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131.
Amundson LM Owen BC Gallardo VA Habicht SC Fu M Shea RC Mossman AB Kenttämaa HI 《Journal of the American Society for Mass Spectrometry》2011,22(4):670-682
Positive-mode atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS
n
) was tested for the differentiation of regioisomeric aromatic ketocarboxylic acids. Each analyte forms exclusively an abundant
protonated molecule upon ionization via positive-mode APCI in a commercial linear quadrupole ion trap (LQIT) mass spectrometer.
Energy-resolved collision-activated dissociation (CAD) experiments carried out on the protonated analytes revealed fragmentation
patterns that varied based on the location of the functional groups. Unambiguous differentiation between the regioisomers
was achieved in each case by observing different fragmentation patterns, different relative abundances of ion-molecule reaction
products, or different relative abundances of fragment ions formed at different collision energies. The mechanisms of some
of the reactions were examined by H/D exchange reactions and molecular orbital calculations. 相似文献
132.
Favaro DC Ducati LC dos Santos FP Contreras RH Tormena CF 《The journal of physical chemistry. A》2011,115(50):14539-14545
Theoretical and experimental studies on (3)J(C2H6eq) NMR spin-spin coupling constants in both the 2-X-4-t-butyl-cyclohexanone (X = H, CH(3), F, Cl, and Br) and in their alcohol derivatives series are reported. Results thus found are rationalized in terms of the transmission of the Fermi contact contribution to such couplings. To this end, dependencies of (3)J(C2H6eq) couplings versus the C(2)-C(1)-C(6) angle are compared in both series for equatorial and axial X orientations. The main trend is described in terms of the rear lobes interaction. Besides, for X = halogen atom in equatorial orientation a rather strong interaction between oxygen and halogen lone pairs is observed, and its influence on (3)J(C2H6eq) couplings is discussed and rationalized in terms of different Fermi contact transmission pathways. 相似文献
133.
Benito Chen-Charpentier Lucas Jódar Aleksey S. Telyakovskiy 《Applied mathematics and computation》2011,218(5):1650-1657
This paper presents a method for constructing polynomial approximations of the solutions of nonlinear initial value systems of differential equations. Given an a priori chosen accuracy, the degree of the vector polynomial can be adapted so that the approximate solution has the required precision. The method is based on the AI-method of Dzyadyk developed for the scalar case, and the computational cost is shown to be competitive with other methods. 相似文献
134.
Lucas R Gómez-Pinto I Aviñó A Reina JJ Eritja R González C Morales JC 《Journal of the American Chemical Society》2011,133(6):1909-1916
Carbohydrate-nucleic acid contacts are known to be a fundamental part of some drug-DNA recognition processes. Most of these interactions occur through the minor groove of DNA, such as in the calicheamicin or anthracycline families, or through both minor and major groove binders such as in the pluramycins. Here, we demonstrate that carbohydrate-DNA interactions are also possible through sugar capping of a DNA double helix. Highly polar mono- and disaccharides are capable of CH/π stacking onto the terminal DNA base pair of a duplex as shown by NMR spectroscopy. The energetics of the carbohydrate-DNA interactions vary depending on the stereochemistry, polarity, and contact surface of the sugar involved and also on the terminal base pair. These results reveal carbohydrate-DNA base stacking as a potential recognition motif to be used in drug design, supramolecular chemistry, or biobased nanomaterials. 相似文献
135.
Lucas D Minami T Iannuzzi G Cao L Wittenberg JB Anzenbacher P Isaacs L 《Journal of the American Chemical Society》2011,133(44):17966-17976
We report that the p-xylylenediammonium ion (11) acts as a template in the cucurbit[n]uril forming reaction that biases the reaction toward the production of methylene bridged glycoluril hexamer (6C) and bis-nor-seco-CB[10]. Hexamer 6C is readily available on the gram scale by a one step synthetic procedure that avoids chromatography. Hexamer 6C undergoes macrocylization with (substituted) phthalaldehydes 12, 14, 15, and 18-in 9 M H(2)SO(4) or concd HCl at room temperature to deliver monofunctionalized CB[6] derivatives 13, 16, 17, and 19-that are poised for further functionalization reactions. The kinetics of the macrocyclization reaction between hexamer and formaldehyde or phthalaldehyde depends on the presence and identity of ammonium ions as templates. p-Xylylenediammonium ion (11) which barely fits inside CB[6] sized cavities acts as a negative template which slows down transformation of 6C and paraformaldehyde into CB[6]. In contrast, 11 and hexanediammonium ion (20) act as a positive template that promotes the macrocyclization reaction between 6C and 12 to deliver (±)-21 as a key intermediate along the mechanistic pathway to CB[6] derivatives. Naphthalene-CB[6] derivative 19 which contains both fluorophore and ureidyl C═O metal-ion (e.g., Eu(3+)) binding sites forms the basis for a fluorescence turn-on assay for suitable ammonium ions (e.g., hexanediammonium ion and histamine). 相似文献
136.
137.
Lalueza P Monzón M Arruebo M Santamaria J 《Chemical communications (Cambridge, England)》2011,47(2):680-682
We show that Ag-containing zeolites are highly effective against Staphylococcus aureus (SA) bacteria even at low Ag loadings and in the presence of high (10(9) CFU per mL) bacterial concentrations. At short contact times the bactericidal efficiency correlates strongly with Ag(+) release. At longer times data dispersion is higher, probably as a consequence of bacterial metabolism. 相似文献
138.
Devillers CH Dime AK Cattey H Lucas D 《Chemical communications (Cambridge, England)》2011,47(6):1893-1895
Regioselective meso-functionalization of the totally unsubstituted magnesium(II) porphine was performed by controlled potential electrolysis with pyridine and triphenylphosphine as nucleophiles leading to the original pyridinium and phosphonium substituted derivatives, respectively. The crystallographic structure of the latter is described as the only meso-phosphonium porphyrin reported to date. 相似文献
139.
140.