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1.
Dissolution of cellulose having different viscosity-average molecular weight (M
η
) in 7 wt%NaOH/12 wt%urea aqueous solution at temperature from 60 to −12.6°C was investigated with optical microscope, viscosity
measurements and wide X-ray diffraction (WXRD). The solubility (Sa) of cellulose in NaOH/urea aqueous solution strongly depended on the temperature, and molecular weight. Their Sa values increased with a decrease in temperature, and cellulose having M
η
below 10.0 × 104 could be dissolved completely in NaOH/urea aqueous solution pre-cooled to −12.6°C. The activation energy of dissolution (Ea,s) of the cellulose dissolution was a negative value, suggesting that the cellulose solution state had lower enthalpy than
the solid cellulose. The cellulose concentration in this system increased with a decrease of M
η
to achieve about 8 wt% for M
η
of 3.1 × 104. Moreover, cellulose having 12.7 × 104 could be dissolved completely in the solvent pre-cooled to −12.6°C as its crystallinity (χ
c) decreased from 0.62 to 0.53. We could improve the solubility of cellulose in NaOH/urea aqueous system by changing M
η
, χ
c and temperature. In addition, the zero-shear viscosity (η
0
) at 0°C for the 4 wt% cellulose solution increased rapidly with an increase of M
η
, as a result of the enhancement of the aggregation and entanglement for the relatively long chains. 相似文献
2.
Magnetic Co3O4 nanoparticles were prepared by using microporous regenerated cellulose films as sacrificial scaffolds. The cellulose macromolecules
and the porous structure of the films made them used as spatially confined reacting sites where Co(OH)2 nanoparticles could be synthesized in situ. When the cellulose matrix was removed by sintering at 500 °C, Co3O4 nanoparticles were obtained. XRD and XPS indicated that the prepared nanoparticles were pure Co3O4 without any impurity. TEM and SEM images revealed that the particle size of the nanoparticles was smaller than 100 nm. The
nanoparticles had weak ferromagnetic properties at 25 °C. Furthermore, the pronounced quantum confinement effects of the synthesized
nanoparticles have been observed, the optical bandgap energies determined were about 1.92 ~ 2.12 and 2.74 ~ 2.76 eV for O2− → Co3+ and O2− → Co2+ charge-transfer processes, respectively. Furthermore, the resulted Co3O4 nanoparticles behaved stable electrochemical performance with promising applications in the electrode for lithium ion battery. 相似文献
3.
S. Subramaniyan 《Applied biochemistry and biotechnology》2012,166(7):1831-1842
Low molecular weight endo-xylanase from Bacillus pumilus SSP-34 was purified to homogeneity using ion exchange and size exclusion chromatographies. Xylanases were isolated by novel
purification protocol which includes the use of anion exchange matrix such as DEAE Sepharose CL 6B with less affinity towards
enzyme protein. The purified B. pumilus SSP-34 have a molecular weight of 20 kDa, with optimum pH and temperature at 6.0 and 50 °C, respectively. The enzyme was
stable at 50 °C for 30 min. It showed remarkable stability at pH values ranging from 4.5 to 9 when the reaction was carried
out at 50 °C. K
m and V
max values, determined with oats spelts xylan were 6.5 mg ml−1 and 1,233 μmol min−1 mg−1 protein, respectively, and the specific activity was 1,723 U mg−1 相似文献
4.
Columns containing immobilized low-density lipoprotein (LDL) were prepared for the analysis of drug interactions with this
agent by high-performance affinity chromatography (HPAC). R/S-Propranolol was used as a model drug for this study. The LDL columns gave reproducible binding to propranolol over 60 h of
continuous use in the presence of pH 7.4 0.067 M potassium phosphate buffer. Experiments conducted with this type of column
through frontal analysis indicated that two types of interactions were occurring between R-propranolol and LDL, while only a single type of interaction was observed between S-propranolol and LDL. The first type of interaction, which was seen for both enantiomers, involved non-saturable binding;
this interaction had an overall affinity (nK
a) of 1.9 (±0.1) × 105 M−1 for R-propranolol and 2.7 (±0.2) × 105 M−1 for S-propranolol at 37 °C. The second type of interaction was observed only for R-propranolol and involved saturable binding that had an association equilibrium constant (K
a) of 5.2 (±2.3) × 105 M−1 at 37 °C. Similar differences in binding behavior were found for the two enantiomers at 20 °C and 27 °C. This is the first
known example of stereoselective binding of drugs by LDL or other lipoproteins. This work also illustrates the ability of
HPAC to be used as a tool for characterizing mixed-mode interactions that involve LDL and related binding agents. 相似文献
5.
Fu Qiang KeNing Sun NaiQing Zhang ShiRu Le XiaoDong Zhu JinHuo Piao 《Journal of Solid State Electrochemistry》2009,13(3):455-467
A-site-deficient perovskite cathode material La0.58Sr0.4Co0.2Fe0.8O3 − δ
(L58SCF) is coated on the yttria-stabilized zirconia electrolyte by screen-printing technique. Several key fabrication parameters
including selection of additives (binder and pore former), effect of coating thickness, sintering temperature and time on
the microstructure, and electrochemical performance of cathode are investigated by scanning electron microscopy and electrochemical
impedance spectroscopy. We study the microstructure and the electrochemical property of the cathode with different kinds of
additives. Results show that the cathode possesses fine microstructure, enough porosity, and ideal electrochemical property
when polyvinyl butyral serves as both binder and pore former in the cathode. The cathode with three screen-printing coats
(thickness 28 ± 7 μm, weight 6.07 ± 0.72 mg cm−2) sintering at 1,000 °C for 2 h shows lower polarization resistance of 0.183 Ω cm2 at 800 °C. Based on the optimized parameters, the polarization resistances of the L58SCF–Ce0.8Gd0.2O1.9 – δ
composite cathode display the R
p values of 0.067 Ω cm2 at 800 °C, 0.106 Ω cm2 at 750 °C, 0.225 Ω cm2 at 700 °C, and 0.550 Ω cm2 at 650 °C. 相似文献
6.
7.
We have investigated tension wood cellulose obtained from Populus maximowiczii using X-ray diffraction at temperatures from room temperature to 250 °C. Three equatorial and one meridional d-spacings showed a gradual linear increase with increasing temperature. For temperatures above 180 °C, however, the equatorial
d-spacing increased dramatically. Thus, the linear and volume thermal expansion coefficients (TECs) below 180 °C were determined
from the d-spacings. The linear TECs of the a-, b-, and c-axes were: α
a
= 13.6 × 10−5 °C−1, α
b
= −3.0× 10−5 °C−1, and α
c
=0.6× 10−5 °C−1, respectively, and the volume TEC was β = 11.1× 10−5 °C−1. The anisotropic thermal expansion in the three coordinate directions was closely related to the crystal structure of the
wood cellulose, and it governed the macroscopic thermal behavior of solid wood. 相似文献
8.
Marcelo H. Gehlen 《Cellulose (London, England)》2009,16(6):1069-1073
Depolymerization of cellulose in homogeneous acidic medium is analyzed on the basis of autocatalytic model of hydrolysis with
a positive feedback of acid production from the degraded biopolymer. The normalized number of scissions per cellulose chain,
S(t)/n° = 1 − C(t)/C0, follows a sigmoid behavior with reaction time t, and the cellulose concentration C(t) decreases exponentially with a linear and cubic time dependence, C(t) = C0exp[−at − bt
3], where a and b are model parameters easier determined from data analysis. 相似文献
9.
Josiane de Lima Souza Marcelo Kobelnik Clóvis Augusto Ribeiro Jorge Manoel Vieira Capela Marisa Spirandeli Crespi 《Journal of Thermal Analysis and Calorimetry》2009,97(2):525-528
Poly(3-hydroxybutyrate), PHB, has been structurally modified through reaction with hydroxy acids (HA) such as tartaric acid
(TA) and malic acid (MA). The crystallization kinetic of the samples was evaluated by isoconversional method through nonlinear
fitting to obtain the estimation for activation energy (E
a
) and pre-exponential (A) values. The thermal behavior of the crystallization temperature, 44.8 and 58.9 °C at 5 °C/min, and results obtained to the
average activation energy, 73 ± 9 kJ mol−1 and 63 ± 1 kJ mol−1, to PHB/MA and PHB, respectively, are suggesting that malic acid may be deriving plasticizer units from its own PHB chain.
PHB/TA show increase in the medium value of E
a, 119 ± 2 kJ mol−1 and T
c = 48.2 °C (at 5 °C/min), indicating that tartaric acid is probably interacts in different way to the of PHB chain (E
a=73 ± 9 kJ mol−1, T
c = 44.8 °C at 5 °C/min). 相似文献
10.
Taibi Z Saoudi B Boudelaa M Trigui H Belghith H Gargouri A Ladjama A 《Applied biochemistry and biotechnology》2012,166(3):663-679
An extracellular thermostable xylanase from a newly isolated thermophilic Actinomadura sp. strain Cpt20 was purified and characterized. Based on matrix-assisted laser desorption–ionization time-of-flight mass
spectrometry analysis, the purified enzyme is a monomer with a molecular mass of 20,110.13 Da. The 19 residue N-terminal sequence
of the enzyme showed 84% homology with those of actinomycete endoxylanases. The optimum pH and temperature values for xylanase
activity were pH 10 and 80 °C, respectively. This xylanase was stable within a pH range of 5–10 and up to a temperature of
90 °C. It showed high thermostability at 60 °C for 5 days and half-life times at 90 °C and 100 °C were 2 and 1 h, respectively.
The xylanase was specific for xylans, showing higher specific activity on soluble oat-spelt xylan followed by beechwood xylan.
This enzyme obeyed the Michaelis–Menten kinetics, with the K
m and k
cat values being 1.55 mg soluble oat-spelt xylan/ml and 388 min−1, respectively. While the xylanase from Actinomadura sp. Cpt20 was activated by Mn2+, Ca2+, and Cu2+, it was, strongly inhibited by Hg2+, Zn2+, and Ba2+. These properties make this enzyme a potential candidate for future use in biotechnological applications particularly in
the pulp and paper industry. 相似文献
11.
Deuk Yong Lee Kyong-Ho Lee Myung-Hyun Lee Nam-Ihn Cho Bae-Yeon Kim 《Journal of Sol-Gel Science and Technology》2010,53(1):43-49
Ba1−x
Sr
x
TiO3(x = 0–0.5, BST) nanofibers with diameters of 150–210 nm were prepared by using electrospun BST/polyvinylpyrrolidone (PVP) composite
fibers by calcination for 2 h at temperatures in the range of 650–800 °C in air. The morphology and crystal structure of calcined
BST/PVP nanofibers were characterized as functions of calcination temperature and Sr content with an aid of XRD, FT-IR, and
TEM. Although several unknown XRD peaks were detected when the fibers were calcined at temperatures less than 750 °C, they
disappeared with increasing the temperature (above 750 °C) due to its thermal decomposition and complete reaction in the formation
of BST. In addition, the FT-IR studies of BST/PVP fibers revealed that the intensities of the O–H stretching vibration bands
(at 3430 and 1425 cm−1) became weaker with increasing the calcination temperature and a broad band at 540 cm−1, Ti–O vibration, appeared sharper and narrower after calcination above 750 °C due to the formation of metal oxide bonds.
However, no effect of Sr content on the crystal structure of the composites was detected. 相似文献
12.
A laccase has been purified from the liquid culture growth medium containing bagasse particles of Fomes durissimus. The method involved concentration of the culture filtrate by ultrafiltration and anion exchange chromatography on diethyl
aminoethyl cellulose. The sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE) and native polyacrylamide
gel electrophoresis both gave single protein band indicating that the enzyme preparation was pure. The molecular mass of the
purified laccase determined from SDS-PAGE analysis was 75 kDa. Using 2,6-dimethoxyphenol as the substrate, the determined
K
m and k
cat values of the laccase are 182 μM and 0.35 s−1, respectively, giving a k
cat/K
m value of 1.92 × 103 M−1 s−1. The pH and temperature optimum were 4.0 and 35 °C, respectively. The purified laccase has yellow colour and does not show
absorption band around 610 nm found in blue laccases. Moreover, it transformed methylbenzene to benzaldehyde in the absence
of mediator molecules, property exhibited by yellow laccases. 相似文献
13.
Liang Zhao Xiaoru Zhao Jinming Liu An Zhang Danhong Wang Bingbo Wei 《Journal of Sol-Gel Science and Technology》2010,53(2):475-479
Anatase Ti0.94Nb0.06O2 (TNO) films were fabricated on glass substrates by sol–gel method using a dip-coating technique. The annealing treatment
was separated into two steps, first in air at 350–550 °C for 1 h and then in vacuum of 4.0 × 10−4 Pa at 550 °C for 1 h. The influence of vacuum annealing treatment to the electrical and optical properties was discussed.
Especially, the role of air annealing treatment from 350 to 550 °C on the crystallization and the structure of the films was
analyzed. It is proved that the films annealed at 550 °C in air and then 550 °C in vacuum exhibited the minimum resistivity
of 19.3 Ω·cm and the average optical transmittance of about 75% in the visible range, indicating that the sol–gel method is a feasible
and promising method to fabricate TNO films. 相似文献
14.
Andre Ricardo de Lima Damásio Tony Márcio da Silva Alexandre Maller Jo?o Atílio Jorge Hector Francisco Terenzi Maria de Lourdes Teixeira de Moraes Polizeli 《Applied biochemistry and biotechnology》2010,160(5):1496-1507
An extracellular polygalacturonase (PG) produced from Paecilomyces variotii was purified to homogeneity through two chromatography steps using DEAE-Fractogel and Sephadex G-100. The molecular weight
of P. variotii PG was 77,300 Da by gel filtration and SDS-PAGE. PG had isoelectric point of 4.37 and optimum pH 4.0. PG was very stable
from pH 3.0 to 6.0. The extent of hydrolysis of different pectins by the purified enzyme was decreased with an increase in
the degree of esterification. PG had no activity toward non-pectic polysaccharides. The apparent K
m and V
max values for hydrolyzing sodium polypectate were 1.84 mg/mL and 432 μmol/min/mg, respectively. PG was found to have temperature
optimum at 65 °C and was totally stable at 45 °C for 90 min. Half-life at 55 °C was 50.6 min. Almost all the examined metal
cations showed partial inhibitory effects under enzymatic activity, except for Na+1, K+1, and Co+2 (1 mM) and Cu+2 (1 and 10 mM). 相似文献
15.
Qi Wu Chen Li Chenglei Li Hui Chen Liu Shuliang 《Applied biochemistry and biotechnology》2010,160(1):129-139
The collagenase, produced extracellular by Bacillus pumilus Col-J, was purified by ammonium sulfate precipitation followed by two gel filtrations, involving Sephadex G-100 column and
Sepharose Fast Flow column. Purified collagenase has a 31.53-fold increase in specific activity of 87.33 U/mg and 7.00% recovery.
The collagenase has a relative molecular weight of 58.64 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
The optimal temperature for the enzyme reaction was 45 °C. More than 50% of the original activity still remained after 5 min
of incubation at 70 °C or 10 min at 60 °C. The maximal enzyme activity of collagenase was obtained at pH 7.5, and it was stable
over a pH range of 6.5–8.0. The collagenase activity was strongly inhibited by Mn2+, Pb2+, ethylenediamine tetraacetic acid, ethylene glycol tetraacetic acid, and β-mercaptoethanol. However, Ca2+ and Mg2+ greatly increased its activity. The collagenase from B. pumilus Col-J showed highly specific activity towards the native collagen from calf skin. The K
m and V
max of the enzyme for collagen were 0.79 mg/mL and 129.5 U, respectively. 相似文献
16.
Ronaldo S. Nunes Felipe S. Semaan Alan T. Riga Éder T. G. Cavalheiro 《Journal of Thermal Analysis and Calorimetry》2009,97(1):349-353
The thermal properties of verapamil hydrochloride (VRP) and its physical association as binary mixtures with some common excipients
were evaluated. Thermogravimetry (TG) was used to determine the thermal mass loss, as well as to study the kinetics of VRP
thermal decomposition, using the Flynn-Wall-Ozawa model. Based on their frequent use in pharmacy, five different excipients
(microcrystalline cellulose, magnesium stearate, hydroxypropyl methylcellulose, polyvinylpyrrolidone and talc) were blended
with VRP. Samples were prepared by mixing the analyte and excipients in a proportion of 1:1 (m/m). DSC curves for pure VRP
presented an endothermic event at 143 ± 2 °C (ΔHmelt = 132 ± 4 J g−1), which corresponds to the melting (literature Tm = 143.7 °C, ΔHmelt = 130.6 J g−1). Comparisons among the observed results for each compound and their binary physical mixtures presented no relevant changes.
This suggests no interaction between the drug and excipient. 相似文献
17.
Zhang Y Ji C Zhang X Yang Z Peng J Qiu R Xie Y Mao Y 《Applied biochemistry and biotechnology》2008,151(1):81-92
A gene-encoding alkaline phosphatase (AP) from thermophilic Geobacillus thermodenitrificans T2, termed Gtd AP, was cloned and sequenced. The deduced Gtd AP protein comprises 424 amino acids and shares a low homology with other known AP (<35% identity), while it exhibits the
conservation of the active site and structure element of Escherichia coli AP. The Gtd AP protein, without a predicted signal peptide of 30 amino acids, was successfully overexpressed in E. coli and purified as a hexa-His-tagged fusion protein. The pH and temperature optima for purified enzyme are 9.0 and 65 °C, respectively.
The enzyme retained a high activity at 45–60 °C, while it could be quickly inactivated by a heat treatment at 80 °C for 15 min,
exhibiting a half-life of 8 min at 70 °C. The K
m and V
max for pNPP were determined to be 31.5 μM and 430 μM/min at optimal conditions. A divalent cation is essential, with a combination
of Mg2+ and Co2+ or Zn2+ preferred. The enzyme was strongly inhibited by 10 mM ethylenediaminetetraacetic acid (EDTA) and vanadate but highly resistant
to urea and dithiothreitol. The properties of Gtd AP make it suitable for application in molecular cloning or amplification. 相似文献
18.
Cellulose films were successfully prepared from NaOH/urea/zincate aqueous solution pre-cooled to −13 °C by coagulating with
5% H2SO4. The cellulose solution and regenerated cellulose films were characterized with dynamic rheology, ultraviolet–visible spectroscope,
scanning electron microscopy, wide angle X-ray diffraction, Fourier transform infrared (FT-IR) spectrometer, thermogravimetry
and tensile testing. The results indicated that at higher temperature (above 65 °C) or lower temperature (below −10 °C) or
for longer storage time, gels could form in the cellulose dope. However, the cellulose solution remained a liquid state for
a long time at 0–10 °C. Moreover, there was an irreversible gelation in the cellulose solution system. The films with cellulose
II exhibited better optical transmittance, high thermal stability and tensile strength than that prepared by NaOH/urea aqueous
solution without zincate. Therefore, the addition of zincate in the NaOH/urea aqueous system could enhance the cellulose solubility
and improve the structure and properties of the regenerated cellulose films. 相似文献
19.
The objective of present research was to sinter nanosized Mn–Zn ferrites (MZF) at low temperature (≤1,000 °C) by avoiding
the formation of nonmagnetic phase (hematite). For this purpose, MZF powder was synthesized by sol–gel auto combustion process
at 220 °C and further calcined at 450 °C. In calcined powder, single phase (spinel) was confirmed by X-ray diffraction analysis.
Pellets were pressed, having 43% of the theoretical density and showing 47 emu gm−1 saturation magnetization (M
s). Various combinations of heating rate, dwelling time and gaseous environment were employed to meet optimum sintering conditions
at low temperature (≤1,000 °C). It was observed that sintering under air or N2 alone had failed to prevent the formation of nonmagnetic (hematite) phase. However, hematite phase can be suppressed by retaining
the green compacts at 1,000 °C for 180 min in air then further kept for 120 min in nitrogen. Under these conditions, spinel
phase (comprising of nano crystallites), 90% of theoretical density and 102 emu gm−1 of saturation magnetization has been achieved. 相似文献
20.
Feng Yu Jingjie Zhang Yanfeng Yang Guangzhi Song 《Journal of Solid State Electrochemistry》2010,14(5):883-888
Composite Li3V2(PO4)3/C cathode material can be synthesized by spray-drying and carbothermal method. The monoclinic-phase Li3V2(PO4)3/C was prepared with the process of double spray drying at 260 °C and subsequent heat treatment at 750 °C for 12 h. The results
indicate that the Li3V2(PO4)3/C presents large reversible discharge capacity of 121.9 mA h g−1 and charge capacity of 131.8 mA h g−1 at the current density of C/5, good rate capability with 61.1 mA h g−1 at 20C, and excellent capacity retention rate close to 100% at various current densities in the region of 3.0–4.3 V. 相似文献