Membrane mimetic media

Structural and energetic properties of studied molecules strongly depend on the solvent membrane-mimetic media significantly promote formation of a-helices capable of traversing the bilayer, whereas a polar environment destabilizes a-helical conformation via reduction of solvent-exposed surface area and packing. 

Membrane-mimetic compartments have provided a viable means for generating monodispersed catalytic particles [500], In particular, reversed micelles and microemulsions have been used extensively as hosts. A complete summary of work reported on the in situ generation of catalysts in membrane-mimetic media, including publications up to 1987, has been produced [500] and, therefore, will not be reiterated here. Attention will be focused on more recent research utilizing monolayers, bilayer lipid membranes (BLMs), Langmuir-Blodgett (LB) films, zeolites, and clay particles as membrane-mimetic templates. 

Artificial biomembrane mimetic model systems are used to characterize peptide-membrane interactions using a wide range of methods. Herein, we present the use of selected membrane model systems to investigate peptide-membrane interactions. We describe methods for the preparation of various membrane mimetic media. Our applications will focus on small unilamellar vesicles (SUVs) and large unilamellar vesicles (LUVs) as well as on media more suited for nuclear magnetic resonance (NMR) techniques, micelles, and fast-tumbling two-component bilayered micelles (bicelles). 

This paper represents a progress report on our beginning research in the exciting area of electrocatalysis in membrane mimetic media. Ongoing work is aimed at exploring the use of oil-in-water and water-in-oil microemulsions, and vesicles, and at controlling the formation of surface aggregates. 

Reverse micelles can also act as a convenient membrane mimetic medium for studying membrane interactions of bioactive peptides [329,330]. Fluorescence behavior of piroxicam in AOT-RMs and Triton X-100 microemulsions was investigated by Andrade and Costa [331].Dutta etal. [332] studied the interactions of an antileprotic drug dapson in dipalmitoyl phosphotidyl choline (DPPC)-RMs in chloroform. The DPPC was found to form RMs just beyond 6 mmol 1" concentration, which is relatively low compared to conventional AOT concentration. 

The supporting medium (aqueous or organic solvents membrane-mimetic compartments) also has a profound influence on the optical and electro-optical properties of nanosized semiconductor particles. This dielectric confinement (or local field effect) originates, primarily, in the difference between the refractive indices of semiconductor particles and the surrounding medium [573, 604], In general, the refractive index of the medium is lower than that of the semiconductor particle, which enhances the local electric field adjacent to the semiconductor particle surface as compared with the incident field intensity. Dielectric confinement of semiconductor particles also manifests in altered optical and electro-optical behavior. 

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. 

Biomimetic artificiai membranes-factors Effects of pH and co-solvents on the BAMPA were investigated to determine the optimal conditions for the prediction of oral absorption. The permeability (Pam) of 33 structurally diverse drugs to the PC/PE/ PS/PI/CHO/1,7-octadiene membrane system [bio-mimetic lipid (BML) membrane] was measured at pH 5.5,6.5, and 7.4. The pH dependence of Pam was in accordance with the pH partition theory. The better prediction of oral absorption (fraction of a dose absorbed) was shown under the pH 5.5 condition for determining the permeability of poorly soluble compounds were examined. Dimethysulfoxide (DMSO), ethanol (EtOH) and polyoxyethyleneglycol 400 (PEG 400) were added up to 30% to the transport medium as solubilizers. DMSO, EtOH and PEG 400 decreased Pam of hydrocortisone and propranolol. For example, DMSO (30%) decreased Pam of hydrocortisone and propanol by 60 and 70%2, respectively. DMSO and PEG 400 also decreased Pam of ketoprofen. In contrast, EtOH produced an opposite effect on permeability, that is, an increased Pam of ketoprofen. Therefore, the high concentration of these co-solvents could lead to the under- or overestimation of drug permeability. 

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