Membrane, artificial models

THE CASE FOR THE IDEAL IN VITRO ARTIFICIAL MEMBRANE PERMEABILITY MODEL... 

The Ideal in vitro Artificial Membrane Permeability Model... 

Abstract To understand how membrane-active peptides (MAPs) function in vivo, it is essential to obtain structural information about them in their membrane-bound state. Most biophysical approaches rely on the use of bilayers prepared from synthetic phospholipids, i.e. artificial model membranes. A particularly successful structural method is solid-state NMR, which makes use of macroscopically oriented lipid bilayers to study selectively isotope-labelled peptides. Native biomembranes, however, have a far more complex lipid composition and a significant non-lipidic content (protein and carbohydrate). Model membranes, therefore, are not really adequate to address questions concerning for example the selectivity of these membranolytic peptides against prokaryotic vs eukaryotic cells, their varying activities against different bacterial strains, or other related biological issues. 

Dibbern HW, Scholz GH (1969) Resorption model experiments with artificial lipoid membranes. 3. Model experiments for gastroenteral resorption. Arzneimittelforschung 19 1140-1145... 

One decade has passed since the parallel artificial membrane permeation assay (PAM PA) was first introduced in 1998 [47]. Since then, PAM PA rapidly gained wide popularity in drug discovery [3, 48-51]. Today, PAMPA is the most widely used physicochemical membrane permeation model. The term PAMPA is nowusedas the general name for a plate-based (HTS enabled), biter-supported (filter immobilized) artificial membrane. Typically, phospholipids dissolved in an organic solvent are impregnated into the filter to construct a PAMPA membrane. 

The points noted in this section are necessarily of a very limited range of vision. Most probably the real biological membrane is of much more complex nature than the artificial model systems. Yet the approaches sketched here may also have initiated the application of electrochemical methods to more practical cases [115]. 

Multilamellar vesicles are the most commonly used model membrane systems. It is important to note that in order to simplify the parameters of the study, in most cases the model membranes are prepared exclusively ftom phospholipids and they do not contain other molecules, usually present in biological membranes that have an important role in their fiinctionality. The complexity of real membranes is not close to the artificial model membranes and these systems, i.e. liposomes, are not an absolute analog of the biological membranes. 

Organic chemists rely on amphiphilic lipids to build up membranes in water—the only organic reaction medium of nature. Biological molecular machinery is based on lipid membrane potentials. Artificial models so far do not work like cell membranes in vectorial transport and charge separation chains, but they look good under the electron microscope. 

The artificial model of a cell membrane was prepared using biomimetic PHB and the calcium polyphosphate complex (poly-P) incorporated into lipid bilayers of 1,2-dierucoylphosphatidylcholine. It was found that PHB/poly-P channels show high conductance for Ca and Na cations . 

Artificial Membrane Permeability Models Immobilized Artificial Membranes... 

In the last few years there has been a dramatic increase in interest in the molecular structure of biological membranes. While model systems composed of artificially prepared (or isolated) amphiphihc materials and associated colloids serve a very useful purpose, a better understanding of the reality of biological systems would be invaluable in many areas of biochemistry, medicine, pharmaceuticals, and other fields. While it is reasonably easy to determine the constituents of a biological membrane, elucidating just how the various components are put together, how they interact, and their exact function within the membrane represents a decidedly more difficult task. 

Curdo S, Calabro V, lorio G (2006b), Reduction and control of flux decline in cross-flow membrane processes modeled by artificial neural networks , /. Membrane ScL, 286(1-2), 125-132. 

The stractural and functional complexity of biomembranes has ehal-lenged researehers to develop simpler artificial models to mimie their properties. Amphiphilic block copolymers are of particular interest, beeause of the dual environmental affinity that is associated with covalently bound hydrophobie and hydrophilic blocks. These strive to minimize their eontaet, and therefore drive self-assembly into assemblies with different arehi-teetures. Based on their chemical specificity, as for example the hydrophilie-to hydrophobie ratio, amphiphilic block copolymers can self-assemble in dilute aqueous solutions into micelles, vesicles, tubes, wire-like structures, nanopartieles, or planar membranes at water-air interfaces. Synthetic membranes have greater mechanical stability than phospholipids because of the higher moleeular weight (Mw) of amphiphilic block copolymers, and thus are thicker and stiffer than lipid bilayers. 

There has been a dramatic increase in interest in the molecular structure of biological membranes. While model systems composed of artificially prepared (or isolated) amphiphilic materials and associated colloids serve a very useful purpose, a... 

In the biological field, much attention has been directed toward the transport phenomena through membrane. Although the function of some natural ionophores has been known, the investigation of active and selective transport of ions using the artificial ionophores in the simple model systems may be important to simulate the biological systems and clarify the transport behaviour of natural membranes. 

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