Direct dissolution of cellulose in NaOH/thiourea/urea aqueous solution

Untreated cellulose was directly and quickly dissolved in NaOH/thiourea/urea aqueous solution. The mechanism of dissolution was investigated by SEM, WXRD and (13)C NMR. The components of this solvent cannot dissolve cellulose on their own, and the interactions between NaOH and urea, as well as between NaOH and thiourea, play an important role in improving the dissolution of cellulose. Moreover, (13)C NMR spectra proved that NaOH, thiourea, and urea were bound to cellulose molecules, which brings cellulose molecules into aqueous solution to a certain extent and prevents cellulose macromolecules from associating. (13)C NMR spectra of the cellulose solution show that this novel mixture is a direct solvent. Optical microscopy and CP MAS (13)C NMR were used to study the process of dissolution. The results reveal that cellulose is dissolved completely and that cellulose I (cotton linter) first changes to amorphous cellulose chains in solution, and then to cellulose II during regeneration. Moreover, a new, more effective dissolution method is proposed, as confirmed by dynamic rheology measurements.     

Microstructure and aggregation behavior of methylcelluloses prepared in NaOH/urea aqueous solutions

Three water-soluble methylcelluloses (MCs) were prepared through homogeneous reaction in NaOH/urea aqueous solution, using dimethyl sulfate as a methylation reagent. The microstructure of the MC samples was characterized by IR, GC/MS, NMR, while dilute solution properties were measured by SEC–LLS, DLS and viscometer. The total degrees of substitution (DS) of the MC samples were 1.09, 1.42 and 1.56, respectively. However, we found that the relative DS value varies with the position of the hydroxyl group, i.e., C-2 > C-3 ≈ C-6, indicating the difference of reaction activity of different hydroxyl groups. In aqueous solution, MC has a trendency to form aggregates and hard to form actual solution, even at low concentration and low temperature, which was confirmed by the SEC–LLS and DLS result that isolated MC chains and large aggregates coexisted in the dilute aqueous solution. MC aqueous solutions showed two-stage temperature dependence of hydrodynamic radius. In the first stage, i.e., the temperature ranges from 20 to 65 °C, the hydrodynamic radius of MC displayed bimodal distribution, corresponding to the single chains and large aggregates. While in the second stage, i.e., the temperature higher than 70 °C, only large aggregates appeared. The results also proved that the microstructure of MC had a great influence on its physical properties.     

Solution properties of the acrylamide-modified cellulose polyelectrolytes in aqueous solutions

A novel cellulose-based polyelectrolyte (AM-C) containing acylamino (DS = 0.625) and carboxyl (DS = 0.148) groups was homogeneously synthesized from cellulose with acrylamide in NaOH/urea aqueous solutions. Solution properties of AM-C in aqueous solutions were investigated by laser light scattering, rheometry, and viscometry. The results indicated that AM-C could form large aggregates spontaneously in water with or without the addition of salts by the strong hydrogen bonds and electrostatic interaction between acylamino and carboxyl groups. Steady-shear flow study showed a Newtonian behavior of the solutions in the dilute regime while a shear-thinning behavior as the concentration increases. The critical concentration (c_e) for transition from dilute to concentrated solution was determined to be 0.7 wt %. Aqueous solutions of AM-C displayed good thermo-stability, reversible liquid-like characters attributing to the chemical modification. The derivation from Cox-Merz rule at relatively low concentration was related to the co-existence of single chain and large aggregates of AM-C in dilute regime. As the polymer concentration increased, the AM-C system was transformed into a homogeneous entanglement structure, resulting in the disappearance of deviations from the Cox-Merz rule.     

Structure study of cellulose fibers wet-spun from environmentally friendly NaOH/urea aqueous solutions

In this study, structure changes of regenerated cellulose fibers wet-spun from a cotton linter pulp (degree of polymerization approximately 620) solution in an NaOH/urea solvent under different conditions were investigated by simultaneous synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). WAXD results indicated that the increase in flow rate during spinning produced a better crystal orientation and a higher degree of crystallinity, whereas a 2-fold increase in draw ratio only affected the crystal orientation. When coagulated in a H2SO4/Na2SO4 aqueous solution at 15 degrees C, the regenerated fibers exhibited the highest crystallinity and a crystal orientation comparable to that of commercial rayon fibers by the viscose method. SAXS patterns exhibited a pair of meridional maxima in all regenerated cellulose fibers, indicating the existence of a lamellar structure. A fibrillar superstructure was observed only at higher flow rates (>20 m/min). The conformation of cellulose molecules in NaOH/urea aqueous solution was also investigated by static and dynamic light scattering. It was found that cellulose chains formed aggregates with a radius of gyration, Rg, of about 232 nm and an apparent hydrodynamic radius, Rh, of about 172 nm. The NaOH/urea solvent system is low-cost and environmentally friendly, which may offer an alternative route to replace more hazardous existing methods for the production of regenerated cellulose fibers.     

Enhanced enzymatic hydrolysis of spruce by alkaline pretreatment at low temperature

Alkaline pretreatment of spruce at low temperature in both presence and absence of urea was studied. It was found that the enzymatic hydrolysis rate and efficiency can be significantly improved by the pretreatment. At low temperature, the pretreatment chemicals, either NaOH alone or NaOH-urea mixture solution, can slightly remove lignin, hemicelluloses, and cellulose in the lignocellulosic materials, disrupt the connections between hemicelluloses, cellulose, and lignin, and alter the structure of treated biomass to make cellulose more accessible to hydrolysis enzymes. Moreover, the wood fiber bundles could be broken down to small and loose lignocellulosic particles by the chemical treatment. Therefore, the enzymatic hydrolysis efficiency of untreated mechanical fibers can also be remarkably enhanced by NaOH or NaOH/urea solution treatment. The results indicated that, for spruce, up to 70% glucose yield could be obtained for the cold temperature pretreatment (-15 degrees C) using 7% NaOH/12% urea solution, but only 20% and 24% glucose yields were obtained at temperatures of 23 degrees C and 60 degrees C, respectively, when other conditions remained the same. The best condition for the chemical pretreatment regarding this study was 3% NaOH/12% urea, and -15 degrees C. Over 60% glucose conversion was achieved upon this condition.     

Transparent cellulose films with high gas barrier properties fabricated from aqueous alkali/urea solutions

Transparent and bendable regenerated cellulose films prepared from aqueous alkali (NaOH or LiOH)/urea (AU) solutions exhibit high oxygen barrier properties, which are superior to those of conventional cellophane, poly(vinylidene chloride), and poly(vinyl alcohol). Series of AU cellulose films are prepared from different cellulose sources (cotton linters, microcrystalline cellulose powder, and softwood bleached kraft pulp) for different dissolution and regeneration conditions. The oxygen permeabilities of these AU cellulose films vary widely from 0.003 to 0.03 mL μm m(-2) day(-1) kPa(-1) at 0% relative humidity depending on the conditions used to prepare the films. The lowest oxygen permeability is achieved for the AU film prepared from 6 wt % cellulose solution by regeneration with acetone at 0 °C. The oxygen permeabilities of the AU cellulose films are negatively correlated with their densities, and AU films prepared from solutions with high cellulose concentrations by regeneration in a solvent at low temperatures generally have low oxygen permeabilities. The AU cellulose films are, therefore, promising biobased packaging materials with high-oxygen barrier properties.     

Isolation and characterization of the glutaminyl cyclases from Solanum tuberosum and Arabidopsis thaliana: implications for physiological functions

Glutaminyl cyclases (QCs) catalyze the formation of pyroglutamic acid at the N-terminus of several peptides and proteins. On the basis of the amino acid sequence of Carica papaya QC, we identified cDNAs of the putative counterparts from Solanum tuberosum and Arabidopsis thaliana. Upon expression of the corresponding cDNAs from both plants via the secretory pathway of Pichia pastoris, two active QC proteins were isolated. The specificity of the purified proteins was assessed using various substrates with different amino acid composition and length. Highest specificities were observed with substrates possessing large hydrophobic residues adjacent to the N-terminal glutamine and for fluorogenic dipeptide surrogates. However, compared to Carica papaya QC, the specificity constants were approximately one order of magnitude lower for most of the QC substrates analyzed. The QCs also catalyzed the conversion of N-terminal glutamic acid to pyroglutamic acid, but with approximately 10(5)- to 10(6)-fold lower specificity. The ubiquitous distribution of plant QCs prompted a search for potential substrates in plants. Based on database entries, numerous proteins, e.g., pathogenesis-related proteins, were found that carry a pyroglutamate residue at the N-terminus, suggesting QC involvement. The putative relevance of QCs and pyroglutamic acid for plant defense reactions is discussed.     

Structures of glycosylated mammalian glutaminyl cyclases reveal conformational variability near the active center

Formation of N-terminal pyroglutamate (pGlu or pE) from glutaminyl or glutamyl precursors is catalyzed by glutaminyl cyclases (QC). As the formation of pGlu-amyloid has been linked with Alzheimer's disease, inhibitors of QCs are currently the subject of intense development. Here, we report three crystal structures of N-glycosylated mammalian QC from humans (hQC) and mice (mQC). Whereas the overall structures of the enzymes are similar to those reported previously, two surface loops in the neighborhood of the active center exhibit conformational variability. Furthermore, two conserved cysteine residues form a disulfide bond at the base of the active center that was not present in previous reports of hQC structure. Site-directed mutagenesis suggests a structure-stabilizing role of the disulfide bond. At the entrance to the active center, the conserved tryptophan residue, W(207), which displayed multiple orientations in previous structure, shows a single conformation in both glycosylated human and murine QCs. Although mutagenesis of W(207) into leucine or glutamine altered substrate conversion significantly, the binding constants of inhibitors such as the highly potent PQ50 (PBD150) were minimally affected. The crystal structure of PQ50 bound to the active center of murine QC reveals principal binding determinants provided by the catalytic zinc ion and a hydrophobic funnel. This study presents a first comparison of two mammalian QCs containing typical, conserved post-translational modifications.     

Unique gelation behavior of cellulose in NaOH/urea aqueous solution

A transparent cellulose solution was prepared by mixing 7 wt % NaOH with 12 wt % urea aqueous solution which was precooled to below -10 degrees C and which was able to rapidly dissolve cellulose at ambient temperature. The rheological properties and behavior of the gel-formed cellulose solution were investigated by using dynamic viscoelastic measurement. The effects of temperature, time, cellulose molecular weight, and concentrations on both the shear storage modulus (G') and the loss modulus (G") were analyzed. The cellulose solution having a viscosity-average molecular weight (M(eta)) of 11.4 x 10(4) had its sol-gel transition temperature decreased from 60.3 to 30.5 degrees C with an increase of its concentration from 3 to 5 wt %. The gelation temperature of a 4 wt % cellulose solution dropped from 59.4 to 30.5 degrees C as the M(eta) value was increased from 4.5 x 10(4) to 11.4 x 10(4). Interestingly, at either higher temperature (above 30 degrees C), or lower temperature (below -3 degrees C), or for longer gelation time, gels could form in the cellulose solutions. However, the cellulose solution remains a liquid state for a long time at the temperature range from 0 to 5 degrees C. For the first time, we revealed an irreversible gelation in the cellulose solution system. The gel having been formed did not dissolve even when cooled to the temperature of -10 degrees C, at which it was dissolved previously. Therefore, this indicates that either heating or cooling treatment could not break such stable gels. A high apparent activation energy (E(a)) of the cellulose solution below 0 degrees C was obtained and was used to explain the gel formation under the cooling process.     

Effects of urea and sodium hydroxide on the molecular weight and conformation of alpha-(1-->3)-D-glucan from Lentinus edodes in aqueous solution

The weight-average molecular weight (Mw) and intrinsic viscosity ([eta]) of the alpha-(1-->3)-D-glucan (L-FV-II) from Lentinus edodes in 0.5 and 1.0 M NaOH aqueous solution containing urea, were studied by light scattering and viscometry. The Mw value of the glucan decreased with increase of the urea and NaOH concentration. A strong intermolecular hydrogen bonding confers water-insolubility on the glucan, but NaOH and especially urea, broke this hydrogen bonding leading to enhanced water-solubility. Use of 1.0 M urea-1.0 M NaOH as solvent broke not only intermolecular hydrogen bonds but also partial covalent bonds of the alpha-glucan in aqueous solution, resulting in a decrease of Mw and [eta]. The urea and NaOH concentrations, storage time with stirring, and mode of preparation of the polysaccharide in aqueous solution significantly affected the determination of Mw and [eta]. The dependences of specific rotation and fluorescence emission ratio of a probe on urea concentration showed that a change in the molecular conformation of the alpha-glucan in 0.5 M NaOH aqueous solution containing urea occurred in the range 0.4-0.6 M urea. The 0.5 M urea-0.5 M NaOH aqueous solution is a suitable solvent for the glucan, and the Mw and [eta] values obtained were 5.21 x 10(5) and 148 cm3 g(-1), respectively. Degradation of the glucan was obvious after storage for 15 months.     

Dynamic viscoelastic properties of cellulose carbamate dissolved in NaOH aqueous solution

Dynamic viscoelastic properties of cellulose carbamate (CC) dissolved in NaOH aqueous solution were systematically studied for the first time. CC was microwave-assisted synthesized from the mixture of cellulose and urea and then dissolved in 7 wt % NaOH aqueous solution precooled to -7 °C. The obtained CC solution is transparent and has good liquidity. To clarify the rheological behavior of the solution, the CC solutions were investigated by dynamic viscoelastic measurements. The shear storage modulus (G') and loss modulus (G') as a function of the angular frequency (ω), concentration (c), nitrogen content (N %), viscosity-average molecular weight (M(η)), temperature (T), and time (t) were analyzed and discussed in detail. The sol-gel transition temperature of CC (M(η) = 7.78 × 10(4)) solution decreased from 36.5 to 31.3 °C with an increase of the concentration from 3.0 to 4.3 wt % and decreased from 35.7 to 27.5 °C with an increase of the nitrogen content from 1.718 to 5.878%. The gelation temperature of a 3.8 wt % CC solution dropped from 38.2 to 34.4 °C with the M(η) of CC increased from 6.35 × 10(4) to 9.56 × 10(4). The gelation time of the CC solution was relatively short at 30 °C, but the solution was stable for a long time at about 15 °C. Moreover, the gels already formed at elevated temperature were irreversible; that is, after cooling to a lower temperature including the dissolution temperature (-7 °C), they could not be dissolved to become liquid.     

A Unique Carboxylic-Acid Hydrogen-Bond Network (CAHBN) Confers Glutaminyl Cyclase Activity on M28 Family Enzymes

Proteins with sequence or structure similar to those of di-Zn exopeptidases are usually classified as the M28-family enzymes, including the mammalian-type glutaminyl cyclases (QCs). QC catalyzes protein N-terminal pyroglutamate formation, a posttranslational modification important under many physiological and pathological conditions, and is a drug target for treating neurodegenerative diseases, cancers and inflammatory disorders. Without functional characterization, mammalian QCs and their orthologs remain indistinguishable at the sequence and structure levels from other M28-family proteins, leading to few reported QCs. Here, we show that a low-barrier carboxylic-acid hydrogen-bond network (CAHBN) is required for QC activity and discriminates QCs from M28-family peptidases. We demonstrate that the CAHBN-containing M28 peptidases deposited in the PDB are indeed QCs. Our analyses identify several thousands of QCs from the three domains of life, and we enzymatically and structurally characterize several. For the first time, the interplay between a CAHBN and the binuclear metal-binding center of mammalian QCs is made clear. We found that the presence or absence of CAHBN is a key discriminator for the formation of either the mono-Zn QCs or the di-Zn exopeptidases. Our study helps explain the possible roles of QCs in life.     

Rheological behaviors and miscibility of mixture solution of polyaniline and cellulose dissolved in an aqueous system

In our previous work, supramolecular films composed of hydrophilic cellulose and hydrophobic polyaniline (PANI) dissolved in NaOH/urea aqueous solution at low temperature through rearrangement of hydrogen bonds have been constructed. To further understand the miscibility and processability of the complex solution, the dynamic rheological behaviors of the PANI/cellulose complex solution were investigated, for the first time, in the present work. Transmission electron microscope (TEM) results demonstrated that the inclusion complexes consisted of PANI and cellulose, existed in the aqueous solution, showing a good miscibility. Time-temperatures superposition (tTs) results indicated that the PANI/cellulose solution exhibited a homogeneous system, and the complex solution was more stable than the cellulose solution in the temperature range from 5 to 25 °C. Winter-Chambon theory was proved to be capable of describing the gelation behavior of the PANI/cellulose complex solution. The relaxation exponent at the gel point was calculated to be 0.74, lower than the cellulose solution, indicating strong interactions between PANI and cellulose chains. Relatively larger flow activation energy of the PANI/cellulose solution suggested the formation and rupture of linkages in "junction zones" during the gelation processes. Furthermore, PANI/cellulose gels could form at elevated temperature as a result of the physical cross-linking and chain entanglement, and it was a thermoirreversible process. Moreover, the PANI/cellulose solution remained a liquid state for a long time at the temperature range from 0 to 8 °C, which is important for the industry process.     

A simple preparative method for the isolation of amylose and amylopectin from potato starch

The defatted starch was dispersed in NaOH (1 M) and neutralized with HCl (1 M). The amylose 1-butanol complex is adsorbed on defatted cellulose powder in the solvent system containing acetate buffer (pH 4.8,0.1 M) + urea (2 M) + 1-butanol (8.5%, v/v). The complex adsorbed on cellulose powder is separated by centrifugation (2418 g). The sediment is washed with the solvent system-I to obtain the intermediate fraction. The adsorbed amylose is eluted with urea (2 M) in acetate buffer (pH 4.8, 0.1 M). The amylose, intermediate fraction and amylopectin were precipitated with ethanol, washed free of urea and air dried. They were characterized by determining their blue value and beta -amylolysis limit.     

Synthesis and properties of anionic cellulose ethers: influence of functional groups and molecular weight on flowability of concrete

The suitability of anionic cellulose ethers as superplasticizers and the effect of chemical structure on the fluidity of cement mixtures was investigated. To elucidate the influence of molecular weight and degree of cellulose backbone substitution, cellulose and hydroxyethyl cellulose with molecular weights <50,000 g/mol were synthesized by acid-catalyzed and oxidative degradation. Commercial as well as degraded samples were functionalized by carboxymethylation and sulfobutylation, controlling the degree of substitution (DS) by the molar ratio of reactants and by taking advantage of the high reactivity of sultones towards salts of carboxylic acids, even in aqueous solutions. The fluidizing effect of the cellulose ethers with anionic ‘cement-anchoring‘ groups was prescreened, measuring the static flow of cement pastes. The results indicated a high potential of sulfobutylated cellulose mixed ethers as dispersing agents for concrete. The fluidizing action increased with increasing DS and an optimum range of molecular weight between 100,000 and 150,000 g/mol was found.     

A Simple Preparative Method for the Isolation of Amylose and Amylopectin from Potato Starch

The defatted starch was dispersed in NaOH (1 M) and neutralized with HCl (1 M). The amylose 1-butanol complex is adsorbed on defatted cellulose powder in the solvent system containing acetate buffer (pH 4.8, 0.1 M) ± urea (2 M) ± 1-butanol (8.5 %, v/v). The complex adsorbed on cellulose powder is separated by centrifugation (2418 g). The sediment is washed with the solvent system-I to obtain the intermediate fraction. The adsorbed amylose is eluted with urea (2 M) in acetate buffer (pH 4.8, 0.1 M). The amylose, intermediate fraction and amylopectin were precipitated with ethanol, washed free of urea and air dried. They were characterized by determining their blue value and β -amylolysis limit.     

Structure of aqueous solutions of microcrystalline cellulose/sodium hydroxide below 0 degrees C and the limit of cellulose dissolution

The aim of the paper is to investigate the structure of solutions of microcrystalline cellulose in NaOH/water mixtures and to determine the limit of cellulose solubility. The binary NaOH/water and the ternary cellulose/NaOH/water phase diagrams in the area of cellulose dissolution (7-10% NaOH below 0 degrees C) are studied by DSC. The NaOH/water binary phase diagram has a simple eutectic behavior. Because of the existence of this eutectic structure, it is possible to measure the influence of the addition of pure low molar mass microcrystalline cellulose. This shows that a minimum of four NaOH molecules should be linked to one anhydroglucose unit to allow for the dissolution of microcrystalline cellulose. The proportions between bound Avicel, NaOH, and water molecules as a function of cellulose concentrations are calculated. A tentative explanation about the origin of the dissolving power of NaOH/water is given.     

Cationic starch: an effective flocculating agent

A series of cationic starches (Cat St) have been developed by incorporating a cationic moiety N-(3-Chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC) onto the backbone of starch in presence of NaOH. The cationic starches are characterized by elemental analysis, FTIR spectroscopy and intrinsic viscosity measurement. The flocculation characteristics of these starches have been evaluated in 0.25 wt% silica suspension by jar test. It has been found that among the four cationic starches, the one with longer CHPTAC chains shows the best performance. The flocculation characteristics of this starch are on silica suspensions compared with various commercially available flocculants.     

Synthesis and characterization of a trifunctional aminoamide cellulose derivative

As part of an effort to synthesize a dendronized cellulose, we have synthesized a trifunctional aminoamide derivative, which is the first generation of a dendron substituent. We anticipate that a dendronized cellulose would have applications in complexing metals and could be employed as an adjuvant for drugs. The trifunctional aminoamide substituent was introduced by coupling di-tert-butyl 4-[2-(tert-butoxycarbonyl)ethyl]-4-aminoheptanedicarboxylate, BA, directly to a (carboxymethyl)cellulose (CMC) backbone and converting the tert-butyl ester peripheral groups to aminoamide substituents by use of N,N-dimethyl-1,3-propanediamine. Confirmation of the proposed chemical structure of the intermediates as well as the water-soluble aminoamide derivative (CMCBADMPDA) was obtained by Fourier transform infrared (FT-IR) and NMR spectroscopy. The degree of substitution (DS) was determined to be 0.40 +/- 0.01 by thermogravimetric analysis. Typical weight average molecular weight (M(w)), molecular weight distribution (MWD), and molecular size of the dendronized polymers were found to be 97,000, 1.7, and 17.4 nm for derivatives of a CMC with corresponding M(w), MWD, and root-mean-square radius (RMS) of 230 000, 3.2, and 24 nm. A differential refractive index (dn/dc) for the aminoamide derivative measured in aqueous 0.40 N ammonium acetate-0.01 N NaOH was found to be 0.1473. The intrinsic viscosity of the dendronized cellulose decreased significantly when compared with that of CMC, that is, 0.40 dL/g relative to 5.60 dL/g. The hydrophobicity of the CMCBADMPDA microenvironment in aqueous solution was probed by evaluating the relative fluorescence intensities of the I(373)/I(384) pyrene bands; a slightly more hydrophobic environment was observed.