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Solid-state NMR indirect detection of nuclei experiencing large anisotropic interactions using spinning
Ming Shen1, Julien Trébosc2, Olivier Lafon2
1UCCS, CNRS, UMR 8181, University of Lille, Villeneuve d'Ascq 59652, France; Physics Department & Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, Shanghai 200062, China.
Solid State Nuclear Magnetic Resonance
|September 29, 2015
Summary
Long radio-frequency pulses selectively excite NMR center bands in Heteronuclear Multiple-Quantum Correlation (HMQC) experiments. This method efficiently detects nuclei with wide spectra, even with moderate radio-frequency fields.
Area of Science:
- Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy
- Advanced pulse sequence development
- Spectroscopic analysis of quadrupolar nuclei
Background:
- Magic-Angle Spinning (MAS) NMR is crucial for high-resolution solid-state studies.
- Selective excitation of wide NMR spectra in HMQC sequences is challenging.
- Detecting quadrupolar nuclei like Nitrogen-14 ((14)N) often requires specialized techniques.
Purpose of the Study:
- To investigate the application of long radio-frequency (rf) pulses for selective center-band excitation in HMQC sequences.
- To evaluate the performance of this method for indirect detection of nuclei with wide spectra, including quadrupolar isotopes.
- To assess the efficiency and spectral quality of long-pulse excitation in J-HMQC and D-HMQC experiments.
Main Methods:
- Numerical simulations of Heteronuclear Multiple-Quantum Correlation (HMQC) sequences.
- Application of long on-resonance rf pulses to the indirect channel.
- Experimental validation using scalar-mediated (J-HMQC) and dipolar-mediated (D-HMQC) experiments on crystalline samples ((14)N/(1)H).
Main Results:
- Long rf pulses enable selective excitation of the center band in wide NMR spectra for HMQC.
- This method is effective for spin-1/2 nuclei with large chemical shift anisotropy (CSA) and spin-1 nuclei with large quadrupole interactions.
- Dipolar-mediated HMQC experiments on (14)N/(1)H showed comparable efficiency to strong pulses with reduced spectral distortion and robustness to experimental variations.
Conclusions:
- Center-band selective weak pulses using long rf pulses are advantageous for HMQC experiments on wide spectra.
- This approach requires moderate rf fields, is easily optimized, and exhibits high robustness to experimental imperfections.
- The method is particularly beneficial for indirect detection of quadrupolar nuclei like (14)N, offering improved spectral quality and experimental flexibility.
Keywords:
Indirect detectionNitrogen-14Overtone.Selective excitationThrough-space HMQCVery broad spectraMore Related Videos
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