Substituent Effects on 13C Chemical Shifts of Aromatic Carbons in β-O-4 and β-5 type Lignin Model Compounds

Abstract

Substituent effects on the chemical shifts of aromatic carbons in lignin model compounds have been elucidated from ¹³C NMR spectra of guaiacyl and syringyl type monomerio and β-O-4 model compounds and guaiacyl type β-5 model compounds. Evaluation of the observed values of substituent chemical shift (SCS) for the aromatic carbons leads to elucidation of a generalized SCS additivity rule, for estimation of the chemical shifts of aromatic carbons in ring A of β-O-4 and β-5 type substructures in model compounds and in ring B of β-O-4 substructures in lignin preparations, with errors of less than 1 ppm. The rule is applicable to substructures of both guaiacyl and syringyl types, using an appropriate parent compound as reference instead of benzene. Signals in the aromatic region of the ¹³C NMR spectra of β-O-4 and β-5 type model compounds are reassigned on the basis of the observed SCS's as well as APT spectra of the compounds.     

The effect of plant residues on plant uptake and leaching of soil and fertilizer nitrogen in a tropical red earth soil

Two field experiments, in which differing amounts and types of plant residues were incorporated into a red earth soil, were conducted at Katherine, N.T., Australia. The aim of the work was to evaluate the effect of the residues on uptake of soil and fertilizer N by a subsequent sorghum crop, on the accumulation and leaching of nitrate, and on losses of N.Stubble of grain sorghum applied at an exceptionally high rate (~ 18 000 kg ha^–1) reduced uptake of N by sorghum by 13% and depressed the accumulation of nitrate under a crop and particularly under a fallow.Loss of fertilizer N, movement of nitrate down the profile, and uptake by the crop was studied in another experiment after application of N as¹⁵NH₄ ¹⁵NO₃ to field microplots. By four weeks after fertilizer application 14% had been lost from the soil-plant system and by crop maturity 36 per cent had been lost. The pattern of¹⁵N distribution in the profile suggested that losses below 150 cm had occurred during crop growth. The recovery of¹⁵N by the crop alone ranged from 16 to 32 per cent. There was an apparent loss of N from the crop between anthesis and maturity. Residue levels common to sorghum crops in the region (~ 2000 kg ha^–1) did not significantly affect uptake by a subsequent sorghum crop, N losses, or distribution of nitrate in the profile.     

Influence of reagent residues and catalysts on formaldehyde release from DMDHEU-treated cotton

Observations and conclusions drawn from a model N-methylol reactant system have been used to study formaldehyde release from cotton fabric treated with N,N′-dimethylol-4,5-dihydroxy-ethyleneurea (DMDHEU). Reagent residues produced by DMDHEU in the presence of sodium bisulfate or zinc nitrate were found to be more complex than those formed from the N-methylolpyrrolidone (NMP) reactant system, and the exact nature of some of the residues from DMDHEU could not be established. Zinc nitrate produces higher fixation of DMDHEU on cotton as compared to sodium bisulfate and also reduces formaldehyde release. As is the case with the NMP system, the lower amount of formaldehyde release with zinc nitrate catalyst is believed to be at least partially due to the formation of a complex between the N-methylol reactant, DMDHEU, and zinc nitrate. The C? OCell bonds in both finishes resist acid-catalyzed cleavage but cleavage of the N? C bonds in N-methylol groups (to release formadehyde) in the presence of acid is greater for the DMDHEU system than for the NMP system. Results with the DMDHEU and NMP systems are similar, but because of the complex nature of the products formed in the DMDHEU system it is very difficult to correlated formaldehyde release with specific chemical structures of residues or reactants.     

Relative reactivities of amylose hydroxyl groups in the reaction with diketene

¹³C nuclear magnetic resonance (n.m.r.) spectra at 75.4 MHz of partially modified amylose with β-keto ester groups (degree of substitution (DS) ranging from 0.52 to 2.42) were studied in order to evaluate the selectivity of the reaction of amylose with diketene in the homogeneous phase. Analysis of the spectra of ring carbons in the anhydroglucose units shows that the reactivity of individual hydroxyl groups decreases in the order C-6>C-3>C-2 for DS values up to ∼1.8. For higher DS values a negative deviation is observed for the hydroxyl group at C-6 and a positive deviation for the hydroxyl groups at C-2 and C-3. The DS values determined by ¹³C n.m.r. spectra are in good agreement with those found by chemical analysis.     

ACCELERATED LIGHT-INDUCED AGING OF α-, β-, AND γ-13C-ENRICHED CELL WALL-DEHYDROGENATION POLYMERS STUDIED WITH SOLID STATE 13C NMR SPECTROSCOPY

ABSTRACT

Light-induced aging of lignocellulosic materials has been studied with a new technique involving selectively α-, β-, and γ-¹³C-enriched cell wall-dehydrogenation polymers (CW-DHPs) and solid state ¹³C NMR spectroscopy. The results from cross-polarization magic angle spinning (CP/MAS) ¹³C NMR experiments of unirradiated and irradiated CW-DHP have revealed mainly a decrease in the amount of end-groups of both coniferaldehyde and coniferyl alcohol type. The results suggest that these end-groups become saturated and that the terminal functionalites, i.e., γ-aldehyde and γ-hydroxymethyl groups, at least to some extent, are retained. The results indicate further that no detectable cleavage of the β-O-4 bonds occurs in the examined lignocellulosic model. In terms of proposed mechanisms of yellowing, there is marginal evidence that up to 2% of the α-labeled sites are converted by irradiation to α-carbonyls (aldehyde or ketones); moreover, we cannot dismiss the possibility that the precursor structures giving rise to these few α-carbonyls are β-O-4 structures. The ¹³C-enriched CW-DHP was formed directly on spruce (Picea abies) wood tissue (differentiating xylem) by administering selectively ¹³C-labeled coniferin at pH 6.0 in the presence of glucose oxidase and β-glucosidase, i.e., no phenol-oxidizing enzyme was added and the wood cells’ own enzymes polymerized the precursor.     

Fate of 13C-labelled alkyl groups on reductively alkylated Liddell coal during hydrogenation at 400°C

Medium volatile bituminous coal from Liddell, Australia, has been methylated and butylated using potassium in tetrahydrofuran (THF) and ¹³C-enriched reagents. The THF-insoluble material was examined by solid state ¹³C n.m.r. spectroscopy and found to have methyl or butyl groups incorporated into structures such as ethers, alkyl aromatics and, possibly, substituted hydroaromatics. The technique of dipolar dephasing was used to measure the relaxation time constants of the introduced alkyl groups in the coal structure which compared favourably with values for similar structures in model compounds. The alkylated coal was liquefied at 400°C and the products examined. It was shown that alkyl groups in ether structures were cleaved and reported as methane and butane in the gaseous products. Labelled alkyl groups were evident in the chloroform-soluble products and appeared to be in similar structures to those in the starting coal except for the loss of ether groups. Solid state n.m.r. examination of the residues, together with combustion analysis, showed that not all the introduced alkyl groups were lost during liquefaction at 400°C.     

New β-diketone-containing styrenic monomers and their polymers: Synthesis, keto-enol tautomerism and related fluorescence behavior

Three new β-diketone-containing styrenic monomers and their polymers were synthesized. The phenol and naphthol groups, and the electron-donating N,N-dimethylaniline groups were covalently attached to the β-diketone monomers at a designed position. The keto-enol tautomerism was characterized by ¹H, ¹³C NMR and UV-vis absorption spectroscopy. It was found that the β-diketone monomers exist in three forms, i.e. two cis-enol forms and one keto form. Their relative contents were determined by NMR spectroscopy. The β-diketone monomers bearing the phenol (1) and naphthol (2) groups display photoinduced enolization during UV irradiation due to the formation of intramolecular hydrogen bonds between the phenolic or naphtholic hydroxyl groups and the carbonyl groups. For their polymers and copolymers, however, photoinduced ketonization occurred during UV irradiation. The β-diketone monomer bearing N,N-dimethylaniline group (3) is a novel charge transfer fluorophore, which can be potentially employed as a dual-purpose functional monomer.     

Characterization of Anacardium occidentale exudate polysaccharide

The composition, structure and molar mass distribution of Anacardium occidentale exudate polysaccharide of Brazilian origin was investigated. The composition from gas–liquid chromatography (GLC) and ¹³C NMR was 72% β-D -galactopyranose, 14% α-D -glucopyranose, 4·6% α-L -arabinofuranose, 3·2% α-L -rhamnopyranose and 4·5% β-D -glucuronic acid. A thorough analysis of high resolution ¹³C NMR spectra from intact, partially hydrolysed and Smith-degraded polysaccharide enabled reliable chemical shift assignments to be made, and indicated the presence of three types of unit within the branched galactan core: linked at C-1 and C-3, at C-1 and C-6, and at C-1, C-3 and C-6. The polysaccharide was fractionated with respect to molar mass using water/ethanol as a solvent/non-solvent system. The polysaccharide and fractions were characterized by gel permeation chromatography (GPC), intensity light scattering, dilute solution viscometry and sedimentation velocity. The intrinsic viscosity in 0·1M aqueous NaCl at 25°C was found to depend on molar mass according to: [η]/(cm³g^-1)=0·052M^0·42. The molar mass distribution for the whole polysaccharide, determined by GPC using a universal calibration, exhibited two main peaks at 28000 and 67000gmol^-1, together with traces of much higher molar mass material. © 1998 SCI.     

d-NMR-Untersuchungen der behinderten Rotation am N?C(X)-Bindungsfragment. XIV. 13C-NMR-Spektren von β-Anilinovinyl-phenyl-thioketonen

d-N.M.R. Investigations of the Restricted Rotation at the N C(X) Bonding Fragment. XIV. ¹³C-N.M.R.-Spectra of β-Anilinovinyl-phenyl-thioketones N-phenyl-substituted β-anilinovinyl-phenyl-thioketones ( 1, 2 ) are investigated for restricted rotations about partial double bonds and preferential conformers by ¹H- and ¹³C-n.m.r. spectroscopy. Substituent dependent ¹³C-chemical shift variations and the strength control of the intramolecular hydrogen bridge are discussed.     

Some physical properties of acetosolv lignins from bagasse

Acetosolv-solubilized lignins were characterized by their solubility in different organic solvents, Fourier transform infrared, ¹³C-NMR, UV, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. Solvents having a solubility parameter in the range of 10–12.7 and a hydrogen-bonding parameter in the range of 3.6–5 were considered good solvents for acetosolv lignins. Fourier transform infrared spectra of the lignins were typical for lignins containing p-hydroxy phenylpropane (H), guaiacyl (G), and syringyl (S) units. The lignins contained more conjugated and fewer nonconjugated CO groups, and the guaiacyl groups were etherified and condensed. ¹³C-NMR confirmed partial acetylation of the lignins and the presence of β-O-4 and β-5 linkages. Acetosolv lignins also showed the typical UV spectrum of annual plants. The effects of the acetic acid concentration and pulping time on the molecular weights of the lignins were explained with the presieving and condensation concepts. The thermal behavior of the acetosolv lignins was also studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Comparing the effectiveness of radish cover crop, oilseed rape volunteers and oilseed rape residues incorporation for reducing nitrate leaching

The soil water and N dynamics have been studied during two long fallow periods (between wheat or oilseed rape and a spring crop) in a field experiment in Châlons-en-Champagne (eastern France, 48°50 N, 2°15 E). The experiment involved frequent measurements of soil water, soil mineral N, dry matter and N uptake by cover crops. Water and N budgets were established using Ritchie's model for calculating evapotranspiration in cropped soils and a model (LIXIM) for calculating water drainage, N leaching and N mineralisation in bare soils. During the first autumn and winter, a radish cover crop (grown from September 1994 to January 1995) was compared to a bare soil. During the second period (July 1995 to April 1996), a comparison was carried out between (i) oilseed rape volunteers, (ii) bare soil with two types of oilseed rape residues incorporated into the soil (R0 and R270 residues) and (iii) bare soil without residues incorporation. R0 and R270 residues came from two preceding oilseed rape crops which received two rates of N fertilizer (0 and 270 kg N ha^-1).Soil mineral N content was markedly reduced by the presence of radish cover crop or oilseed rape volunteers during autumn. The calculated actual evapotranspiration (AET) did not differ much between treatments, meaning that the transpiration by the cover crop or volunteers was relatively low (100–150 L kg^-1 of dry matter). Consequently, nitrate leaching was reduced during the rest of the winter and spring as well as nitrate concentration in the percolating water: 45 vs. 91 mg NO₃ ^- L^-1 for radish cover crop and bare soil, respectively. The incorporation of oilseed rape residues to soil also exerted a beneficial but smaller action on reducing the nitrate content in the soil. This effect was due to extra N immobilisation which reached a maximum of about 20 kg N ha^-1 in mid-autumn for both types of residues. Nine months after the incorporation of the oilseed rape residues, and comparing to the control soil without residues incorporation, N rich residues induced a significant positive N net effect (+ 9 kg N ha^-1) corresponding to 10% of N added whereas for N poor residues no net effect was still obtained at the end of experiment (–3 kg N ha^-1, not significantly different from 0).To reduce nitrate leaching during long fallow periods, it is necessary to promote techniques leading to decrease mineral-N contents in the soil during autumn before the drainage period, such as (i) residue incorporation after harvest (without fertiliser-N) and (ii) allowing volunteers to grow or sowing a cover crop just after the harvest of the last main crop.     

Analysis of SO3-Sulfonation products of 1-Alkenes by spectrometric methods

The preparation and identification of four types of SO₃-sulfonated products of 1-alkenes are described.¹³C and, to a lesser extent,¹H nuclear magnetic resonance spectra are used to ascertain the structures of 2-alkenesulfonic acids, β-sultones (as 2-methoxyalkanesulfonic acids), γ- and δ-sultones. The mass spectra of some methyl 2-methoxyalkanesulfonates and 4-alkyl-δ-sultones are also studied. Sufficiently volatile mixtures are separated by gas liquid chromatography after methylation of the sulfonic groups.     

Study on β-cyclodextrin grafting with chitosan and slow release of its inclusion complex with radioactive iodine

β-CD-2-CTS was synthesized by β-cyclodextrin reacting with p-toluenesulfonyl chloride, then grafting with chitosan. The infrared spectra analysis and ¹³C NMR confirmed that β-cyclodextrin reacted with p-toluenesulfonyl chloride at the 2-position carbon atom in the substituted glucose unit of β-cyclodextrin and formed β-CD-2-OTs. In the ¹³C NMR of β-CD-2-OTs, the characteristic peak of the 2-postion carbon atom in the substituted glucose unit of β-cyclodextrin appeared at 78.43 ppm. β-CD-2-CTS was characterized with infrared spectra analysis and X-ray diffraction. In the infrared spectra of β-CD-2-CTS, the characteristic peak of α-pyanyl vibration of β-CD was at 848.6 cm⁻¹. The characteristic peak of β-pyanyl vibration of CTS was at 894.9 cm⁻¹. The X-ray diffraction analysis showed that the peak at 2θ = 20° decreased greatly in β-CD-2-CTS. The polymer inclusion complex of β-CD-2-CTS with iodine was prepared and its inclusion ability was studied. The experimental results showed that a nice bit of iodine was included with β-CD-2-CTS and formed a stable inclusion complex. After the subcutaneous implantation of the polymer inclusion complex of β-CD-2-CTS with ¹³¹I₂ in rats, ¹³¹I₂ exhibited the property of slow release. ¹³¹I₂ in the blood of rats decreased slowly. ¹³¹I₂ in the blood of rats maintained approximately half of maximum for 70 days later, and maintained much higher radioactivity in the organs of rats compared to the inclusion complex of β-CD with ¹³¹ I₂, too. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2414–2421, 2001     

A study of the low temperature nitration of cellulose in mixed acids

The low temperature surface and bulk nitration of cellulose has been investigated by electron spectroscopy for chemical analysis (ESCA), ¹³C-NMR and X-ray diffraction. Acid mix composition has been probed at room temperature and at low temperatures (0–20°C) by Raman spectroscopy. This multitechnique approach has been employed to elucidate the behavior of surface degree of substitution (DOS) with acid mix composition over a 40°C temperature range. The data obtained have prompted a reinterpretation of previously reported work. Surface “equilibrium DOS” is shown to be established within 1 s at all temperatures investigated. but, at lower temperatures (> 5°C) the surface DOS as monitored by ESCA is observed to “dip” after immersion times of t < 5 s. This change in DOS is correlated with major structural changes in the fiber as observed by SEM. At low temperatures, e.g., ?15°C, nitration is shown to be complete throughout the cellulose fiber after 10 h nitration. Solution state ¹³C-NMR is used to compare the nitrate ester substitution distribution in cellulose nitrates prepared from acid mixes of the same composition at different temperatures.     

Reaction of poly(vinyl alcohol) with diketene

A study has been made on the modification of poly (vinyl alcohol) with diketene using tertiary amines as catalysts. The structure of the resulting polymers was determined by means of IR, ¹H- and ¹³C-NMR spectroscopy as well as by chemical analysis. Vinyl alcohol-vinyl acetoacetate (VAL-VAA) copolymers were obtained. It has been found a linear dependence of reaction rate on polymer, diketene and pyridine concentrations, respectively. The activation energy was found to be 35.5 kJ/mol (8.5 kcal/mol). ¹³C-NMR spectroscopy was used for the determination of the sequence distribution in VAL-VAA copolymers. The obtained results show that VAA units have a little alternating tendency in the copolymer chain. Polymeric chelates between VAL-VAA copolymers and cupric ions have been prepared. It is noteworthy that not all the β-keto ester groups in the VAL-VAA copolymers participate in binding cupric ions.     

Quantitative triacylglycerol analysis of whole vegetable seeds by1H and13C magic angle sample spinning NMR spectroscopy

High-resolution¹³C and¹H magic angle sample spinning nuclear magnetic resonance (NMR) spectra have been obtained and used to define the relative unsaturated acyl distribution of triacylglycerols in whole oil seeds. Inverse gated proton decoupled¹³C and¹H NMR spectra permit the quantitative analysis of seeds containing simple oils,e.g., sunflower seeds containing oleyl and linoleyl unsaturates only. More sensitive¹³C NMR techniques are necessary for the analysis of specific seed classes. One such class is the rapeseed, which is especially difficult due to its low oil content (≈ 2 mg oil/seed) and complex unsaturated acyl profile of oleyl, linoleyl, linolenyl, erucyl, and eicosenoyl. The Distortionless Enhancement by Polarization Transfer technique significantly improves sensitivity to the extent that single rapeseeds can be examined within an hour of acquisition time. Furthermore, some positional (1,3- or 2-glycerol attachment) groups can be identified leading to a partial estimation of the 1,3-, 2-acyl distribution.     

Two-dimensional spin-exchange solid-state NMR study of the crystal structure of cellulose II

A two-dimensional (2D) ¹³C-¹³C spin-exchange NMR experiment was applied to the uniformly ¹³C-enriched cellulose II in order to obtain interatomic distance information in the cellulose II crystal. A radio frequency-driven recoupling (RFDR) rotor-synchronized π pulse sequence was incorporated during the mixing time of the 2D experiment. The 2D spin-exchange NMR recorded with a short mixing time (0.80-2.58 ms) provided the correlations between a pair of strongly coupled ¹³C spins such as neighbor carbon nuclei. This spectrum enabled us to assign all ¹³C resonance lines of two kinds of anhydroglucose residues A and B in the structure of cellulose II. On the basis of the ¹³C resonance assignment of residues A and B, the interatomic distances from each C1 to the other carbon nuclei were compared by measuring the 2D spectra recorded with longer mixing times (5.12-20.48 ms). As a result, it was revealed that the respective residues A and B are composed of independent chains (-A-A- and -B-B- repeating units) and that there are no -A-B- repeating units in the chain. This experimental technique is expected to be applicable to conformation analysis of polysaccharides as well as the other cellulose polymorphs.     

Synthesis of poly(vinyl alcohol) derivatives containing amidoxime groups

The modification reaction of poly(vinyl alcohol) (PVAL) with acrylonitrile in alkaline medium was studied. The structure of the resulting polymers was determined by means of IR, ¹H and ¹³C NMR spectroscopy. The influence of solvent composition, catalyst and temperature was evaluated. ¹³C NMR spectroscopy was used for the determination of the sequence distribution of cyanoethylated PVAL (considered as a vinyl alcohol (VAL)-(2-cyanoethyl) vinyl ether (VCE) copolymer). The ¹³C NMR spectra of the methylene carbons in the main chain show three split peaks, the intensities of which change with copolymer composition. These peaks can be assigned to the three dyad sequences. The obtained results show that VCE units have an alternating tendency in the copolymer. Nitrile groups in cyanoethylated PVAL were converted to amidoxime groups by reaction with hydroxylamine. The reaction showed second order kinetics. The activation energy was found to be 51.6 kJ/mol. Soluble polymeric chelates between amidoximated PVAL and cupric ions have been prepared. It is noteworthy that not all the amidoxime groups participate in binding cupric ions.     

1H- und 13C-NMR-spektroskopische Messungen und MO-Berechnungen zur π-Elektronenstruktur von p,p′-disubstituierten trans-Stilbenen und substituierten trans-β-Styryl-methyl-sulfonen

¹H and ¹³C n.m.r. Spectroscopical Measurements and HMO-π-Calculations to the π-Electronic Structure of p,p′-Disubstituted trans-Stilbenes and Substituted trans-β-Styryl-methyl-Sulfones The ¹H and ¹³C n.m.r. spectra have been measured for a series of donator-acceptor-disubstituted trans-stilbenes 1 and monosubstituted β-styryl-methyl-sulfones 2 . The ¹³C n.m.r.-signals have been identified by comparison with empirical calculated chemical shifts and quantum chemical determined HMO-π-electrons densities. The influence of substitutents to the experimental chemical shifts are discussed in detail. For 1 and 2 exist linear correlations between chemical shifts and HAMMETT values, and π-electron densities, respectively.     

C NMR study of C-enriched single-wall carbon nanotubes synthesized by catalytic decomposition of methane

¹³C NMR spectra and spin-lattice relaxation times were measured for single-wall carbon nanotubes with 99.9 and 50.0% ¹³C enrichments and natural abundance (1.1% ¹³C) prepared by catalytic decomposition of CH₄. The ¹³C isotropic shift is about 116 ppm from tetramethylsilane, being estimated from magic-angle-spinning (MAS) spectra. The value does not depend on the degree of the ¹³C enrichment. The ¹³C MAS NMR spectra show two additional small peaks at 171 and 152 ppm, which are ascribed to carbon species at defects or edges. The line widths of the main isotropic peak in MAS spectra are about 30 ppm, the origin of which is mostly chemical shift dispersion, reflecting a distribution of diameter and helicity. The line width in the ¹³C static spectra originates from chemical shift dispersion, chemical shift anisotropy and dipole–dipole interactions between ¹³C spins as well as between ¹³C and ¹H spins at defects or edges. ¹H NMR spectra confirm the presence of H-containing species. The ¹³C spin-lattice relaxation is dominated presumably by interaction with magnetic impurities.