Structure of a gel phase lipid bilayer prepared by the Langmuir-Blodgett/Langmuir-Schaefer method characterized by sum-frequency vibrational spectroscopy

The structure of a planar supported lipid bilayer (PSLB) prepared by the Langmuir-Blodgett (LB)/Langmuir-Schaefer (LS) method was investigated by sum-frequency vibrational spectroscopy (SFVS). By using asymmetric lipid bilayers composed of selectively deuterated 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) lipids, the orientation of the fatty acid chains and phosphocholine headgroups has been determined independently for both leaflets of the bilayer. The alkyl chains of the lipids were found to be orientated approximately 13 degrees +/- 4 degrees from the surface normal for both leaflets. The lipid chains in both leaflets also contain some gauche content, which is consistent with previous NMR and FTIR studies of similar lipid systems. More importantly, the relative number of gauche defects does not seem to be influenced by the deposition method, LB versus LS. The headgroup orientation for the lipid film in contact with the silica support was determined to be 69 degrees +/- 3 degrees, whereas that in contact with the aqueous phase was 66 degrees +/- 4 degrees from the surface normal. The SFVS results indicate that the structure of the DSPC lipid film in contact with the solid support and the film adjacent to the aqueous phase are nearly identical in structure. These results suggesting the LB/LS deposition method do indeed produce symmetric lipid bilayers. These studies further add to the growing information on the efficacy of PSLBs as suitable models for biological membrane studies.