Abstract
The oriented DPPC multilayers hydrated by D 2O have been studied by a small-angle neutron scattering method in the Guinier range, and the gyration radius of the structural inhomogeneities has been estimated at about 29Å. They are interpreted as the annular defects between adjacent clusters uniting the all- trans chain ‘segments’ adjacent to the polar head group regions. The angle of the ‘segment’ tilt is determined by the hydrated polar group area (59.2Å 2 for DPPC bilayers) and has been estimated to be about 44° under the given experimental conditions. The hydrocarbon interior of a bilayer can be suggested as a ‘sandwich’ that is formed by two clustered layers (approx. 7Åof the thickness) and the central disordered (liquid) layer. The average cluster size along the bilayer surface is estimated to be approx. 24Åwhich correlates with the estimations of the short order region dimensions from the halfwidth of the X-ray ‘packing’ reflex (4.6Å) −1. The average interchain separation of approx. 5Åand the average cross-section area of a chain in a cluster (21.4Å 2) were estimated from the reflex position and the chain cross-section geometry. The total volume of defects and the fraction of a bilayer surface occupied by them were estimated too.
Published Version
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