Mimic of biological membranes

Hosts such as crown ethers and cryptands are useful as phase transfer agents and mimics of biological membrane transporting ionophores. 

Pure lipid membranes are electrical insulators with a specific capacitance of 1 tiF/cm, which separate two electrolytic compartments. The conductance of biological membranes is maiifly determined by highly specialized proteins that act as ion chaimels. For supported membranes to mimic the electrical properties of a biological membrane, it is necessary to measure its electrical characteristics. Even very small defects that are not... 

Compare the selectivity of the best synthetic membranes and ligands for separating ions with the specificities that are achieved by biological membranes. How might we mimic the biological membranes more successfully ... 

Log Kow is the most widely used descriptor for baseline QSARs but has many disadvantages in the context of our model. First, because octanol does not perfectly mimic the physicochemical properties of biological membranes, there are two different QSAR equations for nonpolar and polar compounds. This complication can be overcome by using the liposome-water partition coefficient log Kupw as the descriptor instead [32]. We therefore recalculated the Kow-based QSARs from the EU Technical Guidance Documents [31] using relationships between log Kow and logKupw for nonpolar (Eq. 9) and polar compounds (Eq. 10), which had been experimentally determined by Vaes et al. [33,34]. 

The membrane with the nanometer-sized holes can be used as template of metallic replicas. The holes are filled up with some metal atoms by electrolysis in a galvanic cell, and after deposition, the membrane is removed mechanically or by a suitable solvent. In these ways, little rods with a few pm length and few times 10 nm diameters are produced (Tagawa et al. 2004 Coqueret 2008). By grafting environmental sensitive polymers on the surface of the holes, the permeability of the membrane can be regulated by external signal (temperature, pH, etc.). The operation of such systems may mimic, the operation of biological membranes. 

L-B films are useful in biological studies, as they can easily be prepared to act as mimics of hpid membranes. Thus, modified electrodes of this type are often used in studies of transport phenomena (16) and enzyme activity. These electrodes are also often used as molecular recognition sensors (17-20) and in molecular electronics (20-22). 

A modified carbon paste electrode (CPE) using asolectin, cytochrome c, and cytochrome oxidase were applied for amperometric determination of cyanide [56]. The modified CP matrix mimics a biological membrane environment. The sensor, polarized at —0.15 V versus Ag/AgCl, generates the reduced form of cytochrome c, which in turn is oxidized by the enzyme cytochrome oxidase. The resulting current is related to the enzyme activity and is depressed by inhibitors of cytochrome oxidase such as cyanide. Concentrations of cyanide as low as 0.5 pM can be measured with half-maximal response at about 12 pM. The inhibition is reversible and reproducible (RSD = 4%), allowing cyanide determination for more than 2 months using the same probe. Possible use of this biosensor in flow systems was illustrated. 

The adliesion and fiision mechanisms between bilayers have also been studied with the SEA [M, 100]. Kuhl et al [17] found that solutions of short-chained polymers (PEG) could produce a short-range depletion attraction between lipid bilayers, which clearly depends on the polymer concentration (fignre Bl.20.1 It. This depletion attraction was found to mduce a membrane fusion widiin 10 minutes that was observed, in real-time, using PECO fringes. There has been considerable progress in the preparation of fluid membranes to mimic natural conditions in the SEA [ ], which promises even more exciting discoveries in biologically relevant areas. 

Desalination of sea water, or purification to eliminate dangerous ionic contaminants from industrial waste water involves important technological, scientific and financial risks. Most of them are related to the development of cheaper smart membranes that can mimic biological membranes. 

Recently, unique vesicle-forming (spherical bUayers that offer a hydrophilic reservoir, suitable for incorporation of water-soluble molecules, as well as hydrophobic wall that protects the loaded molecules from the external solution) setf-assembUng peptide-based amphiphilic block copolymers that mimic biological membranes have attracted great interest as polymersomes or functional polymersomes due to their new and promising applications in dmg delivery and artificial cells [ 122]. However, in all the cases the block copolymers formed are chemically dispersed and are often contaminated with homopolymer. 

The majority of CYP enzymes are located in a hydrophobic environment in the endoplasmic reticulum of cells, although cytosolic enzymes also exist, such as CYP101. In order to mimic the physiological environment of CYP enzymes, a number of groups have used phospholipids to construct biosensors such as DDAB, dimeristoyl-L-a-phosphatidylcholine (DMPC), dilauroylphosphatidylethanolamine (DLPE) and distearoylphosphatidylethanolamine (DSPE). Phospholipid layers form stable vesicular dispersions that bear structural relationship with the phospholipid components of biologically important membranes. By this way a membranous environment is created that facilitates electron transfer between the enzyme s redox center and the electrode. 

From the information given above it is obvious that cell surfaces display an enormous complexity. A perfect model to study the interaction of a peptide with a biological membrane would require knowledge about the cell membrane composition in that particular tissue. Even if such information were available it will most probably not be possible to fully mimic the biological environment. However, some important aspects may still be studied with the available models. Whenever possible, one should try to relate the information derived from such a model to information gained from biological data taken on real cells (cell-lines) such as binding affinities etc. in order to prove the validity of the model for the study of a particular aspect. 

In spite of the overwhelming importance of the channel mechanism for the transport of alkali and alkaline earth metal ions in biological systems, only carrier transport has been studied extensively by chemists. Studies on ion channel mimics of simple structures have long been limited to antibiotic families of gramicidin, amphotericin B, and others. Several pioneers have reported successful preparation of non-peptide artificial channels. However, their claims have been based on kinetic characteristics observed for the release of metal ions through liposomal membrane and lacked the very critical proofs of channel formation. Such a situation was... 

A double-carrier membrane system that mimics, in principle, the function of Na, K -ATPase in biological membranes was developed, although chemical compounds involved are completely different (Figure 35). The double-carrier system utilizes dicylohexyl-18-crown-6 (93) and trioctylamine (95) for enhanced transport of K ions from the feed to the receiving solution using picrate ion (pic ) as the pumping ion. The carrier 93 is for uphill transport of using a concentration... 

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