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Veronica Felli Susanna Terracini 《Calculus of Variations and Partial Differential Equations》2006,27(1):25-58
This paper deals with a class of nonlinear elliptic equations involving a critical power-nonlinearity as well as a potential featuring multiple inverse square singularities. When the poles form a symmetric structure, it is natural we wonder how the symmetry affects such mutual interaction. The present paper means to study this aspect from the point of view of the existence of solutions inheriting the same symmetry properties as the set of singularities.
Mathematics Subject Classification (2000) 35J60, 35J20, 35B33 相似文献
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Molecular dynamics simulations were carried out in the presence of 2380 water molecules (TIP3P) to explore the conformational preferences of 3,9-dimethoxy-4-prenylpterocarpan (bitucarpin A) and 3,9-dihydroxy-4,8-diprenylpterocarpan (erybraedin C) and the H-bond network around them, using the empirical general AMBER force field (GAFF). Specific angle and torsional parameters have been improved in order to match the geometries of the minimum energy structures obtained from an earlier DFT/ab initio study in vacuo, taking into account a few configurations [Alagona, G.; Ghio, C.; Monti, S. Phys. Chem. Chem. Phys. 2004, 6, 2849-2857]. RESP partial charges were assigned to reproduce the electrostatic potential determined at the HF/6-31G level of theory. The analysis of trajectories allowed the conformations of bitucarpin and erybraedin as well as the distribution of water molecules around them to be elucidated. During one of the simulations only, the scaffold of erybraedin undergoes interconversion from its most stable Ht conformation to the Ot one and vice versa. Radial distribution functions, coordination numbers, and angular distributions put forward the extent of solvent structure and the hydrogen bonding behavior of their various (methoxy, hydroxyl, or ethereal) oxygen atoms. The distribution of solvent molecules in the first and second solvation shells as well as the residence times for the different solute-solvent interacting sites have been considered. 相似文献
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Herold S Kalinga S Matsui T Watanabe Y 《Journal of the American Chemical Society》2004,126(22):6945-6955
Hemoproteins are known to react with the strong nitrating and oxidizing agent peroxynitrite according to different mechanisms. In this article, we show that the iron(iii) forms of the sperm whale myoglobin (sw Mb) mutants H64A, H64D, H64L, F43W/H64L, and H64Y/H93G catalyze the isomerization of peroxynitrite to nitrate. The two most efficient catalysts are H64A (k(cat) = (5.8 +/- 0.1) x 10(6) M(-1) s(-1), at pH 7.5 and 20 degrees C) and H64D metMb (k(cat) = (4.8 +/- 0.1) x 10(6) M(-1) s(-1), at pH 7.5 and 20 degrees C). The pH dependence of the values of k(cat) shows that HOONO is the species which reacts with the heme. In the presence of physiologically relevant concentrations of CO(2) (1.2 mM), the decay of peroxynitrite is accelerated by these metMb mutants via the concurring reaction of HOONO with their iron(iii) centers. Studies in the presence of free added tyrosine show that the metMb mutants prevent peroxynitrite-mediated nitration. The efficiency of the different sw metMb mutants correlates with the value of k(cat). Finally, we show that sw WT-metMb is nitrated to a larger extent than horse heart metMb, a result that suggests that the additional Tyr151 is a site of preferential nitration. Again, the extent of nitration of the tyrosine residues of the metMb mutants correlates with the values of k(cat). 相似文献
6.
Attilio Citterio Anna Gentile Francesco Minisci Marco Serravalle Susanna Ventura 《Tetrahedron》1985,41(3):617-620
The homolytic decomposition of hydroxylamine-O-sulphonic acid in alcoholic solvents was investigated in the presence or absence of protonated heteroaromatic bases and Fe(II) salt. The addition of the α-hydroxyalkyl radicals to the base and their oxidation by Fe(III) salt to the corresponding alkyl cyanide were competitive processes. A redox chain process involving the amino radical cation, NH3t., is suggested and the factors affecting the yields of the homolytic substitution are discussed. 相似文献
7.
Susanna Tsang 《Talanta》2007,71(4):1560-1568
A modified molybdenum blue method for fast and accurate measurement of arsenate and phosphate in aqueous solution at concentrations below 10 μmol l−1 is reported. The modification consists of optimizing the composition of the molybdenum-containing solution (potassium antimony tartrate, ammonium molybdate, sulfuric acid).Selective reduction of arsenate by sodium dithionite is used to determine phosphate concentrations, and for the speciation of arsenate and arsenite, in an aqueous mixture according to the scheme developed by Johnston and Pilson. Sodium dithionite is used for the first time to achieve complete, fast (<10 min), and selective reduction of arsenate in neutral solution.These two significant improvements afforded a colorimetric limit for As detection near 1 ppb, which easily meets the requirements imposed by the revised EPA threshold levels for As in drinking water. 相似文献
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Anionic liposomes can be coated on fused-silica capillaries for electrophoresis in the presence of N-(hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) (HEPES) as background electrolyte (BGE) solution. In this work, the interaction of various compounds with zwitterionic and anionic phospholipid coatings was studied with HEPES at pH 7.4 as BGE solution. The chromatographic and electrophoretic behavior of three test sample solutions (anionic, cationic, and neutral) was investigated for evaluation of the phospholipid coatings. Our results show that hydrophobic interactions between analytes and the phospholipid coating are important for the migration of charged analytes. In addition, the performances of other piperazine-based buffers, i.e., N-(2-hydroxyethyl)piperazine-N'-(2-hydroxypropanesulfonic acid), piperazine-N,N'-bis(2-ethanesulfonic acid), and piperazine-N,N'-bis(hydroxypropane sulfonic acid), at pH 7.4, as liposome solvent and BGE solution were evaluated and compared with the performance of HEPES at pH 7.4. The anionic liposome solution comprised 80/20 mol% phosphatidylcholine/phosphatidylserine. A simple test solution was selected and the chromatographic and electrophoretic migration behavior of the analytes was evaluated. The results show that, in addition to HEPES, other piperazine-based buffers at pH 7.4 are suitable for coating of fused-silica capillaries with anionic liposomes. 相似文献
9.
Ultrafast and selective labeling of endogenous proteins using affinity-based benzotriazole chemistry
Xiaoyi Xin Yu Zhang Massimiliano Gaetani Susanna L. Lundstrm Roman A. Zubarev Yuan Zhou Dale P. Corkery Yao-Wen Wu 《Chemical science》2022,13(24):7240
Chemical modification of proteins is enormously useful for characterizing protein function in complex biological systems and for drug development. Selective labeling of native or endogenous proteins is challenging owing to the existence of distinct functional groups in proteins and in living systems. Chemistry for rapid and selective labeling of proteins remains in high demand. Here we have developed novel affinity labeling probes using benzotriazole (BTA) chemistry. We showed that affinity-based BTA probes selectively and covalently label a lysine residue in the vicinity of the ligand binding site of a target protein with a reaction half-time of 28 s. The reaction rate constant is comparable to the fastest biorthogonal chemistry. This approach was used to selectively label different cytosolic and membrane proteins in vitro and in live cells. BTA chemistry could be widely useful for labeling of native/endogenous proteins, target identification and development of covalent inhibitors.Affinity-based benzotriazole (BTA) probes selectively and covalently label native proteins or endogenous proteins in cells with a fast reaction rate. It is enormously useful for characterizing protein function in biological systems and for drug development. 相似文献
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长期以来,天文学家精确的预测令世人惊讶。预言3000年4月26日,日全食可观察带,将顺着南美洲、大西洋和北非一线延伸,这一预测没有人反对。但试图描述病原体未来传播的科学家,必须面对非常大的不确定性。研究人员既缺乏关于传染病如何传播的可靠数据,感染能力的微小差异又可以成倍地扩大病毒的传播,从而难以预测各类流行病的严重程度。来自伊利诺伊大学的Nigel Goldenfeld和他的同事,最近以伊利诺伊州为例,开发了一个模型,评估非药物干预时COVID-19病毒传播的短期影响。研究者还探索和量化了模型的局限性,阐明了它无法预测的场景。他们使用该模型,向公民、临床医生和决策者,作出了示范性展示。 相似文献