Effects of Sonication on the Lamellar Structures of L-.ALPHA.-Dipalmitoyl Phosphatidylcholine(DPPC)/Saccharide/Water Systems.

Abstract

The effects of sonication, conducted prior to dehydration by heat drying, on the multilamellar vesicles of L-α-dipalmitoyl phosphatidylcholine (DPPC), DPPC/glucose, DPPC/trehalose or DPPC/maltose systems were examined by differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD). The results were compared with those for the corresponding unsonicated and DPPC systems without saccharide. In the DPPC/glucose system, no clear differences between the unsonicated and sonicated systems were found because glucose did not prevent fusion of vesicles by dehydration. DSC showed one sharp peak at the gel-liquid crystal transition temperature (Tc) of 43°C, indicating that glucose was distributed homogeneously between the DPPC bilayers of the vesicles. Subcells formed by hydrocarbon chains of DPPC changed from the hexagonal gel (Lβ) to the hexagonal liquid crystal (Lα) form at Tc with an increase in temperature, essentially as noted for DPPC systems except for differences in Tc. In the DPPC/disaccharide system, the unsonicated and sonicated systems were clearly different. DSC and XRD of the unsonicated system consistently showed transition from a gel to a liquid crystal state over a wide temperature range, while for the sonicated system, there was only a sharp peak on the DSC curve. The thermal behavior of DPPC/disaccharide systems may be explained as follows. Although disaccharide is distributed homogeneously between the bilayers of multilamellar vesicles, interactions with DPPC depend on the surface curvature of the bilayer. Heating of multilamellar vesicles may possibly result in transition from a gel to a liquid crystal phase since multilamellar vesicles consist of many bilayers differing considerably in their surface curvature, in contrast to sonicated unilamellar vesicles which possess a definite curvature.