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  • 1
    Electronic Resource
    Electronic Resource
    Curvature defects in lamellar phases of amphiphile–water systems (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3030-3041 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Within the framework of two complementary models, we show that the densities and patterns of defects in amphiphile–water systems with lamellar organization are coupled to the strength of the bilayer–bilayer interactions and hence to the overall surfactant concentration. We consider defects which introduce curvature (i.e., larger head-group area per molecule) while preserving the integrity of stacked bilayers at surfactant volume fractions of several tenths. These features are favored if the molecules comprising the lamellae are preferentially packed with a nonplanar aggregate–water interface: curvature defects lower the local free energy in systems constrained by aggregate–aggregate interactions to lamellar geometry. As the amphiphile volume fraction is increased—and the bilayer–bilayer spacing thereby decreased—we predict phase transitions between lamellar phases of different defect patterns on the bilayer surface, with concurrent decrease in the defect area fraction per bilayer. Specifically, there is a progression from a stripe-like pattern of parallel channels to a random network of line defects to a pore phase, with the latter appearing at the highest amphiphile concentrations but characterized by the lowest density of defects. Connection is made with experimental work which has recently suggested various departures from classical lamellar structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459826
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  • 2
    Electronic Resource
    Electronic Resource
    Crystal nucleation and growth from the undercooled liquid: A nonclassical piecewise parabolic free-energy model (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 2139-2148 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An undercooled liquid exhibits crystalline fluctuations, some of which grow into crystal of macroscopic dimension, while smaller fluctuations disappear. We present a model which allows for exact analytic characterization of the inhomogeneous critical nucleus, the smallest fluctuation which will give rise to crystal growth, in terms of a single spatially varying order parameter for the degree of crystallinity. The model is built around the square-gradient approximation for the free energy with a simple double-parabolic form for the homogeneous component. We study the radius, free energy of formation, and profile of the critical nucleus as functions of the liquid undercooling and compare these with results from an earlier nonclassical theory and from the classical capillarity approximation. The time evolution of the order parameter is described by a phase-field equation which is easily solved numerically for growth dynamics of initially supercritical fluctuations or for the regression of subcritical profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466510
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    PROSTANOID RECEPTORS: Subtypes and Signaling 1 (2001)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Pharmacology 41 (2001), S. 661-690 
    Details
    ISSN: 0362-1642
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Chemistry and Pharmacology
    Notes: Abstract Cyclooxygenases metabolize arachidonate to five primary prostanoids: PGE2, PGF2alpha, PGI2, TxA2, and PGD2. These autacrine lipid mediators interact with specific members of a family of distinct G-protein-coupled prostanoid receptors, designated EP, FP, IP, TP, and DP, respectively. Each of these receptors has been cloned, expressed, and characterized. This family of eight prostanoid receptor complementary DNAs encodes seven transmembrane proteins which are typical of G-protein-coupled receptors and these receptors are distinguished by their ligand-binding profiles and the signal transduction pathways activated on ligand binding. Ligand-binding selectivity of these receptors is determined by both the transmembrane sequences and amino acid residues in the putative extracellular-loop regions. The selectivity of interaction between the receptors and G proteins appears to be mediated at least in part by the C-terminal tail region. Each of the EP1, EP3, FP, and TP receptors has alternative splice variants described that alter the coding sequence in the C-terminal intracellular tail region. The C-terminal variants modulate signal transduction, phosphorylation, and desensitization of these receptors, as well as altering agonist-independent constitutive activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.pharmtox.41.1.661
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  • 4
    Electronic Resource
    Electronic Resource
    Quantitative measures of molecular similarity: Methods to analyze transition-state analogs for enzymatic reactions (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 1797-1804 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A formalism is presented for quantifying the similarity between any two molecules. The chemical descriptor used for comparison is the molecular electrostatic potential at the van der Waals surface. Thus, both the spatial properties of a molecule and its chemical features are captured in this approach. For molecules that are geometrically alike, the most useful similarity measure stems from orienting the two species so that their physical surfaces are aligned as well as possible, without regard to chemical patterns. After this alignment is achieved, a single measure sensitive to the spatial distribution of the electrostatic potential is used to rank the electronic similarity. Molecular similarity measures are applied to the enzyme systems AMP deaminase and AMP nucleosidase in order to understand quantitatively why their respective transition-state inhibitors bind more tightly than do their substrates. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 5
    Electronic Resource
    Electronic Resource
    Enzymatic transition states and inhibitor design from principles of classical and quantum chemistry (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 1805-1813 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A procedure is described which leads to experimentally based models for the transition-state structures of enzyme-catalyzed reactions. Substrates for an enzymic reaction are synthesized with isotopically enriched atoms at every position in which bonding changes are anticipated at the enzyme-enforced transition state. Kinetic isotope effects are measured for each atomic substitution and corrected for diminution of the isotope effects from nonchemical steps of the enzymic mechanism. A truncated geometric model of the transition-state structure is fitted to the kinetic isotope effects using bond-energy bond-order vibrational analysis. Full molecularity is restored to the transition state while maintaining the geometry of the bonds which define the transition state. Electronic wave functions are calculated for the substrate and the transition-state molecules. The molecular electrostatic potential energies are defined for the van der Waal surfaces of substrate and transition state and displayed in numerical and color-coded constructs. The electronic differences between substrate and transition state reveal characteristics of the transition state which permits the extraordinary binding affinity of enzyme-transition state interactions. The information has been used to characterize several enzymatic transition states and to design powerfully inhibitory transition-state analogues. Enzymatic examples are provided for the reactions catalyzed by AMP deaminase, nucleoside hydrolase, purine nucleoside phosphorylase, and for several bacterial toxins. The results demonstrate that the combination of experimental, classical, and quantum chemistry approaches is capable of providing reliable transition-state structures and sufficient information to permit the design of transition-state inhibitors. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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