Accessibility of hydroxyl groups in birch kraft pulps quantified by deuterium exchange in D2O vapor

Deuterium exchange in a deuterium oxide (D₂O) atmosphere (95 % relative humidity), quantified by a dynamic vapor sorption (DVS) apparatus, was applied for assessing the accessibility of hydroxyl groups in birch kraft pulps. Achieving the maximum deuteration level exhibited slower kinetics than was earlier reported for experiments with ground wood and bacterial cellulose. The deuterium exchange process followed two parallel phenomena. Applying multiple drying and rewetting cycles gave kinetic information also on the hornification phenomenon occurring during these cycles. Dry birch pulps treated with sodium hydroxide solution of varying alkalinities at elevated temperatures were assessed for their accessible hydroxyl groups by DVS with deuterium exchange. This method was evaluated against deuteration combined with Fourier transform infra-red spectroscopy and water retention value (WRV). DVS measurements were in correlation with WRV and both the methods indicated that an alkaline treatment of dry birch pulp improves cellulose accessibility. The level of irreversible deuteration also decreased as the alkalinity was increased. DVS was shown to provide quantitative information on the accessibility but to be a time-consuming method for the pulp samples. A potential means to decrease the duration of the measurement is increased D₂O exposure by excluding the drying phases.     

Acid Hydrolysis of Hemicellulose in Green Liquor Pre-Pulping Extract of Mixed Northern Hardwoods

Forest biomass is a promising resource for future biofuels and bioproducts. Pre-pulping extraction of hemicellulose by alkaline (Green Liquor) pretreatment produces a neutral-pH extract containing hemicellulose-derived oligomers. A near-term option for use of this extract is to hydrolyze the oligomers to fermentable monomer sugars. Chips of mixed northern hardwoods were cooked in a rocking digester at 160 °C for 110 min in Green Liquor at a concentration of 3% Na₂O equivalent salts on dry wood. The mass of wood extracted into the Green Liquor extract was approximately 11.4% of the debarked wood mass, which resulted in a dilute solution of oligomeric hemicelluloses sugars. The concentration of the extract was increased through partial evaporation prior to hydrolysis. Dilute sulfuric acid hydrolysis was applied at conditions ranging from 100 to 160 °C, 2% to 6% (w/v) H₂SO₄, and 2- to 258-min residence time. The maximum fermentable sugar concentration achieved from evaporated extract was 10.7 g/L, representing 90.7% of the maximum possible yield. Application of the biomass pretreatment severity function to the hydrolysis results proved to offer a relatively poor prediction of temperature and reaction time interaction. The combined severity function, which incorporates reaction time, temperature, and acid concentration, did prove to provide a useful means of trading off the combined effects of these three variables on total sugar yields.     

Purification and Characterization of the Xylanase Produced by Jonesia denitrificans BN-13

Jonesia denitrificans BN-13 produces six xylanases: Xyl1, Xyl2, Xyl3, Xyl4, Xyl5, and Xyl6; the Xyl4 was purified and characterized after two consecutive purification steps using ultrafiltration and anion exchange chromatography. The xylanase-specific activity was found to be 77 unit (U)/mg. The molecular weight of the Xyl4 estimated using sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) revealed a monomeric isoenzyme of about 42 kDa. It showed an optimum pH value of 7.0 and a temperature of 50 °C. It was stable at 50 °C for 9.34 h. The enzyme showed to be activated by Mn⁺², β-mercaptoethanol, and dithiothreitol (DTT) with a high affinity towards birchwood xylan (with a K _m of 1 mg ml^?1) and hydrolysis of oat-spelt xylan with a K _m of 1.85 mg ml^?1. The ability of binding to cellulose and/or xylan was also investigated.     

Cp/mas 13c nmr and Electron Diffraction Study of Bacterial Cellulose Structure Affected by Cell Wall Polysaccharides

Acetobacter xylinum was cultured in Schramm–Hestrin medium containing pectin (pectin medium), xylan (xylan medium), or glucomannan (mannan medium). X-ray diffractometry revealed that xylan and glucomannan affected the size of the cellulose crystals and their d-spacing values. Solid-state cross polarization magic angle spinning carbon-13 nuclear magnetic resonance spectroscopy indicated that the ratio of cellulose I was reduced by the addition of polysaccharides. These effects were more remarkable on the cellulose in the mannan medium than that in the xylan medium, and were scarcely observed in the pectin medium. Electron diffraction analysis revealed that these effects on hemicelluloses along cellulose microfibrils are continuous in the mannan medium and discontinuous in the xylan medium. These findings suggest that the uronic acid in the polysaccharides prevents interactions with cellulose leading to alterations of the structure of the cellulose crystal.     

Mesoporous structures in never-dried softwood cellulose fibers investigated by nitrogen adsorption

Nitrogen adsorption was used to characterize mesoporous structures in never-dried softwood cellulose fibers. Distinct inflections in desorption isotherms were observed over the relative vapor pressure (P/P₀) range of 0.5–0.42 for never-dried cellulose fibers and partially delignified softwood powders. The reduction in N₂ adsorption volume was attributed to cavitation of condensed N₂ present in mesopores formed via lignin removal from wood cell walls during delignification. The specific surface areas of significantly delignified softwood powders were ~150 m² g^?1, indicating that in wood cell walls 16 individual cellulose microfibrils, each 3–4 nm in width, form one cellulose fibril bundle surrounded with a thin layer of lignin and hemicelluloses. Analysis of N₂ adsorption isotherms indicates that mesopores in the softwood cellulose fibers and partially delignified softwood powders had peaks ranging from 4 to 20 nm in diameter.     

Purification and properties of a SDS-resistant xylanase from halophilic Streptomonospora sp. YIM 90494

An extracellular xylanase from halophilic Streptomonospora sp. YIM 90494 was purified to homogeneity from a fermentation broth by ammonium sulphate precipitation, gel filtration chromatography and ion exchange chromatography. The purified xylanase appeared as a single protein band on SDS-PAGE with a molecular mass of approximately 50 kDa. The xylanase had maximum activity at pH 7.5 and 55 °C. The enzyme was stable over a broad pH range (pH 4.0–10.0) and showed good thermal stability when being incubated at 60 °C for 2 h. Kinetic experiments indicated that the enzyme had K _m and V _max values of 19.24 mg/mL and 6.1 μmol/min/mg, respectively, using birch wood xylan as substrate. The inhibitory effects of various metal ions and chemical agents on the xylanase activity were investigated. It is greatly interesting to note that Ag⁺ ion and SDS, which strongly inhibited most xylanases reported previously increases the xylanase activity in this study. These characteristics suggest that the enzyme with new properties has considerable potential in industrial applications.     

Dielectric properties of lignin and glucomannan as determined by spectroscopic ellipsometry and Lifshitz estimates of non-retarded Hamaker constants

We present in this study a quantitative estimate of the dispersive interactions between lignin, hemicellulose and cellulose, which are the dominating components in wood and also extensively used to produce paper and packaging materials. The dielectric properties in the UV-visible region of spin-coated films of pure lignin and glucomannan were determined by spectroscopic ellipsometry. The non-retarded Hamaker constants were estimated from the determined spectral parameters using Lifshitz theory for lignin and glucomannan interacting with cellulose, titania and calcium carbonate in vacuum, water and hexane. The Hamaker constants for the different combinations of cellulose, lignin and glucomannan fall within a relatively narrow range of 35–58 and 8–17 zJ, for the values in vacuum (air) and water, respectively. The estimated Hamaker constants for the interactions of the wood components with TiO₂ and CaCO₃, common additives in paper, in water range from 3 to 19 zJ, thus being similar in magnitude as the interactions between the wood components themselves. In contrast, the Hamaker constant is essentially zero for glucomannan interacting with calcium carbonate in hexane. The Hamaker constants for lignin, hemicellulose and cellulose determined in this study can provide information regarding the surface interactions important for e.g. adhesion, friction, swelling and wetting in paper processing as well as for the resulting behavior of paper products.     

Atmospheric Pressure Plasma Pretreatment of Sugarcane Bagasse: The Influence of Moisture in the Ozonation Process

Sugarcane bagasse samples were pretreated with ozone via atmospheric O₂ pressure plasma. A delignification efficiency of approximately 80 % was observed within 6 h of treatment. Some hemicelluloses were removed, and the cellulose was not affected by ozonolysis. The quantity of moisture in the bagasse had a large influence on delignification and saccharification after ozonation pretreatment of the bagasse, where 50 % moisture content was found to be best for delignification (65 % of the cellulose was converted into glucose). Optical absorption spectroscopy was applied to determine ozone concentrations in real time. The ozone consumption as a function of the delignification process revealed two main reaction phases, as the ozone molecules cleave the strong carbon–carbon bonds of aromatic rings more slowly than the weak carbon–carbon bonds of aliphatic chains.     

Cellulose crystallinity and ordering of hemicelluloses in pine and birch pulps as revealed by solid-state NMR spectroscopic methods

Solid-state ¹³C NMR spectroscopy was used to determine the degree of cellulose crystallinity (CrI) in kraft, flow-through kraft and polysulphide–anthraquinone (PS–AQ) pulps of pine and birch containing various amounts of hemicelluloses. The applicability of acid hydrolysis and the purely spectroscopic proton spin-relaxation based spectral edition (PSRE) method to remove the interfering hemicellulose signals prior to the determination of CrI were also compared. For softwood pulps, the spectroscopic removal of hemicelluloses by PSRE was found to be more efficient than the removal of hemicelluloses by acid hydrolysis. In addition to that, the PSRE method also provides information on the associations between cellulose and hemicelluloses. On the basis of the incomplete removal of xylan from the cellulose subspectra by PSRE, the deposition of xylan on cellulose fibrils and therefore an ordered ultrastructure of xylan in birch pulps was suggested. The ordered structure of xylan in birch pulps was also supported by the observed change of xylan conformation after regeneration. Similarly, glucomannan in pine pulps may have an ordered structure. According to the ¹³C CPMAS measurements conducted after acid hydrolysis, the degree of cellulose crystallinity was found to be slightly lower in birch pulps than in the pine pulps. Any significant differences in cellulose crystallinity were not found between the pulps obtained by the various pulping methods. Only in pine PS–AQ pulp, the degree of cellulose crystallinity may be slightly lower than in the kraft pulps containing less hemicelluloses.     

Characterization of hydrothermally isolated xylan from beech wood by capillary electrophoresis with laser-induced fluorescence and mass spectrometry detection

Hemicelluloses such as xylans play an increasing role as renewable raw materials for technological applications. The complex and variable composition of hemicelluloses requires powerful analytical techniques in order to assess their composition. In the present study, the neutral fraction of hydrothermally isolated xylan from beech wood was characterized by capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) upon derivatization with 8-aminopyrene-1,3,6-trisulfonic acid. Reproducible separation of the xylo-oligosaccharides was achieved using a polyvinyl alcohol coated capillary and a 25 mM sodium acetate buffer, pH 4.75, as background electrolyte at an applied voltage of ?30 kV. Intermediate precision expressed as relative standard deviation was below 2.0 % for migration times and below 10 % for relative peak areas except for the oligomers present at very low concentrations only. At the same time, derivatization conditions proved to be robust as well. Samples obtained by fractionation of the xylan were subsequently characterized by CE-LIF. In addition, capillary electrophoresis with mass spectrometry detection indicated the presence of small amounts of xylo-oligosaccharides containing additional sugar moieties such as 4-O-methylglucuronic acid. Moreover, minor components containing acetyl groups could be detected. The presence of these impurities was confirmed by nuclear magnetic resonance analysis of the fractions. In conclusion, although none of the techniques applied here gave a complete picture of the composition of the investigated xylan or its fractions, the combination provided insight into the complexity of the sample.     

Application of Pigeon Pea (Cajanus cajan) Stalks as Raw Material for Xylooligosaccharides Production

Pigeon pea (Cajanus cajan) is a perennial plant widely cultivated in tropical and subtropical regions of many countries. The present studies aimed to produce xylooligosaccharides (XOS) from pigeon pea stalks in order to do value addition. The chemical analysis of stalks revealed 18.33?±?1.40 % hemicelluloses in addition to cellulose, protein, and lignin. Sodium hydroxide coupled with steam application enabled almost 96 % recovery of original xylan, present in the pigeon pea stalks. Enzymatic hydrolysis of xylan led to production of XOS namely, xylobiose and xylotriose. Response surface model indicated a maximum yield of xylobiose (0.502 mg/ml) under the hydrolysis conditions of pH 4.91, temperature at 48.11 °C, enzyme dose at 11.01 U, and incubation time at 15.65 h. The ideal conditions for higher xylotriose yield (0.204 mg/ml) were pH 5.44, temperature at 39.29 °C, enzyme dose at 3.23 U, and incubation time at 15.26 h. The present investigation was successful in assessing the prospect of using pigeon pea stalks as a raw material for xylan extraction vis-à-vis XOS production.     

A procedure for determining the concentration of Hydroxyl Groups on Silica Surfaces

By determining the concentration of D₂O in D₂O/H₂O liquid mixtures, it has been possible to develop a method to obtain the concentration of hydroxyl groups on the surface of silica gel. The results of 4.4 ± 0.2 –OH groups per 100 Ų of surface are in good agreement with the findings of other workers.     

SEC-MALLS analysis of TEMPO-oxidized celluloses using methylation of carboxyl groups

Two cellouronic acids [sodium (1 → 4)-β-polyglucuronates, CUAs] and one 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized wood cellulose (TOC) became soluble in 8 % lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) after the methylation of C6 carboxyl groups in these samples using trimethylsilyldiazomethane (TMSD). The obtained solutions were diluted to 1 % LiCl/DMAc and subjected to size-exclusion chromatography combined with multi-angle laser-light scattering (SEC-MALLS). Neither depolymerization nor side reactions took place during methylation; this was confirmed by SEC-MALLS and nuclear magnetic resonance analyses, using CUAs as models. The SEC-MALLS analysis of the original wood cellulose and the carboxyl-methylated TOC prepared from it, using 1 % LiCl/N,N-dimethyl-2-imidazolidinone and 1 % LiCl/DMAc, respectively, as eluents, showed that the weight-average degree of polymerization of the original wood cellulose decreased from 3,100 to 2,210 through TEMPO-mediated oxidation. The molecular-mass distributions of the original wood cellulose and the TOC both consisted of one large peak with a small shoulder, indicating that some of the oxidized hemicelluloses remained in the TOC. The combination of methylation of carboxyl groups in polysaccharides using TMSD and subsequent SEC-MALLS analysis using 1 % LiCl/DMAc as an eluent may be applicable not only to TOCs, but also to other polysaccharides with carboxyl groups, for evaluation of their molecular-mass parameters.     

Enhanced deconstruction and dissolution of lignocellulosic biomass in ionic liquid at high water content by lithium chloride

Fabricating an aqueous ionic liquid (IL) for deconstruction and dissolution of lignocellulose is attractive because addition of water could reduce the cost and viscosity of the solvent and improve the biomass processing, but the solvating power of the IL is usually depressed in the presence of water. In the present study, an aqueous IL consisting of 1-butyl-3-methylimidazolium chloride (BmimCl), water, and lithium chloride was fabricated for efficient deconstruction and dissolution of lignocellulose (bamboo). The dissolution of cell wall components (cellulose, lignin, and hemicelluloses) in the aqueous IL was investigated. The results indicated that the presence of water significantly reduced the solvating power of BmimCl; For example, 11.5 % water decreased the dissolution of bamboo in BmimCl from ~97 to ~53 %. Dissolution of cellulose and lignin was specifically depressed. However, addition of lithium chloride was able to improve the tolerance of BmimCl to water and enhance the deconstruction and dissolution of biomass in BmimCl with high water content. It was found that approximately 80 % bamboo could be dissolved in solvent consisting of 45 wt% BmimCl and 55 wt% LiCl·2H₂O (25 wt% overall water content in the solvent). In particular, lignin and hemicelluloses were selectively dissolved by 96 and 92 %, respectively. The undissolved residue was predominantly composed of cellulose (~86 %) with a small amount of lignin (<5 %). BmimCl-LiCl-H₂O is a promising and effective solvent system with low cost and viscosity for biomass processing.     

Modelling the Metabolic Epimerization of Anti-inflammatory 2-Arylpropanoyl-coenzyme-A Conjugates: Solvent effects on the 1H/2H exchange in S-[2-(dimethylamino)ethyl] 2-phenylpropanethioate

The ¹H/²H exchange at the methine position of S-[2-(dimethylamino)ethyl] 2-phenylpropanethioate (DEPP) in solvent/D₂O mixtures was taken as a model reaction for the metabolic epimerization of 2-arylpropanoyl-coenzyme-A thioesters and was monitored by ¹H-NMR spectroscopy at 37°. The solvents used were (D₆)acetone, (D₃)acetonitrile, (D₆)dimethylsulfoxide, and (D₅)pyridine. In the investigated range of D₂O percentage (10–50%), the exchange reaction was found to increase linearily with D₂O content and with the basicity of the organic solvent, the fastest rates being close to 0.09 h^?1 (t_½ ca. 8 h). These rates are slower than those observed in vivo for the configurational inversion of profens, and they are elicited in totally unphysiological concentrations of bases. The hypothesis thus formulated is that the metabolic epimerization of 2-arylpropanoyl-coenzyme-A thioesters cannot occur nonenzymatically.     

Deuterium Isotope Effect on Solution Behavior of Thermoresponsive Star-Shaped Poly(2-isopropyl-2-oxazoline)

Thermosensitive star-shaped poly(2-isopropyl-2-oxazoline) (molar mass M≈21000 g mol^?1) in D₂O solution was studied by the static and dynamic light scattering methods. The behavior of the polymer investigated in deuterated water is similar qualitatively to that observed previously in undeuterated water. At the same time, the considerable quantitative changes of polymer behavior in D₂O were seen. Deuterium substitution of solvent affects the phase transition temperature by decreasing its value by 1°C. The temperature interval of phase transition in D₂O solution expands (by about 1°C) in comparison with that in H₂O solution.     

Gene Cloning, Expression, and Characterization of a Thermostable Xylanase from Nesterenkonia xinjiangensis CCTCC AA001025

An endo-β-1,4-xylanase-encoding gene, xyn11NX, was cloned from Nesterenkonia xinjiangensis CCTCC AA001025 and expressed in Escherichia coli. The gene encoded a 192-amino acid polypeptide and a putative 50-amino acid signal peptide. The deduced amino acid sequence exhibited a high degree of similarity with the xylanases from Streptomyces thermocyaneoviolaceus (68%) and Thermobifida fusca (66%) belonging to glycoside hydrolase family 11. After purification to homogeneity, the recombinant Xyn11NX exhibited optimal activity at pH 7.0 and 55 °C and remained stable at weakly acidic to alkaline pH (pH 5.0–11.0). The enzyme was thermostable, retaining more than 80% of the initial activity after incubation at 60 °C for 1 h and more than 40% of the activity at 90 °C for 15 min. The K _m and V _max values for oat spelt xylan and birchwood xylan were 16.08 mg ml^?1 and 45.66 μmol min^?1 mg^?1 and 9.22 mg ml^?1 and 16.05 μmol min^?1 mg^?1, respectively. The predominant hydrolysis products were xylobiose and xylotriose when using oat spelt xylan or birchwood xylan as substrate.     

Enhancement of Enzymatic Hydrolysis and Klason Lignin Removal of Corn Stover Using Photocatalyst-Assisted Ammonia Pretreatment

Photocatalyst-assisted ammonia pretreatment was explored to improve lignin removal of the lignocellulosic biomass for effective sugar conversion. Corn stover was treated with 5.0–12.5 wt.% ammonium hydroxide, two different photocatalysts (TiO₂ and ZnO) in the presence of molecular oxygen in a batch reactor at 60 °C. Various solid-to-liquid ratios (1:20–1:50) were also tested. Ammonia pretreatment assisted by TiO₂-catalyzed photo-degradation removed 70 % of Klason lignin under the optimum condition (12.5 % ammonium hydroxide, 60 °C, 24 h, solid/liquid?=?1:20, photocatalyst/biomass?=?1:10 with oxygen atmosphere). The enzymatic digestibilities of pretreated corn stover were 85 % for glucan and 75 % for xylan with NH₃-TiO₂-treated solid and 82 % for glucan and 77 % for xylan with NH₃-ZnO-treated solid with 15 filter paper units/g-glucan of cellulase and 30 cellobiase units/g-glucan of β-glucosidase, a 2–13 % improvement over ammonia pretreatment alone.     

Investigations on the Crosslinking Reactions of Melamine Resins in the Presence of Wood

Summary. The crosslinking behavior of MFRs (melamine formaldehyde resins) in the presence of wood was investigated. The influence of various factors (wood content, resin structure, etc.) on the crosslinking temperature of the resins was examined using DMTA and DSC/TGA. Fully methylated MFRs turned out to be more stable in the presence of wood than partially methylated MFRs. A dependence of the crosslinking temperature on the wood content was found. Model reactions with wood components demonstrated, that cellulose, hemicelluloses, and lignin affect the crosslinking temperature to different extends, whereas hemicelluloses (xylan) showed the strongest effect. Solvents, especially water, led to a further decrease of the crosslinking temperature of wood/MFR compounds.     

Investigations on the Crosslinking Reactions of Melamine Resins in the Presence of Wood

The crosslinking behavior of MFRs (melamine formaldehyde resins) in the presence of wood was investigated. The influence of various factors (wood content, resin structure, etc.) on the crosslinking temperature of the resins was examined using DMTA and DSC/TGA. Fully methylated MFRs turned out to be more stable in the presence of wood than partially methylated MFRs. A dependence of the crosslinking temperature on the wood content was found. Model reactions with wood components demonstrated, that cellulose, hemicelluloses, and lignin affect the crosslinking temperature to different extends, whereas hemicelluloses (xylan) showed the strongest effect. Solvents, especially water, led to a further decrease of the crosslinking temperature of wood/MFR compounds.