Supramolecular Formation in Lipids

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This study aims to get evidence for the basic structure of biomembranes, especially to focus upon the supramolecular structure composed of phospholipids. Ripple structure possesses interesting features from mesoscopic structure appearing in phospholipids. In dipalmitoylphosphatidylcholine, it has been found that the secondary ripple structure appears in a metastable state. Furthermore, the condition of the appearance of the metastable state has been clarified. In a phospholipis/cholesterol system, the temperature dependence of the ripple repeat distance has been explained in terms of that for the normal ripple structure. In a similar system, in which a phospholipid molecule has unsaturated hydrocarbon chains, the overall behavior of the phase diagram is almost common among the phospholipids. In a phospholipid/alcohol system, structural study on the interdigitated phase has been performed systematically by changing the length of hydrocarbon chain in a variety of phospholipids and various alcohols. From the electron density profile in the direction normal to the surface of multilamellar, a model of the interdigitated structure has been proposed. In lauroylphosphatidylcholine, a new liquid crystalline phase has been found between ripple and usual liquid crystalline phases : the new liquid crystalline structure has less disordered hydrocarbon chains than in the usual structure. As a model of biomembranes of an extrinsic protein and lipids, a system of poly(L-lysine) and acidic phospholipis has been studied. The main interaction between them has been found to be electrostatic one.