Geometry of multiple-spin systems as reflected in 13C–{ 1H} dipolar spectra measured at Lee-Goldburg cross-polarization (original) (raw)
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Journal of Magnetic Resonance, 1999
Lineshape calculations are reported for a spin system consisting of a spin-1 2 nucleus scalar-coupled to two magnetically equivalent spin-1 nuclei, e.g., a CD 2 group. It is found that, because of the differential line broadening, the peak height ratio of the five spin-1 2 nucleus transitions is expected to deviate from the integrated intensity ratio of 1:2:3:2:1. The deviation is dependent on the extent of cross-correlation between the two quadrupolar interactions. The theoretical predictions for peak height ratios and for bandshapes are tested for the carbon-13 spectrum of perdeuterated ethylene glycol, and iterative fitting is used to obtain an estimate of the extent of the correlation between the quadrupolar interactions for the two deuterons.
Journal of Magnetic Resonance, 2006
We have developed new 2D and 3D experiments for the measurement of C(alpha)-H(alpha) residual dipolar coupling constants in (13)C and (15)N labelled proteins. Two experiments, 2D (HNCO)-(J-CA)NH and 3D (HN)CO-(J-CA)NH, sample the C(alpha)-H(alpha) splitting by means of C(alpha) magnetization, while 2D (J-HACACO)NH and 3D J-HA(CACO)NH use H(alpha) magnetization to achieve a similar result. In the 2D experiments the coupling evolution is superimposed on the evolution of the (15)N chemical shifts and the IPAP principle is used to obtain (1)H-(15)N HSQC-like spectra from which the splitting is determined. The use of a third dimension in 3D experiments reduces spectral overlap to the point where use of an IPAP scheme may not be necessary. The length of the sampling interval in the J-dimension of these experiments is dictated solely by the relaxation properties of C(alpha) or H(alpha) nuclei. This was made possible by the use of C(alpha) selective pulses in combination with either a DPFGSE or modified BIRD pulses. Inclusion of these pulse sequence elements in the J-evolution periods removes unwanted spin-spin interactions. This allows prolonged sampling periods ( approximately 25 ms) yielding higher precision C(alpha)-H(alpha) splitting determination than is achievable with existing frequency based methods.
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.
The Journal of Chemical Physics, 1998
The multidimensional experiment which includes isocorrelating anisotropic interactions of different spins in solids rotropic-shift evolutions for resolving signals requires the evotating at the magic angle. Anisotropic interactions, such as heterolution periods, each of which is dominated by a single type of nuclear dipolar couplings and chemical-shift anisotropies, are reanisotropic interaction under MAS (magic-angle spinning) covered in the evolution periods by newly designed RF pulse seconditions. In this study, we have developed RF multipulses quences. Calculated spectra for this correlation experiment for recovering chemical-shift anisotropy and CH dipolar independed on the mutual orientation of tensorial interactions. Thus, teraction under MAS. These pulse sequences were applied this method can provide structural information, e.g., dihedral to uniformly 13 C-labeled L-alanine. Experimental results for angles, for spin pairs distinguished by isotropic chemical shift. the correlation experiments with the multipulses are com-Experimental and numerically simulated results are presented for pared with numerical calculations to analyze the dependence L-alanine fully labeled with 13 C nuclei.
Magnetic Resonance in Chemistry, 2006
NMR spectra of molecules oriented in liquid crystals provide homo-and heteronuclear dipolar couplings and thereby the geometry of the molecules. Several inequivalent dilute spins such as 13 C and 15 N coupled to protons form different coupled spin systems in their natural abundance and appear as satellites in the proton spectra. Identification of transitions belonging to each spin system is essential to determine heteronuclear dipolar couplings, which is a formidable task. In the present study, using 15 N-1 H and 13 C-1 H HSQC, and HMQC experiments we have selectively detected spectra of each rare spin coupled to protons. The 15 N-1 H and 13 C-1 H dipolar couplings have been determined in the natural abundance of 13 C and 15 N for the molecules pyrazine, pyrimidine and pyridazine oriented in a thermotropic liquid crystal.
Observation of 13C13C couplings with enhanced sensitivity
Journal of Magnetic Resonance (1969), 1982
While information about the structure of an organic molecule may be deduced from several different kinds of NMR parameters, it may be argued that carboncarbon spin coupling provides the most direct and unambiguous evidence about the topology of the molecular framework. The basic skeleton of a molecule is largely constructed of carbon atoms, and each carbon-carbon link may be studied in isolation because molecules with three or more carbon-13 spins can be neglected in materials of natural isotopic abundance.
Chemical Physics Letters, 1995
A new homonuclear dipolar recoupling technique is described which uses a sequence of phase-shifted, windowless irradiations applied synchronously with sample spinning. Experiments performed on a series of doubly labeled dicarboxylie acids, alanine-l,3-t3C2, and 2'-deoxythymidine-4,6-13C2 demonstrate that this new windowless dipolar recoupling pulse ,sequence can accurately determine internuclear distances from polycrystalline solids in cases where the coupled spins have large chemical shift anisotropies and large differences in isotropic chemical shift.
Journal of Magnetic Resonance, 1998
New two-and three-dimensional NMR methods are proposed for the measurement of 3 J(H, H) coupling constants between two adjacent methylene moieties. The new experiment, which is based on a combination of the E.COSY principle and double/zero quantum heteronuclear spectroscopy, has been applied to diacetonglucose and to the protein rhodniin. The coupling constants of CH-CH 2 groups have been compared with those obtained from a HCCH-E.COSY experiment to check the reliability of the results. An analysis of the coupling constants derived by comparison between experimental and simulated spectra is presented. Simulations were done with the program wtest considering fully correlated dipolar relaxation. Side-chain conformations in amino acids with adjacent methylene groups can be determined by the new experiment.