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991.
Alberto de Juan Dr. Yann Pouillon Dr. Luisa Ruiz‐González Dr. Almudena Torres‐Pardo Dr. Santiago Casado Prof. Dr. Nazario Martín Prof. Dr. Ángel Rubio Dr. Emilio M. Pérez 《Angewandte Chemie (International ed. in English)》2014,53(21):5394-5400
Extensive research has been devoted to the chemical manipulation of carbon nanotubes. The attachment of molecular fragments through covalent‐bond formation produces kinetically stable products, but implies the saturation of some of the C? C double bonds of the nanotubes. Supramolecular modification maintains the structure of the SWNTs but yields labile species. Herein, we present a strategy for the synthesis of mechanically interlocked derivatives of SWNTs (MINTs). In the key rotaxane‐forming step, we employed macrocycle precursors equipped with two π‐extended tetrathiafulvalene SWNT recognition units and terminated with bisalkenes that were closed around the nanotubes through ring‐closing metathesis (RCM). The mechanically interlocked nature of the derivatives was probed by analytical, spectroscopic, and microscopic techniques, as well as by appropriate control experiments. Individual macrocycles were observed by HR STEM to circumscribe the nanotubes. 相似文献
992.
Characterizing Methyl‐Bearing Side Chain Contacts and Dynamics Mediating Amyloid β Protofibril Interactions Using 13Cmethyl‐DEST and Lifetime Line Broadening 下载免费PDF全文
Dr. Nicolas L. Fawzi Dr. David S. Libich Dr. Jinfa Ying Dr. Vitali Tugarinov Dr. G. Marius Clore 《Angewandte Chemie (International ed. in English)》2014,53(39):10345-10349
Many details pertaining to the formation and interactions of protein aggregates associated with neurodegenerative diseases are invisible to conventional biophysical techniques. We recently introduced 15N dark‐state exchange saturation transfer (DEST) and 15N lifetime line‐broadening to study solution backbone dynamics and position‐specific binding probabilities for amyloid β (Aβ) monomers in exchange with large (2–80 MDa) protofibrillar Aβ aggregates. Here we use 13Cmethyl DEST and lifetime line‐broadening to probe the interactions and dynamics of methyl‐bearing side chains in the Aβ‐protofibril‐bound state. We show that all methyl groups of Aβ40 populate direct‐contact bound states with a very fast effective transverse relaxation rate, indicative of side‐chain‐mediated direct binding to the protofibril surface. The data are consistent with position‐specific enhancements of 13Cmethyl‐${R{{{\rm tethered}\hfill \atop 2\hfill}}}$ values in tethered states, providing further insights into the structural ensemble of the protofibril‐bound state. 相似文献
993.
M. Sc. Fanzhi Yang Karsten Rauch M. Sc. Katharina Kettelhoit Prof. Dr. Lutz Ackermann 《Angewandte Chemie (International ed. in English)》2014,53(42):11285-11288
Versatile ruthenium(II) complexes allow for site‐selective C? H oxygenations with weakly‐coordinating aldehydes. The challenging C? H functionalizations proceed with high chemoselectivity by rate‐determining C? H metalation. The new method features an ample substrate scope, which sets the stage for the step‐economical preparation of various bioactive heterocycles. 相似文献
994.
Anti‐Inflammatory Activity of a Novel Acetylene Isolated from the Roots of Angelica tenuissima Nakai
Hyun Gyu Choi Hyukjae Choi Jeong‐Hyung Lee Byung Sun Min Jeong Ah Kim 《Helvetica chimica acta》2016,99(6):447-451
Three polyacetylenes, one novel and two known, were isolated from the root of Angelica tenuissima. Using 1H‐ and 13C‐NMR, COSY, HMBC, and HMQC, their structures were found to be (3R,8S)‐heptadeca‐1‐en‐4,6‐diyne‐3,8‐diol ( 1 ), falcarindiol ( 2 ), and oplopandiol ( 3 ). Absolute configurations of compound 1 were established using Mosher's esterification. In addition, the polyacetylenes ( 1 – 3 ) were evaluated for their anti‐inflammatory activity. Compounds 1 and 3 showed potent inhibitory activity against lipopolysaccharide‐induced nitric oxide (NO) production in RAW267.7 macrophage cells with IC50 values of 4.31 and 5.06 μm, respectively. Compound 1 strongly inhibited inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)‐2 in a concentration‐dependent manner. 相似文献
995.
The MReaDy program was designed for studying Multiprocess Reactive Dynamic systems, that is, complex chemical systems involving different and concurrent reactions. It builds a global potential energy surface integrating a variety of potential energy surfaces, each one of them representing an elementary reaction expected to play a role in the chemical process. For each elementary reaction, energy continuity problems may happen in the transition between potential energy surfaces due to differences in the functional form for each of the fragments, especially if built by different authors. A N‐dimensional switch function is introduced in MReaDy in order to overcome such a problem. As an example, results of a collision trajectory calculation for H2 + OH → H3O are presented, showing smooth transition in the potential energy, leading to conservation in the total energy. Calculations for a hydrogen combustion system from 1000 K up to 4000 K shows a variation of 0.012% when compared to the total energy of the system. © 2016 Wiley Periodicals, Inc. 相似文献
996.
Protein environmental effects on iron‐sulfur clusters: A set of rules for constructing computational models for inner and outer coordination spheres 下载免费PDF全文
The structural properties and reactivity of iron‐sulfur proteins are greatly affected by interactions between the prosthetic groups and the surrounding amino acid residues. Thus, quantum chemical investigations of the structure and properties of protein‐bound iron‐sulfur clusters can be severely limited by truncation of computational models. The aim of this study was to identify, a priori, significant interactions that must be included in a quantum chemical model. Using the [2Fe‐2S] accessory cluster of the FeFe‐hydrogenase as a demonstrative example with rich electronic structural features, the electrostatic and covalent effects of the surrounding side chains, charged groups, and backbone moieties were systematically mapped through density functional theoretical calculations. Electron affinities, spin density differences, and delocalization indexes from the quantum theory of atoms in molecules were used to evaluate the importance of each interaction. Case studies for hydrogen bonding and charged side‐chain interactions were used to develop selection rules regarding the significance of a given protein environmental effect. A set of general rules is proposed for constructing quantum chemical models for iron‐sulfur active sites that capture all significant interactions from the protein environment. This methodology was applied to our previously used models in galactose oxidase and the 6Fe‐cluster of FeFe‐hydrogenase. © 2016 Wiley Periodicals, Inc. 相似文献
997.
Ab initio potential energy surface and vibration‐rotation energy levels of silicon dicarbide,SiC2 下载免费PDF全文
Jacek Koput 《Journal of computational chemistry》2016,37(26):2395-2402
The accurate ground‐state potential energy surface of silicon dicarbide, SiC2, has been determined from ab initio calculations using the coupled‐cluster approach. Results obtained with the conventional and explicitly correlated coupled‐cluster methods were compared. The core‐electron correlation, higher‐order valence‐electron correlation, and scalar relativistic effects were taken into account. The potential energy barrier to the linear SiCC configuration was predicted to be 1782 cm?1. The vibration‐rotation energy levels of the SiC2, 29SiC2, 30SiC2, and SiC13C isotopologues were calculated using a variational method. The experimental vibration‐rotation energy levels of the main isotopologue were reproduced to high accuracy. In particular, the experimental energy levels of the highly anharmonic vibrational ν3 mode of SiC2 were reproduced to within 6.7 cm?1, up to as high as the v3 = 16 state. 相似文献
998.
Simple and fast analysis of iohexol in human serums using micro‐hydrophilic interaction liquid chromatography with monolithic column 下载免费PDF全文
Thotsaphorn Chaloemsuwiwattanakan Areeporn Sangcakul Chagriya Kitiyakara Duangjai Nacapricha Prapin Wilairat Patcharin Chaisuwan 《Journal of separation science》2016,39(18):3521-3527
A simple and rapid method based on micro‐liquid chromatography using a synthetic monolithic capillary column was developed for determination of iohexol in human serums, a marker to evaluate the glomerular filtration rate. A hydrophilic methacrylic acid‐ethylene dimethacrylate monolith provided excellent selectivity and efficiency for iohexol with separation time of 3 min using a mobile phase of 40:60 v/v 50 mM phosphate buffer pH 5/methanol. Four serum protein removal, methods using perchloric acid, 50% acetonitrile, 0.1 M zinc sulfate, and centrifuge membrane filter were examined. The method of zinc sulfate was chosen due to its simplicity, compatibility with the mobile phase system, nontoxicity, and low cost. Interday calibration curves were conducted over iohexol concentrations range of 2–500 mg/L (R2 = 0.9997 ± 0.0001) with detection limit of 0.44 mg/L. Intra‐ and interday precisions for peak area and retention time were less than 2.8 and 1.4%, respectively. The method was successfully applied to serum samples with percent recoveries from 102 to 104. The method was applied to monitor released iohexol from healthy subject. Compared with the commercially available reversed‐phase high‐performance liquid chromatography method, the presented method provided simpler chromatogram, faster separation with higher separation efficiency and much lower sample and solvent consumption. 相似文献
999.
Determination and removal of sulfonamides and quinolones from environmental water samples using magnetic adsorbents 下载免费PDF全文
Hao Wu Yating Shi Xiaozhen Guo Shuangli Zhao Juanli Du Hongping Jia Lina He Liming Du 《Journal of separation science》2016,39(22):4398-4407
In this study, the magnetic materials known as polymerized ionic liquid@3‐(trimethoxysilyl)propyl methacrylate@Fe3O4 nanoparticles were synthesized and utilized as potential adsorbents. First, these nanoparticles were applied to the analysis of sulfonamides and quinolones present in different water samples using magnetic solid phase extraction and high‐performance liquid chromatography. Under optimized conditions, the developed method showed excellent detection sensitivity, with limits of detection (S/N = 3) and quantification limits (S/N = 10) within 0.2–1.0 and 0.8–3.4 μg/L, respectively. The spiked recoveries of the SAs and QNs in environmental water samples ranged from 83.5 to 103.0%, with RSDs of less than 4.5%. In addition, the adsorbents effectively removed sulfamethoxazole and ofloxacin present in existing aquatic environments. The adsorption kinetics and isotherms of sulfamethoxazole and ofloxacin on the magnetic adsorbents were studied to assess removal performance. The results indicate that the adsorption process follows a pseudo‐second‐order mechanism, which reveals that the sorption mechanism is the rate‐limiting step and produces high qmax values (sulfamethoxazole = 70.35 mg/g and ofloxacin = 48.95 mg/g), thus demonstrating the enormous adsorption capacity of these magnetic adsorbents. 相似文献
1000.
Phase behavior and Li+ Ion conductivity of styrene‐ethylene oxide multiblock copolymer electrolytes 下载免费PDF全文
Solid polymer electrolytes are attractive materials for use as battery separators. Here, a molecular weight series of polystyrene–polyethylene oxide (PEO) multiblock copolymers was synthesized by the thiol–norbornene click reaction. The subsequent materials were characterized both neat and with a lithium bis‐(trifluoromethane)sulfonimide salt loading [(Li)/(EO)] of 0.1. In general, neat samples demonstrated crystallinity scaling with PEO content. Lithium ion‐containing samples had broad scattering peaks, half of which displayed disordered scattering, even at the lowest block molecular weights (polystyrene = 1 kg/mol, PEO = 1 kg/mol). Fitting of disordered scattering data, using the random phase approximation, yielded χRPA and Rg values that were compared with recent predictive work by Balsara and coworkers. The predictions were accurate near the volume fraction fPEO = 0.5 but deviated symmetrically with volume fraction asymmetry. Samples were also analyzed by electrochemical impedance spectroscopy for their potential to conduct lithium ions. Samples with fPEO ≥ 0.5 demonstrated robust conductivity, whereas samples below this volume fraction conducted very poorly, with one exception (fPEO = 0.24). This work expanded upon our recently reported approach to multiblock copolymer synthesis, demonstrating the improved access of materials to further our fundamental understanding of multiblock copolymers. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献