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Lyndon Emsley - One of the best experts on this subject based on the ideXlab platform.

  • line narrowing in 1h nmr of powdered Organic Solids with top ct mas experiments at ultra fast mas
    Journal of Magnetic Resonance, 2019
    Co-Authors: Federico M Paruzzo, Brennan J Walder, Lyndon Emsley
    Abstract:

    Abstract The residual broadening observed in 1H spectra of rigid Organic Solids at natural abundance under 111 kHz magic angle spinning (MAS) is typically a few hundred Hertz. Here we show that refocusable and non-refocusable interactions contribute roughly equally to this residual at high-fields (21.14 T), and suggest that the removal of the non-refocusable part will produce significant increase in spectral resolution. To this end, we demonstrate an experiment for the indirect acquisition of constant-time experiments at ultra-fast MAS (CT-MAS) which verifies this hypothesis. The combination of this experiment with the two-dimensional one pulse (TOP) transformation reduces the experimental time to a fraction of the original cost while retaining the narrowing effects. Results obtained with TOP-CT-MAS at 111 kHz MAS on a sample of β-AspAla yield up to 30% higher resolution spectra than the equivalent one-pulse experiment, in less than 10 min.

  • Dynamic Nuclear Polarization NMR Spectroscopy of Microcrystalline Solids
    Journal of the American Chemical Society, 2012
    Co-Authors: Aaron J. Rossini, David Gajan, Anne Lesage, Alexandre Zagdoun, Christophe Copéret, Martin Schwarzwalder, Franziska Hegner, Lyndon Emsley
    Abstract:

    Dynamic nuclear polarization (DNP) solid-state NMR has been applied to powdered microcrystalline Solids to obtain sensitivity enhancements on the order of 100. Glucose, sulfathiazole, and paracetamol were impregnated with bis-nitroxide biradical (bis-cyclohexyl-TEMPO-bisketal, bCTbK) solutions of Organic solvents. The Organic solvents were carefully chosen to be nonsolvents for the compounds, so that DNP-enhanced solid-state NMR spectra of the unaltered Solids could be acquired. A theoretical model is presented that illustrates that for externally doped Organic Solids characterized by long spin-lattice relaxation times (T-1(H-1) > 200 s), H-1-H-1 spin diffusion can relay enhanced polarization over micrometer length scales yielding substantial DNP enhancements (epsilon). epsilon on the order of 60 are obtained for microcrystalline glucose and sulfathiazole at 9.4 T and with temperatures of ca. 105 K. The large gain in sensitivity enables the rapid acquisition of C-13-C-13 correlation spectra at natural isotopic abundance. It is anticipated that this will be a general method for enhancing the sensitivity of solid-state NMR experiments of Organic Solids.

  • Proton to carbon-13 INEPT in solid-state NMR spectroscopy
    Journal of the American Chemical Society, 2005
    Co-Authors: Bénédicte Elena, Anja Böckmann, Stefan Steuernagel, Anne Lesage, Lyndon Emsley
    Abstract:

    A refocused INEPT through-bond coherence transfer technique is demonstrated for NMR of rigid Organic Solids and is shown to provide a valuable building block for the development of NMR correlation experiments in biological Solids. The use of efficient proton homonuclear dipolar decoupling in combination with a direct spectral optimization procedure provides minimization of the transverse dephasing of coherences and leads to very efficient through-bond (1)H-(13)C INEPT transfer for crystalline Organic compounds. Application of this technique to 2D heteronuclear correlation spectroscopy leads to up to a factor of 3 increase in sensitivity for a carbon-13 enriched sample in comparison to standard through-bond experiments and provides excellent selectivity for one-bond transfer. The method is demonstrated on a microcrystalline sample of the protein Crh (2 x 10.4 kDa).

  • through bond carbon carbon connectivities in disordered Solids by nmr
    Journal of the American Chemical Society, 1999
    Co-Authors: Anne Lesage, And Michel Bardet, Lyndon Emsley
    Abstract:

    Using a refocused INADEQUATE NMR experiment we show that homonuclear carbon−carbon through-bond correlations can be obtained in disordered Organic Solids where the line widths greatly exceed the value of the scalar coupling. The feasibility of the experiment is demonstrated for inhomogeneous samples of 13C-labeled wood and cellulose. The two-dimensional correlation maps are used to assign unambiguously the carbon resonances of this natural polymer. We show that the efficiency of the refocused INADEQUATE experiment depends on the ratio / , where is the apparent relaxation time, deduced from the line width, and is the transverse dephasing time measured in a spin−echo experiment. For cellulose, we find that is larger than by more than 1 order of magnitude and that the experimental efficiency of the refocused INADEQUATE experiment is around 10%, in agreement with calculations. Even in ordinary crystalline Organic Solids, such as powdered amino acids, large differences are observed between and .

Melinda J Duer - One of the best experts on this subject based on the ideXlab platform.

  • recoupling of chemical shift anisotropy powder patterns in mas nmr
    Journal of Magnetic Resonance, 2006
    Co-Authors: Melinda J Duer
    Abstract:

    Abstract A comparison of three different implementations of the chemical-shift recoupling experiment of Tycko et al. [R. Tycko, G. Dabbagh, P.A. Mirau, Determination of chemical-shift-anisotropy lineshapes in a two-dimensional magic-angle-spinning NMR experiment, J. Magn. Reson. 85 (1989) 265–274] is presented. The methods seek to reduce the effects of artefacts resulting from pulse imperfections and residual C-H dipolar coupling in Organic Solids. An optimised and constant time implementation are shown to give well-defined and artefact free powder pattern lineshapes in the indirectly observed dimension for both sp 2 and sp 3 carbon sites. Experimental setup is no more demanding than for the original experiment, and can be implemented using standard commercial hardware.

  • recoupling of chemical shift anisotropy powder patterns in mas nmr
    Journal of Magnetic Resonance, 2006
    Co-Authors: Melinda J Duer
    Abstract:

    Abstract A comparison of three different implementations of the chemical-shift recoupling experiment of Tycko et al. [R. Tycko, G. Dabbagh, P.A. Mirau, Determination of chemical-shift-anisotropy lineshapes in a two-dimensional magic-angle-spinning NMR experiment, J. Magn. Reson. 85 (1989) 265–274] is presented. The methods seek to reduce the effects of artefacts resulting from pulse imperfections and residual C-H dipolar coupling in Organic Solids. An optimised and constant time implementation are shown to give well-defined and artefact free powder pattern lineshapes in the indirectly observed dimension for both sp 2 and sp 3 carbon sites. Experimental setup is no more demanding than for the original experiment, and can be implemented using standard commercial hardware.

Paul Hodgkinson - One of the best experts on this subject based on the ideXlab platform.

  • temperature dependence of nmr parameters calculated from path integral molecular dynamics simulations
    Journal of Chemical Theory and Computation, 2016
    Co-Authors: Martin Dracinský, Petr Bouř, Paul Hodgkinson
    Abstract:

    The influence of temperature on NMR chemical shifts and quadrupolar couplings in model molecular Organic Solids is explored using path integral molecular dynamics (PIMD) and density functional theory (DFT) calculations of shielding and electric field gradient (EFG) tensors. An approach based on convoluting calculated shielding or EFG tensor components with probability distributions of selected bond distances and valence angles obtained from DFT-PIMD simulations at several temperatures is used to calculate the temperature effects. The probability distributions obtained from the quantum PIMD simulations, which includes nuclear quantum effects, are significantly broader and less temperature dependent than those obtained with conventional DFT molecular dynamics or with 1D scans through the potential energy surface. Predicted NMR observables for the model systems were in excellent agreement with experimental data.

  • effects of quantum nuclear delocalisation on nmr parameters from path integral molecular dynamics
    Chemistry: A European Journal, 2014
    Co-Authors: Martin Dracinský, Paul Hodgkinson
    Abstract:

    The influence of nuclear delocalisation on NMR chemical shifts in molecular Organic Solids is explored using path integral molecular dynamics (PIMD) and density functional theory calculations of shielding tensors. Nuclear quantum effects are shown to explain previously observed systematic deviations in correlations between calculated and experimental chemical shifts, with particularly large PIMD-induced changes (up to 23 ppm) observed for carbon atoms in methyl groups. The PIMD approach also enables isotope substitution effects on chemical shifts and J couplings to be predicted in excellent agreement with experiment for both isolated molecules and molecular crystals. An approach based on convoluting calculated shielding or coupling surfaces with probability distributions of selected bond distances and valence angles obtained from PIMD simulations is used to calculate isotope effects.

Hiroyuki Yoshida - One of the best experts on this subject based on the ideXlab platform.

  • Complete description of ionization energy and electron affinity in Organic Solids: Determining contributions from electronic polarization, energy band dispersion, and molecular orientation
    Physical Review B, 2015
    Co-Authors: Hiroyuki Yoshida, K. Yamada, Jun'ya Tsutsumi, Naoki Sato
    Abstract:

    Ionization energy and electron affinity in Organic Solids are understood in terms of a single molecule perturbedby solid-state effects such as polarization energy, band dispersion, and molecular orientation as primary factors.However, no work has been done to determine the individual contributions experimentally. In this work, theelectron affinities of thin films of pentacene and perfluoropentacene with different molecular orientations aredetermined to a precision of 0.1 eV using low-energy inverse photoemission spectroscopy. Based on the preciselydetermined electron affinities in the solid state together with the corresponding data of the ionization energiesand other energy parameters, we quantitatively evaluate the contribution of these effects. It turns out that thebandwidth as well as the polarization energy contributes to the ionization energy and electron affinity in the Solidstate while the effect of the surface dipole is at most a few eV and does not vary with the molecular orientation.As a result, we conclude that the molecular orientation dependence of the ionization energy and electron affinityof Organic Solids originates from the orientation-dependent polarization energy in the film

  • measuring the electron affinity of Organic Solids an indispensable new tool for Organic electronics
    Analytical and Bioanalytical Chemistry, 2014
    Co-Authors: Hiroyuki Yoshida
    Abstract:

    Electron affinity is a fundamental energy parameter of materials. In Organic semiconductors, the electron affinity is closely related to electron conduction. It is not only important to understand fundamental electronic processes in Organic Solids, but it is also indispensable for research and development of Organic semiconductor devices such as Organic light-emitting diodes and Organic photovoltaic cells. However, there has been no experimental technique for examining the electron affinity of Organic materials that meets the requirements of such research. Recently, a new method, called low-energy inverse-photoemission spectroscopy, has been developed. A beam of low-energy electrons is focused onto the sample surface, and photons emitted owing to the radiative transition to unoccupied states are then detected. From the onset of the spectral intensity, the electron affinity is determined within an uncertainty of 0.1 eV. Unlike in conventional inverse-photoemission spectroscopy, sample damage is negligible and the resolution is improved by a factor of 2. The principle of the method and several applications are reported.

Anne Lesage - One of the best experts on this subject based on the ideXlab platform.

  • Dynamic Nuclear Polarization NMR Spectroscopy of Microcrystalline Solids
    Journal of the American Chemical Society, 2012
    Co-Authors: Aaron J. Rossini, David Gajan, Anne Lesage, Alexandre Zagdoun, Christophe Copéret, Martin Schwarzwalder, Franziska Hegner, Lyndon Emsley
    Abstract:

    Dynamic nuclear polarization (DNP) solid-state NMR has been applied to powdered microcrystalline Solids to obtain sensitivity enhancements on the order of 100. Glucose, sulfathiazole, and paracetamol were impregnated with bis-nitroxide biradical (bis-cyclohexyl-TEMPO-bisketal, bCTbK) solutions of Organic solvents. The Organic solvents were carefully chosen to be nonsolvents for the compounds, so that DNP-enhanced solid-state NMR spectra of the unaltered Solids could be acquired. A theoretical model is presented that illustrates that for externally doped Organic Solids characterized by long spin-lattice relaxation times (T-1(H-1) > 200 s), H-1-H-1 spin diffusion can relay enhanced polarization over micrometer length scales yielding substantial DNP enhancements (epsilon). epsilon on the order of 60 are obtained for microcrystalline glucose and sulfathiazole at 9.4 T and with temperatures of ca. 105 K. The large gain in sensitivity enables the rapid acquisition of C-13-C-13 correlation spectra at natural isotopic abundance. It is anticipated that this will be a general method for enhancing the sensitivity of solid-state NMR experiments of Organic Solids.

  • Proton to carbon-13 INEPT in solid-state NMR spectroscopy
    Journal of the American Chemical Society, 2005
    Co-Authors: Bénédicte Elena, Anja Böckmann, Stefan Steuernagel, Anne Lesage, Lyndon Emsley
    Abstract:

    A refocused INEPT through-bond coherence transfer technique is demonstrated for NMR of rigid Organic Solids and is shown to provide a valuable building block for the development of NMR correlation experiments in biological Solids. The use of efficient proton homonuclear dipolar decoupling in combination with a direct spectral optimization procedure provides minimization of the transverse dephasing of coherences and leads to very efficient through-bond (1)H-(13)C INEPT transfer for crystalline Organic compounds. Application of this technique to 2D heteronuclear correlation spectroscopy leads to up to a factor of 3 increase in sensitivity for a carbon-13 enriched sample in comparison to standard through-bond experiments and provides excellent selectivity for one-bond transfer. The method is demonstrated on a microcrystalline sample of the protein Crh (2 x 10.4 kDa).

  • through bond carbon carbon connectivities in disordered Solids by nmr
    Journal of the American Chemical Society, 1999
    Co-Authors: Anne Lesage, And Michel Bardet, Lyndon Emsley
    Abstract:

    Using a refocused INADEQUATE NMR experiment we show that homonuclear carbon−carbon through-bond correlations can be obtained in disordered Organic Solids where the line widths greatly exceed the value of the scalar coupling. The feasibility of the experiment is demonstrated for inhomogeneous samples of 13C-labeled wood and cellulose. The two-dimensional correlation maps are used to assign unambiguously the carbon resonances of this natural polymer. We show that the efficiency of the refocused INADEQUATE experiment depends on the ratio / , where is the apparent relaxation time, deduced from the line width, and is the transverse dephasing time measured in a spin−echo experiment. For cellulose, we find that is larger than by more than 1 order of magnitude and that the experimental efficiency of the refocused INADEQUATE experiment is around 10%, in agreement with calculations. Even in ordinary crystalline Organic Solids, such as powdered amino acids, large differences are observed between and .