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941.
Laurence Nicod Frederic Chitry Eric Gaubert Marc Lemaire Henri Barnier 《Journal of inclusion phenomena and macrocyclic chemistry》1999,34(2):143-154
Combined nanofiltration-complexation is applied to the separation of caesium and strontium from a solution containing a large concentration of sodium. Caesium and strontium complexation was studied using various water soluble resorcinarene-type ligands. Combined with nanofiltration these ligands improved the separation of caesium and strontium from sodium by the FILMTEC NF 70 membrane. 相似文献
942.
Franquelim HG Loura LM Santos NC Castanho MA 《Journal of the American Chemical Society》2008,130(19):6215-6223
Sifuvirtide, a 36 amino acid negatively charged peptide, is a novel and promising HIV fusion inhibitor, presently in clinical trials. Because of the aromatic amino acid residues of the peptide, its behavior in aqueous solution and the interaction with lipid-membrane model systems (large unilammelar vesicles) were studied by using mainly fluorescence spectroscopy techniques (both steady-state and time-resolved). No significant aggregation of the peptide was observed with aqueous solution. Various biological and nonbiological lipid-membrane compositions were analyzed, and atomic force microscopy was used to visualize phase separation in several of those mixtures. Results showed no significant interaction of the peptide, neither with zwitterionic fluid lipid membranes (liquid-disordered phase), nor with cholesterol-rich membranes (liquid-ordered phase). However, significant partitioning was observed with the positively charged lipid models (K(p) = (2.2 +/- 0.3) x 10(3)), serving as a positive control. Fluorescence quenching using F?rster resonance acrylamide and lipophilic probes was carried out to study the location of the peptide in the membrane models. In the gel-phase DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) membrane model, an adsorption of the peptide at the surface of these membranes was observed and confirmed by using F?rster resonance energy-transfer experiments. These results indicate a targeting of the peptide to gel-phase domains relatively to liquid-disordered or liquid-ordered phase domains. This larger affinity and selectivity toward the more rigid areas of the membranes, where most of the receptors are found, or to viral membrane, may help explain the improved clinical efficiency of sifuvirtide, by providing a local increased concentration of the peptide at the fusion site. 相似文献
943.
Xhaard H Backström V Denessiouk K Johnson MS 《Journal of chemical information and modeling》2008,48(7):1423-1437
The reuptake of neurotransmitters by dopamine, norepinephrine, and serotonin transporters during neuronal transmission requires a sodium gradient. An "ionic mode" of binding proposes that aspartate anchors the ligand's positive charge but ignores the direct role of sodium in ligand binding seen in the only representative structure, the prokaryotic leucine transporter LeuT. Here, we built structural models of human transporters of dopamine, norepinephrine, and serotonin using the LeuT structure. The ligand and sodium-binding sites are highly conserved. We examined the possibilities for ligand binding given the available experimental evidence, including examples of catechol-cation chelates in X-ray structures of protein and other complexes. We conclude that a "chelation mode" of binding with direct interaction between the catechol hydroxyls and sodium is a valid alternative, with consequences for pharmaceutical design. In the modeled serotonin transporter complexes, Y95 is placed where it could select for serotonin through hydrogen bonding to the indole nitrogen. 相似文献
944.
Hassan Allouchi Georges Bravic Nacer Lahrahar Jean‐Pierre Desvergne Henri Bouas‐Laurent 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(11):o620-o622
Anthraquinone derivatives form an important class of dyes and are also known for their medicinal properties. Recently, 2,3‐disubstituted anthraquinones have been shown unexpectedly to jellify various organic solvents. No information on the packing mode of these derivatives was known. Here, the first X‐ray structure of a 2,3‐disubstituted anthraquinone is reported, namely 2,3‐diethoxy‐9,10‐anthraquinone, C18H16O4. The merit of this study lies in the observation of significant differences between the packing in 9,10‐anthraquinone, which displays a herring‐bone arrangement, and that in the title 2,3‐diethoxy derivative, in which the molecules lie on parallel crystallographic morror planes separated by a distance of 3.4081 (1) Å, reminiscent of the graphite layer architecture. 相似文献
945.
We establish propagation and spreading properties for nonnegative solutions of nonhomogeneous reaction-diffusion equations of the type:
t∂u−∇⋅(A(t,x)∇u)+q(t,x)⋅∇u=f(t,x,u) 相似文献
946.
Aryl triflates were found to be suitable partners for the palladium catalyzed direct arylation of heteroaromatics via C-H activation-functionalization. The reaction conditions and the catalyst have a determining influence on the yields. The system combining PPh3 and Pd(OAc)2 using KOAc as base and DMF as solvent promotes the selective 2- or 5-arylations in moderate to high yields. Several heteroaromatics such as furan, thiophene, thiazole or oxazole derivatives have been employed successfully. The electronic properties of the aryl triflates also have a decisive influence on the yields of the coupling products. Electron-rich aryl triflates gave satisfactory results, whereas the electron-poor ones led to the formation of phenols. 相似文献
947.
Mumtaz M Lecommandoux S Cloutet E Cramail H 《Langmuir : the ACS journal of surfaces and colloids》2008,24(20):11911-11920
The synthesis of spherical poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles with a narrow size distribution was achieved in a dispersant aqueous medium. Various oxidants such as ammonium persulfate, iron(III) p-toluenesulfonate, and iron(III) trichloride were tested. A series of end-functionalized poly(ethylene oxide) (PEO) such as alpha-(3,4-ethylenedioxythiophene) PEO, alpha-( N-methyl pyrrole) PEO, alpha-(fluorene) PEO, alpha,omega-( N-methyl pyrrole) PEO, alpha,omega-(thiophene) PEO, and alpha,omega-(fluorene) PEO were compared as reactive stabilizers. The molar mass and the functionality of these reactive PEOs were found to be important parameters with respect to the control of particle size and size distribution. PEDOT samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), size exclusion chromatography (SEC), and conductivity measurements. 相似文献
948.
Manisha Durai Dr. Linhao Liu Prof. Pierre Frère Thierry Roisnel Dr. Véronique Guerchais Dr. Henri Doucet 《European journal of organic chemistry》2023,26(25):e202300303
The reactivity of benzo[1,2-b : 4,5-b′]dithiophene-4,8-dione in Pd-catalyzed C−H arylation was investigated. Using aryl bromides as aryl source in the presence of carbonate bases in 1,4-dioxane, the mono-C2-arylated benzo[1,2-b : 4,5-b′]dithiophene-4,8-diones were regioselectively obtained. This procedure allowed to introduce both electron-rich and electron-poor aryl substituents on the benzo[1,2-b : 4,5-b′]dithiophene-4,8-dione unit. These conditions were also effective for the coupling with 1-bromonaphthalene, 9-bromophenanthrene as well as aryl bromides bearing synthetically useful nitrile, chloro and methoxy substituents. The photophysical properties of representative arylated compounds have been performed by joint experimental and theoretical studies. 相似文献
949.
Prof. Dr. Henri Brunner Dr. Masahiro Ikeshita Prof. Dr. Takashi Tsuno 《European journal of organic chemistry》2023,26(36):e202300427
In this study we investigate the pyramidalization of the sp2-hybridized center at the ipso-carbon atom Ci of phenyl compounds on the theoretical side by DFT calculations of toluene, t-butylbenzene, and ethylbenzene and on the experimental side by a scatter plot analysis of 14,169 structures of ethylbenzene compounds Cβ−CαH2−C6H5 with three open positions for variation at Cβ, accumulated in the Cambridge Structural Database. In a 360° rotation about the bond between Cα of the substituent and the ipso-carbon atom Ci of the phenyl ring, the pyramidalization performs three maxima and minima. A comparison of structures with pyramidalization and its hypothetical counterparts without pyramidalization shows that pyramidalization is associated with a gain of energy. The data reveal that it is the carbon atom Cα of the phenyl substituent, which on pyramidalization bends away from the phenyl plane. Pyramidalization of sp2-hybridized centers is an omnipresent member in molecular weak interactions. 相似文献
950.
Rudy Rubini Suzanne C. Jansen Houdijn Beekhuis Dr. Henriëtte J. Rozeboom Dr. Clemens Mayer 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(2):e202213942
In vivo selections are powerful tools for the directed evolution of enzymes. However, the need to link enzymatic activity to cellular survival makes selections for enzymes that do not fulfill a metabolic function challenging. Here, we present an in vivo selection strategy that leverages recoded organisms addicted to non-canonical amino acids (ncAAs) to evolve biocatalysts that can provide these building blocks from synthetic precursors. We exemplify our platform by engineering carbamoylases that display catalytic efficiencies more than five orders of magnitude higher than those observed for the wild-type enzyme for ncAA-precursors. As growth rates of bacteria under selective conditions correlate with enzymatic activities, we were able to elicit improved variants from populations by performing serial passaging. By requiring minimal human intervention and no specialized equipment, we surmise that our strategy will become a versatile tool for the in vivo directed evolution of diverse biocatalysts. 相似文献