Cellulose Iβ Research Articles

The hydrogen bond network in Iβ cellulose as observed by infrared spectrometry

FT–IR spectra of Iβ cellulose were recorded on films made of hydrothermally treated Valonia microcrystals. Polarized spectra of these not completely disordered systems allowed to define the spectra along the cellulose c chain axis as well as along a perpendicular axis which may slightly vary from one sample to another one. Weakening and ruptures of some hydrogen bonds upon heating the samples at 115°C, as well as evaporation of D2O molecules and H/D exchanges after immersion in a D2O vapor were followed spectroscopically. A critical analysis of the spectra allowed to propose a detailed assignment for most of the bands at wavenumbers higher than 800cm−1. From this analysis it appeared that the majority (more than 2/3) of C2O2H alcohols were involved in weak hydrogen bonds or perhaps even not hydrogen-bonded at all. On the other hand, the minority of C2O2H established a hydrogen bond with the O6 atom of an adjacent primary alcohol of the same chain. This particular hydrogen bond was the strongest found in these crystals. With the proposed assignment, hydroxymethyl moieties were found adopting three conformations (a dominant one and two minor) allowing the formation of different hydrogen bonds on adjacent chains. These conformations corresponded to three slightly different C4–C5–C6–O6 (χ) dihedral angles. Most probably the primary alcohols that accept a hydrogen bond from the adjacent C2O2H alcohols were not the ones which adopt the dominant conformation.

A comparative CP/MAS 13C-NMR study of cellulose structure in spruce wood and kraft pulp

CP/MAS 13C-NMR spectroscopy in combination with spectral fitting was used to study the supermolecular structure of the cellulose fibril in spruce wood and spruce kraft pulp. During pulping, structures contributing to inaccessible surfaces in the wood cellulose are converted to the cellulose Iβ allomorph, that is, the degree of order is increased. This increase is also accompanied by a conversion of cellulose Iα to cellulose Iβ. Cellulose from wood composed of different cell types, that is, compression wood, juvenile wood, earlywood, latewood and normal wood exhibited a similar supermolecular structure. Assignments were made for signals from hemicellulose which contribute significantly to the spectral C-4 region (80–86 ppm) in kraft pulp spectra but substantially less to the corresponding region in wood spectra.

High resolution neutron fibre diffraction data on hydrogenated and deuterated cellulose

High-resolution fibre neutron diffraction data were recorded from cellulose samples on a D19 diffractometer at the Institut Laue-Langevin (Grenoble). Highly crystalline cellulose I samples from Cladophora (cellulose Iα+Iβ) or Halocynthia (cellulose Iβ) origin were prepared in the form of oriented films. Samples were studied in a hydrogenated form and in a hydrogen–deuterium exchanged deuterated form corresponding to all OH moieties being replaced by ODs. These samples, which diffracted to a resolution of around 0.9 Å, gave diffraction diagrams consisting of several hundred independent diffraction spots. Crystalline cellulose II fibres resulting from the mercerization of flax were also studied in a hydrogenated form using NaOH/H 2O as mercerizing medium and in a deuterated form using NaOD/D 2O. Both of these samples diffracted to around 1.2 Å, giving fibre diffraction diagrams slightly less resolved than those of cellulose I, but still consisting of more than one hundred independent diffraction spots. For cellulose I as well as for cellulose II, significant differences between the hydrogenated and deuterated patterns were observed and recorded. These new data should lead to improved structures for cellulose and direct identification of the position of hydrogen atoms involved in hydrogen bonding.

Characterization of Cellulose Fibers Extracted from Water Plants, Elodea nuttallii.

Cellulose fibers were extracted from water plants, Elodea Nuttallii, and the structure of the fibers and the anisotropic texture of the regenerated cellulose films were investigated. Wide-angle X-ray powder diffractions revealed that the coarse fibers extracted showed crystal structure of cellulose Iβ and the crystallinity of the fibers was 36.0%. The coarse fibers were refined by the treatment with 17.5% sodium hydroxide aqueous solution and were dissolved in LiCl/ dimethylacetamide (DMAc) solution. The cotton cellulose/LiCl/DMAc solution were prepared for comparison. The texture of the regenerated film for the refined cellulose of the water plants obtained by heating a drop of the solution on a cover glass showed extremely small anisotropic domains as compared with the regenerated cotton cellulose film.

Crystal Structure of Valonia Cellulose Iβ

The crystal structure of Valonia cellulose Iβ is determined by X-ray fiber diffraction analysis. A careful reanalysis of two existing X-ray diffraction data sets for Valonia cellulose I leads to a consistent, definitive structure of the β-phase. The results resolve ambiguities in existing X-ray analyses between “parallel up” and “parallel down” packing of the cellulose sheets in native Valonia cellulose. The molecular and sheet structures are essentially identical to those previously determined, but these results define precisely the packing of the sheets. The sheet packing is discussed in terms of the energy and density of the crystal structure. The structure of the β-phase has specific implications for the packing of the α-phase of Valonia cellulose I.

Nanodomains of Iα and Iβ Cellulose in Algal Microfibrils

Ultrastructural localization of cellulose Iα and Iβ allomorphs in one microfibril from algal sources was investigated using electron microdiffraction. Both cellulose Iα and Iβ were characterized as one-chain triclinic and two-chain monoclinic unit cells, respectively, in agreement with previous studies. These two structures coexisted in each microfibril, alternating either longitudinally or laterally. The transition zone between the two phases was found to be the interface between adjacent H-bonded molecular sheets (i.e., 0.39-nm lattice planes).

A CP/MAS 13C NMR investigation of molecular ordering in celluloses

The individual states of order of cellulose found within Valonia, Cladophora, Halocynthia, cotton and wood cellulose were quantified by non-linear least-squares fitting of the 13C NMR spectra. The results from the spectral fittings indicated that a cellulose form giving signals at δ 104.5 (C-1 region) and δ 88.1–88.5 (C-4 region) was present in all the investigated samples. Partial signal suppression by spin-lattice relaxation supported the findings from the spectral fittings. The spectral behavior of this cellulose form indicates it is a less-ordered or a para-crystalline ‘in core’ structure with a somewhat larger mobility than the crystalline cellulose Iα and Iβ allomorphs.

Interface between Monoclinic Crystalline Cellulose and Water: Breakdown of the Odd/Even Duplicity

The interface between the (110) crystal face of cellulose Iβ and water was studied by molecular dynamics simulation with cellulose coordinates refined from electron diffraction data as a starting point. Potential energies, pucker parameters, torsion angles, and hydrogen bonding have been used for the characterization. Only the topmost layer in the cellulose differs in terms of structure and dynamics from the crystal bulk, but even these difference are small. At the surface approximately half of the cellulose intermolecular hydrogen bonding is lost, but this is compensated by hydrogen bonds with water molecules. Much of the difference between even and odd (200) planes disappears at the interface, except for the orientation of the glucose ring plane. Water dynamics is retarded by a factor of 2−3 close to the surface. The potential energy of water molecules in the first hydration layer is lower by 2 kJ/mol. The cellulose surface contains about five exposed hydroxyl groups per square nanometer, which accounts for the good hydration of the surface.

Systematic survey on crystalline features of algal celluloses

Algal cellulose from different origins has been analysed with special reference to the crystalline features, such as allomorphism (Iα/Iβ or triclinic/monoclinic two- phase model), dimension and uniplanar orientation behaviour of the specific crystallographic plane to the cell wall surface. Three types of cellulose were identified in the algal system: Iα-rich/broad microfibril/0.6 nm-oriented type; Iβ- dominant/flat-ribbon/0.53 nm-oriented type; and Iβ- dominant/small/random-oriented type. The first type appears to occur in more primitive organisms than the other types. The three types of algal cellulose correlate well with the arrangements of cellulose synthesizing complexes, i.e. multiple-row linear type, consolidated rosette type, and isolated rosette type, respectively. In Chara two types of crystals were found: an Iβ-dominant/ribbon shaped/0.6 nm-oriented type and an Iβ/narrow/random-oriented type. The former type, known to occur in some families of tunicates, was first identified in algal cellulose during this study. Reducing-end staining was successfully applied to microcrystal cellulose samples of Cladophorales and Zygnematales, showing that the cellulose microfibril has a parallel-chain structure for both cellulose Iα and cellulose Iβ

Crystalline forms of cellulose in the silver tree fern Cyathea dealbata

Solid-state 13C NMR spectroscopy was used to characterize fibrous material cut from the midrib of a fern frond. Signals associated with cellulose crystallites were separated from those associated with the lignin--hemicellulosic matrix by exploiting differences in proton rotating-frame relaxation time constants. Heights of signals at 90.2 and 88.5 ppm, assigned to C-4 in cellulose Iα and Iβ, indicated similar proportions of the two crystalline forms. This observation conflicts with a suggestion that plant celluloses can be grouped into the two categories of Iα-rich and Iβ-rich.

Synchrotron-radiated X-ray and neutron diffraction study of native cellulose

Precise determination of d-spacings and compositional ratio of cellulose Iα and Iβ in various native cellulose samples was successfully carried out by synchrotron-radiated X-ray diffraction and time-of-flight (TOF) neutron diffraction from quasi-powder specimens. X-ray diffraction peaks were separated by the deconvolution method using six types of profile function: Gaussian, Lorentzian, intermediate Lorentzian, modified Lorentzian, pseudo-Voigt, and Pearson VII. In terms of R-factors, the pseudo-Voigt function gave the best fit with the observation, and was used for determination of d-spacings. The numerical results for Valonia cellulose were: dIα (1 0 0) = 0.613 nm; dIβ (1 1 0) = 0.603 nm; dIβ (1 1 0) = 0.535 nm; dIα (0 1 0) = 0.529 nm; Iα content = 0.65. The differences determined between dIα (1 0 0) and dIβ (1 1 0) and between dIβ (1 1 0) and dIα (0 1 0) were similar to those previously reported. Comparison between unresolved peaks for the two types of cellulose samples revealed a small but definite difference between dIα (1 1 0) and dIβ (2 0 0). The TOF neutron diffractometry using deuterated samples confirmed this difference.

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 Iα and Iβ 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 Iα 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 Iα, which corresponds to the enhanced crystallization of cellulose Iβ, 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 Iα and Iβ are highly correlated with the crystallite size of microfibrils, indicating that Iα is crystallized in larger-size microfibrils while Iβ is produced in smaller-size microfibrils. On the basis of these experimental results, the mechanism of the crystallization of celluloses Iα and Iβ is discussed in the Acetobactor xylinum system.

The Cellulose System in the Cell Wall ofMicrasterias

The cellulose system of the cell wall ofMicrasterias denticulataandMicrasterias rotatawas analyzed by diffraction contrast transmission electron microscopy, electron diffraction, and X-ray analysis. The studies, achieved on disencrusted cell ghosts, confirmed that the cellulose microfibrils occurred in crisscrossed bands consisting of a number of parallel ribbon-like microfibrils. The individual microfibrils had thicknesses of 5 nm for a width of around 20 nm, but in some instances, two or three microfibrils merged into one another to yield larger monocrystalline domains reaching up to 60 nm in lateral size. The orientation of the cellulose ofMicrasteriasis very unusual, as it was found that in the cell wall, the equatorial crystallographic planes of cellulose having ad-spacing of 0.60 nm [(110) in the Iβ cellulose unit cell defined by Sugiyamaet al.,1991,Macromolecules24, 4168–4175] were oriented perpendicular to the cell wall surface. Up to now, such orientation has been found only inSpirogyra,another member of the Zygnemataceae group. The unusual structure of the secondary wall cellulose ofMicrasteriasmay be tentatively correlated with the unique organization of the terminal complexes, which in this alga occur as hexagonal arrays of rosettes.

NMR Studies on the structure of cellulose. 2‐dimensional solid state NMR approach

AbstractTwo‐dimensional C‐H correlation NMR spectra are presented for the native cellulose types Iα and Iβ from Cladophora sp. A remarkable difference of correlation peaks between Iα and Iβ was observed, which indicates an essential structure difference between the two types of native cellulose.

Crystalline cellulose Iα and Iβ studied by molecular dynamics simulation

A recent structure determination of native cellulose has shown that it is composed of two different crystal structures, a two-chain monoclinic phase and a single-chain triclinic phase. In this article a molecular dynamics study of the two allomorphs is presented, and a general picture of structure and energetics is provided. Consistent with experimental data, the monoclinic phase is more stable than the triclinic phase by −8.7 kJ mol −1 cellobiose −1. In the monoclinic phase a small angle is observed between glucose residues that belong to alternate (200) planes. The glucose residues in every second plane are parallel to the (200) plane, and form more favorable intermolecular hydrogen bonds. In the triclinic phase the glucose residues are not parallel to the (200) plane. The 13C NMR shifts for C-6 are fully accounted for by the distribution of the C-6 dihedral angle. The nonbonded environment is important to the splitting for C-1. The fine structure of IR spectra in the OH-stretching region can be qualitatively correlated with the number of different hydrogen bonds observed. Results indicate that chains in one set of alternating (200)-planes in the monoclinic phase resemble the triclinic phase.

Theoretical investigations on the structure and physical properties of cellulose

AbstractThe structure of cellulose is investigated using a recently derived force field. Published experimental data is taken only as a starting point for purely theoretical investigations. The reliability of the method is validated by calculating physical properties of the obtained geometries. In the course of the investigations, the geometries of cellulose Iα, cellulose Iβ and cellulose II are derived. For these geometries the Young's‐modulus is calculated. The structure of cellulose in aqueous solution is investigated, using cellohexaose (a hexamer of β‐D‐glucose) as a fragment of a cellulose chain. Here, the diffusion coefficient is calculated.

Cellulose I microfibril assembly: computational molecular mechanics energy analysis favours bonding by van der Waals forces as the initial step in crystallization

In vitro and abiotic synthesis of cellulose I have indicated that glucan sheet formation is most likely to be the first stage in crystallization of this allomorph of cellulose. Bonding schemes for the different glucan sheets found in crystals of cellulose Iα and Iβ were analysed energetically with the molecular mechanics program, MM3. Using high and low dielectric constants, favouring van der Waals forces and hydrogen bonding, respectively, van der Waals-associated mini-sheets had lower energies than hydrogen bonded mini-sheets. Furthermore, the first glucan mini-sheet most likely to form is the one with the lowest energy. In the case of cellulose Iβ, this mini-sheet was the one along the (110) plane; in the case of cellulose Iα, it was the one along the (010) plane. Incorporating these results into known experimental evidence, we theorize the requirement of at least three sequential steps for native cellulose I crystallization: (1) formation of mini-sheets by van der Waals forces, (2) association of these sheets by hydrogen bonding into mini-crystals, and (3) the convergence of mini-crystals to form the crystalline microfibril.

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

To obtain further information about the formation of cellulose Iα and Iβ, 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 Iα When xyloglucan (XG) or carboxymethyl cellulose sodium salt (CMC) was added to the incubation medium, the amount of cellulose Iα decreased markedly, from a normal level of 64% to as low as 30%, with the most additive giving the lowest levels of Iα. 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 Iα form. Thus, cellulose Iβ may grow preferentially when the strain caused by aggregation is not present. Lower temperatures (36–10 °C) gave an increase in Iα (from 56 to 72%).

C.p./m.a.s. 13C n.m.r. study on microbial cellulose-fluorescent brightener complexes

The structures of microbial cellulose-fluorescent brightener complexes, produced from the Acetobacter culture in the presence of a fluorescent brightener, and the cellulose samples regenerated from them have been examined by cross-polarization/magic-angle spinning (c.p./m.a.s.) 13C n.m.r. spectroscopy. C4 and C6 resonance lines for the cellulose components of the complexes appear at about 84.0 and 63.0 ppm, respectively, with the disappearance of their downfield crystalline components. Since the chemical shifts of the lines are in good accord with those of the non-crystalline component of native cellulose, it is concluded that the cellulose component of the complex is in the non-crystalline state. 13C spin-lattice relaxation time ( T 1C) measurements have also confirmed that the T 1C values of the dried complexes are of the same order as those for the non-crystalline component of native cellulose. In contrast, the T 1C values of the non-dried complex are much shorter than those of the dried complexes, indicating a much enhanced molecular mobility in the non-dried complex. On the other hand, when the non-dried complex is subjected to dye extraction, C4 and C6 resonance lines assignable to the crystalline component can be observed in the c.p./m.a.s. spectrum. Moreover, selective measurements of the spectrum of the crystalline component have revealed that cellulose Iβ is preferentially grown from the non-dried complex by dye extraction. In the case of the dried complexes, only very small amounts of cellulose I crystals are regenerated, possibly as a result of the formation of tight hydrogen bonds in the complex.