Structural, mesomorphic and time-resolved studies of biological liquid crystals and lipid membranes using synchrotron X-radiation. In: Mandelkow E, editor. Synchrotron Radiation in Chemistry and Biology III. Berlin: Springer Berlin Heidelberg; 1989. pp. 75-109. [DOI: 10.1007/3540512012_14]

Synchrotron X-ray studies of lipids and membranes: a critique

This review gives a description of techniques, suitable for the study of lipid dispersions and unorientated membranes, that are available at synchrotron facilities to determine either the kinetics of transitional phenomena in the time after a temperature or pressure jump is initiated, or the phases present while a sample undergoes a phase transition. Included in this description is information about synchrotron X-ray sources, sample holders and temperature controllers, detection systems, as well as data reduction. Examples involving lipid dispersions are provided to illustrate the application of these methods using synchrotron radiation.

Kinetics and mechanism of the pressure-induced lamellar order/disorder transition in phosphatidylethanolamine: a time-resolved X-ray diffraction study

By using synchrotron radiation, a movie was made of the X-ray scattering pattern from a biological liquid crystal undergoing a phase transition induced by a pressure jump. The system studied includes the fully hydrated phospholipid dihexadecylphosphatidylethanolamine in the lamellar gel (L beta') phase at a temperature of 68 degrees C and a pressure of 9.7 MPa (1400 psig). Following the rapid release of pressure to atmospheric the L beta' phase transforms slowly into the lamellar liquid crystal (L alpha) phase. The pressure perturbation is applied with the intention of producing a sudden phase disequilibrium followed by monitoring the system as it relaxes to its new equilibrium condition. Remarkably, the proportion of sample in the L alpha phase grows linearly with time, taking 37 s to totally consume the L beta' phase. The time dependencies of radius, peak intensity, and width of the powder diffraction ring of the low-angle (001) lamellar reflections were obtained from the movie by image processing. The concept of an "effective pressure" is introduced to account for the temperature variations that accompany the phase transition and to establish that the observed large transit time is indeed intrinsic to the sample and not due to heat exchange with the environment. The reverse transformation, L alpha to L beta', induced by a sudden jump from atmospheric pressure to 9.7 MPa, is complete in less than 13 s. These measurements represent a new approach for studying the kinetics of lipid phase transitions and for gaining insights into the mechanism of the lamellar order/disorder transition.

Phospholipid phase transitions: kinetics and structural mechanisms

A brief review is given on the principles and methods used to investigate structural phase transitions in phospholipid supramolecular structures. The conceptual differences of approaches close to and far from equilibrium are addressed, and the consequences in terms of the limits of interpretation for different types of methods, in particular referring to jump-relaxation and steady-state techniques, are surveyed. With the emphasis on connecting dynamic and structural information, the results obtained so far from different techniques are reviewed, and the open questions addressed. The more recent advances by millisecond time-resolved X-ray diffraction with synchrotron radiation and their main results obtained for transitions triggered by IR-laser temperature jumps are summarized. As a major novel aspect in the field, the necessity of considering martensitic, diffusionless transformation mechanisms and the occurrence of intermediate structures is highlighted.