Changes in the thermotropic and the structural behaviour of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine/water liposomes effected by 2,4-dichlorphenol

Toxic 2,4-dichlorophenol (DCP) molecules, originating from the environment, drastically affect the main functions of organic cell membranes. To yield some information on the destroyed membrane structures, 1,2-dipalmitoyl-snglycero-3-phosphatidylcholine (DPPC)/water liposome systems containing different amounts of DCP were studied by differential scanning calorimetry and small-angle X-ray scattering (SAXS) methods. The transition points of the main transition and its enthalpy are changed only in a relatively narrow range of about 0–2.5%, while the enthalpy of the pretransition is affected by DCP more strongly. The disappearance of the pretransition occurs in a range of about 3 orders of magnitude of the DCP/DPPC ratio (from 10−5 to 10−2). The changes in the first Bragg profiles of the SAXS curves depend not only on the temperature but also very strongly on the DCP/DPPC molar ratios. Especially, at higher concentrations DCP causes a strong broadening in the Bragg profiles and a difference from the profiles of the nonrippled phase. The general destruction in the layer arrangements and the reductions in the transition enthalpies between them indicate defect structures consisting of domains with nonlayer structure which are formed simultaneously by DCP molecules.