title: Solid-state NMR indirect detection of nuclei experiencing large anisotropic interactions using spinning sideband-selective pulses.
abstract: Under Magic-Angle Spinning (MAS), a long radio-frequency (rf) pulse applied on resonance achieves the selective excitation of the center-band of a wide NMR spectrum. We show herein that these rf pulses can be applied on the indirect channel of Hetero-nuclear Multiple-Quantum Correlation (HMQC) sequences, which facilitate the indirect detection via spin-1/2 isotopes of nuclei exhibiting wide spectra. Numerical simulations show that this indirect excitation method is applicable to spin-1/2 nuclei experiencing a large chemical shift anisotropy, as well as to spin-1 isotopes subject to a large quadrupole interaction, such as (14)N. The performances of the long pulses are analyzed by the numerical simulations of scalar-mediated HMQC (J-HMQC) experiments indirectly detecting spin-1/2 or spin-1 nuclei, as well as by dipolar-mediated HMQC (D-HMQC) experiments achieving indirect detection of (14)N nuclei via (1)H in crystalline γ-glycine and N-acetyl-valine samples at a MAS frequency of 60kHz. We show on these solids that for the acquisition of D-HMQC spectra between (1)H and (14)N nuclei, the efficiency of selective moderate excitation with long-pulses at the (14)N Larmor frequency, ν0((14)N), is comparable to those with strong excitation pulses at ν0((14)N) or 2ν0((14)N) frequencies, given the rf field delivered by common solid-state NMR probes. Furthermore, the D-HMQC experiments also demonstrate that the use of long pulses does not produce significant spectral distortions along the (14)N dimension. In summary, the use of center-band selective weak pulses is advantageous for HMQC experiments achieving the indirect detection of wide spectra since it (i) requires a moderate rf field, (ii) can be easily optimized, (iii) displays a high robustness to CSAs, offsets, rf-field inhomogeneities, and fluctuations in MAS frequency, and (iv) is little dependent on the quadrupolar coupling constant.
authors.affiliation: UCCS, 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.
authors.forename: Ming
authors.initials: M
authors.lastname: Shen
authors.affiliation: UCCS, CNRS, UMR 8181, University of Lille, Villeneuve d'Ascq 59652, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Trébosc
authors.affiliation: UCCS, CNRS, UMR 8181, University of Lille, Villeneuve d'Ascq 59652, France. Electronic address: olivier.lafon@univ-lille1.fr.
authors.forename: Olivier
authors.initials: O
authors.lastname: Lafon
authors.affiliation: Center of Interdisciplinary Magnetic Resonance, NHMFL, Tallahassee, FL 32310, USA.
authors.forename: Zhehong
authors.initials: Z
authors.lastname: Gan
authors.affiliation: UCCS, CNRS, UMR 8181, University of Lille, Villeneuve d'Ascq 59652, France.
authors.forename: Frédérique
authors.initials: F
authors.lastname: Pourpoint
authors.affiliation: Physics Department & Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, Shanghai 200062, China.
authors.forename: Bingwen
authors.initials: B
authors.lastname: Hu
authors.affiliation: Physics Department & Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, Shanghai 200062, China.
authors.forename: Qun
authors.initials: Q
authors.lastname: Chen
authors.affiliation: UCCS, 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. Electronic address: jean-paul.amoureux@univ-lille1.fr.
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Amoureux
mesh_terms: D016880:Anisotropy; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D013997:Time Factors
keywords: Indirect detection; Nitrogen-14; Overtone.; Selective excitation; Through-space HMQC; Very broad spectra