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41.
María Yolanda Ríos M. Ángeles Ramírez‐Cisneros Ismael León‐Rivera Samuel Estrada‐Soto Gabriel Navarrete‐Vázquez A. Berenice Aguilar‐Guadarrama 《Magnetic resonance in chemistry : MRC》2012,50(4):329-331
Complete 1H and 13C NMR chemical shift assignments for 3,4‐seco‐lup‐20(29)‐en‐3‐oic acid ( 1 ) have been established by means of two‐dimensional COSY, HSQC, HMBC and NOESY spectroscopic experiments as well as by analysis of MS data. Compound 1 was isolated from Decatropis bicolor (Zucc.) Radlk. (Rutaceae) in addition to six coumarins and one alkaloid of known structure. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
42.
M. Elena Mart��n M. Luz S��nchez Jos�� C. Corchado Aurora Mu?oz-Losa Ignacio Fdez. Galv��n Francisco J. Olivares del Valle Manuel A. Aguilar 《Theoretical chemistry accounts》2011,128(4-6):783-793
The possible influence of the solvent Stark effect (SSE) on the solvatochromic shift in electron transitions has been analyzed by using the ASEP/MD (averaged solvent electrostatic potential from molecular dynamics) method. With this purpose, four molecules, two polar (acrolein and formaldehyde) and two non-polar (p-difluorobenzene and trans-difluoroethene) have been studied in solvents of diverse polarity. Independently of the nature of the system we found that the contribution of SSE on the average value of the solvent shift or on the multipole moment values is negligible. In the case of centro-symmetric molecules, our results permit to discard the SSE as cause of the solvent shift found, which must be assigned to the electrostatic interaction of the solute quadrupole and higher multipoles with the solvent. As the SSE values provide also a measure of the errors introduced by the mean field approximation (MFA), these results indicate that MFA permits a very accurate determination of the solvent shift at the same time that it reduces drastically the computational cost. Finally, a new procedure suited to the ASEP/MD method has been presented that permits to estimate the inhomogeneous broadening of spectral bands, complementing the information provided by mean field theories. This procedure does not need additional quantum calculations and its computational cost is minimal. 相似文献
43.
Stereoselective Csp3–Csp2 Bond‐Forming Reactions by Transition‐Metal‐Free Reductive Coupling of Cyclic Tosylhydrazones with Boronic Acids 下载免费PDF全文
Manuel Plaza Dr. M. Carmen Pérez‐Aguilar Dr. Carlos Valdés 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(18):6253-6257
The reactions between alkenylboronic acids and tosylhydrazones derived from substituted cyclohexanones lead to the construction of disubstituted cyclohexanes with total regio‐ and stereoselectivity. In these transition‐metal‐free processes, a Csp3?Csp2 and Csp3?H bond are formed on the same carbon atom. The stereoselective reaction is general for 2‐, 3‐, and 4‐substituted cyclohexanone tosylhydrazones, as well as for 2‐substituted cyclopentanones. However, no stereoselectivity is observed for acyclic derivatives. DFT computational modeling suggests that the stereoselectivity of the reaction is determined by the approach of the boronic acid to the diazocyclohexane on its most stable chair conformation through an equatorial trajectory. 相似文献
44.
M. Aguilar 《Solid State Communications》1984,50(9):837-840
A study by means of the Electron-Paramagnetic-Resonance (EPR) technique of the valence states of the cobalt ion in oxidized and reduced BaTiO3 is presented. As a result, the identification of high-spin Co+ in reduced crystals was possible. The Co2+ centre is also discussed. 相似文献
45.
The fluorescence of Mn2+ ion as impurity in CaCO3 has been investigated. Emission bands from the 4D(Eg), 4D(T2g) and 4G(T1g) levels have been observed. The analysis of excitation and emission spectra has allowed to obtain the values of field strength (Dq) for the excited energy levels of Mn2+ in CaCO3 lattice. The temperature dependence of excitation and emission spectra yield an activation energy for thermal quenching of luminescence very close to theoretical calculation. The behaviour of luminescence lifetime with temperature has also been obtained. 相似文献
46.
Wiedeking M Tabor SL Pavan J Volya A Aguilar AL Calderin IJ Campbell DB Cluff WT Diffenderfer E Fridmann J Hoffman CR Kemper KW Lee S Riley MA Roeder BT Teal C Tripathi V Wiedenhöver I 《Physical review letters》2005,94(13):132501
Excited states in 20O were populated in the reaction 10Be(14C,alpha) at Florida State University (FSU). Charged particles were detected with a particle telescope consisting of 4 annularly segmented Si surface barrier detectors and gamma radiation was detected with the FSU gamma detector array. Five new states were observed below 6 MeV from the alpha-gamma and alpha-gamma-gamma coincidence data. Shell model calculations suggest that most of the newly observed states are core-excited 1p-1h excitations across the N=Z=8 shell gap. Comparisons between experimental data and calculations for the neutron-rich O and F isotopes imply a steady reduction of the p-sd shell gap as neutrons are added. 相似文献
47.
Pichini S Pellegrini M Pacifici R Marchei E Murillo J Puig C Vall O García-Algar O 《Rapid communications in mass spectrometry : RCM》2003,17(17):1958-1964
A high-performance liquid chromatography (HPLC) method with mass spectrometric detection is described for determination of arecoline in newborn meconium, urine and cord serum, using pilocarpine as internal standard. The analytes were extracted from neonatal biological matrices with chloroform/isopropanol (95:5, v/v) at alkaline pH. Extracts were analyzed by HPLC coupled to an electrospray (ESI) interface and a quadrupole mass spectrometer. Chromatography was performed on a C(8) reversed-phase column using 10 mM ammonium acetate (pH 4.3)/acetonitrile (90:10, v/v) as mobile phase. The mass spectrometer was operated in selected ion monitoring mode. The method was validated over the concentration range 0.005-1.00 micro g/g meconium, 0.004-1.00 micro g/mL cord serum and 0.001-1.00 micro /mL urine. Mean recoveries ranged between 86.5 and 90.7% for arecoline in the different biological matrices, with precision always better than 10%. The quantification limits of arecoline were 0.005 micro g/g meconium, 0.004 micro g/mL cord serum, and 0.001 micro g/mL urine. The method was applied to the analysis of neonatal biological matrices to assess eventual fetal exposition to arecoline. Two newborns from Asian mothers who declared areca nut consumption presented arecoline in meconium with concentrations in the range 0.006-0.008 micro g/g; also the urine from one neonate tested positive for the drug. 相似文献
48.
Barluenga J Fernández-Rodríguez MA Aguilar E Fernández-Marí F Salinas A Olano B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(16):3533-3544
A new procedure for the synthesis of 1,3,4-trisubstituted and 1,4-disubstituted pyrrolidin-2-one derivatives in an enantioselective fashion is reported. The 1,3-dipolar cycloaddition of (+/-)-menthol and (-)-8-phenylmenthol derived Fischer alkoxy alkenyl carbene complexes with in situ generated functionalized azomethine ylides gives the corresponding cycloadducts as chelated tetracarbonyl Fischer carbene complexes. Only one regioisomer is detected in all cases, and the diastereoselectivity of the reaction is very high when (-)-8-phenylmenthol derived carbenes are employed. Oxidation and further transformation of the cycloadducts provide an easy access to pyrrolidin-2-ones. The anti-inflammatory and antidepressant drug (+)-Rolipram is readily prepared in four steps in a 20% overall yield by taking advantage of this newly developed methodology. 相似文献
49.
A. C. Aguilar J. Papavassiliou 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):742-745
The effective gluon propagator constructed with the pinch technique is governed by a Schwinger-Dyson equation with special
structure and gauge properties, that can be deduced from the correspondence with the background field method. Most importantly
the non-perturbative gluon self-energy is transverse order-by-order in the dressed loop expansion, and separately for gluonic
and ghost contributions, a property which allows for a meanigfull truncation. A linearized version of the truncated Schwinger-Dyson
equation is derived, using a vertex that satisfies the required Ward identity and contains massless poles. The resulting integral
equation, subject to a properly regularized constraint, is solved numerically, and the main features of the solutions are
briefly discussed. 相似文献
50.
T. Martínez F. Aguilar J. Lartigue M. Navarrete L. A. Cuapio C. López O. Y. Morales 《Journal of Radioanalytical and Nuclear Chemistry》2008,278(2):365-370
Due to large consumption of tobacco in Mexico and in order to complement previous work performed by total reflection X-ray
fluorescence, the present study has determined 15 elements by INAA in 9 cigarettes brands being marketed in Mexico. As a part
of a Quality Control Program, NIST standard reference materials (SRM) and an IAEA reference material were analyzed to confirm
the accuracy and reproducibility. Average of As and Cd were 0.56 and 1.15 μg·g−1, respectively, in the range of those of foreign brands. 相似文献