Modulation of lipid phase behavior by kosmotropic and chaotropic solutes (original) (raw)

Lipid phase behaviour under steady state conditions

Faraday Discussions, 2013

At the interface between two regions, for example the air-liquid interface of a lipid solution, there can arise non-equilibrium situations. The water chemical potential corresponding to the ambient RH will, in general, not match the water chemical potential of the solution, and the gradients in chemical potential cause diffusional flows. If the bulk water chemical potential is close to a phase transition, there is the possibility of forming an interfacial phase with structures qualitatively different from those found in the bulk. Based on a previous analysis of this phenomenon in a two component systems (C. Åberg, E. Sparr, K. Edler and H. Wennerström, Langmuir 2009, 25, 12177), we here analyse the phenomenon for threecomponent systems. The relevant transport equations are derived, and explicit results are given for some limiting cases. Then the formalism is applied conceptually to four different aqueous lipid systems, which in addition to water and a phospholipid contain i) octyl glucoside, ii) urea, iii) heavy water, iv) sodium cholate as the third component. These four cases are chosen to illustrate i) a method to use a micelle former to transport lipid to the interface where a multi-lamellar structure can form; ii) to use a co-solvent to inhibit the formation of a gel phase at the interface; iii) a method to form pure phospholipid multilamellar structures at the interface; iv) a method to form a sequence of phases in the interfacial region. These four cases all have the character of theoretically based conjectures and it remains to investigate experimentally whether or not the conditions can be realized in practice. 65 water interface. We analysed the general two component wateramphiphile case and applied it the specific AOT (bis(2ethylhexyl)sulfosuccinate)-water system. In this case we could base the quantitative analysis on previous thorough equilibrium characterization of the bulk system. 11, 12 We showed that a 70 multilamellar structure could form at the interface, and that the extent of the phenomenon depended strongly on an interplay 65

The Effects of Solutes on the Freezing Properties of and Hydration Forces in Lipid Lamellar Phases

Biophysical Journal, 1998

Quantitative deuterium nuclear magnetic resonance is used to study the freezing behavior of the water in phosphatidylcholine lamellar phases, and the effect upon it of dimethylsulfoxide (DMSO), sorbitol, sucrose, and trehalose. When sufficient solute is present, an isotropic phase of concentrated aqueous solution may coexist with the lamellar phase at freezing temperatures. We determine the composition of both unfrozen phases as a function of temperature by using the intensity of the calibrated free induction decay signal (FID). The presence of DMSO or sorbitol increases the hydration of the lamellar phase at all freezing temperatures studied, and the size of the increase in hydration is comparable to that expected from their purely osmotic effect. Sucrose and trehalose increase the hydration of the lamellar phase, but, at concentrations of several molal, the increase is less than that which their purely osmotic effect would be expected to produce. A possible explanation is that very high volume fractions of sucrose and trehalose disrupt the water structure and thus reduce the repulsive hydration interaction between membranes. Because of their osmotic effect, all of the solutes studied reduced the intramembrane mechanical stresses produced in lamellar phases by freezing. Sucrose and trehalose at high concentrations produce a greater reduction than do the other solutes.

Phase behavior of selected artificial lipids

Current Opinion in Colloid & Interface Science, 2014

The flexibility of biomembranes is based on the physical-chemical properties of their main componentsglycerophospholipids. The structure of these modular amphiphilic molecules can be modified through organic synthesis making it possible to study specific physical-chemical effects in detail. In particular, the roles of the hydrophobic tails of the phospholipids and their hydrophobic/hydrophilic interfacial backbone on the phase behaviour are highlighted. The spatial orientation of the glycerol backbone changes from sn-1,2 to sn-1,3 phospholipids leading to an increase of the in-p l ane area of the molecu l e. The larger distance between the hydrophobic tails can lead to membrane leaflet interdigitation. The introduction of methyl side groups in the hydrophobic tails increases the fluidity of the bilayer. Depending on the position of the methyl branches partial interdigitation is observed. In the case of bolaamphiphiles, methyl side groups have a similar effect on the fluidity, but interdigitation cannot occur.

Lipid Melting Transitions Involve Structural Redistribution of Interfacial Water

Journal of Physical Chemistry B, 2021

Morphological and gel-to-liquid phase transitions of lipid membranes are generally considered to primarily depend on the structural motifs in the hydrophobic core of the bilayer. Structural changes in the aqueous headgroup phase are typically not considered, primarily because they are difficult to quantify. Here, we investigate structural changes of the hydration shells around large unilamellar vesicles (LUVs) in aqueous solution, using differential scanning calorimetry (DSC), and temperature-dependent ζ-potential and high-throughput angle-resolved second harmonic scattering measurements (AR-SHS). Varying the lipid composition from 1,2-dimyristoyl-sn-glycero-3-phosphocholine(DMPC) to 1,2-dimyristoyl-sn-glycero-3-phosphate (DMPA), to 1,2-dimyristoyl-sn-glycero-3phospho-L-serine (DMPS), we observe surprisingly distinct behavior for the different systems that depend on the chemical composition of the hydrated headgroups. These differences involve changes in hydration following temperature-induced counterion redistribution, or changes in hydration following headgroup reorientation and Stern layer compression.

Thermodynamics of membrane lipid hydration

Pure and Applied Chemistry, 2000

Zwitterionic or polar lipids that form lamellar phases swell in the presence of water to take up between 10 and 30 water molecules per lipid. The degree of the water uptake depends both on the state of the alkyl chains, liquid or solid, and on the nature of the polar group. The swelling behavior has been extensively characterized on the free-energy level through measuring the relation between the chemical potential of the water and the degree of swelling. In spite of the extensive studies of this type, consensus is still lacking concerning the molecular mechanism causing the swelling. The two main ideas that explain the existence of the effectively repulsive force between two opposing bilayers are (i) a water structure effect and (ii) thermal excitations of the lipid molecules. The first is from a thermodynamic perspective caused by a negative partial molar enthalpy of the water, whereas for the second, the repulsion is caused by positive entropy. A further insight into the swelling...