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PubMed2005

Drug release from tableted wet granulations comprising cellulosic (HPMC or HPC) and hydrophobic component.

The effects of component nature, proportion and processing on the release rate and mechanism were investigated for tablets comprising drug, cellulosic polymer and hydrophobic components. Four drugs differing in solubility (diclofenac sodium, ibuprofen, naproxen and indomethacin), two cellulosic polymers (HPC and HPMC) and hydrophobic Emvelop were used in two levels of mass fraction and weight ratio of drug:carrier and of cellulosic-hydrophobic component. Compression was applied after granulation or physical mixing. Drug release was evaluated in pH 6.5 phosphate buffer BP and elucidation of the release mechanism was attempted by fitting kinetic models. Statistical significance of the effects of formulation variables on the release rate and mechanism expressed by the coefficient, k, and exponent, n, of the power law kinetic model, respectively, was evaluated by ANOVA. It was found that for the release mechanism most significant is the effect of drug solubility followed by cellulosic polymer type, mixing procedure and drug mass fraction. Significant interaction between drug solubility and type of cellulosic polymer indicated that alteration in the swelling of HPMC and HPC is caused by the drug solubility. Weight ratio of cellulosic-hydrophobic component does not affect the release mechanism, but only the release rate. Similarly, for the release rate most significant was found the effect of drug solubility, followed by cellulosic polymer type, weight ratio of cellulosic-hydrophobic component, mixing method and drug mass fraction. Also significant were the interactions of drug solubility with the type and proportion of the cellulosic polymer and the processing applied. Depending on the drug solubility and type of polymer present, wet granulation can increase or decrease the release rate.

Cellulose↗
PubMed2005

A new method for cellulose membrane fabrication and the determination of its characteristics.

A novel method to fabricate semipermeable cellulose membranes based on cellulose regeneration of a dry membrane cast by the neutralization reaction is presented in this paper. In this method, an environmentally acceptable cellulose dissolution procedure is employed to prepare the membrane casting solution comprised of microcrystalline cellulose dissolved in aqueous NaOH. Moreover, a new cast drying/cellulose regeneration technique is proposed and successfully applied to prepare membranes after the exploitation of the conventional immersion precipitation method, which results in the formation of granular cellulose particles rather than membranes due to the low cellulose concentration (<5 wt%) in the cast. In the present technique, the cellulose concentration in the membrane cast is dramatically increased through water evaporation, and glycerin is utilized in the cellulose regeneration process to achieve a gentle neutralization reaction. As a result, defect-free membranes with a uniform structure are developed. A detailed investigation is also presented concerning the effects of membrane forming parameters, i.e., the concentrations of cellulose, solvent, and acid, and the membrane thickness, on membrane properties. In addition, by coordinating the molecular separation experiments via the ultrafiltration process against a number of macromolecules with various molecular weights, the fabricated membranes are demonstrated to be capable of sieving molecules with a MW above 50,000.

Cellulose↗
PubMed2002

Molecular ordering of cellulose after extraction of polysaccharides from primary cell walls of Arabidopsis thaliana: a solid-state CP/MAS (13)C NMR study.

Solid-state CP/MAS 13C NMR spectroscopy was used to determine the effects of three different sequential extraction procedures, used to remove non-cellulosic polysaccharides, on the molecular ordering of cellulose in a cell-wall preparation containing mostly primary cell walls obtained from the leaves of the model dicotyledon, Arabidopsis thaliana. The extractions were 50 mM trans-1,2-diaminocyclohexane N,N,N',N'-tetraacetic acid (CDTA) and 50 mM sodium carbonate (giving Residue 1); 50 mM CDTA, 50 mM sodium carbonate and 1 M KOH (giving Residue 2); and 50 mM CDTA, 50 mM sodium carbonate and 4 M KOH (giving Residue 3). The molecular ordering of cellulose in Residue 1 was similar to that in unextracted walls: the cellulose was almost all crystalline, with 43% of molecules contained in crystallite interiors and similar proportions of the triclinic (I(alpha)) and monoclinic (I(beta)) crystal forms. Residue 2 was partly decrystallized and the remaining crystallites were mostly in the I(beta) form. Residue 3 was a mixture of cellulose II, cellulose I and amorphous cellulose. The presence of signals at 100.0 and 102.3 ppm in the spectra of Residues 1 and 2, but not of unextracted cell walls, suggested that the extractions giving these residues caused some of the non-cellulosic polysaccharides, possibly xyloglucans and galactoglucomannans, to become relatively well ordered, for example through interactions with cellulose crystallite surfaces.

Arabidopsis↗
PubMed2002

Polyallylamine-grafted cellulose gel as high-capacity anion-exchanger.

A new cellulose-based anion-exchanger was prepared by grafting polyallylamine onto cellulose. The material was obtained by partial oxidation of a size-exclusion grade cellulose gel by aq. NaIO4, forming dialdehyde cellulose, followed by Schiff base formation with a polyallylamine (PAA, molecular mass 5000) and subsequent reduction for stabilization. Three grades of PAA-cellulose gels, with amino group contents of 0.78, 1.01 and 1.28 mmol/g cellulose, were examined for their ionic interaction with mono- and divalent carboxylic acids at pH 2.5-5.5. While the retention factor for monovalent acids was nearly proportional to the amino group content of the gel, that for divalent acids was remarkably greater for the PAA-cellulose gel than for the conventional diethylaminoethyl (DEAE) cellulose gel bearing more amino groups (1.97 mmol/g cellulose). Such high capacity can be explained by the high local density of amino groups on grafted PAA, in contrast to the random and sparse charge distribution in conventional exchangers.

Anion Exchange Resins↗
PubMed2000

Cellulose microfibrils in plants: biosynthesis, deposition, and integration into the cell wall.

Cellulose occurs in all higher plants and some algae, fungi, bacteria, and animals. It forms microfibrils containing the crystalline allomorphs, cellulose I alpha and I beta. Cellulose molecules are 500-15,000 glucose units long. What controls molecular size is unknown. Microfibrils are elongated by particle rosettes in the plasma membrane (cellulose synthase complexes). The precursor, UDP-glucose, may be generated from sucrose at the site of synthesis. The biosynthetic mechanism may involve lipid-linked intermediates. Cellulose synthase has been purified from bacteria, but not from plants. In plants, disrupted cellulose synthase may form callose. Cellulose synthase genes have been isolated from bacteria and plants. Cellulose-deficient mutants have been characterised. The deduced amino acid sequence suggests possible catalytic mechanisms. It is not known whether synthesis occurs at the reducing or nonreducing end. Endoglucanase may play a role in synthesis. Nascent cellulose molecules associate by Van der Waals and hydrogen bonds to form microfibrils. Cortical microtubules control microfibril orientation, thus determining the direction of cell growth. Self-assembly mechanisms may operate. Microfibril integration into the wall occurs by interactions with matrix polymers during microfibril formation.

Arabidopsis Proteins↗
PubMed2005

Cellulose metabolism in plants.

Many bacterial genomes contain a cellulose synthase operon together with a cellulase gene, indicating that cellulase is required for cellulose biosynthesis. In higher plants, there is evidence that cell growth is enhanced by the overexpression of cellulase and prevented by its suppression. Cellulase overexpression could modify cell walls not only by trimming off the paracrystalline sites of cellulose microfibrils, but also by releasing xyloglucan tethers between the microfibrils. Mutants for membrane-anchored cellulase (Korrigan) also show a typical phenotype of prevention of cellulose biosynthesis in tissues. All plant cellulases belong to family 9, which endohydrolyzes cellulose, but are not strong enough to cause the bulk degradation of cellulose microfibrils in a plant body. It is hypothesized that cellulase participates primarily in repairing or arranging cellulose microfibrils during cellulose biosynthesis in plants. A scheme for the roles of plant cellulose and cellulases is proposed.

Cell Wall↗
PubMed1993

Miniature crystal models of cellulose polymorphs and other carbohydrates.

Miniature crystal models of cellulose and other carbohydrates were evaluated with the molecular mechanics program MM3. The models consisted of groups of 24 to 32 monosaccharide residues, with the models of mono- and disaccharides based on well-established, single-crystal work. Structures of the cellulose forms and cellotetraose were based on published work using fibre diffraction methods. A structure for the single-chain I alpha cellulose unit cell was also tested. A dielectric constant of about 4 was best for this type of work. Calculated intra- and intermolecular energy for glucose agreed with literature values for the heat of combustion. Cellulose II had the lowest calculated energy for a cellulose form, followed by I alpha, cellulose III(I), ramie I, IV(II) and IV(I). Optimization of cellulose IV caused larger mean atomic movements from the original crystallographic positions than the other cellulose forms, and cellotetraose had larger movements than any of the other structures. Lattice energies for the cellulose forms were about 20 kcal/mol of glucose residues, with a dominant van der Waals component.

Carbohydrates↗
PubMed1997

Influence of substituent of direct dye having bisphenylenebis(azo) skeletal structure on structure of nascent cellulose produced by Acetobacter xylinum [I]: different influence of direct red 28, blue 1 and 15 on nascent structure.

The difference of influence of a certain kind of direct dye on the structure of nascent microbial cellulose was examined, with Direct Red 28 have a biphenylenebis(azo) skeletal structure; Direct Blue 1 having two hydroxyl, two methoxy and two sulfonate groups more than Direct Red 28; and Direct Blue 15 whose sulfonate groups position are different compared to Direct Blue 1. It became clear that the product in the presence of a direct dye (in particular, Direct Red 28) has the structure in which the dye molecule is included between the monolayer in the cellulose sheets corresponding to the (110) plane of microbial cellulose. On the other hand, the structure of the product in the presence of Direct Blue 1 and 15 contains conceived cellulose II structure which occurred due to be removal of dye during the rinsing process as a result of larger hydrophilicity than its affinity toward cellulose. Solid state 13C NMR and deuteration-IR measurements showed that the product in the presence of direct dye is in a noncrystalline state, although X-ray measurements indicated that they are in a crystalline state. These results support the inclusion of a dye between the (110) planes. Solid state 13C NMR and deuteration-IR reveal that the crystal structure of cellulose regenerated from the product in the presence of Direct Red 28 is similar to cellulose IVI, while that from each Direct Blue 1 and 15 product is cellulose II. The difference of the influence of the former and the latter on the nascent cellulose seemed to be caused mainly by the number of sulfonate groups, although the influence of hydroxyl and methoxy groups is not clear at present.

Azo Compounds↗
PubMed1999

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 I alpha + I beta) or Halocynthia (cellulose I beta) 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 A, 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/H2O as mercerizing medium and in a deuterated form using NaOD/D2O. Both of these samples diffracted to around 1.2 A, 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.

Cellulose↗
PubMedDate not supplied

Structural details of crystalline cellulose from higher plants.

It is commonly assumed that cellulose from higher plants contains the Ialpha and Ibeta crystalline allomorphs together with surface and disordered chains. For cellulose Ialpha, the evidence for its presence in higher plants is restricted to the C-4 signals in the solid-state (13)C NMR spectrum, which match those of crystalline cellulose Ialpha from algal sources. Algal cellulose Ialpha can be converted to the Ibeta form by high-temperature annealing. We used this approach to generate cellulose samples differing in Ibeta content from flax fibers and celery collenchyma, which respectively are representative of textile (secondary-wall) and primary-wall cellulose. It was then possible to isolate the detailed spectral contributions of the surface, Ibeta and Ialpha-like phases from linear combinations of the observed (13)C NMR and FTIR spectra. The (13)C NMR spectra resembled those of highly crystalline tunicate or algal cellulose Ibeta and Ialpha, with slight differences implying increased disorder and minor conformational discrepancies. The FTIR spectrum of the Ibeta form was closely similar to its more crystalline counterparts, but the FTIR spectrum of the Ialpha form was not. In addition to increased bandwith indicative of lower order, it showed substantial differences in the profile of hydroxyl stretching bands. These results confirm that higher plants synthesize cellulose Ibeta but show that the Ialpha-like chains, although conformationally quite similar to crystalline algal cellulose Ialpha, sit in a different hydrogen-bonding environment in higher plants. The differences are presumably occasioned by the small diameter of the crystallites and the influence of the crystallite surface on chain packing.

Apium↗
PubMed1999

Enzyme-catalyzed saccharification of model celluloses in the presence of lignacious residues.

Experiments were designed to determine the relevance of enzyme partitioning, between the cellulose and non-cellulose components of pretreated biomass, with respect to rates of cellulose saccharification in a typical biomass-to-ethanol process. The experimental system included three cellulose preparations (differing in physicochemical properties): a representative lignin-rich noncellulosic residue (prepared from dilute acid-pretreated switchgrass), an acid-extracted lignin preparation, and a complete Trichoderma reesei cellulase preparation. Enzyme-reactor conditions were typical of those commonly used in biomass-to-ethanol studies. The results were found to be dependent on both the lignin and cellulose preparations used. The noncellulosic lignacious residue, when supplemented at up to 40% (w/w) in cellulose-cellulase reaction mixtures, had little effect on rates and extents of cellulose saccharification. Overall, the results suggest that enzyme partitioning between cellulose and the noncellulosic component of a pretreated feedstock is not likely to have a major impact on cellulose saccharification in typical biomass-to-ethanol processes.

Carbohydrate Metabolism↗
PubMed2004

Thermal gelation of cellulose in a NaOH/thiourea aqueous solution.

Utilizing a novel solvent of cellulose, 6 wt % NaOH/5 wt % thiourea aqueous solution, for the first time, we prepared the thermally induced cellulose gel. We investigated the thermal gelation of cellulose solutions with rheometry and the structure of the gel with 13C NMR, wide-angle X-ray diffraction, environmental scanning electron microscopy, and atomic force microscopy. The cellulose solutions revealed an increase in both the storage modulus (G') and the loss modulus (G") with an increase in the temperature during gelation. The temperature at the turning point, where G' overrides G" because of the onset of gelation, decreased from 38.6 to 20.1 degrees C with an increase of cellulose concentration from 4 to 6 wt %. Given enough time, G' of all solutions can exceed G" at a certain temperature slightly lower than the gelation temperature, indicating that the occurrence of the gelation is also a function of time. Each of the assigned peaks of NMR of the cellulose gel is similar to that of the cellulose solution, suggesting that the gelation resulted from a physical cross-linking. The gels were composed of relatively stable network units with an average diameter of about 47 nm. At either a higher temperature (at 60 degrees C for 30 s) or a longer gelation time (at 30 degrees C for 157 s), the gel in the 5 wt % cellulose solution could form. A schematic gelation process was proposed to illustrate the sol-gel transition: the random self-association of the cellulose chains having the exposed hydroxyl in the aqueous solution promotes the physical cross-linking networks.

Cellulose↗
PubMed1997

Cellulose depolymerization to glucose and other water soluble polysaccharides by shear deformation and high pressure treatment.

The simultaneous action of shear deformation and high pressure (SDHP) creates changes in the structure of wood and its main components (cellulose, hemicelluloses, lignin). The formation of water and alkali soluble polysaccharides under SDHP action, proceeds in seconds in the solid state, without the use of any reagents and solvents. Therefore, SDHP seems to be a technologically safe method and friendly to the environment. The amorphization of cellulose crystallites and depolymerization of cellulose chains were observed under a wide range of pressures (1-6 GPa), both for cellulose samples and the cellulose part of wood. Similar depolymerization occurs in the hemicellulose part of wood. The decomposition of polysaccharides under SDHP causes the formation of the water soluble part, whose content increases with pressure and the applied shear deformation. A maximum solubility of 40% and 55% was registered at 6 GPa following treatment of cellulose and birch wood samples. A higher output in the case of wood can be explained by a specific role of lignin under SDHP, which acts as a 'grinding stone' during cellulose and hemicelluloses destruction. As shown by high-performance size exclusion chromatography, the water soluble fraction obtained from cellulose contained glucose (2.6%), cellobiose (9.6%), cellotriose (16.6%) and other higher water soluble oligomers (71%). Almost complete dissolution (98%) of the treated cellulose sample can be achieved by extraction with 10% NaOH solution. The SDHP treated birch wood was subjected to submerged fermentation (with Trichoderma viride), and a 13% output of proteins was obtained. In this case, the water soluble part played the role of the so called 'start sugars'.

Cellulose↗
PubMed2000

Expression, purification and applications of staphylococcal protein A fused to cellulose-binding domain.

Because staphylococcal Protein A (ProtA) binds specifically to IgG, it has been used for many immunological manipulations, most notably antibody purification and diagnostics. Immobilization is required for most of these applications. Here we describe a genetic-engineering approach to immobilizing ProtA on cellulose, by fusing it to cellulose-binding domain (CBD) derived from the cellulose-binding Protein A of Clostridium cellulovorans. The bifunctional fusion protein was expressed in Escherichia coli, recovered on a cellulose column and purified by elution at alkaline pH. ProtA-CBD was used to purify IgG from rabbit serum and its ability to bind IgG from different sources was determined. The bifunctional chimaeric protein can bind up to 23.4 mg/ml human IgG at a ratio of 1 mol of ProtA-CBD/2 mol of human IgG, and can purify up to 11.6 mg/ml rabbit IgG from a serum. The ability to bind functionally active CBD-affinity reagents to cellulosic microtitre plates was demonstrated. Our results indicate that a combination of CBD-affinity reagents and cellulosic microtitre plates is an attractive diagnostics matrix for the following reasons: (i) cellulose exhibits very low non-specific binding; and (ii) CBD-fusion proteins bind directly to cellulose at high density. A unique signal-amplification method was developed based on the ability of ProtA-CBD to link stained cellulose particles to primary antibody in a Western blot.

Animals↗
PubMed2005

The interaction of carbohydrate-binding modules with insoluble non-crystalline cellulose is enthalpically driven.

Natural cellulose exists as a composite of cellulose forms, which can be broadly characterized as crystalline or non-crystalline. The recognition of both of these forms of cellulose by the CBMs (carbohydrate-binding modules) of microbial glycoside hydrolases is important for the efficient natural and biotechnological conversion of cellulosic biomass. The category of CBM that binds insoluble non-crystalline cellulose does so with an affinity approx. 10-20-fold greater than their affinity for cello-oligosaccharides and/or soluble polysaccharides. This phenomenon has been assumed to originate from the effects of changes in configurational entropy upon binding. The loss of configurational entropy is thought to be less profound upon binding to conformationally restrained insoluble non-crystalline cellulose, resulting in larger free energies of binding. However, using isothermal titration calorimetry, it is shown that this is not the case for the high-affinity interactions of CcCBM17 (the family 17 CBM from EngF of Clostridium cellulovorans) and BspCBM28 (the family 28 CBM from Cel5A of Bacillus species 1139) with regenerated cellulose, an insoluble preparation of primarily non-crystalline cellulose. The enhanced free energy of binding of non-crystalline cellulose relative to cello-oligosaccharides is by virtue of improved enthalpy, not entropy.

Bacillus↗
PubMed1981

Neutral detergent fiber, hemicellulose and cellulose digestibility in human subjects.

The fate of dietary fiber and its components was examined in seven women consuming low cellulose (LC) and high cellulose (HC) diets, each for about 1 month. The diets were of constant daily composition and differed only in that the HC diet contained an additional 16 g/day non-nutritive fiber (Solka Floc), which increased the neutral detergent fiber (NDF) of the diet from 9.5 to 23.5 g/day and Crampton and Maynard cellulose from 5.4 to 19.3 g/day. When apparent fiber digestibilities during 5-day periods were determined, both NDF and cellulose digestibilities varied greatly and inconsistently in each subject throughout both diet periods. Therefore, samples were pooled to form a single 20-30 day composite for each subject during each diet. Mean apparent NDF digestibility, after correcting for protein contamination in fecal NDF, was 70.4 +/- 7.3% during the LC diet and decreased to 23.0 +/- 15.0% during the HC diet. Cellulose digestibility was 69.7 +/- 10.7% without and 15.7 +2- 17.4% with the added cellulose. Hemicellulose was calculated as NDF minus cellulose. When the fecal NDF was corrected for protein contamination, hemicellulose digestibility averaged 71.7 +/- 5.4% during the LC diet and 51.0 +/- 7.9% during the HC diet. In a separate experiment, 16 g/day Solka Floc was ingested with a semi-purified liquid diet and only 8% of the cellulose was digested. These results suggest that more than half of the fiber in a LC diet containing fruits, vegetables and refined grains is degraded, while the apparent digestibility of refined cellulose is minimal.

Adult↗
PubMed2005

Crystalline cellulose reduces plasma glucose concentrations and stimulates water absorption by increasing the digesta viscosity in rats.

Although cellulose is generally considered not to affect the viscosity of the digesta in the upper gastrointestinal tract, we found previously that the ingestion of cellulose elevated the viscosity of the gastric, small intestinal, and cecal contents when particulate matter was included in the measurements. We hypothesized that the digesta viscosity influences absorption. Here, we examined the effects of crystalline cellulose on plasma glucose concentrations by infusing control and cellobiose- and cellulose-containing artificial digesta of approximately 30 mL into the small intestine of rats. Cellulose, but not cellobiose, decreased the postinfusion plasma glucose concentration (P < 0.05), although cellulose did not cause adsorption or dilution of glucose. Among the physical properties of the artificial digesta, only viscosity was responsible for the decrease in the plasma glucose concentration, whereas water content, free water, bound water, and osmotic pressure were not. The cellulose-induced increase in digesta viscosity may delay glucose diffusion in the lumen, as found in our previous study. Cellulose also stimulated water absorption from the small intestine (P < 0.05), which may be attributable to increases in the water potential of the digesta moving through the small intestine. The ingestion of cellulose with meals, which increases digesta viscosity, is likely to modulate the postprandial plasma glucose concentration and to reduce the incidence of diarrhea associated with enteral nutrition.

Animals↗
PubMed2002

Alteration of oriented deposition of cellulose microfibrils by mutation of a katanin-like microtubule-severing protein.

It has long been hypothesized that cortical microtubules (MTs) control the orientation of cellulose microfibril deposition, but no mutants with alterations of MT orientation have been shown to affect this process. We have shown previously that in Arabidopsis, the fra2 mutation causes aberrant cortical MT orientation and reduced cell elongation, and the gene responsible for the fra2 mutation encodes a katanin-like protein. In this study, using field emission scanning electron microscopy, we found that the fra2 mutation altered the normal orientation of cellulose microfibrils in walls of expanding cells. Although cellulose microfibrils in walls of wild-type cells were oriented transversely along the elongation axis, cellulose microfibrils in walls of fra2 cells often formed bands and ran in different directions. The fra2 mutation also caused aberrant deposition of cellulose microfibrils in secondary walls of fiber cells. The aberrant orientation of cellulose microfibrils was shown to be correlated with disorganized cortical MTs in several cell types examined. In addition, the thickness of both primary and secondary cell walls was reduced significantly in the fra2 mutant. These results indicate that the katanin-like protein is essential for oriented cellulose microfibril deposition and normal cell wall biosynthesis. We further demonstrated that the Arabidopsis katanin-like protein possessed MT-severing activity in vitro; thus, it is an ortholog of animal katanin. We propose that the aberrant MT orientation caused by the mutation of katanin results in the distorted deposition of cellulose microfibrils, which in turn leads to a defect in cell elongation. These findings strongly support the hypothesis that cortical MTs regulate the oriented deposition of cellulose microfibrils that determines the direction of cell elongation.

Adenosine Triphosphatases↗