共查询到20条相似文献,搜索用时 15 毫秒
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Hu K Vögeli B Pervushin K 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,174(2):200-208
We propose the use of (13)C-detected 3D HCC-TOCSY experiments for assignment of (1)H and (13)C resonances in protonated and partially deuterated proteins. The experiments extend 2D C-13-start and C-13-observe TOCSY type experiments proposed earlier. Introduction of the third (1)H dimension to 2D TOCSY: (i) reduces the peak overlap and (ii) increases the sensitivity per unit time, even for highly deuterated (>85%) protein samples, which makes this improved method an attractive tool for the side-chain H and C assignment of average sized proteins with natural isotope abundance as well as large partially deuterated proteins. The experiments are demonstrated with a 16 kDa (15)N, (13)C-labeled non-deuterated apo-CcmE and a 48 kDa uniformly (15)N, (13)C-labeled and fractionally ( approximately 90%) deuterated dimeric sFkpA. It is predicted that this method should be suitable for the assignment of methyl (13)C and (1)H chemical shifts of methyl protonated, highly deuterated and (13)C-labeled proteins with even higher molecular weight. 相似文献
3.
Residual dipolar coupling between carbons and 14N nuclei in the 13C CPMAS NMR spectrum of solid imidazole is studied. Calculations of expected splittings with a previously reported equation leads to the complete assignment of the solid state carbon chemical shifts. Additionally, information is provided on the location of 14N electric field gradient axes at the N-H site. 相似文献
4.
Evaluation by empirically derived equations for the Substituent effect (α, β, γ, δ) on the 13C NMR chemical shifts for C-3, C-4. C-5 and halomethyl-substituent carbon (C-6) in isoxazoles 1-5 [where C-3 substituent (R1) = H, alkyl or phenyl, C-4 Substituent (R2) = H, alkyl, and C-5 substituent (R3) = di-or trihalomethyl, methyl and H], taking as reference the compound la, is reported. From the calculated values for the α, β, γ, δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1–5. The 13 C chemical shifts of the C-3, C-4, C-5, C-6 of these compounds, can be estimated with good precision: 94% of the calculated chemical shifts are found to be within ±1.0ppm, and 100% are found to be within ±1.5ppm. 相似文献
5.
A method that allows direct identification and quantitative determination of dipropylene glycol (DPG) using 13C NMR spectroscopy was developed. The quantitative procedure was checked and validated with commercially available DPG, controlled with two DPG-added essential oils, and then applied to commercial “Extraits de parfum” (perfume extracts). 相似文献
6.
The structure of bilirubin and of bilirubin derivatives has been studied by various physical techniques, including optical spectroscopy(1,2), optical rotatory dispersion,(4) isotope exchange(5) and proton magnetic resonance spectroscopy(2,3,5). A good deal of chemical information on bilirubin is also available(6). The interpretation of most of the experimental results, however, have been inconclusive and different possible structures of the molecule could be shown to accommodate the experimental data. 相似文献
7.
Amoureux JP Hu B Trébosc J 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,193(2):305-307
We present a new smooth amplitude-modulated (SAM) method that allows to observe highly resolved 1H spectra in solid-state NMR. The method, which works mainly at fast or ultra-fast MAS speed (νR > 25 kHz) is complementary to previous methods, such as DUMBO, FSLG/PMLG or symmetry-based sequences. The method is very robust and efficient and does not present line-shape distortions or fake peaks. The main limitation of the method is that it requires a modern console with fast electronics that must be able to define the cosine line-shape in a smooth way, without any transient. However, this limitation mainly occurs at ultra-fast MAS where the rotation period is very short. 相似文献
8.
Wulf-Ingo Jung Michael Bunse Otto Lutz 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,152(2):203
Localized 1H NMR spectroscopy using the 90°−t1−180°−t1+t2−180°−t2−Acq. PRESS sequence can lead to a signal loss for the lactate doublet compared with signals from uncoupled nuclei which is dependent on the choice of t1 and t2. The most striking signal loss of up to 78% of the total signal occurs with the symmetrical PRESS sequence (t1=t2) at an echo time of 2/J (290 ms). Calculations have shown that this signal loss is related to the pulse angle distributions produced by the two refocusing pulses which leads to the creation of single quantum polarization transfer (PT) as well as to not directly observable states (NDOS) of the lactate AX3 spin system: zero- and multiple-quantum coherences, and longitudinal spin orders. In addition, the chemical shift dependent voxel displacement (VOD) leads to further signal loss. By calculating the density operator for various of the echo times TE=n/J, n=1, 2, 3, …, we calculated quantitatively the contributions of these effects to the signal loss as well as their spatial distribution. A maximum signal loss of 75% can be expected from theory for the symmetrical PRESS sequence and TE=2/J for Hamming filtered sinc pulses, whereby 47% are due to the creation of NDOS and up to 28% arise from PT. Taking also the VOD effect into account (2 mT/m slice selection gradients, 20-mm slices) leads to 54% signal loss from NDOS and up to 24% from PT, leading to a maximum signal loss of 78%. Using RE-BURP pulses with their more rectangular pulse angle distributions reduces the maximum signal loss to 44%. Experiments at 1.5 T using a lactate solution demonstrated a maximum lactate signal loss for sinc pulses of 82% (52% NDOS, 30% PT) at TE=290 ms using the symmetrical PRESS sequence. The great signal loss and its spatial distribution is of importance for investigations using a symmetrical PRESS sequence at TE=2/J. 相似文献
9.
The complete assignment of the 1H and 13C NMR spectra of benzoylecgonine, a cocaine metabolite, was performed, with the aid of some 2D experiments such as gCOSY and gHSQC. 相似文献
10.
Carbon-13 NMR chemical shifts of a series of (E)- and (Z)-N-ethyl-N-methylamides [RC(O)NEtMe, R=H, Me, Et, i-Pr, t-Bu, CF3, ClCH2, Cl2CH, Cl3C, BrCH2, Br2CH, Br3C and ICH2] are reported. The α-carbon and carbonyl carbon chemical shifts are correlated with the empirical α-substituent effect and Charton's electrical parameter ([sgrave]I), respectively. The N-alkyl carbon resonances were attributed mainly to the γ- and δ-effects of R. 相似文献
11.
13C NMR parameters have been obtained for vicine and convicine in DMSO, D2O/DMSO and D2O. Complete assignment of the spectra has been achieved. Interpretation of spin-lattice relaxation rates and heteronu-clear NOES has yielded evidence of intramolecular structuring in the case of vicine and not in that of ronvirine and also of a complex network of solute-solvent interactions. 相似文献
12.
Prosser RS Luchette PA 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,171(2):537-232
Due to its depth-dependent solubility, oxygen exerts paramagnetic effects which become progressively greater toward the hydrophobic interior of micelles, and lipid bilayer membranes. This paramagnetic gradient, which is manifested as contact shift perturbations (19F and 13C NMR) and spin-lattice relaxation enhancement (19F and 1H NMR), has been shown to be useful for precisely determining immersion depth, membrane protein secondary structure, and overall topology of membrane proteins. We have investigated the influence of oxygen on 19F and 13C NMR spectra and spin-lattice relaxation rates of a semiperfluorinated detergent, (8,8,8)-trifluoro (3,3,4,4,5,5,6,6,7,7)-difluoro octylmaltoside (TFOM) in a model membrane system, to determine the dominant paramagnetic spin-lattice relaxation and shift-perturbation mechanism. Based on the ratio of paramagnetic spin-lattice relaxation rates of 19F and directly bonded 13C nuclei, we conclude that the dominant relaxation mechanism must be dipolar. Furthermore, the temperature dependence of oxygen-induced chemical shift perturbations in 9F NMR spectra suggests a contact interaction is the dominant shift mechanism. The respective hyperfine coupling constants for 19F and 13C nuclei can then be estimated from the contact shifts <(deltav/v0)19F> and <(deltav/v0)13C>, allowing us to estimate the relative contribution of scalar and dipolar relaxation to 19F and 13C nuclei. We conclude that the contribution to spin-lattice relaxation from the oxygen induced paramagnetic scalar mechanism is negligible. 相似文献
13.
Balayssac S Jiménez B Piccioli M 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,182(2):325-329
A novel experiment is proposed to provide inter-residue sequential correlations among carbonyl spins in (13)C detected, protonless NMR experiments. The COCO-TOCSY experiment connects, in proteins, two carbonyls separated from each other by three, four or even five bonds. The quantitative analysis provides structural information on backbone dihedral angles phi as well as on the side chain dihedral angles of Asx and Glx residues. This is the first dihedral angle constraint that can be obtained via a protonless approach. About 75% of backbone carbonyls in Calbindin D(9K), a 75 amino acid dicalcium protein, could be sequentially connected via a COCO-TOCSY spectrum. 49 [Formula: see text] values were measured and related to backbone phi angles. Structural information can be extended to the side chain orientation of aminoacids containing carbonyl groups. Additionally, long range homonuclear coupling constants, (4)J(CC) and (5)J(CC), could be measured. This constitutes an unprecedented case for proteins of medium and small size. 相似文献
14.
Nina Gonnella Mengfen Lin Michael J. Shapiro James R. Wareing Xiaolu Zhang 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,131(2):336-338
A double-editing pulse sequence has been developed that allows the direct observation of protein binding ligand(s) from a mixture of compounds. This technique should aid the discovery of lead pharmaceutical compounds. The proton NMR signals from protein and the nonbinding ligands are simultaneously eliminated using13C isotope editing and PFG diffusion-edited NMR. This new experiment is demonstrated using13C/15N-labeled stromelysin catalytic domain (SCD). 相似文献
15.
Wickramasinghe NP Kotecha M Samoson A Past J Ishii Y 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,184(2):350-356
We discuss a simple approach to enhance sensitivity for (13)C high-resolution solid-state NMR for proteins in microcrystals by reducing (1)H T(1) relaxation times with paramagnetic relaxation reagents. It was shown that (1)H T(1) values can be reduced from 0.4-0.8s to 60-70 ms for ubiquitin and lysozyme in D(2)O in the presence of 10 mM Cu(II)Na(2)EDTA without substantial degradation of the resolution in (13)C CPMAS spectra. Faster signal accumulation using the shorter (1)H T(1) attained by paramagnetic doping provided sensitivity enhancements of 1.4-2.9 for these proteins, reducing the experimental time for a given signal-to-noise ratio by a factor of 2.0-8.4. This approach presented here is likely to be applicable to various other proteins in order to enhance sensitivity in (13)C high-resolution solid-state NMR spectroscopy. 相似文献
16.
Bermel W Bertini I Felli IC Matzapetakis M Pierattelli R Theil EC Turano P 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,188(2):301-310
Attempts are made to efficiently decouple (13)C nuclei without significant loss of coherence during the application of the decoupling package. Such attempts are based on the S(3)E spin-state selection method. A newly developed double S(3)E (DS(3)E) is particularly efficient for C(alpha) detection for proteins as large as 480 kDa. 相似文献
17.
Total assignment of 13C and 1H NMR spectra of the 5-isopropylsulfonyl-2-norbornenes 2 was achieved using the concerted application of two-dimensional homonuclear and heteronuclear chemical shift correlations. The stereochemistry of both the diastereoisomers endo 2a and exo 2b have been established using the magnitude of the proton coupling constants. 相似文献
18.
Siegel R Trébosc J Amoureux JP Gan Z 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,193(2):321-325
Nitrogen-14 (spin I = 1) has always been a nucleus difficult to observe in solid-state NMR and until recently its observation was restricted to one-dimensional (1D) spectra. We present here the first 3D 1H–13C–14N NMR correlation spectrum. This spectrum was acquired on a test sample l-histidine·HCl·H2O using a recently developed technique, which consists in indirectly observing 14N nuclei via dipolar recoupling with an HMQC-type experiment. 相似文献
19.
13C and 17O NMR chemical shifts for a series of isobenzopyrylium salts are reported. The oxygen signal range from 300 to 270 ppm as a double bonded carboxylic oxygen, From the 17O and 13C data valuable informations on the conjugative and substituent effects of isobenzopyrylium salts were obtained. 相似文献