SUPPORTED PHOSPHOLIPID-BILAYERS PREPARED BY THE LB/VESICLE METHOD - A FOURIER-TRANSFORM INFRARED ATTENUATED TOTAL-REFLECTION SPECTROSCOPIC STUDY ON STRUCTURE AND STABILITY

The purpose of this study is to present a reliable and easy method for the preparation of supported phospholipid bilayers which consists of two steps: (1) transfer of a Langmuir-Blodgett (LB) monolayer onto a solid substrate and (2) completion of the bilayer by adsorption of phospholipid molecules from a vesicle solution. Two types of asymmetric bilayers have been prepared, a DPPA/POPC bilayer with the DPPA leaflet in the gel and the POPC leaflet in the liquid crystalline phase, and a DPPA/DPPC bilayer with both leaflets in the gel phase. The method may be applied for the preparation of symmetric bilayers as well. The surface concentration, Gamma, the molecular area A(mol), and the mean molecular order parameter ($) over bar S-mol of the hydrocarbon chains were determined for each leaflet of the resulting bilayers separately by means of quantitative FTIR-ATR spectroscopy (Fourier transform infrared attenuated total reflection spectroscopy). An orientational model which also takes into account a hydrocarbon chain tilt in the gel phase was employed to derive ($) over bar S-mol Values obtained for A(mol) and ($) over bar S-mol in different leaflets coincide with the values for the respective phospholipids given in the literature. The stability of the immobilized LB-DPPA monolayer and the two different supported bilayers in an aqueous environment was monitored over a period of at least 60 h. Possible mechanisms of bilayer formation during preparation are discussed. Finally, the usefulness of these bilayers for quantitative in situ FTIR-ATR studies on the interaction of such model membranes with substrates dissolved in the aqueous environment is stressed.