SUPRAMOLECULAR ORDERING OF BIPOLAR LIPIDS FROM ARCHAEA IN LANGMUIR-BLODGETT-FILMS BY LOW-ANGLE X-RAY-DIFFRACTION

The results of an investigation by X-ray diffraction on the supramolec ular organization of a peculiar class of semisynthetic lipids, namely bipolar lipids from archaebacteria, when organized in layered structur es in Langmuir-Blodgett films are reported. The simplicity of the expe rimental technique and the straightforward interpretation of the data provide a clear and unambiguous determination of the molecular conform ation of bipolar lipids in LB films. The experimental data make it pos sible to reject unequivocally both the model of monolayers of fully ex tended molecules and the model of monolayers of tilted molecules, whil e they strongly support a structural model consisting of the stacking of bilayers made of bent U-shaped molecules. The results reported may constitute a direct clarifying contribution to the controversial matte r of the molecular conformation of bipolar lipids at the air-water int erface.