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  • 1
    Electronic Resource
    Electronic Resource
    A quantitative electron-spin resonance line shape study of the local motion in the micellar and liquid crystalline lamellar phases of the oleoyllysolecithin water system (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7098-7107 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The experimental electron-spin resonance (ESR) line shapes of the micellar (L1) and lamellar (Lα) phases of the binary system 1-oleoyl-sn-glycero-3-phosphocholine (OlLPC)/water have been interpreted quantitatively using a two-dynamic (TD) model. This dynamic model comprises the local dynamics of Freed's model [J. Chem. Phys. 55, 5270 (1971); 58, 3185 (1973); 77, 3915 (1982)] and a second Brownian motion referring to the combined effect of the micellar reorientation and the translational motion of the amphiphile molecule along the micellar surface. With this model, we focus our attention on a comparison of the local dynamics between the L1 and Lα phases. It is found from the TD model that the local ordering (λ) and dynamics (τ⊥) of the L1 phase change compared with those of the Lα phase according to λ(L1)(approximately-greater-than)λ(Lα) and τ⊥(L1)〈τ⊥(Lα). The observed lower local ordering in the lamellar phase compared with that in the micellar phase may be interpreted in terms of the different packing constraints of the OlLPC molecule in the two phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465428
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  • 2
    Electronic Resource
    Electronic Resource
    Electronic energy transfer in liquids. The effect of molecular dynamics (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 6583-6589 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A Liouville formalism has been developed for treating energy transfer processes within the same conceptual framework as other relaxation processes. The theory of Förster, describing energy transfer between a pair of immobile fluorescent molecules has been generalized to include the effects of molecular dynamics the static, intermediate and fast dynamic regimes. Förster's master equation of the excitation populations is derived from the Liouville formalism and we arrive at the proper criteria for its validity within the physical model. A closed form expression is derived for the fluorescence anisotropy of a macromolecular system containing pair of pairwise interacting chromophores where one of the chromophores undergoes a two state conformational change. The expression derived is valid without assuming that the nonradiative state and the conformation dynamic is uncoupled. It is shown that when energy transfer and conformational changes occur on the same time scale, the decay times of the fluorescence anisotropy depend in a complex way on the molecular relaxation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465850
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  • 3
    Electronic Resource
    Electronic Resource
    Slow motion electron-spin resonance line shapes of spin-labeled molecules undergoing restricted rotational diffusion in a cone: Applications to lysolecithin/water systems (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7090-7097 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The restricted diffusion-in-a-cone (DC) model is formulated within the context of a slow-motional electron-spin resonance (ESR) line shape to describe the local reorientation of amphiphile molecules in lipid bilayers. A special program is designed to reduce the computation amount, and the computational time for the DC model is comparable to that for the familiar Maier–Saupe (MS) potential model. Special emphasis is placed on comparing the two potential models in ESR line shape calculations. Illustrative analyses of ESR spectra are presented for some selected bilayers. It is found that the DC model is particularly suitable for describing the local dynamic states of single chain systems. The simulation results show that while the two models give similar values for the reorientational rates, the DC model predicts lower local molecular orders.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465427
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  • 4
    Electronic Resource
    Electronic Resource
    Direct simulation of slow-motion electron spin resonance spectra by solving the stochastic Liouville equation in the time domain with stochastic dynamics in the form of trajectories (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 96-103 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new method to solve the stochastic Liouville equation in the time domain has been developed. The effective and accurate algorithm designed conserve the norm of the propagator at every time step. The algorithm is not dependent on how the fluctuations are generated. The method is applied to solve the stochastic Liouville equation of an electron spin, S=1/2, coupled to a nuclear spin system with spin quantum number I=1. The calculated slow-motion electron spin resonance (ESR) line shapes presented are for a model where the stochastic time dependent spin-lattice coupling was obtained from a Brownian dynamic simulation of restricted reorientation in a cone potential. These spectra were then compared with the spectra obtained by solving the stochastic Liouville equation (SLE) using the eigenfunction expansion method. All spectra conform exactly and the computer power used by the two methods are similar. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469627
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  • 5
    Electronic Resource
    Electronic Resource
    Slow motion electron spin resonance line shapes of lyotropic liquid crystals in hexagonal phase (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 1471-1480 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper the slow motion electron spin resonance (ESR) line shape theory is extended to hexagonal mesophases. The stochastic Liouville equation is applied to the dynamic description of both local molecular reorientation and azimuthal surface translational diffusion of the lipid around the cylinder axis. The established ESR line shape models allow a separation of contributions to the electron spin relaxation from the two motions, if macroscopically aligned hexagonal spectra are simulated. Such simulations can yield, not only the dynamic parameters such as local ordering parameter, local motional rate, and azimuthal surface diffusion coefficient, but also a disorder parameter accounting for residual cylinder disorder and the disorder effects due to finite cylinder length and curved surface along the cylinder axis. To test these models, they are applied to the analyses of X-band ESR spectra of the hexagonal phase of the sodium dodecyl sulphate (SDS)/decanol/water ternary system. The obtained surface diffusion coefficient and disorder parameter are in good agreement with previously reported values in a deuterium nuclear magnetic resonance (NMR) study. The local dynamic properties, which are not readily available by NMR method, are compared with those obtained for the micellar phase of the SDS/water binary system. Such a comparison reveals that while the local orderings are similar, the local dynamics is much slower in the hexagonal phase than in the micellar phase. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468879
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  • 6
    Electronic Resource
    Electronic Resource
    Nuclear-spin relaxation in paramagnetic complexes in the slow-motion regime for the electron spin: The anisotropic pseudorotation model for S=1 and the interpretation of nuclear magnetic relaxation dispersion results for a low-symmetry Ni(II) complex (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 1116-1128 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This work presents the anisotropic pseudorotation (APR) model, which is a new dynamic model for the interpretation of experimental nuclear spin-lattice relaxation times in paramagnetic (S=1) complexes of low symmetry. It comprises two dynamic processes active in modulating the zero-field splitting interaction (ZFS). Reorientation of the complex modulates a static zero-field splitting, defined as a measure of the asymmetry in the equilibrium geometry at the paramagnetic site. Local motions of the ligands surrounding the paramagnetic site further contribute a rapidly fluctuating (transient) zero-field splitting interaction. This dynamic model is evaluated within a general theoretical framework capable of dealing with the electron-spin system in the low- and high-magnetic field limits for both Redfield and slow-motion cases, i.e., where the motions inducing electron-spin relaxation and the electron-spin relaxation itself are characterized by the same time scale. The dynamic model is characterized and discussed by calculating results for a large number of parameter sets. The obtained results are compared with the traditional theory, the Solomon–Bloembergen–Morgan equations (SBM), by least-squares fitting the SBM equations to the APR model. Results show that in most cases the SBM model can fit the nuclear magnetic relaxation dispersion (NMRD) profiles from the APR model at the expense of using a different parameter set. For both models, a restricted fit to experimental NMRD data, from bis(2,2,6,6-tetramethyl-3,5-heptanedionato)Ni(II)(aniline-d5)2 (abbreviated Ni(dpm)2(aniline-d5)2 or simply NIDPM) in solution, has been performed. The parameters obtained suggest that NIDPM is a slow-motion case comprising a static contribution to its zero-field splitting, so that the SBM model is inapplicable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467807
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  • 7
    Electronic Resource
    Electronic Resource
    A low-field paramagnetic nuclear spin relaxation theory (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 4945-4953 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A low-field theory of paramagnetically enhanced proton spin-lattice relaxation is developed resulting in closed analytical expressions. The theory describes paramagnetically enhanced water proton spin-lattice relaxation in complexes of transition metal ions with electron spin quantum number S=1. In the low-field regime the electron spin system is dominated by a static or permanent zero-field splitting interaction which is much larger than the Zeeman interaction. The electron spin is thus quantized in the molecular fixed principal frame of the static ZFS-interaction rather than in the laboratory fixed frame. In the molecular fixed frame the zero-field splitting Hamiltonian is characterized by an axial parameter (D) and a rhombic parameter (E). It is shown how the relative magnitude of D and E strongly influence the magnitude of the paramagnetically enhanced proton spin lattice relaxation rate. In describing electron spin relaxation in the molecular fixed frame, we consider a transient ZFS-interaction and a reorientation modulated Zeeman interaction as the two main relaxation mechanisms. Then, using Redfield theory we derive expressions for the relevant electron spin relaxation rates in terms of spectral densities. In contrast to the Zeeman or high field regime, the electron spin system in the low field limit does not have a permanent magnetic moment. The lack of this magnetic moment implies that electron spin-lattice relaxation processes do not influence the paramagnetically enhanced proton spin-lattice relaxation rates. Instead three spin–spin relaxation rates determine the enhanced proton spin-lattice relaxation profile. We express the electron spin–spin relaxation rates in terms of spectral densities determined by the mean square value of the transient zero-field splitting interaction, its characteristic correlation time, and the reorientational correlation time of rank 1. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475903
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  • 8
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    Mercury Methylation Rates for Geochemically Relevant HgII Species in Sediments (2012)
    American Chemical Society
    Details
    Publication Date: 2012-10-25
    Print ISSN: 0013-936X
    Electronic ISSN: 1520-5851
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Published by American Chemical Society
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  • 9
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    Uptake Kinetics of Methylmercury in a Freshwater Alga Exposed to Methylmercury Complexes with Environmentally Relevant Thiols (2019)
    American Chemical Society
    Details
    Publication Date: 2019-11-04
    Print ISSN: 0013-936X
    Electronic ISSN: 1520-5851
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Published by American Chemical Society
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  • 10
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    Slow motion electron‐spin resonance line shapes of spin‐labeled molecules undergoing restricted rotational diffusion in a cone: Applications to lysolecithin/water systems (1993)
    American Institute of Physics
    Details
    Publication Date: 1993-11-01
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics
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