1
|
Simion A, Schubeis T, Le Marchand T, Vasilescu M, Pintacuda G, Lesage A, Filip C. Heteronuclear decoupling with Rotor-Synchronized Phase-Alternated Cycles. J Chem Phys 2022; 157:014202. [DOI: 10.1063/5.0098135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A new heteronuclear decoupling pulse sequence is introduced, dubbed ROtor-Synchronized Phase-Alternated Cycles (ROSPAC). It is based on a partial refocusing of the coherences (spin operator products, or cross-terms)1,2 responsible for transverse spin-polarization dephasing, on the irradiation of a large pattern of radio-frequencies, and on a significant minimization of the cross-effects implying 1H chemical-shift anisotropy. Decoupling efficiency is analyzed by numerical simulations and experiments, and compared to that of established decoupling sequences (swept-frequency TPPM, TPPM, SPINAL, rCWApa, and RS-HEPT). It was found that ROSPAC offers good 1H offset robustness for a large range of chemical shifts and low radio-frequency (RF) powers, and performs very well in the ultra-fast MAS regime, where it is almost independent from RF power and permits it to avoid rotary-resonance recoupling conditions ( ). It has the advantage that only the pulse lengths require optimization, and has a low duty cycle in the pulsed decoupling regime. The efficiency of the decoupling sequence is demonstrated on a model microcrystalline sample of the model protein domain GB1 at 100 kHz MAS at 18.8 T.
Collapse
Affiliation(s)
| | | | | | | | | | - Anne Lesage
- Laboratoire de Stereochimie, Ecole Normale Superieure, FRANCE
| | - Claudiu Filip
- National Institute for Research and Development of Isotopic and Molecular Technologies, Romania
| |
Collapse
|
2
|
Ahlawat S, Mote KR, Lakomek NA, Agarwal V. Solid-State NMR: Methods for Biological Solids. Chem Rev 2022; 122:9643-9737. [PMID: 35238547 DOI: 10.1021/acs.chemrev.1c00852] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
In the last two decades, solid-state nuclear magnetic resonance (ssNMR) spectroscopy has transformed from a spectroscopic technique investigating small molecules and industrial polymers to a potent tool decrypting structure and underlying dynamics of complex biological systems, such as membrane proteins, fibrils, and assemblies, in near-physiological environments and temperatures. This transformation can be ascribed to improvements in hardware design, sample preparation, pulsed methods, isotope labeling strategies, resolution, and sensitivity. The fundamental engagement between nuclear spins and radio-frequency pulses in the presence of a strong static magnetic field is identical between solution and ssNMR, but the experimental procedures vastly differ because of the absence of molecular tumbling in solids. This review discusses routinely employed state-of-the-art static and MAS pulsed NMR methods relevant for biological samples with rotational correlation times exceeding 100's of nanoseconds. Recent developments in signal filtering approaches, proton methodologies, and multiple acquisition techniques to boost sensitivity and speed up data acquisition at fast MAS are also discussed. Several examples of protein structures (globular, membrane, fibrils, and assemblies) solved with ssNMR spectroscopy have been considered. We also discuss integrated approaches to structurally characterize challenging biological systems and some newly emanating subdisciplines in ssNMR spectroscopy.
Collapse
Affiliation(s)
- Sahil Ahlawat
- Tata Institute of Fundamental Research Hyderabad, Survey No. 36/P Gopanpally, Serilingampally, Ranga Reddy District, Hyderabad 500046, Telangana, India
| | - Kaustubh R Mote
- Tata Institute of Fundamental Research Hyderabad, Survey No. 36/P Gopanpally, Serilingampally, Ranga Reddy District, Hyderabad 500046, Telangana, India
| | - Nils-Alexander Lakomek
- University of Düsseldorf, Institute for Physical Biology, Universitätsstraße 1, 40225 Düsseldorf, Germany
| | - Vipin Agarwal
- Tata Institute of Fundamental Research Hyderabad, Survey No. 36/P Gopanpally, Serilingampally, Ranga Reddy District, Hyderabad 500046, Telangana, India
| |
Collapse
|
3
|
Garg R, Pandey MK, Ramachandran R. Bimodal Floquet theory of phase-modulated heteronuclear decoupling experiments in solid-state NMR spectroscopy. J Chem Phys 2021; 155:104102. [PMID: 34525823 DOI: 10.1063/5.0061883] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A prescription based on bimodal Floquet theory is proposed to describe the nuances of phase-modulated supercycled decoupling experiments in solids. The frequency dependent interaction frames relevant to a particular supercycle are identified to facilitate faster convergence of perturbation corrections to the derived effective Hamiltonians. In contrast to silico-based methods, the proposed analytic method offers an attractive platform for faster optimization of experiments in solids. Additionally, the relevance of supercycling at ultrafast spinning conditions is also discussed.
Collapse
Affiliation(s)
- Rajat Garg
- Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Sector 81, Manauli P.O. Box-140306, Mohali, Punjab, India
| | - Manoj Kumar Pandey
- Department of Chemistry, Indian Institute of Technology (IIT) Ropar, P.O. Box-140001, Rupnagar, Punjab, India
| | - Ramesh Ramachandran
- Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Sector 81, Manauli P.O. Box-140306, Mohali, Punjab, India
| |
Collapse
|
4
|
Sharma K, Equbal A, Nielsen NC, Madhu PK. A unified heteronuclear decoupling picture in solid-state NMR under low radio-frequency amplitude and fast magic-angle-spinning frequency regime. J Chem Phys 2019; 150:144201. [PMID: 30981235 DOI: 10.1063/1.5082352] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Heteronuclear spin decoupling is a highly important component of solid-state NMR experiments to remove undesired coupling interactions between unlike spins for spectral resolution. Recently, experiments using a unification strategy of standard decoupling schemes were presented for high radio-frequency (RF) amplitudes and slow-intermediate magic-angle-spinning (MAS) frequencies, in the pursuit of deeper understanding of spin decoupling under phase-modulated RF irradiation [A. Equbal et al., J. Chem. Phys. 142, 184201 (2015)]. The approach, unified two-pulse heteronuclear decoupling (UTPD), incorporates the simultaneous time- and phase-modulation strategies, commonly used in solid-state NMR. Here, the UTPD based decoupling scheme is extended to the experimentally increasingly important regime of low RF amplitudes and fast MAS frequencies. The unified decoupling approach becomes increasingly effective in identifying the deleterious dipole-dipole and, in particular, J recoupling conditions which become critical for the low-amplitude RF regime. This is because J coupling is isotropic and therefore not averaged out by sample spinning unlike the anisotropic dipole-dipole coupling. Numerical simulations and analytic theory are used to understand the effects of various nuclear spin interactions on the decoupling performance of UTPD, in particular, the crucial difference between the low-phase and high-phase UTPD conditions with respect to J coupling. In the UTPD scheme, when the cycle-frequency of the pulse-sequence is comparable to the RF nutation frequency, the existence of a non-zero effective rotation in the basic two-pulse scheme becomes an essential feature for the efficient and robust averaging out of the scalar J coupling. This broad viewpoint is expected to bring different optimum low-power decoupling pulse schemes under a common footing.
Collapse
Affiliation(s)
- Kshama Sharma
- TIFR Centre for Interdisciplinary Sciences, Tata Institute of Fundamental Research, Gopanpally, Hyderabad 500 107, India
| | - Asif Equbal
- TIFR Centre for Interdisciplinary Sciences, Tata Institute of Fundamental Research, Gopanpally, Hyderabad 500 107, India
| | - Niels Chr Nielsen
- Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| | - P K Madhu
- TIFR Centre for Interdisciplinary Sciences, Tata Institute of Fundamental Research, Gopanpally, Hyderabad 500 107, India
| |
Collapse
|
5
|
Jain MG, Sreedevi KN, Equbal A, Madhu PK, Agarwal V. Refocusing pulses: A strategy to improve efficiency of phase-modulated heteronuclear decoupling schemes in MAS solid-state NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 284:59-65. [PMID: 28961478 DOI: 10.1016/j.jmr.2017.09.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Revised: 09/04/2017] [Accepted: 09/16/2017] [Indexed: 06/07/2023]
Abstract
The strategy of using π pulses in conjunction with continuous-wave radio-frequency fields to refocus spin interactions has lead to robust and efficient family of heteronuclear decoupling schemes in magic-angle spinning solid-state NMR, denoted as, rCW schemes. Here, we investigate the generality of the application of such refocussing pulses in other phase-modulated decoupling schemes, notably the super-cycled XiX decoupling. XiX is a commonly used heteronuclear decoupling scheme under conditions of fast MAS and low-amplitude radio-frequency irradiation. The refocussing of interactions is achieved by inserting π pulses with a phase of 135° in the supercycled XiX scheme. The refocussed XiX, rXiX, scheme has improved decoupling efficiency, better offset tolerance, and easier experimental setup compared to the XiX scheme.
Collapse
Affiliation(s)
- Mukul G Jain
- TIFR Centre for Interdisciplinary Sciences, Tata Institute of Fundamental Research Hyderabad, Sy. No. 36/P, Gopanpally, Ranga Reddy District, Hyderabad 500 017, India
| | - K N Sreedevi
- TIFR Centre for Interdisciplinary Sciences, Tata Institute of Fundamental Research Hyderabad, Sy. No. 36/P, Gopanpally, Ranga Reddy District, Hyderabad 500 017, India
| | - Asif Equbal
- TIFR Centre for Interdisciplinary Sciences, Tata Institute of Fundamental Research Hyderabad, Sy. No. 36/P, Gopanpally, Ranga Reddy District, Hyderabad 500 017, India
| | - P K Madhu
- TIFR Centre for Interdisciplinary Sciences, Tata Institute of Fundamental Research Hyderabad, Sy. No. 36/P, Gopanpally, Ranga Reddy District, Hyderabad 500 017, India; Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
| | - Vipin Agarwal
- TIFR Centre for Interdisciplinary Sciences, Tata Institute of Fundamental Research Hyderabad, Sy. No. 36/P, Gopanpally, Ranga Reddy District, Hyderabad 500 017, India.
| |
Collapse
|
6
|
Equbal A, Shankar R, Leskes M, Vega S, Nielsen NC, Madhu PK. Significance of symmetry in the nuclear spin Hamiltonian for efficient heteronuclear dipolar decoupling in solid-state NMR: A Floquet description of supercycled rCW schemes. J Chem Phys 2017; 146:104202. [PMID: 28298092 DOI: 10.1063/1.4977738] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Symmetry plays an important role in the retention or annihilation of a desired interaction Hamiltonian in NMR experiments. Here, we explore the role of symmetry in the radio-frequency interaction frame Hamiltonian of the refocused-continuous-wave (rCW) pulse scheme that leads to efficient 1H heteronuclear decoupling in solid-state NMR. It is demonstrated that anti-periodic symmetry of single-spin operators (Ix, Iy, Iz) in the interaction frame can lead to complete annihilation of the 1H-1H homonuclear dipolar coupling effects that induce line broadening in solid-state NMR experiments. This symmetry also plays a critical role in cancelling or minimizing the effect of 1H chemical-shift anisotropy in the effective Hamiltonian. An analytical description based on Floquet theory is presented here along with experimental evidences to understand the decoupling efficiency of supercycled (concatenated) rCW scheme.
Collapse
Affiliation(s)
- Asif Equbal
- Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| | - Ravi Shankar
- Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| | - Michal Leskes
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Shimon Vega
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Niels Chr Nielsen
- Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| | - P K Madhu
- TIFR Centre for Interdisciplinary Sciences, 21 Brundavan Colony, Narsingi, Hyderabad 500 075, India
| |
Collapse
|
7
|
Equbal A, Madhu PK, Meier BH, Nielsen NC, Ernst M, Agarwal V. Parameter independent low-power heteronuclear decoupling for fast magic-angle spinning solid-state NMR. J Chem Phys 2017; 146:084202. [DOI: 10.1063/1.4976997] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Asif Equbal
- TIFR Centre for Interdisciplinary Sciences, 21 Brundavan Colony, Narsingi, Hyderabad 500 075, India
- Center for Insoluble Protein Structures (inSpin) and Center for Ultrahigh-Field NMR Spectroscopy, Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| | - P. K. Madhu
- TIFR Centre for Interdisciplinary Sciences, 21 Brundavan Colony, Narsingi, Hyderabad 500 075, India
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
| | - Beat H. Meier
- Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
| | - Niels Chr. Nielsen
- Center for Insoluble Protein Structures (inSpin) and Center for Ultrahigh-Field NMR Spectroscopy, Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| | - Matthias Ernst
- Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
| | - Vipin Agarwal
- TIFR Centre for Interdisciplinary Sciences, 21 Brundavan Colony, Narsingi, Hyderabad 500 075, India
| |
Collapse
|
8
|
Equbal A, Leskes M, Nielsen NC, Madhu PK, Vega S. Relative merits of rCW(A) and XiX heteronuclear spin decoupling in solid-state magic-angle-spinning NMR spectroscopy: A bimodal Floquet analysis. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 263:55-64. [PMID: 26773527 DOI: 10.1016/j.jmr.2015.12.019] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Revised: 12/19/2015] [Accepted: 12/27/2015] [Indexed: 06/05/2023]
Abstract
We present a bimodal Floquet analysis of the recently introduced refocused continuous wave (rCW) solid-state NMR heteronuclear dipolar decoupling method and compare it with the similar looking X-inverse X (XiX) scheme. The description is formulated in the rf interaction frame and is valid for both finite and ideal π pulse rCW irradiation that forms the refocusing element in the rCW scheme. The effective heteronuclear dipolar coupling Hamiltonian up to first order is described. The analysis delineates the difference between the two sequences to different orders of their Hamiltonians for both diagonal and off-diagonal parts. All the resonance conditions observed in experiments and simulations have been characterised and their influence on residual line broadening is highlighted. The theoretical comparison substantiates the numerical simulations and experimental results to a large extent.
Collapse
Affiliation(s)
- Asif Equbal
- Center for Insoluble Protein Structures, Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| | - Michal Leskes
- Weizmann Institute of Science, Department of Materials and Interfaces, Rehovot, Israel.
| | - Niels Chr Nielsen
- Center for Insoluble Protein Structures, Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark.
| | - P K Madhu
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India; TIFR Centre for Interdisciplinary Sciences, 21 Brundavan Colony, Narsingi, Hyderabad 500075, India.
| | - Shimon Vega
- Weizmann Institute of Science, Department of Chemical Physics, Rehovot, Israel.
| |
Collapse
|
9
|
Equbal A, Basse K, Nielsen NC. Highly efficient19F heteronuclear decoupling in solid-state NMR spectroscopy using supercycled refocused-CW irradiation. Phys Chem Chem Phys 2016; 18:30990-30997. [DOI: 10.1039/c6cp06574k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We present heteronuclear19F refocused CW (rCW) decoupling pulse sequences for solid-state magic-angle-spinning NMR applications.
Collapse
Affiliation(s)
- Asif Equbal
- Center for Insoluble Protein Structures (inSPIN)
- Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry
- Aarhus University
- Denmark
| | - Kristoffer Basse
- Center for Insoluble Protein Structures (inSPIN)
- Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry
- Aarhus University
- Denmark
| | - Niels Chr. Nielsen
- Center for Insoluble Protein Structures (inSPIN)
- Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry
- Aarhus University
- Denmark
| |
Collapse
|
10
|
Equbal A, Bjerring M, Sharma K, Madhu P, Nielsen NC. Heteronuclear decoupling in MAS NMR in the intermediate to fast sample spinning regime. Chem Phys Lett 2016. [DOI: 10.1016/j.cplett.2015.12.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
11
|
Sarkar R, Rodriguez Camargo DC, Pintacuda G, Reif B. Restoring Resolution in Biological Solid-State NMR under Conditions of Off-Magic-Angle Spinning. J Phys Chem Lett 2015; 6:5040-5044. [PMID: 26641130 DOI: 10.1021/acs.jpclett.5b02467] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Spin-state-selective excitation (S3E) experiments allow the selection of individual transitions in a coupled two spin system. We show that in the solid state, the dipole-dipole interaction (DD) between (15)N and (1)H in a (1)H-(15)N bond and the chemical shift anisotropy (CSA) of (15)N in an amide moiety mutually cancel each other for a particular multiplet component at high field, when the sample is spun off the magic angle (Arctan [√2] = 54.74°). The accuracy of the adjustment of the spinning angle is crucial in conventional experiments. We demonstrate that for S3E experiments, the requirement to spin the sample exactly at the magic angle is not mandatory. Applications of solid state NMR in narrow bore magnets will be facilitated where the adjustment of the magic angle is often difficult. The method opens new perspectives for the development of schemes to determine distances and to quantify dynamics in the solid state.
Collapse
Affiliation(s)
- Riddhiman Sarkar
- Helmholtz-Zentrum München (HMGU) , Deutsches Forschungszentrum für Gesundheit und Umwelt, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany
- Munich Center for Integrated Protein Science (CIPS-M) at Department Chemie, Technische Universität München (TUM) , Lichtenbergstrasse 4, 85747 Garching, Germany
| | - Diana C Rodriguez Camargo
- Helmholtz-Zentrum München (HMGU) , Deutsches Forschungszentrum für Gesundheit und Umwelt, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany
- Munich Center for Integrated Protein Science (CIPS-M) at Department Chemie, Technische Universität München (TUM) , Lichtenbergstrasse 4, 85747 Garching, Germany
| | - Guido Pintacuda
- Université de Lyon , Institut de Sciences Analytiques, Centre de RMN à Très Hauts Champs, 5 rue de la Doua, 69100 Villeurbanne, France
| | - Bernd Reif
- Helmholtz-Zentrum München (HMGU) , Deutsches Forschungszentrum für Gesundheit und Umwelt, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany
- Munich Center for Integrated Protein Science (CIPS-M) at Department Chemie, Technische Universität München (TUM) , Lichtenbergstrasse 4, 85747 Garching, Germany
| |
Collapse
|
12
|
Purusottam RN, Bodenhausen G, Tekely P. Effects of inherent rf field inhomogeneity on heteronuclear decoupling in solid-state NMR. Chem Phys Lett 2015. [DOI: 10.1016/j.cplett.2015.06.051] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
13
|
Improving spectral resolution in biological solid-state NMR using phase-alternated rCW heteronuclear decoupling. Chem Phys Lett 2015. [DOI: 10.1016/j.cplett.2015.07.008] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
|
14
|
Equbal A, Bjerring M, Madhu PK, Nielsen NC. A unified heteronuclear decoupling strategy for magic-angle-spinning solid-state NMR spectroscopy. J Chem Phys 2015; 142:184201. [PMID: 25978884 DOI: 10.1063/1.4919634] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A unified strategy of two-pulse based heteronuclear decoupling for solid-state magic-angle spinning nuclear magnetic resonance is presented. The analysis presented here shows that different decoupling sequences like two-pulse phase-modulation (TPPM), X-inverse-X (XiX), and finite pulse refocused continuous wave (rCW(A)) are basically specific solutions of a more generalized decoupling scheme which incorporates the concept of time-modulation along with phase-modulation. A plethora of other good decoupling conditions apart from the standard, TPPM, XiX, and rCW(A) decoupling conditions are available from the unified decoupling approach. The importance of combined time- and phase-modulation in order to achieve the best decoupling conditions is delineated. The consequences of different indirect dipolar interactions arising from cross terms comprising of heteronuclear and homonuclear dipolar coupling terms and also those between heteronuclear dipolar coupling and chemical-shift anisotropy terms are presented in order to unfold the effects of anisotropic interactions under different decoupling conditions. Extensive numerical simulation results are corroborated with experiments on standard amino acids.
Collapse
Affiliation(s)
- Asif Equbal
- Center for Insoluble Protein Structures, Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| | - Morten Bjerring
- Center for Insoluble Protein Structures, Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| | - P K Madhu
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
| | - Niels Chr Nielsen
- Center for Insoluble Protein Structures, Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| |
Collapse
|
15
|
Sani MA, Separovic F. Progression of NMR studies of membrane-active peptides from lipid bilayers to live cells. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2015; 253:138-142. [PMID: 25631783 DOI: 10.1016/j.jmr.2014.11.016] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2014] [Revised: 11/24/2014] [Accepted: 11/30/2014] [Indexed: 06/04/2023]
Abstract
Understanding the structure of membrane-active peptides faces many challenges associated with the development of appropriate model membrane systems as the peptide structure depends strongly on the lipid environment. This perspective provides a brief overview of the approach taken to study antimicrobial and amyloid peptides in phospholipid bilayers using oriented bilayers and magic angle spinning techniques. In particular, Boltzmann statistics REDOR and maximum entropy analysis of spinning side bands are used to analyse systems where multiple states of peptide or lipid molecules may co-exist. We propose that in future, rather than model membranes, structural studies in whole cells are feasible.
Collapse
Affiliation(s)
- M-A Sani
- School of Chemistry, Bio21 Institute, University of Melbourne, VIC 3010, Australia
| | - F Separovic
- School of Chemistry, Bio21 Institute, University of Melbourne, VIC 3010, Australia.
| |
Collapse
|
16
|
Takeda K, Wakisaka A, Takegoshi K. Proton decoupling and recoupling under double-nutation irradiation in solid-state NMR. J Chem Phys 2014; 141:224202. [DOI: 10.1063/1.4903173] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
17
|
Purusottam RN, Bodenhausen G, Tekely P. Sensitivity improvement during heteronuclear spin decoupling in solid-state nuclear magnetic resonance experiments at high spinning frequencies and moderate radio-frequency amplitudes. Chem Phys Lett 2014. [DOI: 10.1016/j.cplett.2014.09.044] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
|
18
|
Equbal A, Paul S, Mithu VS, Madhu PK, Nielsen NC. Efficient heteronuclear decoupling in MAS solid-state NMR using non-rotor-synchronized rCW irradiation. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 246:104-109. [PMID: 25123538 DOI: 10.1016/j.jmr.2014.07.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2014] [Revised: 06/30/2014] [Accepted: 07/09/2014] [Indexed: 06/03/2023]
Abstract
We present new non-rotor-synchronized variants of the recently introduced refocused continuous wave (rCW) heteronuclear decoupling method significantly improving the performance relative to the original rotor-synchronized variants. Under non-rotor-synchronized conditions the rCW decoupling sequences provide more efficient decoupling, are easier to setup, and prove more robust towards experimental parameters such as radio frequency (rf) field amplitude and spinning frequency. This is demonstrated through numerical simulations substantiated with experimental results under different sample spinning and rf field amplitude conditions for powder samples of U-(13)C-glycine and U-(13)C-L-histidine·HCl·H2O.
Collapse
Affiliation(s)
- Asif Equbal
- Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| | - Subhradip Paul
- Department of Chemistry, Center for Excellence in Basic Sciences, University of Mumbai and Department of Atomic Energy, Health Centre, University of Mumbai, Vidhyanagari Campus, Mumbai 400098, India
| | - Venus Singh Mithu
- Department of Chemistry, Guru Nanak Dev University, Amritsar 143005, India
| | - P K Madhu
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India; TIFR Centre for Interdisciplinary Sciences, 21 Brundavan Colony, Narsingi, Hyderabad 500 075, India.
| | - Niels Chr Nielsen
- Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark.
| |
Collapse
|
19
|
Equbal A, Paul S, Mithu VS, Vinther JM, Nielsen NC, Madhu PK. r TPPM: towards improving solid-state NMR two-pulse phase-modulation heteronuclear dipolar decoupling sequence by refocusing. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 244:68-73. [PMID: 24879300 DOI: 10.1016/j.jmr.2014.04.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Revised: 03/31/2014] [Accepted: 04/07/2014] [Indexed: 06/03/2023]
Abstract
We present here a simple refocused modification, r TPPM, of the Two-Pulse Phase-Modulation (TPPM) heteronuclear decoupling method, which improves decoupling and makes the sequence much more robust with respect to essential experimental parameters. The modified sequence is compared with the established TPPM sequence and a variety of other decoupling sequences at low to moderate magic-angle spinning frequencies. Simulations are shown to compare TPPM and r TPPM with respect to various experimental parameters. The observations from simulations are corroborated with experimental findings at two spinning frequencies on U-(13)C-glycine and U-(13)C-L-histidine.HCl.H2O.
Collapse
Affiliation(s)
- Asif Equbal
- Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience, Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| | - Subhradip Paul
- Department of Chemistry, Center for Excellence in Basic Sciences, University of Mumbai and Department of Atomic Energy, Health Centre, University of Mumbai, Vidhyanagari Campus, Mumbai 400098, India
| | - Venus Singh Mithu
- Department of Chemistry, Guru Nanak Dev University, Amritsar 143005, India
| | - Joachim M Vinther
- Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience, Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark
| | - Niels Chr Nielsen
- Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience, Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark.
| | - P K Madhu
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India; TIFR Centre for Interdisciplinary Sciences, 21 Brundavan Colony, Narsingi, Hyderabad 500075, India.
| |
Collapse
|
20
|
Madhu PK. Heteronuclear Spin Decoupling in Solid-State Nuclear Magnetic Resonance: Overview and Outlook. Isr J Chem 2013. [DOI: 10.1002/ijch.201300097] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
21
|
Agarwal V, Tuherm T, Reinhold A, Past J, Samoson A, Ernst M, Meier BH. Amplitude-modulated low-power decoupling sequences for fast magic-angle spinning NMR. Chem Phys Lett 2013. [DOI: 10.1016/j.cplett.2013.07.073] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
|
22
|
Takeda K, Kusakabe Y, Noda Y, Fukuchi M, Takegoshi K. Homo- and heteronuclear two-dimensional covariance solid-state NMR spectroscopy with a dual-receiver system. Phys Chem Chem Phys 2012; 14:9715-21. [DOI: 10.1039/c2cp41191a] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
23
|
Mananga ES, Charpentier T. Introduction of the Floquet-Magnus expansion in solid-state nuclear magnetic resonance spectroscopy. J Chem Phys 2011; 135:044109. [DOI: 10.1063/1.3610943] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
|
24
|
Weingarth M, Trébosc J, Amoureux JP, Bodenhausen G, Tekely P. Efficiency at high spinning frequencies of heteronuclear decoupling methods designed to quench rotary resonance. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2011; 40:21-26. [PMID: 21498056 DOI: 10.1016/j.ssnmr.2011.03.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Revised: 03/17/2011] [Accepted: 03/18/2011] [Indexed: 05/30/2023]
Abstract
The performance of two recently developed heteronuclear decoupling schemes designed to quench rotary resonance, phase-inverted supercycled sequence for attenuation of rotary resonance (PISSARRO) and high-phase two-pulse phase modulation (high-phase TPPM), are probed at high spinning frequencies. High-phase TPPM may be useful at the n=1 rotary resonance condition while PISSARRO permits efficient decoupling over a broad commonly used range of rf amplitudes, even at very high spinning frequencies. New insights into the response of spin systems to both decoupling schemes have been gained. High-phase TPPM is sensitive to the offsets of remote protons, their chemical shift anisotropies, and the relative orientations of the heteronuclear dipolar and proton chemical shift tensors. Since PISSARRO is virtually immune against such effects, the method is especially suited for very high magnetic fields.
Collapse
Affiliation(s)
- Markus Weingarth
- Ecole Normale Supérieure, Département de Chimie, 24 rue Lhomond, 75005 Paris, France
| | | | | | | | | |
Collapse
|
25
|
Gerbaud G, Caldarelli S, Ziarelli F, Gastaldi S. The influence of the molecular system on the performance of heteronuclear decoupling in solid-state NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 210:75-81. [PMID: 21382734 DOI: 10.1016/j.jmr.2011.02.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2010] [Revised: 02/09/2011] [Accepted: 02/11/2011] [Indexed: 05/30/2023]
Abstract
The intensity of the carbon signal in a CPMAS experiment has been measured for two CH and three CH(2) moieties in four test molecules under different phase-modulated proton decoupling conditions and as a function of the spinning rate. The proton decoupling schemes investigated were the golden standard TPPM and three of the GTn family. Aim of this analysis was to better describe experimentally the impact and limitations of phase-modulated decoupling. Sizeable differences in the response to decoupling were observed in otherwise chemically identical molecular fragments, such as the CHCH(2) found in tyrosine, phenyl-succinic acid or 9-Anthrylmethyl-malonate, probably due to differences in spin-diffusion rates. In keeping with known facts, the efficiency of the decoupling was observed to decrease with the MAS rate, but with somewhat different trends for the tested systems.
Collapse
|
26
|
Comellas G, Lopez JJ, Nieuwkoop AJ, Lemkau LR, Rienstra CM. Straightforward, effective calibration of SPINAL-64 decoupling results in the enhancement of sensitivity and resolution of biomolecular solid-state NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 209:131-5. [PMID: 21296014 PMCID: PMC3065959 DOI: 10.1016/j.jmr.2010.12.011] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2010] [Revised: 12/21/2010] [Accepted: 12/28/2010] [Indexed: 05/11/2023]
Abstract
We describe a simple yet highly effective optimization strategy for SPINAL-64 ¹H decoupling conditions for magic-angle spinning solid-state NMR. With adjustment of the phase angles in a coupled manner, the optimal conditions resulting from three parameter optimizations can be determined with adjustment of a single phase. Notably, echo T₂ relaxation times for ¹³C and ¹⁵N show significant enhancement (up to 64%), relative to the previous described SPINAL-64 conditions, under the moderate ¹H decoupling levels (60-100 kHz) and MAS rate (13.3 kHz) commonly employed for high-resolution SSNMR spectroscopy of proteins. Additionally, we also investigated the effect at higher spinning rate (33.3 kHz) and compared the results with other ¹H decoupling schemes (TPPM, XiX), as well as SPINAL-64 with the originally reported optimal values.
Collapse
Affiliation(s)
- Gemma Comellas
- Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801
| | - Jakob J. Lopez
- Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801
| | - Andrew J. Nieuwkoop
- Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801
| | - Luisel R. Lemkau
- Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801
| | - Chad M. Rienstra
- Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801
- Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801
- Department of Biochemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801
- Corresponding author information: Chad M. Rienstra, Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL 61801, USA. Telephone: (+01) 217 244-4655. Fax: 217 244-3186.
| |
Collapse
|
27
|
Paul S, Vinod Chandran C, Bräuniger T, Madhu PK. Sweep direction and efficiency of the swept-frequency two pulse phase modulated scheme for heteronuclear dipolar-decoupling in solid-state NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 209:261-268. [PMID: 21345704 DOI: 10.1016/j.jmr.2011.01.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Revised: 01/14/2011] [Accepted: 01/19/2011] [Indexed: 05/30/2023]
Abstract
We present here a bimodal Floquet theoretical and experimental investigation of the direction of sweep in the swept-frequency two pulse phase modulated (SW(f)-TPPM) scheme used for heteronuclear dipolar decoupling in solid-state NMR. The efficiency of the decoupling turns out to be independent of the sweep direction.
Collapse
Affiliation(s)
- Subhradip Paul
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, India
| | | | | | | |
Collapse
|
28
|
Arthanari H, Wagner G, Khaneja N. Heteronuclear decoupling by multiple rotating frame technique. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 209:8-18. [PMID: 21227724 PMCID: PMC3101322 DOI: 10.1016/j.jmr.2010.11.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Revised: 11/30/2010] [Accepted: 11/30/2010] [Indexed: 05/30/2023]
Abstract
The paper describes the multiple rotating frame technique for designing modulated rf fields, that perform broadband heteronuclear decoupling in solution NMR spectroscopy. The decoupling method presented here is understood by performing a sequence of coordinate transformations, each of which demodulates a component of the rf field to a static component, that progressively averages the chemical shift and the dipolar interaction. We show that by increasing the number of modulations in the decoupling field, the ratio of dispersion in the chemical shift to the strength of the static component of the rf field is successively reduced in the progressive frames. The known decoupling methods like continuous wave decoupling, TPPM, etc., can be viewed as special cases of this method and their performance improves by adding additional modulations in the decoupling field. The technique is also expected to find use in design of broadband excitation, inversion and mixing sequences and broadband experiments in solid state NMR.
Collapse
Affiliation(s)
- Haribabu Arthanari
- Department of Biological Chemistry and Molecular Pharamacology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, United States
| | - Gerhard Wagner
- Department of Biological Chemistry and Molecular Pharamacology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, United States
| | - Navin Khaneja
- School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, United States
| |
Collapse
|
29
|
Paul S, Kurur ND, Madhu PK. On the choice of heteronuclear dipolar decoupling scheme in solid-state NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 207:140-148. [PMID: 20870436 DOI: 10.1016/j.jmr.2010.08.023] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Accepted: 08/31/2010] [Indexed: 05/28/2023]
Abstract
We present here a comparison of different heteronuclear dipolar decoupling sequences at the moderate magic-angle spinning (MAS) frequency (ν(r)) of 30 kHz. The radio-frequency (RF) amplitude (ν₁) ranges from the low power (ν₁<ν(r)) to the high power regime (ν₁>2ν(r)) and includes the rotary resonance conditions (ν₁=nν(r)) where n=1, 2. For decoupling at the rotary resonance condition, we recently introduced a modification of TPPM, namely high-phase TPPM, whose properties will be discussed here. Finally, based on earlier published and current experimental results we suggest the optimal sequence for heteronuclear dipolar decoupling at any RF amplitude and MAS frequencies up to 35 kHz.
Collapse
Affiliation(s)
- Subhradip Paul
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India
| | | | | |
Collapse
|
30
|
BECHMANN MATTHIAS, DUSOLD STEPHAN, FÖRSTER HANS, HAEBERLEN ULRICH, LIS TADEUSZ, SEBALD ANGELIKA, STUMBER MICHAEL. 31P and13C chemical shielding tensors in the phosphoenolpyruvate moiety from rotary resonance recoupling13C and31P MAS and single crystal31P NMR. Mol Phys 2009. [DOI: 10.1080/00268970009483327] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- MATTHIAS BECHMANN
- a Bayerisches Geoinstitut, Universität Bayreuth , D-95440 , Bayreuth , Germany
| | - STEPHAN DUSOLD
- a Bayerisches Geoinstitut, Universität Bayreuth , D-95440 , Bayreuth , Germany
| | - HANS FÖRSTER
- b Bruker Analytik GmbH, Silberstreifen, D-76287 , Rheinstetten , Germany
| | - ULRICH HAEBERLEN
- c Max-Planck-Institut für Medizinische Forschung, AG Molekülkristalle , Jahnstr. 29, D-69120, Heidelberg , Germany
| | - TADEUSZ LIS
- d Institute of Chemistry, University of Wroclaw , 50-383 , Wroclaw , Poland
| | - ANGELIKA SEBALD
- a Bayerisches Geoinstitut, Universität Bayreuth , D-95440 , Bayreuth , Germany
| | - MICHAEL STUMBER
- c Max-Planck-Institut für Medizinische Forschung, AG Molekülkristalle , Jahnstr. 29, D-69120, Heidelberg , Germany
| |
Collapse
|
31
|
Scholz I, Hodgkinson P, Meier BH, Ernst M. Understanding two-pulse phase-modulated decoupling in solid-state NMR. J Chem Phys 2009; 130:114510. [DOI: 10.1063/1.3086936] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
32
|
|
33
|
Bayro MJ, Ramachandran R, Caporini MA, Eddy MT, Griffin RG. Radio frequency-driven recoupling at high magic-angle spinning frequencies: homonuclear recoupling sans heteronuclear decoupling. J Chem Phys 2008; 128:052321. [PMID: 18266438 DOI: 10.1063/1.2834736] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We describe solid-state NMR homonuclear recoupling experiments at high magic-angle spinning (MAS) frequencies using the radio frequency-driven recoupling (RFDR) scheme. The effect of heteronuclear decoupling interference during RFDR recoupling at high spinning frequencies is investigated experimentally and via numerical simulations, resulting in the identification of optimal decoupling conditions. The effects of MAS frequency, RF field amplitude, bandwidth, and chemical shift offsets are examined. Most significantly, it is shown that broadband homonuclear correlation spectra can be efficiently obtained using RFDR without decoupling during the mixing period in fully protonated samples, thus considerably reducing the rf power requirements for acquisition of (13)C-(13)C correlation spectra. The utility of RFDR sans decoupling is demonstrated with broadband correlation spectra of a peptide and a model protein at high MAS frequencies and high magnetic field.
Collapse
Affiliation(s)
- Marvin J Bayro
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | | | | | | | | |
Collapse
|
34
|
De Paëpe G, Lewandowski JR, Griffin RG. Spin dynamics in the modulation frame: Application to homonuclear recoupling in magic angle spinning solid-state NMR. J Chem Phys 2008; 128:124503. [DOI: 10.1063/1.2834732] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
35
|
Willans MJ, Sears DN, Wasylishen RE. The effectiveness of 1H decoupling in the 13C MAS NMR of paramagnetic solids: an experimental case study incorporating copper(II) amino acid complexes. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2008; 191:31-46. [PMID: 18086543 DOI: 10.1016/j.jmr.2007.11.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2007] [Revised: 11/17/2007] [Accepted: 11/21/2007] [Indexed: 05/25/2023]
Abstract
The use of continuous-wave (CW) 1H decoupling has generally provided little improvement in the 13C MAS NMR spectroscopy of paramagnetic organic solids. Recent solid-state 13C NMR studies have demonstrated that at rapid magic-angle spinning rates CW decoupling can result in reductions in signal-to-noise and that 1H decoupling should be omitted when acquiring 13C MAS NMR spectra of paramagnetic solids. However, studies of the effectiveness of modern 1H decoupling sequences are lacking, and the performance of such sequences over a variety of experimental conditions must be investigated before 1H decoupling is discounted altogether. We have studied the performance of several commonly used advanced decoupling pulse sequences, namely the TPPM, SPINAL-64, XiX, and eDROOPY sequences, in 13C MAS NMR experiments performed under four combinations of the magnetic field strength (7.05 or 11.75T), rotor frequency (15 or 30kHz), and 1H rf-field strength (71, 100, or 140kHz). The effectiveness of these sequences has been evaluated by comparing the 13C signal intensity, linewidth at half-height, LWHH, and coherence lifetimes, T2('), of the methine carbon of copper(II) bis(dl-alanine) monohydrate, Cu(ala)(2).H2O, and methylene carbon of copper(II) bis(dl-2-aminobutyrate), Cu(ambut)(2), obtained with the advanced sequences to those obtained without 1H decoupling, with CW decoupling, and for fully deuterium labelled samples. The latter have been used as model compounds with perfect 1H decoupling and provide a measure of the efficiency of the 1H decoupling sequence. Overall, the effectiveness of 1H decoupling depends strongly on the decoupling sequence utilized, the experimental conditions and the sample studied. Of the decoupling sequences studied, the XiX sequence consistently yielded the best results, although any of the advanced decoupling sequences strongly outperformed the CW sequence and provided improvements over no 1H decoupling. Experiments performed at 7.05T demonstrate that the XiX decoupling sequence is the least sensitive to changes in the 1H transmitter frequency and may explain the superior performance of this decoupling sequence. Overall, the most important factor in the effectiveness of 1H decoupling was the carbon type studied, with the methylene carbon of Cu(ambut)(2) being substantially more sensitive to 1H decoupling than the methine carbon of Cu(ala)(2).H2O. An analysis of the various broadening mechanisms contributing to 13C linewidths has been performed in order to rationalize the different sensitivities of the two carbon sites under the four experimental conditions.
Collapse
Affiliation(s)
- Mathew J Willans
- Department of Chemistry, University of Alberta, Edmonton, Alta., Canada T6G 2G2
| | | | | |
Collapse
|
36
|
Kotecha M, Wickramasinghe NP, Ishii Y. Efficient low-power heteronuclear decoupling in 13C high-resolution solid-state NMR under fast magic angle spinning. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2007; 45 Suppl 1:S221-30. [PMID: 18157841 DOI: 10.1002/mrc.2151] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The use of a low-power two-pulse phase modulation (TPPM) sequence is proposed for efficient (1)H radio frequency (rf) decoupling in high-resolution (13)C solid-state NMR (SSNMR) under fast MAS conditions. Decoupling efficiency for different low-power decoupling sequences such as continuous-wave (cw), TPPM, XiX, and π-pulse (PIPS) train decoupling has been investigated at a spinning speed of 40 kHz for (13)C CPMAS spectra of uniformly (13)C- and (15)N-labeled L-alanine. It was found that the TPPM decoupling sequence, which was originally designed for high-power decoupling, provides the best decoupling efficiency at low power among all the low-power decoupling sequences examined here. Optimum performance of the low-power TPPM sequence was found to be obtained at a decoupling field intensity (ω(1)) of ~ω(R)/4 with a pulse flip angle of ~π and a phase alternation between ± [Symbol: see text]([Symbol: see text] = 20° ), where ω(R)/2π is the spinning speed. The sensitivity obtained for (13) CO(2)(-), (13)CH, and (13)CH(3) in L-alanine under low-power TPPM at ω(1)/2π of 10 kHz was only 5-15% less than that under high-power TPPM at ω(1) /2π of 200 kHz, despite the fact that only 0.25% of the rf power was required in low-power TPPM. Analysis of the (13)CH(2) signals for uniformly (13) C- and (15) N-labeled L-isoleucine under various low-power decoupling sequences also confirmed superior performance of the low-power TPPM sequence, although the intensity obtained by low-power TPPM was 61% of that obtained by high-power TPPM. (13)C CPMAS spectra of (13)C-labeled ubiquitin micro crystals obtained by low-power TPPM demonstrates that the low-power TPPM sequence is a practical option that provides excellent resolution and sensitivity in (13)C SSNMR for hydrated proteins.
Collapse
Affiliation(s)
- Mrignayani Kotecha
- Department of Chemistry, University of Illinois at Chicago, 845 W Taylor Street, Chicago, IL 60607, USA
| | | | | |
Collapse
|
37
|
Leskes M, Thakur RS, Madhu PK, Kurur ND, Vega S. Bimodal Floquet description of heteronuclear dipolar decoupling in solid-state nuclear magnetic resonance. J Chem Phys 2007; 127:024501. [PMID: 17640131 DOI: 10.1063/1.2746039] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
A theoretical treatment of heteronuclear dipolar decoupling in solid-state nuclear magnetic resonance is presented here based on bimodal Floquet theory. The conditions necessary for good heteronuclear decoupling are derived. An analysis of a few of the decoupling schemes implemented until date is presented with regard to satisfying such decoupling conditions and efficiency of decoupling. Resonance conditions for efficient heteronuclear dipolar decoupling are derived with and without the homonuclear (1)H-(1)H dipolar couplings and their influence on heteronuclear dipolar decoupling is pointed out. The analysis points to the superior efficiency of the newly introduced swept two-pulse phase-modulation (SW(f)-TPPM) sequence. It is shown that the experimental robustness of SW(f)-TPPM as compared to the original TPPM sequence results from an adiabatic sweeping of the modulation frequencies. Based on this finding alternative strategies are compared here. The theoretical findings are corroborated by both numerical simulations and representative experiments.
Collapse
Affiliation(s)
- Michal Leskes
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | | | | | | | | |
Collapse
|
38
|
Trebosc J, Hu B, Amoureux JP, Gan Z. Through-space R3-HETCOR experiments between spin-1/2 and half-integer quadrupolar nuclei in solid-state NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2007; 186:220-7. [PMID: 17379553 DOI: 10.1016/j.jmr.2007.02.015] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2007] [Accepted: 02/25/2007] [Indexed: 05/14/2023]
Abstract
We present several new methods that allow to obtain through-space 2D HETCOR spectra between spin-1/2 and half-integer quadrupolar nuclei in the solid state. These methods use the rotary-resonance concept to create hetero-nuclear coherences through the dipolar interaction instead of scalar coupling into the HMQC and refocused INEPT experiments for spin n/2 (n>1). In opposite to those based on the cross-polarization transfer to quadrupolar nuclei, the methods are very robust and easy to set-up.
Collapse
Affiliation(s)
- J Trebosc
- UCCS, CNRS-8181, Université de Lille, FR-59652 Villeneuve d'Ascq, France
| | | | | | | |
Collapse
|
39
|
Delevoye L, Trébosc J, Gan Z, Montagne L, Amoureux JP. Resolution enhancement using a new multiple-pulse decoupling sequence for quadrupolar nuclei. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2007; 186:94-9. [PMID: 17303456 DOI: 10.1016/j.jmr.2007.01.018] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2006] [Revised: 01/25/2007] [Accepted: 01/26/2007] [Indexed: 05/14/2023]
Abstract
A new decoupling composite pulse sequence is proposed to remove the broadening on spin S=1/2 magic-angle spinning (MAS) spectra arising from the scalar coupling with a quadrupolar nucleus I. It is illustrated on the (31)P spectrum of an aluminophosphate, AlPO(4)-14, which is broadened by the presence of (27)Al/(31)P scalar couplings. The multiple-pulse (MP) sequence has the advantage over the continuous wave (CW) irradiation to efficiently annul the scalar dephasing without reintroducing the dipolar interaction. The MP decoupling sequence is first described in a rotor-synchronised version (RS-MP) where one parameter only needs to be adjusted. It clearly avoids the dipolar recoupling in order to achieve a better resolution than using the CW sequence. In a second improved version, the MP sequence is experimentally studied in the vicinity of the perfect rotor-synchronised conditions. The linewidth at half maximum (FWHM) of 65 Hz using (27)Al CW decoupling decreases to 48 Hz with RS-MP decoupling and to 30 Hz with rotor-asynchronised MP (RA-MP) decoupling. The main phenomena are explained using both experimental results and numerical simulations.
Collapse
Affiliation(s)
- L Delevoye
- UCCS, CNRS-8181, ENSCL-USTL, 59652 Villeneuve d'Ascq, France.
| | | | | | | | | |
Collapse
|
40
|
Takeda K. A highly integrated FPGA-based nuclear magnetic resonance spectrometer. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2007; 78:033103. [PMID: 17411174 DOI: 10.1063/1.2712940] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The digital circuits required for a nuclear magnetic resonance (NMR) spectrometer, including a pulse programmer, a direct digital synthesizer, a digital receiver, and a PC interface, have been built inside a single chip of the field-programmable gate-array (FPGA). By combining the FPGA chip with peripheral analog components, a compact, laptop-sized homebuilt spectrometer has been developed, which is capable of a rf output of up to 400 MHz with amplitude-, phase-, frequency-, and pulse-modulation. The number of rf channels is extendable up to three without further increase in size.
Collapse
Affiliation(s)
- Kazuyuki Takeda
- Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
| |
Collapse
|
41
|
Swept-frequency two-pulse phase modulation for heteronuclear dipolar decoupling in solid-state NMR. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.06.007] [Citation(s) in RCA: 175] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
42
|
Ernst M, Geen H, Meier BH. Amplitude-modulated decoupling in rotating solids: a bimodal Floquet approach. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2006; 29:2-21. [PMID: 16216477 DOI: 10.1016/j.ssnmr.2005.08.004] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2005] [Revised: 09/08/2005] [Indexed: 05/04/2023]
Abstract
This paper centers on a theoretical study of amplitude-modulated heteronuclear decoupling in solid-state NMR under magic-angle spinning (MAS). A spin system with a single isolated rare spin coupled to a large number of abundant spins is used in the analysis. The phase-alternating decoupling scheme (XiX decoupling) is analyzed using bimodal Floquet theory and the operator-based perturbation method developed by van Vleck. An effective Hamiltonian correct to second order is calculated for the spin system under XiX decoupling. The results of these calculations indicate that under XiX decoupling the main contribution to the residual line width comes from a cross-term between the heteronuclear and the homonuclear dipolar couplings. This is in contrast to continuous-wave decoupling, where the residual line width is dominated by the cross-term between the heteronuclear dipolar coupling and the chemical-shielding tensor of the irradiated spin. For high-power decoupling the method results in very good decoupling provided that certain unfavorable recoupling conditions, imposed by specific ratios of the amplitude modulation frequency and the MAS frequency, are avoided. For low-power decoupling, the method leads to acceptable decoupling when the pulse length corresponds to an integer multiple of a 2pi rotation and the rf-field amplitude is less than a quarter of the MAS frequency. The performance of the XiX scheme is analyzed over a range of values of the rf power, and numerical results that agree well with the most recent experimental observations are presented.
Collapse
Affiliation(s)
- Matthias Ernst
- Physical Chemistry, ETH Zürich, CH-8093 Zürich, Switzerland.
| | | | | |
Collapse
|
43
|
Filip X, Tripon C, Filip C. Heteronuclear decoupling under fast MAS by a rotor-synchronized Hahn-echo pulse train. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2005; 176:239-43. [PMID: 16039885 DOI: 10.1016/j.jmr.2005.06.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2005] [Revised: 06/04/2005] [Accepted: 06/12/2005] [Indexed: 05/03/2023]
Abstract
A new heteronuclear decoupling mechanism under fast magic-angle spinning MAS is introduced. It is based on refocusing the coherences responsible for the dephase of low-gamma nuclei ((13)C, (15)N) transverse spin-polarization in the presence of strongly dipolar-coupled protons, and has the advantage that can be implemented by pulsed techniques, with all the benefits resulting from a reduced duty cycle compared with conventional decoupling by continuous rf irradiation. The decoupling efficiency of a simple rotor-synchronized Hahn-echo pulse train is analyzed both theoretically and experimentally. It was found that a substantial improvement in sensitivity and resolution can be achieved in compounds with small (1)H chemical shielding parameters even at moderate sample spinning, and some interesting applications are shown. It is also shown that much faster spinning frequencies, or alternative refocusing sequences, are needed for applications on rigid organic solids, i.e., in systems with larger (1)H chemical shifts.
Collapse
Affiliation(s)
- Xenia Filip
- National Institute for R&D of Isotopic and Molecular Technologies, P.O. Box 700, 400293 Cluj, Romania
| | | | | |
Collapse
|
44
|
Ramachandran R, Bajaj VS, Griffin RG. Theory of heteronuclear decoupling in solid-state nuclear magnetic resonance using multipole-multimode Floquet theory. J Chem Phys 2005; 122:164503. [PMID: 15945689 DOI: 10.1063/1.1875112] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
A formal theory for heteronuclear decoupling in solid-state magic angle spinning (MAS) nuclear magnetic resonance experiments is presented as a first application of multipole-multimode Floquet theory. The method permits a straightforward construction of the multispin basis and describes the spin dynamics via effective Floquet Hamiltonians obtained using the van Vleck transformation method in the Floquet-Liouville space. As a test case, we consider a model three-spin system (I2S) under asynchronous time modulations (both MAS and rf irradiation) and derive effective Hamiltonians for describing the spin dynamics in the Floquet-Liouville space during heteronuclear decoupling. Furthermore, we describe and evaluate the origin of cross terms between the various anisotropic interactions and illustrate their exact contributions to the spin dynamics. The theory presented herein should be applicable to the design and understanding of pulse sequences for heteronuclear and homonuclear recoupling and decoupling.
Collapse
Affiliation(s)
- Ramesh Ramachandran
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | | | | |
Collapse
|
45
|
Riedel K, Leppert J, Ohlenschläger O, Görlach M, Ramachandran R. Heteronuclear decoupling in rotating solids via symmetry-based adiabatic RF pulse schemes. Chem Phys Lett 2004. [DOI: 10.1016/j.cplett.2004.07.106] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
|
46
|
De Paëpe G, Eléna B, Emsley L. Characterization of heteronuclear decoupling through proton spin dynamics in solid-state nuclear magnetic resonance spectroscopy. J Chem Phys 2004; 121:3165-80. [PMID: 15291627 DOI: 10.1063/1.1773155] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The work presented here aims at understanding the performance of phase modulated heteronuclear decoupling sequences such as Cosine Modulation or Two Pulse Phase Modulation. To that end we provide an analytical description of the intrinsic behavior of Cosine Modulation decoupling with respect to radio-frequency-inhomogeneity and the proton-proton dipolar coupling network. We discover through a Modulation Frame average Hamiltonian analysis that best decoupling is obtained under conditions where the heteronuclear interactions are removed but notably where homonuclear couplings are recoupled at a homonuclear Rotary Resonance (HORROR) condition in the Modulation Frame. These conclusions are supported by extensive experimental investigations, and notably through the introduction of proton nutation experiments to characterize spin dynamics in solids under decoupling conditions. The theoretical framework presented in this paper allows the prediction of the optimum parameters for a given set of experimental conditions.
Collapse
Affiliation(s)
- Gaël De Paëpe
- Laboratoire de Chimie (UMR-5182 CNRS-ENS), Laboratoire de Recherche Correspondant du CEA (23 V), Ecole Normale Superieure de Lyon, 69364, France
| | | | | |
Collapse
|
47
|
Ashida J, Asakura T. An application of the XiX decoupling for solid state 13C NMR with mobile samples. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2003; 165:180-183. [PMID: 14568528 DOI: 10.1016/s1090-7807(03)00269-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
It is very important to obtain higher resolution solid state NMR spectra not only for crystal samples but also for mobile solid samples. We demonstrate that a robust proton decoupling technique, XiX (X inverse-X) decoupling, is very effective in high resolution solid state NMR measurement for mobile samples compared with the usual continuous wave proton decoupling.
Collapse
Affiliation(s)
- Jun Ashida
- Varian Technologies Japan Ltd., 4-16-36 Shibaura, Minato, 108-0023, Tokyo, Japan.
| | | |
Collapse
|
48
|
De Paëpe G, Lesage A, Emsley L. The performance of phase modulated heteronuclear dipolar decoupling schemes in fast magic-angle-spinning nuclear magnetic resonance experiments. J Chem Phys 2003. [DOI: 10.1063/1.1595088] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
49
|
Ernst M, Samoson A, Meier BH. Low-power XiX decoupling in MAS NMR experiments. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2003; 163:332-9. [PMID: 12914849 DOI: 10.1016/s1090-7807(03)00155-1] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Low-power XiX proton decoupling under fast magic-angle spinning is introduced. The method is applicable if the MAS frequency exceeds the proton-proton interactions. For rigid organic solids this is the case for MAS frequencies above approximately 40 kHz. It is shown that the quality of the decoupling as well as the sensitivity to frequency offsets can be improved compared to low-power continuous-wave decoupling. The decoupling efficiency is somewhat reduced compared to optimized high-power decoupling: in a peptide sample investigated at an MAS frequency of 50 kHz a loss of about 10% in signal intensity for CH3 and CH groups, and of about 40% for CH2 groups was observed. Taking into consideration, that the rf amplitude in the low-power XiX was about 15 times lower than in high-power XiX decoupling, such a reduction in line intensity is sometimes tolerable.
Collapse
Affiliation(s)
- Matthias Ernst
- Physical Chemistry, ETH-Zürich, CH-8093 Zürich, Switzerland.
| | | | | |
Collapse
|
50
|
Gerbaud G, Ziarelli F, Caldarelli S. Increasing the robustness of heteronuclear decoupling in magic-angle sample spinning solid-state NMR. Chem Phys Lett 2003. [DOI: 10.1016/s0009-2614(03)01056-x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
|