Liquid crystals and living systems

Abstract

Most lipids do not pass, on heating, directly from a crystalline structure to an isotropic structure. They are often characterized by a number of intermediate phases, ranging from the plastic crystal, where the center of gravity of the molecule may rotate about one or more axes while the three‐dimensional order of the crystal remains, to nematic liquid crystals, which have birefrigent properties of crystals and yet are characterized by completely random ordering of the molecular centers. The smectic and cholesteric liquid crystalline structures are most commonly encountered in lipids. The structural characteristics of these systems are discussed. Of particular interest in living systems are liquid crystals, which are formed by cholesteric esters and many protein materials, and the two‐dimensional crystals (smectic structure), which are formed by fatty acid derivatives. The mechanisms of energy transfer and the mechanical alignment in these liquid crystalline systems are unique and require different considerations from those found adaptable to liquids or solids. The properties of liquid crystals which might best be associated with living systems will be discussed, including surface properties and diffusivity.

The mechanism of vesicle formation

“…The energy considerations of open disks were qualitatively discussed by Ferguson & Brown (1968). Finer et al (1972 proposed a mechanism ofvesicle formation by sonication suggesting that ultrasound induces collisions between vesicles which in turn disrupt and the resulting short-lived bilayer fragments or other forms of small aggregates rearrange into vesicles.…”

“…It was based on energy considerations developed earlier (Franck, 1958;Ferguson & Brown, 1968;Helfrich, 1974) and which predicted a disk-like phospholipid micelle as an intermediate structure in the vesicle formation process. Such structures were already described in the literature in the studies of bile salt/lecithin micelles (Small et al, 1969;Mazer et al, 1980).…”

Evidence for two-dimensional solitary sound waves in a lipid controlled interface and its implications for biological signalling

“…For example, sound waves at the membrane interface have been proposed as the physical basis of nerve pulses and it is believed that key features of action potentials (shape stability, all-or-none nature, etc.) result from nonlinear properties of cell membranes [7][8][9][10][11], an idea first put forward by Kaufmann [10]. Theoretically, it is not the complexity of membrane composition, which includes proteins (ion channels and pumps), lipid heterogeneity, etc., but the nonlinearity in the elasticity of the interface that is necessary to support such sound waves.…”

Self-Organizing Molecular Systems

“…The shape of liquid crystalline droplets that are uniformly aligned may exhibit a variety of forms from an oblate to a prolate spheriod, depending on the properties of the liquid in which they are immersed. The liquid crystalline structure responds readily to energy changes, and the model could have many other behavioral properties of a living cell (Fergason and Brown, 1968;Brown and Wolken, 1979).…”

“…4a), and, as they line up, they generate a "layer" of molecules that serves as a substrate on which chemical reactions can take place. Simple organic reactions such as isomerization and enzymatic oxidation-reduction reactions Fergason andBrown, 1968, andBrown andWolken, 1979).…”