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  • 1
    Digitale Medien
    Digitale Medien
    The reaction field of a water molecule in liquid water: Comparison of different quantum/classical models (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 5220-5227 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The reaction field of a water molecule in liquid water has been computed with the help of continuum, discrete-continuum, and discrete models, using density functional theory calculations. In the continuum model, the liquid is simply described by a polarizable dielectric medium. The solute is placed in a cavity defined by a scaled van der Waals surface. Two different sets of van der Waals radii have been used for the atomic spheres. The discrete-continuum model consists of a quantum molecule surrounded by four classical molecules, the resulting aggregate being embedded in a dielectric continuum. Finally, in the discrete model, a molecular dynamics simulation is carried out for a quantum molecule in a box containing 215 classical molecules with periodic boundary conditions. The reaction field and the induced dipole moment in the standard continuum model are substantially underestimated. However, the use of optimized van der Waals radii for the atomic spheres produces a notable improvement. The discrete-continuum and discrete models lead to close results that are in good agreement with experimental data and previous theoretical estimations. For instance, the induced dipole moment (0.80 and 0.82 D for discrete-continuum and discrete models, respectively) compares well with the experimental estimate (0.75 D) and with Car–Parrinello simulations (1.08 D). The reaction field potential is analyzed in terms of multipole moment contributions. The role of the first shell and bulk solvent are also examined. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1389094
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  • 2
    Digitale Medien
    Digitale Medien
    Effect of Solvation on Ozonolysis Reaction Intermediates and Transition States (2000)
    Springer
    Journal of molecular modeling 6 (2000), S. 608-617 
    Details
    ISSN: 0948-5023
    Schlagwort(e): Ozonolysis ; Ozone ; Reaction mechanisms ; Solvent effects ; Theoretical calculations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Electrostatic solvent effects on the ozonolysis of ethylene have been investigated using correlated ab initio and density functional approaches. We use a simple polarizable continuum model for the solvent. It allows us to evaluate the medium effect on both the electronic and nuclear structure of the chemical species involved in the reaction. The computations confirm that basically the reaction proceeds through the Criegee mechanism. However, formation of the van der Waals complexes ethyl-ene/ozone and carbonyl oxide/formaldehyde also appears to play a role. All the calculated species are stabilized with respect to the reactants except the transition state corresponding to the primary ozonide formation. In general, electrostatic solvent effects are relatively small for activation barriers of single reaction steps and more substantial for the corresponding reaction energies. Moreover, the medium significantly modifies the structure of some species for which polarization effects are crucial.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s0089400060608
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  • 3
    Digitale Medien
    Digitale Medien
    Insights in the Peptide Hydrolysis Mechanism by Thermolysin: A Theoretical QM/MM study (2000)
    Springer
    Journal of molecular modeling 6 (2000), S. 527-538 
    Details
    ISSN: 0948-5023
    Schlagwort(e): Hybrid methods ; QM/MM ; LSCF ; Zinc metalloproteases ; Thermolysin ; Peptide hydrolysis ; Enzymatic mechanism
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The hydrolysis by thermolysin of a Gly-Phe-Leu peptide, considered as a model substrate of the enkephalin family, has been studied with a mixed QM/MM method with the AM1/AMBER parameterization. This study is based on the mechanism proposed by Matthews in which the Glu-143 residue plays the role of a proton shuttle in the course of the reaction. The study focused on the description of every step of the process, reaction intermediates and transition states, and on the influence, both energetical and structural, of the whole protein on these stationary points. The overall mechanism appears to be quite realistic, but the study shows that some reaction steps that were assumed to be concerted should occur in two phases. Analysis of the role of the amino-acids surrounding the active site has shown their important participation in the fluctuations of the energy. In particular, the major role of His-231 on the overall mechanism has been confirmed. This study shows that modeling reaction mechanisms for enzymes is quite feasible and opens the way for computer experiments that may be helpful in devising and interpreting detailed experimental investigations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s0089400060527
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  • 4
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    Unbekannt
    Children's Libraries: Nineteenth Century American Origins (1976)
    Austin, Tex. : Periodicals Archive Online (PAO)
    Libraries and culture. 11:4 (1976:Oct.) 316 
    Details
    ISSN: 0894-8631
    Thema: Buch- und Bibliothekswesen, Informationswissenschaft
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:q610-1976-011-04-000004
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  • 5
    Digitale Medien
    Digitale Medien
    An auto-anti-B in an A1B person. Serological studies (1976)
    Springer
    Annals of hematology 32 (1976), S. 371-374 
    Details
    ISSN: 1432-0584
    Schlagwort(e): an auto-anti-B in a regular A1B blood group ; no hemolytic disease
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Das Serum eines Patienten (Mr. Lat) mit der normalen Blutgruppe A1B enthält Anti-B, das mit allen Zellen reagiert, die ein B-Antigen aufweisen, ausgenommen Bx und cis AB. Das Anti-B reagiert bei 4° C und gelegentlich bei Zimmertemperatur, was durch Agglutination, Absorption-Elution und durch thermodynamische Unter-suchungen gezeigt wurde. Der Antikörper wird als irregulärer Autoantikörper angesehen, der zur Gruppe der „supprimierten“ oder „latenten“ Antikörper gehört.
    Notizen: Summary The serum of a patient (Mr. Lat) with the regular blood group A1B contains an anti-B reacting with all cells having a B antigen except bx and cis AB. The anti-B reacts at 4° C and occasionally at room temperature as shown by agglutination, absorption-elution and by thermo-dynamic assays. The antibody is regarded as an irregular autoantibody belonging to the group of the so called “suppressed” or “latent” antibodies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00996477
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  • 6
    Digitale Medien
    Digitale Medien
    Intramolecular proton transfer of serine in aqueous solution. Mechanism and energetics (2000)
    Springer
    Theoretical chemistry accounts 104 (2000), S. 89-95 
    Details
    ISSN: 1432-2234
    Schlagwort(e): Key words: Proton transfer – Serine – Continuum solvent model – Nonequilibrium effects
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract. Serine amino acid in aqueous solution is theoretically studied at the B3PW91/6-31+G** level using a dielectric continuum solvent model. Neutral and zwitterionic structures in the gas phase and in solution are described and the proton-transfer mechanism is discussed. A neutral conformation in which the carboxyl hydrogen atom is already oriented toward the amino group seems to be the absolute energy minimum in the gas phase and the most stable neutral form in solution. The absolute energy minimum in solution is a zwitterionic form. The energy barrier for proton transfer is predicted to be very small, in particular when zero-point-energy contributions are added. Our calculations allow the dynamic aspects of the ionization mechanism to be discussed by incorporating nonequilibrium effects.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002149900109
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  • 7
    Digitale Medien
    Digitale Medien
    Penicillin production by mutants ofPenicillium chrysogenum resistant to polyene macrolide antibiotics (1979)
    Springer
    Biotechnology letters 1 (1979), S. 233-238 
    Details
    ISSN: 1573-6776
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Polyene-resistant mutants ofPenicillium chrysogenum Wis. 54–1255 have been obtained by stepwise selection in increasing concentrations of polyene antibiotics. From the parent strain, sensitive to 10 μg/ml of polyene antibiotics, mutants resistant to fungimycin (1.3 mg/ml), amphotericin B (0. 5 mg/ml), or nystatin (167 μg//ml) were obtained. Their penicillin production is different from that of the parent strain and in particular some of the fungimycin-resistant mutants produce higher levels of penicillin.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01386994
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