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Duong NT, Lee D, Mentink-Vigier F, Lafon O, De Paëpe G. On the use of radio-frequency offsets for improving double-quantum homonuclear dipolar recoupling of half-integer-spin quadrupolar nuclei. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2021; 59:991-1008. [PMID: 33624858 DOI: 10.1002/mrc.5142] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2020] [Revised: 02/15/2021] [Accepted: 02/19/2021] [Indexed: 06/12/2023]
Abstract
Detecting proximities between nuclei is crucial for atomic-scale structure determination with nuclear magnetic resonance (NMR) spectroscopy. Different from spin-1/2 nuclei, the methodology for quadrupolar nuclei is limited for solids due to the complex spin dynamics under simultaneous magic-angle spinning (MAS) and radio-frequency irradiation. Herein, the performances of several homonuclear rotary recoupling (HORROR)-based homonuclear dipolar recoupling sequences are evaluated for 27 Al (spin-5/2). It is shown numerically and experimentally on mesoporous alumina that BR 2 2 1 outperforms the supercycled S3 sequence and its pure double-quantum (DQ) (bracketed) version, [S3 ], both in terms of DQ transfer efficiency and bandwidth. This result is surprising since the S3 sequence is among the best low-power recoupling schemes for spin-1/2. The superiority of BR 2 2 1 is thoroughly explained, and the crucial role of radio-frequency offsets during its spin dynamics is highlighted. The analytical approximation of BR 2 2 1 , derived in an offset-toggling frame, clarifies the interplay between offset and DQ efficiency, namely, the benefits of off-resonance irradiation and the trough in DQ efficiency for BR 2 2 1 when the irradiation is central between two resonances, both for spin-1/2 and half-integer-spin quadrupolar nuclei. Additionally, density matrix propagations show that the BR 2 2 1 sequence, applied to quadrupolar nuclei subject to quadrupolar interaction much larger than radio-frequency frequency field, can create single- and multiple-quantum coherences for near on-resonance irradiation. This significantly perturbs the creation of DQ coherences between central transitions of neighboring quadrupolar nuclei. This effect explains the DQ efficiency trough for near on-resonance irradiation, in the case of both cross-correlation and autocorrelation peaks. Overall, this work aids experimental acquisition of homonuclear dipolar correlation spectra of half-integer-spin quadrupolar nuclei and provides theoretical insights towards improving recoupling schemes at high magnetic field and fast MAS.
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Affiliation(s)
- Nghia Tuan Duong
- Univ. Grenoble Alpes, CEA, IRIG-MEM, Grenoble, 38000, France
- Univ. Lille, CNRS, Centrale Lille, Univ. Artois, UMR 8181 - UCCS - Unité de Catalyse et Chimie du Solide, Lille, F-59000, France
| | - Daniel Lee
- Univ. Grenoble Alpes, CEA, IRIG-MEM, Grenoble, 38000, France
| | | | - Olivier Lafon
- Univ. Lille, CNRS, Centrale Lille, Univ. Artois, UMR 8181 - UCCS - Unité de Catalyse et Chimie du Solide, Lille, F-59000, France
- Institut Universitaire de France, Paris, 75231, France
| | - Gaël De Paëpe
- Univ. Grenoble Alpes, CEA, IRIG-MEM, Grenoble, 38000, France
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Yu Y, Keil P, Stevensson B, Hansen MR, Edén M. Assessment of new symmetry-based dipolar recoupling schemes for homonuclear magnetization exchange between quadrupolar nuclei in two-dimensional correlation MAS NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 316:106734. [PMID: 32590307 DOI: 10.1016/j.jmr.2020.106734] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Revised: 04/13/2020] [Accepted: 04/15/2020] [Indexed: 06/11/2023]
Abstract
We provide an extensive experimental and numerical evaluation of MQ-phase (S)M supercycles with M={3,4} of three groups of symmetry-based homonuclear dipolar recoupling rf-pulse sequences, [Formula: see text] , for establishing proximities among half-integer spin quadrupolar nuclei under moderately fast magic-angle-spinning (MAS) conditions in single-quantum-single-quantum (1Q-1Q) correlation NMR experiments. The relative merits of the (S)M schemes for variations in resonance offsets and rf-amplitude errors were assessed by numerically simulated magnetization transfers in spin-3/2 pairs with variable isotropic chemical shifts and quadrupolar coupling constants. Experimental demonstrations of 23Na (spin-3/2) NMR on Na2MoO4·2H2O and 27Al (spin-5/2) NMR on AlPO-CJ19 [(NH4)2Al4(PO4)4HPO4·H2O] are presented at 14.1 T and 24 kHz MAS. We recommend using the (SR221)3 or (SR221)4 supercycles for samples that exhibit small chemical-shift dispersions (<3 kHz), and any (SRNNN/2)3 scheme with N⩾10 for larger spreads of isotropic chemical shifts. However, because the (SRNNN/2)3 sequences recouple heteronuclear dipolar interactions, their application to proton-bearing samples requires high-power proton decoupling during the mixing period. Alternatively, the (SR241)3 and (SR241)4 schemes may be employed in the absence of proton decoupling, but with poorer compensation to resonance-offsets and rf-amplitude errors.
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Affiliation(s)
- Yang Yu
- Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Philipp Keil
- Institute for Physical Chemistry, Westfälische Wilhelms-Universität Münster, DE-48 149 Münster, Germany
| | - Baltzar Stevensson
- Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Michael Ryan Hansen
- Institute for Physical Chemistry, Westfälische Wilhelms-Universität Münster, DE-48 149 Münster, Germany
| | - Mattias Edén
- Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden.
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Yu Y, Keil P, Hansen MR, Edén M. Improved Magnetization Transfers among Quadrupolar Nuclei in Two-Dimensional Homonuclear Correlation NMR Experiments Applied to Inorganic Network Structures. Molecules 2020; 25:molecules25020337. [PMID: 31947638 PMCID: PMC7024165 DOI: 10.3390/molecules25020337] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2019] [Revised: 01/08/2020] [Accepted: 01/09/2020] [Indexed: 11/17/2022] Open
Abstract
We demonstrate that supercycles of previously introduced two-fold symmetry dipolar recoupling schemes may be utilized successfully in homonuclear correlation nuclear magnetic resonance (NMR) spectroscopy for probing proximities among half-integer spin quadrupolar nuclei in network materials undergoing magic-angle-spinning (MAS). These (SR221)M, (SR241)M, and (SR281)M recoupling sequences with M=3 and M=4 offer comparably efficient magnetization transfers in single-quantum–single-quantum (1Q–1Q) correlation NMR experiments under moderately fast MAS conditions, as demonstrated at 14.1 T and 24 kHz MAS in the contexts of 11B NMR on a Na2O–CaO–B2O3–SiO2 glass and 27Al NMR on the open framework aluminophosphate AlPO-CJ19 [(NH4)2Al4(PO4)4HPO4·H2O]. Numerically simulated magnetization transfers in spin–3/2 pairs revealed a progressively enhanced tolerance to resonance offsets and rf-amplitude errors of the recoupling pulses along the series (SR221)M< (SR241)M< (SR281)M for increasing differences in chemical shifts between the two nuclei. Nonetheless, for scenarios of a relatively minor chemical-shift dispersions (≲3 kHz), the (SR221)M supercycles perform best both experimentally and in simulations.
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Affiliation(s)
- Yang Yu
- Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden;
| | - Philipp Keil
- Institute for Physical Chemistry, Westfälische Wilhelms-Universität Münster, DE-48 149 Münster, Germany; (P.K.); (M.R.H.)
| | - Michael Ryan Hansen
- Institute for Physical Chemistry, Westfälische Wilhelms-Universität Münster, DE-48 149 Münster, Germany; (P.K.); (M.R.H.)
| | - Mattias Edén
- Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden;
- Correspondence:
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Martin RW, Kelly JE, Collier KA. Spatial reorientation experiments for NMR of solids and partially oriented liquids. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2015; 90-91:92-122. [PMID: 26592947 PMCID: PMC6936739 DOI: 10.1016/j.pnmrs.2015.10.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2015] [Revised: 10/13/2015] [Accepted: 10/15/2015] [Indexed: 06/05/2023]
Abstract
Motional reorientation experiments are extensions of Magic Angle Spinning (MAS) where the rotor axis is changed in order to average out, reintroduce, or scale anisotropic interactions (e.g. dipolar couplings, quadrupolar interactions or chemical shift anisotropies). This review focuses on Variable Angle Spinning (VAS), Switched Angle Spinning (SAS), and Dynamic Angle Spinning (DAS), all of which involve spinning at two or more different angles sequentially, either in successive experiments or during a multidimensional experiment. In all of these experiments, anisotropic terms in the Hamiltonian are scaled by changing the orientation of the spinning sample relative to the static magnetic field. These experiments vary in experimental complexity and instrumentation requirements. In VAS, many one-dimensional spectra are collected as a function of spinning angle. In SAS, dipolar couplings and/or chemical shift anisotropies are reintroduced by switching the sample between two different angles, often 0° or 90° and the magic angle, yielding a two-dimensional isotropic-anisotropic correlation spectrum. Dynamic Angle Spinning (DAS) is a related experiment that is used to simultaneously average out the first- and second-order quadrupolar interactions, which cannot be accomplished by spinning at any unique rotor angle in physical space. Although motional reorientation experiments generally require specialized instrumentation and data analysis schemes, some are accessible with only minor modification of standard MAS probes. In this review, the mechanics of each type of experiment are described, with representative examples. Current and historical probe and coil designs are discussed from the standpoint of how each one accomplishes the particular objectives of the experiment(s) it was designed to perform. Finally, applications to inorganic materials and liquid crystals, which present very different experimental challenges, are discussed. The review concludes with perspectives on how motional reorientation experiments can be applied to current problems in chemistry, molecular biology, and materials science, given the many advances in high-field NMR magnets, fast spinning, and sample preparation realized in recent years.
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Affiliation(s)
- Rachel W Martin
- Department of Chemistry, University of California, Irvine 92697-2025, United States; Department of Molecular Biology and Biochemistry, University of California, Irvine 92697-3900, United States.
| | - John E Kelly
- Department of Chemistry, University of California, Irvine 92697-2025, United States
| | - Kelsey A Collier
- Department of Physics and Astronomy, University of California, Irvine 92697-4575, United States
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Iuga D, Holland D, Dupree R. A 3D experiment that provides isotropic homonuclear correlations of half-integer quadrupolar nuclei. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 246:122-129. [PMID: 25123541 DOI: 10.1016/j.jmr.2014.07.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2014] [Revised: 06/30/2014] [Accepted: 07/09/2014] [Indexed: 06/03/2023]
Abstract
Two 3D experiments, capable of producing enhanced resolution two-spin double-quantum (DQ) homonuclear correlations for half-integer quadrupolar nuclei, are described. The first uses a split-t1 MQMAS sequence followed by a sandwiched oR(3) symmetry-based dipolar recoupling sequence to directly excite DQ coherences. In this case an isotropic single-quantum (SQ) coherence starts the homonuclear DQ excitation. In the second experiment a single strong pulse is used to create triple quantum (TQ) coherence followed by a further single pulse conversion to zero-order before a non-sandwiched oR(3) DQ sequence. The first experiment is demonstrated using (87)Rb in RbNO3, with three Rb sites in a ∼5ppm range, and the second to (11)B in caesium triborate, CsB3O5, with two three-coordinated sites separated by ∼2ppm and one four-coordinated boron site. In both cases, all sites are clearly resolved and their connections observed. The second experiment has higher sensitivity and a good signal to noise is obtained in a reasonable time despite the long T1 relaxation time of (11)B in this material.
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Affiliation(s)
- Dinu Iuga
- Physics Department, University of Warwick, CV4 7AL Coventry, UK.
| | - Diane Holland
- Physics Department, University of Warwick, CV4 7AL Coventry, UK
| | - Ray Dupree
- Physics Department, University of Warwick, CV4 7AL Coventry, UK
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Perras FA, Bryce DL. Measuring dipolar and J coupling between quadrupolar nuclei using double-rotation NMR. J Chem Phys 2013; 138:174202. [DOI: 10.1063/1.4802192] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
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Wu G, Zhu J. NMR studies of alkali metal ions in organic and biological solids. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2012; 61:1-70. [PMID: 22340207 DOI: 10.1016/j.pnmrs.2011.06.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2010] [Accepted: 05/31/2011] [Indexed: 05/31/2023]
Affiliation(s)
- Gang Wu
- Department of Chemistry, Queen's University, 90 Bader Lane, Kingston, Ontario, Canada.
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9
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Fernandez C, Pruski M. Probing quadrupolar nuclei by solid-state NMR spectroscopy: recent advances. Top Curr Chem (Cham) 2011; 306:119-88. [PMID: 21656101 DOI: 10.1007/128_2011_141] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Solid-state nuclear magnetic resonance (NMR) of quadrupolar nuclei has recently undergone remarkable development of capabilities for obtaining structural and dynamic information at the molecular level. This review summarizes the key achievements attained during the last couple of decades in solid-state NMR of both integer spin and half-integer spin quadrupolar nuclei. We provide a concise description of the first- and second-order quadrupolar interactions, and their effect on the static and magic angle spinning (MAS) spectra. Methods are explained for efficient excitation of single- and multiple-quantum coherences, and acquisition of spectra under low- and high-resolution conditions. Most of all, we present a coherent, comparative description of the high-resolution methods for half-integer quadrupolar nuclei, including double rotation (DOR), dynamic angle spinning (DAS), multiple-quantum magic angle spinning (MQMAS), and satellite transition magic angle spinning (STMAS). Also highlighted are methods for processing and analysis of the spectra. Finally, we review methods for probing the heteronuclear and homonuclear correlations between the quadrupolar nuclei and their quadrupolar or spin-1/2 neighbors.
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Litvak IM, Espinosa CA, Shapiro RA, Oldham AN, Duong VV, Martin RW. Pneumatic switched angle spinning NMR probe with capacitively coupled double saddle coil. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 206:183-189. [PMID: 20673643 DOI: 10.1016/j.jmr.2010.07.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2010] [Revised: 06/26/2010] [Accepted: 07/02/2010] [Indexed: 05/29/2023]
Abstract
Switched angle spinning (SAS) experiments can be used for generating isotropic-anisotropic correlations in oriented samples in a single experiment. In order for these methods to become widespread, specialized hardware is required. Here we describe the electronic and mechanical design and performance of a double-resonance SAS probe. Unlike many previous SAS probe implementations, the focus here is on systems where the dipolar couplings are partially averaged by molecular motion. This probe has a moving double saddle coil capacitively coupled to the stationary circuit. Angle switching is accomplished by a steam engine-type pneumatic mechanism. The speed and stability of the switching hardware for SAS experiments are demonstrated using spectra of model compounds.
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Affiliation(s)
- Ilya M Litvak
- Department of Chemistry, University of California, Irvine, CA 92697-2025, United States
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Edén M. Homonuclear dipolar recoupling of half-integer spin quadrupolar nuclei: techniques and applications. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2009; 36:1-10. [PMID: 19595580 DOI: 10.1016/j.ssnmr.2009.06.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2009] [Accepted: 06/16/2009] [Indexed: 05/28/2023]
Abstract
We review recent advances in solid state NMR methodology for recovering homonuclear dipolar interactions among half-integer quadrupolar spins undergoing sample rotation. Existing dipolar recoupling techniques are contrasted, based on (i) the form of their associated dipolar Hamiltonian, (ii) the different experimental conditions necessitating their realization and (iii) their roles as components in multi-dimensional NMR correlation spectroscopy. Various types of structural information accessible from such solid state NMR experimentation is reviewed. Promises and limitations of methodologies targeting homonuclear dipolar couplings between half-integer spins under high-resolution conditions are discussed, with particular focus on the demands set for structural investigations of crystalline as well as structurally disordered (amorphous) inorganic network materials.
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Affiliation(s)
- Mattias Edén
- Physical Chemistry Division, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden.
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Brinkmann A, Kentgens APM, Anupõld T, Samoson A. Symmetry-based recoupling in double-rotation NMR spectroscopy. J Chem Phys 2009; 129:174507. [PMID: 19045358 DOI: 10.1063/1.3005395] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In this contribution, we extend the theory of symmetry-based pulse sequences of types CN(n) (nu) and RN(n) (nu) in magic-angle-spinning nuclear resonance spectroscopy [M. H. Levitt, in Encyclopedia of Nuclear Magnetic Resonance, edited by D. M. Grant and R. K. Harris (Wiley, Chichester, 2002), Vol. 9]. to the case of rotating the sample simultaneously around two different angles with respect to the external magnetic field (double-rotation). We consider the case of spin-1/2 nuclei in general and the case of half-integer quadrupolar nuclei that are subjected to weak radio frequency pulses operating selectively on the central-transition polarizations. The transformation properties of the homonuclear dipolar interactions and J-couplings under central-transition-selective spin rotations are presented. We show that the pulse sequence R2(2) (1)R2(2) (-1) originally developed for homonuclear dipolar recoupling of half-integer quadrupolar nuclei under magic-angle-spinning conditions [M. Eden, D. Zhou, and J. Yu, Chem. Phys. Lett. 431, 397 (2006)] may be used for the same purpose in the case of double rotation, if the radio frequency pulses are synchronized with the outer rotation of the sample. We apply this sequence, sandwiched by central-transition selective 90 degrees pulses, to excite double-quantum coherences in homonuclear spin systems consisting of (23)Na and (27)Al nuclei.
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Affiliation(s)
- Andreas Brinkmann
- Physical Chemistry/Solid State NMR, Institute for Molecules and Materials, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands.
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Mali G. Spin-locking and recoupling of homonuclear dipolar interaction between spin-3/2 nuclei under magic-angle sample spinning. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2007; 185:318-25. [PMID: 17258483 DOI: 10.1016/j.jmr.2007.01.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2006] [Revised: 01/09/2007] [Accepted: 01/10/2007] [Indexed: 05/13/2023]
Abstract
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.
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Affiliation(s)
- Gregor Mali
- National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia.
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Hung I, Howes A, Anupõld T, Samoson A, Massiot D, Smith M, Brown S, Dupree R. 27Al double rotation two-dimensional spin diffusion NMR: Complete unambiguous assignment of aluminium sites in 9Al2O3·2B2O3. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.10.085] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Affiliation(s)
- Cecil Dybowski
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716-2522, USA
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Kentgens APM, van Eck ERH, Ajithkumar TG, Anupõld T, Past J, Reinhold A, Samoson A. New opportunities for double rotation NMR of half-integer quadrupolar nuclei. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2006; 178:212-9. [PMID: 16249109 DOI: 10.1016/j.jmr.2005.09.014] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2005] [Revised: 09/30/2005] [Accepted: 09/30/2005] [Indexed: 05/05/2023]
Abstract
A combined approach is presented which expands the applicability of double rotation (DOR) by overcoming its most prominent disadvantages: spinning stability and sensitivity. A new design using air-bearings for the inner rotor and a computer-assisted start-up procedure allows DOR operation over in principle unlimited time at outer rotor speeds of up to 2000Hz. Sensitivity enhancement of the DOR experiment is achieved by applying amplitude-modulated adiabatic pulses such as the double frequency sweep (DFS) before pulse excitation. Repeating the DFS enhancement and signal readout several times without allowing for spin-lattice relaxation leads to sensitivity enhancements of a factor 3 for (27)Al in various minerals. As a result, it becomes possible to study low sensitivity quadrupolar nuclei and various long duration 2D measurements can be performed routinely. Spinning is adequate to suppress residual homonuclear dipolar couplings in the spectral dimension of typical quadrupolar spin systems. In 2D-exchange spectroscopy, however, homonuclear correlation can still be established through dipolar-quadrupolar cross-terms.
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Affiliation(s)
- Arno P M Kentgens
- Department of Physical Chemistry/Solid-State NMR, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 1, The Netherlands.
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Edén M, Annersten H, Zazzi Å. Pulse-assisted homonuclear dipolar recoupling of half-integer quadrupolar spins in magic-angle spinning NMR. Chem Phys Lett 2005. [DOI: 10.1016/j.cplett.2005.04.030] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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