Monday, June 11, 2007

Journal of Magnetic Resonance, up to May 2007

Journal of Magnetic Resonance
Vol: 186, Issue: 1, May, 2007
pp. 26-33

Title: The role of 15N CSA and CSA/dipole cross-correlation in 15N relaxation in solid proteins
Authors: Sein, Juliena; Giraud, Nicolasa; Blackledge, Martinb; Emsley, Lyndona
Affiliations: a. Laboratoire de Chimie (UMR 5182 CNRS/ENS Lyon), Ecole Normale Supérieure de Lyon, 69364 Lyon, France
b. Institut de Biologie Structurale Jean Pierre Ebel (UMR 5075 CNRS/CEA/UJF), 38027 Grenoble, France
Keywords: Nitrogen-15 longitudinal relaxation; Solid-state NMR; Protein dynamics; Cross-correlation; Magic angle spinning

The influence of the 15N CSA on 15N longitudinal relaxation is investigated for an amide group in solid proteins in powder form under MAS. This contribution is determined to be typically 20–33% of the overall longitudinal relaxation rate, at 11.74 and 16.45T, respectively. The improved treatment is used to analyze the internal dynamics in the protein Crh, in the frame of a motional model of diffusion in a cone, using the explicit average sum approach. Significant variations with respect to the determined dynamics parameters are observed when properly accounting for the contribution of 15N CSA fluctuations. In general, the fit of experimental data including CSA led to the determination of diffusion times (tw) which are longer than when considering only an 15N–1H dipolar relaxation mechanism. CSA-Dipole cross-correlation is shown to play little or no role in protonated solids, in direct contrast to the liquid state case.
# 10.1016/j.jmr.2007.01.010

Journal of Magnetic Resonance
Vol: 186, Issue: 1, May, 2007
pp. 94-99

Title: Resolution enhancement using a new multiple-pulse decoupling sequence for quadrupolar nuclei
Authors: Delevoye, L.a; Trébosc, J.a; Gan, Z.b; Montagne, L.a; Amoureux, J-P.a
Affiliations: a. UCCS, CNRS-8181, ENSCL-USTL, 59652 Villeneuve d’Ascq, France
b. NHMFL, 32310 Tallahassee, FL, USA
Keywords: Solid-state NMR; Quadrupolar nuclei; Decoupling; Scalar coupling

A new decoupling composite pulse sequence is proposed to remove the broadening on spin S=1/2 magic-angle spinning (MAS) spectra arising from the scalar coupling with a quadrupolar nucleus I. It is illustrated on the 31P spectrum of an aluminophosphate, AlPO4-14, which is broadened by the presence of 27Al/31P scalar couplings. The multiple-pulse (MP) sequence has the advantage over the continuous wave (CW) irradiation to efficiently annul the scalar dephasing without reintroducing the dipolar interaction. The MP decoupling sequence is first described in a rotor-synchronised version (RS-MP) where one parameter only needs to be adjusted. It clearly avoids the dipolar recoupling in order to achieve a better resolution than using the CW sequence. In a second improved version, the MP sequence is experimentally studied in the vicinity of the perfect rotor-synchronised conditions. The linewidth at half maximum (FWHM) of 65Hz using 27Al CW decoupling decreases to 48Hz with RS-MP decoupling and to 30Hz with rotor-asynchronised MP (RA-MP) decoupling. The main phenomena are explained using both experimental results and numerical simulations.
# 10.1016/j.jmr.2007.01.018

Journal of Magnetic Resonance
Vol: 186, Issue: 1, May, 2007
pp. 156-159

Title: Multiple Ca2+ environments in silicate glasses by high-resolution 43Ca MQMAS NMR technique at high and ultra-high (21.8T) magnetic fields
Authors: Shimoda, Keijia; Tobu, Yasuhiroa; Shimoikeda, Yuichib; Nemoto, Takahirob; Saito, Kojia
Affiliations: a. Advanced Technology Research Laboratories, Nippon Steel Corporation, 20-1 Shintomi, Futtsu 293-8511, Japan
b. JEOL Ltd., 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan
Keywords: 7QMAS; Ca-43; Silicate glass; Ultra-high magnetic field; Solid-state NMR

We here show the 43Ca 5QMAS NMR spectra at high field (16.4T) and the first 7QMAS spectrum at ultra-high field (21.8T) for geologically important Ca-containing glasses. The high-resolution MQMAS spectra present a clear evidence of multiple Ca sites in the amorphous structures that have never been identified by other analytical methods. The present study suggests that the Ca2+ ions are mainly in 7- and 8-fold coordination sites. This will offer valuable insights for dynamic properties of magmatic liquids. The MQMAS NMR technique at high magnetic field is a unique tool to understand the detailed structural information on a specific element in solids including organic and inorganic compounds.
# 10.1016/j.jmr.2007.01.019

Journal of Magnetic Resonance
Vol: 185, Issue: 2, April, 2007
pp. 326-330

Title: Spectral editing in solid-state MAS NMR of quadrupolar nuclei using selective satellite inversion
Authors: Dey, Krishna K.a; Prasad, S.a; Ash, Jason T.a; Deschamps, Michaelb; Grandinetti, Philip J.a
Affiliations: a. Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210-1173, USA
b. CRMHT-CNRS, UPR4212, 45071 Orleans cedex2, France
Keywords: Quadrupolar nuclei; Sensitivity enhancement; Inversion; Spectral editing; Satellite inversion

A sensitivity enhancement method based on selective adiabatic inversion of a satellite transition has been employed in a (p/2)CT– Formula Not Shown –(p/2)CT spectral editing sequence to both enhance and resolve multisite NMR spectra of quadrupolar nuclei. In addition to a total enhancement of 2.5 times for spin 3/2 nuclei, enhancements up to 2.0 times is reported for the edited sites in a mixture of rubidium salts.
# 10.1016/j.jmr.2006.12.013

Journal of Magnetic Resonance
Vol: 185, Issue: 2, April, 2007
pp. 318-325

Title: Spin-locking and recoupling of homonuclear dipolar interaction between spin-3/2 nuclei under magic-angle sample spinning
Author: Mali, Gregora
Affiliations: a. National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia
Keywords: Quadrupolar nuclei; MAS; Spin-lock; Homonuclear dipolar recoupling

Numerical simulations and experiments were used to examine the possibility of employing strong spin-lock fields for recoupling of homonuclear dipolar interactions between spin-3/2 quadrupolar nuclei and to compare it to the rotary-resonance recoupling at weak spin-lock fields. It was shown that strong spin-lock pulses under MAS conditions can lead to recoupling, provided that the electric-field gradient principal axes systems of the coupled nuclei are aligned and that their quadrupolar coupling constants are approximately the same. The phenomenon is based on the fact that strong spin-lock pulses induce adiabatic transfer of magnetization between the central-transition coherence and the triple-quantum coherence with equal periodicity as is the periodicity of the time-dependent dipolar coupling. Because of the synchronous variation of the state of the spin system and of the dipolar interaction, the effect of the latter on the central-transition coherence and on the triple-quantum coherence is not averaged out by sample rotation. The approach is, however, very sensitive to the relative orientation of the electric-field gradient principal axes systems and therefore less robust than the approach based on weak spin-lock pulses that satisfy rotary-resonance condition.
# 10.1016/j.jmr.2007.01.008

Journal of Magnetic Resonance
Vol: 185, Issue: 1, March, 2007
pp. 159-163

Title: Long-term stability of rotor-controlled MAS frequencies to 0.1Hz proved by 14N MAS NMR experiments and simulations
Authors: Jakobsen, Hans J.a; Hove, Anders R.a; Bildsøe, Henrika; Skibsted, Jørgena; Brorson, Michaelb
Affiliations: a. Instrument Centre for Solid-State NMR Spectroscopy, Department of Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark
b. Haldor Topsøe A/S, Nymøllevej 55, DK-2800 Lyngby, Denmark
Keywords: 0.1Hz MAS stability; Air pressure stabilization; 14N MAS NMR; Ammonium monomolybdate polymorphs; STARS simulations

Experimental and simulated 14N MAS NMR spectra of the Formula Not Shown ions in the two polymorphs, mS60 and mP60, of (NH4)2MoO4 are used to illustrate that a long-term stability of rotor-controlled MAS frequencies to 0.1Hz can be achieved using commercial instrumentation (MAS speed controller and 7.5mm MAS probe with a single marked rotor) attached to a highly pressure-stabilized air supply. A new modification of the STARS simulation software employs a Gaussian distribution for the experimental spinning frequency around the frequency set for the MAS speed controller. A simulated spectrum is then obtained by summation of several calculated spectra for evenly spaced spinning frequencies around the set frequency with relative weight factors corresponding to the Gaussian distribution.
# 10.1016/j.jmr.2006.12.008

Journal of Magnetic Resonance
Vol: 185, Issue: 1, March, 2007
pp. 173-178

Title: Symmetry-based recoupling of proton chemical shift anisotropies in ultrahigh-field solid-state NMR
Authors: Brouwer, Darren H.a; Ripmeester, John A.a
Affiliations: a. Steacie Institute for Molecular Sciences, National Research Council, 100 Sussex Drive, Ottawa, Ont., Canada K1A 0R6
Keywords: Proton MAS NMR; Chemical shift anisotropy; Recoupling; CRAMPS; Hydrogen bonding

A two-dimensional NMR experiment for estimating proton chemical shift anisotropies (CSAs) in solid powders under magic-angle spinning conditions is demonstrated in which 1H CSAs are reintroduced with a symmetry-based recoupling sequence while the individual proton sites are resolved according to their isotropic chemical shifts by magic-angle spinning (MAS) or combined rotation and multiple pulse (CRAMPS) homonuclear decoupling. The experiments where carried out on an ultrahigh-field solid-state NMR instrument (900MHz 1H frequency) which leads to increased resolution and reliability of the measured 1H CSAs. The experiment is expected to be important for investigating hydrogen bonding in solids.
# 10.1016/j.jmr.2006.12.003

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