摘要:

2-Dimensional FT NMR techniques have greatly expanded the power of NMR to unravel complex chemical structures. Homonuclear 2D J-resolved experiments can be helpful in sorting out complex over lapping coupling patterns, while homonuclear chemical shift correla tion experiments can be used to determine the homonuclear coupling networks. Heteronuclear chemical shift correlation experiments can indicate the source of direct or long-range heteronuclear couplings, and hence can be used to relate the proton spectrum to the carbon spectrum. Carbon-carbon connectivity experiments reflect carbon homonuclear couplings, and, while the most insensitive of all the techniques, can be the most powerful in directly revealing the molecular framework. Techniques such as these can be used either individually or in combination to reveal part or all of the structural features of both simple and complex carbohydrates. The general features of 2D experiments are discussed in the context of their application to carbohydrates.

ISSN:0732-8303    

DOI:10.1080/07328308408057914

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A combination of two-dimensional NMR techniques has been applied to unambiguously assign the1H and13C spectra of methyl 4-O-β-d-xylopyranosyl-β-d-xylopyranoside.

ISSN:0732-8303    

DOI:10.1080/07328308408057915

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The hydroxyl proton coupled1H NMR spectra of solutions of β-d-digitoxopyranose and of an equilibrated mixture of the four ring forms ofd-digitoxose in dimethylsulfoxide-d6have been assigned completely by two-dimensional, proton chemical shift correlated NMR spectroscopy and spin decoupling at 400 MHz. Analysis of resolution enhanced, one-dimensional1H NMR spectra yielded an almost complete set of CH and OH proton-proton coupling constants for the four ring forms. The freealdehydoform ofd-digitoxose in dimethylsulfoxide-d6solution has been detected by means of its characteristic H-l quartet at 6 9.687. Quantitative analysis of the equilibrated mixture of the five forms ofd-digitoxose gave the composition:- α-pyranose, β-pyranose, α-furanose, β-furanose,aldehydoform, 11.2, 67.3, 8.4, 13.0, and 0.1%, respectively. The4C1chair conformations have been assigned to the α- and β-pyranose forms by analysis of the coupling constants and are discussed qualitatively in terms of their relative stabilities.

ISSN:0732-8303    

DOI:10.1080/07328308408057916

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The1H NMR spectrum of a solution of neomycin B free base (Structure1) in D2O has been assigned completely by two-dimensional, homonuclear J-resolved NMR spectroscopy and spin decoupling at 400 MHz. Proton chemical shifts and proton-proton couplings are reported for all glycoside residues in neomycin B along with their computer simulated spectra. The4C1chair conformation has been assigned to the 2,6-diamino-2,6-dideovy-β-l-idopyranosyl (ring D) portion of the antibiotic (1b) by analysis of the proton coupling constants and chemical shifts. The β-furanose form of the ribosyl portion (ring C) has been assigned. Vicinal proton couplings for the 2-deoxystreptaminyl group (ring B) are consistent with a chair conformation in which all ring substituents are equatorial, and proton chemical shift assignments are based on protonation studies. A computer simulated composite of the individual calculated spectra is presented for comparison with the experimental spectrum of neomycin B.

ISSN:0732-8303    

DOI:10.1080/07328308408057917

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

High resolution one and two dimensional proton nuclear magnetic resonance (2D-NMR) spectra of the glycosphingolipid globoside (the P blood group antigen) have been obtained at 500 MHz and 40-50 degrees C in dimethylsulfoxide-d6-deuterium oxide (98:2 v/v). Analysis of a scalar coupling correlated spectrum (SECSY) allows assignment of resonances to residue types. Analysis of the oligosaccharide anomeric proton signals in the 3-6 ppm region of the 2D nuclear Overhauser effect (2D-NOE) spectrum of globoside reveals inter-residue couplings that allow identification of glycosidic linkage interactions and hence a primary structure. The diversity of linkage types in globoside demonstrates that oligosaccharide sequence determination via 2D-NMR spectroscopy may be considered a general approach, regardless of the type of anomeric linkage involved. Measurement of the intra-oligosaccharide and inter-oligosaccharide NOE-conplings allows an estimation of the glycosidic interproton distances for each glycosidic linkage. These distances are shown to be consistent with current views of preferred glycosidic bond conformations.

ISSN:0732-8303    

DOI:10.1080/07328308408057918

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The proton and carbon nuclear magnetic resonance spectroscopic data for methyl 4-O-α-d-glucopyranosyl-[6-O-a-u-glucopyranosyl]-β-d-glucopyranoside (1), a model for the branch-point trisacch-aride of amylopectin, have been analysed using 2-D-heteronuclear correlated spectroscopy. Similar data are presented for the related disaccharide structures methyl β-d-maltopyranoside and β-d-isomal topyranoside.

ISSN:0732-8303    

DOI:10.1080/07328308408057919

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

This paper describes several new NMR techniques for structure determination and spectral assignment of polysaccharides. Positions of linkages between sugar units can be determined unambigously and with high sensitivity using a modified version of the well known INEPT experiment. A new two-dimensional experiment is shown to provide excellent resolution and sensitivity in correlating1H and13C chemical shifts.

ISSN:0732-8303    

DOI:10.1080/07328308408057920

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The experimental concepts of high resolution solid state13C cross-polarization magic angle spinning (CP-MAS) NMR spectroscopy are examined and contrasted with those used for obtaining NMR spectra in the liquid state. The setting of the critical experimental parameters necessary for obtaining quantitative responses in the solid state experiment are discussed in terms of the relative magnitudes of relaxation processes that are essential for the successful implementation of the technique. Methods for evaluating morphological changes and identifying resonances of the spectra with regard to chemical and/or physical diversity are also described and illustrated with spectral studies of different carbohydrates.

ISSN:0732-8303    

DOI:10.1080/07328308408057921

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Cross-polarization,13C rotating frame spin-lattice relaxation and C laboratory frame spin-lattice relaxation processes have been studied for different cellulose samples by CP/MAS13C NMR spectroscopy. It was found that the CP process can be described by a simple thermodynamic model and relative intensities of the respective resonance lines are consistent with the atomic ratios for the spectra obtained at a contact time of about 1 ms. The observed rotating frame spin-lattice relaxation times TC10were dominantly dependent on the time constant TDCHby which13C nuclei were coupled to the1H dipolar spin system. It was, therefore, impossible to obtain information about molecular

ISSN:0732-8303    

DOI:10.1080/07328308408057922

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The chemical shifts and multiplicities of the high-resolution13C CP/MAS NMR spectrum of cellulose II are quite diagnostic of the lattice structure of this polymorph. Particularly important is the chemical shift of C-1 and its clear splitting into two lines of equal intensity. Similar chemical shifts and multiplicities are seen in the spectrum of cellotetraose. Thus cellotetraose is considered to be a good model for the lattice structure of the polymer. A detailed investigation of the multiplicity of the C-1 resonance of cellotetraose shows that the two peaks are of equal intensity in this case also. Because of the limited number of repeat units in the tetramer, this observation implies that the unit cell contains two independent chains rather than a “double” repeat unit. This gives support for a similar lattice structure, with two independent chains, for cellulose II itself.

ISSN:0732-8303    

DOI:10.1080/07328308408057923

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor