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41.
Complexes of Dioxocyanogen (OCN)2 with TiCl4 and ZrCl4 A solution of (OCN)2 was obtained by reaction of AgOCN with Br2 in H2CCl2 at ?70°C. From this the complexes TiCl4(NCO)2 and ZrCl4(NCO)2 were obtained by addition of equimolar amounts of TiCl4 and ZrCl4, respectively. According to the i.r. and Raman spectra, the (NCO)2 ligand is bonded via its N atoms to the metal. 相似文献
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Sodiun borohydride reacts with oxazolidinium methiodides derived from ephedrine and pseudoephedrine, in ethereal solvents, cleaving regioselectively the C-N bond of the ring and leading, in good yields, to chiral amine-borane adducts of know absolute configuration. The 1HNMR data allow to predict the most stable conformation. 相似文献
44.
Unexpected reactivity of pyridinium salts toward alkynyl Fischer complexes to produce oxo‐heterocycles
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María Inés Flores‐Conde Fabiola N. de la Cruz Julio López J. Óscar C. Jiménez‐Halla Eduardo Peña‐Cabrera Marcos Flores‐Álamo Francisco Delgado Miguel A. Vázquez 《应用有机金属化学》2018,32(3)
The unprecedented reaction of ketone‐containing aromatic pyridinium salts 3a ‐ e and alkynyl Fischer complexes 1a ‐ f proceeds via a mild domino process to provide 4,6‐disubstituted pyran‐2‐ones 5a ‐ k and 2,3,5‐trisubstituted furans 6a ‐ h (45‐97%). According of the results of isotopic labeling experiments, a mechanism involving an initial Michael addition appears to be the key step, obtaining a mesomeric structure responsible for the formation of both products. 相似文献
45.
A QM/MM study on the reaction pathway leading to 2‐Aceto‐2‐hydroxybutyrate in the catalytic cycle of AHAS
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Leslie Sánchez Gonzalo A. Jaña Eduardo J. Delgado 《Journal of computational chemistry》2014,35(6):488-494
The reaction between the intermediate 2‐hydroxyethyl‐thiamin diphosphate (HEThDP?) and 2‐ketobutyrate, in the third step of the catalytic cycle of acetodydroxy acid synthase, is addressed from a theoretical point of view by means of hybrid quantum/molecular mechanical calculations. The QM region includes one molecule of 2‐ketobutyrate, the HEThDP? intermediate, and the residues Arg 380 y Glu 139; whereas the MM region includes the rest of the protein. The study includes potential energy surface scans to identify and characterize critical points on it, transition state search and activation barrier calculations. The results show that the reaction occurs via a two‐step mechanism corresponding to the carboligation and proton transfer in the first stage; and the product release in the second step. © 2014 Wiley Periodicals, Inc. 相似文献
46.
Paula A. Delgado Piotr Matloka Fabio Zuluaga Kenneth B. Wagener 《Journal of polymer science. Part A, Polymer chemistry》2012,50(3):431-440
Acyclic diene metathesis (ADMET) polymerization has been used in the synthesis of telechelic materials using alkoxy‐functionalized carbosiloxane or oligo(oxyethylene)‐based polymers, varying from internal to terminal cured materials or the combination of them. Previous investigations demonstrated that introduction of chain‐end crosslinking improves the stress–strain behavior of such materials. A series of saturated and unsaturated carbosiloxane and oligo(oxyethylene)‐based polymers were synthesized by ADMET polymerization using silacyclobutane as chain‐end, thermally induced crosslinker. The carbosiloxane derivatives presented pure amorphous behavior, whereas the oligo(oxyethylene) polymers were semicrystalline. The thermal curing process was monitored by differential scanning calorimetry via the exotherm between 160 and 210 °C. Mechanical properties on thermoset polymers were measured, where cured polymers showed moduli from 0.6 to 9.3 MPa, tensile strengths from 0.3 to 1.0 MPa, and elongations from 12 to 76%. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
47.
G. E. Delgado J. A. Rodríguez A. J. Mora J. Bruno-Colmenárez J. Uzcátegui C. Chacón 《Molecular Crystals and Liquid Crystals》2016,629(1):96-104
The crystal structure of heterocyclic compound 5-methyl-5-phenyl hydantoin has been determined from X-ray single crystal structural characterization. This material crystallizes in the orthorhombic system and noncentrosymmetric space group P21 (N°4). The crystal packing is governed by N–H···O hydrogen bond-type intermolecular interactions, forming chains and edge-fused 12-membered rings with graph-set C(4) C(5) C22(8) R33(12) in a similar hydrogen-bonding pattern of another chiral 5,5′-substituted hydantoins. 相似文献
48.
Jorge‐Aarn Rangel‐Mndez Manlio‐Joaquin Graniel‐Sabido Juan‐Francisco Snchez‐Cruz Rosa Moo‐Puc 《Biomedical chromatography : BMC》2019,33(4)
To date, several methods for the quantification of tamoxifen and its metabolites have been developed, most of which employ liquid chromatography tandem–mass spectrometry (LC–MS/MS). These methods are highly sensitive and reproducible, but are also time‐consuming and require expensive equipment; one of their main disadvantages is matrix ionization effects. A more viable option, particularly in developing countries, is high‐performance liquid chromatography coupled with UV or fluorescence detection. We developed and validated a method for simultaneous quantification of tamoxifen, endoxifen and 4‐hydroxytamoxifen based on high‐performance liquid chromatography with fluorescence detection in a reverse‐phase column. The method is rapid (16 min plus 5 min of column re‐equilibrium), accurate (80–100%) and precise (0.23–6.00%), and does not require any additional irradiation process. Sample pretreatment consists of protein precipitation with acetonitrile under alkaline conditions, employing only 200 μL plasma. The validated method's wide range allowed quantification of steady‐state levels in patients under standard tamoxifen treatment (20 mg/day). This assay is ready for application in clinical studies and routine quantification of tamoxifen, endoxifen and 4‐hydroxytamoxifen in healthcare institutions. 相似文献
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