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1.
M N Matos Reyes M L Cervera M de la Guardia 《Analytical and bioanalytical chemistry》2009,394(6):1557-1562
A sensitive and simple analytical method has been developed for determination of Sb(III), Sb(V), Se(IV), Se(VI), Te(IV), Te(VI),
and Bi(III) in garlic samples by using hydride-generation–atomic-fluorescence spectrometry (HG–AFS). The method is based on
a single extraction of the inorganic species by sonication at room temperature with 1 mol L−1 H2SO4 and washing of the solid phase with 0.1% (w/v) EDTA, followed by measurement of the corresponding hydrides generated under two different experimental conditions directly
and after a pre-reduction step. The limit of detection of the method was 0.7 ng g−1 for Sb(III), 1.0 ng g−1 for Sb(V), 1.3 ng g−1 for Se(IV), 1.0 ng g−1 for Se(VI), 1.1 ng g−1 for Te(IV), 0.5 ng g−1 for Te(VI), and 0.9 ng g−1 for Bi(III), in all cases expressed in terms of sample dry weight. 相似文献
2.
Wietecha-Posłuszny R Garbacik A Woźniakiewicz M Kościelniak P 《Analytical and bioanalytical chemistry》2011,399(9):3233-3240
The objective of this research was to develop, optimize, and validate a modern, rapid method of preparation of human hair
samples, using microwave irradiation, for analysis of eight tricyclic antidepressants (TCADs): nordoxepin, nortriptyline,
imipramine, amitriptyline, doxepin, desipramine, clomipramine, and norclomipramine. It was based on simultaneous alkaline
hair microwave-assisted hydrolysis and microwave-assisted extraction (MAH–MAE). Extracts were analyzed by high-performance
liquid chromatography with diode-array detection (HPLC–DAD). A mixture of n-hexane and isoamyl alcohol (99:1, v/v) was used as extraction solvent and the process was performed at 60°C. Application of 1.0 mol L−1 NaOH and microwave irradiation for 40 min were found to be optimum for hair samples. Limits of detection ranged from 0.3
to 1.2 μg g−1 and LOQ from 0.9 to 4.0 μg g−1 for the different drugs. This enabled us to quantify them in hair samples within average therapeutic concentration ranges. 相似文献
3.
A new adsorbent is proposed for the solid-phase extraction of phenol and 1-naphthol from polluted water. The adsorbent (TX-SiO2) is an organosilica composite made from a bifunctional immobilized layer comprising a major fraction (91%) of hydrophilic
diol groups and minor fraction (9%) of the amphiphilic long-chain nonionic surfactant Triton X-100 (polyoxyethylated isooctylphenol)
(TX). Under static conditions phenol was quantitatively extracted onto TX-SiO2 in the form of a 4-nitrophenylazophenolate ion associate with cetyltrimethylammonium bromide. The capacity of TX-SiO2 for phenol is 2.4 mg g−1 with distribution coefficients up to 3.4 × 104 mL g−1; corresponding data for 1-naphthol are 1.5 mg g−1 and 3 × 103 mL g−1. The distribution coefficient does not change significantly for solution volumes of 0.025–0.5 L and adsorbent mass less than
0.03 g; 1–90 μg analyte can be easily eluted by 1–3 mL acetonitrile with an overall recovery of 98.2% and 78.3% for phenol
and 1-naphthol, respectively. Linear correlation between acetonitrile solution absorbance (A
540) and phenol concentration (C) in water was found according to the equation A
540 = (6 ± 1) × 10−2 + (0.9 ± 0.1)C (μmol L−1) with a detection range from 1 × 10−8 mol L−1 (0.9 μL g−1) to 2 × 10−7 mol L−1 (19 μL g−1), a limit of quantification of 1 μL g−1 (preconcentration factor 125), correlation coefficient of 0.936, and relative standard deviation of 2.5%. A solid-phase colorimetric
method was developed for quantitative determination of 1-naphthol on adsorbent phase using scanner technology and RGB numerical
analysis. The detection limit of 1-naphthol with this method is 6 μL g−1 while the quantification limit is 20 μL g−1. A test system was developed for naked eye monitoring of 1-naphthol impurities in water. The proposed test kit allows one
to observe changes in the adsorbent color when 1-naphthol concentration in water is 0.08–3.2 mL g−1. 相似文献
4.
Ramadan A. Abuknesha Fiona Jeganathan Rens DeGroot Dirk Wildeboer Robert G. Price 《Analytical and bioanalytical chemistry》2010,396(7):2547-2558
A simplified method for the measurement of proteases utilising solid-phase substrates incorporating an ELISA end-point detection
step is described. Gelatin–hapten conjugates adsorbed onto polystyrene surfaces were found to be efficient substrates for
proteases. Digestion of the solid-phase protein–hapten complexes resulted in proportional desorption of the attached conjugates
and decrease in the detectable hapten species. Gelatin–cholic acid conjugates, affinity-purified sheep anti-cholic acid antibody–HRP
and a chromogenic substrate were incorporated into a convenient and highly sensitive solid-phase immunochemical method. The
detectable signal is inversely proportional to enzyme activity. Bacterial proteases (alpha-chymotrypsin Type II, Type IX from
Bacillus polymyxa, Type XIV from Streptomyces griseus, Type XXIV from Bacillus licheniformens) were assayed. Dose–response curves for enzyme activities were measured within ranges of 0–550 μunits mL−1 for chymotrypsin, 0–12 μunits mL−1 for type IX, 0–35 μunits mL−1 for type XIV and 0–100 μunits mL−1 for type XXIV. The detection limits of the proteases studied were 89 μunits mL−1 for chymotrypsin, 0.26 μunits mL−1 for type IX, 5.8 μunits mL−1 for type XIV and 6.5 μunits mL−1 for type XXIV. It was demonstrated that the two-step immunochemical method combines the simplicity and sensitivity of solid-phase
enzyme immunoassays, the broad specificity of gelatin as a protease substrate and the flexibility of the solid-phase format. 相似文献
5.
L. D. Belyakova E. Kurbanbekov O. G. Larionov M. P. Tsyurupa V. A. Duvankov 《Russian Chemical Bulletin》1999,48(8):1484-1487
The effect of the conditioning temperature of the hypercross-linked polystyrene sorbents Styrosorb on the retention ofn-hexane, benzene. and acetone was studied by gas chromatography. The rigid but mobile structure of 100% cross-linked polymers
with a specific surface area of 300–500 m2 g−1 prepared in cyclohexane slightly shrinks by conditioning above 200 °C. This results in a significant increase in the specific
retention volumes of the adsorbates. The commercial hypercross-linked sorbents MN-100 and MN-200 with specific surface areas
of −1000 m2 g−1 retain their structure up to 250 °C.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1502–1506, August. 1999. 相似文献
6.
Tatyana S. Baptista Marcelo M. Redígolo Cibele B. Zamboni Ivone M. Sato Jose R. Marcelino 《Journal of Radioanalytical and Nuclear Chemistry》2012,291(2):399-403
The World Health Organization states that envenomation is responsible for a high number of deaths per year, especially in
equatorial areas. The only effective specific treatment is the use of hyperimmune serum (antivenom). In Brazil, Crioula breed
horses are used for antivenom production, with great importance in the maintenance of public health programs. A strict biochemical
and metabolic control is required to attain specificity in antiserum. Inorganic elements represent only a small fraction of
whole blood. Nonetheless, they play important roles in mammalian metabolism, being responsible for controlling enzymatic reactions,
respiratory and cardiac functions and ageing. In this work, whole blood samples from Crioula breed horses were analyzed by
EDXRF technique. The reference interval values were determined for the elements Na (1955–2013 μg g−1), Mg (51–75 μg g−1), P (523–555 μg g−1), S (1628–1730 μg g−1), Cl (2388–2574 μg g−1), K (1649–1852 μg g−1), Ca (202–213 μg g−1), Cu (4.1–4.5 μg g−1) and Zn (2.4–2.8 μg g−1) and a comparative study with NAA results was outlined. The samples were obtained from Instituto Butantan. Both techniques
showed to be appropriate for whole blood sample analyses and offer a new perspective in Veterinary Medicine. 相似文献
7.
Gy. Kiss Z. Varga-Puchony A. Gelencsér Z. Krivácsy Á. Molnár J. Hlavay 《Chromatographia》1998,48(1-2):149-153
Summary Concentrations of polycyclic aromatic hydrocarbons (PAHs) were determined in water and sediment samples at 15 sites in Lake
Balaton during three sampling campaigns in 1996. PAHs were concentrated from water samples by solid phase extraction. Sediment
samples were extracted with acetone in an ultrasonic bath then cleaned by solid phase extraction. The total concentration
of PAHs ranged from 30–360 ng g−1 and from 170–720 ng L−1 in sediment and water samples, respectively. Spatial and temporal variations of the concentration of PAHs were also investigated.
Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997. 相似文献
8.
Mohammed A. Abounassif Mohammed M. Hefnawy Gamal A. E. Mostafa 《Monatshefte für Chemie / Chemical Monthly》2012,73(Z1):365-371
Abstract
A stereoselective HPLC method has been developed for the simultaneous determination of oxprenolol enantiomers in urine and pharmaceutical products. Enantiomeric resolution of oxprenolol was achieved on cellulose tris(3,5-dichlorophenylcarbamate) immobilized onto a 5 μm spherical porous silica chiral stationary phase (CSP) known as Chiralpak IC with UV detection at 273 nm. The mobile phase consisted of n-hexane:isopropanol:triethylamine 70:30:0.1 (v/v/v) at a flow rate of 1.0 cm3/min. The method was validated for its linearity, accuracy, precision, and robustness. The calibration curves were linear over the range of 0.5–75 μg/cm3, with a detection limit of 0.1 μg/cm3 for each enantiomer. An average recovery of 99.0% and a mean relative standard deviation of 2.6% at 40.0 μg/cm3 for S-(−)- and R-(+)-enantiomers were obtained. The overall recoveries of oxprenolol enantiomers from pharmaceutical formulations were in the range 97.5–99.0%, with RSDs ranging from 0.6 to 0.8%. The mean extraction efficiency of oxprenolol from urine was in the range of 86.0–93.0% at 0.5–5 μg/cm3 for each enantiomer. The assay method proved to be suitable as a chiral quality control for oxprenolol formulations using HPLC and for therapeutic drug monitoring. 相似文献9.
In this work we prepared the hybrid material (SG) by the sol–gel method through the reaction between tetraethylortosilicate
(TEOS) and acetylacetonatepropyltrimethoxysilane (ACACSIL). We also immobilized the acetylacetonate on silica surface (GR)
by the grafting method through the reaction between a commercial silica and ACACSIL. Infrared thermal analysis showed that
these materials were thermally stable until 200 °C. SG is a microporous material and has surface area of 500 m2 g−1, average porous volume of 0.09 cm3 g−1 and organic content of 1 mmol g−1. GR is a mesoporous material and has surface area of 300 m2 g−1, average porous volume of 0.7 cm3 g−1 and organic content of 0.4 mmol g−1. Iron(III) was coordinated to SG and GR resulting in the SG–Fe and GR–Fe silicas which were tested as catalysts on the aerobic
epoxidation of cis-cyclooctene. SG–Fe yielded 100% of conversion and 94% of selectivity in epoxide whereas GR–Fe silica led
to a maximum conversion of 50% and 100% of selectivity. 相似文献
10.
Sheng-Yao Chen Bo Gao Ling-Hao Su Chang-Huan Mi Xiao-Gang Zhang 《Journal of Solid State Electrochemistry》2009,13(9):1361-1366
LiFePO4/C composites were synthesized by pyrolysis of LiFePO4/polypyrrole (PPy), which was obtained by an in situ chemical polymerization involving pyrrole monomer and hydrothermal synthesis LiFePO4. All samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy,
cyclic voltammetry, and galvanostatic charge–discharge techniques. The results showed the LiFePO4/C sintered at 800 °C containing 2.8 wt.% carbon exhibited a higher discharge capacity of 49.6 mAh·g−1 at 0.1 C, and bare LiFePO4 only delivered 11.6 mAh·g−1 in 2 M LiNO3 aqueous electrolyte. The possible reason for the improvement of electrochemical performance was discussed and could be attributed
to the formation of aromatic compounds during the carbonization of PPy. 相似文献
11.
A rapid, specific, and sensitive method utilizing ultra-performance liquid chromatography tandem mass spectrometry was developed
and validated to determine albendazole, albendazole sulfoxide, albendazole sulfone, and albendazole 2-aminosulfone in fish
muscle tissue. The fish samples were extracted with ethyl acetate, then the organic phase was evaporated to dryness, and the
residue was reconstituted in methanol–water solution and cleaned up by n-hexane. Reversed-phase separation of target compounds was achieved using a BEH C18 column and a gradient consisting of 0.2%
(v/v) formic acid and methanol. Tandem mass spectrometry analyses were performed on a triple–quadrupole tandem mass spectrometer.
In the whole procedure, the isotope-labeled internal standards were used to correct the matrix effect and variations associated
with the analysis. The method was validated with respect to linearity, specificity, accuracy, and precision. The method exhibited
a linear response from 0.1 to 20 ng mL-1 (r
2 > 0.9985). The limit of quantitation for albendazole (ABZ), albendazole sulfoxide (ABZSO), albendazole sulfone (ABZSO2), and albendazole 2-aminosulfone (ABZ-2-NH2SO2) was 0.1, 0.1, 0.1, and 0.2 ng g-1, respectively. The mean recoveries of ABZ, ABZSO, ABZSO2, and ABZ-2-NH2SO2 spiked at a level of 0.2–5.0 ng g-1 were 95.3–113.7%, and the relative standard deviations of intra- and inter-day measurements were less than 6.38%. The method
was later successfully applied to the determination of albendazole and its three metabolites in 60 fish samples collected
from local markets. 相似文献
12.
Zhang Fang Jiang Jianwei Yuan Changzhou Hao Liang Shen Laifa Zhang Luojiang Zhang Xiaogang 《Journal of Solid State Electrochemistry》2012,16(5):1933-1940
Nanostructured Co
x
Ni1−x
–Al layered triple hydroxides (Co
x
Ni1−x
–Al LTHs) have been successfully synthesized by a facile hydrothermal method using glycine as chelating agent. The samples
were characterized by X-ray diffraction, thermogravimetry, Fourier transform infrared spectroscopy and scanning electron microscopy.
The morphologies of Co
x
Ni1−x
–Al LTHs varied with the Co content and its effect on the electrochemical behavior was studied by cyclic voltammetry and galvanostatic
charge–discharge techniques. Electrochemical data demonstrated that the Co
x
Ni1−x
–Al LTHs with Co/Ni molar ratio of 3:2 owned the best performance and delivered a maximum specific capacitance of 1,375 F g−1 at a current density of 0.5 A g−1 and a good high-rate capability. The capacitance retained 93.3% of the initial value after 1,000 continuous charge–discharge
cycles at a current density of 2 A g−1. 相似文献
13.
The air quality in the Aragón valley, in the central Pyrenees, has been assessed by evaluation of lichen biodiversity and
mapped by elaboration of the Index of Air Purity (IAP) based on observations of the presence and abundance of eight kinds
of lichen with different sensitivity to air pollution. The IAP values obtained have been compared with quantitative analytical
measures of 16 PAHs in the lichen Evernia prunastri, because this species was associated with a wide range of traffic exposure and levels of urbanization. Analyses of PAHs were
carried out by the DSASE method followed by an SPE clean-up step and GC–MS analysis. The concentration of total PAHs found
in lichen samples from the Aragón valley ranged from 692 to 6420 ng g−1 and the PAHs profile showed predominance of compounds with three aromatic rings. The influence of the road traffic in the
area has been shown because values over the median concentration of PAHs (>1092 ng g−1), percentage of combustion PAHs (>50%), and equivalent toxicity (>169) were found in lichens collected at places exposed
to the influence of traffic. The combination of both methods suggests IAP as a general method for evaluating the air pollution
referenced to PAHs because it can be correlated with the content of combustion PAHs and poor lichen biodiversity can be partly
explained by the air pollution caused by specific PAHs.
Figure Map of the air pollution level in the Aragón valley (Pyrenees) based on the Index of Air Purity (IAP) calculation (lichen
biodiversity) 相似文献
14.
A novel method for the determination of five sulfonylurea herbicides in soil was developed by a dispersive solid-phase extraction
(DSPE) clean-up followed by dispersive liquid–liquid microextraction (DLLME), prior to sweeping micellar electrokinetic chromatography
(MEKC). In the DSPE-DLLME, 10 g of soil sample was first extracted with 10 mL of acetonitrile containing 5% formic acid (pH 3.0).
The extract was then cleaned-up by a DSPE with C18 as sorbent. A 1 mL aliquot of the resulting extract was then added into a centrifuge tube containing 5 mL of water adjusted
to pH 2.0 and 60.0 μL chlorobenzene (as extraction solvent) for DLLME procedure. Then, the organic sample extraction solution
was evaporated to dryness, and reconstituted with 20.0 μL of 1.0 mmol L−1 Na2HPO4 (pH 10.0) for sweeping-MEKC analysis after DLLME. Under optimized conditions, the method provided as high as 3,000- to 5,000-fold
enrichments factors. The linearity of the method was in the range of 3.3–200 ng g−1 for chlorimuron ethyl and bensulfuron methyl, and in the range of 1.7–200 ng g−1 for tribenuron methyl, chlorsulfuron and metsulfuron methyl, with the correlation coefficients (r) ranging from 0.9965 to 0.9983, respectively. The limits of detection (LODs) ranged from 0.5 to 1.0 ng g−1. The intraday relative standard deviations (RSDs, n = 5) were below 5.3% and interday RSDs (n = 15) within 6.8%. The recoveries of the method for the five sulfonylureas from soil samples at spiking levels of 5.0, 20.0,
and 100.0 ng g−1 were 76.0–93.5%, respectively. The developed method has been successfully applied to the analysis of the target sulfonylurea
herbicide residues in soil samples with a satisfactory result. 相似文献
15.
Dao-Lai Fang Bing-Cai Wu Yong Yan Ai-Qin Mao Cui-Hong Zheng 《Journal of Solid State Electrochemistry》2012,16(1):135-142
Mesoporous Mn–Ni oxides with the chemical compositions of Mn1-x
Ni
x
O
δ
(x = 0, 0.2, and 0.4) were prepared by a solid-state reaction route, using manganese sulfate, nickel chloride, and potassium
hydroxide as starting materials. The obtained Mn–Ni oxides, mainly consisting of the phases of α- and γ-MnO2, presented irregular mesoporous agglomerates built from ultra-fine particles. Specific surface area of Mn1–x
Ni
x
O
δ
was 42.8, 59.6, and 84.5 m2 g−1 for x = 0, 0.2, and 0.4, respectively. Electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge/discharge
in 6 mol L−1 KOH electrolyte. Specific capacitances of Mn1-x
Ni
x
O
δ
were 343, 528, and 411 F g−1 at a scan rate of 2 mV s−1 for x = 0, 0.2, and 0.4, respectively, and decreased to 157, 183, and 130 F g−1 with increasing scan rate to 100 mV s−1, respectively. After 500 cycles at a current density of 1.24 A g−1, the symmetrical Mn1–x
Ni
x
O
δ
capacitors delivered specific capacitances of 160, 250, and 132 F g−1 for x = 0, 0.2, and 0.4, respectively, retaining about 82%, 89%, and 75% of their respective initial capacitances. The Mn0.8Ni0.2O
δ
material showed better supercapacitive performance, which was promising for supercapacitor applications. 相似文献
16.
Changzhou Yuan Long Yang Linrui Hou Diankai Li Laifa Shen Fang Zhang Xiaogang Zhang 《Journal of Solid State Electrochemistry》2012,16(4):1519-1525
A facile hydrothermal strategy was first proposed to synthesize flower-like Co(OH)2 hierarchical microspheres. Further physical characterizations revealed that the flower-like Co(OH)2 microspherical superstructures were self-assembled by one-dimension nanobelts with rich mesopores. Electrochemical performance
of the flower-like Co(OH)2 hierarchical superstructures were investigated by cyclic voltammgoram, galvanostatic charge–discharge and electrochemical
impedance spectroscopy in 3 M KOH aqueous electrolyte. Electrochemical data indicated that the flower-like Co(OH)2 superstructures delivered a specific capacitance of 434 F g−1 at 10 mA cm−2 (about 1.33 A g−1), and even kept it as high as 365 F g−1 at about 5.33 A g−1. Furthermore, the SC degradation of about 8% after 1,500 continuous charge–discharge cycles at 5.33 A g−1 demonstrates their good electrochemical stability at large current densities. 相似文献
17.
Xiaoying Xie Wenwen Liu Luyang Zhao Chengde Huang 《Journal of Solid State Electrochemistry》2010,14(9):1585-1594
Manganese–vanadium oxide had been synthesized by a novel simple precipitation technique. Scanning electron microscopy, X-ray
diffraction, Brunauer–Emmett–Teller, thermogravimetric analysis/differential scanning calorimetry, and X-ray photoelectron
spectroscopy were used to characterize Mn–V binary oxide and δ-MnO2. Electrochemical capacitive behavior of the synthesized Mn–V binary oxide and δ-MnO2 was investigated by cyclic voltammetry, galvanostic charge–discharge curve, and electrochemical impedance spectroscope methods.
The results showed that, by introducing V into δ-MnO2, the specific surface area of the mixed oxide increased due to a formation of small grain size. The specific capacitance
increased from 166 F g−1 estimated for MnO2 to 251 F g−1 for Mn–V binary oxide, and the applied potential window extended to −0.2–1.0 V (vs. saturated calomel electrode). Through
analysis, it is suggested that the capacitance performance of Mn–V binary oxide materials may be improved by changing the
following three factors: (1) small grain and particle size and large activity surface area, (2) appropriate amount of lattice
water, and (3) chemical state on the surface of MnO2 material. 相似文献
18.
Consuelo Cháfer-Pericás Ángel Maquieira Rosa Puchades Javier Miralles Amelia Moreno 《Analytical and bioanalytical chemistry》2010,396(2):911-921
An indirect competitive enzyme-linked immunosorbent assay (ELISA) was developed in plate to detect three sulfonamide residues
(sulfamerazine (SMR), sulfadimetoxine (SDM), and sulfadiazine (SDZ)) in gilthead sea bream (Sparus aurata) samples. Different extraction methodologies—using methanol/water 1:1 (v/v) + ethylene diamine tetraacetic acid (EDTA) 0.5% (m/v), acetonitrile, phosphate-buffered saline (PBS) 10 mmol L−1 pH 7 and acetate buffer 100 mmol L−1 pH 5—and cleanup steps, based on solid-phase extraction (C18, SCX, Si) or liquid extraction with hexane, were assayed. As optimum, a fast and simple method using acetonitrile was selected
to extract the sulfonamide residues from the edible muscle of fish. Due to matrix effects, a standard addition calibration
curve in fish extract is necessary for quantification purposes. Sulfonamide-free samples were spiked at different concentration
levels (between 30 and 90 ng g−1, 5–15 ng mL−1 in plate) and average recoveries (n = 8), ranging from 71% to 95%, 65% to 79%, and 72% to 95%, were obtained for SMR, SDM, and SDZ, respectively. The assay detection
limits for these antibiotics were lower than 100 μg kg−1 (maximum residue level established by the European Union). The accuracy was evaluated by spiking blank fish extracts at different
concentrations (10–40 ng mL−1, 5–20 ng mL−1 in plate), and the relative errors ranged between ±20%. Finally, in order to confirm the utility of the developed ELISA as
a screening methodology, fish samples from different supermarkets were analyzed, and results were compared with those obtained
by a validated high-performance liquid chromatography (HPLC) method. The correlation between the results obtained by both
ELISA and HPLC methods is satisfactory.
相似文献
19.
Mervat Morsy A. El-Gendy 《Applied biochemistry and biotechnology》2010,162(3):780-794
Among all endophytic keratinolytic fungal isolates recovered from marine soft coral Dendronephthya hemprichii, Penicillium spp. Morsy1 was selected as the hyperactive keratinolytic strain under solid substrate fermentation of different agriculture
and poultry wastes. The optimization of extraction process, physicochemical parameters affecting the keratinase production
in solid-state fermentation, and the purified keratinase parameters were studied. Maximum keratinase activity (1,600 U g−1, initial dry substrate) was recovered from moldy bran with 0.1% Tween 80. The optimized production conditions were rice straw
as carbon source, pH of medium 6, growth temperature 26 °C, initial moisture content of 80% (v/w), inoculum size of 105 spores ml−1, and an average particle size of the substrate 0.6 mm (3,560 U g−1, initial dry substrate after 5 days of fermentation). Two types of keratinase (Ahm1 and Ahm2) were purified from the culture
supernatant through ammonium sulfate precipitation, DEAE-Sepharose, and gel filtration chromatography. Enzyme molecular weights
were 19 kDa (Ahm1) and 40 kDa (Ahm2). The kinetic parameters of purified keratinases were optimized for the hydrolysis of
azokeratin by Ahm1 (pH 7.0–8.0, stable in pH range of 6.0 to 8.0 at 50 °C) and Ahm2 enzymes (pH 10.0–11.0, stable in pH range
of 6.0 to 11.0 at 60–65 °C). Whereas inhibitors of serine (phenylmethylsulfonyl fluoride) and cysteine (iodoacetamide) proteases
had minor effects on both Ahm1 and Ahm2 activity, both keratinases were strongly inhibited by chelating agents EDTA and EGTA.
These findings suggest that serine and cysteine residues are not involved in the catalytic mechanisms, and they are metalloproteases. 相似文献
20.
Parimal Gaikwad A. Barik K. I. Priyadarsini B. S. M. Rao 《Research on Chemical Intermediates》2010,36(9):1065-1072
Studies on the antioxidant activity of two model phenols containing either an electron withdrawing (p-nitrophenol) or electron donating (p-aminophenol) group and p-hydroxyacetophenone in different solvents are reported using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay by spectrophotometry
and stopped-flow techniques. The second-order rate constants measured with p-nitrophenol were found to be (1.2–5.5) × 10−2 dm3 mol−1 s−1 but the DPPH radical reacts much faster with p-aminophenol (k = 0.5–1.1 × 104 dm3 mol−1 s−1). The normal kinetic solvent effect in H atom transfer was seen in the case of p-nitrophenol with the solvent independent rate constant k
o = 0.1 dm3 mol−1 s−1. The IC50 values in p-nitrophenol are similar to those measured in p-hydroxyacetophenone. On the other hand, much lower IC50 values of more than four orders of magnitude with p-aminophenol were observed. This work demonstrates that the phenol with the electron donating –NH2 substituent is a better antioxidant. 相似文献