Effect of 2,4-dichlorophenol on DPPC/water liposomes studied by X-ray and freeze-fracture electron microscopy

The effect of 2,4-dichlorophenol (DCP) was studied on the fully hydrated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)-water liposomes. The structure and the thermotropic phase behaviour of the liposomes was examined in the presence of DCP (DCP/DPPC molar ratio, varied from 2 x 10(-2) up to 1) using small- and wide-angle X-ray scattering (SAXS, WAXS) and freeze-fracture electron microscopy. The structural behaviour of the DPPC/DCP/water system was strongly dependent on the concentration of the DCR In the pretransition range the DCP molecules (at 2 x 10(-2) DCP/DPPC molar ratio) induced the interdigitated phase beside the parent (gel and rippled gel) phases, locally which can be form at higher DCP concentration. When the DCP/DPPC molar ratio was increased the pretransition disappeared and the main transition was shifted to lower temperatures. In the molar ratio range from 2 x 10(-1) up to 5 x 10(-1), a coexistence of different phases was observed in the wide temperature range from 20 up to 40 degreesC. With a further increase of the DCP/DPPC molar ratio (6 x 10(-1) to 1) only the interdigitated gel phase occurred below 25 degreesC. A schematic phase diagram of DPPC/DCP/water system was constructed to summarise the results. (C) 2003 Elsevier Ireland Ltd. All rights reserved.