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Solid-state NMR spectra @ 21.1 Tesla
(Click on a picture to enlarge)

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A standard QCPMG NMR pulse sequence consists of a 90 pulse followed by a train of 180 pulses (more). Ideally, the resulting spikelet envelope should outline the static lineshape (middle spectrum, 90-180). If the first pulse deviates from 90 due to incorrect calibration, the QCPMG spikelet pattern does not change significantly, the only effect is somewhat lower overall intensity (Figure A).

While the miscalibrated 90 pulse alone has little impact on the QCPMG lineshape, of course it is often used to calculate the 180 pulse. As can be seen both, experimentally and using SIMPSON calculations, the miscalibrated 180 pulse leads to significantly distorted spikelet patterns (Figure B). The 180 pulse misset by as little as 20-30 degrees could produce considerable oscillations in spikelet intensity across the envelope. This illustrates that the QCPMG NMR experiments are much more sensitive to proper setup of the 180 degree pulse than the Hahn-echo experiments.

QCPMG spectra shown were calculated by Eric Ye (900 Facility) using the SIMPSON software for a central transition of a spin 3/2 nucleus resonating at 295 MHz, CQ=10 MHz, etaQ=0.7, CS anisotropy -200 ppm, coincidental EFG and CSA tensors.

For more information see

Renée Siegel, Thomas T. Nakashima and Roderick E. Wasylishen, "Signal-to-Noise Enhancement of NMR Spectra of Solids Using Multiple-Pulse Spin-Echo Experiments", Conc. Magn. Reson. 26A (2005) 62-77. http://dx.doi.org/10.1002/cmr.a.20038

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A WURST-QCPMG NMR technique has recently been introduced by Luke O'Dell and Rob Schurko (Windsor) to achieve uniform excitation of quadrupolar nuclei across very wide bandwidth. Using this approach wideline spectra of stationary samples can now be acquired with no need or just minimal transmitter frequency adjustment. The spectrum shown was acquired in about 1 hour by co-adding 10 individual pieces. Experiments were performed by Luke O'Dell, who also kindly provided the WURST-QCPMG pulse sequence for the 900 MHz NMR instrument. This pulse program is now available to our users. For more information about WURST-QCPMG:

L.A. O'Dell and R.W. Schurko, "QCPMG Using Adiabatic Pulses for Faster Acquisition of Ultra-Wideline NMR Spectra," Chem. Phys. Lett. 464 (2008) 97-102. http://dx.doi.org/10.1016/j.cplett.2008.08.095

May, 2009

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Recently developed Polarization Inversion Spin Exchange at the Magic Angle (PISEMA) technique finds applications in correlation experiments and is used for accurate measurements of chemical shift and heteronuclear dipolar interactions (see Annual Reports on NMR Spectroscopy, 2004, volume 52, p.1-52). This 1H-15N PISEMA experiment with 5N-labeled N-acetyl valine was performed on the 900 MHz instrument using the Facility's flat-coil E-free probe (M. Monette, Bruker).

December, 2008

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Two new NMR probes have been recently added to a growing array of tools at the 900 Facility. The previously announced 4 mm CP/MAS 1H/13C/15N probe has passed its first tests in mapping 13C-15N REDOR distances, as in this experiment with Glycine performed by Eric Ye (the 900 Facility).

The second probe is a flat-coil E-free probe built by Bruker U.S.A for experiments with biological samples oriented on glass plates. The probe is equipped with four r.f. channels, 1H/13C/15N/31P and is scheduled for testing. All probes from our unique probe collection are readily available to the Facility users. Please enquire.

November, 2008

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Very Fast MAS allows straightforward implementation of advanced 2D pulse schemes. In this experiment 1H-1H DQ-SQ correlation spectroscopy at 60 kHz MAS is applied to resolve proton resonances and couplings in solid L-Tyrosine hydrochloride. Experiments performed by Darren Brouwer (SIMS NRC) using the 1.3 mm MAS Bruker probe.

March, 2008

 

 

 

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Considerably improved resolution in 1H MAS NMR spectra of glycine at Very Fast MAS spinning speeds. No additional homonuclear decoupling, i.e. CRAMPS, is necessary. Experiments performed by Darren Brouwer (SIMS NRC) using the 1.3 mm MAS Bruker probe.

March, 2008

 

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Another example when NMR experiments with low-gamma low-sensitivity quadrupolar nuclei, here Sr-87, performed at 21 T in a straightforward simple manner. Done by V. Terskikh (the 900 Facility) with a home-built 5 mm solenoid probe.

January, 2007

 

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1H CSA recoupled spectra of citric acid. Experiments performed by Darren Brouwer (SIMS NRC) with the 2.5 mm MAS probe. Journal of Magnetic Resonance 185 (2007) 173-178

December, 2006

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19F-13C CP MAS spectrum recorded for a hydrated Nafion film. In such high-resolution spectra various C-F species can readily be identified. Experiments performed by Shane Pawsey (the 900 Facility) with the 2.5 mm MAS probe.

October, 2006

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High-speed MAS 17O NMR spectrum for 4-nitrobenzaldehyde. Experiments performed by Gang Wu (Queen's University) with the 2.5 mm MAS probe. Journal of Physical Chemistry A 112 (2008) 1024-1032.

August, 2006

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Similar to MQMAS, satellite transition MAS of half-integer quadrupole nuclei (STMAS) can be used to separate anisotropic from isotropic interactions. Experiments performed by S. Steuernagel (Bruker) with the 2.5 mm MAS probe.

July, 2006

 

 

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The 3Q-MAS spectrum of RbNO3 displaying the HR spectra of the three components that make up the powder pattern. Experiment performed by V. Terskikh (the 900 Facility) with the 4 mm MAS probe.

 

 

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Sensitivity enhancement in MAS spectra of half-integer quadrupole nuclei, DFS (double frequency sweep), RAPT (rotor assisted population transfer), compared with a SP (single pulse) experiment. Performed by S. Steuernagel (Bruker) with the 2.5 mm MAS probe.

July, 2006

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127I NMR of NaIO4 revisited at 21.1 T. Cq=42.3 MHz, CSA is negligible (the span is <20 ppm). For more see: G. Wu and S. Dong, SSNMR 20 (2001) 100-107

March, 2006

 

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In materials ultrahigh magnetic fields are beneficial when studying low-gamma (and) quadrupolar nuclei. These 39K NMR spectra of KNO3 were recorded on our 900 instrument at the resonance frequency of 42 MHz (compare with 23 MHz at 11.7 T). Experiments performed by I. Moudrakovski (SIMS-NRC) with the wideline static probe built by J. Bennett (NRC).

Journal of Physical Chemistry B 111 (2007) 491-495.

February, 2006

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The resolution in proton spectra of solids is improved by applying combined rotation and multiple-pulse spectroscopy (CRAMPS). Experiments performed by M. Monette (Bruker) with the 2.5 mm MAS probe.

January, 2006

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1H/13C HETCOR with Frequency-Switched Lee-Goldberg (FSLG) 1H homonuclear decoupling for alpha-Hydroquinone. Experiments performed by D. Brouwer (NRC-SIMS) with the 3.2 mm MAS probe.

December, 2005

 

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Both experiments were performed with the 3.2 mm MAS probe. With very short rf-pulses available on the 900 very broad static lineshapes can be correclty recorded. In this case a solid-state 90-pulse for 55Mn was 0.6 us.

November, 2005

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Quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) pulse sequence dramatically improves signal-to-noise in solid-state NMR experiments of quadrupolar nuclei, here for 87Rb (I=3/2).


October, 2005

 

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13C CP/MAS spectrum of caffeine. At 21.1 T note absence of the line splitting due to the dipolar coupling with the quadrupolar 14N. At lower magnetic fields such coupling results in very complicated spectra.

Crystal Growth and Design 8 (2007) 1406-1410.

September, 2005

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11B MAS NMR spectra of sodium tetraborate (borax). Even at 14.1 T two non-equivalent boron sites would partially overlap complicating interpretation and quantitative analysis of the spectra.

September, 2005

 

 

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13C CP/MAS spectrum of tetracycline hydrochloride. Resonances from all 22 carbon atoms are well resolved.

September, 2005