Coarsening Dynamics of Domains in Lipid Membranes

Abstract

the phase diagram itself. Brewster angle microscopy allows one to image the domains in a Langmuir monolayer with and without the probe molecules to directly test their effect. The combined Brewster angle (BAM)/ fluorescence microscope allows us to image simultaneously with the two techniques exactly the same domains in the Langmuir film. In general, the images taken by the two microscopes compare well. Comparison of the techniques can then make it easier to correlate the different domain properties leading to contrast in the two techniques. Some types of domains may however be much more evident with BAM than with FM. When placed in water, lipid molecules form multilamellar vesicles (MLVs) in which lipid layers are separated by water regions. These interlamellar water regions have thicknesses on the order of 1 to 10 nanometers depending on lipid type. What happens if water contains buffer molecules? Will buffer molecules be taken inside the MLVs? If yes, then to what extent? These questions arise because the physical properties of water regions next to lipid membranes have been shown to differ from bulk water [1]. We would like to know how buffer molecules and other solutes partition between MLVs and the outer solution. To determine this partitioning, we use lipid membranes that sink in pure water but float in buffer solutions of certain concentrations. We then find the exact concentration for which the mass density of the solution matches that of the MLVs. This density matching allows us to calculate the ratio between water and buffer molecules present inside MLVs by using data from smallangle x-ray scattering. For KCl solutions, as well as for solutions of common buffers, we find that solutes are excluded from the interlamellar water regions creating a solute deficit inside the MLVs. [1] Petrache et al., Biophys.

Physical mechanisms of micro- and nanodomain formation in multicomponent lipid membranes

“…These theoretical predictions have been verified by Keller and coworkers [60,61] using fluorescence microscopy on model multicomponent membranes and the expected power law behavior was confirmed within the experimental error. The same group also studied the dynamics of thermal fluctuations close to T c [101] and the dynamics of phase separation and coarsening below T c [102] and again found good agreement with theoretical predictions. Connell et al showed by AFM studies of supported bilayers that the critical behavior persists up to temperatures where the correlation length is only of the order of a few nanometers [54].…”

Swarm Hunting and Cluster Ejections in Chemically Communicating Active Mixtures

“…calculating cluster sizes via L 1 (t) and calculating clusterdistances L 2 (t) basically leads to the same growth law (Fig. 7) [47]. Thus, there is only one independent macroscopic length scale in the system.…”

“…(5,6)), allowing to analytically understand the transition line between cluster phases, which originate from a stationary instability of the uniform phase, and hunting swarms, emerging from an oscillatory instability. As a further characteristic difference between these phases, we find that clusters (and the distance between them) grow diffusively (L(t) ∝ t 0.35 [41][42][43][44][45]47]), whereas hunting swarms grow significantly faster (L(t) ∝ t 0.56 [48]). Future work might include more specific biological details and could address the effect of confining boundaries or obstacles [49][50][51][52].…”

Minimal Effect of Lipid Charge on Membrane Miscibility Phase Behavior in Three Ternary Systems

“…All compositions were measured at least twice (i.e., reheated and cooled at least once) to ensure that domains were indicative of equilibrium phenomena. Liquid domains have round shapes and merge quickly upon collision with other liquid domains (36,37). Solid domains have static, typically noncircular shapes.…”