Electron paramagnetic resonance and transmission electron microscopy study of the interactions between asbestiform zeolite fibers and model membranes

Different asbestiform zeolite fibers of the erionite (termed GF1 and MD8, demonstrated carcinogenic) and offretite (termed BV12, suspected carcinogenic) families were investigated by analyzing the electron paramagnetic resonance (EPR) spectra of selected surfactant spin probes and transmission electron microscopy (TEM) images in the presence of model membranes-cetyltrimethylammonium (CTAB) micelles, egg-lecithin liposomes, and dimyristoylphosphatidylcholine (DMPC) liposomes. This was undertaken to obtain information on interactions occurring at a molecular level between fibers and membranes which correlate with entrance of fibers into the membrane model or location of the fibers at the external or internal membrane interfaces. For CTAB micelles, all fibers were able to enter the micelles, but the hair-like structure and chemical surface characteristics of GF1 modified the micelle structure toward a bilayer-like organization, while MD8 and BV12, being shorter fibers and with a high density of surface interacting groups, partially destroyed the micelles. For liposomes, GF1 fibers partially penetrated the core solution, but DMPC liposomes showed increasing rigidity and organization of the bilayer. Conversely, for MD8 and BV12, the fibers did not cross the membrane demonstrating a smaller membrane structure perturbation. Scolecite fibers (termed SC1), used for comparison, presented poor interactions with the model membranes. The carcinogenicity of the zeolites, as postulated in the series SC1