SMALL AMOUNTS OF LANOSTEROL IN DPPC DISPERSIONS - A X-RAY FINGERPRINTANALYSIS

In a classical paper it is reported that small amounts of sterol stron gly influence the structure of lipid dispersions in respect to the bil ayer packing as well as the lateral packing within the bilayers. Other wise only slight differences in the thermodynamic properties of DPPC a re detected in mixture with small amounts of sterol, For a dispersion of DPPC/2 mol% lanosterol/50 wt% water a quantitative analysis of the X-ray powder pattern shows, that under the influence of the added ster ol a great differentiation in the,eel phase structure appears. During repeated heating and cooling cycles different lattice expansion and/or lattice deformation modes were observed and interpretated in terms of changes of the orthorhombic subcells O perpendicular to and O'perpend icular to. The corresponding long spacings show different temperature dependences on heating and cooling, respectively, This behavior is int erpretated as a miscibility, which minimizes the frustration in the DP PC headgroup packing.