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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5707-5721 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Static and dynamic properties related to the internal configurational motions have been calculated for the alkyl chains of phospholipid molecules in a membrane environment in the liquid crystal phase. The calculations have been performed for the chain 1 of 1,2-dipalmitoyl 3-sn-phosphatidylcholine (DPPC), a typical constituent of phospholipid membranes. Under the assumption of fixed bond lengths and bond angles, the internal dynamics of the chain is described in terms of 15 dihedral angles. The time evolution of the angular variables is assumed to be diffusional in character, and a master equation for transitions among the stable conformers is constructed from the energetics and hydrodynamics of the chain. This method is an extension to the time domain of the rotational isomeric state (RIS) approximation, which has been widely used to compute static properties of the chains. After calculation of the suitable correlation functions, effective rate constants relevant for spectroscopic and kinetic observables have been computed, and the results have been compared with those obtained by recent Brownian dynamics (BD) calculations. The position dependence of the rate constants along the chain has been examined with special reference to understanding the effects resulting from cooperativity in the conformational transitions. The overall spinning and tumbling of the chain has also been described by a diffusive model. The calculated spectral densities for the composite motional process have been used to rationalize the behavior of the relaxation times T1, T2, and T1ρ measured in deuterium nuclear magnetic resonance (NMR) experiments.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2397-2414 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method for the calculation of the dielectric permittivity of isotropic and anisotropic homogeneous fluids is presented which, in the framework of the continuum approximation, adopts a realistic description of the molecular features, so overcoming some of the limits of the Onsager model. The Poisson equation for the molecular charge distribution contained in a cavity in a dielectric continuum in the presence of an external field is solved by a boundary element technique, which allows a detailed description of the cavity shape associated with a given molecular structure. The charge distribution is described in terms of point charges derived from ab initio calculations in vacuum, in addition to a set of interacting atom dipoles induced by all the electric fields experienced by the molecule in the condensed phase. The link between molecular features and bulk properties is established in a general way suitable for isotropic liquids and nematic phases, through the orientational distribution function of the molecule interacting with the applied field and the surrounding fluid. Numerical results are reported for the liquid phase of a set of selected organic compounds of different shape and polarity, and for the isotropic and nematic phases of 4-n-pentyl-4′-cyanobiphenyl (5CB). They show that a realistic description of the molecular features can have dramatic effects in the case of strongly anisometric molecules. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 596-608 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A molecular model for orientational ordering in liquid crystal phases is presented. A van der Waals picture is adopted, with repulsive and attractive interactions described, respectively, in terms of excluded volume and surface contact interactions for pairs of molecules. The model, based on a realistic representation of the molecular structure, is applied to the nematic phase of para-azoxyanisole (PAA). Temperature and pressure dependence of order parameters is analyzed, by discussing the role played by repulsive and attractive interactions between molecules. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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