Entropic Attraction Condenses Like-Charged Interfaces Composed of Self-Assembled Molecules

Abstract

Like-charged solid interfaces repel and separate from one another as much as possible. Charged interfaces composed of self-assembled charged-molecules such as lipids or proteins are ubiquitous. The present study shows that although charged lipid-membranes are sufficiently rigid, in order to swell as much as possible, they deviate markedly from the behavior of typical like-charged solids when diluted below a critical concentration (ca. 15 wt %). Unexpectedly, they swell into lamellar structures with spacing that is up to four times shorter than the layers should assume (if filling the entire available space). This process is reversible with respect to changing the lipid concentration. Additionally, the research shows that, although the repulsion between charged interfaces increases with temperature, like-charged membranes, remarkably, condense with increasing temperature. This effect is also shown to be reversible. Our findings hold for a wide range of conditions including varying membrane charge density, bending rigidity, salt concentration, and conditions of typical living systems. We attribute the limited swelling and condensation of the net repulsive interfaces to their self-assembled character. Unlike solids, membranes can rearrange to gain an effective entropic attraction, which increases with temperature and compensates for the work required for condensing the bilayers. Our findings provide new insight into the thermodynamics and self-organization of like-charged interfaces composed of self-assembled molecules such as charged biomaterials and supramolecular assemblies that are widely found in synthetic and natural constructs.

Multi-lamellar organization of fully deuterated lipid extracts of yeast membranes

“…Two additional stacking distances were present in the hydrogenous samples, suggesting a larger heterogeneity of the lamellar arrangement. In particular, the most intense peak for the hydrogenous extracts was related to a real-space distance of about 60 Å and therefore is in agreement with the typical dspacing values characterizing stacks of zwitterionic phospholipids (Cavalcanti et al, 2007;Trapp et al, 2010;Schneck et al, 2011;Steiner et al, 2012;Foglia et al, 2012;Knoll et al, 2014). This feature was also present for a few deuterated samples and, in this case, the intensity of the peak was very close to the background level.…”

“…The periodicity associated with this feature is d ' 60 (1) Å . Such a value is compatible with the typical d-spacing values found for stacks of zwitterionic natural (Zaccai et al, 1975;Cowley et al, 1978) and synthetic (Cavalcanti et al, 2007;Trapp et al, 2010;Schneck et al, 2011;Steiner et al, 2012;Foglia et al, 2012;Knoll et al, 2014) phospholipid bilayers. At higher temperatures (the middle and bottom panels in Fig.…”

“…These authors found that the presence of a large amount of anionic phospholipids, such research papers as phosphatidylglycerol (PG), to zwitterionic phospholipids, such as phosphatidylcholine (PC), induces swelling of the bilayer stack. In the case of zero ionic strength, electrostatic repulsion between neighbouring bilayers has been shown to be the main repulsive force, promoting very large bilayer-tobilayer separations (Cowley et al, 1978;Schneck et al, 2011;Steiner et al, 2012).…”

Cochleate characterization by cryogenic electron microscopy methods: Cryo-TEM and Cryo-SEM

“…As a result, fusion of vesicles may be mostly hindered by hydration forces [23,26]. As recently pointed by Raviv and coworkers, membranes can rearrange to gain an effective entropic attraction, to compensate for the work required for condensing the bilayers [29]. showing different behavior than the one obtained by simply salt screening.…”

Changes in aggregation states of light-harvesting complexes as a mechanism for modulating energy transfer in desert crust cyanobacteria

“…SANS was performed at the KWS-2 instrument operated by Jülich Centre for Neutron Science (JCNS) at the Heinz Maier-Leibnitz Zentrum, Garching, Germany (60, 61) (SI Text). The scattering intensity, I, as a function of the magnitude of the momentum transfer vector, q, was then plotted and analyzed to determine the typical RDs between membranes (62).…”