The cellulose-based hydrogel with abundant aldehyde groups was prepared by periodate oxidation of cellulose hydrogel prepared by dissolution-regeneration of cellulose by aqueous LiOH/urea solvent. Aldehyde groups could be introduced retaining the nanoporosity of the cellulose gel. The enzymatic degradation of three grades of oxidized cellulose hydrogel, with aldehyde contents of 3.3, 8.1 and 18.6 per 100 glucose unit, was carried out using solutions containing cellulase and β-glucosidase at 37 °C up to 48 h. The degradation of oxidized gels was remarkably slower than that of original cellulose gel, depending strongly on the degree of oxidation. The portion except for the amount of glucose released was greater than the degree of oxidation, but became closer to the latter with increase in the degree of oxidation. This behavior can be interpreted in terms of the enzymatic recognition of the chemically modified cellulose chains. 相似文献
A cellulose-based anion exchanger bearing water-soluble polycation was tested for separation of proteins. The exchanger was obtained by partial oxidation of cellulose gel by aq. NaIO4 followed by Schiff base formation with polyallylamine (PAA, molecular mass 5000). The retention behavior of proteins for three grades of PAA-cellulose gels, with amino group contents of 0.35, 0.59 and 0.96 mmol/g cellulose, was examined at several pH values and compared with that for conventional DEAE-cellulose gel with amino group content of 1.07 mmol/g cellulose. The retention of proteins by PAA-cellulose gels was remarkably greater than that for the DEAE-cellulose gel. Pairs of proteins having close isoelectric points and molecular masses (human and bovine serum albumins; beta-lactoglobulin A and B) could be separated by the PAA-cellulose gel columns. Such efficiency can be ascribed to high local density of grafted polyallylamine, in contrast to the random and sparse charge distribution in DEAE-cellulose. 相似文献
A new lyophilization technique was used for immobilization of Saccharomyces cerevisiae cells in hydroxyethylcellulose (HEC) gels. The suitability of the lyophilized HEC gels to serve as immobilization matrices
for the yeast cells was assessed by calculating the immobilization efficiency and the cell retention in three consecutive
batches, each in duration of 72 h. Throughout the repeated batch fermentation, the immobilization efficiency was almost constant
with an average value of 0.92 (12–216 h). The maximum value of cell retention was 0.24 g immobilized cells/g gel. Both parameters
indicated that lyophilized gels are stable and capable of retaining the immobilized yeast cells. Showing the yeast cells propagation
within the polymeric matrix, the scanning electron microscope images also confirmed that the lyophilization technique for
immobilization of S. cerevisiae cells in the HEC gels was successful. The activity of the immobilized yeast cells was demonstrated by their capacity to convert
glucose to ethanol. Ethanol yield of 0.40, 0.43 and 0.30 g ethanol/g glucose corresponding to 79%, 84% and 60% of the theoretical
yield was attained in the first, second and third batches, respectively. The cell leakage was less than 10% of the average
concentration of the immobilized cells. 相似文献
The effect of chemical structures of TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy radical) derivatives and its analogous compounds on oxidation efficiency of C6 primary hydroxyls of wood cellulose was investigated using the NaClO/NaBr system at pH 10. Because the oxidation takes place selectively on the surfaces of cellulose microfibrils, individualized and surface-oxidized cellulose nanofibrils can be obtained by simple mechanical treatment in water, when sufficient amounts of carboxylate groups are formed homogeneously in cellulose microfibrils. 4-acetamide-TEMPO and 4-methoxy-TEMPO showed efficient catalytic behavior with short reaction times (<4 h) and high carboxylate contents (>1.1 mmol/g) in oxidation of wood cellulose, comparable to TEMPO. Correspondingly, these TEMPO derivatives as well as TEMPO gave high nanofibril yields >56%. On the other hand, the use of 4-hydroxy-TEMPO and 4-oxo-TEMPO resulted in the lowest efficiency in oxidation: oxidation times >24 h, carboxylate contents <0.3 mmol/g, and individualized and surface-oxidized nanofibril yields <2%. 相似文献
A novel boronic acid and carboxyl-modified glucose molecularly imprinted polymer were prepared through suspension polymerization, which is based on 1.0 mmol glucose as a template, 1.2 mmol methacrylamidophenylboronic acid, and 6.8 mmol methacrylic acids as monomers, 19 mmol ethyleneglycol dimethacrylate, and 1 mmol methylene-bis-acrylamide as crosslinkers. The prepared glucose-molecularly imprinted polymer had a particle size of 25–70 μm, and was thermally stable below 215°C, with a specific surface area of 174.82 m2/g and average pore size of 9.48 nm. The best selectivity between glucose and fructose was 2.71 and the maximum adsorption capacity of glucose- molecularly imprinted polymer was up to 236.32 mg/g which was consistent with the Langmuir adsorption model. The similar adsorption abilities in six successive runs and the good desorption rate (99.4%) verified glucose-molecularly imprinted polymer could be reused. It was successfully used for extracting glucose from cellulose hydrolysis. The adsorption amount of glucose was 2.61 mg/mL and selectivity between glucose and xylose reached 4.12. A newly established chromatography (glucose-molecularly imprinted polymer) mediated hollow fiber membrane method in time separated pure glucose from cellulose hydrolysates on a large scale, and purified glucose solution with a concentration of 3.84 mg/mL was obtained, which offered a feasible way for the industrial production of glucose from cellulose hydrolysates. 相似文献
Bilayer glucose isomerase was immobilized in porousp-trimethylaminepolystyrene (TMPS) beads through a molecular deposition technique. Some of the factors that influence the activity
of immobilized glucose isomerase were optimized, with the enzyme concentration of 308 IU/mL, enzyme-to-matrix ratio of 924
IU/g wet carrier, and hexamethylene bis(trimethylammonium iodine) concentration of 15 mg/mL giving the maximum catalytic activity
(2238 IU/g dry gel) of the immobilized bilayer glucose isomerase, retaining 68.5% of the initially added activity. The half-life
of the immobilized bilayer glucose isomerase was approx 45 d at pH 8.5, 60°C, with 50% (w/v) glucose as substrate. The specific
productivity of the immobilized bilayer glucose isomerase was 223 g dry D-glucose/g dry immobilized enzyme per d. 相似文献
Eucalyptus cellulose is usually pre-treated by oxidation with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), NaBr and NaClO at pH 10.5 and 25 °C before the mechanical process required to obtain cellulose nanofibers (CNFs). In this study, different aspects to improve the effectiveness and sustainability of the TEMPO-mediated oxidation are analyzed. The optimization was carried out at different reaction times by modifying both the concentration of the NaClO and the amount of the catalysts (TEMPO and NaBr). Results show that the carboxyl groups increased up to 1.1 mmol/g with 5 mmol NaClO/g after 50 min, and that the catalyst concentration can be reduced to 0.025 mmol TEMPO/g and 0.5 mmol NaBr/g to minimize costs while maintaining the high fibrillation degree of the CNFs. The kinetic of the reaction can be considered as zero-order with respect to NaClO, and as first order with respect to cellulose. As a result of this work, the catalyst doses are reduced up to 75% compared to the most widely used catalyst doses (0.1 mmol/g TEMPO and 1 mmol/g NaBr), obtaining highly fibrillated CNFs with a lower environmental impact. This reduction of catalyst doses will reduce the costs and facilitate the implementation of CNF production at industrial scale.
β-Glucosidase is a key enzyme in the hydrolysis of cellulose for producing feedstock glucose for various industrial processes.
Reuse of enzyme through immobilization can significantly improve the economic characteristics of the process. Immobilization
of the fungal β-glucosidase by covalent binding and physical adsorption on silica gel and kaolin was conducted for consequent
application of these procedures in large-scale industrial processes. Different immobilization parameters (incubation time,
ionic strength, pH, enzyme/support ratio, glutaric aldehyde concentration, etc.) were evaluated for their effect on the thermal
stability of the immobilized enzyme. It was shown that the immobilized enzyme activity is stable at 50 °C over 8 days. It
has also been shown that in the case of immobilization on kaolin, approximately 95% of the initial enzyme was immobilized
onto support, and loss of activity was not observed. However, covalent binding of the enzyme to silica gel brings significant
loss of enzyme activity, and only 35% of activity was preserved. In the case of physical adsorption on kaolin, gradual desorption
of enzyme takes place. To prevent this process, we have carried out chemical modification of the protein. As a result, after
repeated washings, enzyme desorption from kaolin has been reduced from 75 to 20–25% loss. 相似文献
Bilayer glucose isomerase was immobilized in porousp-trimethylamine-polystyrene (TMPS) beads, through a molecular deposition technique. Some of the factors that influence the
activity of immobilized glucose isomerase were optimized, with the enzyme concentration of 308 IU/mL, enzyme:matrix ratio
of 924 IU/g wet carrier, and hexamethylenebis(trimethylammonium iodine) concentration of 15 mg/mL, giving the maximum catalytic activity (2238 IU/g dry gel) of the immobilized
bilayer glucose isomerase, retaining 68.5% of the initially added activity. The half-life of the immobilized bilayer glucose
isomerase was approx 45 d at pH 8.5, 60°C, with 50% (w/v) glucose as substrate. The specific productivity of the immobilized
bilayer glucose isomerase was 223 g dry D-glucose/g dry immobilized enzyme per day. 相似文献
Mercerized wood cellulose was oxidized by 4-acetamide-TEMPO/NaClO/NaClO2 system at 60 °C and pH 4.8 for 1–5 days. Mostly individual nanocrystals 4–7 nm in width and 100–200 nm in length were obtained
by ultrasonication of the oxidized product in water. The nanocrystals had the cellulose II structure, and carboxylate contents
of 2.0–2.4 mmol/g, indicating that these carboxylate groups were selectively formed on the cellulose II crystallite surfaces
in mercerized cellulose. Moreover, the original wood cellulose and mercerized cellulose were acid-hydrolyzed, and then subjected
to the TEMPO-mediated oxidation under the same conditions at pH 4.8 to prepare reference samples. TEM images, light transmittance
and rheological properties of water dispersions showed that the nanocrystals prepared from mercerized cellulose by the TEMPO
oxidation and sonication in water had the highest dispersibility of individual nanocrystals with less amounts of bundles in
water, resulting from the highest carboxylate contents. 相似文献
β-Glucosidase was covalently immobilized alone and coimmobilized with cellulase using a hydrophilic polyurethane foam (Hypol®FHP 2002). Immobilization improved the functional properties of the enzymes. When immobilized alone, the Km for cellobiose of β-glucosidase was decreased by 33% and the pH optimum shifted to a slightly more basic value, compared to the free enzyme. Immobilized β-glucosidase was extremely stable (95% of activity remained after 1000 h of continuous use). Coimmobilization of cellulase and β-glucosidase produced a cellulose-hydrolyzing complex with a 2.5-fold greater rate of glucose production for soluble cellulose and a four-fold greater increase for insoluble cellulose, compared to immobilized cellulase alone. The immobilized enzymes showed a broader acceptance of various types of insoluble cellulose substrates than did the free enzymes and showed a long-term (at least 24 h) linear rate of glucose production from microcrystalline cellulose. The pH optimum for the coimmobilized enzymes was 6.0. This method for enzyme immobilization is fast, irreversible, and does not require harsh conditions. The enhanced glucose yields obtained indicate that this method may prove useful for commercial cellulose hydrolysis. 相似文献
Various sorbent/ion exchange materials have been reported in the literature for metal ion entrapment. We have developed a highly innovative and new approach to obtain high metal pick-up utilizing poly-amino acids (poly-l-glutamic acid, 14,000 MW) covalently attached to membrane pore surfaces. The use of microfiltration (0.2–0.6 μm) membrane-based sorbents containing multiple functional groups is a novel technique to achieve high metal sorption under convective flow conditions. For our studies, both commercial membranes and laboratory prepared cellulose membranes containing aldehyde groups were used for the attachment of poly-amino acids. Cellulose membranes were prepared by converting cellulose acetate microfiltration membranes to cellulose (using alkali treatment), subsequent oxidation of hydroxyl groups to aldehyde using sodium periodate, and attachment of poly-l-glutamic acid via Schiff base chemistry. Extensive experiments (pH 3–6) were conducted (under convective flow mode) with the derivatized membranes involving the heavy metals: lead, cadmium, nickel, copper, and selected mixtures with calcium in aqueous solutions. Metal sorption results were found to be a function of derivatization (aldehydes) density of membranes and degree of attachment of the polyfunctional groups, number of functional groups per chain, membrane surface area, and the type of metals to be sorbed. We have obtained metal sorption capacities as high as 1.5 g metal/g membrane. Of course, depending on the desired goals the membrane containing metal could be regenerated or stabilized for appropriate disposal. 相似文献
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. 相似文献
Hollow porous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate)(HEMA-co-EDMA) spheres were prepared by emulsifier-free emulsion polymerization, swelling, seed emulsion polymerization and extraction. Then the spheres activated with 2,4,6-trichloro-1,3,5-triazine were functioned with adipohydrazide (AH). After periodate oxidation of its carbohydrate moieties, horseradish peroxidase was immobilized on the hydrazide-functionalized hollow porous poly(HEMA-co-EDMA) spheres. The amount of immobilized enzyme was up to 43.4 μg of enzyme/g of support. Moreover, the immobilized horseradish peroxidase exhibited high activity and good stability. 相似文献
The use of variable forward flow with small packed enzyme reactors is shown to be valuable for improving the efficiency of enzymatic conversion. Designs with stopped flow, oscillating flow and variable (fast/slow/fast) flow are compared for the spectrophotometric determination of glucose with glucose oxidase and horseradish peroxidase immobilized on controlled-pore glass in the same reactor. Variable forward flow increased the sensitivity considerably without excessive time consumption. The technique is also useful for characterizing the activity of immobilized enzyme reactors, e.g., peroxidase reactors for hydrogen peroxide determinations. 相似文献
To enhance the conversion of the cellulose and hemicellulose, the corncob pretreated by aqueous ammonia soaking was hydrolyzed
by enzyme complexes. The saturation limit for cellulase (Spezyme CP) was determined as 15 mg protein/g glucan (50 filter paper
unit (FPU)/g glucan). The accessory enzymes (β-glucosidase, xylanase, and pectinase) were supplemented to hydrolyze cellobiose
(cellulase-inhibiting product), hemicellulose, and pectin (the component covering the fiber surfaces), respectively. It was
found that β-glucosidase (Novozyme 188) loading of 1.45 mg protein/g glucan [30 cellobiase units (CBU)/g glucan] was enough
to eliminate the cellobiose inhibitor, and 2.9 mg protein/g glucan (60 CBU/g glucan) was the saturation limit. The supplementation
of xylanase and pectinase can increase the conversion of cellulose and hemicellulose significantly. The yields of glucose
and xylose enhanced with the increasing enzyme loading, but the increasing trend became low at high loading. Compared with
xylanase, pectinase was more effective to promote the hydrolysis of cellulose and hemicellulose. The supplementation of pectinase
with 0.12 mg protein/g glucan could increase the yields of glucose and xylose by 7.5% and 29.3%, respectively. 相似文献
A wood cellulose was oxidized with catalytic amounts of 2-azaadamantane N-oxyl (AZADO) or 1-methyl-AZADO, in an NaBr/NaClO system, in water at pH 10. The oxidation efficiency, carboxylate/aldehyde contents, and degree of polymerization (DPv) of the oxidized celluloses thus obtained were evaluated in terms of the amount of AZADO or 1-methyl-AZADO catalyst added, in comparison with those prepared using the TEMPO/NaBr/NaClO system. When the AZADO/NaBr/NaClO and 1-methyl-AZADO/NaBr/NaClO oxidation systems were applied to wood cellulose using the same molar amount of TEMPO, the oxidation time needed for the preparation of oxidized celluloses with carboxylate contents of 1.2–1.3 mmol/g was reduced from ≈80 to 10–15 min. Moreover, the molar amounts of AZADO and 1-methyl-AZADO that had to be added for the preparation of oxidized celluloses with carboxylate contents of 1.2–1.3 mmol/g were reduced to 1/32 and 1/16 of the amount of TEMPO added, respectively. The DPv values for the AZADO- and 1-methyl-AZADO-oxidized celluloses after NaBH4 treatment were in the range of 600–800. This indicated that not only C6-carboxylate groups but also C2/C3 ketones were formed to some extent on the crystalline cellulose microfibril surfaces during the AZADO- and 1-methyl-AZADO-mediated oxidation. When the AZADO-oxidized wood cellulose, which had a carboxylate content of 1.2 mmol/g, was mechanically disintegrated in water, an almost transparent dispersion consisting of individually nano-dispersed oxidized cellulose nanofibrils was obtained, with a nanofibrillation yield of 89 %. 相似文献