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831.
Zhang SY Wang MT Liu QH Hu BW Chen Q Li HX Amoureux JP 《Physical chemistry chemical physics : PCCP》2011,13(13):5617-5620
To overcome the separation difficulty of the palladium-based homogeneous catalyst, the palladium complex can be anchored on various supports such as silica. However, it is difficult to determine the amounts of the two coordination modes of the Pd nucleus, that is, Pd coordinates with one phosphorus atom and Pd coordinates with two phosphorus atoms. Here a (31)P double-quantum filtered (DQ-filtered) method in solid-state NMR is introduced for the palladium-based heterogenous catalyst system. With the DQ-filtered method, we can not only determine the amounts of the two different kinds of palladium coordination modes, we can also estimate the interatomic distance of two (31)P nuclei bonded to a palladium nucleus. With the help of this method, we can quickly estimate interatomic distances in our designed system and accurately re-design the palladium system to accommodate either one (31)P or two (31)P. 相似文献
832.
Wang Q Lu X Lafon O Trébosc J Deng F Hu B Chen Q Amoureux JP 《Physical chemistry chemical physics : PCCP》2011,13(13):5967-5973
We show that (13)C-(1)H dipolar couplings in fully protonated organic solids can be measured by applying a Symmetry-based Resonance-Echo DOuble-Resonance (S-REDOR) experiment at ultra-fast Magic-Angle Spinning (MAS). The (13)C-(1)H dipolar couplings are recovered by using the R12 recoupling scheme, while the interference of (1)H-(1)H dipolar couplings are suppressed by the symmetry properties of this sequence and the use of high MAS frequency (65 kHz). The R12 method is especially advantageous for large (13)C-(1)H dipolar interactions, since the dipolar recoupling time can be incremented by steps as short as one rotor period. This allows a fine sampling for the rising part of the dipolar dephasing curve. We demonstrate experimentally that one-bond (13)C-(1)H dipolar coupling in the order of 22 kHz can be accurately determined. Furthermore, the proposed method allows a rapid evaluation of the dipolar coupling by fitting the S-REDOR dipolar dephasing curve with an analytical expression. 相似文献
833.
Lafon O Trébosc J Hu B De Paëpe G Amoureux JP 《Chemical communications (Cambridge, England)》2011,47(24):6930-6932
We report the application of a dipolar recoupling sequence for the observation of (13)C-(13)C connectivities in biomolecules at high magnetic fields (B(0)≥ 21.1 T) and ultra-high magic angle spinning frequencies (ν(R) = 60 kHz). The efficiency and the robustness of this double-quantum technique are demonstrated on the YajG protein (19.6 kDa). 相似文献
834.
Benzal chlorides and benzal bromides were conveniently synthesized by reaction of aryl aldehydes with a Vilsmeier type reagent formed in situ by reduction of CC14 or CBr4 in dimethylformamide (DMF) as solvent. 相似文献
835.
Fameau AL Douliez JP Boué F Ott F Cousin F 《Journal of colloid and interface science》2011,362(2):397-405
The ethanolamine salt of 12-hydroxy stearic acid is known to form tubes having a temperature tunable diameter. Here, we study the behavior of those tubes at the air/water interface by using Neutron Reflectivity. We observed that tubes indeed adsorbed at this interface below a fatty acid monolayer and exhibit the same temperature behavior as in bulk. There is however a peculiar behavior at around 50 °C for which the increase of the diameter of the tubes at the interface yields an unfolding of those tubes into a multilamellar layer. Upon further heating, the tubes re-fold and their diameter re-decreases after which they melt into micelles as observed in the bulk. All structural transitions at the interface are nevertheless reversible. This provides to the system a high interest for its interfacial properties because the structure at the air/water interface can be tuned easily by the temperature. 相似文献
836.
Human carbonic anhydrase (hCA) IX and XII are isoenzymes which are highly overexpressed in many cancer types. Recently, it has been shown that hCA IX contributes to the acidification of the tumor environment leading to chemoresistance with basic antitumoral drugs. The development of selective hCA inhibitors constitutes a new therapeutic axis. In order to elucidate the specific interactions between hCA and inhibitors, physico-chemical properties of hCA must be evaluated. This work reports the determination of the isoelectric point (pI) of a series of hCA isoforms by capillary isoelectric focusing. First, the method was optimized with synthetic UV-detectable pI markers using a central composite design. The separation was performed in a fused-silica capillary chemically derivatized with hydroxypropylcellulose and using a glycerol-water medium as the anticonvective gel. Three main factors (ampholyte content, focusing time and mobilization pressure) were optimized in order to obtain the best resolution, detection threshold and precision on the pI determination. Then, the model was validated through the analysis of standard proteins mixture having known pI values, before investigating the pI of hCA isoforms. 相似文献
837.
838.
Silvestri F Jordan M Howes K Kivala M Rivera-Fuentes P Boudon C Gisselbrecht JP Schweizer WB Seiler P Chiu M Diederich F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(22):6088-6097
The substrate scope of the [2+2] cycloaddition-cycloreversion (CA-CR) reaction between electron-deficient (2,2-dicyanovinyl)benzene (DCVB) or (1,2,2-tricyanovinyl)benzene (TCVB) derivatives and N,N-dimethylanilino (DMA)-substituted acetylenes was investigated. The structural features of the cyanobutadiene products of these transformations were examined and the rates of selected CA-CR reactions were measured. Rate constants for reactions utilizing pentafluorinated TCVB and DCVB were found to be one to two orders of magnitude larger than those for the unsubstituted analogues. Multiple, consecutive CA-CR reactions were performed with substrates incorporating two reactive 2,2-cyanovinyl or 4-ethynylanilino sites. 1,4-Bis(2,2-dicyanovinyl)-2,3,5,6-tetrafluorobenzene and 1,4-bis[(4'-dihexylamino)phenylethynyl]benzene were selected as suitably reactive monomers for the synthesis of regular [AB] oligomers wherein the push-pull chromophores were formed in the chain-growth step. Oligomers of two types were isolated: macrocyclic [AB](n) and open-chain B[AB](n) oligomers, with n≤4. 相似文献
839.
Hu B Lafon O Trébosc J Chen Q Amoureux JP 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,212(2):320-329
We propose a new broadband second-order proton-assisted 13C–13C correlation experiment, SHANGHAI. The 13C–13C magnetization transfer is promoted by 1H irradiation with interspersed four phases super-cycling. This through-space homo-nuclear sequence only irradiates on the proton channel during the mixing time. SHANGHAI benefits from a large number of modulation sidebands, hence leading to a large robustness with respect to chemical shift differences, which permits its use in a broad MAS frequency range. At ultra-fast MAS (νR ? 60 kHz), SHANGHAI is only efficient when the amplitude of 1H recoupling rf-field is close to half the spinning speed (ν1 ≈ νR/2). However, at moderate to fast MAS (νR = 20–35 kHz), SHANGHAI is efficient at any rf-power level larger than ν1 ≈ 10 kHz, which simultaneously permits avoiding excessive heating of bio-molecules, and using large sample volumes. We show that SHANGHAI can be employed at the very high magnetic field of 23.5 T and then allows the observation of correlation between 13C nuclei, even if their resonance frequencies differ by more than 38 kHz. 相似文献
840.
Siegel R Trébosc J Amoureux JP Gan Z 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,193(2):321-325
Nitrogen-14 (spin I = 1) has always been a nucleus difficult to observe in solid-state NMR and until recently its observation was restricted to one-dimensional (1D) spectra. We present here the first 3D 1H–13C–14N NMR correlation spectrum. This spectrum was acquired on a test sample l-histidine·HCl·H2O using a recently developed technique, which consists in indirectly observing 14N nuclei via dipolar recoupling with an HMQC-type experiment. 相似文献