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Niels Chr Nielsen - One of the best experts on this subject based on the ideXlab platform.
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A general theoretical description of the influence of isotropic chemical shift in Dipolar Recoupling experiments for solid-state NMR
The Journal of chemical physics, 2017Co-Authors: Ravi Shankar, Niels Chr Nielsen, Thomas Vosegaard, Matthias Ernst, Perunthiruthy K. Madhu, Anders B NielsenAbstract:We present a general theoretical description that allows us to describe the influence of isotropic chemical shift in homonuclear and heteronuclear Dipolar Recoupling experiments in magic-angle-spinning solid-state NMR. Through a transformation of the Hamiltonian into an interaction frame with the combined radio-frequency irradiation and the isotropic chemical shift, we determine an effective Hamiltonian to first order with respect to the relevant internal nuclear spin interactions. This unravels the essential resonance conditions for efficient Dipolar Recoupling. Furthermore, we propose how to handle situations where the resonance conditions are not exactly fulfilled. To verify the general theoretical description, we compare numerical simulations using a time-sliced time-dependent Hamiltonian with simulations using the calculated effective Hamiltonian for propagation. The comparisons are exemplified for the homonuclear Dipolar Recoupling experiments C721 and POST-C721.
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handling the influence of chemical shift in amplitude modulated heteronuclear Dipolar Recoupling solid state nmr
Journal of Chemical Physics, 2016Co-Authors: Kristoffer Basse, Niels Chr Nielsen, Morten Bjerring, Thomas Vosegaard, Ravi Shankar, Anders B NielsenAbstract:We present a theoretical analysis of the influence of chemical shifts on amplitude-modulated heteronuclear Dipolar Recoupling experiments in solid-state NMR spectroscopy. The method is demonstrated using the Rotor Echo Short Pulse IRrAdiaTION mediated Cross-Polarization (RESPIRATIONCP) experiment as an example. By going into the pulse sequence rf interaction frame and employing a quintuple-mode operator-based Floquet approach, we describe how chemical shift offset and anisotropic chemical shift affect the efficiency of heteronuclear polarization transfer. In this description, it becomes transparent that the main attribute leading to non-ideal performance is a fictitious field along the rf field axis, which is generated from second-order cross terms arising mainly between chemical shift tensors and themselves. This insight is useful for the development of improved Recoupling experiments. We discuss the validity of this approach and present quaternion calculations to determine the effective resonance condit...
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Handling the influence of chemical shift in amplitude-modulated heteronuclear Dipolar Recoupling solid-state NMR.
The Journal of chemical physics, 2016Co-Authors: Kristoffer Basse, Niels Chr Nielsen, Morten Bjerring, Thomas Vosegaard, Ravi Shankar, Anders B NielsenAbstract:We present a theoretical analysis of the influence of chemical shifts on amplitude-modulated heteronuclear Dipolar Recoupling experiments in solid-state NMR spectroscopy. The method is demonstrated using the Rotor Echo Short Pulse IRrAdiaTION mediated Cross-Polarization ((RESPIRATION)CP) experiment as an example. By going into the pulse sequence rf interaction frame and employing a quintuple-mode operator-based Floquet approach, we describe how chemical shift offset and anisotropic chemical shift affect the efficiency of heteronuclear polarization transfer. In this description, it becomes transparent that the main attribute leading to non-ideal performance is a fictitious field along the rf field axis, which is generated from second-order cross terms arising mainly between chemical shift tensors and themselves. This insight is useful for the development of improved Recoupling experiments. We discuss the validity of this approach and present quaternion calculations to determine the effective resonance conditions in a combined rf field and chemical shift offset interaction frame transformation. Based on this, we derive a broad-banded version of the (RESPIRATION)CP experiment. The new sequence is experimentally verified using SNNFGAILSS amyloid fibrils where simultaneous (15)N → (13)CO and (15)N → (13)Cα coherence transfer is demonstrated on high-field NMR instrumentation, requiring great offset stability.
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Adiabatic Rotor-Echo-Short-Pulse-Irradiation mediated cross-polarization.
Journal of magnetic resonance (San Diego Calif. : 1997), 2013Co-Authors: Anders B Nielsen, Matthias Ernst, Sheetal Jain, Beat H. Meier, Niels Chr NielsenAbstract:We present a new Dipolar Recoupling method for efficient and robust heteronuclear polarization transfer in solid-state NMR under magic-angle-spinning (MAS) conditions. The method combines the recent RESPIRATIONCP method with a modulation of the amplitude of the rotor-synchronized pulses at one of the involved rf channels through the Recoupling condition. In this manner, it is possible to achieve high transfer efficiencies while maintaining robustness towards rf-field inhomogeneities and resonance offsets. The performance of the so-called adiabatic-RESPIRATIONCP experiment is demonstrated numerically and experimentally using uniformly 13C,15N-labeled samples of alanine and ubiquitin. In particular for cases with relatively high rf inhomogeneity, the scheme offers advantages over the commonly used Dipolar Recoupling pulse sequences.
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Dipolar Recoupling.
Topics in current chemistry, 2011Co-Authors: Niels Chr Nielsen, Lasse A Strassø, Anders B NielsenAbstract:We describe the principles and applications of Dipolar Recoupling in solid-state NMR spectroscopy as a means to access information about molecular structure and transfer magnetization between spins. In this manner, Dipolar Recoupling forms an essential basis for multiple-dimensional solid-state NMR experiments from which information about structure and dynamics can be extracted. We introduce the basic formalism needed to understand such experiments, present some powerful design principles, and on this basis describe in a coherent way a series of homo- and heteronuclear Dipolar Recoupling experiments. These experiments serve to highlight design strategies, the gradual development of increasingly advanced and powerful methods, and reflect the application of Dipolar Recoupling in biological solid-state NMR spectroscopy.
Ramadurai Ramachandran - One of the best experts on this subject based on the ideXlab platform.
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MAS solid state NMR of proteins: simultaneous ^15N–^13CA and ^15N–^13CO Dipolar Recoupling via low-power symmetry-based RF pulse schemes
Journal of Biomolecular NMR, 2015Co-Authors: Christian Herbst, Matthias Görlach, Peter Bellstedt, Ramadurai RamachandranAbstract:The generation of efficient RN_ n ^νs,^νk symmetry-based low-power RF pulse schemes for simultaneous ^15N–^13CA and ^15N–^13CO Dipolar Recoupling is demonstrated. The method involves mixing schemes employing phase and amplitude-modulated dual band - selective 180° pulses as basic “ R ” element and tailoring of the RF field-modulation profile of the 180° pulses so as to obtain efficient magnetisation transfer characteristics over the resonance offset range of the nuclei involved. Mixing schemes leading to simultaneous ^15N–^13CA and ^15N–^13CO Dipolar Recoupling would permit the one-shot acquisition of different chemical shift correlation spectra that are typically utilized for protein backbone resonance assignments and thereby save data acquisition time. At representative MAS frequencies the efficacies of the mixing schemes presented here have been experimentally demonstrated via the simultaneous acquisition of {3D CONH and 3D CANH}, {3D CONH and 3D CO(CA)NH} and {3D CONH, 3D CANH, 3D CO(CA)NH and 3D CA(CO)NH} spectra generated via the magnetisation transfer pathways ^1H → ^13CO → ^15N → ^1H (CONH), ^1H → ^13CA → ^15N → ^1H (CANH) and ^1H → ^13CO → ^13CA → ^15N → ^1H (CO(CA)NH) and ^1H → ^13CA → ^13CO → ^15N → ^1H (CA(CO)NH).
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mas solid state nmr of proteins simultaneous 15n 13ca and 15n 13co Dipolar Recoupling via low power symmetry based rf pulse schemes
Journal of Biomolecular NMR, 2015Co-Authors: Christian Herbst, Matthias Görlach, Peter Bellstedt, Ramadurai RamachandranAbstract:The generation of efficient RN n (ν)s,(ν)k symmetry-based low-power RF pulse schemes for simultaneous (15)N-(13)CA and (15)N-(13)CO Dipolar Recoupling is demonstrated. The method involves mixing schemes employing phase and amplitude-modulated dual band-selective 180° pulses as basic "R" element and tailoring of the RF field-modulation profile of the 180° pulses so as to obtain efficient magnetisation transfer characteristics over the resonance offset range of the nuclei involved. Mixing schemes leading to simultaneous (15)N-(13)CA and (15)N-(13)CO Dipolar Recoupling would permit the one-shot acquisition of different chemical shift correlation spectra that are typically utilized for protein backbone resonance assignments and thereby save data acquisition time. At representative MAS frequencies the efficacies of the mixing schemes presented here have been experimentally demonstrated via the simultaneous acquisition of {3D CONH and 3D CANH}, {3D CONH and 3D CO(CA)NH} and {3D CONH, 3D CANH, 3D CO(CA)NH and 3D CA(CO)NH} spectra generated via the magnetisation transfer pathways (1)H → (13)CO → (15)N → (1)H (CONH), (1)H → (13)CA → (15)N → (1)H (CANH) and (1)H → (13)CO → (13)CA → (15)N → (1)H (CO(CA)NH) and (1)H → (13)CA → (13)CO → (15)N → (1)H (CA(CO)NH).
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Broadband ^15N–^13C Dipolar Recoupling via symmetry-based RF pulse schemes at high MAS frequencies
Journal of Biomolecular NMR, 2010Co-Authors: Christian Herbst, Jirada Herbst, Michela Carella, Jörg Leppert, Oliver Ohlenschläger, Matthias Görlach, Ramadurai RamachandranAbstract:An approach for generating efficient $$ {\rm{RN}}_{n}^{\nu_{\rm{S}}, {\nu_{\rm{k}}}} $$ symmetry-based dual channel RF pulse schemes for γ-encoded broadband ^15N–^13C Dipolar Recoupling at high magic angle spinning frequencies is presented. The method involves the numerical optimisation of the RF phase-modulation profile of the basic “ R ” element so as to obtain heteronuclear double quantum Dipolar Recoupling sequences with satisfactory magnetisation transfer characteristics. The basic “ R ” element was implemented as a sandwich of a small number of short pulses of equal duration with each pulse characterised by a RF phase and amplitude values. The performance characteristics of the sequences were evaluated via numerical simulations and ^15N–^13C chemical shift correlation experiments. Employing such ^13C–^15N double-quantum Recoupling sequences and the multiple receiver capabilities available in the current generation of NMR spectrometers, the possibility to simultaneously acquire 3D NCC and CNH chemical shift correlation spectra is also demonstrated.
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broadband 15n 13c Dipolar Recoupling via symmetry based rf pulse schemes at high mas frequencies
Journal of Biomolecular NMR, 2010Co-Authors: Christian Herbst, Jirada Herbst, Michela Carella, Jörg Leppert, Oliver Ohlenschläger, Matthias Görlach, Ramadurai RamachandranAbstract:An approach for generating efficient \( {\rm{RN}}_{n}^{\nu_{\rm{S}}, {\nu_{\rm{k}}}} \) symmetry-based dual channel RF pulse schemes for γ-encoded broadband 15N–13C Dipolar Recoupling at high magic angle spinning frequencies is presented. The method involves the numerical optimisation of the RF phase-modulation profile of the basic “R” element so as to obtain heteronuclear double quantum Dipolar Recoupling sequences with satisfactory magnetisation transfer characteristics. The basic “R” element was implemented as a sandwich of a small number of short pulses of equal duration with each pulse characterised by a RF phase and amplitude values. The performance characteristics of the sequences were evaluated via numerical simulations and 15N–13C chemical shift correlation experiments. Employing such 13C–15N double-quantum Recoupling sequences and the multiple receiver capabilities available in the current generation of NMR spectrometers, the possibility to simultaneously acquire 3D NCC and CNH chemical shift correlation spectra is also demonstrated.
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Solid state NMR at high magic angle spinning frequencies: Dipolar chemical shift correlation with adiabatic inversion pulse based RF pulse schemes
Journal of Biomolecular NMR, 2006Co-Authors: Christian Herbst, Jörg Leppert, Oliver Ohlenschläger, Matthias Görlach, Kerstin Riedel, Ramadurai RamachandranAbstract:The efficacy of hetero- and homonuclear Dipolar Recoupling employing tanh/tan adiabatic inversion pulse based RF pulse schemes has been examined at high magic angle spinning (MAS) frequencies via numerical simulations and experimental measurements. An approach for minimising the Recoupling RF power level is presented, taking into consideration the spinning speed, the range of resonance offsets and H_1 inhomogeneities and the available RF field strength. This involves the tailoring of the frequency and amplitude modulation profiles of the inversion pulses. The applicability of tanh/tan pulse based Dipolar Recoupling schemes to spinning speed regimes where the performance with conventional rectangular pulses may not be satisfactory is demonstrated.
Robert Tycko - One of the best experts on this subject based on the ideXlab platform.
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Optimization of band-selective homonuclear Dipolar Recoupling in solid-state NMR by a numerical phase search.
The Journal of chemical physics, 2019Co-Authors: Zhengfeng Zhang, Robert Tycko, Hui Liu, Jing Deng, Jun YangAbstract:Spin polarization transfers among aliphatic 13C nuclei, especially 13Cα–13Cβ transfers, permit correlations of their nuclear magnetic resonance (NMR) frequencies that are essential for signal assignments in multidimensional solid-state NMR of proteins. We derive and demonstrate a new radio-frequency (RF) excitation sequence for homonuclear Dipolar Recoupling that enhances spin polarization transfers among aliphatic 13C nuclei at moderate magic-angle spinning (MAS) frequencies. The phase-optimized Recoupling sequence with five π pulses per MAS rotation period (denoted as PR5) is derived initially from systematic numerical simulations in which only the RF phases are varied. Subsequent theoretical analysis by average Hamiltonian theory explains the favorable properties of numerically optimized phase schemes. The high efficiency of spin polarization transfers in simulations is preserved in experiments, in part because the RF field amplitude in PR5 is only 2.5 times the MAS frequency so that relatively low 1H decoupling powers are required. Experiments on a microcrystalline sample of the β1 immunoglobulin binding domain of protein G demonstrate an average enhancement factor of 1.6 for 13Cα → 13Cβ polarization transfers, compared to the standard 13C–13C spin-diffusion method, implying a two-fold time saving in relevant 2D and 3D experiments.
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Zero-quantum stochastic Dipolar Recoupling in solid state nuclear magnetic resonance
The Journal of chemical physics, 2012Co-Authors: Wei Qiang, Robert TyckoAbstract:We present the theoretical description and experimental demonstration of a zero-quantum stochastic Dipolar Recoupling (ZQ-SDR) technique for solid state nuclear magnetic resonance (NMR) studies of (13)C-labeled molecules, including proteins, under magic-angle spinning (MAS). The ZQ-SDR technique combines zero-quantum Recoupling pulse sequence blocks with randomly varying chemical shift precession periods to create randomly amplitude- and phase-modulated effective homonuclear magnetic dipole-dipole couplings. To a good approximation, couplings between different (13)C spin pairs become uncorrelated under ZQ-SDR, leading to spin dynamics (averaged over many repetitions of the ZQ-SDR sequence) that are fully described by an orientation-dependent N × N polarization transfer rate matrix for an N-spin system, with rates that are inversely proportional to the sixth power of internuclear distances. Suppression of polarization transfers due to non-commutivity of pairwise couplings (i.e., Dipolar truncation) does not occur under ZQ-SDR, as we show both analytically and numerically. Experimental demonstrations are reported for uniformly (13)C-labeled L-valine powder (at 14.1 T and 28.00 kHz MAS), uniformly (13)C-labeled protein GB1 in microcrystalline form (at 17.6 T and 40.00 kHz MAS), and partially labeled (13)C-labeled protein GB1 (at 14.1 T and 40.00 kHz MAS). The experimental results verify that spin dynamics under ZQ-SDR are described accurately by rate matrices and suggest the utility of ZQ-SDR in structural studies of (13)C-labeled solids.
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Restraints on backbone conformations in solid state NMR studies of uniformly labeled proteins from quantitative amide 15N-15N and carbonyl 13C-13C Dipolar Recoupling data.
Journal of magnetic resonance (San Diego Calif. : 1997), 2012Co-Authors: Wei Qiang, Guillermo A. Bermejo, Charles D. Schwieters, Robert TyckoAbstract:Recent structural studies of uniformly (15)N, (13)C-labeled proteins by solid state nuclear magnetic resonance (NMR) rely principally on two sources of structural restraints: (i) restraints on backbone conformation from isotropic (15)N and (13)C chemical shifts, based on empirical correlations between chemical shifts and backbone torsion angles; (ii) restraints on inter-residue proximities from qualitative measurements of internuclear dipole-dipole couplings, detected as the presence or absence of inter-residue crosspeaks in multidimensional spectra. We show that site-specific dipole-dipole couplings among (15)N-labeled backbone amide sites and among (13)C-labeled backbone carbonyl sites can be measured quantitatively in uniformly-labeled proteins, using Dipolar Recoupling techniques that we call (15)N-BARE and (13)C-BARE (BAckbone Recoupling), and that the resulting data represent a new source of restraints on backbone conformation. (15)N-BARE and (13)C-BARE data can be incorporated into structural modeling calculations as potential energy surfaces, which are derived from comparisons between experimental (15)N and (13)C signal decay curves, extracted from crosspeak intensities in series of two-dimensional spectra, with numerical simulations of the (15)N-BARE and (13)C-BARE measurements. We demonstrate this approach through experiments on microcrystalline, uniformly (15)N, (13)C-labeled protein GB1. Results for GB1 show that (15)N-BARE and (13)C-BARE restraints are complementary to restraints from chemical shifts and inter-residue crosspeaks, improving both the precision and the accuracy of calculated structures.
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Dipolar Recoupling homonuclear experiments
eMagRes, 2009Co-Authors: Robert TyckoAbstract:Dipolar Recoupling techniques are RF pulse sequences that are applied in synchrony with magic-angle spinning (MAS) to restore nuclear magnetic dipole–dipole couplings that are averaged to zero by MAS alone. Such techniques are used in quantitative measurements of dipole–dipole couplings, and hence internuclear distances, in multidimensional spectroscopy to produce nuclear spin polarization transfers that lead to crosspeak signals, in double-quantum or multiple-quantum filtering, and for other purposes. This article presents the basic theoretical concepts behind the development of Dipolar Recoupling techniques, especially techniques for restoring homonuclear couplings. Several distinct Recoupling mechanisms are described and illustrated by specific techniques. Symmetry principles that are useful in the design of Recoupling techniques are discussed briefly, as are recent developments in frequency-selective Recoupling, stochastic Recoupling, and three-spin Recoupling. Keywords: magic-angle spinning; average Hamiltonian theory; pulse sequences; structure determination
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theory of stochastic Dipolar Recoupling in solid state nuclear magnetic resonance
Journal of Physical Chemistry B, 2008Co-Authors: Robert TyckoAbstract:Dipolar Recoupling techniques in solid-state nuclear magnetic resonance (NMR) consist of radio frequency (rf) pulse sequences applied in synchrony with magic-angle spinning (MAS) that create nonzer...
Jean-paul Amoureux - One of the best experts on this subject based on the ideXlab platform.
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Observation of proximities between spin-1/2 and quadrupolar nuclei: Which heteronuclear Dipolar Recoupling method is preferable?
The Journal of chemical physics, 2012Co-Authors: Olivier Lafon, Julien Trébosc, Gregory Tricot, Laurent Delevoye, Francois O Mear, Lionel Montagne, Jean-paul AmoureuxAbstract:We have recently shown that the Dipolar-mediated heteronuclear multiple-quantum coherence (D-HMQC) method allows observing through-space proximities between spin-1/2 ((1)H, (13)C, (31)P...) and quadrupolar ((23)Na, (27)Al...) nuclei. However, the D-HMQC effectiveness depends on the choice of the heteronuclear Dipolar Recoupling sequence. Here, we compare the efficiency and the robustness of four rotor-synchronized sequences: the symmetry-based ones, R4(1)(2)R4(1)(-2) and its super-cycled version, SR4(1)(2), and two schemes based on simultaneous amplitude and frequency modulations, denoted SFAM-1 and SFAM-2. For the SFAM methods, we point out efficient Recoupling conditions that facilitate their experimental optimization and we introduce analytical expressions for the buildup of D-HMQC signal in the case of an isolated spin pair. We show that the main differences between these four sequences lie in the number of adjustable parameters and in their robustness with respect to chemical shift and homonuclear Dipolar interactions. The relative performances of these four Recoupling sequences are analyzed using average Hamiltonian theory, numerical simulations, and (27)Al-{(31)P} D-HMQC experiments on crystalline aluminophosphate.
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observation of proximities between spin 1 2 and quadrupolar nuclei which heteronuclear Dipolar Recoupling method is preferable
Journal of Chemical Physics, 2012Co-Authors: Olivier Lafon, Julien Trébosc, Gregory Tricot, Laurent Delevoye, Francois O Mear, Lionel Montagne, Jean-paul AmoureuxAbstract:We have recently shown that the Dipolar-mediated heteronuclear multiple-quantum coherence (D-HMQC) method allows observing through-space proximities between spin-1/2 (1H, 13C, 31P…) and quadrupolar (23Na, 27Al…) nuclei. However, the D-HMQC effectiveness depends on the choice of the heteronuclear Dipolar Recoupling sequence. Here, we compare the efficiency and the robustness of four rotor-synchronized sequences: the symmetry-based ones, R412R41−2 and its super-cycled version, SR 412, and two schemes based on simultaneous amplitude and frequency modulations, denoted SFAM-1 and SFAM-2. For the SFAM methods, we point out efficient Recoupling conditions that facilitate their experimental optimization and we introduce analytical expressions for the buildup of D-HMQC signal in the case of an isolated spin pair. We show that the main differences between these four sequences lie in the number of adjustable parameters and in their robustness with respect to chemical shift and homonuclear Dipolar interactions. The r...
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Observing 13C-13C connectivities at high magnetic fields and very high spinning frequencies.
Chemical communications (Cambridge England), 2011Co-Authors: Olivier Lafon, Julien Trébosc, Gael De Paepe, Jean-paul AmoureuxAbstract:We report the application of a Dipolar Recoupling sequence for the observation of 13C–13C connectivities in biomolecules at high magnetic fields (B0 ≥ 21.1 T) and ultra-high magic angle spinning frequencies (νR = 60 kHz). The efficiency and the robustness of this double-quantum technique are demonstrated on the YajG protein (19.6 kDa).
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Homonuclear Dipolar Recoupling under ultra-fast magic-angle spinning: probing 19F-19F proximities by solid-state NMR.
Journal of magnetic resonance (San Diego Calif. : 1997), 2009Co-Authors: Qiang Wang, Julien Trébosc, Olivier Lafon, Feng Deng, Jean-paul AmoureuxAbstract:We describe Dipolar Recoupling methods that accomplish. at high magic-angle spinning (MAS) frequencies, the excitation of double-quantum (DQ) coherences between spin-1/2 nuclei We employ rotor-synchronized symmetry-based pulse sequences which are either gamma-encoded or non-gamma-encoded The sensitivity and the robustness to both chemical-shift anisotropy and offset are examined. We also compare different techniques to avoid signal folding in the indirect dimension of two-dimensional double-quantum single-quantum (DQ-SQ) spectra This comprehensive analysis results in the identification of satisfactory conditions for Dipolar F-19-F-19 Recoupling at high magnetic fields and high MAS frequencies The utility of these Recoupling methods is demonstrated with high-resolution DQ-SQ NMR spectra, which allow probing F-19-F-19 proximities in powered fluoroluminates (C) 2009 Elsevier Inc All rights reserved
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double quantum 19f 19f Dipolar Recoupling at ultra fast magic angle spinning nmr application to the assignment of 19f nmr spectra of inorganic fluorides
Physical Chemistry Chemical Physics, 2009Co-Authors: Qiang Wang, Franck Fayon, Julien Trébosc, Christophe Legein, Olivier Lafon, Feng Deng, Jean-paul AmoureuxAbstract:A broadband Dipolar Recoupling method robust to chemical shift is introduced to observe 19F–19F proximities in fluoroaluminates in high magnetic field and at ultra-fast magic angle spinning (>60 kHz).
Navin Khaneja - One of the best experts on this subject based on the ideXlab platform.
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Triple oscillating field technique for accurate distance measurements by solid-state NMR.
The Journal of chemical physics, 2008Co-Authors: Navin Khaneja, Niels Chr NielsenAbstract:We present a new concept for homonuclear Dipolar Recoupling in magic-angle-spinning (MAS) solid-state NMR experiments which avoids the problem of Dipolar truncation. This is accomplished through the introduction of a new NMR pulse sequence design principle: the triple oscillating field technique. We demonstrate this technique as an efficient means to accomplish broadband Dipolar Recoupling of homonuclear spins, while decoupling heteronuclear Dipolar couplings and anisotropic chemicals shifts and retaining influence from isotropic chemical shifts. In this manner, it is possible to synthesize Ising interaction (2IzSz) Hamiltonians in homonuclear spin networks and thereby avoid Dipolar truncation--a serious problem essentially all previous homonuclear Dipolar Recoupling experiments suffer from. Combination of this Recoupling concept with rotor assisted Dipolar refocusing enables easy readout of internuclear distances through comparison with analytical Fresnel curves. This forms the basis for a new class of solid-state NMR experiments with potential for structure analysis of uniformly 13C labeled proteins through accurate measurement of 13C-13C internuclear distances. The concept is demonstrated experimentally by measurement of C alpha-C', C beta-C', and C gamma-C' internuclear distances in powder samples of the amino acids L-alanine and L-threonine.
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Optimal control based design of composite Dipolar Recoupling experiments by analogy to single-spin inversion pulses
Chemical Physics Letters, 2007Co-Authors: Jonas Ø. Hansen, Steffen J. Glaser, Morten Bjerring, Cindie Kehlet, Thomas Vosegaard, Navin Khaneja, Niels Christian NielsenAbstract:Abstract It is demonstrated that a simple analogy between single-spin composite radiofrequency (rf) pulses and solid-state NMR Dipolar Recoupling may be exploited to reduce the operator space dimensionality in design of Recoupling experiments by optimal control based algorithms. The use of single-spin calculations speeds up numerical optimizations by an order of magnitude and allows for fast development of high-sensitivity experiments with good compensation for experimental artifacts such as off-resonance effects and rf inhomogeneity. By optimization in terms of error-compensating composite rf pulses, the corresponding Recoupling experiments intrinsically benefit from reduced powder-angle dependencies and thereby offer higher transfer efficiencies than commonly used γ-encoded Recoupling experiments. We demonstrate 50% gain in sensitivity for a 2D NCO experiment on 13C,15N-labeled ubiquitin using composite Recoupling experiments with 9–30 pulse elements.
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Triple oscillating field technique for accurate measurements of couplings in homonuclear spin systems
arXiv: Quantum Physics, 2007Co-Authors: Navin Khaneja, Niels Chr NielsenAbstract:We present a new concept for homonuclear Dipolar Recoupling in magic-angle-spinning (MAS) solid-state NMR experiments which avoids the problem of Dipolar truncation. This is accomplished through the introduction of a new NMR pulse sequence design principle: the triple oscillating field technique. We demonstrate this technique as an efficient means to accomplish broadband Dipolar Recoupling of homonuclear spins, while decoupling heteronuclear Dipolar couplings and anisotropic chemicals shifts and retaining influence from isotropic chemical shifts. In this manner, it possible to synthesize Ising interactions in homonuclear spin networks and thereby avoid Dipolar truncation - a serious problem essentially all previous homonuclear Dipolar Recoupling experiments suffer from. Combination of this Recoupling concept with rotor assisted Dipolar refocusing enables easy readout of internuclear distances through comparison with analytical Fresnel curves. This forms the basis for a new class of solid-state NMR experiments with potential for structure analysis of uniformly carbon labelled proteins through accurate measurement of {13}C-{13}C internuclear distances. The concept is demonstrated experimentally by measurement of C_alpha-C', C_\beta-C', and C_\gamma-C' internuclear distances in powder samples of the amino acids \textit{L}-alanine and \textit{L}-threonine.
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Effective Hamiltonians by optimal control: solid-state NMR double-quantum planar and isotropic Dipolar Recoupling.
The Journal of chemical physics, 2006Co-Authors: Zdeněk Tošner, Steffen J. Glaser, Navin Khaneja, Niels Chr NielsenAbstract:We report the use of optimal control algorithms for tailoring the effective Hamiltonians in nuclear magnetic resonance (NMR) spectroscopy through sophisticated radio-frequency (rf) pulse irradiation. Specifically, we address Dipolar Recoupling in solid-state NMR of powder samples for which case pulse sequences offering evolution under planar double-quantum and isotropic mixing Dipolar coupling Hamiltonians are designed. The pulse sequences are constructed numerically to cope with a range of experimental conditions such as inhomogeneous rf fields, spread of chemical shifts, the intrinsic orientation dependencies of powder samples, and sample spinning. While the vast majority of previous Dipolar Recoupling sequences are operating through planar double-or zero-quantum effective Hamiltonians, we present here not only improved variants of such experiments but also for the first time homonuclear isotropic mixing sequences which transfers all I(x), I(y), and I(z) polarizations from one spin to the same operators on another spin simultaneously and with equal efficiency. This property may be exploited to increase the signal-to-noise ratio of two-dimensional experiments by a factor of square root 2 compared to conventional solid-state methods otherwise showing the same efficiency. The sequences are tested numerically and experimentally for a powder of (13)C(alpha),(13)C(beta)-L-alanine and demonstrate substantial sensitivity gains over previous Dipolar Recoupling experiments.
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effective hamiltonians by optimal control solid state nmr double quantum planar and isotropic Dipolar Recoupling
Journal of Chemical Physics, 2006Co-Authors: Zdeněk Tošner, Steffen J. Glaser, Navin Khaneja, Niels Chr NielsenAbstract:We report the use of optimal control algorithms for tailoring the effective Hamiltonians in nuclear magnetic resonance (NMR) spectroscopy through sophisticated radio-frequency (rf) pulse irradiation. Specifically, we address Dipolar Recoupling in solid-state NMR of powder samples for which case pulse sequences offering evolution under planar double-quantum and isotropic mixing Dipolar coupling Hamiltonians are designed. The pulse sequences are constructed numerically to cope with a range of experimental conditions such as inhomogeneous rf fields, spread of chemical shifts, the intrinsic orientation dependencies of powder samples, and sample spinning. While the vast majority of previous Dipolar Recoupling sequences are operating through planar double-or zero-quantum effective Hamiltonians, we present here not only improved variants of such experiments but also for the first time homonuclear isotropic mixing sequences which transfers all Ix, Iy, and Iz polarizations from one spin to the same operators on an...