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排序方式: 共有214条查询结果,搜索用时 15 毫秒
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Reported herein is a novel reaction engineering protocol to enhance the efficiency of a transition metal-catalysed process by strategically preventing ligand degradation. Based on spectroscopic investigations, a decomposition pathway of a chiral phosphoramidite ligand during a Cu-catalysed reaction was identified. The involvement of the destructive process could be minimized under the modified reaction conditions that control the amount of nucleophilic alkoxide base, which is the origin of ligand decomposition. Overall, the strategy has been successfully applied to a new class of asymmetric conjugate addition reactions with bis[(pinacolato)boryl]methane, in which α,β-unsaturated enones are utilised as substrates.A novel Cu-catalysed asymmetric conjugate addition reaction with bis[(pinacolato)boryl]methane using α,β-unsaturated enones as substrates has been developed on the basis of strategic preservation of the supporting ligand. 相似文献
3.
Hohyun Kim Hyeongjin Roh Seung-Bock Yeom Hee Joo Lee Sang Beom Han 《Chromatographia》2003,58(3-4):235-240
Summary A sensitive and selective liquid chromatographic method coupled with electrospray ionization tandem mass spectrometry (LC–ESI–MS–MS) has been developed for quantification of felodipine in human and dog plasma. Compounds were separated on a 2.0 mm × 150 mm, 5.0 m particle, C8 column with 1 m m ammonium acetate–acetonitrile, 20:80, pH 6.0, as mobile phase at a flow rate of 200 L min–1. Nifedipine was used as internal standard. Plasma samples were extracted with diethyl ether, the centrifuged upper layer was evaporated, the residue was reconstituted with mobile phase, and the reconstituted samples were injected. The analytical column lasted for at least 1000 injections. By use of multiple reaction monitoring (MRM) mode in MS–MS felodipine and nifedipine were detected without severe interference from the human or dog plasma matrix. Felodipine produced a protonated precursor ion ([M + H]+) at m/z 384 and a corresponding product ion at m/z 338. And internal standard (nifedipine) produced a protonated precursor ion ([M + H]+) at m/z 347 and a corresponding product ion at m/z 315. Detection of felodipine in human and dog plasma was accurate and precise, with a limit of quantification of 0.05 ng mL–1. The method has been successfully applied to preliminary pharmacokinetic study of felodipine in human and dog plasma. 相似文献
4.
Keum SR Roh HJ Choi YK Lim SS Kim SH Koh K 《Magnetic resonance in chemistry : MRC》2005,43(10):873-876
(1)H and (13)C NMR spectra of symmetric and asymmetric bis-spiropyrans, Series 1-3, were completely assigned. Especially, the (1)H assignment of asymmetric spiropyrans was achieved by utilizing (1)H-(1)H COSY and nOe experiments. All of the carbons in the dye molecules were investigated through a combination of heteronuclear 2D-shift correlation spectroscopy (HETCOR), together with an attached proton test (APT). 相似文献
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Le Faou JH Suomijärvi T Blumenfeld Y Piattelli P Agodi C Alamanos N Alba R Auger F Bellia G Chomaz P Coniglione R Del Zoppo A Finocchiaro P Frascaria N Gaardhoje JJ Garron JP Gillibert A Lamehi-Rachti M Liguori-Neto R Maiolino C Migneco E Russo G Roynette JC Santonocito D Sapienza P Scarpaci JA Smerzi A 《Physical review letters》1994,72(21):3321-3324
7.
Akiba Y Beavis D Beery P Britt HC Budick B Chasman C Chen Z Chi CY Chu YY Cianciolo V Cole BA Costales JB Crawford HJ Cumming JB Debbe R Engelage J Fung SY Gonin M Gushue S Hamagaki H Hansen O Hayano RS Hayashi S Homma S Kaneko H Kang J Kaufman S Kehoe WL Kurita K Ledoux RJ Levine MJ Miake Y Morrison DP Morse RJ Moskowitz B Nagamiya S Namboodiri MN Nayak TK Olness J Parsons CG Remsberg LP Roehrich D Rothschild P Sakurai H Sangster TC Seto R Soltz R Stankus P Steadman SG Stephans GS Sung T 《Physical review letters》1996,76(12):2021-2024
8.
Lenhart JL van Zanten JH Dunkers JP Zimba CG James CA Pollack SK Parnas RS 《Journal of colloid and interface science》2000,221(1):75-86
Silane coupling agents are commonly applied to glass fibers to promote fiber/resin adhesion and enhance durability in composite parts. In this study, a coupling agent multilayer on glass was doped with trace levels of the dimethylaminonitrostilbene (DMANS) fluorophore. The fluorophore was immobilized on the glass surface by tethering the molecule to a triethoxy silane coupling agent, creating the DMANS/silane coupling agent molecule (DMSCA). DMSCA was then diluted with commonly used coupling agents and grafted to a glass microscope coverslip to create a model composite interface. A 53-nm blue shift in fluorescence from the immobilized DMSCA can be followed during cure of an epoxy resin overlayer, giving this technique potential to monitor the properties of the fiber/resin interface during composite processing. Contact angle measurements on these coupling agent layers were similar in the presence or absence of the DMSCA molecule, suggesting that trace levels of the fluorescent probe did not affect the structure of the layer. The immobilized DMSCA molecule behaved similarly to the DMANS precursor in solution. Both showed longer wavelength fluorescence in more polar environments. Copyright 2000 Academic Press. 相似文献
9.
Garcia Ruano JL Alemparte C Martin Castro AM Adams H Rodriguez Ramos JH 《The Journal of organic chemistry》2000,65(23):7938-7943
The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles. 相似文献
10.
Junwye Lee Jonghyun Koo Si Un Hwang Sunmin Min Sang Jung Ahn Yonghan Roh Sung Ha Park 《Current Applied Physics》2012,12(4):1207-1211
We report the structural and functional stabilities of artificially synthesized DNA ultra-thin films. Fully covered DNA ultra-thin films on a silica substrate were fabricated by the silica-assisted growth method and those samples were then incubated in various chemicals and physical conditions. The DNA ultra-thin films showed high maintainability under those harsh conditions and these results would aid to facilitate the use of artificial DNA ultra-thin films in advanced research areas such as biophotonics and bioelectronics. 相似文献