Characterization of the supermolecular structure of cellulose in wood pulp fibres

The hierarchic organization of cellulose fibrils (microfibrils) was investigated in holocellulose, sulphite pulp and kraft pulp using TEM, XRD, ED and FTIR. There were remarkable differences in both the fibril structure and fibril aggregation between the samples. TEM observations revealed more intimately associated fibrils in the kraft pulp compared to the sulphite pulp and the holocellulose, results in agreement with previous CP/MAS ¹³C-NMR data [Hult E.-L. et al. (2002) Holzforschung 56: 231–234]. Furthermore, the cellulose crystallinity was higher in the kraft pulp sample. With respect to the cellulose I and I allomorphs, these samples were controversial when different analytical techniques were applied. Due to the small fibril size and the low degree of order of cellulose in these samples, the concept of crystalline triclinic and monoclinic components as determined by diffraction analysis may not be adequate. Instead the fibril can be regarded to have different degrees of lateral order (including paracrystalline ordering) that can be reoriented to I type conformation and packing upon pulping.     

On the accessibility and structure of xylan in birch kraft pulp

The structure of -(14)-xylan, both in isolated form and as a component of bleached birch kraft pulp, was studied employing CP/MAS ¹³C NMR spectroscopy. Bleached birch kraft pulp was treated with xylanases or alkali in order to distinguish between accessible and inaccessible xylan. In xylan which was alkali-extracted from bleached birch kraft pulp, the relative contents of xylose and 4-O-methylglucuronic acid were 99.4 and 0.6 weight %, respectively, and the degree of polymerization was 70. The supermolecular structure of xylan is very sensitive to the surrounding environment. All extracted xylan chains were accessible to water and methanol and the solvent molecules easily exchanged. In bleached birch kraft pulp, cellulose fibrils interact with xylan chains, causing these to adopt a conformation similar to one of the configurations observed for dry xylan. In birch pulp, about 1/3 of the xylan was found to be accessible to digestion by xylanases or extraction with 5% w/w potassium hydroxide (aq). A signal at 81.7ppm in the C-4 region of the CP/MAS ¹³C NMR spectrum of bleached birch kraft pulp originated from xylan at the accessible fibril surfaces. A portion of a broad signal at 83.5ppm reflected inaccessible xylan, which is probably present as co-aggregates with cellulose fibril aggregates.     

The cellulose system in viscin from mistletoe berries

The cellulose system of the viscous fibrous cellulosic polysaccharide (viscan) in the viscin tissue of the European mistletoe, Viscum album L., was analyzed by chemical and physicochemical techniques including sugar analysis, optical and transmission electron microscopy, X-ray and electron diffraction together with solid state CP/MAS ¹³C-NMR spectroscopy. The results confirmed that in the elongated thin viscin cells, the cellulose microfibrils (having a diameter of around 3 nm) were tightly coiled with their axes perpendicular to the long axis of the cell. Upon stretching these cells became deformed by more than a hundred fold. In such a deformation, the cellulose microfibrils became unwound to be perfectly aligned along the stretching direction. Based on solid-state CP/MAS ¹³C-NMR spectroscopic analysis of the viscin tissue, it was found that its cellulose consisted of I and I polymorphs in the ratio 1:1.     

13C-NMR-Untersuchungen von Substituenteneffekten in mehrfach substituierten Benzen-und Naphthalenverbindungen: Inkrementberechnungen der13C-chemischen Verschiebungen

Summary The aryl¹³C chemical shifts of Cl-substituted 4-amino-, 4-diazonium-N,N-dimethylanilines, N,N-dimethylanilines and differently substituted naphthalenes were assigned by means of different NMR methods. The assignments were compared with chemical shifts obtained by using empirical additivity relationship for mono substituted aromatic substances. As a means of substitutent interactions, the chemical shift difference between calculated and experimental values ( _c ⁱ ) has been used. In the presence of remarkable steric and electronic substituent interactions, large deviations from additivity ( _c ⁱ values up to 15.4 ppm) were found. Which originate primarily from steric interactions between the substitutents. In order to account therefore, correction increments have been developed by employing the _c ⁱ values obtained from 1,2-disubstituted benzenes or naphthalenes. The¹³C chemical shifts of more than seventy substituted benzenes and naphthalenes have been predicted. The results corroborate that reasonable calculation of chemical shifts in sterically hindered benzenes is possible by using the extended additivity rule. The _c ⁱ values are much lower and allow reasonable structural assignments.For external users of this incremental system, a computer program for IBM compatible PC/AT was developed. By means of this program, the¹³C chemical shifts for different benzenes and naphthalenes with or without 1,2-disubstituted correction increments will be calculated and the corresponding spectrum displayed. The program can assist the successful assignment of experimental¹³C chemical shifts.

     

Interaction of cellulose with amine oxide solvents

Cellulose I, mainly as ramie or as Avicel microcrystalline cellulose, has been monitored by optical microscopy and by ¹³C CPMAS NMR, over the course of its dissolution in hot N-methylmorpholine N-oxide solvent. Its interaction with the near-solvent N-ethylmorpholine N-oxide and related non-solvents has also been investigated. NMR shows that N-methylmorpholine N-oxide partly converts crystalline cellulose I into amorphous solid cellulose. The changes in chemical shift imply increased flexibility at the glycosidic bonds. In contrast, N-ethylmorpholine N-oxide converts cellulose I to cellulose III_I, without dissolution. Microscopy shows that the ramie fibres swell laterally, and at least some also shorten longitudinally, during dissolution. Model studies using methyl--d-glucopyranose show no evidence from ¹³C chemical shifts for different modes of binding with different solvents. However, N-methylmorpholine N-oxide binds more strongly to methyl--d-glucopyranose in DMSO than does N-ethylmorpholine N-oxide, whereas N-ethylmorpholine N-oxide binds better to H₂O. Also, ¹³C T ₁ values for aqueous cellobioside show increasing rotational freedom of the –CH₂OH sidechains as N-methylmorpholine N-oxide is added. Together, these observations imply the initial penetration of solvents and near-solvents between the molecular cellulose sheets. Subsequently, N-methylmorpholine N-oxide breaks H-bonds, particularly to O-6, just sufficiently to loosen individual chains and then dissolve the sheets.     

In Situ crystallization of bacterial cellulose I. Influences of polymeric additives,stirring and temperature on the formation celluloses I α and I β as revealed by cross polarization/magic angle spinning (CP/MAS)13C NMR spectroscopy

To obtain further information about the formation of cellulose I and I, cross polarization/magic angle spinning (CP/MAS)¹³C NMR spectroscopy was used to study the effects of polymeric additives, stirring and culture temperature on the I When xyloglucan (XG) or carboxymethyl cellulose sodium salt (CMC) was added to the incubation medium, the amount of cellulose I decreased markedly, from a normal level of 64% to as low as 30%, with the most additive giving the lowest levels of I. Moreover, stirring causes mixtures containing even small amounts of XG to have a large effect. These results suggest that CMC or XG interferes with the aggregation of fibrillar units into the normal ribbon assemblies. It may be that there is a strain associated with this aggregation that results in the higher-energy I form. Thus, cellulose I may grow preferentially when the strain caused by aggregation is not present. Lower temperatures (36–10 °C) gave an increase in I (from 56 to 72%).     

pH-dependence of 31P-NMR spectroscopic parameters of monofluorophosphate, phosphate, hypophosphate, phosphonate, phosphinate and their dimers and trimers

³¹P-NMR chemical shifts and coupling constants of nine inorganic phosphorus compounds composed of different structural units or oxidation numbers P^V, P^IV, P^III, and P^I were measured in the pH-range 3 11. A concise map of NMR data providing the pH-dependence of the chemical shift (-pH map) was set up to be used for identifying phosphorus compounds under varying pH-conditions. Chemical shifts of monofluorophosphate, as well as most phosphorus compounds of oxidation numbers 5 and 4, were greatly dependent on pH, in contrast to the less or negligible pH-dependence of phosphorus compounds of oxidation numbers 1 and 3. Monofluorophosphate gave the parameters: =+1.3±0.2 ppm and ¹J_PF=870±0.2 Hz, that remained unchanged at pH>6, but varied at pH<6. The practical use of the -pH map was shown with a few kinetic experiments in which monofluorophosphate was enzymatically hydrolyzed by alkaline phosphatase (EC3.1.3.1) at pH 7.2 and non-enzymatically at pH 3.     

Substituent Distribution of Cyanoethyl Cellulose

Estimation of the substitution distribution for cyanoethyl cellulose was carried out by ¹H and ¹³C NMR spectroscopic analyses after the additional acetylation. Based on the complemental function of cyanoethyl and acetyl substituents, the degree of substitution (DS) of cyanoethyl groups could be calculated from the ratios of the ¹H integrated intensities in acetyl methyl ( 1.8–2.1) and cyanoethyl methylene ( 2.6–2.9) protons, and also from the corresponding ratios for acetyl methyl carbon signals ( 19.7–21.3) and cyanoethyl methylene carbon signals ( 17.5–19.0). Good agreement was obtained between the DS values obtained from the NMR spectroscopic analyses and those determined by the conventional nitrogen content method, indicating the validity of the NMR method used. In addition, the NMR method was found to be effective in determining the positional substituent distribution by the quantitative analysis of the three cyan carbon signals ( 118–120).     

A multivariate characterization of crystal transformations of cellulose

A spectroscopic study of cellulose transformation processes, such as alkali treatment and annealing, showed that, in combination with multivariate data analysis techniques, a detailed understanding of the crystalline transformation processes could be reached.¹³C cross-polarization magic-angle spinning (CPMAS) NMR and near-infrared (NIR) spectroscopy of cotton linters and softwood pulps analysed during the processing revealed information, after data reduction using principal components data analysis, that could be connected to structural changes of the cellulose polymorphs. The data showed that alkali treatment of cotton linters led to a cellulose conversion from cellulose I to II, while annealing, both for linters and pulps, yielded a transformation from I to I.     

In situ crystallization of bacterial cellulose II. Influences of different polymeric additives on the formation of celluloses Iα and Iβ at the early stage of incubation

Effects of polymeric additives with different degrees of polymerization (DP) or substitution (DS) on the crystallization of celluloses I and I have been examined at an early stage of the incubation of Acetobactor xylinum by using newly developed FT-IR spectroscopy. It was found that the mass fraction of cellulose I is greatly decreased with increasing concentrations of carboxymethyl cellulose sodium salt (CMC) or xyloglucan (XG) in the incubation medium. Such a decrease in the mass fraction of cellulose I, which corresponds to the enhanced crystallization of cellulose I, is more prominent for CMC or XG with lower DPs, but the additives with too low DPs are not so effective probably due to higher solubility and the lower adhesion on the surface of microfibrils. Moreover, the mass fractions of celluloses I and I are highly correlated with the crystallite size of microfibrils, indicating that I is crystallized in larger-size microfibrils while I is produced in smaller-size microfibrils. On the basis of these experimental results, the mechanism of the crystallization of celluloses I and I is discussed in the Acetobactor xylinum system.     

The phase equilibria in some binary systems containing stearic alcohol

The liquid — liquid and liquid — solid equilibrium temperatures are taken for the binary systems octadecanol + A (A=dicarboxylic acids, biphenyl or (K, Na) stearate). The results are discussed and a relation connecting the composition of the eutectics with the thermodynamic properties of fusion of the components is derived from the ideal equation and compared with the experimental one.

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Zusammenfassung Die Flüssig-Flüssig- und Flüssig-Fest-Gleichgewichtstemperaturen der binÄren Systeme Octadecanol + A (A=DicarboxylsÄuren, Diphenyl oder (K, Na/ Stearat) wurden ermittelt. Die Ergebnisse werden diskutiert und ein Zusammenhang zwischen der Zusammensetzung der Eutektika und den Thermodynamischen Eigenschaften der Schmelze der Komponenten wird aus dem Vergleich der idealen und der auf dem Versuchswege erhaltenen Gleichungen abgeleitet.

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Résumé On a mesuré les températures des équilibres liquide-liquide et liquide-solide des systèmes binaires octadécanol + A (A=acides dicarboxyliques, diphényle ou stéarate de potassium, sodium). On discute les résultats et l'on établit une relation entre la composition des eutectiques et les propriétés thermodynamiques de fusion des constituants, dérivée de l'équation initiale et comparée avec la relation expérimentale.

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- - + A (A = , (K, Na) ). , .

     

Error of Atomic Charges Derived from Electrostatic Potential

The purpose of this article is to show that CHELP, CHELPG, and Merz and Kollman undergo error for the charge on atoms of HCOO^– (H₂O) _n for n = 1 6. We also demonstrate that the CHELP, CHELPG, and Merz and Kollman show error for the tendency toward change in the charges on carbons for CH₃NH⁺ ₃ (CH₃)₂NH⁺ ₂ (CH₃)₃NH⁺ (CH₃)₄N⁺.     

Determination of the <Superscript>13</Superscript>C chemical shift anisotropies of cellulose I and cellulose II

The chemical shift anisotropies (CSAs) of cellulose I and I, the two crystalline constituents of bacterial cellulose produced by Acetobacter xylinum (DSM 14666), and regenerated cellulose II are reported for each of the spectroscopically resolved carbon resonances using the phase adjusted spinning sideband (PASS) experiment. The data are compared with experimental results using the recoupling of anisotropy information (RAI) technique and with theoretical calculations of the structure of cellulose, including the hydrogen bonding systems.     

Use of13C chemical shift/charge density linear relationship for ranking chemical structures

A novel approach to molecular structure elucidation based on ranking chemical structures in agreement with the¹³C NMR chemical shift/charge density linear relationship is suggested. The structure having the lowest standard approximation error (SAE) is considered to be the correct one. Each ranked structure is additionally tested for the¹³C chemical shift equivalence corresponding to its constitutional symmetry (in terms of the charge densities).This paper is Part VI of the series Automatic assignment of¹³C NMR signals. For Part V see ref. [1].     

Synthesis of 2-[β-(5′-halogenofur-2′-yl)vikyl]benzimidazoles

2-[-(5-halogenofur-2-yl)vinyl]benzimidazoles (I) have been synthesized by the condensation of o-phenylenediamine with 5-halogeno-fur-2-ylacroleins or of 2-methylbenzimidazole with 5-halogenofurfurals. The methiodides of the 1-methyl-substituted derivatives ofI readily react with secondary amines (piperidine, dimethylamine)giving methiodides of 2-[-(5-dialkylaminofur-2-yl)vinyl]-1-methylbenzimidazoles.     

Secondary structure of peptides 16th. Characterization of proteins by means of13C NMR CP/MAS spectroscopy

50.3 or 75.4 MHz¹³C NMR cross-polarization/magic angle spinning spectra of human hair, horse hair, horse hoof, parrot feather, sperm whale myoglobin, and horse heart cytochrome C were measured. The spectra of human hair and horse hair indicate nearly equal mole fractions of-sheets and-helices and a low percentage of amorphous regions, whereas horse hoof contains a higher fraction of amorphous proteins. The parrot feathers contain a small-helix fraction (ca. 10±5 %) in additon to a large-sheet fraction whereas cytochrome C contains 70–90%-helices. The spectrum of myoglobin could not interpreted in terms of defined secondary structures. The usefulness of the¹³C NMR CP/MAS spectroscopy for the characterization of proteins is compared with that of IR spectroscopy and X-ray diffraction.     

Comparative study of measured and critically evaluated resonance integral to thermal cross-section ratios. Part II

The present paper deals with the experimental determination and the critical evaluation of Q_o, the ratio of the resonance integral (I_o) to the 2200 m.s^–1 cross-section (_o) for 57 analytically interesting (n, ) reactions, including a revision and updating of formerly published results for 13 isotopes. Full account is given for deviations from the ideal epithermal neutron flux distribution. The Budapest-Gent cooperative determinations, yielding parallel but independent results, lead to recommended Q_o-values with an average uncertainty as low as 3%. Finally, with the aid of independently evaluated or measured _o-data, a list of recommended I_o-values is given.     

Alkaloids of Arundo donax. XII. Structure of the New Dimeric Indole Alkaloid Arundacine

The new dimeric indole alkaloid arundacine is isolated from the polar fraction of the total alkaloids from Arundo donax L. roots. The structure 3-N,N-dimethylaminoethyl-5-hydroxy-4-(3-N-acetyl-N-methylaminoethylindol-1-yl)indole is established using spectral data (IR, UV, mass, one-dimensional ¹H and ¹³C NMR, various two-dimensional spectra).     

X-ray diffraction studies on homologous thallium soaps below the temperature range of the neat phase 1. Calculation and comparison of the structure parameters of unit cells

The results of X-ray diffraction patterns of homologous thallium soaps TlC _n (n-8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 20 and 22) in dependence on the temperature showed that the structures of the phases below the temperature range of the liquid-crystalline neat phase (so called phase C₁, phase C₂, phase I, phase II) are crystalline-like, not liquid-crystalline.As function of the chain length of the fatty acid group, we found the following phase sequences to be a function of temperature: TlC₈: phase Ineat phase: TlC₉–Tl₁₄: phase C₂phase IIphase Ineat phase; TlC₁₅, TlC₁₆: phase C₁phase IIphase Ineat phase; TlC₁₇–TlC₂₂: phase C₁phase IIneat phase.From the X-ray patterns of the thallium soaps were calculated the lattice parameters and the unit cells of these homologues at various temperatures. The comparison between the lattice parameters of the homologues showed, surprisingly, that these parameters were independent of chain length and temperature. This X-ray data are the basis for the following development of structure models of the phase C₁, phase C₂, phase I, and phase II, including the neat phase (see Part 2).     

NMR study of diastereoisomerism of 2-(1-aminoethyl)bicyclo[2.2.1]heptane and its hydrochloride (deitiforin)

The assignment of the signals for the H and C atoms of four diastereomers (without their separation) of 2-(1-aminoethyl)bicyclo[2.2.1]heptane (1) and its hydrochloride (2) (the antiviral drug deitiforin) was performed for the first time by two-dimensional ¹H and ¹³C NMR spectroscopy. The effects of the substituent at position 2 of norbornane on the chemical shifts of the -, -, and -carbon atoms of the bicycle were examined using the increments for alkanes. The changes in the chemical shifts of the C(6) and C(7) atoms are substantially larger than those for the other C atoms, which made it possible to identify the exo and endo forms. Each of these forms exists as a mixture of two diastereomers. The effect of the positive charge of the N atom on the -protons, which are closely spaced, but separated by a number of covalent bonds, was considered on going from amine 1 to hydrochloride 2. Based on significant changes in shielding of these H atoms, the configurations of the asymmetric center in the CHMe(NH₂) substituent of the diastereomers were established.