Novel methods for studying lipids and lipases and their mutual interaction at interfaces. Part II. Surface sensitive synchrotron X-ray scattering.

Monolayers of lipids have been studied for more than a century. During the past decade new insight into the field has resulted from the development of surface sensitive X-ray scattering methods utilizing synchrotron radiation: grazing-incidence X-ray diffraction (GIXD) and specular X-ray reflectivity (XR). These novel methods provide direct microscopic information about the systems in question and allow in situ investigations under near physiological conditions. GIXD gives information about the in-plane molecular structure, e.g., lattice symmetry and structural parameters; XR provides the electron density profile across the interface. The present review describes the theory, experimental procedures and sample requirements for surface sensitive X-ray scattering. An overview of recent results is presented as well, with special emphasis on biologically important systems, e.g., investigations by GIXD and/or XR of lipid and protein structures at interfaces and of lipid/protein interactions.