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991.
Kamil Samigullin Yashar Soltani Hans-Wolfram Lerner Matthias Wagner Michael Bolte 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(3):189-197
Organoboranes carrying electron‐withdrawing substituents are commonly used as Lewis acidic catalysts or cocatalysts in a variety of organic processes. These Lewis acids also became popular through their application in `frustrated Lewis pairs', i.e. combinations of Lewis acids and bases that are unable to fully neutralize each other due to steric or electronic effects. We have determined the crystal and molecular structures of four heteroleptic arylboranes carrying 2‐(trifluoromethyl)phenyl, 2,6‐bis(trifluoromethyl)phenyl, 3,5‐bis(trifluoromethyl)phenyl or mesityl substituents. [3,5‐Bis(trifluoromethyl)phenyl]bis[2‐(trifluoromethyl)phenyl]borane, C22H11BF12, (I), crystallizes with two molecules in the asymmetric unit which show very similar geometric parameters. In one of the two molecules, both trifluoromethyl groups of the 3,5‐bis(trifluoromethyl)phenyl substituent are disordered over two positions. In [3,5‐bis(trifluoromethyl)phenyl]bis[2,6‐bis(trifluoromethyl)phenyl]borane, C24H9BF18, (II), only one of the two meta‐trifluoromethyl groups is disordered. In [2,6‐bis(trifluoromethyl)phenyl]bis[3,5‐bis(trifluoromethyl)phenyl]borane, C24H9BF18, (III), both meta‐trifluoromethyl groups of only one 3,5‐bis(trifluoromethyl)phenyl ring are disordered. [3,5‐Bis(trifluoromethyl)phenyl]dimesitylborane, C26H25BF6, (IV), carries only one meta‐trifluoromethyl‐substituted phenyl ring, with one of the two trifluoromethyl groups disordered over two positions. In addition to compounds (I)–(IV), the structure of bis[2,6‐bis(trifluoromethyl)phenyl]fluoroborane, C16H6BF13, (V), is presented. None of the ortho‐trifluoromethyl groups is disordered in any of the five compounds. In all the structures, the boron centre is in a trigonal planar coordination. Nevertheless, the bond angles around this atom vary according to the bulkiness and mutual repulsion of the substituents of the phenyl rings. Also, the ortho‐trifluoromethyl‐substituted phenyl rings usually show longer B—C bonds and tend to be tilted out of the BC3 plane by a higher degree than the phenyl rings carrying ortho H atoms. A comparison with related structures corroborates the conclusions regarding the geometric parameters of the boron centre drawn from the five structures in this paper. On the other hand, CF3 groups in meta positions do not seem to have a marked effect on the geometry involving the boron centre. Furthermore, it has been observed for the structures reported here and those reported previously that for CF3 groups in ortho positions of the aromatic ring, disorder of the F atoms is less probable than for CF3 groups in meta or para positions of the ring. 相似文献
992.
993.
Prof. Steven J. Langford Dr. Toby D. M. Bell 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(10):4133-4140
Two new amino core‐substituted naphthalene diimides (cNDIs) bearing fluorinated side chains have been synthesised. Steady‐state and time‐resolved fluorescence spectroscopy reveals unprecedented optical properties for the cNDIs with high quantum yields of ~0.8 and fluorescence lifetimes of ~13 ns in a range of solvents. These properties are apparent at the level of single molecules, where the compounds also show exceptional photostability under pulsed‐laser excitation. Photon emission is remarkably consistent with very few long timescale (millisecond or longer) interruptions with molecules regularly undergoing >107 cycles of excitation and emission. Intermittencies owing to triplet‐state formation occur on a sub‐millisecond timescale with a low yield of 1–2 %, indicating that the presence of the fluorine atoms does not lead to a significant triplet yield through the heavy‐atom effect. These properties make the compounds excellent candidates for single‐molecule labelling applications. 相似文献
994.
Liquid chromatography–tandem mass spectrometric assay for the determination of vaccarin in rat plasma: application to a pharmacokinetic study 下载免费PDF全文
Tiance Wang Shudong Zhang Rihao Xu Zhicheng Zhu Kexiang Liu 《Biomedical chromatography : BMC》2014,28(12):1789-1794
Vaccarin, a flavonoid glycoside, is considered one of the major active constituents of Vaccaria segetalis. A simple and specific liquid chromatography–tandem mass spectrometric method was developed and validated for quantifying vaccarin in rat plasma following intravenous dosing. Plasma samples were precipitated with methanol and separated on a Venusil‐C18 analytical column (2.1 × 50 mm, 5 µm particles) with gradient elution consisting of methanol and 0.1% (v/v) formic acid as the mobile phase. The detection was performed on an Agilent Triple Quad LC/MS with electrospray ionization inlet in the positive multiple reaction monitoring mode. Good linearity was achieved over the concentration range of 12.5–25,000 ng/mL (r2 > 0.99). Intra‐ and inter‐day precisions were <9.1%, and accuracy ranged from ?2.8 to 8.7%. The lower limit of quantification for vaccarin was 12.5 ng/mL, and the analyte was stable under various storage conditions. This validated method was successfully applied to the preliminary pharmacokinetic studies of vaccarin following intravenous administrations of 1.21, 2.41, and 4.82 mg/kg vaccarin in rats. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
995.
《Current Applied Physics》2015,15(3):201-207
l-Valine Ferric Chloride single crystal is a new semi organic nonlinear optical material. It has been grown from a mixture of aqueous solutions of l-Valine and Ferric Chloride by slow evaporation solution growth technique at room temperature for the first time. Single crystal XRD analysis revealed that the crystal system belongs to Cubic P with cell parameters are a = 24.38 Å, b = 24.38 Å, c = 24.38 Å and volume is 14,485 Å3. The UV spectrum shows existence of wide transparency window suitable for optoelectronic applications. Thermal stability and melting temperature of the as grown crystal was identified from TG-DTA analysis. Spectroscopic studies have been carried out for analyzing the presence of functional groups, thermal stability and phase transition of the grown crystal. The dielectric loss and the dielectric constant of the crystals were measured as a function of frequency. Photoluminescence study was carried out for grown crystals and the maximum emission occurs has good optical transmission in the entire visible region. Second harmonic generation (SHG) conversion efficiency has been estimated. 相似文献
996.
997.
998.
Structural Investigation of the High Spin→Low Spin Relaxation Dynamics of the Porous Coordination Network [Fe(pz)Pt(CN)4]⋅2.6 H2O 下载免费PDF全文
Teresa Delgado Dr. Antoine Tissot Dr. Céline Besnard Dr. Laure Guénée Dr. Philip Pattison Prof. Andreas Hauser 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(9):3664-3670
The Hoffman‐type coordination compound [Fe(pz)Pt(CN)4] ? 2.6 H2O (pz=pyrazine) shows a cooperative thermal spin transition at around 270 K. Synchrotron powder X‐Ray diffraction studies reveal that a quantitative photoinduced conversion from the low‐spin (LS) state into the high‐spin (HS) state, based on the light‐induced excited spin‐state trapping effect, can be achieved at 10 K in a microcrystalline powder. Time‐resolved measurements evidence that the HS→LS relaxation proceeds by a two‐step mechanism: a random HS→LS conversion at the beginning of the relaxation is followed by a nucleation and growth process, which proceeds until a quantitative HS→LS transformation has been reached. 相似文献
999.
《Magnetic resonance in chemistry : MRC》2003,41(4):246-252
The solution conformations of the novel estrogen receptor ligands (17α,20E)‐(p‐trifluoromethylphenyl)vinylestradiol ( 1 ) and (17α,20E)‐(o‐trifluoromethylphenyl)vinylestradiol ( 2 ) were investigated in 2D and 1D NOESY studies and by comparison of 13C NMR chemical shifts with theoretical shieldings. The 1H and 13C assignments of 1 and 2 were determined by DEPT, COSY and HMQC experiments. The conformations of the 17α‐phenylvinyl substituents of 1 and 2 are of interest because of their differing receptor binding affinities and effects in in vivo uterotrophic growth assays. A statistical method of evaluating contributing conformers of 1 and 2 from predicted 13C shifts of possible structures correlated fairly well with conformational conclusions derived from the NOE data. The 17α substituents of 1 and 2 apparently exist in similar conformational equilibria, suggesting that while 1 and 2 would occupy a similar receptor volume, interactions with the protein may shift the equilibrium and thereby influence the expression of the ligand. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
1000.