Heteronuclear decoupling in rotating solids
22 Oct 1995-Journal of Chemical Physics (American Institute of Physics)-Vol. 103, Iss: 16, pp 6951-6958
TL;DR: In this article, a simple two pulse phase modulation (TPPM) scheme was proposed to reduce the residual linewidths arising from insufficient proton decoupling power in double resonance magic angle spinning (MAS) experiments.
Abstract: A simple two pulse phase modulation (TPPM) scheme greatly reduces the residual linewidths arising from insufficient proton decoupling power in double resonance magic angle spinning (MAS) experiments. Optimization of pulse lengths and phases in the sequence produces substantial improvements in both the resolution and sensitivity of dilute spins (e.g., 13C) over a broad range of spinning speeds at high magnetic field. The theoretical complications introduced by large homo‐ and heteronuclear interactions among the spins, as well as the amplitude modulation imposed by MAS, are explored analytically and numerically. To our knowledge, this method is the first phase‐switched sequence to exhibit improvement over continuous‐wave (cw) decoupling in a strongly coupled homogeneous spin system undergoing sample spinning.
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TL;DR: It is found that a stepwise variation of the phase angle in the TPPM sequence offers even better results, and the application of this new method to a liquid crystalline compound and a solid, L-tyrosine hydrochloride, is reported.
1,698 citations
TL;DR: The program is designed to emulate a NMR spectrometer by letting the user specify high-level NMR concepts such as spin systems, nuclear spin interactions, RF irradiation, free precession, phase cycling, coherence-order filtering, and implicit/explicit acquisition using the Tcl scripting language.
1,539 citations
Cites methods from "Heteronuclear decoupling in rotatin..."
...The examples include rotational resonance, homonuclear dipolar recoupling using DRAMA/DRAWS/HORROR/C7, heteronuclear dipolar recoupling using TEDOR, dipolar decoupling using CW or TPPM irradiation, separated-localfield (SLF) experiments without or with FSLG/MSHOT-3 homonuclear decoupling, and QCPMG-MAS experiments for sensitivity-enhanced quadrupolar-echo NMR of halfinteger quadrupolar nuclei....
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...To our knowledge this represent the first numerical simulations comparing the decoupling performance of CW and TPPM decoupling despite it has been extensively demonstrated analytically and experimentally during the past couple of years....
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...9 by a series of simulations illustrating the effect of CW and TPPM decoupling for a heteronuclear four-spin system....
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...E-mail: ncn@imsb.au.dk by numerical simulations of various aspects for REDOR, rotational resonance, DRAMA, DRAWS, HORROR, C7, TEDOR, POST-C7, CW decoupling, TPPM, FSLG, SLF, SEMA-CP, PISEMA, RFDR, QCPMG-MAS, and MQ-MAS experiments....
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..., BR-24 [28], FSLG [29], MSHOT-3 [30], TPPM [31]), cross-polarization [32, 33], QCPMG-MAS [34], or MQ-MAS [35] pulse sequences are indispensable building blocks....
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TL;DR: Solid-state nuclear magnetic resonance measurements on fibrils formed by the 40-residue beta-amyloid peptide associated with Alzheimer's disease are described and full molecular models using restrained molecular dynamics simulations and restrained energy minimization are constructed.
Abstract: We describe solid-state nuclear magnetic resonance (NMR) measurements on fibrils formed by the 40-residue β-amyloid peptide associated with Alzheimer's disease (Aβ1-40) that place constraints on the identity and symmetry of contacts between in-register, parallel β-sheets in the fibrils. We refer to these contacts as internal and external quaternary contacts, depending on whether they are within a single molecular layer or between molecular layers. The data include (1) two-dimensional 13C-13C NMR spectra that indicate internal quaternary contacts between side chains of L17 and F19 and side chains of I32, L34, and V36, as well as external quaternary contacts between side chains of I31 and G37; (2) two-dimensional 15N-13C NMR spectra that indicate external quaternary contacts between the side chain of M35 and the peptide backbone at G33; (3) measurements of magnetic dipole−dipole couplings between the side chain carboxylate group of D23 and the side chain amine group of K28 that indicate salt bridge interact...
1,048 citations
Cites background from "Heteronuclear decoupling in rotatin..."
...Proton decoupling fields were typically 110 kHz, with two-pulse phase modulation (63) during chemical shift evolution periods in all pulse sequences....
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TL;DR: Insight is provided into the structural changes that occur when RIP kinases are triggered to execute different signaling outcomes and the realm of amyloids is expanded to complex formation and signaling.
981 citations
TL;DR: A good agreement was found between the observed and calculated structural parameters and also for the vibrational frequencies of melem according to temperature-dependent X-ray powder diffractometry investigations above 560 degrees C, melem transforms into a graphite-like C-N material.
Abstract: Single-phase melem (2,5,8-triamino-tri-s-triazine) C6N7(NH2)3 was obtained as a crystalline powder by thermal treatment of different less condensed C−N−H compounds (e.g., melamine C3N3(NH2)3, dicyandiamide H4C2N4, ammonium dicyanamide NH4[N(CN)2], or cyanamide H2CN2, respectively) at temperatures up to 450 °C in sealed glass ampules. The crystal structure was determined ab initio by X-ray powder diffractometry (Cu Kα1: P21/c (No. 14), a = 739.92(1) pm, b = 865.28(3) pm, c = 1338.16(4) pm, β = 99.912(2)°, and Z = 4). In the solid, melem consists of nearly planar C6N7(NH2)3 molecules which are arranged into parallel layers with an interplanar distance of 327 pm. Detailed 13C and 15N MAS NMR investigations were performed. The presence of the triamino form instead of other possible tautomers was confirmed by a CPPI (cross-polarization combined with polarization inversion) experiment. Furthermore, the compound was characterized using mass spectrometry, vibrational (IR, Raman), and photoluminescence spectrosco...
890 citations
References
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TL;DR: In this article, the NMR signals of isotopically or chemically dilute nuclear spins S in solids can be enhanced by repeatedly transferring polarization from a more abundant species I of high abundance (usually protons) to which they are coupled.
Abstract: The NMR signals of isotopically or chemically dilute nuclear spins S in solids can be enhanced by repeatedly transferring polarization from a more abundant species I of high abundance (usually protons) to which they are coupled. The gain in power sensitivity as compared with conventional observation of the rare spins approaches NII(I+1)γI2/NSS(S+1)γS2, or ∼ 103 for S = 13C, I = 1H in organic solids. The transfer of polarization is accomplished by any of a number of double resonance methods. High‐frequency resolution of the S ‐spin signal is obtained by decoupling of the abundant spins. The experimental requirements of the technique are discussed and a brief comparison of its sensitivity with other procedures is made. Representative applications and experimental results are mentioned.
2,244 citations
Book•
20 Dec 1982
Abstract: 1 Introduction.- 2 Nuclear Spin Interactions in Solids.- 2.1 Basic Nuclear Spin Interactions in Solids.- 2.2 Spin Interactions in High Magnetic Fields.- 2.3 Transformation Properties of Spin Interactions in Real Space.- 2.4 Powder Spectrum Line Shape.- 2.5 The NMR Spectrum. Lineshapes and Moments.- 2.6 Magic Angle Spinning (MAS).- 2.7 Rapid Anisotropic Molecular Rotation.- 2.8 Line Shapes in the Presence of Molecular Reorientation.- 3 Multiple-Pulse NMR Experiments.- 3.1 Idealized Multiple-Pulse Sequences.- 3.2 The Four-Pulse Sequence (WHH-4).- 3.3 Coherent Averaging Theory.- 3.4 Application of Coherent Averaging Theory to Multiple-Pulse Sequences.- 3.5 Arbitrary Rotations and Finite Pulse Width in Multiple-Pulse Experiments.- 3.6 Second Averaging.- 3.7 The Influence of Pulse Imperfections on Multiple-Pulse Experiments.- 3.8 Resolution of Multiple-Pulse Experiments.- 3.9 Magic Angle Rotating Frame Line Narrowing Experiments.- 3.10 Modulation Induced Line Narrowing.- 3.11 Applications of Multiple-Pulse Experiments.- 4 Double Resonance Experiments.- 4.1 Basic Principles of Double Resonance Experiments.- 4.2 Cross-Polarization of Dilute Spins.- 4.3 Cross-Polarization Dynamics.- 4.4 Spin-Decoupling Dynamics.- 4.5 Application of Cross-Polarization Experiments.- 5 Two-Dimensional NMR Spectroscopy.- 5.1 Basic Principles of 2 D-Spectroscopy.- 5.2 2D-Spectroscopy of 13C-1H Interactions in Solids.- 5.3 Applications of 2D-Spectroscopy.- 6 Multiple-Quantum NMR Spectroscopy.- 6.1 Double-Quantum Decoupling.- 6.2 The Three-Level System Double Quantum Coherence.- 6.3 Multiple-Quantum Coherence.- 6.4 Selective Multiple-Quantum Coherence.- 6.5 Double-Quantum Cross-Polarization.- 7 Magnetic Shielding Tensor.- 7.1 Ramsey's Formula.- 7.2 Approximate Calculations of the Shielding Tensor.- 7.3 Proton Shielding Tensors.- 7.4 19F Shielding Tensors.- 7.5 13C Shielding Tensors.- 7.6 Other Shielding Tensors.- 8 Spin-Lattice Relaxation.- 8.1 Spin-Lattice Relaxation in the Weak Collision Limit.- 8.2 Spin-Lattice Relaxation in Multiple-Pulse Experiments.- 8.3 Application of Multiple-Pulse Experiments to the Investigation of Spin-Lattice Relaxation.- 8.4 Spin-Lattice Relaxation in Dilute Spin Systems.- 8.5 Selective Excitation and Spectral Diffusion.- 9 Appendix.- A Irreducible Tensor Representation of Spin Interactions.- B Rotations.- C General Line Shape Theory.- D Homogeneous, Inhomogeneous and Heterogeneous Lineshapes.- E Lineshape and Relaxation due to Fluctuating Chemical Shift Tensors.- F Time Evolution and Magnus Expansion.- G Coherent Versus Secular Averaging Theory.- H Applications of Average Hamiltonian Theory.- I Relaxation Theory.- 10 References.- 11 Subject Index.
1,280 citations
TL;DR: In this article, it was shown that when these weak side-spectra are included the second moment does indeed remain invariant even though the second moments of the central portion, which is all that is observed experimentally, becomes smaller.
Abstract: HINDERED molecular rotation in solids reduces the width of their observed nuclear magnetic resonance spectra, with a consequent decrease in the measured second moments1. By contrast, on general theoretical grounds it has been shown2 that the second moments of dipolar-broadened spectra should remain invariant and should not be reduced by such motion. In a recent explanation3 of this apparent discrepancy the nuclear magnetic interaction was divided into two parts, namely, a steady mean interaction and a fluctuating part. The steady mean interaction is less than the interaction in a static crystal devoid of hindered rotation and generates an observed spectrum narrower than that of the static crystal. The fluctuating part of the interaction generates side-spectra set at integral multiples of the frequency of molecular rotation on either side of the central narrowed spectrum. Since the molecules do not rotate uniformly, but are re-oriented with an irregular motion, these side-spectra are dispersed over a band of frequencies with an intensity too weak to be observed. It was shown, however3, that when these weak side-spectra are included the second moment does indeed remain invariant even though the second moment of the central portion, which is all that is observed experimentally, becomes smaller.
1,081 citations
1,071 citations
TL;DR: In this paper, the effects of the proton irradiation sequence by means of a train of spin rotation operators, the overall effect at the end of the cycle being calculated by explicit matrix multiplication, the offset dependence of this proton response determined the residual splitting of the carbon-13 resonance and hence the effectiveness of the decoupling.
1,026 citations