Structure and Dynamics of Planar and Spherical Supported Phospholipid Bilayers

Abstract

The structure and dynamics of planar and spherical supported phospholipid bilayers is studied by NMR methods, specular reflection of neutrons (SRN), DSC and computer simulations. The combination of these methods allows the assessment of a number of basic physical properties of these new membrane model systems. Spherical supported vesicles (SSV), which offer the advantage over multilamcllar vesicles (MLV) of being geometrically well defined and adjustable in their size, are shown to exhibit a structure similar to the MLV. The existence of an ultrathin water layer of ≈15Å thickness between the bilaycr and the solid support is confirmed by both NMR and SRN. The main phase transition temperature of SSV’s of DPPC is reduced by 2°C as compared to MLV’ and there is no prctransition. A new method is applied to determine the lateral diffusion coefficients of SSV’s at various temperatures. Moreover, the new model system is used to study the effect of slow motions (on the NMR timescale) on the anisotropy of the transverse relaxation time T_2c. The results suggest that the major relaxation contribution comes from the lateral diffusion of the phospholipids.