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701.
Heimel G Daghofer M Gierschner J List EJ Grimsdale AC Müllen K Beljonne D Brédas JL Zojer E 《The Journal of chemical physics》2005,122(5):54501
The absorption and emission spectra of most luminescent, pi-conjugated, organic molecules are the mirror image of each other. In some cases, however, this symmetry is severely broken. In the present work, the asymmetry between the absorption and fluorescence spectra in molecular systems consisting of para-linked phenyl rings is studied. The vibronic structure of the emission and absorption bands is calculated from ab initio quantum chemical methods and a subsequent, rigorous Franck-Condon treatment. Good agreement with experiment is achieved. A clear relation can be established between the strongly anharmonic double-well potential for the phenylene ring librations around the long molecular axis and the observed deviation from the mirror image symmetry. Consequences for related compounds and temperature dependent optical measurements are also discussed. 相似文献
702.
Pirat JL Monbrun J Virieux D Volle JN Tillard M Cristau HJ 《The Journal of organic chemistry》2005,70(18):7035-7041
[reaction: see text] Diastereoselective additions of 2-hydrogeno-2-oxo-1,4,2-oxazaphosphinanes to aldehydes and imines are described. alpha,alpha'-Diaminophosphinic and alpha-amino-alpha'-hydroxyphosphinic derivatives were obtained with de's ranging from 24 to 90%. 相似文献
703.
Benzodiazepines, namely flunitrazepam and its three major metabolites, were successfully separated by microemulsion electrokinetic chromatography. Separation was achieved using an untreated fused-silica capillary (48 cm (effective length 40 cm) x 50 num) at 25 kV; detection was performed by UV at 220 nm. The microemulsion system consisted of 70 mM octane, 800 mM 1-butanol, 80 mM sodium dodecyl sulfate (SDS) and 10 mM borate buffer, pH 9. Very high efficiencies (up to 400 000 plates) and resolution better than 3 were achieved. Since this technique is not compatible with mass spectrometry (MS) detection, a capillary electrochromatographic (CEC) method was developed to separate flunitrazepam and its metabolites. The effects of mobile phase composition and pH as well as voltage and temperature were systematically investigated. The optimized CEC method allowed the baseline separation of the investigated compounds. For the on-line coupling of CEC with electrospray ionization-mass spectrometry, the column was connected to a void fused-silica capillary using a Teflon connection. This configuration was found efficient and suitable for hyphenation of commercial CEC and MS instrumentation using commercially available CEC columns. 相似文献
704.
Lahrech M Thibonnet J Hacini S Santelli M Parrain JL 《Chemical communications (Cambridge, England)》2002,(6):644-645
The reaction of 1-trimethylsilylbuta-2,3-diene with tin tetrachloride, antimony trichloride or antimony pentachloride gave the corresponding buta-1,3-dien-2-yl halostannane or stibine derivatives; this ligand exchange was extended to other beta-allenylsilanes. 相似文献
705.
Bimodal (4 and 8 nm) mesoporous silicas with interconnected three-dimensional structure were synthesized by mild-temperature post-synthesis hydrothermal treatment of MCM-41 mesoporous materials in ammonia solution. 相似文献
706.
707.
708.
The enantioseparation of baclofen (4-amino-3-p-chlorophenylbutyric acid) was achieved by CE-LIF with highly sulfated beta-CD (HS-beta-CD) as chiral selector. Naphthalene-2,3-dicarboxaldehyde was used for the derivatization of nonfluorescent baclofen. HS-beta-CD (2%) containing 50 mM borate buffer at pH 9.5 was chosen as the optimal running electrolyte and applied to the analysis of baclofen enantiomers in human plasma. The linearity of calibration curves (R2 > or = 0.998) for R-(-) and S-(+)-baclofen was in the 0.1-2.0 microM concentration range. After a simple ACN-protein precipitation, the LOD of baclofen in plasma sample was found as low as 50 nM. 相似文献
709.
[reaction: see text] A reusable polymer-supported hydrophosphinylation catalyst is described for the preparation of H-phosphinic acids. The polystyrene-based ligand is prepared in one step from commercially available compounds. The polymeric catalyst generally gives good yields for a variety of substrates and is water- and air-tolerant, although the scope of alkenes and alkynes which can be employed is somewhat narrower than with our original xantphos/Pd(2)dba(3) catalyst. 相似文献
710.
Jacques Boulanger Jean-Luc Chabert 《Transactions of the American Mathematical Society》2004,356(12):5071-5088
Let be a cyclotomic field with ring of integers and let be a polynomial whose values on belong to . If the ideal of generated by the values of on is itself, then every algebraic integer of may be written in the following form:
for some integer , where the 's are roots of unity of . Moreover, there are two effective constants and such that the least integer (for a fixed ) is less than , where
for some integer , where the 's are roots of unity of . Moreover, there are two effective constants and such that the least integer (for a fixed ) is less than , where