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Geoffrey Bodenhausen - One of the best experts on this subject based on the ideXlab platform.

  • determination of the antisymmetric part of the Chemical Shift Anisotropy tensor via spin relaxation in nuclear magnetic resonance
    Journal of Chemical Physics, 2010
    Co-Authors: Raphael Paquin, Luminita Duma, Philippe Pelupessy, Christel Gervais, Geoffrey Bodenhausen
    Abstract:

    Relaxation processes induced by the antisymmetric part of the Chemical Shift Anisotropy tensor (henceforth called anti-CSA) are usually neglected in NMR relaxation studies. It is shown here that anti-CSA components contribute to longitudinal relaxation rates of the indole N15 nucleus in tryptophan in solution at different magnetic fields and temperatures. To determine the parameters of several models for rotational diffusion and internal dynamics, we measured the longitudinal relaxation rates R1=1/T1 of N15, the N15–H1 dipole-dipole (DD) cross-relaxation rates (Overhauser effects), and the cross-correlated CSA/DD relaxation rates involving the second-rank symmetric part of the CSA tensor of N15 at four magnetic fields B0=9.4, 14.1, 18.8, and 22.3 T (400, 600, 800, and 950 MHz for protons) over a temperature range of 270tensor is assumed to comprise first-rank antisymmetric (anti-CSA) components. The magni...

  • proton Chemical Shift Anisotropy measurements of hydrogen bonded functional groups by fast magic angle spinning solid state nmr spectroscopy
    Chemical Communications, 2008
    Co-Authors: Luminita Duma, Daniel Abergel, Piotr Tekely, Geoffrey Bodenhausen
    Abstract:

    The suitability of fast MAS solid-state NMR spectroscopy for probing 1H Chemical Shift Anisotropy of hydrogen-bonded species has been demonstrated.

  • Chemical Shift Anisotropy tensors of carbonyl nitrogen and amide proton nuclei in proteins through cross correlated relaxation in nmr spectroscopy
    Journal of the American Chemical Society, 2005
    Co-Authors: Karine Loth, Philippe Pelupessy, Geoffrey Bodenhausen
    Abstract:

    The principal components and orientations of the Chemical Shift Anisotropy (CSA) tensors of the carbonyl (C‘), nitrogen (N), and amide proton (HN) nuclei of 64 distinct amide bonds in human ubiquitin have been determined in isotropic solution by a set of 14 complementary auto- and cross-correlated relaxation rates involving the CSA interactions of the nuclei of interest and several dipole−dipole (DD) interactions. The CSA parameters thus obtained depend to some degree on the models used for local motions. Three cases have been considered:  restricted isotropic diffusion, three-dimensional Gaussian axial fluctuations (3D-GAF), and independent out-of-plane motions of the NHN vectors with respect to the peptide planes.

  • cross correlations between 13c 1h dipolar interactions and 15n Chemical Shift Anisotropy in nucleic acids
    Journal of Biomolecular NMR, 2003
    Co-Authors: Sapna Ravindranathan, Geoffrey Bodenhausen
    Abstract:

    Two sets of cross-correlated relaxation rates involving Chemical Shift Anisotropy and dipolar interactions have been measured in an RNA kissing complex. In one case, both the CSA and dipolar interaction tensors are located on the same nucleotide base and are rigidly fixed with respect to each other. In the other case, the CSA tensor is located on the nucleotide base whereas the dipolar interaction is located on the adjoining ribose unit. Analysis of the measured rates in terms of isotropic or anisotropic rotational diffusion has been carried out for both cases. A marked difference between the two models is observed for the cross-correlation rates involving rigidly fixed spin interactions. The influence of internal motions about the glycosidic linkage between the nucleotide base and the ribose unit on cross-correlated relaxation rates has been estimated by applying a model of restricted rotational diffusion. Local motions seem to have a more pronounced effect on cross-correlated relaxation rates when the two spin interactions are not rigidly fixed with respect to each other.

  • average liouvillian theory revisited cross correlated relaxation between Chemical Shift Anisotropy and dipolar couplings in the rotating frame in nuclear magnetic resonance
    Molecular Physics, 1999
    Co-Authors: Ranajeet Ghose, Thomas R Eykyn, Geoffrey Bodenhausen
    Abstract:

    A review is given of the mathematical foundations of average Liouvillian theory and examples are provided of average Liouvillian expressions derived for sequences in nuclear magnetic resonance which possess temporal symmetry or antisymmetry. The utility of this approach is demonstrated in the design of pulse sequences to measure the effect of cross-correlation between Chemical Shift Anisotropy and dipolar couplings on relaxation rates in biomolecules. Experimental verification of the theory is carried out on a 15N labelled sample of ubiquitin.

Ayyalusamy Ramamoorthy - One of the best experts on this subject based on the ideXlab platform.

  • cytochrome p450 cytochrome b5 interaction in a membrane environment changes 15n Chemical Shift Anisotropy tensors
    Journal of Physical Chemistry B, 2013
    Co-Authors: Manoj Kumar Pandey, Subramanian Vivekanandan, Shivani Ahuja, Sang Choul Im, Lucy Waskell, Rui Huang, Ayyalusamy Ramamoorthy
    Abstract:

    It has been well realized that the dependence of Chemical Shift Anisotropy (CSA) tensors on the amino acid sequence, secondary structure, dynamics, and electrostatic interactions can be utilized in the structural and dynamic studies of proteins by NMR spectroscopy. In addition, CSA tensors could also be utilized to measure the structural interactions between proteins in a protein–protein complex. To this end, we report the experimentally measured backbone amide-15N CSA tensors for a membrane-bound 16.7 kDa full-length rabbit cytochrome-b5 (cytb5), in complexation with a 55.8 kDa microsomal rabbit cytochrome P450 2B4 (cytP4502B4). The 15N-CSAs, determined using the 15N CSA/15N–1H dipolar coupling transverse cross-correlated rates, for free cytb5 are compared with those for the cytb5 bound to cytP4502B4. An overall increase in backbone amide-15N transverse cross-correlated rates for the cytb5 residues in the cytb5–cytP450 complex is observed as compared to the free cytb5 residues. Due to fast spin–spin rela...

  • quantum Chemical calculations of amide 15n Chemical Shift Anisotropy tensors for a membrane bound cytochrome b5
    Journal of Physical Chemistry B, 2013
    Co-Authors: Manoj Kumar Pandey, Ayyalusamy Ramamoorthy
    Abstract:

    There is considerable interest in determining amide-15N Chemical Shift Anisotropy (CSA) tensors from biomolecules and understanding their variation for structural and dynamics studies using solution and solid-state NMR spectroscopy and also by quantum Chemical calculations. Due to the difficulties associated with the measurement of CSA tensors from membrane proteins, NMR-based structural studies heavily relied on the CSA tensors determined from model systems, typically single crystals of model peptides. In the present study, the principal components of backbone amide-15N CSA tensors have been determined using density functional theory for a 16.7 kDa membrane-bound paramagnetic heme containing protein, cytochrome-b5 (cytb5). All the calculations were performed by taking residues within 5 A distance from the backbone amide-15N nucleus of interest. The calculated amide-15N CSA spans agree less well with our solution NMR data determined for an effective internuclear distance rN–H = 1.023 A and a constant angl...

  • determination of 15n Chemical Shift Anisotropy from a membrane bound protein by nmr spectroscopy
    Journal of Physical Chemistry B, 2012
    Co-Authors: Manoj Kumar Pandey, Subramanian Vivekanandan, Kumar Pichumani, Shivani Ahuja, Sang Choul Im, Lucy Waskell, Ayyalusamy Ramamoorthy
    Abstract:

    Chemical Shift Anisotropy (CSA) tensors are essential in the structural and dynamic studies of proteins using NMR spectroscopy. Results from relaxation studies in biomolecular solution and solid-state NMR experiments on aligned samples are routinely interpreted using well-characterized CSA tensors determined from model compounds. Since CSA tensors, particularly the 15N CSA, highly depend on a number of parameters including secondary structure, electrostatic interaction, and the amino acid sequence, there is a need for accurately determined CSA tensors from proteins. In this study, we report the backbone amide-15N CSA tensors for a 16.7-kDa membrane-bound and paramagnetic-heme containing protein, rabbit Cytochrome b5 (cytb5), determined using the 15N CSA/15N–1H dipolar transverse cross-correlation rates. The mean values of 15N CSA determined for residues in helical, sheet, and turn regions are −187.9, −166.0, and −161.1 ppm, respectively, with an overall average value of −171.7 ppm. While the average CSA v...

  • ab initio study of 13cα Chemical Shift Anisotropy tensors in peptides
    Journal of the American Chemical Society, 2004
    Co-Authors: Jeff Birn, Alan Poon, Ayyalusamy Ramamoorthy
    Abstract:

    This study reports magnitudes and the orientation of the 13Cα Chemical Shift Anisotropy (CSA) tensors of peptides obtained using quantum Chemical calculations. The dependency of the CSA tensor parameters on the energy optimization of hydrogen atom positions and hydrogen bonding effects and the use of zwitterionic peptides in the calculations are examined. Our results indicate that the energy optimization of the hydrogen atom positions in crystal structures is necessary to obtain accurate CSA tensors. The inclusion of intermolecular effects such as hydrogen bonding in the calculations provided better agreement between the calculated and experimental values; however, the use of zwitterionic peptides in calculations, with or without the inclusion of hydrogen bonding, did not improve the results. In addition, our calculated values are in good agreement with tensor values obtained from solid-state NMR experiments on glycine-containing tripeptides. In the case of peptides containing an aromatic residue, calcula...

  • Chemical Shift Anisotropy and offset effects in cross polarization solid state nmr spectroscopy
    Journal of Magnetic Resonance, 2002
    Co-Authors: Srinivasan C Shekar, Ayyalusamy Ramamoorthy
    Abstract:

    Abstract The effect of an offset term in the cross-polarization (CP) Hamiltonian of a heteronuclear spin- 1 2 pair due to off-resonant radio frequency (rf) irradiation and/or Chemical Shift Anisotropy on one of the rf channels is investigated. Analytical solutions, simulations, and experimental results are presented. Formulating the CP spin dynamics in terms of an explicit unitary evolution operator enables the CP period to be inserted as a module in a given pulse scheme regardless of the initial density matrix present. The outcome of post-CP manipulation via pulses can be calculated on the resulting density matrix as the phases and amplitudes of all coherence modes are available. Using these tools it is shown that the offset can be used to reduce the rf power on that channel and the performance is further improved by a post-CP pulse whose flip angle matches and compensates the tilt of the effective field on the offset channel. Experimental investigations on single crystalline and polycrystalline samples of peptides confirm the oscillatory nature of CP dynamics and prove the slowing down of the dynamics under offset and/or mismatch conditions.

Jeremy J Titman - One of the best experts on this subject based on the ideXlab platform.

  • Chemical Shift Anisotropy measurements via two dimensional experiments advances
    eMagRes, 2013
    Co-Authors: Jeremy J Titman
    Abstract:

    Many two-dimensional solid-state NMR experiments have been designed to measure the Chemical Shift Anisotropy in systems with a number of sites. These correlate the anisotropic information contained in a powder line shape or a spinning-sideband manifold with a well-resolved isotropic Chemical Shift spectrum. This article describes the advances that have been made in this area over the last decade. Keywords: solid-state NMR; Chemical Shift Anisotropy; two-dimensional NMR; magic-angle spinning; sideband separation; PASS; magic-angle turning; CSA amplification; recoupling

  • caesura measurement of slow molecular dynamics by solid state nuclear magnetic resonance Chemical Shift Anisotropy modulation amplification
    Journal of Chemical Physics, 2006
    Co-Authors: Limin Shao, Jeremy J Titman
    Abstract:

    An alternative magic angle spinning (MAS) exchange NMR experiment based on Chemical Shift Anisotropy (CSA) amplification is described. The CSA amplification experiment correlates a standard MAS spectrum in the ω2 dimension with a sideband pattern in ω1 in which the intensities are identical to those expected for a sample spinning at some fraction 1∕N of the actual rate ωr. In common with 2D-PASS, the isotropic Shift appears only in the ω2 dimension, and long acquisition times can be avoided without loss of resolution of different Chemical sites. The new CSA amplification exchange experiment provides information about the time scale and geometry of molecular motions via their effect on the sideband intensities in a one-dimensional pattern. The one-dimensional patterns from different Chemical sites are separated across two frequency dimensions according to the isotropic Shifts.

  • Chemical Shift Anisotropy amplification with high amplification factor and improved sensitivity
    Journal of Magnetic Resonance, 2006
    Co-Authors: Limin Shao, Charles Crockford, Jeremy J Titman
    Abstract:

    Abstract An improved version of the recently proposed Chemical Shift Anisotropy amplification experiment is described. The original experiment correlates a fast magic angle spinning spectrum in the ω2 dimension with a sideband pattern in ω1 in which the intensities mimic those for a sample spinning at a fraction of the rate ωr/N. Advantages of the experiment include the use of standard methods to extract the principal tensor components from the ω1 sideband patterns and the small number of t1 increments required. The improved version described here permits large amplification factors N to be obtained without resort to prohibitively long sequences of π-pulses and allows sensitivity to be maximized by eliminating the need to store the magnetization along the z-axis for t1. Amplification factors up to 32 are demonstrated experimentally.

  • Chemical Shift Anisotropy amplification
    Journal of Magnetic Resonance, 2004
    Co-Authors: Limin Shao, Charles Crockford, Helen Geen, Giuseppe Grasso, Jeremy J Titman
    Abstract:

    Abstract A new NMR experiment which allows a measurement of the Chemical Shift Anisotropy (CSA) tensor under magic angle spinning (MAS) is described. This correlates a fast MAS spectrum in the ω 2 dimension with a sideband pattern in ω 1 in which the intensities mimic those for a sample spinning at a fraction of the rate ω r / N , and these sidebands result from an amplification by a factor N of the modulation caused by the CSA. Standard methods can be used to extract the principal tensor components from the ω 1 sideband patterns, and the nature of the experiment is such that the use of a large number of t 1 increments can avoided without compromising the resolution of different Chemical sites. The new experiment is useful for accurately measuring narrow Shift anisotropies.

  • eMagRes - Chemical Shift Anisotropy Measurements via Two‐dimensional Experiments: Advances
    eMagRes, 1996
    Co-Authors: Jeremy J Titman
    Abstract:

    Many two-dimensional solid-state NMR experiments have been designed to measure the Chemical Shift Anisotropy in systems with a number of sites. These correlate the anisotropic information contained in a powder line shape or a spinning-sideband manifold with a well-resolved isotropic Chemical Shift spectrum. This article describes the advances that have been made in this area over the last decade. Keywords: solid-state NMR; Chemical Shift Anisotropy; two-dimensional NMR; magic-angle spinning; sideband separation; PASS; magic-angle turning; CSA amplification; recoupling

Eugene Stephane Mananga - One of the best experts on this subject based on the ideXlab platform.

Lixin Liang - One of the best experts on this subject based on the ideXlab platform.

  • measurement of proton Chemical Shift Anisotropy in solid state nmr spectroscopy
    Solid State Nuclear Magnetic Resonance, 2018
    Co-Authors: Lixin Liang
    Abstract:

    Abstract Proton Chemical Shift Anisotropy (CSA) is significantly important as it provides the information of the dynamics and local environmental structure of the proton. The measurement of proton CSA keeps drawing the attention of NMR researchers, and great efforts have been expended. In the early years, measuring proton CSA in solid-state NMR, especially with the strong 1H-1H dipolar network, was hampered by ineffective decoupling or selectively recoupling techniques, and the applications were only limited to those with sparse proton sites or single crystals. Till the latest decades, the dramatic progress on NMR methodology and magic-angle spinning (MAS) technology enable accurate detection of proton CSA in complicated powder samples even proteins. In this review, following a brief description of the measurement of proton CSA in solution and LCs NMR, a retrospect of the experimental development of proton CSA measurement in solid state NMR is presented, from the continuous wave (CW) and multiple pulse sequences for static solid samples, to combined rotation and multiple pulse spectroscopy (CRAMPS), then to the latest methods including rotary resonance, CSA amplification and R-symmetry pulse sequences under MAS conditions.