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排序方式: 共有213条查询结果,搜索用时 15 毫秒
1.
The enantiomers of 34 pharmaceutical weak-base analytes were separated by nonaqueous capillary electrophoresis in acidic methanol background electrolytes using the sodium salt of the new, single-isomer chiral resolving agent, octakis(2,3-O-dimethyl-6-O-sulfo)-gamma-cyclodextrin (ODMS). The effective mobilities, separation selectivities and peak resolution values of the weak-base analytes were determined as a function of the ODMS concentration in the 0-40 mM range and were found to follow the theoretical predictions of the charged resolving agent migration model (CHARM model) modified for ionic strength effects. Fast, efficient separations were achieved for both comparatively small and large enantiomers. 相似文献
2.
The extraction of Al(III) and Zn(II) from an aqueous solution with two water-in-oil microemulsions, one containing di(2-ethylhexyl)phosphoric acid (DEHPA), was investigated to aid the understanding of the role of the extractant and the metal specific characteristics in the mechanism of microemulsion extraction. The extraction of Al with the DEHPA microemulsion increased by a factor of about 10 with respect to that in the conventional DEHPA system, whereas the extraction of Zn was lower than that in the single DEHPA system. Extraction with the DEHPA-free microemulsion was very low, showing that metal ion solubilization was not important in the mechanism of microemulsion extraction. It is proposed that the effect of the mixed microemulsion on the metal distribution coefficient is the result of the balance between a decrease in the complexation reaction yield due to the interaction between butanol and DEHPA, and the adsorption of the metal complex at the macro- and microinterfaces. The former leads to a decrease in Zn(II) extraction and the latter to Al(III) extraction synergism. Copyright 2000 Academic Press. 相似文献
3.
4.
N Rosas P SharmaC Alvarez E GómezY Gutiérrez M MéndezR.A Toscano L.A Maldonado 《Tetrahedron letters》2003,44(43):8019-8022
The condensation of substituted α-keto alkynes with p-nitrobenzaldehyde in the presence of lithium diisopropylamide (LDA) affords highly substituted 5,6-dihydro-4H-oxocin-4-ones in good yields. Surprisingly, no six-membered carbocycles were formed in this 8-endo-dig cyclization to the oxocinone system. 相似文献
5.
LaChance-Galang KJ Maldonado I Gallagher ML Jian W Prock A Chacklos J Galang RD Clarke MJ 《Inorganic chemistry》2001,40(3):485-492
Pentaammineruthenium moves on ambidentate nitrogen heterocycles by both rotation and linkage isomerization, which may affect the biological activity of potential ruthenium metallopharmaceuticals. The rapid rotation rates of [(NH3)5RuIII] coordinated to the exocyclic nitrogens of isocytosine (ICyt) and 6-methylisocytosine (6MeICyt) have been determined by 1H NMR. Since these rotamers can be stabilized by hydrogen bonding between the coordinated ammines and the N1 and N3 endocyclic nitrogens, rotamerization is under pH control. Spectrophotometrically (UV-vis) measured pKa values for the two endocyclic sites for the ICyt complex are 2.78 and 9.98, and for 6MeICyt are 3.06 and 10.21, which are probably weighted averages for ionization from N3 and N1, respectively. Activation parameters for the rotamerizations were determined by variable-temperature NMR at pKa1 < pH < pKa2 for the complexes with (ICyt-kappa N2)-, (6MeICyt kappa N2)-, and 2AmPym kappa N2. For [(6MeICyt kappa N2)(-)-(NH3)5RuIII]2+, delta H* = 1.6 kcal/mol, delta S* = -37 cal/mol K, and Ea = 2.2 kcal/mol. Due to strong RuIII-N pi-bonding, the activation enthalpies are approximately 10 kcal lower than the expected values for the free ligands. Rotameric structure is correlated with pKa values, pH-dependent reduction potentials, and 1H NMR parameters. Linkage isomers of [(2AmPym)(NH3)5Ru]n+ are reported in which RuII is coordinated to the endocyclic nitrogen (N1) and RuIII to the exocyclic nitrogen (N2). The rate constant for the kappa N2-->kappa N1 isomerization as part of an ECE mechanism is 3.9 s-1 at pH 3. The pH dependence of the acid-catalyzed hydrolysis of [(2AmPym kappa N1)(NH3)5Ru]2+ is determined. 相似文献
6.
The pyrazole alkaloid withasomnine 1, has been synthesized by construction of the 1,2-diazabicyclo [3.3.0] octa-2,4-diene system in a single step. 相似文献
7.
Novel organometallic chalcones functionalized with a crown ether fragment as optical ion chemosensors
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Fernando Godoy Tamara Maldonado Erick Flores Nicolás Agurto Rodrigo González Guillermo Ferraudi Graham Lappin 《应用有机金属化学》2018,32(3)
We previously reported the synthesis and characterization of new organometallic chalcones derived from ferrocene, cyrhetrene and cymantrene functionalized with a benzo‐15‐crown‐5 fragment. The ferrocene and cyrhetrene chalcones have been investigated as chemosensors for metal ions with optical response in acetonitrile. Several metal ions were selected considering the diameter of the cavity and the charge‐to‐radius ratio of the cation. The stoichiometry of the complexes was determined using Job's method. It was found that Na+ and Ca2+ complexes have a 1:1 stoichiometry while a 2:1 (metaloligand‐to‐cation) stoichiometry was determined for Ba2+ and Pb2+ complexes. The association constants were calculated according to the stoichiometry of the complex and the results showed that they are directly affected by the electron‐withdrawing nature of the organometallic fragment. Moreover, complexes of ferrocenyl chalcone have larger association constants than those of the cyrhetrenyl analogue. This experimental observation is consistent with the electronic properties of the ferrocenyl fragment. 相似文献
8.
José Gustavo Ávila‐Zárraga Adrián Vázquez‐Sánchez Luis Ángel Maldonado 《Helvetica chimica acta》2013,96(7):1331-1338
The results of an aromatic Cope rearrangement of a trans‐1‐aryl‐2‐ethenylcyclobutanecarbonitrile are reported (Scheme). The use of this rearrangement for the construction of the fused benzocyclooctene ring system and a preliminary study of the electronic requirements to favor such a transformation are also described. 相似文献
9.
The reaction of dimethyl 1,3-acetonedicarboxylate anion 1 with a number of alkyl alkynoates gives unsymmetrical (from alkynoates 2a-g) or symmetrical (from alkynoates 2h-i) resorcinols, in a one pot synthesis. 相似文献
10.
Homogeneous and unimolecular gas‐phase thermal decomposition kinetics of methyl benzoylformate: experimental and theoretical study
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Yeljair Monascal Alexis Maldonado José R. Mora Tania Córdova Gabriel Chuchani 《Journal of Physical Organic Chemistry》2015,28(1):40-46
The kinetics of the gas‐phase thermal decomposition of the α‐ketoester methyl benzoylformate was carried out in a static system with reaction vessel deactivated with allyl bromide, and in the presence of the free radical inhibitor propene. The rate coefficients were determined over the temperature range of 440–481 °C and pressures from 32 to 80 Torr. The reaction was found to be homogenous, unimolecular and obey a first‐order rate law. The products are methyl benzoate and CO. The temperature dependence of the rate coefficient gives the following Arrhenius parameters: log10 k (s?1) = 13.56 ± 0.31 and Ea (kJ mol?1) = 232.6 ± 4.4. Theoretical calculations of the kinetic and thermodynamic parameters are in good agreement with the experimental values using PBE1PBE/6‐311++g(d,p). A theoretical Arrhenius plot was constructed at this level of theory, and the good agreement with the experimental Arrhenius plot suggests that this model of transition state may describe reasonably the elimination process. These results suggest a concerted non‐synchronous semi‐polar three‐membered cyclic transition state type of mechanism. The most advanced coordinate is the bond breaking Cδ+‐‐‐δ‐OCH3 with an evolution of 66.7%, implying this as the limiting factor of the elimination process. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献