Analysis of water state adsorbed by cellulose fibers

Modernized model of microfibril cellulose layered structure is proposed. This model considers presence of slit-shaped micropores in space between elementary fibrils and cellulose microfibrils. It’s discussed the nature of donor-acceptor hydrogen bonds formation: intra-, intermolecular, and interlayer bonds inherent in each glucopyranous cellulose link. It’s described the mechanism of water molecules specific adsorption interactions in a monolayer with active centers located on the hydrophilic surfaces of elementary fibrils. Dipole-dipole energy transition into energy of hydrogen bond is discussed during adsorption process between active centers of cellulose and water adsorptive molecules. Analysis of water molecules dipole-dipole interactions with surface hydroxyl groups of cellulose showed that at distance of 2.5-3 Å energy of this interaction transforms into energy of hydrogen bond. It is discussed the formation mechanism of water molecules donor-acceptor bonds with cellulose surface hydroxyl groups. Thermodynamic parameters characterizing adsorbate state the in these layers are determined by proton magnetic relaxation and sorption measurements. It’s established the possibility of determining adsorption net heat in bilayer considering Arrhenius nature of adsorbate thermal molecular motions correlation times. Increase in entropy of adsorbed water during adsorption process is revealed basis on Vant Hoff equation and certain adsorption equilibrium constant. The calculation established that distance between nearest active centers of cellulose is 6.5 Å. This leads to disunity of adsorbed water molecules and allows application of Langmuir and BET adsorption theory. Analysis of spin-lattice relaxation times dependence on cellulose moisture content made it possible to establish the cause of its crystallite wedging from adsorbed water molecules at adsorption initial stages. Decline of the spin-lattice relaxation unambiguously indicates the process of cellulose dispersion into its structural elements. It was established that during adsorption a part of the internal regions of crystallites passes to their surface with participation of cellulose hydroxyl groups. During desorption reverse process is observed.

Quantitative and Structure Analysis of Cellulose in Tobacco by 13C CP / MAS NMR Spectroscopy

SUMMARY A new method utilizing 13C cross-polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectra was developed for the simultaneous quantitative determination and structure analysis of tobacco cellulose from hot water or acid detergent extraction. A reference spectrum of tobacco noncellulose components was subtracted from the spectrum of each sample to obtain a subspectrum of the cellulose components. The NMR spectra in combination with spectral fitting were analyzed in detail and some parameters, such as the content of cellulose, crystallinity, allomorph composition and lateral dimensions for cellulose elementary fibrils and microfibrils were determined. The quantitative results showed that the average recovery was 94.0% with a relative standard deviation (RSD) of 4.6–4.8%. The structure results obtained by the spectral fitting for the cellulose C1-region showed that the main allomorph composition in tobacco cellulose was Iβ. The cellulose crystallinity calculated by the spectral fitting in C4 -region was about 50%. The lateral dimensions for cellulose elementary fibrils and microfibrils were in the range of 3.0–6.0 nm and 6.0–13.0 nm, respectively. Therefore, this NMR method could provide important information on both amount and structure of cellulose in tobacco.

From cellulose fibrils to single chains: understanding cellulose dissolution in ionic liquids

Continued improvement on the structure of elementary fibrils, simulation of larger elementary fibrils and systematic work on the solution structure of cellulose in ILs are three interacting modules to unravel the mechanism of cellulose dissolution in ILs.

Ultrastructure of the elementary fibril in extended and condensed chromatin and in metaphase chromosomes

The chromatin Ultrastructure of nuclei in ultrathin sections of root meristem in <i>Cucurbita pepo</i> - the species poor in DNA, and in <i>Haemanthus katharinae</i> - rich in DNA was compared. Four combinations of fixation and embedding were used: 1) OsO₄ (pH 7.2), methacrylates; 2) OsO₄ (pH 7.2), Epon; 3) OsO₄ (pH 6.8), Epon; 4) glutaraldehyde (pH 7.2-7.4) with OsO4 postfixation, Epon embedding. Most suitable was OsO₄ fixation (pH 7.2) and embedding in Epon because of the smallest dispersion of dimensions of chromatin fibrils and good visibility of their substructure. Fibrils of condensed chromatin, components of chromocenters (heterochromatin) in <i>Cucurbita pepo</i>, bands of chromonemata visible in the light microscope and metaphase chromosomes in <i>Haemanthus katharinae</i> showed a diameter of about 11.5 nm after OsO₄ fixation, or 14-19 nm after glutaraldehyde. Fibrils of extended chromatin (euchromatin) in <i>Cucurbita pepo</i> are thinner, their diameter is about 10 nm after OsO₄ fixation and Epon embedding, and about 14.5 nm after glutaraldehyde. There are no visible differences in the width of elementary fibrils after OsO₄ fixation and embedding in methacrylates. In both species the fibrils of extended chromatin are built up of one coiled deoxyribonucleohistone (DNH) thread about 2.3 nm in diameter, while the fibrils of condensed chromatin consist of two DNH threads, each about 3 nm in diameter. The diameter of DNH threads is determined neither by the fixative nor by the way of embedding; they are less visible in the material embedded in methacrylates. The results obtained show that the structure of chromatin fibrils depends on the kind of chromatin, but not on DNA content. In <i>Haemanthus katharinae</i>, the species rich in DNA, the greater amount of chromatin appears in condensed form.

Dimer/tetramer motifs determine amphiphilic hydrazine fibril structures on graphite

Fibril structures are produced at a solvent–graphite interface by self-assembly of custom-designed symmetric and asymmetric amphiphilic benzamide derivatives bearing C10 aliphatic chains. Scanning tunnelling microscopy (STM) studies reveal geometry-dependent internal structures for the elementary fibrils of the two molecules that are distinctly different from known mesophase bulk structures. The structures are described by building-block models based on hydrogen-bonded dimer and tetramer precursors of hydrazines. The closure and growth in length of building units into fibrils takes place through van der Waals forces acting between the dangling alkyl chains. The nanoscale morphology is a consequence of the basic molecular geometry, where it follows that a closure to form a fibril is not always likely for the doubly substituted hydrazine. Therefore, we also observe crystallite formation.

Mechanical properties of cellulose nanofibrils determined through atomistic molecular dynamics simulations

We have carried out atomistic molecular dynamics simulations to study the mechanical properties of cellulose nanofibrils in water and ethanol. The studied elementary fibrils consisted of regions having 34 or 36 cellulose chains whose cross-sectional diameter across the fibril was roughly 3.4 nm. The models used in simulations included both crystalline and non-crystalline regions, where the latter were designed to describe the essentials parts of amorphous cellulose nanofibrils. We examined different numbers of connecting chains between the crystallites, and found out that the elastic constants, inelastic deformations, and strength of the fibril depend on this number. For example, the elastic modulus for the whole fibril can be estimated to increase by 4 GPa for each additional connecting chain.