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71.
Palumbo Piccionello A Guarcello A Buscemi S Vivona N Pace A 《The Journal of organic chemistry》2010,75(24):8724-8727
The reaction of various 1,2,4-oxadiazoles with an excess of hydrazine in DMF has been investigated. 3-Amino-1,2,4-triazoles are produced through a reductive ANRORC pathway consisting of the addition of hydrazine to the 1,2,4-oxadiazole followed by ring-opening, ring-closure, and final reduction of the 3-hydroxylamino-1,2,4-triazole intermediate. The general applicability of 1,2,4-oxadiazoles ANRORC reactivity is demonstrated also in the absence of C(5)-linked electron-withdrawing groups. 相似文献
72.
Lucia Ambrosio M. Carla Aragoni Dr. Massimiliano Arca Dr. Francesco A. Devillanova Prof. Michael B. Hursthouse Prof. Dr. Susanne L. Huth Dr. Francesco Isaia Prof. Vito Lippolis Prof. Dr. Annalisa Mancini Dr. Anna Pintus Dr. 《化学:亚洲杂志》2010,5(6):1395-1406
The tetrabutylammonium (TBA+) salts of square‐planar monoanionic gold complexes of the unsymmetrically substituted Ar,H‐edt2? 1,2‐dithiolene ligands (Ar,H‐edt2?=arylethylene‐1,2‐dithiolato; Ar=phenyl ( 1 ?), 2‐naphthyl ( 2 ?), and 1‐pyrenyl ( 3 ?)) were synthesized and characterized by spectroscopic and electrochemical methods and the corresponding neutral species ( 1 , 2 , and 3 , respectively) were obtained in CH2Cl2 solution at room temperature by diiodine oxidation. The single‐crystal X‐ray diffraction structural data collected for (TBA+)( 2 ?), supported by DFT theoretical calculations, are consistent with the ene‐1,2‐dithiolate form of the ligand and the AuIII oxidation state. All complexes feature intense near‐IR absorptions (at about 1.5 μm) in their neutral states and Vis‐emitting properties in the 400–550 nm range, the energy of which is controlled by the charge of the complex in the case of the 3 ?/ 3 couple. The spectroscopic and electrochemical features of 1 x? and 2 x? (x=0, 1), both in their cis and trans conformations, were investigated by means of DFT and time‐dependent (TD) DFT calculations. 相似文献
73.
Romani A Vignolini P Tanini A Pampaloni B Heimler D 《Natural product communications》2010,5(11):1775-1780
Isoflavones are polyphenolic compounds found mainly in legumes the benefits of which have been widely studied and attributed in particular to their phytoestrogenic activity. The aim of this study was to evaluate the quali-quantitative composition of food supplements based on soy isoflavones (Glycine max L.) and red clover (Trifolium pratense). Six commercial food supplements (five soy-based and one red clover-based) were analyzed by HPLC/DAD/MS. Genistein, daidzein, glycitein, biochanin A and formononetin derivatives (glycosides and acylglycosides) were identified in the analyzed samples. Also the antiradical activities (towards the DPPH* radical) and Fe2+ chelating abilities were compared. 相似文献
74.
The theory of non-uniform flexure and torsion of Saint-Venant's beam with arbitrary multiply connected cross section is revisited in a coordinate-free form to provide a computationally convenient context. Numerical implementations, by Matlab, are performed to evaluate the maximum elastic shear stresses in beams with rectangular cross sections for different Poisson's ratios. The deviations between the maximum and mean stresses are then diagrammed to adjust the results provided by Jourawski's method. 相似文献
75.
Valerio B. Di Marco Luca Raveane Annalisa Dean Pietro Traldi 《Rapid communications in mass spectrometry : RCM》2010,24(7):868-874
Electrospray ionization mass spectrometry (ESI‐MS) is very often employed to study metal/ligand equilibria in aqueous solution. However, the ionization process can introduce perturbations which affect the speciation results in an unpredictable way. It is necessary to identify these perturbations in order to correctly interpret the ESI‐MS speciation results. Aluminium(III)/1,6‐dimethyl‐4‐hydroxy‐3‐pyridinecarboxylate (DQ716) aqueous solutions at various pH were analysed by ESI‐MS, and speciation results were compared with those obtained by equilibrium techniques. Differences observed were both qualitative and quantitative. The ESI‐MS spectral changes due to different settings of the following instrumental parameters were analyzed: the solution flow rate (FS), the nebulizer gas flow rate (FG), the potential applied at the entrance capillary (EC), and the temperature of the drying gas (TG). The effects produced by FS and EC on the spectra strongly suggest the key role of surface activity in determining the relative fraction of the ions reaching the detector. The experimental effects of FS and TG were interpreted considering the presence of at least two reactions in the gas phase and a dimerization occurring in the droplets. These perturbations cannot be generalized because they appear to be chemical system‐related and instrument‐dependent. Therefore, the identification of perturbations is a required task for any metal‐ligand equilibrium study performed by ESI‐MS. Our results indicate that perturbations can be identified by evaluating the effects produced in the spectra by a change of instrumental parameters. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
76.
Differential equations are derived for a continous limit of iterated Schwarzian reflection of analytic curves, and solutions are interpreted as geodesics in an infinite-dimensional symmetric space geometry.
Mathematics Subject Classification (1991):53C35, 53A30, 30D05. 相似文献
77.
Carla Carfagna Giuseppe Gatti Luca Mosca Paola Paoli Annalisa Guerri 《Helvetica chimica acta》2006,89(8):1660-1671
The migratory insertions of cis or trans olefins CH(X)?CH(Me) (X = Ph, Br, or Et) into the metal–acyl bond of the complex [Pd(Me)(CO)(iPr2dab)]+ [B{3,5‐(CF3)2C6H3}4]? ( 1 ) (iPr2dab = 1,4‐diisopropyl‐1,4‐diazabuta‐1,3‐diene = N,N′‐(ethane‐1,2‐diylidene)bis[1‐methylethanamine]) are described (Scheme 1). The resulting five‐membered palladacycles were characterized by NMR spectroscopy and X‐ray analysis. Experimental data reveal some important aspects concerning the regio‐ and stereochemistry of the insertion process. In particular, the presence of a Ph or Br substituent at the alkene leads to the formation of highly regiospecific products. Moreover, in all cases, the geometry of the substituents in the formed palladacycle was the same as in the starting olefin, as a consequence of a cis addition of the Pd–acyl fragment to the C?C bond. Reaction with CO and MeOH of the five‐membered complex derived from trans‐β‐methylstyrene (= [(1E)‐prop‐1‐enyl]benzene) insertion, yielded the 2,3‐substituted γ‐keto ester 9 with an (2RS,3SR)‐configuration (Scheme 3). 相似文献
78.
Stereocontrol in alkyne cyclocarbonylation reactions promoted by a bioxazoline palladium(II) complex
Carfagna C Gatti G Mosca L Paoli P Guerri A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(11):3268-3278
Insertion of 1,2-disubstituted alkynes into [Pd(CH3)(CO)(BIOX)]+[B{3,5-(CF3)2C6H3}4]- (1), where BIOX=(4S,4'S)-(-)-4,4',5,5'-tetrahydro-4,4'-bis(1-methylethyl)-2,2'-bioxazole, leads to the formation of five-membered palladacycles, which, by reaction with carbon monoxide, produce a mixture of two diastereomeric forms of a palladium complex containing an eta3-allylic gamma-lactone ligand. On leaving the mixture in solution, one isomer was converted into the other, reaching a diastereomeric excess of up to 94 %. The steric and electronic factors responsible for the epimerization process were investigated by theoretical methods. Cleavage of the eta3-allyl--palladium bond by nucleophiles allowed highly substituted chiral butenolides to be synthesized in good enantiomeric excess. 相似文献
79.
Solfrizzo M De Girolamo A Vitti C Visconti A van den Bulk R 《Journal of AOAC International》2004,87(1):101-106
A liquid chromatographic (LC) method was developed for the determination of Alternaria radicina and A. alternata toxins in carrots. Toxins were extracted from carrot with an acidified mixture of water-methanol-acetonitrile. The filtered extract was divided in 2 parts that were purified by solid-phase extraction on a C18 column for the analysis of radicinin (RAD), altertoxin-I (ATX-I), alternariol (AOH), and alternariol methyl ether (AME), and on a polymeric Oasis HLB column for tenuazonic acid (TeA). Toxins were quantified by reversed-phase LC with UV diode array detection by using 2 consecutive isocratic mixtures of acetonitrile-sodium dihydrogen phosphate solution. Mean recoveries of TeA, ATX-I, AME, RAD, and AOH from carrots spiked at levels between 0.5 and 3.0 microg/g were 69, 71, 90, 36, and 78%, with mean within-laboratory repeatability of 14, 5, 4, 6, and 18%, respectively. The mean between-laboratory reproducibilities for the determination of TeA, ATX-I, AME, and RAD in spiked samples were 25, 22, 6, and 12%, respectively. Limits of detection (signal-to-noise ratio of 3) for RAD, TeA, ATX-I, AME, and AOH were 0.006, 0.02, 0.02, 0.01, and 0.005 microg/g, respectively. RAD was detected (0.16-13.9 microg/g) in 3 out of 266 carrot samples produced under organic conditions in 3 European locations, whereas A. alternata mycotoxins were not found in any tested samples. 相似文献
80.