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  • 1
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1349-9432
    Keywords: optical frequency domain reflectometer ; multi mode laser ; optical signal processing ; optical interference measurements ; laser coherence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We propose and confirm a novel technique of optical frequency domain reflectometry based on multidigitized coherence using a multimode laser. The proposed system can easily provide the potential for high resolution on the order of 10 μm without scanning frequencies as in frequency domain reflectometers of either continuous or stepwise sweep. The theoretical approach agrees well with the experimental results demonstrated using a commercially available multimode laser diode.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-5001
    Keywords: 1H NMR ; 13C NMR ; Oxytocin ; Assignment ; Solution structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary With the combined use of various two-dimensional (2D) NMR techniques, a complete assignment of the 1H and 13C resonances of oxytocin, $${\text{C}}{\text{s - Pro - Leu - Gly - NH}}_{\text{2}}$$ , for two molecular states, protonated and unprotonated at the N-terminal group, was performed in dimethyl sulfoxide. A small but distinct change in the backbone conformation of the six-residue cyclic moiety, associated with the protonation, was first suggested from those NMR parameters relevant to conformation, such as change with temperature in the chemical shifts of the peptide amide protons and changes in chemical shifts and homonuclear as well as heteronuclear three-bond coupling constants. The solution structures of oxytocin for the protonated and unprotonated forms were then calculated using distance analysis in dihedral-angle space, based on a relaxation matrix evaluated from quantitative NOE intensities at different mixing times. Total amounts of 93 and 105 distances were determined for the protonated and the unprotonated forms, respectively. There were 25 interresidue distances relevant to the structure of the cyclic moiety for the protonated form of oxytocin and 43 for the unprotonated form. Overall structures with the lowest target penalty function were similar between the two forms, having a β-turn structure at the endocyclic residues of the Tyr-Ile-Gln-Asn moiety. The local backbone conformations near the N-terminus, however, were significantly different between the two forms. This was found to be due to a change in the dihedral angle of the disulfide bridge (χss around C-S-S-C), which closes the ring in the cyclic peptide. The dihedral angle was about +90° for the unprotonated form and an intermediate value of about +45° for the protonated form.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 476-488 
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The extended simulated annealing process (ESAP) is a useful method for modeling the partial structure of proteins [J. Higo et al., Biopolymers, 32, 33 (1992)]. In ESAP, a protein molecule is divided into two parts: small, flexible fragments constituting the concerned partial structure, and the remaining part, for which the structure is kept rigid during the simulation. We have improved the program of ESAP so that it can be adapted to general macromolecules. Any sidechain on the rigid part can be set to rotate. Soft repulsion between van der Waals spheres is introduced to avoid conformational trapping into local minima. This improved program was tested for modeling structural changes caused by eight kinds of amino acid mutation at the 86th residue in T4 lysozyme. For each mutant we obtained a model structure that was close to the X-ray structure. The root mean square (rms) deviations from the X-ray structure were 0.3 to 0.8 Å for all heavy atoms and about 0.2 Å for the main-chain atoms. We also modeled the structure of an Ile mutant, for which the X-ray structure has not yet been reported. ESAP can be used to model structural changes due to a single residue mutation in proteins. © 1996 by John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 15 (1994), S. 1278-1290 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Two-dimensional protein (ferritin) aggregates with a square lattice symmetry, which were formed within a thin liquid layer on a mercury surface, were studied by molecular dynamics (MD) simulation. For the simulation, the ferritin molecule was modeled by an assembly of 49 spheres, and the intermolecular interactions were given by simple formulae. During the simulation, molecules were confined within a layer, which corresponds to the thin liquid layer. An annealing MD simulation was done starting from a random molecular configuration within the layer, and aggregates with the square lattice symmetry were also obtained. To study the stability of aggregates, dissociation processes of the aggregates were analyzed using MD simulations at room temperature. Interactions between the nearest-neighbor molecules were regarded as bonds. Mean bond energies and correlation coefficients between the bond energies were calculated from the MD trajectories. A decay profile according to the dissociation was obtained, yielding a dissociation rate constant. Buried bonds were stronger than peripheral bonds. The larger the aggregate size, the stronger the bond for each of the buried and peripheral bonds. A simple theoretical account, which is applicable to a general bonded network, was introduced to analyze the dynamics of the aggregates. © 1994 by John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The special-purpose computer GRAPE-2A accelerates the calculation of pairwise interactions in many-body systems. This computer is a back-end processor connected to a host computer through a Versa Module Europe (VME) bus. GRAPE-2A receives coordinates and other physical data for particles from the host and then calculates the pairwise interactions. The host then integrates an equation of motion by using these interactions. We did molecular dynamics simulations for two systems of liquid water: System 1 (1000 molecules), and System 2 (1728 molecules). The time spent for one step of molecular dynamics was 3.9 s (System l), and 10.2 s (System 2). The larger the molecular system, the higher the performance. The speed of GRAPE-2A did not depend on the formula describing the pairwise interaction. The cost performance was about 20 times better than that of the fastest workstations available today, and GRAPE-2A cost only $22,000. © 1994 by John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The phase morphology and polymer chain orientation in polyethylene-polycarbonte blends is investigated. A blend with a dispersed polyethylene phase was found to exhibit phase growth under quiescent conditions. Addition of a styrene-(ethylene/butene) block copolymer controls the phase morphology and prevents phase growth. Melt spun tapes and tubular film have been prepared from polyethylene-polycarbonate blends. Orientation of the crystallo-graphic axes of the polyethylene and the chain axis of the polycarbonate were determined by infrared dichroism. The addition of polycarbonate to polyethylene is found to decrease chain orientation at the same drawdown stress.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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