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51.
Bajor G Veszprémi T Riague el H Guillemin JC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(15):3649-3656
Vinyl, allyl, and homoallyl selenols were easily prepared by a chemoselective reduction of the corresponding selenocyanates with aluminum hydrides. Two stable vinyl and five stable allyl conformers of both series were predicted on the potential-energy surface. The interaction of SeH or SeCN groups with the vinyl group has been investigated with UV photoelectron spectroscopy and quantum chemical calculations, using the MP2/cc-pVTZ and B3LYP/cc-pVTZ levels. In the vinyl derivatives, a surprisingly strong direct conjugation of the selenium lone electron pair and the C=C double bond was observed. On the other hand, in allyl position the selenium lone pair is independent on the C=C double bond, and the hyperconjugation between the Se-C bond and the double bond is the ruling effect. Thus is clarified the type and extent of the interaction between the SeH or SeCN group and the unsaturated moiety. 相似文献
52.
ZnBr2-catalysed phenylthioalkylation of ketene bis(trimethylsilyl)acetals, obtained from carboxylic acids, with appropriate α-chlorosulphides can be used to prepare γ- and δ- lactones. 相似文献
53.
Hassan M. Badawi 《Journal of Molecular Structure》1995,343(1-3):117-124
The conformational stability and structure of 2,3-dimethylpropenal, 2,3-difluoropropenal and their 3,3-dimethyl and 3,3-difluoro derivatives were investigated utilizing ab initio calculations with 3-21G and 6-31G basis sets. For 2,3-dimethylpropenal and 3,3-difluoropropenal the s-trans was predicted to be the low-energy form. In the case of 3,3-dimethylpropenal and 2,3-difluoropropenal the s-cis was predicted by both levels of calculation to be the more stable conformer. Full optimization was performed at the transition states and the barriers to internal rotation were calculated. Methyl and fluorine substitution were found to significantly increase the barrier to interconversion in propenal. The relative change in the barrier depends on the position and the type of the substituent. The trans to cis barrier in 2,3-dimethylpropenal was calculated to be about 3 kcal mol−1 greater than that in 3,3-dimethylpropenal, while the cis to trans barrier in 2,3-difluoropropenal was predicted to be about 7 kcal mol−1 higher than the corresponding one in 3-3-difluoropropenal. 相似文献
54.
A. E. Mohamed R. M. Awadallah A. A. Hassan 《Journal of Radioanalytical and Nuclear Chemistry》1989,129(2):453-457
Multielement neutron activation analysis has been applied to the determination of macro, micro and trace amounts of Al, Br, Ca, Cl, Co, Cr, Cs, Fe, K, La, Mg, Mn, Na, Rb, Sc and V in molasses of Kom Ombo, Edfu, Armant, Naga Hammady and Abu Korkass cane sugar factories. The threshold element concentrations are acceptable and below the safety. Differences in element concentrations may be related to different botanic textures and structures, different compositions of sugar cane plants, corrosion of containers or changes in soil as a result of geochemical differentiation. The method is sensitive down to 0.038 ppm of V. The relative errors due to counting statistics are in the range of 0.2–11%. 相似文献
55.
Summary A new simple, rapid and accurate amplification micro method for fluoride determination is described. It is based on the reaction between the sparingly soluble calcium iodate and the fluoride ion. After adding isopropyl alcohol to the solution, so that its final concentration is 65%, and filtering, an equivalent amount of the iodate is obtained. The latter is titrated iodometrically resulting in a six-fold amplification of the titre. The method is reproducible over a range from 0.4–8 mg fluoride ion. The mean recovery is 99.69%, after applying a correction factor due to potassium iodate solubility.
Zusammenfassung Ein Multiplikationsverfahren zur Mikrobestimmung von Fluorid wurde beschrieben. Es beruht auf der Umsetzung zwischen dem schlecht löslichen Calciumjodat und Fluorid. Nach Zusatz von i-Propylalkohol, bis die Lösung 65% davon enthält, wird filtriert. Die äquivalente Jodatmenge wird jodometrisch titriert. Zwischen 0,4 und 8 mg Fluorid sind die Ergebnisse reproduzierbar. Bei Anwendung eines Korrekturfaktors wegen der Löslichkeit von Kaliumjodat wurden 99,69% Fluorid wieder gefunden.相似文献
56.
A simple synthesis has been devised for the tripodal 3,3,4-tetraamine ligand N{(CH2)3NH2}2{(CH2)4NH2} (L). This ligand forms
a copper(II) complex, [Cu (LH)Cl2]ClO4 (7), the structure of which has been determined by X-ray diffraction. The cation contains
a five-coordinate copper atom, bonded to two chloride ions, the two propylamine groups and the tertiary nitrogen atom of the
ligand; the arrangement is a distorted trigonal bipyramid, in which the two primary amine groups occupy the axial positions.
The butylamine group of the ligand does not coordinate to copper but is protonated. It is involved in hydrogen bonding to
the perchlorate ion. The e.p.r. spectrum of [Cu(dpt)Cl2] is very similar to that of (7), suggesting that it also has a trigonal
bipyramidal structure.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
57.
J. L. Martínez Vidal A. Garrido Frenich T. López López I. Martínez Salvador L. Hajjaj el Hassani M. Hassan Benajiba 《Chromatographia》2005,61(3-4):127-131
An analytical method for determining residues of twenty pesticides by liquid chromatography (LC) coupled to electrospray ionisation (ESI) tandem mass spectrometry (MS-MS) in eight commodities, cucumber, tomato, pepper, green bean, eggplant, zucchini, melon and watermelon, has been developed and validated. On one hand, calibration curves prepared in solvent were compared with calibration curves prepared in a blank matrix extract of each target matrix. On the other hand, calibration curves and recoveries for each commodity were compared. Cucumber was selected as potential reference matrix for the target vegetables. 相似文献
58.
The potentiometric response properties and applications of a tetra-coordinate nickel(II) complex with relatively high selectivity toward nitrate ion are described. The nickel(II) complex of 5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,6,11,13-tetraene was used as a neutral carrier into plasticized poly(vinyl chloride) (PVC) membrane. The influence of several variables was investigated in order to optimize the potentiometric response and selectivity of the electrode. The resulting membrane electrode incorporating 31.0% PVC, 61.0% dioctyl phthalate (DOP) as plasticizer, 3% methyltrioctylammonium chloride (MTOAC) as a cationic additive and 5% carrier (all w/w) demonstrates a Nernstian response slope of −59.6 mV per decade over the concentration range of 5×10−6-1×10−1 M NO3−. The electrode exhibits a fast response time (≤10 s), a detection limit of 2.5×10−6 M, and can be used over a wide pH range of 4-12. The electrode shows improved selectivity in comparison to most of the previously reported nitrate-selective electrodes. It was successfully applied to the determination of nitrate ion in natural water samples. 相似文献
59.
Hassan Acherki Carlos Alvarez-Ibarra Juan F. Collados Lujn María L. Quiroga-Feijo 《Tetrahedron: Asymmetry》2005,16(24):4034-4044
The base-mediated reaction of enantiomerically pure -sulfinylketimine (+)-1 with (E)-,β-disubstituted propenoate esters afforded 3,4-disubstituted-5-(p-tolylsulfinyl)-5,6-dehydropiperidin-2-ones 9-13 and 14 with high or complete diastereoselectivity. A sole diastereomer of the four possible ones, with regard to the nature of ester, was isolated, which revealed the stereocontrol of the chiral sulfinyl group in the Michael reaction and transenolization steps. In addition, the enantioselective synthesis of ethyl (+)-(3S,4aS,7aS)-1-oxo-octahydro-1H-cyclopenta[c]pyridine-3-carboxylates (+)-17 is described (five steps; 47% yield; ee 97%). The absolute configuration of stereocentres introduced in (+)-17 was assigned on the basis of 1H NMR data. 相似文献
60.
New antimalarial drugs 总被引:6,自引:0,他引:6
Wiesner J Ortmann R Jomaa H Schlitzer M 《Angewandte Chemie (International ed. in English)》2003,42(43):5274-5293
Approximately 40% of the world population live in areas with the risk of malaria. Each year, 300-500 million people suffer from acute malaria, and 0.5-2.5 million die from the disease. Although malaria has been widely eradicated in many parts of the world, the global number of cases continues to rise. The most important reason for this alarming situation is the rapid spread of malaria parasites that are resistant to antimalarial drugs, especially chloroquine, which is by far the most frequently used. The development of new antimalarial drugs has been neglected since the 1970s owing to the end colonialism, changes in the areas of military engagement, and the restricted market potential. Only in recent years, in part supported by public funding programs, has interest in the development of antimalarial drugs been renewed. New data available from the recently sequenced genome of the malaria parasite Plasmodium falciparum and the application of methods of modern drug design promise to bring significant development in the fight against this disease. 相似文献