CHARACTERIZATION OF THE SUB-MAIN-TRANSITION IN DISTEAROYLPHOSPHATIDYLCHOLINE STUDIED BY SIMULTANEOUS SMALL-ANGLE AND WIDE-ANGLE X-RAY-DIFFRACTION

Simultaneous small- and wide-angle X-ray diffraction was used to inves tigate the structural conversions in the so-called sub-main-transition of fully hydrated multilamellar vesicles of distearoyl phosphatidylch oline (DSPC). The small-angle diffraction patterns show a modification in the supramolecular structure of the corrugated lipid bilayer and r eveal that the sub-main-transition does not abolish the general featur es of the ripple phase (P-beta'). Concomitantly in the wide-angle regi on the diffraction patterns exhibit a rearrangement of the hydrocarbon chain packing and an onset of chain melting. The presence of KCl show an enhancement of the effects of the sub-main-transition Moreover, in the ripple phase (P-beta') below the sub-main-transition the hydrocar bon chains are positioned on an orthorhombic lattice in the presence o f KCl. (C) 1997 Elsevier Science B.V.