NMR Relaxation (nmr + relaxation)

Distribution by Scientific Domains

Terms modified by NMR Relaxation

  • nmr relaxation rate

  • Selected Abstracts

    On the inversion of multicomponent NMR relaxation and diffusion decays in heterogeneous systems

    Raffaele Lamanna
    Abstract The analysis of the decay of NMR signals in heterogeneous samples requires the solution of an ill-posed inverse problem to evaluate the distributions of relaxation and diffusion parameters. Laplace transform is the most widely accepted algorithm used to describe the NMR decay in heterogeneous systems. In this article we suggest that a superposition of Fredholm integrals, with different kernels, is a more suitable model for samples in which liquid and solid-like phases are both present. In addition, some algorithms for the inversion of Laplace and Fredholm inverse problems are illustrated. The quadrature methods and regularization function in connection with the use of nonlinear discretization grids are also discussed. The described inversion algorithms are tested on simulated and experimental data, and the role of noise is discussed. © 2005 Wiley Periodicals, Inc. Concepts Magn Reson Part A 26A: 78,90, 2005 [source]

    NMR studies of surfactants

    Olle Söderman
    Abstract Surfactant molecules are amphipathic and posses complicated solution chemistry and self-assembly properties. In addition to being of enormous practical significance, the physical characterization of surfactant systems presents a rich area of condensed matter physics. This article focuses on the application and interpretation of the commonly used NMR approaches for probing these systems. In particular, the use of NMR relaxation, diffusometry and, more briefly, electrophoretic NMR to determine characteristics such as micellar size and structure, ion-binding and solubilization are considered. The application of these NMR techniques is illustrated by a number of pertinent examples. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson 23A:, 121,135, 2004. [source]

    NMR Studies of Proton Transport in Anhydrous Polymer Electrolytes for High Temperature Fuel Cells,

    FUEL CELLS, Issue 3-4 2008
    H. A. Every
    Abstract This paper presents an NMR study of the dynamic processes related to proton transport in a new polymer consisting of two blocks , poly(2,6-diphenylphenol) (P3O) and an imidazole functionalised poly(2,6-dimethylphenol) (imi-PPE) , and subsequently doped with polyphosphoric acid (PPA). From 1H and 31P NMR relaxation and diffusion measurements of the individual homopolymers and block copolymer, it was observed that addition of PPA significantly enhanced the mobility of imi-PPE and the imi-block copolymer, but not of P3O. The similarity in 1H T2 values between imi-PPE and the imi-block copolymer suggests that the relaxation behaviour in the block copolymer is dominated by the imi-PPE phase. 1H diffusion in P3O and the imi-block copolymer were comparable to pure PPA, suggesting that the proton diffusion is similar in each case. For imi-PPE, the diffusion coefficients were several orders of magnitude lower, reflecting a restricted diffusion process that is not indicative of the proton mobility. For all three polymers, the 31P T2 relaxation behaviour and inability to measure 31P diffusion coefficients imply hindered translational motion of the phosphonate groups. From these results, it can be concluded that hydrogen bonds between the phosphoric acid and the polymer form a network that facilitates proton transport via a hopping mechanism. [source]

    A lattice Boltzmann-BGK algorithm for a diffusion equation with Robin boundary condition,application to NMR relaxation

    A. Hiorth
    Abstract We present a lattice Boltzmann-BGK (LBGK) algorithm for a diffusion equation together with a Robin boundary condition, which we apply in the case of nuclear magnetic resonance relaxation. The boundary condition we employ is independent of the direction of the wall. This makes the algorithm very suitable for complicated geometries, such as porous media. We discuss the effect of lattice topology by using, respectively, an eight-speed and a four-speed lattice. The numerical algorithm is compared with analytical results for a square and an equilateral triangle. The eight-speed lattice performs well in both cases. The four-speed lattice performs well for the square, but fails in the case of an equilateral triangle. Comparison with a random walk algorithm is also included. The LBGK algorithm presented here can also be used for a convective diffusion problem if the speed of the fluid can be neglected close to the boundary. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    29Si spin-lattice NMR relaxation in microporous silica-based materials with high Mn2+ concentrations

    Vladimir I. Bakhmutov
    Abstract The 29Si T1 time measurements have been performed under magic angle spinning for supermicroporous Si/Mn materials 1,6 containing Mn2+ in concentrations of 0 (1), 1.2 (2), 2.5 (3), 3.8 (4), 15 (5) and 19.8 wt% (6). It has been found that the central lines, corresponding to isotropic chemical shifts, and their sidebands relax differently in samples 2,4 with relatively small Mn2+ contents. Because the relaxation curves for 1,6 are nonexponential and identical for 6 at spinning rates of 5, 10 and 12 kHz, dipolar relaxation via the paramagnetic centers is dominant. The relaxation data have been interpreted as a function of Mn2+ concentrations in terms of incorporation of the Mn2+ ions into the silica lattice when their concentration is small (,2.5 wt%). At higher concentrations, most of the manganese is located on the surface of the silica. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Functionalization of PAMAM dendrimers with nitronyl nitroxide radicals as models for the outer-sphere relaxation in dentritic potential MRI contrast agents

    Giancarlo Francese
    Abstract PAMAM dendrimers functionalized with nitronyl nitroxide radicals were characterized. Quantitative determination of substitution with radicals was performed using EPR and electrochemical methods. The study of the 1H NMR relaxation of the surrounding water showed how the outer-sphere contribution to the relaxivity may be limited by the presence of the dendrimer core. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Backbone dynamics of the human MIA protein studied by 15N NMR relaxation: Implications for extended interactions of SH3 domains

    PROTEIN SCIENCE, Issue 3 2003
    Raphael Stoll
    MIA, melanoma inhibitory activity; NMR, nuclear magnetic resonance Abstract The melanoma inhibitory activity (MIA) protein is a clinically valuable marker in patients with malignant melanoma as enhanced values diagnose metastatic melanoma stages III and IV. Here, we report the backbone dynamics of human MIA studied by 15N NMR relaxation experiments. The folded core of human MIA is found to be rigid, but several loops connecting ,-sheets, such as the RT-loop for example, display increased mobility on picosecond to nanosecond time scales. One of the most important dynamic features is the pronounced flexibility of the distal loop, comprising residues Asp 68 to Ala 75, where motions on time scales up to milliseconds occur. Further, significant exchange contributions are observed for residues of the canonical binding site of SH3 domains including the RT-loop, the n-Src loop, for the loop comprising residues 13 to 19, which we refer to as the"disulfide loop", in part for the distal loop, and the carboxyl terminus of human MIA. The functional importance of this dynamic behavior is discussed with respect to the biological activity of several point mutations of human MIA. The results of this study suggest that the MIA protein and the recently identified highly homologous fibrocyte-derived protein (FDP)/MIA-like (MIAL) constitute a new family of secreted proteins that adopt an SH3 domain-like fold in solution with expanded ligand interactions. [source]

    Dynamical characterization of residual and non-native structures in a partially folded protein by 15N NMR relaxation using a model based on a distribution of correlation times

    PROTEIN SCIENCE, Issue 4 2002
    Françoise Ochsenbein
    Abstract A spectral density model based on a truncated lorentzian distribution of correlation times is used to analyze the nanosecond time-scale dynamics of the partially unfolded domain 2 of annexin I from its 15N NMR relaxation parameters measured at three magnetic field strengths. The use of a distribution of correlation times enables the characterization of the dynamical features of the NH bonds of the protein in terms of heterogeneity of dynamical states in the nanosecond range. The variation along the sequence of the two dynamical parameters introduced, namely the center and the width of the distribution, points out the different types of residual secondary structures present in the D2 domain. Moreover, it allows a physically sensible interpretation of the dynamical behavior of the different residual helices and of the non-native structures. Also, a striking correspondence is found between the parameters obtained using an extended Lipari and Szabo model and the parameters obtained using the distribution of correlation times. This result led us to propose a specific interpretation of the model-free order parameter for internal motions in the nanosecond range in the case of unfolded states. [source]