Spin dynamics in the modulation frame: Application to homonuclear recoupling in magic angle spinning solid-state NMR (original) (raw)
Related papers
2012
We report novel symmetry-based radio-frequency (rf) pulse sequences for efficient excitation of doublequantum (2Q) coherences under very fast (>60 kHz) magic-angle spinning (MAS) conditions. The recursively generated pulse-scheme series, R2 1 2 p R2 À1 2 p ðp ¼ 1; 2; 3; . . .), offers broadband 13 C-13 C recoupling in organic solids at a very low rf power. No proton decoupling is required. A high-order average Hamiltonian theory analysis reveals a progressively enhanced resonance-offset compensation for increasing p, as verified both by numerical simulations and 2Q filtration NMR experiments on 13 C 2 -glycine, [2,3-13 C 2 ]alanine, and [U-13 C]tyrosine at 14.1 T and 66 kHz MAS, where the pulse schemes with p P 3 compare favorably to current state-of-the-art recoupling options.
Journal of Magnetic Resonance, 2009
H-1 H decoupling CRAMPS 2D 1 H-1 H single-quantum-doublequantum spectra wDUMBO Double-quantum recoupling Homonuclear correlation Rotor-synchronised symmetry sequences a b s t r a c t Two-dimensional 1 H homonuclear correlation NMR spectra of solids of biological interest have been recorded at high magnetic fields (14.1 and 18.8 T) and MAS rates up to 67 kHz, using RN m n symmetrybased homonuclear recoupling and CRAMPS decoupling; this method affords exceptional spectral resolution and is well suited to probe 1 H-1 H proximities in powdered solids.
The Journal of Physical Chemistry Letters, 2010
We present a novel solid-state NMR method for heteronuclear dipolar recoupling without decoupling. The method, which introduces the concept of exponentially modulated rf fields, provides efficient broadband recoupling with large flexibility with respect to hetero-or homonuclear applications, sample spinning frequency, and operation without the need for highpower 1 H decoupling. For previous methods, the latter has been a severe source of sample heating which may cause detoriation of costly samples. The so-called EXPonentially mOdulated Recoupling Technique (EXPORT) is described analytically and numerically, and demonstrated experimentally by 1D 13 C spectra and 2D 13 C-15 N correlation spectra of 13 C, 15 N-labeled samples of GB1, ubiquitin, and fibrils of the SNNFGAILSS fragment of amylin. Through its flexible operation, robustness, and strong performance, it is anticipated that EXPORT will find immediate application for both hetero-and homonuclear dipolar recoupling in solid-state NMR of 13 C, 15 Nlabeled proteins and compounds of relevance in chemistry.
Broadband Dipolar Recoupling for Magnetization Transfer in Solid-State NMR Correlation Spectroscopy
ChemPhysChem, 2008
Recent developments in solid-state nuclear magnetic resonance have opened the way to detailed structural and dynamic analysis of crystalline and non-crystalline biological solids. In isotopically enriched molecules of biological interest, 13 C-13 C magnetization transfer via spin-exchange processes (also called spin diffusion) allows one both to assign the resonances and to determine internuclear distances. Chemical-shift correlation experiments commonly employed for such purposes exploit different means of compensating for the energy imbalances of 13 C spins with different resonance frequencies and use a variety of recoupling schemes which inhibit the quenching of homo-and heteronuclear dipolar interactions by magic angle spinning (MAS). Spin exchange can be promoted by any of three methods: 1) Proton-driven spin diffusion (PDSD) which does not require any radio-frequency (RF) irradiation and relies on line broadening due to carbon-proton dipolar couplings, so that its efficiency strongly depends on the spinning frequency and on local motions. 2) Rotor-driven spin exchange which occurs in rotational resonance (R 2 ) methods, and does not use any RF irradiation either. It strongly favors flip-flop processes between pairs of 13 C spins which have a difference in isotropic chemical shifts that matches an integer multiple of the spinning frequency. 3) RF-driven spin exchange which relies on homo-and heteronuclear recoupling of the dipolar interactions. A wide range of recoupling sequences has been developed, including a number of broadband homonuclear recoupling schemes. For optimal performance, especially at high MAS frequencies, most known recoupling methods require high RF power which can lead to excessive sample heating at longer transfer times. Some dipolar recoupling methods employ reduced RF power on 13 C or on 1 H, like dipolar assisted rotational resonance (DARR) [21] or RF-assisted diffusion (RAD) experiments with RF amplitudes adjusted to the spinning frequency n r . This enhances 13 C-13 C spin exchange through recoupling of homo-and heteronuclear dipolar interactions. In fact, rotary resonance recoupling (R 3 ) using various ratios n = n 1H /n r = 1/2, 1 and 2 leads to the restoration of different anisotropic spin interactions. However, the efficiency of rotary resonance recoupling, including DARR/RAD-like experiments, is critically dependent on resonance offsets and on the homogeneity of the RF fields, and may lead to non-uniform 13 C-13 C spin exchange between various sites.
Proton Assisted Recoupling at High Spinning Frequencies †
The Journal of Physical Chemistry B, 2009
We demonstrate the successful application of 13 C-13 C proton assisted recoupling (PAR) on [U-13 C, 15 N] N-ƒ-MLF-OH and [U-13 C, 15 N] protein GB1 at high magic angle spinning (MAS) frequencies (ω r /2π=65 kHz). Specifically, by combining PAR mixing with low power heteronuclear decoupling (ω 1H /2π~16 kHz) and high spinning frequencies, we obtain high resolution 2D spectra displaying long range 13 C-13 C contacts from which distances can be extracted. These experiments therefore demonstrate the possibility of performing high resolution structural studies in the limit of high spinning frequency and low power 1 H decoupling, a regime which optimizes resolution of protein samples and preserves their integrity.
Heteronuclear Recoupling in Solid-State Magic-Angle-Spinning NMR via Overtone Irradiation
Journal of the American Chemical Society, 2001
A heteronuclear dipolar recoupling scheme applicable to IS spin pairs undergoing magic-anglespinning (MAS) is introduced, based on the overtone irradiation of one of the coupled nuclei. It is shown that when I is a quadrupole, for instance 14 N, irradiating this spin at a multiple of its Larmor frequency prevents the formation of MAS dipolar echoes. The ensuing S-spin signal dephasing is significant and dependent on a number of parameters, including the IS dipolar coupling, the magnitude of I's quadrupolar coupling, and the relative orientations between these two coupling tensors. When applied to a spin-1 nucleus, this overtone recoupling method differs from hitherto proposed recoupling strategies in that it involves only the |(1〉 I z eigenstates. Its dephasing efficiency becomes independent of first-order quadrupolar effects yet shows a high sensitivity to second-order offsets. A constant-time/variable-offset recoupling sequence thus provides a simple route to acquire, in an indirect fashion, 14 N overtone spectra from rotating powders. The principles underlying this kind of S-14 N experiments and different applications involving S) 13 C, 59 Co sites are presented.
Truncated dipolar recoupling in solid-state nuclear magnetic resonance
Chemical Physics Letters, 2006
We describe a solid-state NMR concept for the estimation of individual spinspin couplings in strongly-coupled homonuclear spin systems. A radiofrequency pulse sequence, synchronized with the magic-angle sample rotation, recouples zero-quantum dipolar interactions as well as a frequency-dispersing interaction such as the chemical shift anisotropy. The combination of these two recoupled interactions causes the spin system to behave in an approximately weaklycoupled fashion. Individual spin-spin couplings may then be disentangled by using frequency-selective radiofrequency pulses. Theoretical results and numerical simulations are compared with experimental data for the 13 C nuclei in
The Journal of Chemical Physics, 2006
We present the theoretical principles of supercycled symmetry-based recoupling sequences in solid-state magic-angle-spinning NMR. We discuss the construction procedure of the SR26 pulse sequence, which is a particularly robust sequence for double-quantum homonuclear dipole-dipole recoupling. The supercycle removes destructive higher-order average Hamiltonian terms and renders the sequence robust over long time intervals. We demonstrate applications of the SR26 sequence to double-quantum spectroscopy, homonuclear spin counting, and determination of the relative orientations of chemical shift anisotropy tensors.
1 H-Observe 1 H 2 H Dipolar Recoupling by REDOR and Rotary Resonance Recoupling
Israel Journal of Chemistry, 2014
The measurement of heteronuclear dipolar couplings by solid-state NMR is an important tool for determining structures in solids. 1 H-observe 1 HÀ 2 H REDOR and rotary resonance recoupling experiments with fast magicangle spinning are presented. These dipolar recoupling ex-periments show promise for measuring heteronuclear dipolar couplings with 1 H nuclei. Potential limitations of the experiments include short transverse relaxation times of the 1 H magnetization and BlochÀSiegert effects.
The Journal of Chemical Physics, 2002
Investigations were made of rotary resonance recouplings (R 3) of chemical shift anisotropy ͑CSA͒, heteronuclear dipolar ͑HTD͒, and homonuclear dipolar ͑HMD͒ couplings involving half-integer quadrupolar nuclei under magic-angle sample spinning condition. Under rotary resonance conditions provided by a low amplitude rf field and a high spinning speed, the spectrum of the central transition coherence of half-integer quadrupolar nuclei shows recouplings of CSA, HTD, and HMD interactions that depend on the ratio of the rf field to the spinning speed. These new properties can be used to extract electronic and structural information about the sample that are otherwise difficult to extract in the presence of a dominant quadrupolar interaction. An average Hamiltonian theory is used to explain the recoupling properties of various interactions. Experimental implementations of the R 3 are demonstrated on model compounds with spin-3/2 systems.