Small-Angle X-ray Scattering Studies on the Structure of Mixed DPPC/diC_(7)PC Micelles in Aqueous Solutions

摘要

The phase behavior of mixed DPPC/diC_(7)PC micelles in aqueous solutions was investigated using small-angle x-ray scattering (SAXS) and Transmission electron microscopy (TEM). Phase transitions from multilamellar vesicle (MLV) to disc bicelle, ribbon-like, and rod-like aggregates are observed as the percentage of the short-chain diC_(7)PC is increased. At DPPC/diC_(7)PC molar ratio 3/1, the multilamellar liposomes are all transformed into disc bicelles. The long-chain DPPC lipid and short-chain diC_(7)PC lipid, respectively, form the planar and rim part of the bicelle with a radius and thickness of 98.4 and 55.3 A, respectively, for the DPPC/diC_(7)PC mixing ratio of 3/1. Temperature-induced structure transformation is also observed for such a mixed system. The structural transformation is induced by the solubilization of diC_(7)PC into the planar long-chain lipid bilayer. An intermediate ribbon phase was found and coexisted with DPPC/diC_(7)PC multilamellar liposome phase at 40 deg C; while only multilamellar liposome phase was found at 45 deg C which is higher above the chain melting temperature of DPPC.