Distribution of carboxylate groups introduced into cotton linters by the TEMPO-mediated oxidation

The 2,2,6,6-tetramethylpiperidine-1-oxy radial (TEMPO)-mediated oxidation was applied to aqueous slurries of cotton linters. The water-insoluble fibrous fractions thus obtained in the yields of more than 78% were characterized by solid-state ¹³C-NMR, X-ray diffraction and scanning electron microscopic analyses for evaluation of distribution of carboxylate groups formed in the TEMPO-oxidized celluloses. The patterns of solid-state ¹³C-NMR spectra revealed that the oxidation occurred at the C6 primary hydroxyl groups of cellulose. X-ray diffraction and scanning electron microscopic analyses showed that such C6 oxidation took place at the surfaces of cellulose I crystallites without any oxidation at the C6 of inside cellulose I crystallites. Thus, carboxylate and aldehyde groups introduced into the TEMPO-oxidized celluloses are densely present on the surfaces of cellulose I crystallites. In addition, the obtained results revealed that the shoulder signal due to non-crystalline C6 carbons at about 63 ppm in solid-state ¹³C-NMR spectra of native celluloses is ascribed to those of surfaces of cellulose I crystallites or those of cellulose microfibrils.     

Crystallite Features of Valonia cellulose by Electron Diffraction and Dark-Field Electron Microscopy

Individual cellulose crystallites from the cell wall of Valonia ventricosa have been studied by electron diffraction and observed by dark-field electron microscopy. These two techniques reveal that the crystalline zones which run along the fibrils are above 1000 Å in length without any longitudinal periodicity. The width of the crystallites covers the width of the microfibrils and ranges from 140 to 180Å without persistent 35 Å subunits. In several instances, the crystalline zones terminate in the manner of a fork with two arms of 30 to 40 Å in width.     

Studies of crystallinity of Scots pine and Norway spruce cellulose

The variation in the mass fraction of crystalline cellulose (crystallinity of wood), the intrinsic crystallinity of cellulose, and the thickness of cellulose crystallites in early wood of Norway spruce [Picea abies (L.) Karst.], and Scots pine (Pinus sylvestris L.) grown in Finland were studied using wide angle X-ray scattering and nuclear magnetic resonance spectroscopy. The mass fraction of crystalline cellulose in wood increased slightly with the distance from the pith and was about 30±4% in mature wood of both species. The crystallinity of cellulose and the thickness of cellulose crystallites were almost constant for both species. The crystallinity of cellulose was 52±3% for both species and the average thickness of the cellulose crystallites was 32±1 Å and 31±1 Å for Norway spruce and Scots pine, respectively. The mass fraction of cellulose in wood, calculated from the crystallinity values, increased with the distance from the pith for both species.     

Peculiarity of Phase Transition CI into CII for Nanocrystallites of Cellulose

In this paper, using a method of wide-angle X-ray diffraction, sizes of cellulose nanoscale crystallites were determined and phase transition of nanosized crystallites CI into CII was studied after treatment of cellulose samples with solutions of sodium hydroxide with various concentrations, 5 to 20% (1.3 to 6.1 M). It was found that the phase transition proceeds in a certain interval of hydroxide concentrations; moreover, a correlation between average concentration (C) of hydroxide and average lateral sizes (D) of nanocrystallites was observed. Methods of chemical thermodynamics of nanophases allowed to derive an equation, which describes the relationship between C and D: lnC = lnC_o–KD^–1, where C_o is maximum concentration of hydroxide, which is required for the phase transition of large crystals of CI. Thus, the decrease in hydroxide concentration at the phase transition CI into CII, is explained by decreasing of lateral size of CI nanocrystallites. By means of the derived equation, minimum, average and maximum lateral sizes of CI nanocrystallites were determined, as well as polydispersity in lateral sizes of crystallites was studied. It has been shown that crystallites of organo-solvent celluloses were the most uniform, whereas aggregated crystallites of Kraft celluloses were the most heterogeneous.     

X-ray microdiffraction reveals the orientation of cellulose microfibrils and the size of cellulose crystallites in single Norway spruce tracheids

The microfibril angle (MFA) distribution and the size of cellulose crystallites in isolated double cell walls of Norway spruce (Picea abies [L.] Karst.) tracheids were determined by synchrotron X-ray microdiffraction using the reflections 200 and 004. Samples were 25 μm thick longitudinal sections of earlywood from annual rings 6–18 of several stems. The asymmetric MFA distributions extended from ?20° to 90°. The mean MFA of tangential cell walls decreased from an average of 24° into 19° from the pith to the bark. The mode of the MFA distribution was about 10° smaller than the mean MFA. The standard deviation of the MFA distribution varied between 18° and 25°. The mean MFA and the mode of the MFA distribution were larger in radial than in tangential cell walls. MFA distributions of mature wood samples exhibited a separate small peak at around 90°. The average width and length of cellulose crystallites varied between 28.9–30.9 Å and 192–284 Å, respectively. Both increased slightly as a function of annual ring number from the pith up to the 15th annual ring. An irrigation–fertilisation treatment of some of the stems resulted in longer cellulose crystallites compared to the untreated stems.     

Transparent cellulose sheets as synthesis matrices for inorganic functional particles

Transparent cellulose sheets were prepared through tape-casting a solution of cellulose. Flexible, luminescent sheets were produced by adding europium trichloride to the casting solution and treating the sheets with an aqueous solution of ammonium fluoride. Scanning electron micrographs of the resulting sheets showed europium trifluoride particles with diameters from 200 nm to 500 nm. These were found by transmission electron microscopy to be agglomerates of crystallites in the size range of 10-20 nm. The structure of supercritically dried sheets was further assessed by small-angle X-ray scattering and suggests a preferred orientation of slightly elongated pores of roughly 12 nm in diameter. Evaluation of the emission characteristics of the sheets showed the band pattern between 580 nm and 700 nm typical for Eu³⁺ phosphors. Our developed process is a versatile tool for the fabrication of transparent cellulose structures with different shapes and various embedded functional particles.     

Lattice resolution in alpha-chitin

The lattice images of the alpha-chitin microfibrils from lobster tendon were recorded with a transmission electron microscope operated at 120 keV. It was concluded that a close resemblance exists between alpha-chitin microfibrils and cellulose microfibrils. In both cases, the microfibrils are elongated single crystals (crystallites) of high perfection, with the chains aligned and probably fully extended along the microfibril axis.     

WAXS and 13C NMR study of Gluconoacetobacter xylinus cellulose in composites with tamarind xyloglucan

- Model composites, produced using cellulose from stationary cultures of the bacterium Gluconoacetobacter xylinus and tamarind xyloglucan, were examined by wide-angle X-ray scattering (WAXS) and CP/MAS solid-state (13)C NMR spectroscopy. The dominant crystallite allomorph of cellulose produced in culture media with or without xyloglucan was cellulose I(alpha) (triclinic). The presence of xyloglucan in the culture medium reduced the cross-section dimensions of the cellulose crystallites, but did not affect the crystallite allomorph. However, when the composites were refluxed in buffer, the proportion of cellulose I(beta) allomorph increased relative to that of cellulose I(alpha). In contrast, cellulose I(alpha) remained the dominant form when cellulose, produced in the absence of xyloglucan, was then heated in the buffer. Hence the presence of xyloglucan has a profound effect on the formation of the cellulose crystallites by G. xylinus.     

Structural changes in microcrystalline cellulose in subcritical water treatment

Subcritical water is a high potential green chemical for the hydrolysis of cellulose. In this study microcrystalline cellulose was treated in subcritical water to study structural changes of the cellulose residues. The alterations in particle size and appearance were studied by scanning electron microscopy (SEM) and those in the degree of polymerization (DP) and molar mass distributions by gel permeation chromatography (GPC). Further, changes in crystallinity and crystallite dimensions were quantified by wide-angle X-ray scattering and (13)C solid-state NMR. The results showed that the crystallinity remained practically unchanged throughout the treatment, whereas the size of the remaining cellulose crystallites increased. Microcrystalline cellulose underwent significant depolymerization in subcritical water. However, depolymerization leveled off at a relatively high degree of polymerization. The molar mass distributions of the residues showed a bimodal form. We infer that cellulose gets dissolved in subcritical water only after extensive depolymerization.     

Antheridial dehiscence in ferns

We investigated the mechanism of antheridial dehiscence in ferns for the first time using fluorescence microscopy as well as scanning and transmission electron microscopy. The mechanism leading to antheridial dehiscence in Polystichum setiferum, Asplenium trichomanes and A. onopteris was found to depend on the different cellulose contents of the inner and outer walls of the ring cells detected with calcofluor white stain and the Thiéry test. The extremely low cellulose content of the ring cell walls facing spermatozoids made them less mechanically resilient than external wall cells. When the ring cells absorbed water they expanded only into the antheridial cavity, pushing the gametes against the cap cell, which detached from the ring cell below and enabled spermatozoid release. The newly released spermatozoids were spherical bodies covered in cellulose fibrils. The significance of cellulose fibrils could be to isolate the gametes from each other, to reinforce the electron transparent material and to protect the gamete from pressure created by the ring cells during release.     

Electron microscopy study of the transformation of cellulose I into cellulose IIII in Valonia

The ‘reversible’ fibrous transformation cellulose I?cellulose III_I has been investigated by electron microscopy, (electron diffraction, bright and dark-fiedldaimaging) for Valonia cellulose. The transformation, performed in ethylenediamine, maintained the external appearance of the microfibrils during both the direct I→III_I and the reverse III_I→I transformations. At the crystal level, drastic modifications were revealed by dark-field imaging and negative staining. The conversion of Valonia cellulose into cellulose III_I involves a fracturing and firbrillation of the initial crystals. Such a phenomenon eplains the enhanced accessibility of the material.     

Almost pure I(alpha) cellulose in the cell wall of Glaucocystis.

Crystalline features of cellulose microfibrils in the cell walls of Glaucocystis (Glaucophyta) were studied by combined spectroscopy and diffraction techniques, and the results were compared with those of Oocystis (Chlorophyta). Although these algae are grouped into two different classes, by the composition of their chloroplasts for instance, their cell walls are quite similar in size and morphology. The most striking features of their cellulose crystallites are that they have the highest cellulose I(alpha) contents reported to date. In particular, the I(alpha) fraction of cellulose from Glaucocystis was found to be as high as 90% from (13)C NMR analysis. The mode of preferential orientation of cellulose crystallites in their cell walls is also interesting; equatorial 0.53-nm lattice planes were oriented parallel to the cell surface in the case of Glaucocystis, while the 0.62-nm planes were parallel to the Oocystis cell surface. Such a structural variation provides another link to the evolution of cellulose structure, biosynthesis, and its biocrystallization mechanism.     

Almost Pure Iα Cellulose in the Cell Wall of Glaucocystis

Crystalline features of cellulose microfibrils in the cell walls of Glaucocystis (Glaucophyta) were studied by combined spectroscopy and diffraction techniques, and the results were compared with those of Oocystis (Chlorophyta). Although these algae are grouped into two different classes, by the composition of their chloroplasts for instance, their cell walls are quite similar in size and morphology. The most striking features of their cellulose crystallites are that they have the highest cellulose I_α contents reported to date. In particular, the I_α fraction of cellulose from Glaucocystis was found to be as high as 90% from ¹³C NMR analysis. The mode of preferential orientation of cellulose crystallites in their cell walls is also interesting; equatorial 0.53-nm lattice planes were oriented parallel to the cell surface in the case of Glaucocystis, while the 0.62-nm planes were parallel to the Oocystis cell surface. Such a structural variation provides another link to the evolution of cellulose structure, biosynthesis, and its biocrystallization mechanism.     

The effect of the cellulose-binding domain from Clostridium cellulovorans on the supramolecular structure of cellulose fibers

The cellulose-binding domain (CBD) is the second important and the most wide-spread element of cellulase structure involved in cellulose transformation with a great structural diversity and a range of adsorption behavior toward different types of cellulosic materials. The effect of the CBD from Clostridium cellulovorans on the supramolecular structure of three different sources of cellulose (cotton cellulose, spruce dissolving pulp, and cellulose linters) was studied. Fourier-transform infrared spectroscopy (FTIR) was used to record amides I and II absorption bands of cotton cellulose treated with CBD. Structural changes as weakening and splitting of the hydrogen bonds within the cellulose chains after CBD adsorption were observed. The decrease of relative crystallinity index of the treated celluloses was confirmed by FTIR spectroscopy and X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to confirm the binding of the CBD on the cellulose surface and the changing of the cellulose morphology.     

Cellulose-Enriched Microbial Communities from Leaf-Cutter Ant (Atta colombica) Refuse Dumps Vary in Taxonomic Composition and Degradation Ability

Deconstruction of the cellulose in plant cell walls is critical for carbon flow through ecosystems and for the production of sustainable cellulosic biofuels. Our understanding of cellulose deconstruction is largely limited to the study of microbes in isolation, but in nature, this process is driven by microbes within complex communities. In Neotropical forests, microbes in leaf-cutter ant refuse dumps are important for carbon turnover. These dumps consist of decaying plant material and a diverse bacterial community, as shown here by electron microscopy. To study the portion of the community capable of cellulose degradation, we performed enrichments on cellulose using material from five Atta colombica refuse dumps. The ability of enriched communities to degrade cellulose varied significantly across refuse dumps. 16S rRNA gene amplicon sequencing of enriched samples identified that the community structure correlated with refuse dump and with degradation ability. Overall, samples were dominated by Bacteroidetes, Gammaproteobacteria, and Betaproteobacteria. Half of abundant operational taxonomic units (OTUs) across samples were classified within genera containing known cellulose degraders, including Acidovorax, the most abundant OTU detected across samples, which was positively correlated with cellulolytic ability. A representative Acidovorax strain was isolated, but did not grow on cellulose alone. Phenotypic and compositional analyses of enrichment cultures, such as those presented here, help link community composition with cellulolytic ability and provide insight into the complexity of community-based cellulose degradation.     

Chiral nematic ordering of polysaccharides

In this paper, evidence for the chiral nematic (cholesteric) self-ordering of cellulose-derived materials is reviewed. A wide range of cellulose derivatives, and some other polysaccharides, form chiral nematic phases, both in concentrated solution and in the melt. Solid films and gels retaining the chiral nematic ordering of the polymer chains may be prepared from these liquid crystalline phases. Optical and electron microscopic techniques may be used to elucidate the helicoidal structure of chiral nematic cellulosics in the liquid crystalline phase, and of the films, gels and solids prepared from such phases. Remarkably, dilute aqueous suspensions of cellulose crystallites prepared by acid degradation also show chiral nematic order; the order is preserved in dry films prepared from the suspensions. The structure of some of these samples prepared in vitro shows a marked resemblance to structures observed in vivo.     

Image analysis of modified cellulose fibers from sugarcane bagasse by zirconium oxychloride

Surface modification of natural fibers has been made using different methods. In this paper, cellulose fibers from sugarcane bagasse were bleached and modified by zirconium oxychloride in situ. The chemically modified cellulose fibers were compared to those of bleached ones. Cellulose fibers were modified with ZrO₂·nH₂O nanoparticles through the use of zirconium oxychloride in acidic medium in the presence of cellulose fibers using urea as the precipitating agent. The spatial distribution characterization of hydrous zirconium oxide on cellulose fibers was carried out by combining both processing and image analyses obtained by SEM and statistical methodologies. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TG) were also used to characterize the nanocomposite. Results indicated that ZrO₂·nH₂O nanoparticles of about 30-80 nm diameter deposited on cellulose fibers were heterogeneously dispersed.     

Evaluating Models of Cellulose Degradation by Fibrobacter succinogenes S85

Fibrobacter succinogenes S85 is an anaerobic non-cellulosome utilizing cellulolytic bacterium originally isolated from the cow rumen microbial community. Efforts to elucidate its cellulolytic machinery have resulted in the proposal of numerous models which involve cell-surface attachment via a combination of cellulose-binding fibro-slime proteins and pili, the production of cellulolytic vesicles, and the entry of cellulose fibers into the periplasmic space. Here, we used a combination of RNA-sequencing, proteomics, and transmission electron microscopy (TEM) to further clarify the cellulolytic mechanism of F. succinogenes. Our RNA-sequence analysis shows that genes encoding type II and III secretion systems, fibro-slime proteins, and pili are differentially expressed on cellulose, relative to glucose. A subcellular fractionation of cells grown on cellulose revealed that carbohydrate active enzymes associated with cellulose deconstruction and fibro-slime proteins were greater in the extracellular medium, as compared to the periplasm and outer membrane fractions. TEMs of samples harvested at mid-exponential and stationary phases of growth on cellulose and glucose showed the presence of grooves in the cellulose between the bacterial cells and substrate, suggesting enzymes work extracellularly for cellulose degradation. Membrane vesicles were only observed in stationary phase cultures grown on cellulose. These results provide evidence that F. succinogenes attaches to cellulose fibers using fibro-slime and pili, produces cellulases, such as endoglucanases, that are secreted extracellularly using type II and III secretion systems, and degrades the cellulose into cellodextrins that are then imported back into the periplasm for further digestion by β-glucanases and other cellulases.     

Identification of a fungus able to secrete enzymes that degrade regenerated cellulose films and analyses of its extracellular hydrolases

The LW03 strain was isolated from Chinese farmland soil and found to be able to secrete certain enzymes degrading regenerated cellulose films at low temperature. The LW03 strain was systematically identified as Rhizopus arrhizus var. arrhizus by morphological, physiological, and molecular methods. Incubation of regenerated cellulose films with the extracted crude enzyme of LW03 was done to measure morphological changes by using scanning electron microscopy. Microscopic observations showed that the morphology of the regenerated cellulose films changed drastically due to enzymatic hydrolysis. The extracellular hydrolases of LW03 strain incubated on bran medium were also assessed. The predominant activity in the crude enzyme was glucoamylase activity, followed by acid proteinase, phytase and pectinase activity. Interestingly, activities of β-glucosidase, endoglucanase, exoglucanase, and cellulase were also observed, but at a much lower extent. Based on initial evidence, the crude enzyme is most likely to contain some new constituents capable of degrading regenerated cellulose films.     

Cross-linking chitosan into UV-irradiated cellulose fibers for the preparation of antimicrobial-finished textiles

Chitosan cross-linked cellulose fibers were prepared using non-toxic procedures in order to confer antimicrobial properties to cellulose fibers. Citric acid was used as the cross-linker and NaH₂PO₄ as catalyst in previously UV-irradiated cellulose fibers. Further heat dried-cure process and washing with detergent, water and acetic acid (0.1 M) gave a maximum incorporation of chitosan of 27 mg per gram of functionalized textile. The thermogravimetric analysis of the material with the highest chitosan content showed an increased thermal stability compared to cellulose and chitosan. The UV-irradiation induced morphological changes, such as less entangled cellulose fibers, as observed by scanning electron microscopy, which was prompted to enhance the chitosan incorporation. The biomass and spore germination percentage of Penicillium chrysogenum and colony forming units per millilitre for Escherichia coli decreased significantly on the composed materials as compared to raw cellulose fiber and it was similar to that obtained with a commercial antimicrobial cellulose fiber.