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排序方式: 共有140条查询结果,搜索用时 62 毫秒
131.
132.
Matos MA Miranda MS Martins DV Pinto NA Morais VM Liebman JF 《Organic & biomolecular chemistry》2004,2(9):1353-1358
The standard molar enthalpies of combustion and sublimation of 2- and 4-biphenylcarboxylic acid, 2,2'- and 4,4'-biphenyldicarboxylic acid were measured and the gas-phase enthalpies of formation, at T= 298.15 K, were determined. Ab initio calculations were performed and a theoretical study on molecular structure of all the biphenyl acid isomers has been carried out. Calculated enthalpies of formation using appropriate isodesmic reactions are compared with experimental values, and a good agreement is observed. Estimates of enthalpies of formation for the isomers, which were not studied experimentally, are presented. All the acids containing at least one ortho COOH are comparatively less stable than their isomers having just meta or para COOH group(s). 相似文献
133.
A urea-formaldehyde resin (UF) continuous bed has been prepared through in-situ condensation polymerization in a confined tube. The monolith is an agglomerate of 2-microm irregular particles. Nitrogen adsorption shows that the monolith has a bimodal pore size distribution. It has low resistance to flow. A dyed monolith is obtained through modification of the UF monolith with Cibacron blue F3GA. Although its dye concentration and dynamic capacity are low compared to Sepharose type affinity media, the dyed monolith can separate some proteins in the affinity mode of liquid chromatography. 相似文献
134.
Gulaboski R Pereira CM Cordeiro MN Bogeski I Ferreira E Ribeiro D Chirea M Silva AF 《The journal of physical chemistry. B》2005,109(25):12549-12559
The ion transfer of acetylcholine (AcH(+)) ions across the unmodified and phospholipid-modified water|1,2-dichloroethane (DCE) interface has been studied by means of square-wave and cyclic voltammetry, as well as by electrochemical impedance spectroscopy. After being transferred in the organic phase, the AcH(+) ions undergo chemical reactions with the phospholipids. The overall behavior of the experimental system studied in the presence of phospholipids has been compared with the theoretical results of an ECrev reaction. The kinetic parameters of the chemical interactions between AcH(+) and the phospholipids have been determined from the voltammetric and impedance measurements. Additional characterization of those interactions has been made by using the surface tension measurements. 相似文献
135.
Given complex numbers α1,...,αn, β1,...,βn, what can we say about the determinant of A+B, where A (B) is an n×n normal matrix with eigenvalues α1,...,αn (β1,...,βn)? Some partial answers are offered to this question. 相似文献
136.
A number of bioactive peptides find their potential applications in food or pharmaceutical industry; however, there arise some limitations of their large-scale production to satisfy market demands. Although pressure-driven membrane processes are able of continuous production and separation of peptides, these technologies often demonstrate insufficient selectivity. Electrophoresis is a well-known purification process characterized by high resolution of separated species but it is limited by relatively low production capacity. On the other hand, electromembrane processes offer high production capacity but their limitation is the size of separated molecules. Electrodialysis with inserted ultrafiltration membranes is an alternative method of peptide separation into fractions, their concentration and possibly demineralization at the same time to achieve large production quantities. It is a hybrid process combining conventional electrodialysis and electrophoresis principles using ultrafiltration membranes. These membranes serve as a molecular barrier separating two types of solution while the driving force remains electric potential difference. This article offers state-of-the-art summary in the field of bioactive peptide separation and fractionation by electrodialysis with ultrafiltration membranes. 相似文献
137.
de Araújo ME Contesini FJ Franco YE Sawaya AC Alberto TG Dalfré N Carvalho Pde O 《Molecules (Basel, Switzerland)》2011,16(8):7171-7182
Response surface methodology (RSM) based on a five-level, three-variable central composite design (CCD) was employed for modeling and optimizing the conversion yield of the enzymatic acylation of hesperidin with decanoic acid using immobilized Candida antarctica lipase B (CALB) in a two-phase system containing [bmim]BF(4). The three variables studied (molar ratio of hesperidin to decanoic acid, [bmim]BF(4)/acetone ratio and lipase concentration) significantly affected the conversion yield of acylated hesperidin derivative. Verification experiments confirmed the validity of the predicted model. The lipase showed higher conversion degree in a two-phase system using [bmim]BF(4) and acetone compared to that in pure acetone. Under the optimal reaction conditions carried out in a single-step biocatalytic process when the water content was kept lower than 200 ppm, the maximum acylation yield was 53.6%. 相似文献
138.
We develop the new variational calculus introduced in 2011 by J. Cresson and I. Greff, where the classical derivative is substituted by a new complex operator called the scale derivative. In this paper, we consider several nondifferentiable variational problems with free terminal point with and without constraints of first and higher‐order type. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
139.
Eva Pospíšilová Natálie Paškanová Martin Kuchař Tatiana V. Shishkanova 《Electroanalysis》2023,35(6):e202200468
This work presents a potentiometric approach for the detection of two cathinone derivatives, namely mephedrone (4-MMC) and clephedrone (4-CMC). Contrary to neutral-carriers (dibenzo-18-crown-6-ether and calix[4]arene), cation-exchanger (tetraphenylborate sodium) as active component of ion-selective membrane showed near-Nernstian response (+47 mV/decade from 1.7 ⋅ 10−6 to 5.6 ⋅ 10−4 mol l−1) and selectivity for 4-MMC in oral fluids (OF). The agreement between the quantitative results obtained with the potentiometric approach and the HPLC/MS-MS method determination of 4-MMC in OF shows the potential of the proposed potentiometric approach for forensic analysis. 相似文献
140.
This paper determines the existence of a unique local solution for the 3D generalized magnetohydrodynamics equations. In order to be more precise, our solution is obtained by involving Lei–Lin–Gevrey spaces as well as Lei–Lin spaces. Furthermore, we present five new blow-up criteria for this same system when the maximal time of existence is finite. It is important to point out that one of these criteria is obtained by assuming fractional Laplacians with equal powers. 相似文献