Quantitation of water in membranes by neutron diffraction and X-ray techniques

Present understanding of the ubiquitous membrane places significant importance on the role of water in membrane structure and function. The interaction of water with membranes and membrane components has been studied in some detail by a variety of techniques. Often more detailed information on the water associated with the membrane is required. The unique ability of neutron diffraction techniques to image the water directly, coupled with information from complementary X-ray diffraction analysis, permits a detailed study of the membrane water, including a quantitative analysis in many situations. The application of these techniques is now well established, and a number of excellent reviews on neutron diffraction and X-ray diffraction methods are available. To obtain sufficient experimental data for an estimate of the quantity of water in the membrane system, stacks of membranes in a well-ordered state are required. Certain biological membranes occur naturally in stacks and can be studied intact. Membrane fragments or large membrane vesicles can be stacked artificially to give an adequate diffraction pattern, and highly oriented multibilayers of pure lipids or lipid/proterin mixture can be formed by evaporative deposition