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31.
Jesús Valdés-Martínez Ruben A. Toscano Roberto Salcedo Raymundo Cea-Olivares Adrian Meléndez 《Monatshefte für Chemie / Chemical Monthly》1990,121(8-9):641-647
Summary The crystal and molecular structure of salicylaldehyde semicarbazone was obtained by single crystal X-ray diffraction. The O atom of the semicarbazone fragment isanti to the N atom of the hydrazinic group. The distribution of bond lengths in the semicarbazone fragment indicates delocalization of the -electrons. The crystal structure is stabilized by intra- and intermolecular hydrogen bonds.
Semicarbazone und Thiosemicarbazone, 12. Mitt.: Die Kristallstruktur des Salicylaldehyd-Semicarbazons
Zusammenfassung Die Kristallstruktur und die molekulare Struktur des Salicylaldehyd-Semicarbazons wurde über Einkristall-Röntgenstreuung ermittelt. Das O-Atom des Semicarbazonteils stehtanti zum N-Atom der Hydrazin-Gruppierung. Die Bindungslängen in der Semicarbazoneinheit zeigen eine Delokalisierung der -Elektronen an. Die Geometrie der Verbindung wird durch stabilisierende intra- und intermolekulare Wasserstoffbrückenbindungen bestimmt.相似文献
32.
Alberto Avenoza Jesús H Busto Carlos Cativiela Francisco Corzana Jesús M Peregrina María M Zurbano 《The Journal of organic chemistry》2002,67(2):598-601
A short and efficient asymmetric synthesis of the (6R,7S)-7-tert-butoxycarbonylamino-2-ketocarbacepham is described. The key step involves the hetero Diels-Alder reaction of the benzylimine derived from the enantiomer of Garner's aldehyde with Danishefsky's diene. 相似文献
33.
I. Kúdelka P.K. Misro J. Pospíšil H. Korbanka T. Riedel G. Pfahler 《Polymer Degradation and Stability》1985,12(4):303-313
The hydroperoxide decomposing efficiencies of dioctadecylsulfide (I), dioctadecyldisulfide (IV) and dioctadecyl 3,3-thio-dipropionate (VII) have been compared at 75°C and 85°C. The formation of oxidation products from (I) and (IV) has been checked. Experimental evidence is given of the important rôle of the activation of the molecule of (IV) by the presence of two sulfidic sulfur atoms compared with the activation of the sulfur atom in (VII) by the alkoxycarbonyl group in the beta position. The explanation of the high efficiency of disulfide has been based on the formation of thiosulfinate—the key intermediate for the generation of peroxidolytic species—in the first reaction step. 相似文献
34.
A simple technique is described for the routine simultaneous capillary electrophoretic determination of 6 cations in wine. Separation was achieved on a fused silica capillary column with a UV-Cat-1, alpha-hydroxysobutyric acid and 18-crown-6-ether buffer at pH 4.5 and indirect UV detection at 214 nm. The content of magnesium, sodium, potassium, calcium, manganese, and lithium was determined. The method is quantitative, with recoveries in the 92-102% range, and linear over more than one order of magnitude. The precision is better than 2.5-3.4%. The method is sensible, with detection limits between 0.01 and 0.06 mg/L. Twenty-five red wines with a Certified Brand of Origin from Galicia (north-western Spain) were analyzed by the proposed method. Various wines showed very similar electrophoretic profiles, but significant quantitative differences were observed. 相似文献
35.
Determination of fluquinconazole, pyrimethanil, and clofentezine residues in fruits by liquid chromatography with ultraviolet detection 总被引:1,自引:0,他引:1
A simple method was developed for the determination of fluquinconazole, pyrimethanil, and clofentezine in whole fruit; peel; and pulp of mango, apple, and papaya. These compounds were extracted from fruit samples with a mixture of ethyl acetate-n-hexane (1 + 1, v/v). An aliquot (2 mL) of the extract was evaporated to near dryness under a stream of nitrogen, and the residue was dissolved with 2 mL methanol. The analysis was performed by means of liquid chromatography with ultraviolet detection at 254 nm using a gradient solvent system. The method was validated with fortified fruit samples at concentration levels of 0.05, 0.10, 0.20, and 0.50 mg/kg. Average recoveries (4-8 replicates) ranged from 80 to 95% with relative standard deviations between 3.5 and 12.7%. Detection limits ranged from 0.03 to 0.05 mg/kg for fruit pulp and 0.03 mg/kg for whole fruit. The quantitation limits ranged from 0.05 to 0.10 mg/kg for fruit pulp and 0.05 mg/kg for whole fruit. The analytical method was applied to fruit samples obtained from local markets. 相似文献
36.
Let T be a c.n.u. contraction on a Hilbert spaceH and let u-(u1,...,un) be an n-tuple of H(T). We calculate various joint spectra of u(T) and apply the results to study the spectral and index theories of elementary operators associated with n-tuples of the above type.Both authors have been partially supported by NSF grants. 相似文献
37.
V. Degiorgio M. Corti R. Piazza L. Cantú A. R. Rennie 《Colloid and polymer science》1991,269(5):501-505
The structure of aqueous solutions of two polyoxyethylene non-ionic amphiphiles, C10E5 and C8E4, is studied by small-angle neutron-scattering along isothermal paths crossing the isotropic single-phase region from 0% to 100% amphiphile volume fractions. The scattered intensityI(k) shows a peak at a valuek
m
, which grows monotonically as the amphiphile volume fraction increases. The interpretation of the scattering data lead to the following conclusion: as increases the micellar structure becomes less and less sharp, but some orientational correlations between neighboring amphiphile molecules are preserved even in the pure amphiphile phase. 相似文献
38.
2-Deoxy-2-[18F]fluoro-D-glucose ([18F] FDG), the most popular positron emitting radiopharmaceutical, may oxidise by autoradiolysis in aqueous solution. The aim of this work was to use LC-MS for determination of the oxidation products of fluorodeoxyglucose and glucose (Glc) obtained by oxidation with Fenton's reagent. Asahipak NH2P-50 polyamide silica column and acetonitrile-0.025% aqueous ammonium formate (80:20 (v/v)) eluent were utilised with an Agilent 1100 HPLC-MS instrument. Ten major oxidation products of FDG and Glc were separated and identified by mass spectrometry: 2-fluorogluconic acid, 2-fluoroglucuronic acid, 2-oxoerythronic acid, arabinose, arabonic acid, araburonic acid, erythrose, erythrulose, gluconic acid, and glucuronic acid. The most intensive electrospray ionisation signals were found in the negative ion spectra and were due to HCOO- adducts, the other acids being in their lactone forms. 相似文献
39.
Villorbina G Roura L Camps F Joglar J Fabriàs G 《The Journal of organic chemistry》2003,68(7):2820-2829
The formation of methylenecyclopropanes by enzymatic desaturation of 11-cyclopropylundecanoic acid (1) and its disubstituted derivatives cis- and trans-3-5 has been investigated using the Delta(11) desaturase of Spodoptera littoralis as model enzyme. Gas chromatography coupled to mass spectrometry analyses of methanolyzed lipidic extracts from tissues incubated with each probe revealed that all the cyclopropyl fatty acids were transformed into the corresponding 11-cyclopropylidene acids, except for compound trans-5 (5b), which was not desaturated at C11. The formation of methylenecyclopropane 9 as the only reaction product from 1 indicates that a potential radical intermediate is too short-lived to allow rearrangement reactions. Information on the Delta(11) desaturase substrate binding domain is provided considering the cyclopropyl probes 3-5 as conformationally restricted analogues of the straight-chain substrates. 相似文献
40.
Stability constant for mercury binding by commercial and natural humic acids (HA) were determined using a new potentiometric mercury(II) sensor based on dithiosalicylic acid modified carbon paste electrode. The sensor present a high selective and sensitive response to mercury(II) ions, and a low detection limit of 1.8×10?8 M. The potentiometric titrations curves of humic acids against mercury(II) ions were modeled. For 1.00×10?7 to 3.00×10?4 M mercury(II) ion concentration levels the results are consistent with the presence of two different binding sites in the humic acid macromolecule. The strongest binding sites (log K1 ranging from 10.1 to 6.8) are probably due to interaction with carboxylic acid and amine groups in the molecule, whereas weakest binding sites (log K2 ranging from 8.8 to 4.5) can be associated to phenolic groups. 相似文献