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Polar Surface (polar + surface)
Selected AbstractsLiposome/water lipophilicity: Methods, information content, and pharmaceutical applicationsMEDICINAL RESEARCH REVIEWS, Issue 3 2004Georgette Plemper van Balen Abstract This review discusses liposome/water lipophilicity in terms of the structure of liposomes, experimental methods, and information content. In a first part, the structural properties of the hydrophobic core and polar surface of liposomes are examined in the light of potential interactions with solute molecules. Particular emphasis is placed on the physicochemical properties of polar headgroups of lipids in liposomes. A second part is dedicated to three useful methods to study liposome/water partitioning, namely potentiometry, equilibrium dialysis, and 1H-NMR relaxation rates. In each case, the principle and limitations of the method are discussed. The next part presents the structural information encoded in liposome/water lipophilicity, in other words the solutes' structural and physicochemical properties that determine their behavior and hence their partitioning in such systems. This presentation is based on a comparison between isotropic (i.e., solvent/water) and anisotropic (e.g., liposome/water) systems. An important factor to be considered is whether the anisotropic lipid phase is ionized or not. Three examples taken from the authors' laboratories are discussed to illustrate the factors or combinations thereof that govern liposome/water lipophilicity, namely (a) hydrophobic interactions alone, (b) hydrophobic and polar interactions, and (c) conformational effects plus hydrophobic and ionic interactions. The next part presents two studies taken from the field of QSAR to exemplify the use of liposome/water lipophilicity in structure,disposition and structure,activity relationships. In the conclusion, we summarize the interests and limitations of this technology and point to promising developments. © 2004 Wiley Periodicals, Inc. Med Res Rev, 24, No. 3, 299,324, 2004 [source] Structure of XynB, a highly thermostable ,-1,4-xylanase from Dictyoglomus thermophilum Rt46B.1, at 1.8,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 11 2000Andrew A. McCarthy Microorganisms employ a large array of enzymes to break down the cellulose and hemicelluloses of plant biomass. These enzymes, especially those with high thermal stability, have many uses in biotechnology. We have solved the crystal structure of a ,-1,4-xylanase, XynB, from the extremely thermophilic bacterium Dictyoglomus thermophilum, isolate Rt46B.1. The protein crystallized from 1.6,M ammonium sulfate, 0.2,M HEPES pH 7.2 and 10% glycerol, with unit-cell parameters a = b = 91.3, c = 44.9,Å and space group P43. The structure was solved at high resolution (1.8,Å) by X-ray crystallography, using the method of isomorphous replacement with a single mercury derivative, and refined to a final R factor of 18.3% (Rfree = 22.1%). XynB has the single-domain fold typical of family 11 xylanases, comprising a jelly roll of two highly twisted ,-sheets that create a deep substrate-binding cleft. The two catalytic residues, Glu90 and Glu180, occupy this cleft. Compared with other family 11 xylanases, XynB has a greater proportion of polar surface and has a slightly extended C-terminus that, combined with the extension of ,-strand A5, gives additional hydrogen bonding and hydrophobic packing. These factors may account for the enhanced thermal stability of the enzyme. [source] Self-Assembled Highly Faceted Wurtzite-Type ZnS Single-Crystalline Nanotubes with Hexagonal Cross-Sections,ADVANCED MATERIALS, Issue 16 2005L.-W. Yin Highly faceted wurtzite-type ZnS nanotubes with hexagonal cross-sections have been self-assembled via a thermochemistry process. The self-assembled growth along the c -axis is associated with the non-central and polar surfaces of the ZnS structure (see Figure and inside cover). Photoluminescence at room temperature shows a weak blue and a strong green emission band. [source] Ab initio investigation of the LiNbO3 (0001) surfacePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010Simone Sanna Abstract The polar surfaces of ferroelectric LiNbO3 have been investigated by an ab initio thermodynamical approach. Basing on density functional theory total energy calculations, we discuss the relative stability of a series of candidate surface structures with varying stoichiometry and surface reconstruction in dependence on the chemical environment. We determine the equilibrium geometry for the positively and negatively polarised surfaces and then discuss the influence of different stabilising mechanisms on the preferred terminations. Positive and negative surfaces are found to have different structure, stoichiometry and ionisation energy. The positive surface is found to contain more oxygen than the negative surface at similar conditions. Different stabilisation mechanisms like stoichiometry modification and reconstruction contribute to stabilise the polar surfaces (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||