共查询到20条相似文献,搜索用时 31 毫秒
1.
Four peracetylated disaccharides 13C-labelled at the C-1′ position and having α-d-(1′→3), β-d-(1′→3), α-d-(1′→4), and β-d-(1′→4) linkages were prepared starting from the commercially available d-[1-13C]glucose. They were studied on the basis of their 3J13CH coupling constants in relation with the conformation in solution of oligosaccharides as models for the corresponding polymer. A method of analysis of the n.m.r. spectra is described and the coupling constants J13C-1′H given, particularly the 2J coupling (in the same cycle and with sign determination) and the 3J coupling (through the glycosidic bond). In that case, the values obtained give experimental information on the ψ angle values. They are compared with the known X-ray data for similar compounds. 相似文献
2.
Oana Dima Kris Morreel Bartel Vanholme Hoon Kim John Ralph Wout Boerjan 《The Plant cell》2015,27(3):695-710
Lignin is an aromatic polymer derived from the combinatorial coupling of monolignol radicals in the cell wall. Recently, various glycosylated lignin oligomers have been revealed in Arabidopsis thaliana. Given that monolignol oxidation and monolignol radical coupling are known to occur in the apoplast, and glycosylation in the cytoplasm, it raises questions about the subcellular localization of glycosylated lignin oligomer biosynthesis and their storage. By metabolite profiling of Arabidopsis leaf vacuoles, we show that the leaf vacuole stores a large number of these small glycosylated lignin oligomers. Their structural variety and the incorporation of alternative monomers, as observed in Arabidopsis mutants with altered monolignol biosynthesis, indicate that they are all formed by combinatorial radical coupling. In contrast to the common believe that combinatorial coupling is restricted to the apoplast, we hypothesized that the aglycones of these compounds are made within the cell. To investigate this, leaf protoplast cultures were cofed with 13C6-labeled coniferyl alcohol and a 13C4-labeled dimer of coniferyl alcohol. Metabolite profiling of the cofed protoplasts provided strong support for the occurrence of intracellular monolignol coupling. We therefore propose a metabolic pathway involving intracellular combinatorial coupling of monolignol radicals, followed by oligomer glycosylation and vacuolar import, which shares characteristics with both lignin and lignan biosynthesis. 相似文献
3.
Elin Säwén 《Carbohydrate research》2010,345(8):984-1319
The synthesis of two novel carbasugar analogues of α-l-iduronic acid is described in which the ring-oxygen is replaced by a methylene group. In analogy with the conformational equilibrium described for α-l-IdopA, the conformation of the carbasugars was investigated by 1H and 13C NMR spectroscopy. Hadamard transform NMR experiments were utilised for rapid acquisition of 1H,13C-HSQC spectra and efficient measurements of heteronuclear long-range coupling constants. Analysis of 1H NMR chemical shifts and JH,H coupling constants extracted by a total-lineshape fitting procedure in conjunction with JH,C coupling constants obtained by three different 2D NMR experiments, viz., 1H,13C-HSQC-HECADE, J-HMBC and IPAP-HSQC-TOCSY-HT, as well as effective proton-proton distances from 1D 1H,1H T-ROE and NOE experiments showed that the conformational equilibrium 4C1?2S5a?1C4 is shifted towards 4C1 as the predominant or exclusive conformation. These carbasugar bioisosteres of α-l-iduronic acid do not as monomers show the inherent flexibility that is anticipated to be necessary for biological activity. 相似文献
4.
Pt(II) complexes of the types cis- and trans-Pt(amine)2I2 with amines containing a phenyl group were synthesized and studied mainly by IR and multinuclear (195Pt, 1H and 13C) magnetic resonance spectroscopies. The compounds are not very soluble. In 195Pt NMR spectroscopy, the cis isomers were observed at slightly lower fields than the trans analogues (average Δδ = 11 ppm) in acetone. In 1H NMR, the NH groups were also found at slightly lower fields in the cis isomers. The coupling constants 2J(195Pt-1HN) varied from 53 to 85 Hz and seem slightly smaller in the trans configuration. The 13C NMR spectra of most of the complexes were measured. No coupling constants J(195Pt-13C) were detected due to the low solubility of the compounds. The cis isomers containing a phenyl group on the N atom could not be isolated except for Ph-NH2 which was shown to be a mixture of isomers in acetone. The tetrasubstituted ionic compounds [Pt(amine)4]I2 for the less crowded ligands were also studied mainly by NMR spectroscopy in aqueous solution. The 195Pt chemical shifts vary between −2855 and −2909 ppm. The coupling constants 3J(195Pt-1H) are about 40 Hz. The iodo-bridged dinuclear species I(amine)Pt(μ-I)2Pt(amine)I were also synthesized and characterized. Two isomers are present in acetone solution for most of the compounds. Their δ(Pt) signals were observed at about −4000 ppm and their coupling constants 2J(195Pt-1HN) are around 69 Hz. 相似文献
5.
《Inorganica chimica acta》1988,141(2):263-274
Reduction of some N-alkylimines has been achieved with NaBH4 to give the corresponding secondary amines with high yields (85–95%). These amines were characterized on the bases of their 1H and 13C NMR spectra. The reaction of these amines with mercuric chloride to afford the corresponding complexes was found to occur through a weak dative bond between the nitrogen lone pair of electrons and the mercury atom to form HgCl2L2 complexes. The 1H, 13C and 199Hg NMR chemical shifts have been obtained as well as 1J(13CH) and 2J(13CH) coupling constants. Labelling with nitrogen-15 revealed that there is a weak coupling between the nitrogen and the 199Hg. 相似文献
6.
The 13C NMR spectra of a variety of furocoumarins, dihydrofurocoumarins and furochromones are reported. The signals were assigned using carbon-proton coupling constants, ring annullation shifts, nuclear Overhauser effect considerations and shift effects caused by monothioester formation. Substituent effects on 13C chemical shifts and carbon-proton coupling constants are discussed. Methoxyl induced shifts of 5- and 8-substituted furocoumarins are additive, but their effects cannot be transferred to the furochromone system. 相似文献
7.
F. Toma M. Monnot F. Piriou J. Savrda S. Fermandjian 《Biochemical and biophysical research communications》1980,97(2):751-758
The vicinal coupling constants 13C′-13Cγ were measured in aspartic acid and phenylalanine (85 % 13C enrichment) as free amino acids and in the peptides Asp-Pro and Gly-Pro-Phe. These coupling constants used in connection with those between the α -and the β-protons provide the unambiguous assignment of rotamers I and II in the Asp and Phe side chains. The method is generally applicable to other amino acids and residues even in large peptides. A possible set of Jgc,c and Jtc,c values is proposed for the use of carbon 13-carbon 13 vicinal coupling constants in the side chain conformational studies of amino acid residues with a free carboxyl group. 相似文献
8.
Aydin Severge Friedrich Jüttner Eberhard Breitmaier Günther Jung 《Biochimica et Biophysica Acta (BBA)/General Subjects》1976,437(1):289-300
The alga Ankistrodesmus braunii was grown with [15N]nitrate under the optimized conditions of a large-scale mass cultivation. 19.7% of the dried algae were isolated as a mixture of amino acids. The 15N-labelled amino acids (15N content up to 98%) were separated by ion exchange chromatography using pyridine acetate gradients. The 15N content of the analytically pure amino acids was determined by combined gas-liquid chromatography-mass spectrometry of the trifluoroacetylated methylesters and by emission spectroscopy in the 15N analysator. Using pulse Fourier transform 13C nuclear magnetic resonance, the pH dependence of the 13C-15N coupling constants of Asp, Pro, Ser, Glu, Gly, Ala, Val, Ile and Leu was determined in aqueous solutions. Increasing coupling constants were found with pH and decreasing electron density, respectively. The relation of Binsch et al. (Binsch, G., Lambert, J.B., Roberts, B.W. and Roberts, J.D. (1964) J. Am. Chem. Soc. 86, 5564–5570) between the coupling constant and the product of the S-part of the 13C and 15N hybridization fits best in acidic medium. The magnitude of the coupling constants correlates well with the electron densities calculated by Del Re et al. (Del Re, G., Pullman, B. and Yonezawa, T. (1963) Biochim. Biophys. Acta 75, 153–182). The recording of 13C nuclear magnetic resonance spectra over the entire pH range revealed no change in the sign of the 13C-15N coupling constants of the amino acids. 相似文献
9.
The high resolution 1H and 13C nuclear magnetic resonance (NMR) spectra of galactosylceramides containing n-fatty acids and α-hydroxy fatty acids were recorded in dimethylsulfoxide solution with and without addition of D2O. From the coupling constants of the sugar ring protons, a 4C1 conformation can be deduced. In contrast to the conformation in aqueous solution, the C6 hydroxymethylene group is freely rotating around the C6C5 bond. In the ceramide residue all signals produced by protons linked to carbons bearing electronegative substituents could be attributed. The large difference in coupling constants of the methylene protons of C1′ to the C2′ methine proton of the sphingosine indicates a restricted rotation around the C1′C2′ bond. The assignments of the hydroxy and amino protons follow from the decoupling of the corresponding methine protons. 相似文献
10.
Jaroslav Vicar Karel Blaha Franois Piriou Michel Juy Hung Lam-thanh Serge Fermandjian 《Biopolymers》1982,21(12):2317-2328
The cyclodipeptides cyclo(L -alanyl-L -phenylalanyl) and cyclo(D -alanyl-L -phenylalanyl) were synthesized with various atoms substituted by the isotopes 15N and 13C. Thus, the coupling constants 15N–1H, 13C–1H, and 13C–15N could be obtained, in addition to the commonly used 1H–1H constants. The applicability of these coupling constants for obtaining conformational information on side chains and substituted 2,5-piperazinedione rings is discussed. 相似文献
11.
Donald W. Pettigrew 《Archives of biochemistry and biophysics》2009,481(2):151-156
IIAGlc, the glucose-specific phosphocarrier protein of the phosphoenolpyruvate:glycose phosphotransferase system, is an allosteric inhibitor of Escherichia coli glycerol kinase. A linked-functions initial-velocity enzyme kinetics approach is used to define the MgATP-IIAGlc heterotropic allosteric interaction. The interaction is measured by the allosteric coupling constants Q and W, which describe the mutual effect of the ligands on binding affinity and the effect of the allosteric ligand on Vmax, respectively. Allosteric interactions between these ligands display K-type activation and V-type inhibition. The allosteric coupling constant Q is about 3, showing cooperative coupling such that each ligand increases the affinity for binding of the other. The allosteric coupling constant W is about 0.1, showing that the allosteric inhibition is partial such that binding of IIAGlc at saturation does not reduce Vmax to zero. E. coli glycerol kinase is a member of the sugar kinase/heat shock protein 70/actin superfamily, and an element of the superfamily conserved ATPase catalytic core was identified as part of the IIAGlc inhibition network because it is required to transplant IIAGlc allosteric control into a non-allosteric glycerol kinase [A.C. Pawlyk, D.W. Pettigrew, Proc. Natl. Acad. Sci. USA 99 (2002) 11115-11120]. Two of the amino acids at this locus of E. coli glycerol kinase are replaced with those from the non-allosteric enzyme to enable determination of its contributions to MgATP-IIAGlc allosteric coupling. The substitutions reduce the affinity for IIAGlc by about 5-fold without changing significantly the allosteric coupling constants Q and W. The insensitivity of the allosteric coupling constants to the substitutions may indicate that the allosteric network is robust or the locus is not an element of that network. These possibilities may arise from differences of E. coli glycerol kinase relative to other superfamily members with respect to oligomeric structure and location of the allosteric site in a single domain far from the catalytic site. 相似文献
12.
An experiment is presented to determine 3JHNHα coupling constants, with significant advantages for applications to unfolded proteins. The determination of coupling constants
for the peptide chain using 1D 1H, or 2D and 3D 1H-15N correlation spectroscopy is often hampered by extensive resonance overlap when dealing with flexible, disordered proteins.
In the experiment detailed here, the overlap problem is largely circumvented by recording 1H-13C′ correlation spectra, which demonstrate superior resolution for unfolded proteins. J-coupling constants are extracted from
the peak intensities in a pair of 2D spin-echo difference experiments, affording rapid acquisition of the coupling data. In
an application to the cytoplasmic domain of human neuroligin-3 (hNlg3cyt) data were obtained for 78 residues, compared to 54 coupling constants obtained from a 3D HNHA experiment. The coupling constants
suggest that hNlg3cyt is intrinsically disordered, with little propensity for structure. 相似文献
13.
Rebaudioside A is a natural sweetener from Stevia rebaudiana in which four β-d-glucopyranose units are attached to the aglycone steviol. Its 1H and 13C NMR spectra in pyridine-d5 were assigned using 1D and 2D methods. Constrained molecular dynamics of solvated rebaudioside using NMR constraints derived from ROESY cross peaks yielded the orientation of the β-d-glucopyranose units. Hydrogen bonding was examined using the temperature coefficients of the hydroxyl chemical shifts, ROESY and long-range COSY spectra, and proton-proton coupling constants. 相似文献
14.
《Carbohydrate research》1986,147(2):247-264
l-(1-13C, 5-2H)Arabinose (6D) and l-(2-13C, 5-2H)arabinose (8D) have been synthesized by degradation of 2,3-O-isopropylidene-α-l-rhamnofuranose (2) to l-(4-2H)erythrose (5β,5αD), with subsequent chain elongation to 6D plus l-(1-13C, 5-2H)ribose (7D), the latter being converted into 8D. Intermediates were identified by complete assignment of the 13C chemical shifts employing carbon-carbon and carbon-deuterium coupling constants, deuteration shifts, differential isotope-shifts, and deuterium spectra. The anomeric carbon atoms of 2 and 2,3-O-isopropylidene-l-(1-2H) erythrose (4D) gave only single 13C resonances, suggesting that these two compounds exists in only one major anomeric configuration, clarifying previously reported work. The synthesis of 2,3-O-isopropylidene-l-(1-2H)rhmanitol (3D) facilitated the assignment of the signals in the 13C spectra of the nondeuterated analog. Specific deuterium-enrichment and the observed carbon-deuterium coupling (1JC,D ∼22 Hz) not only served to identify the deuterated carbon atom unambiguously in 3 but also permitted assignment of closely spaced resonances. The deuterium spectrum of 2,3-O-isopropylidene-l-(1-2H)erythrofuranose (4D) showed only a single resonance, indicating preponderance of one anomer, in accord with the observation of a single C-1 resonance in the 13C spectrum. 相似文献
15.
The first isolation of a trachylobane from an African specimen of Psiadia punctulata (Asteraceae) is presented in this paper. A complete 1H and 13C NMR spectral analysis of this compound and two other trachylobane diterpenes, previously isolated from the same plant, are also provided. The use of NMR techniques such as gCOSY, gHSQC, gHMBC and 2D-J-resolved, in combination with a software-assisted methodology, led to a complete and unequivocal assignment of 1H and 13C signals. This was achieved together with the measurement of all homonuclear hydrogen coupling constants. The presented detail level of the assignment data has never been published before for trachylobanes. Furthermore, with all determined NMR experimental data from the spectra and to obtain a reliability assessment, signals were simulated in the FOMSC3 and NMR_MultSim software. 相似文献
16.
The conformation of tetranactin, an ionophore, in chloroform was investigated by infrared and Raman spectra and by proton and 13C magnetic resonances. The infrared spectra show that the structure of its K+ complex in the solution is quite similar to that in crystals. The proton spin–spin coupling constants are explained well by assuming that the crystalline structure is retained in solution. The spin–lattice relaxation times of the 13C nuclei of the K+ complex indicate that its framework is rigid. The correlation time of the overall reorientation of the molecule was calculated to be 9 X 10?11 sec. On the other hand, the conformation of the complexed form in chloroform differs from that in crystals. Despite the geometrical nonequivalence of the four subunits in the crystalline state, the nuclear magnetic resonance spectra show their magnetic equivalence in the solution. The proton spin–spin coupling constants have values that are averaged by rapid internal rotation. The spin–lattice relaxation times of the 13C nuclei in its framework are unexplained by the overall reorientation of the molecule, and reveal the existence of internal motion in the framework. The rate of the local motion of the framework is between 102–1010 sec?1. By comparison of the infrared spectra, it can be said that the mean conformation of the fluctuated framework of the uncomplexed tetranactin in the solution is similar to that of nonactin in the crystalline form, which has an S4 symmetry axis through the center of the macrocyclic ring. 相似文献
17.
Moschos Polissiou Minh Tan Phan Viet Maurice St-Jacques Theophile Theophanides 《Inorganica chimica acta》1985,107(3):203-210
The molecular mode of action leading to the anticancer activity of the drug cis-diamminedichloroplatinum(II), cis-DDP or cis-platinum is still the subject of speculation. In the present high field (400 MHz) 1H NMR study the results on coupling constants for cis- and trans-diammine bis(guanosine- 5′-monophosphate) and (d-guanosine-5′-monophosphate)platinum(II) complexes are presented and discussed. The 1H and 13C NMR chemical shifts obtained are consistent with the drug binding to N7 of each guanine. It has been found that the drug induces different conformational changes in the nucleotide from the trans-DDP isomer. 相似文献
18.
13C NMR resonances of 15 simple tetrahydroisoquinolines have been assigned on the basis of chemical shift theory, 13C-1H coupling constants 相似文献
19.
H. Schwalbe W. Samstag J. W. Engels W. Bermel C. Griesinger 《Journal of biomolecular NMR》1993,3(4):479-486
Summary A method for measuring J(C,P) and J(H,P) coupling constants is presented, based on fitting a target multiplet containing the heteronuclear coupling to a reference multiplet that lacks the heteronuclear coupling. In DNA and RNA oligonucleotides, information on backbone torsion angles can be obtained from these couplings. Experimental multiplets are obtained from 31P-coupled and 31P-decoupled 1H, 13C HSQC spectra of Rp-cyclic methylphosphonate. The accuracy to which the heteronuclear coupling constants can be determined depends on the signal-to-noise ratio of the experimental data and is analyzed in detail.Dedicated to Prof. R.R. Ernst on the occasion of his 60th birthday. 相似文献
20.
The coaggregation of Streptococcus mitis strain J22 in the early stages of dental plaque formation has been shown to result from interaction of cell wall polysaccharides with lectins on the surface of other oral bacterial species. This bacterium was grown in a medium containing 13C as the sole carbon source. We have isolated the lectin receptor polysaccharide from this strain with full enrichment in 13C and have determined a number of two-bond and three-bond 13C-1H coupling constants from measurements of the offsets in two-dimensional homonuclear nmr spectra [exclusive correlated spectroscopy (E-COSY) method]. A scheme for reliable extraction of these coupling constants from homonuclear Hartmann-Hahn and nuclear Overhauser effect spectroscopy spectra is tested in model compounds. We interpret the three-bond coupling across the glycosidic linkage in terms of dihedral angles in order to provide conformational information to supplement molecular modeling and nuclear Overhauser effect data. We show that the E-COSY method works well even for coupling constants smaller than the nmr line width and that a number of the 3JCH across the glycosidic linkage are in the range of 1–2 Hz, which is much smaller than many previously reported values. © 1994 John Wiley & Sons, Inc. 相似文献