Bilayer inhomogenous

When liposomes are prepared from a molecular mixture of lipid components it is important that all lipids be homogeneously dissolved in an organic solvent in order to obteiin bilayers with evenly distributed lipids after hydration. For example, the solubilities of phosphatidylcholine and cholesterol in chloroform are similar their solubility in benzene differs. Upon removal of benzene from the lipid solution an inhomogeneous lipid film is formed on the glass wall and... 

S-layer cover prevents the formation of inhomogenities in the bilayer [137]... 

As a consequence, the presentation of the results will also differ from that in a MD or MC box, where a full set of molecules can be depicted (as snapshots). In an SCF model, all properties will be presented in, for example, (average) numbers of molecules per unit area of the membrane, or equivalent, i.e. the (average) densities of molecules as a function of the z-coordinate. The box thus consists, if one insists, only of one coordinate. For this reason, we can refer to this method as a one-gradient SCF theory or simply 1D-SCF theory. Extensions towards 2D-SCF are available, where lateral inhomogeneities in the bilayer can also be examined [80], There are even implementations of 3D SCF-like models, but here the interpretation is somewhat more delicate [78],... 

Meanwhile, computational methods have reached a level of sophistication that makes them an important complement to experimental work. These methods take into account the inhomogeneities of the bilayer, and present molecular details contrary to the continuum models like the classical solubility-diffusion model. The first solutes for which permeation through (polymeric) membranes was described using MD simulations were small molecules like methane and helium [128]. Soon after this, the passage of biologically more interesting molecules like water and protons [129,130] and sodium and chloride ions [131] over lipid membranes was considered. We will come back to this later in this section. 

Photophysical studies allow the measurement of rate constants for transmembrane electron transfer. The distributed kinetics observed in describing the decay of photovoltage across a BLM is consistent with a highly inhomogeneous disposition of donors and relays within the membrane [111, 112]. A typical value for the rate constant for electron transfer across a BLM (about 10 sec-1) would predict a spatial separation of about 10 A, whereas the thickness of the bilayer is usually about 40-50 A. This apparent discrepancy can be resolved if transmembrane electron transfer occurs by several sequential steps involving deeply buried redox sites, thus decreasing the operational tunnelling distance [113]. 

The transition between the monolayer and bilayer formation is rather gradual. Local inhomogeneities of the solid surface will produce wide size distributions of hemimicelles. 

The SSH signal is obtained as long as the molecule stays in an inhomogeneous region, i.e., at the lipid bilayer. Above the transition temperature of the lipids, the SSH signal decays in a time scale of 100 s, which denotes the residency time of the probe in the bilayer or the time taken by the probe to diffuse through the bilayer membrane from bulk water to the iimer water pool. For lipids below... 

MAGIC ANGLE SAMPLE SPINNING IN INHOMOGENEOUSLY BROADENED SPIN SYSTEMS— APPLICATION TO UNSONICATED PHOSPHOLIPID BILAYERS. 

More recently, it has been emphasized that inhomogeneous distribution or phase separation in fluid multicomponent lipid membranes could cause structural transformations from lamellar to intermediate nonlamellar phases or to bicontinuous bilayer phases of nonuniform interfacial curvature [30]. An example of a lipid mesophase with nonperiodic organization is the sponge (L3) phase [31,32]. The sponge (L3) mesophase appears to be an isotropic fluid devoid of... 

Silicon substrates have been covered by a closed S-layer lattice and subsequently bilayers have been deposited by the Langmuir-Blodgett technique [142-144]. The lateral diffusion of fluorescently labeled lipid molecules in both layers has been investigated by fluorescence recovery after photo-bleaching studies [145]. In comparison with hybrid lipid bilayers (lipid monolayer on alkylsilanes) and lipid bilayers on dextran, the mobility of lipids is highest in S-layer-supported bilayers. Furthermore, an S-layer cover causes an enhanced mobility of the labeled molecules in the adjacent lipid layer. In addition, the S-layer cover can also prevent the formation of cracks and other inhomogenities in the bilayer [21,145]. 

Another type of inclusion relates to polymers attached covalently to a fraction of the lipids of the bilayer. If these lipid anchors are far apart, the membrane tries to bend away from the polymer in order to increase the volume available to the fluctuating polymer. Therefore, the polymer creates a local spontaneous curvature [42]. If the polymers become denser, the membrane gets effectively thicker which leads to a strong increase of the bending rigidity. If such a decorated membrane forms a nonspherical vesicle, coupling between polymer composition and local curvature will lead to an inhomogeneous distribution of the anchored polymers. 

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