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排序方式: 共有68条查询结果,搜索用时 15 毫秒
1.
Poly (n-butylisocyanate)-benzene solutions prepared by solubilization at 45°C, followed by aging at room temperature were found to be metastable for months, although, eventually, they separated into a birefringent polymer-rich phase and an isotropic solution. These metastable solutions, as well as isothermally phase-separated biphasic samples, flowed and exhibited dynamic moduli indicative of low polymer connectivity. By contrast samples prepared by a freeze-thaw cycle were uniformly and highly birefringent and showed network (gel) behavior at room temperature. The mechanism of gel formation is most likely the exclusion of the polymer from the benzene crystal during crystallization, forcing the polymer to align and exist at grain boundaries. Films formed from solutions have different moduli than those formed from gels, and are consistent with the proposed mechanism. 相似文献
2.
Wilmer H. Perera Siddanagouda R. Shivanagoudra Jose L. Prez Da Mi Kim Yuxiang Sun Guddadarangavvanahally K. Jayaprakasha Bhimanagouda S. Patil 《Molecules (Basel, Switzerland)》2021,26(4)
Diabetes mellitus is a chronic disease and one of the fastest-growing health challenges of the last decades. Studies have shown that chronic low-grade inflammation and activation of the innate immune system are intimately involved in type 2 diabetes pathogenesis. Momordica charantia L. fruits are used in traditional medicine to manage diabetes. Herein, we report the purification of a new 23-O-β-d-allopyranosyl-5β,19-epoxycucurbitane-6,24-diene triterpene (charantoside XV, 6) along with 25ξ-isopropenylchole-5(6)-ene-3-O-β-d-glucopyranoside (1), karaviloside VI (2), karaviloside VIII (3), momordicoside L (4), momordicoside A (5) and kuguaglycoside C (7) from an Indian cultivar of Momordica charantia. At 50 µM compounds, 2–6 differentially affected the expression of pro-inflammatory markers IL-6, TNF-α, and iNOS, and mitochondrial marker COX-2. Compounds tested for the inhibition of α-amylase and α-glucosidase enzymes at 0.87 mM and 1.33 mM, respectively. Compounds showed similar α-amylase inhibitory activity than acarbose (0.13 mM) of control (68.0–76.6%). Karaviloside VIII (56.5%) was the most active compound in the α-glucosidase assay, followed by karaviloside VI (40.3%), while momordicoside L (23.7%), A (33.5%), and charantoside XV (23.9%) were the least active compounds. To better understand the mode of binding of cucurbitane-triterpenes to these enzymes, in silico docking of the isolated compounds was evaluated with α-amylase and α-glucosidase. 相似文献
3.
Víctor Manuel Castor-Villegas José Manuel Guevara-Vela Wilmer E. Vallejo Narváez Ángel Martín Pendás Tomás Rocha-Rinza Alberto Fernández-Alarcón 《Journal of computational chemistry》2020,41(26):2266-2277
Hydrogen bonds (HB) are arguably the most important noncovalent interactions in chemistry. We study herein how differences in connectivity alter the strength of HBs within water clusters of different sizes. We used for this purpose the interacting quantum atoms energy partition, which allows for the quantification of HB formation energies within a molecular cluster. We could expand our previously reported hierarchy of HB strength in these systems (Phys. Chem. Chem. Phys., 2016, 18 , 19557) to include tetracoordinated monomers. Surprisingly, the HBs between tetracoordinated water molecules are not the strongest HBs despite the widespread occurrence of these motifs (e.g., in ice Ih). The strongest HBs within H2O clusters involve tricoordinated monomers. Nonetheless, HB tetracoordination is preferred in large water clusters because (a) it reduces HB anticooperativity associated with double HB donors and acceptors and (b) it results in a larger number of favorable interactions in the system. Finally, we also discuss (a) the importance of exchange-correlation to discriminate among the different examined types of HBs within H2O clusters, (b) the use of the above-mentioned scale to quickly assess the relative stability of different isomers of a given water cluster, and (c) how the findings of this research can be exploited to indagate about the formation of polymorphs in crystallography. Overall, we expect that this investigation will provide valuable insights into the subtle interplay of tri- and tetracoordination in HB donors and acceptors as well as the ensuing interaction energies within H2O clusters. 相似文献
4.
5.
C70X2(X=H,F, Cl)的稳定性和电子光谱 总被引:1,自引:0,他引:1
用INDO方法研究C70H2四种异构体的稳定性, 表明其最稳定异构体为1, 9-C70H2和7, 8-C70H2, 两者能量差为16.3KJ.mol^-^1, 与实验值及ab initio计算值接近; 光谱计算表明, 其特征吸收峰与实验值一致。在此基础上预测C70F2和C70Cl2的稳定性和电子光谱, 表明C70F2四种异构体的稳定性顺序与C70H2一致, 而C70Cl2则以21, 42-异构体最为稳定。二者的电子光谱与C70H2极其相似只是在500nm以上有细微差别。 相似文献
6.
Joseph A. N. Zasadzinski Paul C. Vosejpka Wilmer G. Miller 《Journal of colloid and interface science》1986,110(2)
Polymerized liposomes and vesicles are under close scrutiny as long-lived, stable substitutes for their natural and synthetic unpolymerized counterparts. The monomer surfactant, which contains one or more polymerizable groups, is dispersed in water at the proper temperature and concentration to form the lyotropic liquid crystalline phase of interest and polymerized while in the liquid crystalline state. In addition to their applications to slow-release and site-specific drug delivery, membrane-mediated chemistry, artificial photosynthesis, etc., polymerized surfactant liposomes and vesicles hold great promise as model systems for TEM investigations of lamellar liquid crystal structure. One such model polymerizable surfactant is DBPAl, or N,N-dimethyl-N,N-bis(1,3-pentadecadienyl-carbonyloxyethyl) ammonium iodide. Polarized light microscopy and differential scanning calorimetry (DSC) confirm that DBPAI forms lamellar liquid crystalline liposomes in water. The DBPAI liposomes were polymerized while in the liquid crystalline state by ultraviolet (UV) irradiation. The DBPAI liposomes were shown to be identical in structure before and after polymerization by a combination of X-ray diffraction and freeze-fracture TEM. However, turbidity measurements showed that the polymerized DBPAI liposomes were much more stable in acetone and ethanol than the monomer DBPAI liposomes, demonstrating that the chemical nature of the surfactant in the liposome had changed. The combination of structural preservation and enhanced chemical stability makes DBPAI a natural choice for TEM thin-sections. A method of preparing DBPAI liposomes for thin-section TEM is outlined and bilayer resolution images of the DBPAI liposomes are presented. Polymerized bilayers in thin-section TEM promise the enhanced resolution required to answer many important structural questions left unresolved by freeze-fracture TEM. 相似文献
7.
Prema Ranganathan Wilmer K. Fife Martel Zeldin 《Journal of polymer science. Part A, Polymer chemistry》1990,28(10):2711-2717
4-Vinylpyridinium trifluoromethanesulfonate monomers substituted at nitrogen with H, O, CH3, C2H5, C6H13, and C12H25 were synthesized and characterized spectroscopically. Thermal analyses (DSC and TGA) were carried out on all the compounds. The solid monomers (N? H, N? CH3, N? C6H13, and N? C12H25) exhibited endothermic melting followed by exothermic polymerization and exothermic decomposition (>400°C). Liquid N? C2H5 monomer revealed only exothermic polymerization and decomposition. The N? O polymer underwent thermal decomposition below 300°C. The N–C12H25 homopolymer, prepared from monomer in the DSC or in bulk, displayed an unusual thermal transition at 250°C, which has been attributed to a polymer backbone reorientation leading to side-chain ordering of the dodecyl groups. 相似文献
8.
9.
A. Wilmer T. D. Frank P. J. Beek R. Friedrich 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(2):203-215
In this work a method is developed for analyzing time series of
periodically driven stochastic systems involving time-delayed feedback.
The proposed data-analysis method yields
dynamical models in terms of stochastic delay differential equations. On
the basis of these dynamical models differential effects of driving
forces and time-delayed feedback forces can be identified. 相似文献
10.
Jack Deruiter Deborah Ann Carter Wilmer Scott Arledge Patrick J. Sullivan 《Journal of heterocyclic chemistry》1987,24(1):149-153
The reactions of 4-isopropylidene-1-aryl-3-methyl-2-pyrazolin-5-ones 4a-d were investigated under a variety of conditions. In the presence of thiols or piperidine, 4a-d failed to yield conjugate addition products, presumably due to the steric bulk provided by the two methyl substituents of the isopropylidene side chain. Reaction of 4a-d with hydrazine derivatives gave the 1-aryl-3-methyl-2-pyrazolin-5-ones 3a-d and isopropyl-hydrazones. Treatment of 4a with potassium cyanide yielded a stable conjugate addition product which exists as a mixture of tautomers in different solvents. Also, oxidation of 4a with hydrogen peroxide gave a spiroepoxide 22 , while m-chloroperbenzoic acid oxidation afforded both the spiroepoxide 22 , and a small quantity of a hydroxyspiroepoxide 23. 相似文献