A broad-banded z-rotation windowed phase-modulated Lee-Goldburg pulse sequence for 1H spectroscopy in solid-state NMR (original) (raw)
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Journal of Magnetic Resonance, 2008
Elucidating the local environment of the hydrogen atoms is an important problem in materials science. Because 1 H spectra in solid-state nuclear magnetic resonance (NMR) suffer from low resolution due to homogeneous broadening, even under magic-angle spinning (MAS), information of chemical interest may only be obtained using certain high-resolution 1 H MAS techniques. 1 H Lee-Goldburg (LG) CRAMPS (Combined Rotation And Multiple-Pulse Spectroscopy) methods are particularly well suited for studying inorganic-organic hybrid materials, rich in 1 H nuclei. However, setting up CRAMPS experiments is timeconsuming and not entirely trivial, facts that have discouraged their widespread use by materials scientists. To change this status quo, here we describe and discuss some important aspects of the experimental implementation of CRAMPS techniques based on LG decoupling schemes, such as FSLG (Frequency Switched), and windowed and windowless PMLG (Phase Modulated). In particular, we discuss the influence on the quality of the 1 H NMR spectra of the different parameters at play, for example LG (Lee-Goldburg) pulses, radio-frequency (rf) phase, frequency switching, and pulse imperfections, using glycine and adamantane as model compounds. The efficiency and robustness of the different LG-decoupling schemes is then illustrated on the following materials: organo-phosphorus ligand, N-(phosphonomethyl)iminodiacetic acid [H 4 pmida] [I], and
Chemical Physics Letters, 2004
We present a new solid-state NMR pulse sequence that accomplishes efficient broad-band dipolar recoupling in systems with small dipolar couplings and large chemical shift anisotropies. The method involves a supercycled symmetry-based recoupling sequence incorporated in a constant-interval data acquisition strategy. The supercycle removes destructive higher-order average Hamiltonian terms, and makes the method more robust at long time intervals. We demonstrate 38.4% double-quantum filtering efficiency on diammonium [1,4-13 C 2 ]-fumarate in which the internuclear distance, as estimated by X-ray diffraction, is 387.8 pm. The estimated 13 C-13 C dipolar coupling was )136.5 AE 5.1 Hz, corresponding to an internuclear distance of 382.5 AE 4 pm.
Improved magnetization transfer in solid-state NMR with fast magic angle spinning
Chemical Physics Letters, 2009
The efficiency of magnetization transfer between different spins S such as chemically inequivalent carbon-13 nuclei in solid samples that are spinning at high frequencies about the magic angle can be enhanced by a phase-alternated recoupling irradiation scheme (PARIS). Dipolar recoupling is assisted by a radio-frequency (rf) field applied to the abundant I (proton) spins. In contrast to rotary resonance-based recoupling schemes, the new method does not depend critically on the rf amplitude, which need not be matched with the spinning frequency. Modest rf amplitudes suffice to bring about efficient magnetization transfer even at high spinning speeds, thus avoiding excessive sample heating. The new method compensates efficiently for rf field inhomogeneity, so that the full sample volume is used more effectively.
High-resolution 1 H NMR in solids with frequency-switched multiple-pulse sequences
Solid State Nuclear Magnetic Resonance, 1993
A new pulse sequence for abundant-spin NMR in solids, called FSLG240W, is demonstrated. The sequence employs phase-coherent frequency-switching of the rf irradiation to induce opposite rotations around the magic-angle axis in the rotating frame. Three 4~/3 rotations in one sense are followed by three 4~/3 rotations in the opposite sense. Observation windows separate each rotation. The pulse sequence cancels out the average dipolar Hamiltonian, the first-order correction terms, and the most deliterious second-order terms. The pulse sequence has a short cycle time and a high scaling factor K = 1,/a, but is sensitive to rf inhomogeneity. We demonstrate slightly better resolution than either MREV8 or BR24 on a small spherical sample of L-alanine.
Supercycled homonuclear dipolar decoupling sequences in solid-state NMR
Journal of Magnetic Resonance, 2009
We compare the performance of the windowed Phase-Modulated Lee-Goldburg (wPMLG) and the windowed Decoupling Using Mind Boggling Optimisation (wDUMBO) sequences at various magic-angle spinning rates and nutation frequencies of the pulses. Additionally, we introduce a supercycled version of wDUMBO and compare its efficiency with that of the non-supercycled implementation of wDUMBO. The efficiency of the supercycled version of wPMLG, denoted wPMLG-S2, is compared with a new supercycled version of wPMLG that we notate as wPMLG-S3. The results indicate that a well-performing supercycled wPMLG sequence can be found at all spinning frequencies.
Magic-angle spinning solid-state multinuclear NMR on low-field instrumentation
Journal of Magnetic Resonance, 2014
Mobile and cost-effective NMR spectroscopy exploiting low-field permanent magnets is a field of tremendous development with obvious applications for arrayed large scale analysis, field work, and industrial screening. So far such demonstrations have concentrated on relaxation measurements and lately highresolution liquid-state NMR applications. With high-resolution solid-state NMR spectroscopy being increasingly important in a broad variety of applications, we here introduce low-field magic-angle spinning (MAS) solid-state multinuclear NMR based on a commercial ACT 0.45 T 62 mm bore Halbach magnet along with a homebuilt FPGA digital NMR console, amplifiers, and a modified standard 45 mm wide MAS probe for 7 mm rotors. To illustrate the performance of the instrument and address cases where the low magnetic field may offer complementarity to high-field NMR experiments, we demonstrate applications for 23 Na MAS NMR with enhanced second-order quadrupolar coupling effects and 31 P MAS NMR where reduced influence from chemical shift anisotropy at low field may facilitate determination of heteronuclear dipole-dipole couplings.
Chemical Physics Letters, 2003
It is shown that a direct spectral optimization scheme can be implemented to obtain improved heteronuclear dipolar decoupling schemes for solid-state magic-angle-spinning NMR experiments. The resulting schemes, which turn out to have a particularly simple form, are shown to be applicable over the whole range of commercially available spinning speeds (from 5 to 35 kHz), and are shown to improve on the performance of the best existing sequences.