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1.
Thomas Rosenau Antje Potthast Karin Krainz Yuko Yoneda Thomas Dietz Zenaida Peralta-Inga Shields Alfred D. French 《Cellulose (London, England)》2011,18(6):1623-1633
In the present work, aged cotton linters have been analyzed for their chromophore content according to the CRI (“chromophore
release & identification”) method. Despite the very low contents in the ppb range, nine chromophores have been unambiguously
identified, which makes this account the first one on defined chromophoric structures isolated from cotton. A common feature
of the chromophores are 2-hydroxy-[1,4]benzoquinone, 2-hydroxyacetophenone and 5,8-dihydroxynaphthoquinone moieties, which
resemble chromophoric structures found in other cellulosic substrates, such as bleached pulps or fibers. The finding of these
compounds in lignin-free cotton linters confirms the previous hypothesis that those chromophores are formed from (oxidized)
carbohydrate structures rather than from lignin fragments. 相似文献
2.
McCarter Suzanne L. Adney William S. Vinzant Todd B. Jennings Edward Eddy Fannie Posey Decker Stephen R. Baker John O. Sakon Joshua Himmel Michael E. 《Applied biochemistry and biotechnology》2002,98(1-9):273-287
Understanding the interactions between cellulases and cellulosic substrates is critical to the development of an efficient
artificial cellulase system for conversion of biomass to sugars. We directed specific mutations to the interactive surface
of the Acidothermus cellulolyticus EI endoglucanase catalytic domain. The cellulose-binding domain is not translated in these mutants. Amino acid mutations
were designed either to change the surface charge of the protein or to modify the potential for hydrogen bonding with cellulose.
The relationship between cellulase-to-cellulose (Avicel PH101) binding and hydrolysis activity was determined for various
groupings of mutations. While a significant increase in hydrolysis activity was not observed, certain clusters of residues
did significantly alter substrate binding and some interesting correlations emerged. In the future, these observations may
be used to aid the design of endoglucanases with improved performance on pretreated biomass. 相似文献
3.
The wood-rotting basidiomyceteCoriolus versicolor has been grown under a variety of conditions ranging from stationary cultures on spruce wood chips or milled-wood lignin,
known to be actively ligninolytic, to agitated submerged cultures, with glucose or carboxymethylcellulose as the main carbon
source, that had no ligninolytic activity. Extracellular proteins have been recovered from the growth medium by ammonium sulfate
precipitation and fractionated into their polypeptide components by a combination of ion exchange, affinity column chromatography,
and polyacrylamide gel electrophoresis, thus providing a “fingerprint” technique for different growth conditions.
Characterization of some of the polypeptide components on the PAGE plates can be made by the use of selected staining techniques
for proteins, glycoproteins, peroxidase activity, and heme-containing polypeptides. Variations in the “fingerprints” from
different cultures can be demonstrated, in addition to showing the development of the extracellular protein population in
an actively ligninolytic culture during the change from primary to secondary growth phases.
The effect of some of the extracellular enzymes on polymeric lignin has been demonstrated. A crude protein extract isolated
from rotting wood chips was incubated with milled-wood lignin extracted from spruce sapwood. Analysis of the lignin after
48 h incubation by UV and NMR spectroscopy showed there to be an increase in aromatic hydroxyl groups with a decrease in aliphatic
hydroxyl groups in comparison with sound milled-wood lignin. There was also a small reduction in the mean molecular weight
of the lignin, analyzed by HPLC size-exclusion chromatography.
By contrast, lignin that had been incubated with purified laccase A showed a considerable increase in the mean molecular weight,
almost doubling over a 48-h period of incubation. 相似文献
4.
When pine wood decayed by white- and brown-rot fungi was observed in TEM after fixation and staining with glutaraldehyde/osmium
tetroxide/ uranylacetate and embedding in Spurr’s ultralow viscosity resin electron dense particles, called “osmiophilic particles,”
a typical distribution for the two decay types could be observed: in white-rotted wood the particles could be found in and
around the hyphae and on the lumen surface of the wood cell wall, mostly aggregated to thick clusters. During the whole course
of decay the wood cell walls were free of the particles, but they were present on the corroded surfaces. In brown-rotted wood
the “osmiophilic particles” also could be found in and around the hyphae, but in contrast the particles were distributed over
all the wood cell wall layers from the early to late stages of decay.
The distribution of the “osmiophilic particles” coincides with the place where the major cell wall degradation takes place:
in white-rot the cell walls are degraded from the lumen to the middle lamella; in brown-rot a depolymerization and degradation
of the carbohydrates takes place all over the wood cell wall. Since the “osmiophilic particles” can be found where the degradation
takes place, it can be concluded that they are causally connected with wood decay.
The fact that they also were found in, and some of them also around, hyphae grown on malt-agar or Sabouraud-dextrose-agar
proves that they are produced by the fungi and cannot be degradation products.
The possibility that they could be preparative artifacts can be excluded because uncolonized wood was free of “osmiophilic
particles.”
Since the “osmiophilic particles” are produced by the fungi and can be found in places where wood is decaying, it can be further
concluded that they are a fungal agent that is involved in wood degradation, probably fungal enzymes. The observation that
the large “osmiophilic particles,” which may have a size of up to 20 nm, are composed of globular subunits of a diameter of
2—3 nm also speaks for their enzymatic nature.
To find out which type of enzyme they might be, the white-rot fungusTrametes hirsuta was grown on wood pulp with 7% lignin, on delignified wood pulp containing cellulose and hemicellulose, and on filterpaper
(pure cellulose). The hyphae on wood pulp containing 7% lignin were surrounded by thick sheaths of “osmiophilic particles,”
whereas with the hyphae grown on delignified wood pulp and pure cellulose only a few particles could be found. This makes
it clear that the production of the “osmiophilic particles” is induced by lignin. 相似文献
5.
Cellulases and their interaction with cellulose 总被引:3,自引:0,他引:3
Bernard Henrissat 《Cellulose (London, England)》1994,1(3):169-196
Most effective cellulolytic enzymes are made of at least two constitutive domains, a catalytic domain and a non-catalytic cellulose-binding domain linked by a flexible peptide. There are several families of catalytic domains and of cellulose-binding domains resulting in a large number of their possible combinations. Removal of the cellulose-binding domain drastically reduces the binding capacity of cellulases to insoluble cellulose while the catalytic efficiency on soluble substrates is usually maintained. Isolated cellulose-binding domains bear most of the binding properties of cellulases (quasi-irreversibility and dispersive effect) but do not hydrolyse cellulose. The multiple types of synergy that cellulases display when acting in combination on cellulose appear to result from their different activities and selectivity, from the substrate microheterogeneity, and sometimes from both.To the memory of Prof. Elwyn T. Reese. 相似文献
6.
L. P. Oleksenko L. A. Belyakova V. K. Yatsimirskii O. Yu. Boldyreva D. Yu. Lyashenko 《Theoretical and Experimental Chemistry》1998,34(3):153-157
By binding platinum ions with acetylacetone immobilized on a silica surface, we have obtained a metal complex catalyst containing
Pt(II). We have also studied its catalytic activity in the model reaction of oxidation of hydrogen. We have shown that over
the course of the catalytic process, this catalyst exhibits high catalytic activity at room temperatures and displays the
“surface memory” effect with respect to a previous reaction. The activity of the grafted Pt complex is significantly higher
than the activity of a supported platinum catalyst.
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 3, pp. 170–175, May–June, 1998. 相似文献
7.
Using time-resolved CIDEP and conventional ESR as well as optical studies much can be elucidated concerning the initial photochemical
reactions of lignin model compounds such as α-guaiacoxyacetoveratrone and α-guaiacoxy-β-propioveratrone. The resulting transient
radicals are models for intermediates in the processes of photoyellowing of lignin containing mechanical pulps and papers.
Model solution experiments which produce evidence for the roles of free radicals in reductive bleaching of mechanical pulps
and in the oxidative aging of papers are also described. The more thorough understanding of these complex processes allows
the development of strategies to try to “protect” mechanical pulps and papers from light and thermally induced damage and
to “repair” any damage which invevitably occurs. 相似文献
8.
Alvaro de Jesús Martínez-Gómez Sorin O. Manolache Víctor Gónzalez-Álvarez Raymond A. Young Ferencz Sandor Denes 《Cellulose (London, England)》2009,16(3):501-517
The surface functionalization process was accomplished in a consecutive 3 step process including: (1) Argon- and oxygen-plasma
enhanced generation of free radical sites on cellophane surfaces; (2) “In situ” gas phase derivatization in the absence of
plasma using hydrazine, ethylene diamine, or propylene diamine; (3) Second “in situ”, gas phase derivatization in the absence
of plasma using oxallyl chloride or “ex situ” derivatization in the presence of glutaraldehyde. The presence of free radical
sites on the plasma exposed cellophane surfaces was demonstrated using “in situ” sulfur dioxide and nitric oxide labeling
techniques. It was shown that the free radical sites readily react under “in situ” conditions with the stable chain-precursor
components and generate the desired spacer-chain molecules. ESCA, ATR-FTIR analysis and dying techniques were used to monitor
the cellophane surface changes. A factorial design was used for selecting the optimal plasma parameters. Functionalized cellophane
substrates were used for immobilization of α-chymotrypsin in the presence of spacer-chain molecules. The activity of the immobilized
α-chymotrypsin was found to be lower in comparison to the activity of the free enzyme and the presence of virgin cellophane
in the free enzyme solution also reduced significantly the activity of the enzyme. It is suggested that the swollen state
of the cellophane plays a significant role in the decrease of the immobilized enzyme activity. 相似文献
9.
M. A. Osina G. A. Kiselev V. A. Bogdanovskaya I. V. Yaminskii 《Russian Journal of Electrochemistry》2009,45(8):887-894
Morphology of nanostructured composite material “horse-radish peroxidase-Nafion” is studied by using atomic-force microscope.
The results of the AFM-measurements are compared with the electrochemical data on the hydrogen peroxide reduction in the presence
of the horse-radish peroxidase adsorbed from aqueous solution and from the “horse-radish peroxidase-Nafion” composite. The
results of the electrochemical measurements and the AFM-data are in qualitative agreement with each other. It is shown that
the co-immobilization of the horse-radish peroxidase and Nafion results in the enzyme strong immobilization on the carbonaceous
material surface; cluster-structured composites are formed, in which the horse-radish peroxidase demonstrates high catalytic
activity. 相似文献
10.
K Seshadri Saraswathi Vishveshwara Mahendra K. Jain 《Journal of Chemical Sciences》1994,106(5):1177-1189
Molecular constraints for the localization of active site directed ligands (competitive inhibitors and substrates) in the
active site of phospholipase A2 (PLA2) are characterized. Structure activity relationships with known inhibitors suggest that
the head group interactions dominate the selectivity as well as a substantial part of the affinity. Theab initio fitting of the amide ligands in the active site was carried out to characterize the head group interactions. Based on a systematic
coordinate space search, formamide is docked with known experimental constraints such as coordination of the carbonyl group
to Ca2+ and hydrogen bond between amide nitrogen and ND1 of His48. An optimal position for a bound water molecule is identified and
its significance for the catalytic mechanism is postulated. Unlike the traditional “pseudo-triad” mechanism, the “Ca-coordinated-oxyanion”
mechanism proposed here invokes activation of the catalytic water to form the oxyanion in the coordination sphere of calcium.
As it attacks the carbonyl carbon of the ester, a near-tetrahedral intermediate is formed. As the second proton of the catalytic
water is abstracted by the ester oxygen, its reorientation and simultaneous cleavage form hydrogen bond with ND1 of His48.
In this mechanism of esterolysis, a catalytic role for the water co-ordinated to Ca2+ is recognised. 相似文献
11.
Whole cells ofBrevibacterium flavum having fumarase activity were immobilized using K-carrageenan. The stabilities of fumarase activity in the immobilized cells
against external factors, including heat, pH, organic solvents, and protein denaturing reagents, were compared with those
of free cells and native enzyme. The stabilities of fumarase activity in immobillized cells against external factors were
highest, and those of native enzyme were lowest. In the “gel-state,” K-carrageenan-immobilized cells showed a much higher
stabilization effect for external factors than “sol-state” immobilized cells. 相似文献
12.
Thomas Rosenau Antje Potthast Falk Liebner Gerald Ebner A. Hunter M. Renfrew Stephan Eichhorn Eva-Barbara Fürst-Wiesmann 《Cellulose (London, England)》2009,16(5):929-942
Novel trifunctional triazines (“TATORT reagents”) for the modification of cellulosic material were prepared from cyanuric
chloride. The compounds employ a cellulose-reactive anchor group for fixation, an active substance showing slow release properties,
and a reactivity tuner to facilitate release control. According to this approach, humidity acts as an external trigger to
“switch on” the slow-release. While the release-compounds are completely stable under dry conditions, the active substances
are released simply by surrounding moisture. The reactivity tuner controls the rate of the release: by choosing an appropriate
tuner, the concentration maximum can be set anytime between minutes and several weeks. The release kinetics depends mainly
on the structure of reactivity tuner and active substance, but only insignificantly on the type of the (cellulosic) carrier
matrix. Apart from the inherent limitation to phenolic and carboxylic active substances, the approach is quite general as
the active substances may encompass wide ranges of compounds and applications. 相似文献
13.
José M. Escovar-Kousen David Wilson Diana Irwin 《Applied biochemistry and biotechnology》2004,113(1-3):287-297
Cellulases are a complex group of enzymes that are fundamental for the degradation of amorphous and crystalline cellulose
in lignocellulosic material. Unfortunately, cellulases have a low catalytic efficiency on their substrates when compared to
similar enzymes such as amylases, which has led to a strong interest in improving their activities. Thermobifida fusca secretes six cellulose degrading enzymes: two exo- and three endocellulases and an endo/exocellulase Cel9A (formerly called
E4). Cel9A shows unique properties because of its endo- and exocellulase characteristics, strong activity on crystalline cellulose,
and good synergistic properties. Therefore, it is an excellent target for mutagenesis techniques to improve crystalline cellulose
degradation. In this article, we describe research conducted to improve Cel9A catalytic efficiency using a rational design
and computer modeling. A computer model of Cel9A was created using the program CHARMM plus its PDB structure and a cellohexose
molecule attached to the catalytic site as a starting model. Initially molecular graphics and energy minimization were used
to extend the cellulose chain to 18 glucose residues spanning the catalytic domain and cellulose-binding domain (CBD). The
interaction between this cellulose chain and conserved CBD residues was determined in the model, and mutations likely to improve
the binding properties of the CBD were selected. Site-directed mutations were carried out using the pET vector pET26b, Escherichia coli DH5-α, and the QuickChange mutagenesis method. E. coli BL21-DE3 was used for protein production and expression. The purified proteins were assayed for enzymatic activity on filter
paper, swollen cellulose, bacterial microcrystalline cellulose, and carboxymethylcellulose (CMC). Mutation of the conserved
residue F476 to Y476 gave a 40% improved activity in assays with soluble and amorphous cellulose such as CMC and swollen cellulose. 相似文献
14.
Response surface methodology (RSM) was employed for optimization of medium components and cultural parameters in cost effective
cane molasses based medium for attaining high yield of succinic acid. The important factors obtained by “one-variable-at-a-time-approach”
(cane molasses, corn steep liquor, sodium carbonate, and inoculum density) were further optimized by RSM. The optimum values
of the parameters obtained through RSM (cane molasses 12.5%, corn steep liquor 7.5%, and sodium carbonate 25 mM) led to almost
double yield of succinic acid (15.2 g/l in 36 h) as against “one-variable-at-a-time-approach” (7.1 g/l in 36 h) in 500-ml
anaerobic bottles containing 300-ml cane molasses based medium. Subsequently, in 10-l bioreactor succinic acid production
from Escherichia coli was further improved to 26.2 g/l in 30 h under conditions optimized through RSM. This fermentation-derived succinic acid
will definitely help in replacing existing environmentally hazardous and cost-intensive chemical methods for the production
of succinic acid. 相似文献
15.
Werner Unterberger Bernd Jenewein Bernhard Kl?tzer Simon Penner Wolfgang Reichl Günther Rupprechter Di Wang Di Wang Robert Schl?gl Konrad Hayek 《Reaction Kinetics and Catalysis Letters》2006,87(2):215-234
Summary The effect of hydrogen reduction on the structure and catalytic properties of “thin film”and “inverse”model systems for supported
metal catalysts is discussed. Thin film model catalysts were obtained by epitaxial growth of Pt and Rh nanoparticles on NaCl(001),
which were coated with amorphous or crystalline supports of alumina, silica, titania, ceria and vanadia. Structural and morphological
changes upon hydrogen reduction between 473 and 973 K were examined by high resolution electron microscopy. Metal-oxide interaction
sets in at a specific reduction temperature and is characterized by an initial “wetting”stage, followed by alloy formation
at increasing temperature, in the order VOx< TiOx< SiO2< CeOx< Al2O3. “Inverse”model systems were prepared by deposition of oxides on a metal substrate, e.g. VOx/Rh and VOx/Pd. Reduction of inverse systems at elevated temperature induces subsurface alloy formation. In contrast to common bimetallic
surfaces, the stable subsurface alloys of V/Rh and V/Pd have a purely noble metal-terminated surface, with V positioned in
near-surface layers. The uniform composition of the metallic surface layer excludes catalytic ensemble effects in favor of
ligand effects. Activity and selectivity, e.g. for CO and CO2methanation and for partial oxidation of ethene, are mainly controlled by the temperature of annealing or reduction. Reduction
above 573 K turned out to be beneficial for the catalytic activity of the subsurface alloys, but not for the corresponding
thin film systems which tend to deactivate viaparticle encapsulation.</o:p> 相似文献
16.
Hydrotalcite-like compounds (HTlcs) can be used as the catalysts as it is since they contain various transition metal cations
as the catalytically active species well dispersed on the basic support materials. Moreover, increasing numbers of the applications
of HTlcs after the heat treatment have been found since the oxides with very small crystal size, stable to thermal treatments,
are obtained after the calcination. The oxides possess interesting properties such as high surface area, basic properties
and further form small and thermally stable metal crystallites by reduction. Moreover, the calcined oxides show a unique property,
i.e., “memory effect,” which allows the reconstitution of the original hydrotalcite structure. We have developed the catalytic
applications of hydrotalcites as it is and moreover the mixed oxides derived from hydrotalcites for various catalytic reactions,
i.e., oxidation, dehydrogenation and reforming of hydrocarbons, and even for the reforming of methanol and the CO shift reaction.
Aerobic oxidation of alcohols, Baeyer−Villiger oxidation of ketones and O3 oxidation of oxalic acid have been successfully carried out with the Mg−Al hydrotalcites containing Ni, Fe and Cu, respectively,
as the catalysts in liquid phase. In the O3 oxidation of oxalic acid, the catalytic activity was enhanced by the “memory effect,” i.e., Mg(Cu)–Al hydrotaclite was reconstituted
on the surface of Mg(Cu,Al)O periclase particles and oxalic acid was incorporated as anions in the hydrotalcite layer, resulting
in an enhanced oxidation of oxalic acid. As the catalysts in the vapor phase reactions, Mg/Fe/Al mixed oxides prepared from
Mg–Al(Fe) hydrotalcites and effectively catalyzed the dehydrogenation of ethylbenzene. Supported Ni metal catalysts have been
prepared from Mg(Ni)–Al hydrotalcites and successfully used in the steam reforming and the oxidative reforming of methane
and propane. Moreover, the Ni catalysts have been improved by combining a trace amount of noble metals by adopting the “memory
effect” and used in the production of hydrogen for the PEFC under the daily startup and shutdown operation. Also starting
from aurichalcite or hydrotalcite precursor as the precursor, Cu/Zn/Al catalysts with high Cu metal surface area have been
prepared and successfully applied in the steam reforming of methanol and dimethyl ether, and moreover in the CO shift reaction. 相似文献
17.
Th. Spanos V. Simeonov S. Tsakovski D. Thiokas 《Central European Journal of Chemistry》2004,2(2):402-416
The present paper deals with chemometric interpretation of soil analysis data collected from 31 sampling sites in the region
of Kavala and Drama, Northern Greece. The determination of 16 different chemical and physicochemical characteristics is principally
needed for prognosis of the land treatment and fertilizing. The study carried out indicates that the application of multivariate
statistical approaches could reveal new and specific information about sampling sites. It has been found that they could be
divided into four general patterns: pattern 1 contains dominantly inorganic and alkaline soil samples from semi-mountainous
regions in close proximity to the seacoast; pattern 2 indicates the same soil sample type and regional location as pattern
1 but is far from the coastal line; pattern 3 includes samples from sites from the plains with organic and alkaline soils
with close proximity to the coast; pattern 4 resembles pattern 3 as soil type but involves samples from sites far from the
shore. Further, six latent factors were identified, conditionally named “structural”, “acidic”, “nutritional”, “salt”, “microcomponents”
and “organic”. Finally, an apportioning procedure was carried out to find the source contributions in the measured analytical
values. In this way the routine estimation of the soil quality could be improved. 相似文献
18.
Multivariate statistical assessment of polluted soils 总被引:9,自引:0,他引:9
Vasil Simeonov Juergen Einax Stafan Tsakovski Joerg Kraft 《Central European Journal of Chemistry》2005,3(1):1-9
This study deals with the application of several multivariate statistical methods (cluster analysis, principal components
analysis, multiple regression on absolute principal components scores) for assessment of soil pollution by heavy metals. The
sampling was performed in a heavily polluted region and the chemometric analysis revealed four latent factors, which describe
84.5 % of the total variance of the system, responsible for the data structure. These factors, whose identity was proved also
by cluster analysis, were conditionally named “ore specific”, “metal industrial”, “cement industrial”, and “steel production”
factors. Further, the contribution of each identified factor to the total pollution of the soil by each metal pollutant in
consideration was determined. 相似文献
19.
This review article summarizes our recent researches for molecular design of polyoxometalates (POMs) and their related compounds
for environmentally-friendly functional group transformations. The divacant POM [γ-SiW10O34(H2O)2]4− exhibits high catalytic performance for mono-oxygenation-type reactions including epoxidation of olefins and allylic alcohols,
sulfoxidation, and hydroxylation of organosilanes with H2O2. We have successfully synthesized several POM-based molecular catalysts (metal-substituted POMs) with controlled active sites
by the introduction of metal species into the divacant POM as a “structural motif”. These molecular catalysts can efficiently
activate H2O2 (vanadium-substituted POM for epoxidation) and alkynes (copper-substituted POM for click reaction and oxidative homocoupling
of alkynes). The aluminum-substituted POM exhibits Lewis acidic catalysis for diastereoselective cyclization of (+)-citronellal
to (−)-isopulegol. In addition, we have developed POM-based “molecular heterogeneous catalysts” by the “solidification” and
“immobilization” of catalytically active POMs. 相似文献
20.
In an earlier binding study conducted in our laboratory using Thermobifida fusca cellulases Cel6B, Cel9A, and Cel5A (formally Thermomonospora fusca E3, E4, and E5), it was observed that binding capacities for these three cellulases were 18–30 times higher on BMCC than on Avicel. These
results stimulated an interest in how the difference in accessibility between the two cellulosic substrates would affect synergism
observed with cellulase mixtures. To explore the impact of substrate, accessibility on the extent of conversion and synergism,
three binary T. fusca cellulase mixtures were tested over a range of cellulase ratios and total molar cellulase concentrations on Avicel and BMCC.
Higher extents of conversion were observed for BMCC due to the higher enzyme to substrate ratio resulting from the higher
binding The processive endoglucanase, Cel9A, had four times the extent of conversion of the end endocellulase Cel5A, while
the exocellulase Cel6B had three times the extent of conversion of Cel5A. Approximately 500 nmol/g of the cel9A+Cel6B mixture
was needed to obtain 80% conversion, while the Cel6B+Cel5A and Cel9A+Cel5A mixtures required 1500 and 1250 nmol/g, respectively,
to obtain 80% conversion. Thus, it appears that the more accessible structure of BMCC, as reflected by its binding capacity,
results in relative higher processive activity. 相似文献