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1.
A comparative study was performed on thermal stability of mesophilic and thermophilic α-amylases, and the effects of various
denaturing agents, organic solvents, and stabilizers were investigated. As expected, the thermophilic enzyme showed higher
resistance toward denaturation in water as its natural medium, but such a difference could not be detected in nonaqueous environments.
Furthermore, stability of these molecules was improved by including various stabilizing agents. Of the compounds tested, sorbitol
provided the highest degree of protection, which was found to be owing to its effect on increasing T
m and its ability in totally preventing deamidation of amino acid residues in the protein molecules. 相似文献
2.
A PVC membrane electrode for aluminium ion based on bis(5-phenyl azo salicylaldehyde) 2,3-naphthalene diimine (5PHAZOSALNPHN) as an ion carrier was developed. The electrode exhibits a Nernstian slope of 19.3+/-0.8 mV per decade and a linear range of 5.0x10(-6)-1.0x10(-2) M for Al(NO(3))(3). The limit of detection is 2.5x10(-6) M. It has a fast response time of about 10 s and can be used for at least 10 weeks without observing any deviation. The proposed membrane sensor revealed good selectivity for Al(3+) over a wide variety of other metal ions and could be used in pH range of 2.9-5.0. It was used as an indicator electrode in potentiometric titration of aluminium ion. 相似文献
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N. Azizi A. Khajeh Amiri M. Bolourtchian M. R. Saidi 《Journal of the Iranian Chemical Society》2009,6(4):749-753
An environmentally benign and efficient process for the preparation of thioethers was developed by simple and practical reactions of alkyl halides and thiols in water in the presence of K2CO3 or Et3N in very high yields. The reaction of aryl, alkyl, aliphatic and hindered thiols with various alkyl halides gave the corresponding products with significant advantages such as high conversions, short reaction time, mild reaction conditions, and low cost, simple workup with good to quantitative yields. 相似文献
6.
Saeed Aminzadeh Hossein Naderi-Manesh Khosro Khajeh Bijan Ranjbar Naser Farrokhi 《Applied biochemistry and biotechnology》2010,160(7):1921-1932
Acid-induced unfolding of a Tetracoccosporium sp. polygalacturonase enzyme (PG) was studied by a comprehensive series of biophysical and biochemical techniques. At pH 1.0,
PG acquires partially folded state, which reveals characteristics of molten globule (MG) state, i.e., reduction of defined
tertiary structure with minimal changes in the secondary structure. In this study PG unfolds exposing its hydrophobic surface
to a greater extent than the native form at acidic pH with more tryptophan residues exposed to the solvent. Collectively,
our data imply the presence of MG state of PG at low pH, suggesting the phenomenon of hydrophobic collapse model for folding
and integration into cell membrane. 相似文献
7.
Mostafa Khajeh Maryam Dahmardeh Mousa Bohlooli Ali Khatibi Mansour Ghaffari-Moghaddam 《Journal of Dispersion Science and Technology》2018,39(3):311-315
In this work, an electromembrane extraction (EME) technique was used for the extraction and determination of gold from water samples prior to UV-Vis spectrophotometry. An artificial neural network (ANN) combined with imperialist competitive algorithm (ICA) has been applied to optimize the EME. The effective parameters including pH of acceptor phase, extraction time (t), volume of sample solution (V), stirring rate (S), and voltage (E) were chosen as input variables and the extraction recovery of gold was considered as output variable. The mean of squared error (i.e., 0.0009) and determination coefficient (i.e., 0.9821) were applied to estimate the performance of the ANN model. The limit of detection was 4.5?µg L?1 (S/N?=?3) on the optimized variables. The intra- and interday precisions (%) were found to be 6.7% and 2.6%, respectively. This technique was then applied for analysis of gold from environment water samples. 相似文献
8.
Taking Advantage of Hydrophobic Fluorine Interactions for Self‐Assembled Quantum Dots as a Delivery Platform for Enzymes 下载免费PDF全文
Dr. Carolina Carrillo‐Carrion Mona Atabakhshi‐Kashi Dr. Mónica Carril Prof. Dr. Khosro Khajeh Prof. Dr. Wolfgang J. Parak 《Angewandte Chemie (International ed. in English)》2018,57(18):5033-5036
Self‐assembly of nanoparticles provides unique opportunities as nanoplatforms for controlled delivery. By exploiting the important role of noncovalent hydrophobic interactions in the engineering of stable assemblies, nanoassemblies were formed by the self‐assembly of fluorinated quantum dots in aqueous medium through fluorine–fluorine interactions. These nanoassemblies encapsulated different enzymes (laccase and α‐galactosidase) with encapsulation efficiencies of ≥74 %. Importantly, the encapsulated enzymes maintained their catalytic activity, following Michaelis–Menten kinetics. Under an acidic environment the nanoassemblies were slowly disassembled, thus allowing the release of encapsulated enzymes. The effective release of the assayed enzymes demonstrated the feasibility of this nanoplatform to be used in pH‐mediated enzyme delivery. In addition, the as‐synthesized nanoassemblies, having a diameter of about 50 nm, presented high colloidal stability and fluorescence emission, which make them a promising multifunctional nanoplatform. 相似文献
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Najmedin Azizi Alireza Khajeh Amiri Roya Baghi Mohammad Bolourtchian Mohammad M. Hashemi 《Monatshefte für Chemie / Chemical Monthly》2009,3(2):1471-1473
Abstract
p-Toluenesulfonic acid (10 mol%) was found to be an effective and efficient catalyst for the synthesis of 2-substituted benzothiazoles from aromatic aldehydes and 2-aminothiophenol in moderate to excellent yields in water. This method provides a simple and efficient protocol in terms of mild reaction conditions, clean reaction profiles, small quantity of catalyst, and simple workup procedure. 相似文献10.
Aminzadeh S Naderi-Manesh H Khajeh K Naderi-Manesh M 《Applied biochemistry and biotechnology》2006,135(3):193-208
For the first time, a polygalacturonase from the culture broth of Tetracoccosporium sp. was isolated and incubated at 30°C in an orbital shaker at 160 rpm for 48h. The enzyme was purified by ammonium sulfate
precipitation and two-step ion-exchange chromatography and had an apparent molecular mass of 36 kDa, as shown by sodium dodecyl
sulfate (SDS)-polyacrylamide gel electrophoresis. Its optimum activity was at pH 4.3 and 40°C, and the K
m
and V
max values of this enzyme (for polygalacturonic acid) were 3.23 mg/mL and 0.15 μmol/min, respectively. Ag+, Co2+, EDTA, Tween-20, Tween-80, and Triton X-100 stimulated polygalacturonase activity whereas Al3+, Ba2+, Ca2+, Fe2+, Fe3+, Ni2+, Mg2+, Mn2+, and SDS inhibited it. In addition, iodoacetamide and iodoacetic acid did not inhibit enzyme activity at a concentration
of 1 mM, indicating that cysteine residues are not part of the catalytic site of polygalacturonase. We studied the kinetic properties
and thermal inactivation of polygalacturonase. This enzyme exhibited a t
1/2 of 63 min at 60°C and its specific activity, turnover number, and catalytic efficiency were 6.17 U/mg, 113.64 min−1, and 35.18 mL/(min·mg), respectively. The activation energy (ΔE
#) for heat inactivation was 5.341 kJ/mol, and the thermodynamic activation parameters ΔG
#, ΔH
#, and ΔS
# were also calculated, revealing a potential application for the industry. 相似文献