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211.
212.
213.
Dual Role of the 1,2,3‐Triazolium Ring as a Hydrogen‐Bond Donor and Anion–π Receptor in Anion‐Recognition Processes
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Dr. Fabiola Zapata Lidia Gonzalez Dr. Antonio Caballero Prof. Ibón Alkorta Prof. Jose Elguero Prof. Pedro Molina 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9797-9808
Several bis(triazolium)‐based receptors have been synthesized as chemosensors for anion recognition. The central naphthalene core features two aryltriazolium side‐arms. NMR experiments revealed differences between the binding modes of the two triazolium rings: one triazolium ring acts as a hydrogen‐bond donor, the other as an anion–π receptor. Receptors 92+?2BF4 ? (C6H5), 112+?2BF4 ? (4‐NO2?C6H4), and 132+?2BF4? (ferrocenyl) bind HP2O73? anions in a mixed‐binding mode that features a combination of hydrogen‐bonding and anion–π interactions and results in strong binding. On the other hand, receptor 102+?2 BF4 ? (4‐CH3O?C6H4) only displays combined Csp2?H/anion–π interactions between the two arms of the receptors and the bound anion rather than triazolium (CH)+???anion hydrogen bonding. All receptors undergo a downfield shift of the triazolium protons, as well as the inner naphthalene protons, in the presence of H2PO4? anions. That suggests that only hydrogen‐bonding interactions exist between the binding site and the bound anion, and involve a combination of cationic (triazolium) and neutral (naphthalene) C?H donor interactions. Theoretical calculations relate the electronic structure of the substituent on the aromatic group with the interaction energies and provide a minimum‐energy conformation for all the complexes that explains their measured properties. 相似文献
214.
215.
Dr. Debasish Chakraborty Prof. Christian Danvad Damsgaard Dr. Hugo Silva Dr. Christian Conradsen Dr. Jakob Lind Olsen Prof. Hudson W. P. Carvalho Benjamin Mutz Dr. Thomas Bligaard Dr. Max J. Hoffmann Prof. Jan-Dierk Grunwaldt Prof. Felix Studt Prof. Ib Chorkendorff 《Angewandte Chemie (International ed. in English)》2017,56(30):8711-8715
A novel nanoparticulate catalyst of copper (Cu) and ruthenium (Ru) was designed for low-temperature ammonia oxidation at near-stoichiometric mixtures using a bottom-up approach. A synergistic effect of the two metals was found. An optimum CuRu catalyst presents a reaction rate threefold higher than that for Ru and forty-fold higher than that for Cu. X-ray absorption spectroscopy suggests that in the most active catalyst Cu forms one or two monolayer thick patches on Ru and the catalysts are less active once 3D Cu islands form. The good performance of the tuned Cu/Ru catalyst is attributed to changes in the electronic structure, and thus the altered adsorption properties of the surface Cu sites. 相似文献
216.
For a compact symplectic manifoldM of dimension 2n, Brylinski proved that the canonical homology groupH
k
can
(M) is isomorphic to the de Rham cohomology groupH
2n-k
(M), and the first spectral sequence {E
r
(M)} degenerates atE
1(M). In this paper, we show that these isomorphisms do not exist for an arbitrary Poisson manifold. More precisely, we exhibit
an example of a five-dimensional compact Poisson manifoldM
5 for whichH
1
can
(M
5) is not isomorphic toH
4(M
5), andE
1(M
5) is not isomorphic toE
2(M
5).
This work has been partially supported through grants DGICYT (Spain), Projects PB91-0142 and PB89-0571, PB94-0633-C02-02;
and through grants UPV, Project 127.310-EA 191/94, 127.310-EC248/96. 相似文献
217.
218.
Herrero M Vicente MJ Cifuentes A Ibáñez E 《Rapid communications in mass spectrometry : RCM》2007,21(11):1729-1738
Microalgae have been suggested as a potential source for new functional ingredients, making possible the development of new functional foods from natural origin. Among the natural ingredients, polyunsaturated fatty acids (PUFAs) have generally been identified as an interesting group of compounds with biological activity, mainly related to their anti-inflammatory properties. In this regard, the use of environmentally friendly extraction procedures (e.g. pressurized liquid extraction, PLE) to obtain such natural ingredients is also becoming necessary. In this work, an exhaustive characterization of the lipid fraction of a pressurized ethanolic extract of the microalga Spirulina platensis is carried out. To achieve this objective high-performance liquid chromatography (HPLC) coupled to quadrupole time-of-flight mass spectrometry (QTOF-MS) is employed. The use of the QTOF analyzer allows the selection and isolation of precursor ions as well as providing the high efficiency, sensitivity and mass accuracy required. By means of this powerful hyphenated technique, it was possible to identify several polar lipids in an extract of S. platensis (some of them, to our knowledge, described for the first time in this work), including four free fatty acids, four monogalactosyl monoacylglycerols, three phosphatidylglycerols and two sulfoquinovosyl diacylglycerols. 相似文献
219.
Bernal J Rodríguez-Meizoso I Elvira C Ibáñez E Cifuentes A 《Journal of chromatography. A》2008,1204(1):104-109
In this work, a new copolymer synthesized in our laboratory is used as physically adsorbed coating for capillary electrophoresis (CE). The copolymer is composed of ethylpyrrolidine methacrylate (EPyM) and methylmethacrylate (MMA). The capillary coating is easily obtained by simply flushing into the tubing an EPyM/MMA solution. It is demonstrated that the composition of the EPyM/MMA copolymer together with the selection of the background electrolyte (BGE) and pH allow tailoring the direction and magnitude of the electroosmotic flow (EOF) in CE. It is also shown that the EOF obtained for the EPyM/MMA-coated capillaries was reproducible in all cases independently on pH or polymer composition. Thus, RSD values lower than 1.9% (n=5) for the same capillary and day were obtained for the migration time, while the repeatability interdays (n=5) was observed to provide RSD values lower than 0.5%. The stability of the coating procedure was also tested between capillaries (n=3) obtaining RSD values lower than 0.6%. It is demonstrated with several examples that the use of EPyM/MMA coatings in CE can drastically reduce the analysis time and/or to improve the resolution of the separations. It is shown that EPyM/MMA-coated capillaries allow the separation of basic proteins by reducing their adsorption onto the capillary wall. Also, EPyM/MMA-coated capillaries provide a faster separation of samples containing simultaneously positive and negative analytes. Moreover, it is demonstrated that the use of EPyM/MMA-coated capillaries can incorporate an additional chromatographic-like interaction with nucleosides that highly improves the separation of this group of solutes. 相似文献
220.
Many pesticide transformation products (TPs) can reach environmental waters as a consequence of their normally having a higher polarity than their parent pesticides. This makes the development of analytical methodology for reliable identification and subsequent quantification at the sub-microgram per liter levels necessary, as required under current legislation. In this paper we report the photodegradation of several pesticides frequently detected in environmental waters from the Spanish Mediterranean region using the high-resolution and exact-mass capabilities of hybrid quadrupole time-of-flight mass spectrometry (QTOF MS) hyphenated to liquid chromatography (LC). Once the main photodegradation/hydrolysis products formed in aqueous media were identified, analytical methodology for their simultaneous quantification and reliable identification in real water samples was developed using on-line solid-phase extraction (SPE)-LC-tandem MS with a triple-quadrupole (QqQ) analyzer. The methodology was validated in both ground and surface water samples spiked at the limit of quantification (LOQ) and 10 x LOQ levels, i.e. 50 and 500 ng/l, obtaining satisfactory recoveries and precision for all compounds. Subsequent analysis of ground and surface water samples resulted in the detection of a number of TPs higher than parent pesticides. Additionally, several soil-interstitial water samples collected from the unsaturated zone were analyzed to explore the degradation/transformation of some pesticides in the field using experimental plots equipped with lisimeters. Several TPs were found in these samples, with most of them having also been detected in ground and surface water from the same area. This paper illustrates the extraordinary potential of LC-MS(/MS) with QTOF and QqQ analyzers for qualitative/structural and quantitative analysis, respectively, offering analytical chemists one of the most powerful tools available at present to investigate the presence of pesticide TPs in water. 相似文献