Lipid membranes chemistry

The previous result is an important one. It indicates that there can be yet another fruitful route to describe lipid bilayers. The idea is to consider the conformational properties of a probe molecule, and then replace all the other molecules by an external potential field (see Figure 11). This external potential may be called the mean-field or self-consistent potential, as it represents the mean behaviour of all molecules self-consistently. There are mean-field theories in many branches of science, for example (quantum) physics, physical chemistry, etc. Very often mean-field theories simplify the system to such an extent that structural as well as thermodynamic properties can be found analytically. This means that there is no need to use a computer. However, the lipid membrane problem is so complicated that the help of the computer is still needed. The method has been refined over the years to a detailed and complex framework, whose results correspond closely with those of MD simulations. The computer time needed for these calculations is however an order of 105 times less (this estimate is certainly too small when SCF calculations are compared with massive MD simulations in which up to 1000 lipids are considered). Indeed, the calculations can be done on a desktop PC with typical... 

Figure 5.25 — Flow-through ion-selective optrode based on a multilayer lipidic membrane prepared by the Langmuir-Blodgett method. (A) Cross-sectional view of the composite six-layer membrane (four layers of arachidic acid/ valinomycin covered by an arachidic acid and rhodamine dye bilayer). (B) Optical arrangement integrated with the sensor, which is connected to a flow system. LS light source Ml and M2 excitation and emission monochromator, respectively FI and F2 primary filters M mirror LB lipid-sensitive membrane in a glass platelet FC flow-cell A amplifier D display P peristaltic pump. (Reproduced from [107] with permission of the Royal Society of Chemistry).

The confusion between these two characteristics is common in medicinal chemistry. It comes from the usual empirical measurement of the lipophilicity, which is the logarithm of the partition coefficient between 1-octanol and water (log P). This parameter gives a representative overview of a compound absorbed by a lipidic membrane, an essential datum in medicinal chemistry. It is often considered that the higher the log P value is, the more lipophilic the compound is. Acmally, the log P value is only a measurement of relative solubility. Considering that the solubility of a fluorinated substance decreases more in water than in octanol, this measurement leads one to think that fluorinated compounds are more lipophilic. Actually, this represents the relative lack of affinity of fluorinated compounds for both phases. 

The bimolecular lipid membrane (BLM) produced in aqueous solution described in this paper is of considerable interest for two main reasons. First, the BLM is a new type of interfacial film of ultrathinness. The limiting thickness of BLM is 40-130 A. as estimated from various measurements. The values obtained by optical methods are probably most reliable, indicating that the thickness of the BLM is equal to about twice the length of the lipid molecules. The environment in which the BLM is formed and the molecular orientation at the biface lends itself as a promising tool in understanding some outstanding problems in colloid and interfacial chemistry such as Van der Waals attraction and... 

The bllayer lipid membrane (BLM) has become one artificial membrane model which has permitted extensive investigation of the chemistry associated with the structural lipids present in natural membranes.(1 -2)... 

Kruglyakov, P.M. and Rovin, I.G. "Physical Chemistry of Black Hydrocarbon Fioms - Biomolecular Lipid Membrane, Nauka, Moscow,... 

Ortiz, A. and Gomez-Femandez, J. C. A Differential scanning calorimetry study of the interaction of free fatty acids with phospholipid membranes. Chemistry and Physics of Lipids 45 75-9, 1987. 

Lipid Domains, Chemistry of Receptor Tyrosine Kinases Receptor-Ligand Interactions Receptors, Chemistry of Signal Transduction Across Membranes Virus-Based Drug Delivery... 

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Afonin, S., Durr, U. H. N., Glaser, R. W. and Ulrich, A. S. (2004) Boomerang -like insertion of a fusogenic peptide in a lipid membrane revealed by sohd-state 19F NMR. Magnetic Resonance in Chemistry, 42, 195-203. 

Afonin, S., Durr, U. H. N., Wadhwani, P., et al. (2008) Solid state NMR structure analysis of the antimicrobial peptide gramicidin S in lipid membranes concentration-dependent realignment and self-assembly as a P-barrel, in Topics in Current Chemistry, 273, Bioactive Conformation (ed. T. Peteas) Springer, Berlin, pp. 139-154. 

Fuhrhop, J.-H., Krull, M. (1991). Self-assembling lipid membranes—from planar bilayer sheets to cloth-like aggregates of micellar fibers, Frontiers in Supramolecular Organic Chemistry and Photochemistry (Schneider, H.-J., Diirr, H., eds.), VCH, Weinheim. 

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