Liquid ordering

Scheme 2.2-1 Typical ions making up ionic liquids, ordered according to their...

The liquid-ordered gel-like state of liposomes is stabilized by S-layer coating [123]... 

Recently, due to increased interest in membrane raft domains, extensive attention has been paid to the cholesterol-dependent liquid-ordered phase in the membrane (Subczynski and Kusumi 2003). The pulse EPR spin-labeling DOT method detected two coexisting phases in the DMPC/cholesterol membranes the liquid-ordered and the liquid-disordered domains above the phase-transition temperature (Subczynski et al. 2007b). However, using the same method for DMPC/lutein (zeaxanthin) membranes, only the liquid-ordered-like phase was detected above the phase-transition temperature (Widomska, Wisniewska, and Subczynski, unpublished data). No significant differences were found in the effects of lutein and zeaxanthin on the lateral organization of lipid bilayer membranes. We can conclude that lutein and zeaxanthin—macular xanthophylls that parallel cholesterol in its function as a regulator of both membrane fluidity and hydrophobicity—cannot parallel the ability of cholesterol to induce liquid-ordered-disordered phase separation. 

Subczynski, W. K., A. Wisniewska, J. S. Hyde, and A. Kusumi. 2007b. Tree-dimensional dynamic structure of the liquid-ordered domain in lipid membranes as examined by pulse-EPR oxygen probing. Biophys. J. 92 1573-1584. 

Belostotskii VF, Bemkin VM (1988) Ordre dans les solutions solides au cours de la deformation par les ultrasons aux temperatures de l helium liquide Ordering in solid solution during ultrasonic deformation at liquid helium temperatures. Metallokfizika 10(6) 99-101... 

Pseudo-glycolipids. The interest for glycolipids is connected with their occurrence in biological systems, as well as their physicochemical properties, the two viewpoints being sometimes correlated. For example in membranes, lipid rafts are sub-domains which contain liquid-ordered phases.73... 

There is a large cholesterol concentration gradient in cells from 0-5 mol% in the ER membrane to 25-40 mol% in the plasma membrane [12], Cholesterol has a condensing effect on liquid-crystalline bilayers, causing increased rigidity and thickness [13]. At high concentrations, cholesterol induces an intermediate liquid-ordered phase between the gel and liquid-disordered phases [13]. A number of... 

McMullen, T.P.W., Lewis, R.N.A.H., McElhaney, R.N. Cholesterol-phospholipid interactions, the liquid-ordered phase and lipid rafts in model and biological membranes. Curr. Opin. Colloid Interface Sci. 2004, 8, 459-68. 

Although the lipid bilayer structure is quite stable, its individual phospholipid and sterol molecules have some freedom of motion (Fig. 11-15). The structure and flexibility of the lipid bilayer depend on temperature and on the kinds of lipids present. At relatively low temperatures, the lipids in a bilayer form a semisolid gel phase, in which all types of motion of individual lipid molecules are strongly constrained the bilayer is paracrystalline (Fig. ll-15a). At relatively high temperatures, individual hydrocarbon chains of fatty acids are in constant motion produced by rotation about the carbon-carbon bonds of the long acyl side chains. In this liquid-disordered state, or fluid state (Fig. 11—15b), the interior of the bilayer is more fluid than solid and the bilayer is like a sea of constantly moving lipid. At intermediate temperatures, the lipids exist in a liquid-ordered state there is less thermal motion in the acyl chains of the lipid bilayer, but lateral movement in the plane of the bilayer still takes place. These differences in bilayer state are easily observed in liposomes composed of a single lipid,... 

Lipids in a biological membrane can exist in liquid-ordered or liquid-disordered states in the latter state, thermal motion of acyl chains makes the interior of the bilayer fluid. Fluidity is affected by temperature, fatty acid composition, and sterol content. 

Dissolution of alkali metal cations such as Cs+ results in short-range liquid order in water as a primary solvation shell of about eight water molecules is established about the metal cation. Lithium, however, exerts a much greater polarising power and is capable of organising a first- and second-coordination sphere of about 12 water molecules about itself, resulting in a much larger hydrated radius for the ion and hence decreased ionic mobility. 

The model of the solution behaviour of liquid clathrates that appears to best fit the observations is depicted in Figure 13.26. Large regions of liquid order exist in which cations and anions interact strongly with one another. This prevents simple dissolution, but association into aggregates such as dimers and trimers (possibly leading to crystal nucleation) is also prevented by the steric properties of the anions and/or cations. The role of the aromatic solvent is to support the structure and stabilise... 

From your understanding of the non-covalent interactions outlined in Chapter 1, discuss the driving force behind the formation of surface monolayers, micelles and other forms of liquid order. 

Ahmed, S.N., Brown, D.A., and London, E. (1997) On the origin of sphingolipid/cholesterol-rich detergent-insoluble cell membranes physiological concentrations of cholesterol and sphingohpid induce formation of a detergent-insoluble, liquid-ordered lipid phase in model membranes. Biochemistry 36 10944-10953. 

Quantitative investigation of recognition of this pair of liposomes was performed with isothermal titration microcalorimetry (ITC). It has been found that one-to-one binding between adenine and barbituric acid in the lipid/water/lipid interface occurs. However at T= 58°C, above the main lipid phase transition, the situation is different and no liposomal binding is detected. This is mainly due to the molecular disorder within the bilayer (liquid-disordered/liquid ordered phase coexistence) that limits the capacity of complementary moieties to bind, due to the weakening of the hydrogen bonds at these high temperatures. 

Lipid rafts are thought to participate in signal transduction by forcing specific types of proteins that partition into the liquid ordered environment into close proximity with... 

La liquid-ordered phase bilayers prepared from binary mixtures of the same phosphatidylcholine and cholesterol but is much slower ( 10 s ) in Lx liquid-ordered phase membranes prepared from sphingomyelin and cholesterol (55). The activation free energy for the process, which corresponds to the energy necessary to put the translocating lipid molecule at the bilayer mid-plane, is 100kJmol In contrast, the rate constant for transmembrane translocation of cholesterol may be 1 s (56). 

Moreno MJ, Estronca LMB, Vaz WLC. Translocation of phospholipids and dithionite permeability in liquid-ordered and liquid-disordered membranes. Biophys. J. 2006 91 873-881. 

---