo-microscopy, cooling down the specimen to the temperature of liquid helium. Cryo-micrographs revealed spherical, ellipsoidal and/or cylindrical micelles with an inhomogeneous size distribution at pH 7, 9.5, and 12. The appearance at low pH and disappearance at pH 12 of a characteristic FT-IR band of a lactone group in surfactin suggested that the micelles are formed differently in structures with cyclic and linear head groups at these respective pH values. At pH 9.5, the addition of 100 mM NaCl and 20 mM CaCl 2 to a surfactin solution transformed the cylindrical micelles into spherical and/or ellipsoidal micelles of small size. This small size was explained by a common understanding model with a high or low degree of internal order in the structure of alkyl chains. The large size of the spherical, ellipsoidal, and cylindrical micelles was explained in terms of bilayered unilamellar or multilamellar structures such as vesicles.

Electrocapillary phenomena at oil-water interfaces

SummaryThe electrocapillary phenomena at oil-water interfaces, i. e. the change in the interfacial tension with an applied potential difference, take place over a moderate polarization range of ca. 20 to −20 V, when the systems have sufficiently high electric conductance and contain surface active agents. Experiments were carried out in the presence of potassium chloride in the aqueous phase and ionic surface active agents in the oil phase, respectively. It was found that the interfacial tension was suppressed over the cathodic or anodic polarization range, depending on whether the surface active agent used was cationic or anionic, respectively. Here the sign of polarization was conventionally taken as that of the water phase with respect to the oil phase. It was then concluded by the use of theLippmann-Helmholtz equation that the water side of the interface is charged positively or negatively in the respective case mentioned above. It appears that this charge is due to the counter ion layer which is formed corresponding to the adsorption of ionic surface active agents on the oil side.ZusammenfassungDie Elektrokapillarität von Öl-Wasser-Grenzflächen mit Kaliumchlorid in den wässerigen und grenzflächenaktiven Ionen in der Ölphase wurde bei geringer Polarisation im Bereich von +20 V bis −20 V untersucht. Dabei wurde beobachtet, daß die Grenzflächenspannung durch kationische bzw. anionische Polarisation erniedrigt wurde, je nachdem, ob die grenzflächenaktiven Stoffe kationisch oder anionisch waren. Die Ergebnisse wurden mit Hilfe derLippmann-Helmholtz-Gleichung gedeutet. Es bildet sich eine elektrische Doppelschicht mit den grenzflächenaktiven Ionen an der Ölschicht und den anorganischen Gegenionen an der wässerigen Seite der Grenzfläche.

Interfacial properties and emulsification in systems of perfluoropolyether/non-fluorinated oil/partially fluorinated oligomeric and polymeric compounds

Abstract Interfacial properties and emulsification were studied in the systems perfluoropolyether (PFPE)/non-fluorinated oil (NFO)/partially fluorinated oligomeric or polymeric compounds (Rf-Rh). All the Rf-Rh compounds were synthesized. The polymeric Rf-Rh compounds were random and graft copolymers with 1 H ,1 H ,2 H ,2 H -heptadecafluorodecyl acrylate (17FA) repeating units introduced into a trunk polymer chain. The Rf-Rh compounds dissolved or dispersed in most NFOs, but did not dissolve in PFPE. They depressed interfacial tensions at PFPE-toluene interfaces, which were mainly used in this study, with an increase in their concentrations. The polymeric Rf-Rh compounds were effective emulsifying agents for the formation of macroemulsions. The graft copolymers permitted the formation of very stable emulsions w ith a droplet diameter of about 200 nm, in particular. No direct relationship was found between the depression of the interfacial tensions and the stability of the emulsions. However, low interfacial tensions and sterically stable protection of an adsorbed film served for the formation of small-sized emulsion droplets, which contributed to reduce the sedimentation due to the gravitational force.

A trough with radial compression for studies of monolayers and fabrication of Langmuir-Blodgett films

Abstract A new type of Langmuir trough with radial compression is reported for studies of monolayer properties and fabrication of Langmuir-Blodgett (LB) films. The trough included twenty curved diaphragms, which form a circular shape on water and compress monolayers. Typical monolayers of arachidic acid, DL-α-phosphatidylcholine dipalmitoyl, cellulose tridecanoate, and poly (butyl methacrylate) showed reproducible surface pressure-area isotherms with radial compression. Flow profiles were studied of monolayers on cellulose tridecanoate and poly(butyl methacrylate) and suggested that the monolayers are radially compressed with no particular film disturbance. A Wilhelmy glass plate preserved no deflection in the subphase surface from low to high surface pressures during the film compression and decompression; no pressure excess causing the deflection, which is frequently observed in the case of the film compression with a sliding barrier, was found on both sides of the Wilhelmy plate. Application of the radial compression enabled to do a symmetrical deposition for the fabrication of LB films.