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1.
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
2.
A complete assignment of the signals in the 1H and 13C NMR spectra and the stereostructural analysis of the compounds prepacifenol epoxide and the new dehydroxyprepacifenol epoxide are presented. These compounds were extracted from the marine mollusc Aplysia dactylomela and represent the first occurrence of chamigrenes found in Brazilian waters. The NMR analyses are supported by NOE difference and COSY experiments and also by gradient selected HMBC, HSQC-TOCSY and HSQC-DE. 1H spectra simulations were done for the final fitting of the chemical shifts and coupling constants. 相似文献
3.
Strohmeier M Alderman DW Grant DM 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,155(2):263-277
The effect of dipolar coupling to 14N on 13C FIREMAT (five pi replicated magic angle turning) experiments is investigated. A method is developed for fitting the 13C FIREMAT FID employing the full theory to extract the 13C-14N dipolar and 13C chemical shift tensor information. The analysis requires prior knowledge of the electric field gradient (EFG) tensor at the 14N nucleus. In order to validate the method the analysis is done for the amino acids alpha-glycine, gamma-glycine, l-alanine, l-asparagine, and l-histidine on FIREMAT FIDs recorded at 13C frequencies of 50 and 100 MHz. The dipolar and chemical shift data obtained with this analysis are in very good agreement with the previous single-crystal 13C NMR results and neutron diffraction data on alpha-glycine, l-alanine, and l-asparagine. The values for gamma-glycine and l-histidine obtained with this new method are reported for the first time. The uncertainties in the EFG tensor on the resultant 13C chemical shift and dipolar tensor values are assessed. 相似文献
4.
5.
Mansoureh Mousavi Steve S.-F. Yu Der-Lii M. Tzou 《Solid state nuclear magnetic resonance》2009,36(1):24-31
13C cross-polarization/magic-angle spinning (CP/MAS) solid-state NMR spectroscopy has been employed to analyze four vitamin D compounds, namely vitamin D3 (D3), vitamin D2 (D2), and the precursors ergosterol (Erg) and 7-dehydrocholesterol (7DHC). The 13C NMR spectrum of D3 displays a doublet pattern for each of the carbon atoms, while that of Erg contains both singlet and doublet patterns. In the cases of 7DHC and D2, the 13C spectra display various multiplet patterns, viz. singlets, doublets, triplets, and quartets. To overcome the signal overlap between the 13C resonances of protonated and unprotonated carbons, we have subjected these vitamin D compounds to 1D 1H-filtered 13C CP/MAS and {1H}/13C heteronuclear correlation (Hetcor) NMR experiments. As a result, assisted by solution NMR data, all of the 13C resonances have been successfully assigned to the respective carbon atoms of these vitamin D compounds. The 13C multiplets are interpreted due to the presence of s-cis and s-trans configurations in the α- and β-molecular conformers, consistent with computer molecular modeling determined by molecular dynamics and energy minimization calculations. To further characterize the ring conformations in D3, we have successfully extracted chemical shift tensor elements for the 13C doublets. It is demonstrated that 13C solid-state NMR spectroscopy provides a robust and high sensitive means of characterizing molecular conformations in vitamin D compounds. 相似文献
6.
Lu JX Damodaran K Lorigan GA 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,178(2):283-287
Membrane topology changes introduced by the association of biologically pertinent molecules with membranes were analyzed utilizing the (1)H-(13)C heteronuclear dipolar solid-state NMR spectroscopy technique (SAMMY) on magnetically aligned phospholipid bilayers (bicelles). The phospholipids (1)H-(13)C dipolar coupling profiles lipid motions at the headgroup, glycerol backbone, and the acyl chain region. The transmembrane segment of phospholamban, the antimicrobial peptide (KIGAKI)(3) and cholesterol were incorporated into the bicelles, respectively. The lipids (1)H-(13)C dipolar coupling profiles exhibit different shifts in the dipolar coupling contour positions upon the addition of these molecules, demonstrating a variety of interaction mechanisms exist between the biological molecules and the membranes. The membrane topology changes revealed by the SAMMY pulse sequence provide a complete screening method for analyzing how these biologically active molecules interact with the membrane. 相似文献
7.
Trebosc J Hu B Amoureux JP Gan Z 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,186(2):220-227
We present several new methods that allow to obtain through-space 2D HETCOR spectra between spin-1/2 and half-integer quadrupolar nuclei in the solid state. These methods use the rotary-resonance concept to create hetero-nuclear coherences through the dipolar interaction instead of scalar coupling into the HMQC and refocused INEPT experiments for spin n/2 (n>1). In opposite to those based on the cross-polarization transfer to quadrupolar nuclei, the methods are very robust and easy to set-up. 相似文献
8.
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
9.
Troganis AN Tsanaktsidis C Gerothanassis IP 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,164(2):294-303
The 14N nuclear magnetic resonance (NMR) linewidths of the alpha-amino groups of several protein amino acids were measured in aqueous solution, with and without composite proton decoupling, to estimate the effect of proton exchange and molecular weight on the linewidths. It is shown that, contrary to earlier claims, the increase in the linewidth at low pH is not exclusively due to the effect of proton exchange broadening. The 14N linewidths, under composite proton decoupling, increase with the bulk of the amino acid, and increase at low pH. Statistical treatment of the experimental 14N and literature 17O NMR data was performed assuming two models: (i) an isotropic molecular reorientation of a rigid sphere in a medium of viscosity eta, (ii) a stochastic diffusion of the amino and carboxyl groups comprising contributions from internal (tauint) and overall (taumol) motions. Assuming a single correlation time from overall molecular reorientation (taumol), then, a linear correlation was found between the linewidths and the molecular weights of the protein amino acids at the pH values 0.5 and 6.0, which are characteristic of the cationic and zwitterionic forms, respectively. The slopes of the straight-lines were found to be dependent of pH for 14N, contrary to the 17O linear correlations whose slopes were found to be independent of pH. Assuming effective correlation times of the amino and carboxyl groups, which comprise contributions from the internal (tauint) and overall (taumol) motions, then, a significant improvement of the statistics of the regression analysis was observed. The 14N relaxation data, in conjunction with 17O NMR linewidths, can be interpreted by assuming that the 14N quadrupole coupling constants (NQCCs) are influenced by the protonation state of the carboxyl group, the 17O NQCCs remain constant, and the cationic form of the amino acids is hydrated by an excess of 1-3 molecules of water relative to the zwitterionic state. 相似文献
10.
Michael Caffrey Joshua Kaufman Stephen J. Stahl Paul T. Wingfield Angela M. Gronenborn G.Marius Clore 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,135(2):368-372
A suite of 3D NMR experiments for measuring15N–{1H} NOE,15NT1, and15NT1ρvalues in large proteins, uniformly labeled with15N and13C, is presented. These experiments are designed for proteins that exhibit extensive spectral overlap in the 2D1H–15N HSQC spectrum. The pulse sequences are readily applicable to perdeuterated samples, which increases the spectral resolution and signal-to-noise ratio, thereby permitting the characterization of protein dynamics to be extended to larger protein systems. Application of the pulse sequences is demonstrated on a perdeuterated13C/15N-labeled sample of the 44 kDa ectodomain of SIV gp41. 相似文献
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12.
Marchione AA 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,210(1):31-37
The application of common two-dimensional NMR correlation experiments to gaseous analytes for structural elucidation is reported. Standard sequences such as COSY, HSQC, and HMBC are readily applied to volatile hydrocarbons and fluorocarbons. In experiments using (19)F or (13)C as the observed nucleus, it is possible to take advantage of efficient spin-rotation relaxation to perform common experiments swiftly (a (19)F COSY acquired in 6s is shown) or to render insensitive experiments possible on a practical timescale (e.g. a gas phase INADEQUATE at natural isotopic abundance in 14h). NOE-based experiments were not successful on the gaseous systems studied. 相似文献
13.
I. Mukhopadhyay R. M. Lees 《International Journal of Infrared and Millimeter Waves》1995,16(1):99-115
The torsion-rotation structure of the far-infrared (FIR) spectrum of the C-13 isotopic species of methyl alcohol has been investigated by high-resolution Fourier transform spectroscopy in the 25–350 cm–1 region, with emphasis on subbands involving excited torsional states. In this study, 89 such subbands have been identified, with torsional states fromn=1 ton=3 included. As well, a further 4 assignments have been added to our previous work on then=0 ground torsional state. The subband origins together with known microwave results have been fitted by least-squares to our torsion-rotation Hamiltonian, and improved molecular structural and torsional constants for the vibrational ground state are reported. Tables of state-specific constants representing the three leading terms in aJ(J+1) power-series expansion of the torsion-rotation energy levels are given for torsional statesn=0 to 3 and rotationalK values from 0 to 16. 相似文献
14.
Franco Cristiant Francesco A. Devillanova Angelo Diaz Francesco Isaia Gaetano Verani 《光谱学快报》2013,46(8):767-777
The 15N NMR chemical shifts and 1(15N-1H) coupling constants of a series of imidazolidine-2,4-dichalcogen (O, S) derivatives are reported.The 15N NMR chemical shifts show a linear correlatlon wlth the vNH stretchlng vlbratlons. The influence of the substitution of the oxygen at C2 and/or C4 with the sulphur, and of the hydrogen at C5 wlth the methyls and phenyls has been considered. The 1J(15N-1H)'s found In thls serles of molecules agrees well with the expected values. 相似文献
15.
The 1H NMR spectra of the title benzodiazepines derivatives is highly congested because all the protons are in aromatic environment so many proton signals remain overlap even 300 MHz or higher fields. With this in mind, the assignment of the 1H and 13C spectra of these compounds obtained using COSY, NOESY, HMQC and HMBC experiments is reported. 相似文献
16.
Marcin Sobczak Tadeusz Chreptowicz Joanna Kolmas Waclaw Kolodziejski 《Solid state nuclear magnetic resonance》2009,35(4):230-234
Commercial Dexon surgical sutures, made of polyglycolide (PGA), were examined using 13C CP/MAS NMR. The study shows that detailed analysis of the cross-polarization (CP) process is useful in the peak assignments and in the assessment of molecular mobility in the polymer domains. Crystallinity of PGA in the sutures was estimated at ca. 55%. 相似文献
17.
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
18.
The 1H NMR spectra of the title benzodiazepines derivatives is highly congested because all the protons are in aromatic enviroment so many proton signals remain overlap even 300 MHz or higher fields. With this in mind, the assignment of the 1H and 13C spectra of these compounds obtained using COSY, NOESY, HMQC and HMBC experiments is reported. 相似文献
19.
The 14N NQR frequencies of selected aromatic C-nitroso compounds were measured using cross relaxation double resonance. The monomers
have high 14N NQR frequencies with Χ and η values of 5700 to 6100 kHz and 0.5 ± 0.1, respectively. The dimers and polymer show lower frequencies with values of 2300
to 2600 kHz and 0.8 ± 0.05. Benzofuroxan has values typical of both the monomer and dimer. 相似文献
20.
The 1H- and 13C-NMR spectra of 6,7-dihalo-1,4-dihydro-4-oxo-1-(2,3,5-tri-0-benzoyl-pβ-D-ribofuranosyl)quinoline-3-carboxylic acids (3), (4), the ester (3a), 6-chloro-1-(2-deoxy-3,5-di-O-tolouyl-α- and β-D-erythropentofuranosyl)-7-fluoro-1,4-dihydro-4-oxo-quinoline-3-carboxylic acid (5), and its free a-nucleoside (5a) have been investigated. Resonance signals were assigned by homo- and heteronuclear two dimensional NMR methods (DQF-COSY, HMQC, and HMBC) for (3), (4), (5), and (5a). Ribosylation sites and anomeric configurations were identified from ROESY spectra. 相似文献