JMR: Journal of Magnetic Resonance update to February 2007

Journal of Magnetic Resonance
Vol: 184, Issue: 2, February, 2007
pp. 322-329

Title: Improved resolution in 13C solid-state spectra through spin-state-selection
Authors: Verel, Renéa; Manolikas, Theofanisa; Siemer, Ansgar B.a; Meier, Beat H.a
Affiliations: a. Physical Chemistry, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland
Keywords: Solid-state NMR; Spin-state selection; High resolution
Abstract (English):

The application of a spin-state-selective coherence transfer experiment (INADEQUATE-SSS) to solid-state NMR spectroscopy is described. Two-dimensional 13C double-quantum/single-quantum spectra without J splittings in both dimensions lead to enhanced spectral resolution. The method is demonstrated to significantly improve the spectral resolution of the crowded C’–Ca region of two proteins.


Journal of Magnetic Resonance
Vol: 184, Issue: 2, February, 2007
pp. 350-356

Title: Sensitivity enhancement in 13C solid-state NMR of protein microcrystals by use of paramagnetic metal ions for optimizing 1H T1 relaxation
Authors: Wickramasinghe, Nalinda P.a; Kotecha, Mrignayania; Samoson, Agob; Past, Jaanb; Ishii, Yoshitakaa
Affiliations: a. Department of Chemistry, University of Illinois at Chicago, 845 W Taylor St., Chicago, IL 60607, USA
b. National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia
Keywords: Solid-state NMR; Protein microcrystal; T1 relaxation; Paramagnetic doping; 13C CPMAS
Abstract (English):

We discuss a simple approach to enhance sensitivity for 13C high-resolution solid-state NMR for proteins in microcrystals by reducing 1H T1 relaxation times with paramagnetic relaxation reagents. It was shown that 1H T1 values can be reduced from 0.4–0.8s to 60–70ms for ubiquitin and lysozyme in D2O in the presence of 10mM Cu(II)Na2EDTA without substantial degradation of the resolution in 13C CPMAS spectra. Faster signal accumulation using the shorter 1H T1 attained by paramagnetic doping provided sensitivity enhancements of 1.4–2.9 for these proteins, reducing the experimental time for a given signal-to-noise ratio by a factor of 2.0–8.4. This approach presented here is likely to be applicable to various other proteins in order to enhance sensitivity in 13C high-resolution solid-state NMR spectroscopy.


Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 1-14

Title: HMQC and refocused-INEPT experiments involving half-integer quadrupolar nuclei in solids
Authors: Amoureux, J.P.a; Trebosc, J.a; Wiench, J.b; Pruski, M.b
Affiliations: a. UCCS, CNRS-8181, ENSCL-USTL, Fr-59652 Villeneuve d’Ascq, France
b. Ames Laboratory, Iowa State University, Ames, IA 50011, USA
Keywords: Solid-state NMR; J-coupling; R-INEPT; HMQC; Quadrupolar nuclei; MAS; MQMAS; STMAS
Abstract (English):

Hetero-nuclear coherence transfers in HMQC and refocused-INEPT experiments involving half-integer quadrupolar nuclei in solids are analyzed. 1D and 2D schemes are considered under MAS for the general case of multi-spin systems SIn (n4), where S is an observed nucleus. These results are also discussed in the context of high-resolution schemes featuring MQMAS or STMAS. The theoretical predictions are verified experimentally in a series of 1D and 2D experiments performed at 9.4 and 18.8T.


Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 15-19

Title: Three-dimensional through-bond homonuclear–heteronuclear correlation experiments for quadrupolar nuclei in solid-state NMR applied to 27Al–O–31P–O–27Al networks
Authors: Deschamps, Michaëla; Massiot, Dominiquea
Affiliations: a. CRMHT-CNRS, 1D Avenue de la Recherche Scientifique, 45071 ORLEANS cedex 2, France
Keywords: 3D; J-coupling; Quadrupolar nuclei; Aluminium; Phosphate
Abstract (English):

We present here the first 3D homonuclear/heteronuclear correlation experiment applied to quadrupolar nuclei and making use of the sole scalar J-coupling. This experiment, based on the 2D-Homonuclear–Heteronuclear Single Quantum Correlation (H–HSQC) experiment, uses a relayed transfer from the 27Al central transition to neighbouring 31P spins and to the central transition of a second 27Al. It confirms the correlation map characterizing the two 27Al and the 31P NMR signatures of 27Al–O–31P–O–27Al chemically bonded molecular motifs.


Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 39-43

Title: 13C/14N heteronuclear multiple-quantum correlation with rotary resonance and REDOR dipolar recoupling
Author: Gan, Zhehonga
Affiliations: a. Center of Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
Keywords: 13C/14N Correlation; HMQC; Dipolar recoupling; MAS; Rotary resonance; REDOR
Abstract (English):

A two-dimensional 13C/14N heteronuclear multiple quantum correlation (HMQC) experiment using dipolar recoupling under magic-angle spinning (MAS) is described. The experiment is an extension of the recent indirect 13C detection scheme for measuring 14N quadrupolar coupling under MAS. The recoupling allows the direct use of the much larger dipolar interaction instead of the small J and residual dipolar couplings for establishing 13C/14N correlations. Two recoupling methods are incorporated into the HMQC sequence, both applying rf only to the observed 13C spin. The first one uses the REDOR sequence with two p-pulses per rotor cycle. The second one uses a cw rf field matching the spinning frequency, known as rotary resonance. The effects of CSA, Formula Not Shown signal loss, MAS frequency and stability and t1-noise are compared and discussed.


Journal of Magnetic Resonance
Vol: 183, Issue: 2, December, 2006
pp. 235-241

Title: Rotary resonance echo double resonance for measuring heteronuclear dipolar coupling under MAS
Author: Gan, Zhehonga
Affiliations: a. Center of Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
Keywords: Rotary resonance; R-REDOR; REDOR; MAS; Dipolar coupling
Abstract (English):

A rotary resonance echo double resonance (R-REDOR) experiment is described for measuring heteronuclear dipolar coupling under magic-angle spinning. Rotary resonance reintroduces both dipolar coupling and chemical shift anisotropy with an rf field matching the spinning frequency. The resonance effect from chemical shift anisotropy can be refocused with a rotary resonance echo. The R-REDOR experiment thus measures the dephasing of the rotary resonance echo from the heteronuclear dipolar coupling to determine the dipolar coupling constant. The rotary resonance experiment is suitable for measuring dipolar coupling with quadrupolar nuclei because it applies the recoupling rf only to the observed spin-1/2. The rotary resonance scheme has the advantages of a long Formula Not Shown and susceptible to spinning frequency fluctuation.


Journal of Magnetic Resonance
Vol: 183, Issue: 1, November, 2006
pp. 68-76

Title: Polarization transfer from remote protons in 13C CP/MAS
Authors: Tripon, Carmena; Aluas, Mihaelab; Filip, Xeniaa; Filip, Claudiua
Affiliations: a. National Institute for R&D of Isotopic and Molecular Technologies, P.O. Box 700, 400293 Cluj, Romania
b. Physics Department, Babes-Bolyai University, Cluj, Romania
Keywords: Solid-state NMR; Cross-polarization; CP/MAS; Spin dynamics
Abstract (English):

An experimental procedure for CP/MAS polarization transfer from remote 1H nuclear spins is introduced, which is applicable to protonated carbons in organic solids. It is based on preparing a state of non-uniform polarization, where directly bonded 13C–1H nuclei are de-polarized prior to recording the CP buildup curve. This curve is then expected to quantify the polarization transfer from remote protons only. The ability of the cross-polarization/polarization-inversion (CPPI) sequence to generate an initial state suitable for remote 1H CP/MAS scheme is analyzed both theoretically and experimentally. Confining to aliphatic groups, it was found that complete de-polarization of bonded proton is possible in the case of CH, whereas for CH2 and CH3 moieties only a partial de-polarization can be achieved. The theoretical predictions have been verified in practice for the particular case of l-alanine. The significance of the results from fundamental, as well as practical point of view, is also discussed. In particular, it is shown that: (i) the coherent description of polarization transfer under CP/MAS, including 1H polarization redistribution, is valid over time-scales longer than commonly assumed in many treatments of cross-polarization, and (ii) the remote protons polarization transfer curve can be used in combination with the conventional CP/MAS curve to get additional structural and dynamical information in organic systems.

Journal of Magnetic Resonance
Vol: 183, Issue: 1, November, 2006
pp. 123-133

Title: Bayesian and information theory analysis of MAS sideband patterns in spin 1/2 systems
Author: Sachleben, Joseph R.a
Affiliations: a. Department of Chemistry, Otterbein College, Westerville, OH 43081, USA
Keywords: Magic angle spinning; Errors; Bayesian analysis; Chemical shift tensor
Abstract (English):

Bayesian statistics and information theory are used to analyze the reliability of extracting chemical shift parameters from spinning sideband patterns of spin 1/2 systems. Efficient code has been written to calculate the two-dimensional posterior probability as a function of the chemical shift anisotropy, d, and the asymmetry parameter, , given the sideband intensities and the signal-to-noise ratio. This method has the advantage of assuming only that the noise in the sideband intensities is distributed as a Gaussian. It assumes nothing about the distribution of the values of parameters d and , which are shown in some cases to be highly non-Gaussian. The utility of Bayesian analysis is demonstrated on 1D slow-spinning MAS spectra and on sideband patterns extracted from 2D PASS spectra. Previous investigations have shown that there is an optimal range of spinning frequencies for determining d. In this study, information theory is used to determine the signal-to-noise ratio dependence of the entropy in d, , and total entropy in spinning sideband spectra. The entropy is a measure of the information content of a probability distribution. When the entropy is zero, there is perfect information on a system, while if it is infinite, there is no information on the system. It is found that for all values of and for signal-to-noise ratios in the range 50–1000, an entropy minimum in nd/nr occurs for values 1.5nd/nr3. In the same range of signal-to-noise ratios, the entropy in is a monotonically decreasing function of nd/nr. The global information content of a spinning sideband pattern (i.e., the total entropy) is dependent on the signal-to-noise ratio and has an optimal value at nd/nr2 at a signal-to-noise ratio of 50 and increasing to 2.5 for signal-to-noise ratios of 1000. Finally, the increase of information in a sideband pattern as a function of the number of sidebands used in the analysis is examined. Most of the information about d and is contained in the five central sidebands; i.e., sidebands -2 to 2.