Effects of contaminants on biological model membranes: The advantage of the ASAXS method for the study of the location of copper ions and dihalogenated phenol molecules

The features of the location of copper ions and the dihalogenated phenol molecules were investigated at their low concentration in the dipalmitoylphosphatidylcholine (DPPC)-water liposomes by using small-angle X-ray scattering (SAXS) and anomalous small-angle X-ray scattering (ASAXS) methods. Only the ASAXS method can provide information about the structural features of the domains rich in these ions and organic guest molecules. The copper ions are mainly located in large domains between the lamellae and only partly in the characteristic periodic water shells of the liposomes. The dihalogenated phenol molecules are embedded in the layers and do not destroy the lamellar arrangement. Their inhomogeneous distribution appears laterally and phase separation occurs. The local structures induced by the copper ions and the dihalogenated phenols were also visualised by freeze-fracture method.