Total Correlation Spectroscopy Across All NMR-Active Nuclei by Mixing at Zero Field (original) (raw)
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Magnetic Resonance in Chemistry, 2004
New spin-state-selective (S3) NMR pulse sequences exclusively applying cross-polarization schemes to achieve optimum homonuclear and heteronuclear 1HX coherence transfer are reported for the simple and accurate measurement of the magnitude and sign of heteronuclear coupling constants for samples at natural abundance. The proposed spin-edited HCP-TOCSY experiments are based on clean heteronuclear S3 excitation, generated by simultaneous co-addition of two independent in-phase and anti-phase components created during the mixing heteronuclear J-cross-polarization (HCP) step, which is finally transferred to other protons by a conventional homonuclear TOCSY mechanism. Selective 1D and non-selective 2D approaches for the easy determination of long-range proton–carbon and proton–nitrogen coupling constants on any protonated and non-protonated heteronuclei are presented and discussed for several organic molecules. Copyright © 2004 John Wiley & Sons, Ltd.
Journal of Magnetic Resonance, 2007
The robustness of the refocused INADEQUATE MAS NMR pulse sequence for probing through-bond connectivities has been demonstrated in a large range of solid-state applications. This pulse sequence nevertheless suffers from artifacts when applied to multispin systems, e.g. uniformly labeled 13 C solids, which distort the lineshapes and can potentially result in misleading correlation peaks. In this paper, we present a detailed account that combines product-operator analysis, numerical simulations and experiments of the behavior of a three-spin system during the refocused INADEQUATE pulse sequence. The origin of undesired anti-phase contributions to the spectral lineshapes are described, and we show that they do not interfere with the observation of long-range correlations (e.g. two-bond 13 C-13 C correlations). The suppression of undesired contributions to the refocused INADEQUATE spectra is shown to require the removal of zero-quantum coherences within a z-filter. A method is proposed to eliminate zero-quantum coherences through dephasing by heteronuclear dipolar couplings, which leads to pure in-phase spectra. 4 Abbreviations: TOBSY, total through-bond spectroscopy; INADE-QUATE, incredible natural abundance double quantum transfer experiment; CR, composite refocusing; UC2QF COSY, uniform-sign cross-peak double quantum filtered correlation spectroscopy; TQ, triplequantum; DD, dipole-dipole; CSA, chemical shift anisotropy, DQ, double quantum; ZQ, zero-quantum; CP, cross polarization; PDSD, protondriven spin diffusion.
Journal of the American Chemical Society, 1999
A comprehensive description is presented of the effects on two-spin coherences (i.e., superpositions of zero-and double-quantum coherences) of cross-correlation between the fluctuations of two different relaxation mechanisms in nuclear magnetic resonance (NMR). Dipole-dipole (DD) interactions between four nuclei and chemical shift anisotropy (CSA) of two of these nuclei are considered. Two complementary experiments have been designed for 15 N, 13 C-labeled proteins to quantify the effects of cross-correlation between the 13 C R-1 H R and 15 N-1 H N dipolar interactions on two-spin coherences involving 13 C R of the ith residue with the 15 N of the (i+1)th amino acid. Two other experiments allow one to quantify the effect of cross-correlation between the 13 C′ (carbonyl) CSA and the 13 C R-1 H R dipolar coupling on the relaxation of two-spin coherences involving the 13 C′ and 13 C R nuclei on the same residue of the protein. These experiments have been used to extract relevant cross-correlation rates in 15 N, 13 C-labeled human ubiquitin. These rates show a high degree of correlation with the backbone Ψ angles in proteins.
Variable-angle correlation spectroscopy in solid-state nuclear magnetic resonancea)
The Journal of Chemical Physics, 1992
We describe here a new solid-state nuclear-magnetic-resonance (NMR) experiment for correlating anisotropic and isotropic chemical shifts of inequivalent nuclei in powdered samples. Spectra are obtained by processing signals arising from a spinning sample, acquired in independent experiments as a function of the angle between the axis of macroscopic rotation and the external magnetic field. This is in contrast to previously proposed techniques, which were based on sudden mechanical flippings or multiple-pulse sequences. We show that the time evolution of variable-angle-spinning signals is determined by a distribution relating the isotropic frequencies of the spins with their corresponding chemical shift anisotropies. Fourier transformation of these data therefore affords a twodimensional NMR spectrum, in which line shapes of isotropic and anisotropic interactions are correlated. Theoretical and experimental considerations involved in the extraction of this spectral information are discussed, and the technique is illustrated by an analysis of 13C NMR anisotropy in glycine, cysteine, and p-anisic acid. 4800
The Journal of Physical Chemistry A, 2009
Multidimensional nuclear magnetic resonance (NMR) experiments measure spin-spin correlations, which provide important information about bond connectivities and molecular structure. However, direct observation of certain kinds of correlations can be very time-consuming due to limitations in sensitivity and resolution. Covariance NMR derives correlations between spins via the calculation of a (symmetric) covariance matrix, from which a matrix-square root produces a spectrum with enhanced resolution. Recently, the covariance concept has been adopted to the reconstruction of nonsymmetric spectra from pairs of 2D spectra that have a frequency dimension in common. Since the unsymmetric covariance NMR procedure lacks the matrix-square root step, it does not suppress relay effects and thereby may generate false positive signals due to chemical shift degeneracy. A generalized covariance formalism is presented here that embeds unsymmetric covariance processing within the context of the regular covariance transform. It permits the construction of unsymmetric covariance NMR spectra subjected to arbitrary matrix functions, such as the square root, with improved spectral properties. This formalism extends the domain of covariance NMR to include the reconstruction of non-symmetric NMR spectra at resolutions or sensitivities that are superior to the ones achievable by direct measurements.
J-GFT NMR for Precise Measurement of Mutually Correlated Nuclear Spin−Spin Couplings
Journal of the American Chemical Society, 2007
G-matrix Fourier transform (GFT) NMR spectroscopy is presented for accurate and precise measurement of chemical shifts and nuclear spin-spin couplings correlated according to spin system. The new approach, named "J-GFT NMR", is based on a largely extended GFT NMR formalism and promises to have a broad impact on projection NMR spectroscopy. Specifically, constant-time J-GFT (6,2)D (HA-CA-CO)-N-HN was implemented for simultaneous measurement of five mutually correlated NMR parameters, that is, 15 N backbone chemical shifts and the four one-bond spin-spin couplings 13 C R-1 H R , 13 C R-13 C′, 15 N-13 C′, and 15 N-1 H Ν. The experiment was applied for measuring residual dipolar couplings (RDCs) in an 8 kDa protein Z-domain aligned with Pf1 phages. Comparison with RDC values extracted from conventional NMR experiments reveals that RDCs are measured with high precision and accuracy, which is attributable to the facts that (i) the use of constant time evolution ensures that signals do not broaden whenever multiple RDCs are jointly measured in a single dimension and (ii) RDCs are multiply encoded in the multiplets arising from the joint sampling. This corresponds to measuring the couplings multiple times in a statistically independent manner. A key feature of J-GFT NMR, i.e., the correlation of couplings according to spin systems without reference to sequential resonance assignments, promises to be particularly valuable for rapid identification of backbone conformation and classification of protein fold families on the basis of statistical analysis of dipolar couplings.
Magnetic resonance, 2020
Strong coupling of nuclear spins, which is achieved when their scalar coupling 2π J is greater than or comparable to the difference ω in their Larmor precession frequencies in an external magnetic field, gives rise to efficient coherent longitudinal polarization transfer. The strong coupling regime can be achieved when the external magnetic field is sufficiently low, as ω is reduced proportional to the field strength. In the present work, however, we demonstrate that in heteronuclear spin systems these simple arguments may not hold, since heteronuclear spin-spin interactions alter the ω value. The experimental method that we use is two-field nuclear magnetic resonance (NMR), exploiting sample shuttling between the high field, at which NMR spectra are acquired, and the low field, where strong couplings are expected and at which NMR pulses can be applied to affect the spin dynamics. By using this technique, we generate zero-quantum spin coherences by means of a nonadiabatic passage through a level anticrossing and study their evolution at the low field. Such zero-quantum coherences mediate the polarization transfer under strong coupling conditions. Experiments performed with a 13 C-labeled amino acid clearly show that the coherent polarization transfer at the low field is pronounced in the 13 C spin subsystem under proton decoupling. However, in the absence of proton decoupling, polarization transfer by coherent processes is dramatically reduced, demonstrating that heteronuclear spin-spin interactions suppress the strong coupling regime, even when the external field is low. A theoretical model is presented, which can model the reported experimental results.
Journal of Magnetic Resonance, 2010
C solid-state NMR DTOCSY Homonuclear dipolar recoupling Uniformly labeled sample Isolation/individualization of 13 C-13 C dipolar interaction a b s t r a c t Herein is described a useful approach in solid-state NMR, for selecting homonuclear 13 C-13 C spin pairs in a multiple-13 C homonuclear dipolar coupled spin system. This method builds upon the zero-quantum (ZQ) dipolar recoupling method introduced by Levitt and coworkers (Marin-Montesinos et al., 2006 [30]) by extending the originally introduced one-dimensional (1D) experiment into a two-dimensional (2D) method with selective irradiation scheme, while moving the 13 C-13 C mixing scheme from the transverse to the longitudinal mode, together with a dramatic improvement in the proton decoupling efficiency. Selective spin-pair recoupling experiments incorporating Gaussian and cosine-modulated Gaussian pulses for inverting specific spins were performed, demonstrating the ability to detect informative, simplified/individualized, long-range 13 C-13 C homonuclear dipolar coupling interactions more accurately by removing less informative, stronger, short-range 13 C-13 C interactions from 2D correlation spectra. The capability of this new approach was demonstrated experimentally on uniformly 13 C-labeled Glutamine and a tripeptide sample, GAL.
Fully Resolved NMR Correlation Spectroscopy
Chemistry - A European Journal, 2015
An ew correlation experiment cited as "push-G-SERF" is reported. In the resulting phased 2D spectrum, the chemical shift information is selected alongt he direct dimension, whereas scalar couplings involving as elected proton nucleusa re edited in the indirect domain. The robustness of this pulse sequence is demonstrated on compounds with increasing structural and spectral complexity, using state-of-the-arts pectrometers. It allows for full resolution of both dimensions of the spectrum,y ielding as traightforward assignment and measurement of the coupling network around ag iven proton in the molecule. This experiment is intended for chemists who want to address efficiently the structurala nalysiso fm olecules with an overcrowdeds pectrum.