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  • 51.
    Åman, Ken
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lindahl, Erik
    Edholm, Olle
    Håkansson, Pär
    Umeå University, Faculty of Science and Technology, Chemistry.
    Westlund, Per-Olof
    Umeå University, Faculty of Science and Technology, Chemistry.
    Structure and Dynamics of Interfacial Water in an L Phase Lipid Bilayer from Molecular Dynamics Simulations2003In: Biophysical Journal, Vol. 84, p. 102-15Article in journal (Refereed)
    Abstract [en]

    Based on molecular dynamics simulations, an analysis of structure and dynamics is performed on interfacial water at a liquid crystalline dipalmitoylphosphatidycholine/water system. Water properties relevant for understanding NMR relaxation are emphasized. The first and second rank orientational order parameters of the water O–H bonds were calculated, where the second rank order parameter is in agreement with experimental determined quadrupolar splittings. Also, two different interfacial water regions (bound water regions) are revealed with respect to different signs of the second rank order parameter. The water reorientation correlation function reveals a mixture of fast and slow decaying parts. The fast (ps) part of the correlation function is due to local anisotropic water reorientation whereas the much slower part is due to more complicated processes including lateral diffusion along the interface and chemical exchange between free and bound water molecules. The 100-ns-long molecular dynamics simulation at constant pressure (1 atm) and at a temperature of 50°C of 64 lipid molecules and 64 x 23 water molecules lack a slow water reorientation correlation component in the ns time scale. The 2H2O powder spectrum of the dipalmitoylphosphatidycholine/water system is narrow and consequently, the NMR relaxation time T2 is too short compared to experimental results.

  • 52.
    Åman, Ken
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Westlund, Per-Olof
    Umeå University, Faculty of Science and Technology, Chemistry.
    Direct calculation of (H2O)-H-1 T-1 NMRD profiles and EPR lineshapes for the electron spin quantum numbers S=1, 3/2, 2, 5/2, 3, 7/2, based on the stochastic Liouville equation combined with Brownian dynamics simulation2007In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ISSN 1463-9076, Vol. 9, no 6, p. 691-700Article in journal (Refereed)
    Abstract [en]

    Direct calculation of electron spin relaxation and EPR lineshapes, based on Brownian dynamics simulation techniques and the stochastic Liouville equation approach (SLE-L) [Mol. Phys., 2004, 102, 1085-1093], is here generalized to high spin systems with spin quantum number S = 3/2, 2, 5/2, 3 and 7/2. A direct calculation method is demonstrated for electron spin-spin and spin-lattice relaxation, S-, X- and Q-band EPR-lineshapes and paramagnetic enhanced water proton T1- NMRD profiles. The main relaxation mechanism for the electron spin system is a stochastic second rank zero field splitting (ZFS). Brownian dynamics simulation techniques are used in describing a fluctuating ZFS interaction which comprises two parts namely the permanent part which is modulated by isotropic reorientation diffusion, and the transient part which is modulated by fast local distortion, which is also modelled by the isotropic rotation diffusion model. The SLE-L approach present is applicable both in the perturbation (Redfield) regime as well as outside the perturbation regime, in the so called slow motion regime.

  • 53.
    Åman, Ken
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Westlund, Per-Olof
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    The Electron Spin Relaxation and Paramagnetic Relaxation Enhancement: an Application of the Stochastic Liouville Equation in the Langevin Form2004In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 102, no 9-10, p. 1085-1093Article in journal (Refereed)
    Abstract [en]

    A novel theoretical approach, based on the stochastic Liouville equation (SLE) in its Langevin form, is developed to describe paramagnetic relaxation enhancement (PRE). This approach is more applicable to different dynamic models than the old slow-motion theory which was based on the SLE in the operator or Fokker-Planck form. Moreover, the SLE in the Langevin form supplies a detailed description of the electron spin relaxation in the time domain. This new approach is applied to the analysis of the T1-NMRD profile of water protons in Ni2+(H2O)6.

12 51 - 53 of 53
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