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1.
M. Patri Varsha R. Hande Swati Phadnis B. Somaiah Suhasini Roychoudhury P. C. Deb 《先进技术聚合物》2004,15(5):270-274
A Novel solid polymer electrolyte (SPE) membrane containing both ? COOH and ? SO3H group has been prepared by simultaneous method of radiation grafting of acrylic acid onto FEP followed by sulfonation. The presence of weakly acidic acrylic acid controls the swelling in water while ? SO3H group provides conductivity due to its strongly ionic characteristic. FEP‐g‐acrylic acid and its sulfonated derivatives were characterized by their properties. While the mechanical properties decreased, other properties such as ion exchange capacity (IEC), water uptake and ionic conductivity increased with increase in graft content. These properties further changed on sulfonation. Acrylic acid being weakly acidic in nature, conductivity values of the grafted membrane were quite low. However, introduction of strong ? SO3H group resulted in conductivity closer to Nafion 117. Few sulfonated membranes have been tested with respect to H2/O2 fuel cell performance. Short‐term fuel cell test for 100 hr gave a stable performance. These membranes are less expensive compared to Nafion. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
2.
Willem Jespers Dr. Grégory Verdon Dr. Jhonny Azuaje Dr. Maria Majellaro Dr. Henrik Keränen Prof. Xerardo García-Mera Dr. Miles Congreve Dr. Francesca Deflorian Dr. Chris de Graaf Dr. Andrei Zhukov Dr. Andrew S. Doré Dr. Jonathan S. Mason Prof. Johan Åqvist Dr. Robert M. Cooke Prof. Eddy Sotelo Dr. Hugo Gutiérrez-de-Terán 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(38):16679-16686
We present a robust protocol based on iterations of free energy perturbation (FEP) calculations, chemical synthesis, biophysical mapping and X-ray crystallography to reveal the binding mode of an antagonist series to the A2A adenosine receptor (AR). Eight A2AAR binding site mutations from biophysical mapping experiments were initially analyzed with sidechain FEP simulations, performed on alternate binding modes. The results distinctively supported one binding mode, which was subsequently used to design new chromone derivatives. Their affinities for the A2AAR were experimentally determined and investigated through a cycle of ligand-FEP calculations, validating the binding orientation of the different chemical substituents proposed. Subsequent X-ray crystallography of the A2AAR with a low and a high affinity chromone derivative confirmed the predicted binding orientation. The new molecules and structures here reported were driven by free energy calculations, and provide new insights on antagonist binding to the A2AAR, an emerging target in immuno-oncology. 相似文献
3.
Son Tung Ngo Trung Hai Nguyen Nguyen Thanh Tung Pham Cam Nam Khanh B. Vu Van V. Vu 《Journal of computational chemistry》2020,41(7):611-618
Determination of the ligand-binding affinity is an extremely interesting problem. Normally, the free energy perturbation (FEP) method provides an appropriate result. However, it is of great interest to improve the accuracy and precision of this method. In this context, temperature replica exchange molecular dynamics implementation of the FEP computational approach, which we call replica exchange free energy perturbation (REP) was proposed. In particular, during REP simulations, the system can easily escape from being trapped in local minima by exchanging configurations with high temperatures, resulting in significant improvement in the accuracy and precision of protein–ligand binding affinity calculations. The distribution of the decoupling free energy was enlarged, and its mean values were decreased. This results in changes in the magnitude of the calculated binding free energies as well as in alteration in the binding mechanism. Moreover, the REP correlation coefficient with respect to experiment ( RREP = 0.85 ± 0.15 ) is significantly boosted in comparison with the FEP one ( RFEP = 0.64 ± 0.30 ). Furthermore, the root-mean-square error (RMSE) of REP is also smaller than FEP, RMSEREP = 4.28 ± 0.69 versus RMSEFEP = 5.80 ± 1.11 kcal/mol, respectively. © 2019 Wiley Periodicals, Inc. 相似文献
4.
Bhuvanesh Gupta Felix N. Büchi Markus Staub D. Grman Günther G. Scherer 《Journal of polymer science. Part A, Polymer chemistry》1996,34(10):1873-1880
The structure and some physico-chemical properties of radiation grafted FEP-g-polystyrenesulfonic acid proton exchange membranes were studied as a function of the degree of grafting. The distribution of grafted polymer across the membrane thickness was obtained from microprobe measurements. It was found that for low levels of grafting (ca. 3%), polystyrene chains are located near the membrane surface only, and the interior of the membrane remains ungrafted. With the increasing degree of grafting, polystyrene chains were incorporated into the interior of the membrane as well. An almost homogeneous distribution of grafts in the membrane was obtained at a graft level of > 13%. The influence of the degree of grafting on membrane properties, such as ion exchange capacity, swelling, and specific resistivity was studied. Three different states of water, viz., freezing free, freezing bound, and nonfreezing water have been identified in noncrosslinked membranes. However, the nature and the amount of crosslinker had a profound influence on the states of water in a membrane. © 1996 John Wiley & Sons, Inc. 相似文献
5.
M. Šiljegovi? Z.M. Ka?arevi?-Popovi? N. Bibi? Z.M. Jovanovi? S. Maleti? M. Stchakovsky A.N. Krklješ 《Radiation Physics and Chemistry》2011,80(12):1378-1385
Fluorinated ethylene propylene (FEP) and tetrafluoroethylene–perfluoro(alkoxy vinyl ether) (PFA) copolymer films were irradiated in vacuum with 60 keV C4+ and N4+ ions to fluences ranging from 1.0×1012 to 5.0×1015 cm−2. Changes in optical and dielectric properties were analyzed by spectroscopic ellipsometry and ultraviolet–visible (UV–vis), Raman and dielectric relaxation spectroscopies. Direct and indirect energy band gap values were determined from the absorption edge in the 200–800 nm region using Tauc's relation. The values of the direct energy gap have been found to be greater than the corresponding values of the indirect energy gap. Significant changes in the index of refraction, and β and γ dielectric relaxations were observed in the case of N4+ irradiated FEP and PFA samples. 相似文献
6.
The rheology of tetrafluoroethylene/hexafluoropropylene (TFE/HFP) copolymers, also known as Teflon FEP polymers, having different
molecular weight and composition (HFP content) was studied by means of a parallel-plate rheometer. Two groups of polymers
having different molecular weights with nearly constant polydispersity (around 2.5) were considered; namely, one group having
a relatively low melting temperature (amorphous with a high content of HFP) and a second group having a higher melting point
(semi-crystalline with a lower content of HFP). The relaxation time spectrum, H(λ), calculated by use of the BSW model (developed for monodisperse linear polymers) followed a scaling relationship in the
terminal zone with scaling exponent of 0.13. However, at higher frequencies the model fails to predict adequately the experimental
data. The longest relaxation time calculated from both the BSW model and discrete relaxation spectra (λ
i
,g
i
), which was determined by use of a parsimonious fitting software, depends on the molecular weight in a similar way as the
zero-shear viscosity does with the well-established scaling factor of 3.4. The critical molecular weight for the onset of
entanglements, M
c
, was found to be about 100000, a value much higher than those previously reported in literature for other polymers. The rheology
of resins in the second group (higher melting point) was found to exhibit a strong dependence on thermal history during oscillatory-shear
measurements. The data obtained in experiments at different temperatures without a preheating to a certain value (330°C) exhibited
a violation of the time-temperature superposition principle and no well-defined values of the zero-shear viscosity. This is
attributed to residual crystallinity even at temperatures well above their melting point (260°C). However, the same experiments
with preheating and subsequent cooling to desired temperature resulted into a very good time-temperature scaling.
Received: 13 January 1998 Accepted: 6 April 1998 相似文献
7.
8.
Grigor L. Georgiev Ronald J. Baird Golam Newaz Gregory Auner Hans Herfurth 《Applied Surface Science》2009,255(15):7078-7083
Teflon® FEP (fluorinated ethylene propylene) is resistant to most chemical solvents, is heat sealable and has low moisture uptake, which make this polymer attractive as a packaging materials for electronics and implantable devices. Teflon® FEP/Ti microjoints were fabricated by using focused infrared laser irradiation. Teflon® FEP/Ti interfaces were studied by using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). The XPS results give evidence for the formation of Ti-F bonds in the interfacial region. The AES and SEM-EDS results show that the chemical bond formation occurs only in the actual bond area. No evidence for chemical bond formation was found in the heat affected zone surrounding the laser bonds. 相似文献
9.
Acrylic acid was grafted onto fluorinated ethylene propylene copolymer (FEP) using a simultaneous radiation technique and the resulting membranes were subsequently sulfonated. Thermal and mechanical properties of these membranes were investigated and were found to be strongly influenced by the degree of grafting. Thermogravimetric analysis (TGA) of these membranes showed that these membranes undergo multistep degradation unlike virgin FEP which degrades in a single step. Glass transition temperature and degree of crystallinity were determined by differential scanning calorimetry (DSC). Glass transition temperature increased while crystallinity decreased with increase in degree of grafting. Tensile strength and elongation at break were found to decrease on grafting and further on sulfonation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
10.
Abstract Discrimination of chiral amines by dimethyldiketopyridino-18-crown-6 (1) is studied by free energy peturbation (FEP) and molecular dynamics (MD) methods. 1 has two (S)-chiral centers and discriminates chiral amines through host-guest interactions. The optically active amines in this study are α-(1-naphthyl)ethylamine, methylbenzylamine, cyclohexylethylamine, and sec-butylamine. The trends in binding free energy differences obtained from FEP calculations were in excellent agreement with experimental results obtained in the gas phase. In order to explain the enantioselectivity of the host in terms of the host-guest interactions at the molecular level, we analyzed the structures generated by 10-ns MD simulations of host-guest complexes. The suggested chiral discrimination mechanism, the π-π interaction and the steric repulsion between the guest and the host, was verified by our MD simulation analysis. 相似文献