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  • 1
    Electronic Resource
    Electronic Resource
    Heteronuclear cross polarization in liquid-state nuclear magnetic resonance: Mismatch compensation and relaxation behavior (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 30-38 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nuclear spin dynamics in liquid-state heteronuclear cross-polarization experiments were explored by experiments on di-15N -labeled histidine in DMSO-d6. Compensation for Hartmann–Hahn mismatch was achieved by simultaneously shifting the phases of both spin-locking fields by π at intervals short compared to the spin–spin coupling. With rf compensation, slightly more 15N polarization was achieved than with the conventional selective INEPT scheme. This was attributed to relaxation by slowly fluctuating random fields associated with proton exchange. Theory for the rf mismatch compensation and relaxation behavior of the Hartmann–Hahn method is presented for the case of a heteronuclear 2-spin system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460398
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  • 2
    Electronic Resource
    Electronic Resource
    Rotational resonance with multiple-pulse scaling in solid-state nuclear magnetic resonance (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 5533-5545 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multiple-pulse techniques are applied to rotational resonance experiments in solid-state nuclear magnetic resonance. The usual rotational resonance condition is satisfied when an integral multiple of the magic-angle spinning speed equals the difference in isotropic chemical shifts of the two members of a homonuclear spin-1/2 pair. We show that sequences of rapid periodic radio-frequency pulses scale and rotate both the Zeeman and dipole–dipole Hamiltonians, leading to a modification of the resonance condition and to the introduction of new, single- and double-quantum, rotational resonances. Experimental results are presented which demonstrate these effects in the spectra of doubly 13C-labeled solids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467171
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  • 3
    Electronic Resource
    Electronic Resource
    Suppression of sidebands in magic-angle-spinning nuclear magnetic resonance: General principles and analytical solutions (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 130-140 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Several theoretical and experimental aspects of sideband suppression in the nuclear magnetic resonance (NMR) spectra of rotating solids are considered. The principles of sideband suppression are explored using general symmetry arguments and previous treatments are examined critically. Analytical solutions are given for sideband suppression pulse sequences employing four, five, six, and nine π pulses. The analytical solutions for four π pulses are complete. Experimental demonstrations are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466983
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  • 4
    Electronic Resource
    Electronic Resource
    NMR solvent peak suppression by nonlinear excitation (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3481-3496 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Most existing NMR solvent peak suppression sequences provide a satisfactory dependence of the intensity of excited signals on frequency but poor phase characteristics. In practice this leads to spectral distortions which generally become more severe as the frequency selectivity of the sequence is increased. However, it is shown that by working well outside the linear response regime, excitation schemes which combine high frequency selectivity with good phase properties may be devised. Sequences of six rectangular radio-frequency pulses were discovered using a combination of coherent averaging theory to treat the near-resonant behavior and numerical simulation further from resonance. Extensive use of symmetry greatly simplifies both the coherent averaging calculations and the numerical simulations. The new pulse sequences have been given the acronym NERO (nonlinear excitation rejecting on-resonance). Experimental spectra of an enzyme in dilute aqueous solution are shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453897
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  • 5
    Electronic Resource
    Electronic Resource
    Synchronous helical pulse sequences in magic-angle spinning nuclear magnetic resonance: Double quantum recoupling of multiple-spin systems (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 8539-8554 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Some general principles of radio-frequency pulse sequence design in magic-angle spinning nuclear magnetic resonance are discussed. Sequences with favorable dipolar recoupling properties may be designed using synchronous helical modulations of the space and spin parts of the spin Hamiltonian. The selection rules for the average Hamiltonian may be written in terms of three symmetry numbers, two defining the winding numbers of the space and spin helices, and one indicating the number of phase rotation steps in the radio-frequency modulation. A diagrammatic technique is used to visualize the space-spin symmetry selection. A pulse sequence C1445 is designed which accomplishes double-quantum recoupling using a low ratio of radio frequency field to spinning frequency. The pulse sequence uses 14 radio frequency modulation steps with space and spin winding numbers of 4 and 5, respectively. The pulse sequence is applied to the double-quantum spectroscopy of 13C3-labeled L-alanine. Good agreement is obtained between the experimental peak intensities, analytical results, and numerically exact simulations based on the known molecular geometry. The general symmetry properties of double quantum peaks in recoupled multiple-spin systems are discussed. A supercycle scheme which compensates homonuclear recoupling sequences for chemical shifts is introduced. We show an experimental double-quantum 13C spectrum of [U–13C]–L-tyrosine at a spinning frequency of 20.000 kHz. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481458
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  • 6
    Electronic Resource
    Electronic Resource
    Pulse sequence symmetries in the nuclear magnetic resonance of spinning solids: Application to heteronuclear decoupling (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1511-1519 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop the average Hamiltonian theory of a class of symmetrical radio-frequency pulse sequences in the NMR of rotating solids. Theorems are presented which allow one to predict the elimination of many average Hamiltonian terms, without detailed calculation. These results are applied to the problem of heteronuclear decoupling in the presence of rapid magic angle spinning. We present sequences which minimize the number of heteronuclear terms at the same time as recoupling the homonuclear interactions of the irradiated spins. The performance of the new sequences is tested on 13C labeled calcium formate. Experimental measurements of double-quantum 1H excitation indicate a relationship between good heteronuclear decoupling of the observed spin species and efficient recoupling of the irradiated spin species. The heteronuclear decoupling performance of the new sequences is significantly better than that obtained with an unmodulated radio-frequency field. The decoupling performance is improved further by breaking the pulse sequence symmetry in a controlled fashion. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479410
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  • 7
    Electronic Resource
    Electronic Resource
    NMR solvent peak suppression with a soft-pulse nonlinear excitation sequence (1987)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 109 (1987), S. 6540-6541 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00255a065
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  • 8
    Electronic Resource
    Electronic Resource
    Quenching spin diffusion in selective measurements of transient overhauser effects in nuclear magnetic resonance. Applications to oligonucleotides (1994)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 116 (1994), S. 362-368 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00080a041
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  • 9
    Electronic Resource
    Electronic Resource
    Longitudinal rotational resonance echoes in solid state nuclear magnetic resonance: Investigation of zero quantum spin dynamics (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 5493-5507 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the magic angle spinning NMR of rotating solids, it is possible to drive nuclear spin transitions by the macroscopic sample rotation. This rotational resonance phenomenon arises when the chemical shift frequency difference between two neighboring spin sites matches a small integer multiple of the sample rotation frequency. The mechanically driven spin evolution may be reversed by applying a radio-frequency pulse cycle, leading to the formation of rotational resonance echoes. A detailed theory based on a Liouville space formalism is developed. Experimental demonstrations are given for a polycrystalline sample of zinc 13C2 acetate. The decay of zero quantum coherence is examined at two different magnetic fields. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477168
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  • 10
    Electronic Resource
    Electronic Resource
    Symmetry principles in the nuclear magnetic resonance of spinning solids: Heteronuclear recoupling by generalized Hartmann–Hahn sequences (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 357-384 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: General symmetry principles for rotor-synchronized pulse sequences in magic-angle spinning solid-state nuclear magnetic resonance are presented. The theory of symmetry-based pulse sequences using π pulse elements is presented for the first time. The symmetry theory is extended to the case of generalized Hartmann–Hahn sequences, in which rotor-synchronized rf irradiation is applied simultaneously to two isotopic spin species. The symmetry principles lead to heteronuclear selection rules. The symmetry theory is used to design pulse sequences which implement heteronuclear dipolar recoupling at the same time as decoupling homonuclear spin–spin interactions, and which also suppress chemical shift anisotropies. A number of specific pulse sequences based on these principles are listed. Experimental demonstrations are given of heteronuclear two-dimensional correlation spectroscopy, heteronuclear multiple-quantum spectroscopy, and the estimation of internuclear dipolar couplings. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1377031
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