Novel regenerated cellulose films prepared by coagulating with water: Structure and properties

Regenerated films were successfully prepared from cellulose/NaOH/urea solution by coagulating with water at temperature from 25 to 45 °C. The results of solid ¹³C NMR, wide angle X-ray diffraction, scanning electron microscopy (SEM) and tensile testing revealed that the cellulose films possessed homogeneous structure and cellulose II crystalline, similar to that prepared previously by coagulating with 5 wt% H₂SO₄. By changing the coagulation temperature from 25 to 45 °C, tensile strength of the films was in the range of 85-139 MPa. Interestingly, the RC35 film coagulated at 35 °C exhibited the highest tensile strength (σ_b = 139 MPa). The inclusion complex associated with cellulose, NaOH and urea hydrates in the cellulose solution were broken by adding water (non-solvent), leading to the self-association of cellulose to regenerate through rearrangement of the hydrogen bonds. This work provided low-cost and “green” pathway to prepare cellulose films, which is important in industry.     

Preparation of levoglucosenone through sulfuric acid promoted pyrolysis of bagasse at low temperature

Fast pyrolysis of bagasse pretreated by sulfuric acid was conducted in a fixed bed reactor to prepare levoglucosenone (LGO), a very important anhydrosugar for organic synthesis. The liquid yield and LGO yield were studied at temperatures from 240 to 350 °C and sulfuric acid loadings from 0.92 to 7.10 wt.%. An optimal LGO yield of 7.58 wt.% was obtained at 270 °C with a sulfuric acid pretreatment concentration of 0.05 M (corresponding to 4.28 wt.% sulfuric acid loading). For comparison, microcrystalline cellulose pretreated by 0.05 M sulfuric acid solution was pyrolyzed at temperature from 270 °C to 320 °C, and bagasse loaded with 3-5 wt.% phosphoric acid was pyrolyzed at temperature from 270 °C to 350 °C. The highest yield of LGO from bagasse was 30% higher than that from microcrystalline cellulose, and treatment with sulfuric acid allowed a 21% higher yield than treatment with phosphoric acid.     

Investigations about dissolution of cellulose in the 1-allyl-3-alkylimidazolium chloride ionic liquids

In this work, the 1-allyl-3-alkylimidazolium chloride ionic liquids were synthesized and characterized by increasing carbon atoms (n ≤ 6) of alkyl chains on a cationic 3-imidazole ring. The results indicated that 1-allyl-3-alkylimidazolium chloride with asymmetrical structure on the two sides of a cationic 3-imidazole ring (i.e., n = 1, 2, 6) exhibited alkalinity and lower thermal stabilities, and showed better solubility to the cellulose samples at 60-120 °C than those with symmetrical structures (n = 3, 4). The cellulose samples treated by 20% (w/w) ethylenediamine solution showed better solubility in 1-allyl-3-ethyl, hexyl-imidazolium chloride ionic liquids than that treated with 20% (w/w) NaOH solution at 5 °C for 72 h. XRD and TG analysis indicated that 0 0 2 plane apparent crystallite size as well as thermal stability of the regenerated cellulose samples from the ionic liquids decreased significantly compared with the untreated cellulose samples.     

A novel mechanism and kinetic model to explain enhanced xylose yields from dilute sulfuric acid compared to hydrothermal pretreatment of corn stover

Pretreatment of corn stover in 0.5% sulfuric acid at 160 °C for 40 min realized a maximum monomeric plus oligomeric xylose yield of 93.1% compared to a maximum of only 71.5% for hydrothermal (no added mineral acid) pretreatment at 180 °C for 30 min. To explain differences in dilute acid and hydrothermal yields, a fast reacting xylan fraction (0.0889) was assumed to be able to directly form monomeric xylose while a slow reacting portion (0.9111) must first form oligomers during hydrothermal pretreatment. Two reactions to oligomers were proposed: reversible from fast reacting xylan and irreversible from slow reacting xylan. A kinetic model and its analytical solution simulated xylan removal data well for dilute acid and hydrothermal pretreatment of corn stover. These results suggested that autocatalytic reactions from xylan to furfural in hydrothermal pretreatment were controlled by oligomeric xylose decomposition, while acid-catalytic reactions in dilute acid pretreatment were controlled by monomeric xylose decomposition.     

Oxidation of oat β-glucan in aqueous solutions during processing

The study investigated carbonyl group formation along the chain and the chain cleavage of cereal β-glucan during heat treatments, high pressure homogenisation, cold storage and ascorbic acid treatment of aqueous solutions of this soluble dietary fibre. The carbonyl group content and its distribution along the chain were simultaneously determined with the chain cleavage using a HPSEC/labelling method, originally developed for water-insoluble cellulose. Ascorbic acid treatment resulted in a relatively high degree of carbonyl content and extensive degradation of β-glucan, even in concentrations typically found in foods. The thermal oxidation of the β-glucan was considerable at 120 °C in a β-glucan solution with co-extracted compounds from oat ingredient, and in the highly purified solutions in presence of ferrous ions. Oxidation also probably contributed to the molecular properties during high pressure homogenisation, even thou the main degradation mechanism is the hydrolysis caused by mechanical energy. In addition to the cleavage of the β-glucan chain, the formation of compact, high molar mass species or molecule clusters were obtained in the study after ascorbic acid, heat (120 °C) and homogenisation treatments.     

Biocomposite films prepared from ionic liquid solutions of chitosan and cellulose

Blends of chitosan and cellulose were successfully produced using 1-butyl-3-methylimidazolium acetate (BMIMAc) as solvent media. Films were prepared from the blends by manually spreading the solution on a flat surface and precipitating the polymers in a mixture of methanol and water. To prevent the shrinkage of films, most of the absorbed water was removed by freeze drying under vacuum. Films prepared from the polymeric solutions were investigated by means of FT-IR, TGA, X-ray diffraction and SEM measurements. The shifting of the bands corresponding to -NH and CO groups of chitosan (FT-IR), the absence of the diffraction peaks at 2θ = 10.7 and 14.9° (XRD), the increased E_a for thermal decomposition for all the polymeric blends (MTGA), and the presence of an apparent homogeneous structure with no phase separation of the two polymers (SEM) provide evidence for the miscibility between chitosan and cellulose in the solid state.     

Inherent toxicity of organ preservation solutions to cultured hepatocytes

Organ preservation solutions have been designed to protect grafts against the injury inflicted by cold ischemia. However, toxicity of University of Wisconsin (UW) solution during rewarming has been reported. Therefore, we here assessed the toxicity of UW, histidine-tryptophan-ketoglutarate (HTK), Euro-Collins, histidine-lactobionate (HL), sodium-lactobionate-sucrose and Celsior solutions in cultured hepatocytes under hypothermic (4 °C), intermediate (21 °C) and physiological (37 °C) conditions. Marked toxicity of UW, HTK, HL and Euro-Collins solutions was observed at both 37 and 21 °C. With the exception of UW solution, these solutions also increased cell injury during cold incubation (LDH release after 18 h at 4 °C: HTK 76 ± 2%, Euro-Collins 78 ± 17%, HL 81 ± 15%; control: Krebs-Henseleit buffer 20 ± 6%). Testing of individual components using modified Krebs-Henseleit buffers suggested that histidine and phosphate are responsible for (part of) this toxicity. These potential toxicities should be taken into account in the development of future preservation solutions.     

Zinc chloride mediated degradation of cellulose at 200 °C and identification of the products

The effect of ZnCl₂ on the degradation of cellulose was studied to develop conditions to produce useful feedstock chemicals directly from cellulosic biomass. Cellulose containing 0.5 mol of ZnCl₂/mol of glucose unit of cellulose was found to degrade at 200 °C when heated for more than 60 s in air. The major non-gaseous products of the degradation were identified as furfural, 5-hydroxymethylfurfural and levulinic acid. The maximum yields for furfural and 5-hydroxymethylfurfural are 8% and 9%, respectively, based on glucose unit of cellulose. These yields are reached after 150 s of heating at 200 °C. A cellulose sample containing 0.5 mol of ZnCl₂/mol of glucose unit of cellulose and 5.6 equivalents of water when heated for 150 s at 200 °C produced levulinic acid as the only product in 6% yield. The ZnCl₂ mediated controlled degradation of cellulose at 200 °C is shown to produce useful feedstock chemicals in low yield.     

Endothelial cell preservation at hypothermic to normothermic conditions using clinical and experimental organ preservation solutions

Introduction

Endothelial barrier function is pivotal for the outcome of organ transplantation. Since hypothermic preservation (gold standard) is associated with cold-induced endothelial damage, endothelial barrier function may benefit from organ preservation at warmer temperatures. We therefore assessed endothelial barrier integrity and viability as function of preservation temperature and perfusion solution, and hypothesized that endothelial cell preservation at subnormothermic conditions using metabolism-supporting solutions constitute optimal preservation conditions.Methods: Human umbilical vein endothelial cells (HUVEC) were preserved at 4–37 °C for up to 20 h using Ringer's lactate, histidine–tryptophan–ketoglutarate solution, University of Wisconsin (UW) solution, Polysol, or endothelial cell growth medium (ECGM). Following preservation, the monolayer integrity, metabolic capacity, and ATP content were determined as positive parameters of endothelial cell viability. As negative parameters, apoptosis, necrosis, and cell activation were assayed. A viability index was devised on the basis of these parameters.Results: HUVEC viability and barrier integrity was compromised at 4 °C regardless of the preservation solution. At temperatures above 20 °C, the cells' metabolic demands outweighed the preservation solutions' supporting capacity. Only UW maintained HUVEC viability up to 20 °C. Despite high intracellular ATP content, none of the solutions were capable of sufficiently preserving HUVEC above 20 °C except for ECGM.Conclusion: Optimal HUVEC preservation is achieved with UW up to 20 °C. Only ECGM maintains HUVEC viability at temperatures above 20 °C.     

Asymmetry of the GroEL-GroES complex under physiological conditions as revealed by small-angle x-ray scattering

Despite the well-known functional importance of GroEL-GroES complex formation during the chaperonin cycle, the stoichiometry of the complex has not been clarified. The complex can occur either as an asymmetric 1:1 GroEL-GroES complex or as a symmetric 1:2 GroEL-GroES complex, although it remains uncertain which type is predominant under physiological conditions. To resolve this question, we studied the structure of the GroEL-GroES complex under physiological conditions by small-angle x-ray scattering, which is a powerful technique to directly observe the structure of the protein complex in solution. We evaluated molecular structural parameters, the radius of gyration and the maximum dimension of the complex, from the x-ray scattering patterns under various nucleotide conditions (3 mM ADP, 3 mM ATPγS, and 3 mM ATP in 10 mM MgCl₂ and 100 mM KCl) at three different temperatures (10°C, 25°C, and 37°C). We then compared the experimentally observed scattering patterns with those calculated from the known x-ray crystallographic structures of the GroEL-GroES complex. The results clearly demonstrated that the asymmetric complex must be the major species stably present in solution under physiological conditions. On the other hand, in the presence of ATP (3 mM) and beryllium fluoride (10 mM NaF and 300 μM BeCl₂), we observed the formation of a stable symmetric complex, suggesting the existence of a transiently formed symmetric complex during the chaperonin cycle.     

Pyrolysis characteristics and kinetics of Arundo donax using thermogravimetric analysis

The increase of the price of fossil means, as well as their programmed disappearing, contributed to increase among appliances based on biomass and energy crops. The thermal behavior of Arundo donax by thermogravimetric analysis was studied under inert atmosphere at heating rates ranging from 5 to 20 °C min⁻¹ from room temperature to 750 °C. Gaseous emissions as CO₂, CO and volatile organic compounds (VOC) were measured and global kinetic parameters were determined during pyrolysis with the study of the influence of the heating rate. The thermal process describes two main phases. The first phase named active zone, characterizes the degradation of hemicellulose and cellulose polymers. It started at low temperature (200 °C) comparatively to wood samples and was finished at 350 °C. The pyrolysis of the lignin polymer occurred during the second phase from 350 to 750 °C, named passive zone. Carbon oxides are emitted during the active zone whereas VOC are mainly formed during the passive zone. Mass losses, mass loss rates and emission factors were strongly affected by the variation of the heating rate in the active zone. It was found that the global pyrolysis of A. donax can be satisfactorily described using global independent reactions model for hemicellulose and cellulose in the active zone. The activation energy for hemicellulose was not affected by a variation of the heating rate with a value close to 110 kJ mol⁻¹ and presented a reaction order close to 0.5. An increase of the heating rate decreased the activation energy of the cellulose. However, a first reaction order was observed for cellulose decomposition. The experimental results and kinetic parameters may provide useful data for the design of pyrolytic processing system using A. donax as feedstock.     

Pretreatment and enzymic saccharification of water hyacinth cellulose

Water hyacinth was pretreated, under variable conditions, with NaOH, alkaline H₂O₂, peracetic acid and sodium chlorite. Combined pretreatments included sodium chlorite with each of NaOH, alkaline H₂O₂ and peracetic acid. Combined pretreatment with 0.1% NaClO₂ for 1 h at 100 °C and peracetic acid at 100 °C for 15 min afforded the most promising sample. The recovered lignin, cellulose and hemicellulose of this sample was 2.56%, 96.69%, and 81.38%, respectively. The same sample, by cellulase hydrolysis showed the highest cellulose conversion (80.8%) and 90% saccharification using 200 FPU/g substrate. Some ambient factors affecting saccharification of pretreated water hyacinth were investigated. Enzymic saccharification after 6 h was about 50% of that at 48 h, indicating a slow hydrolysis rate by time. Addition of 8% glucose at the beginning of the enzymic hydrolysis decreased the saccharification to about its half while addition of 8% ethanol brought about complete inhibition of the enzyme. Addition of cellobiase to the reaction mixture increased cellulose conversion and saccharification by 10%.     

Selective production of hemicellulose-derived carbohydrates from wheat straw using dilute HCl or FeCl3 solutions under mild conditions. X-ray and thermo-gravimetric analysis of the solid residues

The present work explores the combined production of hemicellulose-derived carbohydrates and an upgraded solid residue from wheat straw using a dilute-acid pretreatment at mild temperature. Dilute aqueous HCl solutions were studied at temperatures of 100 and 120 °C, and they were compared to dilute FeCl₃ under the same conditions. Comparable yields of soluble sugars and acetic acid were obtained, affording an almost complete removal of pentoses when using 200 mM aqueous solutions at 120 °C. The solid residues of pretreatment were characterized showing a preserved crystallinity of the cellulose, and a almost complete removal of ash forming matter other than Si. Results showed upgraded characteristic of the residues for thermal conversion applications compared to the untreated wheat straw.     

The biological activity of Humanin analogs correlates with structure stabilities in solution

A single mutation has resulted in large differences in neuroprotective activity of a 24 amino acid Humanin (HN). A mutation of Ser7Ala (S7A-HN) resulted in loss of activity, while a mutation of Ser14Gly (S14G-HN) resulted in about 1000-fold increase. The mechanism of the effects conferred by these mutations have been totally unclear, although our recent structure analysis suggested a possibility of the effect of mutation on the structure stability. Here, we have studied the effects of buffer and temperature on the structure of these three HN peptides. These peptides showed a similar disordered structure at 10 °C in 10 mM phosphate, pH 6.0. They were also similar in phosphate-buffered saline (PBS) as long as the temperature was kept low at 10 °C. However, a large difference was observed in both phosphate buffer and PBS between the peptides, when the temperature was raised to a physiological temperature of 37 °C. While S14G-HN showed small changes in both solutions at 37 °C, the less active HN and inactive S7A-HN showed much larger changes under the identical conditions. In addition, it appeared that structure change at 37 °C was faster for S7A-HN than HN. These results show that the structure stability at 37 °C increases in the order of S7A-HN, HN and S14G-HN, in correlation with their neuroprotective activities.     

Effect of vegetation on alpha cellulose decomposition in littoral lake sediments

The effect of vegetation cover on the decomposition of organic matter (alpha cellulose) was studied at three sediment depths (5, 15 and 25 cm) in the littoral area of a small Lake Kiruvere (Estonia). The experiment was carried out in two adjacent sites, with and without vegetation, using the litter bag method. At all sediment depths decomposition was faster at the site covered with vegetation, and was highest at 5 cm sediment depth (decomposition rate k = 0.0037 day⁻¹) and lower at 15 and 25 cm depths (k = 0.0014 day⁻¹ and k = 0.0013 day⁻¹). Higher decomposition rates coincided with higher root mass in the sediment. Decomposition rates were similar at all sediment depths in the site without a vegetation cover (k = 0.0007-0.0009 day⁻¹). The presence of a vegetation cover also affected temperatures in sediments. Temperatures were several degrees higher at all sediment depths in the area with vegetation cover, than in the area without. Mean sediment temperature differences between the two experiment areas were 1.4 °C at 5 cm sediment depth, 2.5 °C at 15 cm depth and 3.1 °C at 25 cm depth. Higher decomposition rates in the site covered with vegetation can be explained by oxygen dispersion from young roots in the higher sediment layers and by higher sediment temperatures due to the internal gas flow enhancing the microbial activity in the lower sediment layers.     

A study of binary iron/lithium organometallic complexes as single source precursors to solid state cathode materials for potential Li ion battery application

Solid state and solution phase decomposition of organometallic half sandwich and sandwich complexes of type [CpFeCODLi × DME] 1, [CpFeCODLi × TMEDA] 2 and [(Cp)₂FeLi₂ × 2 TMEDA] 3 (Cp = cyclopentadienyl, COD = 1,5-cyclooctadiene, DME = dimethoxyethane, TMEDA = tetramethylethylenediamine) derived from ferrocene, yield different kinds of lithium ferrites under oxidative and inert conditions. Thermogravimetry (TG) and TG coupled mass spectrometry of these compounds indicate that the decomposition begins above 170 °C for 1, 185 °C for 2 and 190 °C for 3 with removal of all the organic ligands. In the absence of oxygen, compounds 1, 2 and 3 decompose to a mixture of Fe, Fe₃C and Li₂O/Li₂CO₃ at temperatures above 200 °C. Amorphous α-LiFeO₂ is formed in the temperature range of 200-400 °C in the presence of oxygen. Crystalline α-LiFeO₂ is formed only above 400 °C using 1. Elemental analysis of the LiFeO₂ obtained from 1 indicates a drastic decrease in the carbon and hydrogen content with the increase in the oxidation temperature. XRD reveals the presence of Li₂CO₃ as second phase formed for precursors 1, 2, and 3 under oxidative conditions. Solution phase decomposition of 2 and 3 in the absence of oxygen followed by annealing at 600 °C yields Li₂Fe₃O₅, Li₅FeO₄ and Fe₃C depending on the solvent to precursor ratio in contrast to the α-LiFeO₂ phase formed under pure solid state decomposition conditions. However, all lithium ferrites (Li₂Fe₃O₅, Li₅FeO₄) are converted to α-LiFeO₂ when oxidized above 500 °C. The α-LiFeO₂ products were further characterized by IR, XPS, and TEM. Electrochemical analysis of the α-LiFeO₂ was performed, showing a moderate initial capacity of 13 mAh/g.     

Liquid hot water and alkaline pretreatment of soybean straw for improving cellulose digestibility

Soybean straw was pretreated with either liquid hot water (LHW) (170-210 °C for 3-10 min) or alkaline soaking (4-40 g NaOH/100 g dry straw) at room temperature to evaluate the effects on cellulose digestibility. Nearly 100% cellulose was recovered in pretreated solids for both pretreatment methods. For LHW pretreatment, xylan dissolution from the raw material increased with pretreatment temperature and time. Cellulose digestibility was correlated with xylan dissolution. A maximal glucose yield of 70.76%, corresponding to 80% xylan removal, was obtained with soybean straw pretreated at 210 °C for 10 min. NaOH soaking at ambient conditions removed xylan up to 46.37% and the subsequent glucose yield of pretreated solids reached up to 64.55%. Our results indicated LHW pretreatment was more effective than NaOH soaking for improving cellulose digestibility of soybean straw.     

Preparation of crystalline starch nanoparticles using cold acid hydrolysis and ultrasonication

Waxy maize starch in an aqueous sulfuric acid solution (3.16 M, 14.7% solids) was hydrolyzed for 2–6 days, either isothermally at 40 °C or 4 °C, or at cycled temperatures of 4 and 40 °C (1 day each). The starch hydrolyzates were recovered as precipitates after centrifuging the dispersion (10,000 rpm, 10 min). The yield of starch hydrolyzates depended on the hydrolysis temperature and time, which varied from 6.8% to 78%. The starch hydrolyzed at 40 °C or 4/40 °C exhibited increased crystallinity determined by X-ray diffraction analysis, but melted in broader temperature range (from 60 °C to 110 °C). However, the starch hydrolyzed at 4 °C displayed the crystallinity and melting endotherm similar to those of native starch. The starch hydrolyzates recovered by centrifugation were re-dispersed in water (15% solids), and the dispersion was treated by an ultrasonic treatment (60% amplitude, 3 min). The ultrasonication effectively fragmented the starch hydrolyzates to nanoparticles. The hydrolyzates obtained after 6 days of hydrolysis were more resistant to the ultrasonication than those after 2 or 4 days, regardless of hydrolysis temperatures. The starch nanoparticles could be prepared with high yield (78%) and crystallinity by 4 °C hydrolysis for 6 days followed by ultrasonication. Scanning electron microscopy revealed that the starch nanoparticles had globular shapes with diameters ranging from 50 to 90 nm.     

Cellulose isolation and core-shell nanostructures of cellulose nanocrystals from chardonnay grape skins

This is the first report on the derivation and structures of cellulose nanocrystals from grape skins. Pure cellulose was isolated from chardonnay grape skins at a 16.4% yield by a process involving organic extraction, acid and base dissolutions, and basic and acidic oxidation. The as-extracted cellulose was 54.9% crystalline and microfibrillar. Acid hydrolysis (64-65% H₂SO₄ 45 °C, 30 min) of grape skin cellulose produced the more crystalline (64.3%) cellulose nanocrystals (CNCs) that appeared mostly as spherical nanoparticles with diameters ranging from 10 to 100 nm and a mean diameter of 48.1 (±14.6) nm as observed by TEM. AFM further disclosed the spherical nanoparticles actually consist of a nano-rod core (seed) surrounded by numerous tiny cellulose fragments as the shell. Interestingly, the spherical core-shell nanoparticles resemble the shape of grape bundles, the starting biomass, may be assembled via interfacial hydrogen bonds.     

Effect of temperature on chitin and astaxanthin recoveries from shrimp waste using lactic acid bacteria

The chitin and astaxanthin recoveries by lactic acid fermentation of shrimp wastes (Litopenaeus sp) were conducted in bed-column reactors at 15, 20, 25, 30, 35, 40 and 45 °C. The response surface methodology showed that the fermentations carried out in the 27–36 °C temperature range with lactic acid above 0.319 mmol/g resulted in the highest demineralization. The maximal deproteinizations were attained from 30 to 40 °C. The extraction of free-astaxanthin did not present significant differences between 20 and 35 °C and the proportion of cis-stereoisomer forms increased with temperature. The growth rates of Lactobacillus plantarum were estimated in the 15–45 °C range and analyzed by Arrhenius and square root models. The cardinal values were 3.94 and 51.7 °C for minimum and maximum temperatures, respectively, with activation energy of 43.38 Jmol⁻¹.