The use of low temperature X-ray diffraction to evaluate freezing methods used in freeze-fracture electron microscopy

Abstract

Two methods of freezing samples for freeze-fracture electron microscopy have been compared using X-ray diffraction and freeze-fracture results from lipid-water model systems. Perturbations of the molecular organization of hydrocarbon chains and the extent of ice crystal formation have been evaluated for lamellar phases of egg lecithin containing 16% water and egg lecithin-phosphatidylinositol containing 55% water, both freeze quenched in liquid Freon-22 near its melting temperature (113 K). Very thin samples sandwiched between copper sheets separated by an electron microscope grid show much less freezing induced structural rearrangement than small smaples contained on conventional Balzers-type gold planchettes. These results show that the rate of freezing in the very thin preparations is greater than in the conventional ones, which is probably due in part to the improved dissipation of heat from a poorly conductive sample through highly conductive copper sheets.