Membrane-mimetic system

Montenegro, M.A. Nazareno, M.A Durantini, E.N. Borsarelli, G.D. (2002). Singlet oxygen quenching ability of carotenoids in a reverse micelle membrane mimetic system. Photochemistry and Photobiology, Vol. 75, No. 4, (April 2002), pp.353-361, ISSN 0031-8655... 

Kosol S, Zangger K (2010) Dynamics and orientation of a cationic antimicrobial peptide in two membrane-mimetic systems. J Struct Biol 170 172-179... 

Hink M. and Visser A. J. W. G. (1999) Characterization of Membrane Mimetic Systems with Fluorescence, in Rettig W. et al. (Eds), Applied Fluorescence in Chemistry, Biology and Medicine, Springer-Verlag,... 

Creative interplay between colloid and polymer chemistries has increasingly contributed to the development of membrane-mimetic systems and advanced materials. On the one hand, the employment of polymer methodologies and/or the addition of polymers have favorably altered the properties of colloidal systems. On the other hand, the introduction of surfactants and surfactant assemblies prior, during, or subsequent to polymerization has resulted in distinctly different polymers. 

Construction of artificial systems which imitate the essentia] functions of biological membranes molecular compartmentalization, organization, and discrimination. Advanced materials are in situ generated in, or incorporated into, membrane-mimetic systems. A molecular-level understanding of the membrane-mimetic hosts and the advanced-material guests is a given. 

Generally refers to the change from a crystalline to a liquid-like state in membranes and membrane-mimetic systems. The temperature (or the range of temperatures) at which the crystalline phase is converted to the liquid phase is referred to as the phase transition temperature. 

Reviews have already been published by J. H. Fendler on Polymerized Surfactant Vesicles 91 92,931 which refer to Novel Membrane Mimetic Systems , synthetic strategies leading to them and their characterization and potential utilization in various areas such as solar energy conversion and reactivity control. It is the intend of this appendix to bring the reader up to date on the state of the art of polymerized liposomes. 

Micelles and microemulsions have been explored as membrane mimetic systems since they possess charged microscopic interfaces which act as barriers to the charge recombination process (Fendler et al., 1980 Hurst et al., 1983). Namely, the influence of the location of the sensitizer on photoinduced electron transfer kinetics and on charge separation between photolytic products in reversed micelles has been studied (Pileni etal., 1985). 

Substrate organization in membrane mimetic systems leads to altered solvation, ionization and reduction potentials and, hence, to altered reaction rates, paths and stereochemistries. These properties have been advantageously exploited, in turn, for reactivity control, catalysis, drug delivery and artificial photosynthesis (8). There are only limited examples of the utilization of membrane mimetic systems in permeability control. In order to gain insight into this important area, we have initiated a research program in BLMs. A status report of our activities in this area will be summarized in the next section. 

Chatenay, D., Urbach, W., Cazabat, A. M., Vacher, M., and Waks, M., 1985, Proteins in membrane mimetic systems. Insertion of myelin basic protein into microemulsion droplets, Biophys. J. 48 893-898. 

Most of the difficulties outlined above can be avoided by considering a simplified system in which the membrane is replaced by a lamella of an alkane, e.g., hexane or octane, of the same width as the bilayer [80-84]. These membrane-mimetic systems capture the most important characteristic of the water-membrane system — the coexistence of a polar, aqueous phase and a nonpolar medium in close association. The utility of membrane-mimetics is underscored by experimental studies, which have shown that peptides built of L-leucine and L-lysine fold into the same secondary structures at a water-membrane and as at a water-hydrocarbon interface [85-87]. However, such model systems also have important limitations, chief among which are the absence of specific, electrostatic interactions between the protein and the lipid head groups and the effects of membrane ordering on protein behavior. 

The structure and stability of several other channels have also been addressed in computer simulations. In a recent study of the HIV-Vpu transmembrane domain in a water-octane system [84], the calculations were started in a pentameric, coiled-coil bundle that had been suggested as the equilibrium structure, based on simulations of the bundle with water-caps and restraining forces [125]. After initial equilibration periods of 0.5-1.5 ns, the bundle evolved into a conical structure that resembled the K+ channel [117]. This structural rearrangement had a significant effect on the channel region while the initial coiled-coil contained a continuous column of water, most of the water was expelled from the conical structure breaking a continuous water path across the channel. Similar slow relaxation times were seen in simulations of tetrameric bundles of LS3 channels in a water-octane membrane-mimetic system [82], These simulations were started... 

In general, atomic-level computer simulations of channels in membranes or membrane-mimetic systems have proven to be quite useful in refining model structures, often postulated somewhat ad hoc. However, full assessments of channel stability from simulations on the currently accessible timescales is not nearly as reliable. Owing to the long relaxation times required to equilibrate membrane-bound systems, it is not currently feasible to arrive at the correct, equilibrium structure starting from an arbitrary initial conditions. Even if the potential energy functions used in simulations were accurate, correct results could be expected only if the initial and equilibrium structures were not too different. 

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