Bilayer chemistry

Shibata A, Kiba Y, Akati N, Fukuzawa K, and Terada H. 2001. Molecular characteristics of astaxanthin and P-carotene in the phospholipid monolayer and their distributions in the phospholipid bilayer. Chemistry and Physics of Lipids 113(1-2) 11-22. 

Formation of a bilayer structure is therefore driven by the self-assembhng behavior of amphiphilic molecules or molecular complexes. This research topic started from the dispersion of naturally-occurring phosphohpids in aqueous media, but the development of molecular design and systematic research has lead to the study of bilayer chemistry in various media. 

Marsh, D. (2006) Elastic curvature constants of lipid monolayers and bilayers. Chemistry and Physics of Lipids, 144 (2), 146-159. 

There has been a surge of research activity in the physical chemistry of membranes, bilayers, and vesicles. In addition to the fundamental interest in cell membranes and phospholipid bilayers, there is tremendous motivation for the design of supported membrane biosensors for medical and pharmaceutical applications (see the recent review by Sackmann [64]). This subject, in particular its biochemical aspects, is too vast for full development here we will only briefly discuss some of the more physical aspects of these systems. The reader is referred to the general references and some additional reviews [65-69]. 

Michaelides A, Alavi A, King DA. 2003. Different surface chemistries of water on RufOOOl From monomer adsorption to partially dissociated bilayers. J Am Chem Soc 125 2746-2755. 

Jemiola-Rzeminska M, Pasenkiewicz-Gierula M, and Strzatka K. 2005. The behaviour of beta-carotene in the phosphatidylcholine bilayer as revealed by a molecular simulation study. Chemistry and Physics of Lipids 135(1) 27-37. 

Nakano, M., Kamo, T., Sugita, A. and Handa, T. (2005) Detection of bilayer packing stress and its release in lamellar-cubic phase transition by time-resolved fluorescence anisotropy. Journal of Physical Chemistry B, 109 (10), 4754—4760. 

Regev, D., Backov, R. and Faure, C. (2004) Gold nanopartides spontaneously generated in onion-type multilamellar vesides bilayers. Particle coupling imaged by cryo-TEM. Chemistry of Materials, 16, 5280-5285. 

A second approach with respect to anisotropic flavin (photo-)chemistry has been described by Trissl 18°) and Frehland and Trissl61). These authors anchored flavins in artificial lipid bilayers by means of C18-hydrocarbon chains at various positions of the chromophore. From fluorescence polarization analysis and model calculations they conclude, that the rotational relaxation time of the chromophore within the membrane is small compared to the fluorescence lifetime (about 2 ns74)). They further obtain the surprising result that the chromophore is localized within the water/lipid interface, with a tilt angle of about 30° (long axis of the chromophore against the normal of the membrane), irrespective of the position where the hydrocarbon chain is bound to the flavin nucleus. They estimate an upper limit of the microviscosity of the membrane of 1 Poise. 

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... 

Much of industrial chemistry takes place in organic solvents, or involves apolar compounds. Biocatalysis, in contrast, typically involves aqueous environments. Nevertheless, enzymes and microorganisms do in fact encounter apolar environments in Nature. Every cell is surrounded by at least one cell membrane, and more complex eukaryotic cells contain large amounts of intracellular membrane systems. These membranes consist of lipid bilayers into which many proteins are inserted present estimates, based on genomic information, are that about one-third of all proteins are membrane proteins, many of which are so-called intrinsic proteins that are intimately threaded through the apolar bilayer. These proteins are essentially dissolved in, and function partly within, an apolar phase. 

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).

Fendler JH (1982) Membrane mimetic chemistry characterizations and applications of micelles, microemulsions, monolayers, bilayers, vesicles, host-guest systems, and polyions. Wiley, New York... 

Much interest for ion transport has its origin in the field of crown ether chemistry. Therefore, most model studies of ion channels have been more or less based on crown ether chemistries. Pioneering work has been undertaken by Fylcs, who not only synthesized varieties of gigantic molecules starting from crown ethers, " but established a method of the rate assay for ion transport across lipid bilayer membranes, a pH sCat technique. Vesicles having different inside and outside... 

Figure 12.16 Typical planar bilayer Na+ conductance traces for 10 pmol 12.36 at +50 mV (top trace) and -50 mV (bottom trace) in aqueous buffer using symmetrical KC1 conditions. The arrows at the left hand side of the traces indicates the current level of the closed state. Peaks indicate the opening of individual ion channels (reproduced by permission of The Royal Society of Chemistry).

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