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1.
α,β-Unsaturated nitriles can be hydrogenated with enantioselectivities up to 88% ee using chiral ruthenium-diphenylphosphino bisaryl and bisheteroaryl complexes such as ruthenium(II)-BINAP and ruthenium(II)-BINP. Mechanistic investigations indicate that conversion is accelerated by electron-rich ligands and that an additional coordinative group needs be present in order to promote conversion. The chiral products are useful building blocks for the synthesis of histamine H2 agonists of the arpromidine type. 相似文献
2.
Tiziana Cardinali Raffaella Servadei 《Proceedings of the American Mathematical Society》2004,132(8):2339-2349
In this paper we obtain the existence of periodic solutions for nonlinear ``invariance' problems monitored by impulsive differential inclusions subject to impulse effects.
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A method for detecting carbonate in marine solid samples (sediments, corals) by Fourier transform infrared spectroscopy (FTIR) coupled to the total attenuated reflectance (ATR) technique is described. Compared to other techniques, the proposed method is not based on the measurement of CO2 evolved by combustion or acidification of the sample, but on the direct measurement of carbonate present in the sample. For this reason, the method by FTIR-ATR spectroscopy does not require any chemical pre-treatment. The proposed method allows determination of carbonate in the range 6-100% (w/w) as Na2CO3 and gives comparable results with the determination of inorganic carbon by elemental analysis. 相似文献
6.
A simple rapid method of determining lead in gasoline by AAS with use of stable emulsions has been developed. The emulsions were stabilized with propan-2-ol or a mixture of ethanol and a surface-active agent. The results obtained showed good reproducibility and accuracy and the method is suitable for routine analysis. 相似文献
7.
An automated procedure for correcting the interference due to mixing the reagents in the determination of ATP by a bioluminescent
technique is described. The measurements were performed by an in-house interfaced PC photometer. An automated procedure based
on a robust regression method and outliers detection was applied to exclude the time of the mixing of the reagents from the
global time of reaction. In fact the mixing of the reagents is responsible of the poor analytical precision (RSD%>25) and
low sensitivity (limit of detection≈2×10-8 mol/l). By this procedure, the precision (RSD%<7) and sensitivity (limit of detection≈8×10-10 mol/l) were improved. The method was applied to the determination of ATP in marine sediments and good recovery within 90–108%
was obtained. For non-polluted samples the measurement can be carried out by direct comparison with standard solutions. The
standard addition procedure is recommended for polluted samples.
Received: 25 April 1996/Revised: 28 June 1996/Accepted: 3 July 1996 相似文献
8.
Benincori T Brenna E Sannicolò F Trimarco L Antognazza P Cesarotti E Demartin F Pilati T 《The Journal of organic chemistry》1996,61(18):6244-6251
The synthesis and application of three examples of a new class of chiral (C(2)) atropisomeric diphosphines characterized by two interconnected five-membered heteroaromatic rings, with hindered rotation around the interanular bond, are described. Optically pure (+)- and (-)-2,2'-bis(diphenylphosphino)-4,4',6,6'-tetramethyl-3,3'-bibenzo[b]thiophene (tetraMe-bitianp) (1a) and the parent unsubstituted system (+)- and (-)-bitianp (1b) were synthesized. They were found to be optically stable at 100 degrees C and were successfully employed as ligands in the Ru(II)-catalyzed hydrogenation of alpha- and beta-oxo esters to the corresponding alpha- and beta-hydroxy esters and in the hydrogenation of olefinic substrates. The optical and chemical yields were comparable with those reported for the same Ru(II)-binap-catalyzed reactions carried out under the same experimental conditions. The 2,2'-bis(diphenylphosphino)-3,3'-bibenzo[b]furan (1c), the oxygenated analogue of bitianp, was found to be configurationally unstable at room temperature. Complete structural X-ray elucidation of the Pd complexes of 1a-c is reported. The advantages of these biheteroaromatic ligands over the classical biaryl systems are discussed. 相似文献
9.
One hundred and one volatile compounds, reported in literature as powerful odorants of wine, were quantified by Gas Chromatography-Selective Ion Monitoring/Mass Spectrometry (GC-SIM/MS) in Primitivo, Aglianico, Merlot and Cabernet Sauvignon red wines. Wine samples were extracted by 3 different extraction methods: 1) separation of the alcoholic fraction from the aqueous phase by salting-out and subsequent extraction by liquid-liquid micro-extraction with 1,1,2-trichlorotrifluoroethane (Freon 113); 2) extraction by liquid-liquid micro-extraction with dichloromethane; 3) solid phase extraction (SPE cartridge: 800 mg of LiChrolut EN resin) with pentane-dichloromethane (20:1) and dichloromethane. The selection of the ion fragments used for quantification was directly performed on a red wine sample. For each compound the area of the corresponding peak was normalized respect to the peak of the internal standard and then interpolated in a calibration curve obtained analysing a model wine solution (water, ethanol, tartaric acid and known amounts of analytes and of internal standard). The methods showed a good linearity: r2>0.990, except for farnesol (isomer a and c), octanal, decanal, furaneol and phenylacetic acid with 0.966 < or = r2 < or = 0.990. The 7 most powerful odorants were: beta-damascenone, acetaldehyde, maltol, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate, 3-methylbutanoic acid and acetal; 7 other slightly less important were: ethyl hexanoate, ethyl acetate, 1-octen-3-ol, butanoic acid, rose oxide, furaneol and sotolon. The Aglianico wines were characterised by the major fermentation compounds (esters, fatty acids and 2-phenylethanol), beta-damascenone, beta-ionone and linalool. The Primitivo wines were characterized by furaneol, methoxypyrazine, gamma-nonalactone and acetaldehyde, while Cabernet Sauvignon and Merlot wines principally by cask derivates (vanillin, (Z) 3-methyl-gamma-octalactone [(Z) wiskylactone], maltol and eugenol), some aldehydes and 3-isopropyl-2-methoxypyrazine. 相似文献