Influence of chirality on the structure of phospholipid monolayers.

A new liquid surface neutron reflectometer and its application to the study of DPPC in a monolayer at the air/water interface

A constant wavelength neutron reflectometer is described. Using this reflectometer, the neutron reflectivities from phosphatidylcholine monolayers in the highly condensed LC phase on ultra pure H2O and D2O have been measured on a Wilhelmy film balance. The neutron reflectivities have been carefully compared with those obtained by the X-ray method applied to the same monolayer under similar conditions. A new approach to analyzing a combined set of data composed of X-ray and neutron reflectivities has been used. From the analysis it is concluded that despite their limited qz range neutron reflectivities are as essential as X-ray reflectivities for the unique determination of the monolayer str…

Behenic Acid as a Structural Model for Fatty Acid Monolayers at the Air/Water Interface: An X-Ray Diffraction Study

We present an X-ray diffraction study of behenic (docosanoic) acid films at the air/water interface. Analysis of the rod profiles parallel and perpendicular to the surface provides detailed information on the unit cells of five different phases.

An X-ray scattering study of lipid monolayers at the air-water interface and on solid supports

Abstract Monolayers of the lipid arachidic acid (C20) and of the phospholid dimyristolyphosphatidic acid (PMDA) have been studied by X-ray reflection and diffraction technique, using a purpose-built Langmuir trough installed at the sample stage of our high-resolution X-ray diffractometer at the DORIS synchroton X-ray source in Hamburg. For comparison we also report data for monolayers of C20 on a solid support using a 10 kW rotating anode X-ray source. By the X-ray reflection method, the density profile across the interface is probe, while in-plane diffraction measurements gauge the two-dimensional crystalline properties of the monolayers. Flourescence microscopy experiments of DMPA monolay…

The Phases of Phosphatidyl Ethanolamine Monolayers

For the first time phospholipid monolayers at the air/water interface have been studied by X-ray diffraction and reflection along the whole isotherm from the isotropic fluid to the ordered phases [1]. The model used to analyze the data — and the accuracy of the parameters deduced — were tested by comparing the results obtained with two lipids having the same head group but different chain lengths.

Influence of a hydrophilic spacer on the structure of a phospholipid monolayer

We present the results of thermodynamical and X-ray grazing incidence diffraction experiments performed on Langmuir monolayers of ether lipids with hydrophilic spacers between the glycerol backbone and the phosphatidylcholine head group: DHPC, DH-E01-PC, and DH-E02-PC. As a spacer the oxy-ethylene group is used, which is a typical hydrophilic unit of non-ionic tensides. It turns out that the introduction of the hydrophilic spacers leads to a fluidization of the monolayer and reduces the tilt angle of the chains.

Monolayers of Amphiphilic Molecules

There are good reasons why the organizers have placed this lecture at the beginning of a conference on the multip1e aspects of membranes. In many respects the monolayer may be considered half of a membrane and it obviously is the most simple and best-defined model system. Yet we will show that the system is more complex than many have anticipated. On the other hand, there are many general features which can be discussed without looking into chemical details.

Chirality effects on 2D phase transitions

Monolayers of the racemate and pure enantiomers of 1-hexadecyl-glycerol were investigated by grazing incidence X-ray diffraction (GID) at 5 and 20 °C on compression from 0 mN m−1 to pressures greater than 30 mN m−1. The racemate lattice is centred-rectangular for both temperatures at all investigated pressures. However, at both temperatures, there is a sharp phase transition from a low-pressure phase, in which the molecules are tilted towards nearest neighbours (NN) and the distortion azimuth also points towards NN, to a high-pressure phase, in which the molecules are tilted towards next-nearest neighbours (NNN) and an NNN-distorted lattice is observed. At 5 °C, the transition pressure is 1…

Influence of surface chemistry on the structural organization of monomolecular protein layers adsorbed to functionalized aqueous interfaces.

The molecular organization of streptavidin (SA) bound to aqueous surface monolayers of biotin-functionalized lipids and binary lipid mixtures has been investigated with neutron reflectivity and electron and fluorescence microscopy. The substitution of deuterons (2H) for protons (1H), both in subphase water molecules and in the alkyl chains of the lipid surface monolayer, was utilized to determine the interface structure on the molecular length scale. In all cases studied, the protein forms monomolecular layers underneath the interface with thickness values of approximately 40 A. A systematic dependence of the structural properties of such self-assembled SA monolayers on the surface chemistr…

Head-group variations and monolayer structures of diol derivatives

Monolayers of 5 chemically modified diols varying the headgroup (nonadecane-1,2-diol (C1), hexadecyl-propane-1,3-diol (C2), hexadecyl-oxy-propane-1,2-diol (C3), hexadecyl-oxy-butane-1,2-diol (C4), hexadecanoyl-oxy-propane-1,2-diol (C5)) have been investigated by grazing incidence x-ray diffraction at 20°C and at different lateral pressures. C1 and C5 exhibit a centred-rectangular lattice with NN (nearest neighbour) tilt and NN distortion directions. In the case of C1 on increasing the lateral pressure the distortion changes to NNN (next-nearest neighbour direction) without a change in tilt direction (NN). This behaviour could not be observed for the other compounds. C3 and C4 display a phas…

X-Ray Scattering Studies of Organic Monolayers on Electrolytic Solutions: Arachidic Acid on CdCl2

The interaction between a charged monolayer of fatty acid molecules on the surface of a CdCl2 aqueous solution and the ions below has been investigated by means of X-ray Reflection and Grazing-Incidence Diffraction. A stoichiometric, localised layer of Cd++ ions forms an epitaxial 2×3 superstructure below the 2D-crystalline fatty acid monolayer.