Quantitative1H and13C NMR spectroscopy of lignins isolated from aspen wood by various methods

A comparative analysis has been made of the chemical structures of aspen milled wood lignin, aspen dioxane lignin, and lignin from the explosive autohydrolysis of aspen wood.Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 878–886, November–December, 1995. Original article submitted November 22, 1994.     

Destruction of aspen wood by the fungusPhanerochaete sanguinea quantitative1H and13C NMR spectroscopies of biologically degraded lignin

The lignin of mechanically ground aspen wood and lignins isolated from aspen wood attacked by the fungusPhanerochaete sanguinea have been investigated by quantitative¹H and¹³C NMR spectroscopies. It has been shown that the biodestruction of the lignin takes place through the cleavage of alkyl-aryl and aryl-aryl bonds and is accompanied by demethylation (demethoxylation) reactions, and the oxidation of C_α and C_γ atoms. In addition to reactions in which the C—C bonds are cleaved, the formation of ether bonds has been observed. An interconnection has been shown between the variations in the amount of functional groups, fragments, and the bonds in biolignins and the loss in mass of the wood. A method is proposed for evaluating the carbohydrate content in lignin preparations using the NMR method.     

Protonation of pyrimidotriazinediones by1H and13C NMR spectroscopy

On the basis of an analysis of the changes in the chemical shifts of the signals in the¹H and¹³C NMR spectra on the pyrimidotriazinedione and trifluoric acid concentrations in CDCl₃ it was established that the protonation of rheumycin and fervenulin takes place at the N(₂) atom, whereas the protonation of isofervenulin takes place competitively at the N(₁), N(₂), and O(₆) atoms. The equilibrium constants of the investigated protonation processes were measured.A study of the chemical peculiarities of the behavior of Ia, b in aqueous acidic media (H₂O-HCl, D₂O-DCl) was described in [6].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1532–1538, November, 1988.     

Synthesis and1H NMR and13C spectroscopy of L-arabinopyranosyl biosides

Conclusions The 3-0- and 4-0-trityl ethers of the acetates of methyl -L- arid methyl -L-arabinopyranosides were synthesized. The glycosylation of the ethers with the aid of 3,4-di-0-acetyl-1,2-0-(1-exo-cyano)ethylidene--L-arabinopyranose and the subsequent deacetylation of the synthesized products yielded the disaccharides: methyl 4-0-(-L-arabinopyranosyl)-,methyl 4-0-(-L-arabinopyranosyl)-, and methyl 3-0-(-L-arabinopyranosyl)--L-arabinopyranoside; and methyl 4-0-(-L-arabinopyranosyl)-, methyl 4-0-(-L-arabinopyranosyl)-, methyl 3-0-(-L-arabinopyranosyl)-, and methyl 3-0-(-L-arabinopyranosyl)--L-arabinopyranoside.The assignment of the signals in the PMR and¹³C NMR spectra of the synthesized arabinopyranosyl biosides was carried out, allowing the determination of the type and configuration of the glycosidic bond by means of which the arabinopyranose residues are linked in the oligo- and polysaccharide chains.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 200–209, January, 1986.     

Structural analysis of 1-vinylbenzazoles by 1H and 13C NMR spectroscopy

Analysis of ¹H and ¹³C NMR spectral parameters for 1-vinylbenzazoles has shown that the vinyl group has a predominantly trans orientation with respect to the condensed benzene ring. Additional evidence is given for a long range effect of the nitrogen lone pair electrons on the one bond ¹³C-¹H and ¹H-¹H spin-spin couplings and on the ¹H chemical shifts.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 499–501, April, 1988.     

Microenvironmental and conformational structure of triblock copolymers in aqueous solution by 1H and 13C NMR spectroscopy

1H and 13C nuclear magnetic resonance (NMR) spectra of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers in D2O solutions have been systematically investigated. The detailed assignments of various 1H and 13C NMR signals are presented. The hyperfine structure of PO -CH2- protons was clearly assigned, the arising reason of this hyperfine structure was attributed to the influence of the chiral center of -CHCH3- groups and the direct coupling between the PO -CH2- and -CH3 protons. The external standard 2,2-dimethyl-2-silapentane-5-sulfonate sodium salt (DSS) was firstly applied in this system. Accurate chemical shift values referenced to the external standard DSS were obtained. 1H NMR chemical shift of PO -CH2- and -CH3 signals shows a larger decrease in ppm values than that of EO -CH2- signal with the increase of PPO/PEO ratio or temperature indicating that PO segments exist in a more hydrophobic microenvironment. A new resonance signal assigned to the PO -CH2- protons appeared when the temperature is above the CMT, which is attributed to the breakdown of the intra-molecular (C-H)...O hydrogen bond between the PO -CH2- protons and the ester oxygens. The breakdown of this intra-molecular hydrogen bond may result in a decrease of gauche conformers of the PPO chain. The increase of 13C NMR chemical shift of block copolymers validates this conformational change assumption. It can be inferred that the amount of gauche conformers decreases whereas that of trans conformers increases in both PO and EO chains when elevating the PPO/PEO ratio or temperature. The observed 13C NMR chemical shifts of PO segments show a bigger increase than those of EO segments, supporting the formation of a nonpolar microenvironment around PO segments.     

Quantitative1H and13C NMR spectroscopies of cottonplant dioxane lignin

A comparative analysis has been made of the dioxane lignins of the stems, seedling shoots, and seed coats of the cotton plant. The ratio of p-hydroxyaromatic, guaiacyl, and syringyl units in the macromolecules of the lignins has been determined, and so have the amounts of functional groups and bonds. It has been established that the main difference between the dioxane lignins from seedling shoots and seed coats of the cotton plant, on the one hand, and the lignin from the woody stems, on the other hand is a lower content of syringyl and guaiacyl units in the former.     

Investigation of substituted 1,3-oxazolidines using 1H and 13C NMR spectroscopy

The characteristics of the ¹H and ¹³C NMR spectra of 1,3-oxazolidines with substituents in the 2-, 3-, and 5-positions have been studied. The relation of the spectral characteristics to the structure and configuration of the compounds has been examined, and information on the transmission of the substituent effect through the atoms of nitrogen and oxygen has been obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1255–1260, September, 1986.     

Characterization of two minor saponins from Cordia piauhiensis by 1H and 13C NMR spectroscopy

A careful NMR analysis with full assignment of the 1H and 13C spectral data for two minor saponins isolated from stems of Cordia piauhiensis is reported. These saponins were isolated by high-performance liquid chromatography and characterized as 3beta-O-[alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl]pomolic acid 28-O-[beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl] ester (1) and 3beta-O-[alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl]oleanolic acid 28-O-[beta-D-xylopyranosyl-(1 --> 2)-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl] ester (2). Their structures were established using a combination of 1D and 2D (1H, 1H-COSY, TOCSY, NOESY, gs-HMQC and gs-HMBC) NMR techniques, electrospray ionization mass spectrometry and chemical evidence.     

Application of two-dimensional NMR spectroscopy to the complete analysis of the 1H and 13C NMR spectra of d-biotin in aqueous solution

The ¹H and ¹³C NMR spectra of d-biotin were observed at 400 and 100 MHz, respectively. Various types of two-dimensional NMR spectroscopy were performed to assign the spectra. The previous assignment of ¹³C NMR spectrum of d-biotin reported by Bradbury and Johnson was modified, and the dihedral angles between the C? H bonds of the ring were determined. The populations of the conformers produced by internal rotation around the C-2? C-δ bond were estimated.     

1H, 13C and 15N NMR spectroscopy and tautomerism of nitrobenzotriazoles

Benzotriazole nitro derivatives were prepared by nitration of the corresponding benzotriazoles and by methylation or cyclization of appropriate nitro‐1,2‐phenylenediamines. Structures and tautomerism of the nitrobenzotriazoles were studied by multinuclear ¹H, ¹³C, ¹⁵N, and 2D NMR spectroscopy and quantum chemistry. Copyright © 2008 John Wiley & Sons, Ltd.     

Determination of pK a of N-alkyl-N,N-dimethylamine-N-oxides using 1H NMR and 13C NMR spectroscopy

The pK _a values of N-alkyl-N,N-dimethylamine-N-oxides were determined from the pH dependences of chemical shifts in ¹H NMR and ¹³C NMR spectra. The dependences were measured at concentrations below and above the critical micelle concentration of the amine oxides. Above the critical micelle concentration, the plots of the peak positions vs. pH were either sigmoid (the groups close to the nitrogen) or “peak type” (farther groups). The sigmoidal behaviour was a direct result of the acid-base reaction; on the other hand, the “peak type” behaviour was probably an indirect consequence of the pH variation, mediated with the change in micelle size.     

Structure determination of di-O-benzylidene derivatives of L-iditol by 1H and 13C NMR spectroscopy

The configuration and stable conformation of two dibenzylidene-L -iditol isomers formed upon benzalation of L -iditol, as well as that of a third isomer obtained by partial hydrolysis of the tribenzylidene derivative—the main product of the benzalation reaction—were determined by ¹H and ¹³C NMR spectroscopy.     

1H and 13C NMR spectra of N-vinylpyrroles

The position of the substituants in 2, 3-dialkyl-1-vinylpyrroles and 7-methyl-1 vinyl-4,5,6,7-tetrahydroindole was established on the basis of the ¹H and ¹³C NMR spectra. It was found that the S-trans conformation of the N-vinyl group is preferred. It is shown that the condensation of ketoximes with acetylene proceeds through the formation of free pyrroles and that vinyl oximes are not intermediates in the condensation.     

Two-dimensional1H and13C NMR spectroscopy and the structural aspects of amylose and amylopectin

Summary A complete assignment of the¹³C and¹H NMR signals of amylose dissolved in dimethylsulfoxide was achieved using two-dimensional H-H and C-H correlated spectroscopy and deuterium exchange. The same methods together with an INEPT experiment provided the assignments of the¹H and¹³C NMR signals of the amylose type glucan units, the branch end glucan fragments, and a few assignments of nuclei within the branching glucan units of amylopectin dissolved in dimethylsulfoxide. From these assignments and from the integration of pertinent proton signals the branching degrees of amylose and amylopectin were derived to amount to 3.9 and 8–9%.

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Zweidimensionale¹H und¹³C-NMR-Spektroskopie und die strukturellen Aspekte von Amylose und Amylopektin

Zusammenfassung Die vollständige Zuordnung der¹³C- und¹H-NMR-Signale von in Dimethylsulfoxid gelöster Amylose konnte mit Hilfe zweidimensionaler H-H- und C-H-Korrelationsspektroskopie und Deuteriumaustausch erzielt werden. Die gleichen Methoden sowie ein INEPT-Experiment ermöglichten auch die Zuordnung der¹³C- und¹H-NMR-Signale der amylosischen Glucaneinheiten, der Verzweigungsendfragmente und einzelner Kerne im Bereich der Verzweigungsstellen von in Dimethylsulfoxid gelöstem Amylopektin. Aus diesen Zuordnungen und der Integration entsprechender Protonensignale konnte ein Verzweigungsgrad von Amylose und Amylopektin von 3.9 und 8–9% abgeleitet werden.