Structural properties of phosphatidylcholine in a monolayer at the air/water interface

Abstract

Neutron reflectivities of phosphatidylcholine monolayers in the liquid condensed (LC) phase on ultrapure H(2)O and D(2)O subphases have been measured on a Langmuir film balance. Using a dedicated liquid surface reflectometer, reflectivities down to R = 10(-6) in the momentum transfer range Q(z) = 0-0.4 A(-1) were accessed.In a new approach, by refining neutron reflectivity data from chain-perdeuterated DPPC-d(62) in combination with x-ray measurements on the same monolayer under similar conditions it is shown that the two techniques mutually complement one another. This analysis leads to a detailed conception of the interface structure. It is found that in the LC phase (which is analogous to the L(beta), phase in vesicle dispersions) the head group is interpenetrated with subphase water (4 +/- 2.5 molecules per lipid) and the average tilt angle of the hydrophobic chains from the surface normal is 33 +/- 3 degrees.

AND/R: Advanced neutron diffractometer/reflectometer for investigation of thin films and multilayers for the life sciences

“…These beam stops can be removed from the downstream polarizer, if the PSD is used to measure both polarizations simultaneously. Alternatively, when using the PSD for diffuse polarized beam measurements, the polarizer after the sample can be replaced with an 3 He polarizer. 13 …”

“…Specific deuteration of lipids, for example, permits determination of the transmembrane location of labeled groups within lipid bilayers 2 and monolayers. 3 Specular reflectivity provides information about the compositional depth profile along the nominal surface normal. The technique accesses relatively small values of the wave-vector transfer Q ͓=k f − k i , equivalent to ͑4 sin ͒ / in the specular condition͔, corresponding to spatial length scales down to the nanometer range with subÅngström accuracy.…”

Cholesterol-Induced Interfacial Area Condensations of Galactosylceramides and Sphingomyelins with Identical Acyl Chains

“…Long-axis molecular tilt of lipids is not restricted to bilayers or to lipids with phosphocholine head groups. Indeed, long-axis molecular tilt has been reported in monolayers of condensed-phase PC as well as PA and PE (Vaknin et al, 1991;Helm et al, 1987Helm et al, , 1991. In fact, the tilt angle in PC monolayers is sensitive to whether acyl chains are ether-or ester-linked (Brezesinski et al, 1995).…”

Ion distributions at charged aqueous surfaces: Synchrotron X-ray scattering studies

“…3.10), n is the number of measured points, and P is the number of parameters used to calculate the reflectivity, fixing it at different values away from its optimum and readjusting all other parameters to a new minimum until χ 2 increases by 50% [75,76].…”

“…The minimum number of slabs is the one for which the addition of another slab does not improve the quality of the fit, i.e., does not improve χ 2 . In the second stage, we apply space filling and volume constraints [75,76,78] to calculate ρ i by assigning to each slab a different portion of the molecule, the ions and water molecules, to a profile that has the same number of slabs as obtained in stage one of the analysis.…”