Bilayer assembly

VMD is designed for the visualization and analysis of biological systems such as proteins, nucleic acids, and lipid bilayer assemblies. It may be used to view more general molecules, as VMD can read several different structural file formats and display the contained structure. VMD provides a wide variety of methods for rendering and coloring a molecule. VMD can be used to animate and analyze the trajectory of a molecular dynamics (MD) simulation. 

Charych, D. H. Nagy, J. O. Spevak, W. Bednarski, M. D., Direct colorimetric detection of a receptor ligand interaction by a polymerized bilayer assembly, Science. 1993, 261, 585 588... 

Structural characterizations of the immobilized bilayer assemblies are essential for the molecular design of the functional materials. On the bases of the systematic crystallographic investigation of single crystals of double-chain ammonium amphiphiles [9], Okuyama wrote a computer simulation program for the calculation of bilayer structures in cast bilayer films and bilayer thicknesses estimated from the repeating period in the X-ray diffraction data have been exclusively used for structural discussions [10,11]. 

Recently, Okuyama et al. succeeded to prepare single crystals of some azobenzene amphiphiles and decided molecular and aggregation structure of single crystals [14-19], The spectral prediction of the chromophore orientation in the bilayer assemblies were very consistent with the X-ray structural analyses of the single crystals. 

Spectral shift (in wave number Av) of the azobenzene chromophore caused by intermolecular interaction can be estimated by using Kasha s equation (2), which is a function of the transition moment (n), distance between dipoles (r), and number of interacting molecules in bilayer assemblics(V). 

Design of charge transfer complexes in bilayer assemblies... 

In order to verify Okuyama s prediction on molecular orientation in bilayer assemblies, azobenzene amphiphiles having a viologen moiety as a hydrophilic head group, CnAzoCmV2+ 2Br, were newly prepared. Bathochromic shift to 390 nm in the visible absorption band of the... 

Spectral experiments on incorporation of sodium alkylsulfonates as guest molecules into the host bilayer assembly strongly suggest formation of the void space expected in the structural model I. Cast films of 1 1 mixture of CsAzoCioN+Br and sodium n-butylsulfonate (kmax = 303 nm) or sodium propylsulfonate (kmax = 302 nm) showed a similar absorption spectrum of pure C5AzoCjoN+Br cast film (kmax = 301 nm). Longer guest molecules sodium n-pentylsulfonate (kmax = 326 nm), n-hexylsulfonate (kmax = 329 nm), and n-heptylsulfonate... 

Liposome Formation. The pioneering investigations of Bang-ham (5) have shown that thin films of natural phospholipids form bilayer assemblies if they are lyophilized in excess water by simple handshaking above the phase transition temperature. While this procedure results in the formation of large, multibilayered spherical structures, by ultrasonication of such lipid dispersions small unilamellar liposomes are formed (16), which are schematically shown in Figure 10. Additional metTiods for liposome preparation are described in a number of reviews (17,44,45,46). 

Figure 12.3 Colorimetric detection of influenza by sialoside bilayer assembly (2% sialoside lipid 2 and 98% matrix lipid 1). (a) The colorimetric response of the film, supported on a glass microscope slide, is readily visible to the naked eye for quahtative evaluation of the presence of virus. The film on the left (blue) has been exposed to a blank solution of PBS. The film on the right (red) has been exposed to 100 hemagglutinin units (HAU) of vims (CR = 77%). (b) The...

This volume has excellent reviews of biosynthetic pathways to glycerophospholipids and sphingolipids, phospholipid transfer proteins, and bilayer assembly. 

All four types of polymerizable lipids shown in Fig. 4 have been realized synthetically. In this context, one need not attempt to reproduce mother nature slavishly (Fendler 8)). Kunitake 9) was able to show that simple molecules like dialkyldimethyl-ammonium salts also form bilayer assemblies. Fuhrhop 10) and Kunitake U) could accomplish the formation of monolayer liposomes with molecules containing only one alkyl chain and two hydrophilic head groups. Acryloylic and methacryloylic groups (type a and d, Table 1), as well as diacetylenic, butadienic, vinylic and maleic acid groups (type b and c), have been used as polymerizable moieties. A compilation of amphiphilic, photopolymerizable molecules is given in Table 1. 

Polyunsaturated fatty acids were epoxidized less regioselectively, generally <2 1 in favor of the double bond closer to the hydrophobic terminus. This result can be explained by a well known decrease of the rigidity of phospholipid bi layers on the addition of unsaturated fatty acids. However, when less than 20% cholesterol was added to the bilayer assembly the rigidity increased significantly and thus the regioselectivity. 

Murakami et al. studied alternative pyridoxamine-surfactant systems [23]. These authors synthesized hydrophobic pyridoxamine derivatives (30 and 31) and peptide lipid molecules (32-35). Catalyst 30 or 31 and the peptide lipids formed bilayer membranes in water, which showed transamination reactivity in the presence of metal ions such as Cu(ii). It was proposed that the pyridoxamine moiety was placed in the so-called hydrogen-belt domain interposed between the polar surface region and the hydrophobic domain that is composed of double-chain segments within the bilayer assembly. The basic group (such as imidazole) in the peptide lipid molecules could catalyze the proton transfer involved in the transamination reaction. In addition, marked substrate discrimination by these bilayer membrane systems was performed through hydrophobic interactions between substrates and the catalytic site. 

Murakami et al. have utilized Mayer vesides to study aldolase-type reactions [48]. Formation of [i-phenylserinc from glydne and benzaldehyde proceeded effectively by cooperative catalysis of a hydrophobic pyridoxal derivative (47) and Zn(n) ions in the bilayer vesicle formed with 32. The threo isomer was dominantly produced over the erythro form. A marked enantioselectivity was observed in the co-veside of 32 and 35 in combination with 47 and Cu(ii) the ee for formation of (2S,3R)-P-phcnylscrinc over its enantiomeric (2R,3S)-isomer was 58%. Enantioselectivity also arose with another bilayer assembly, formed with 32, 35, and 37 in the presence of Cu(ii), where the (2R,3S) isomer was dominant over the (2S,3R) species in 13% ee. The opposite enantioselectivity performed by the second system, as compared with that for 47, might reflect a different stereochemical environment around the quinoid intermediate that allows the attack of benzaldehyde. 

T. Kunitake, Y. Okahata, M. Shimomura, S. Yasunami, K. Takarabe, Formation of Stable Bilayer Assemblies in Water from Single-Chain Amphiphiles Relationship between the... 

Y. Ishikawa, H. Kuwahara, T. Kunitake, Self-Assembly of BUayers from Double-Chain Fluorocarbon Amphiphiles in Aprotic Organic Solvents Thermodynamic Origin and Generalization of the Bilayer Assembly , J. Am. Chem. Soc., 116,5579 (1994)... 

Fig. 6.6. Schematic illustration of molecular imprinting of proteins on the surface of a metal-coordinating bilayer assembly.

Shinomura, M., Ando, R., and Kunitake, T. (1983) Orientation and spectral characteristics of the azohenzene chromophore in the ammonium bilayer assembly. Ber. Bunsenges. Physik. Chem. 87, 1134-1143. ... 

Names given to differentiate between supramolecular mono- and bilayer assemblies should be clear and relate to structure in a simple and general way. Micelle (Latin mic(a), grain -t- ella, diminutive suffix) indicates nothing but the ultimate smallness of these assemblies. The word microemulsion (Greek micro, small Latin emulsus, milked out) evokes a milk-like aqueous system containing (fat) droplets similar to those found in milk but much smaller. Both names produce, to a first approximation, an appropriate impression of the real systems. 

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