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排序方式: 共有166条查询结果,搜索用时 15 毫秒
101.
102.
103.
Davy‐Louis Versace Jean‐Pierre Fouassier Jacques Laleve 《Macromolecular rapid communications》2014,35(8):821-826
Bis(cyclopentadienyl)titanium dichloride (Cp2TiCl2) is a high performance additive under UV light activation for both i) radical photopolymerization reactions (when added to a Type I photoinitiator such as 2,2‐dimethoxy‐2‐phenylacetophenone, the oxygen inhibition is reduced) and ii) a concomitant in situ photoinduced and oxygen mediated formation of Ti‐based nanoparticles (diameters ranging from 45 to 220 nm). The photochemical properties of Cp2TiCl2 are investigated by steady state photolysis and electron spin resonance, and its photoinitiation ability checked. The nanoparticles (NPs) are well characterized by transmission electron microscopy. The high reactivity of Cp2TiCl2 under air is ascribed to a bimolecular homolytic substitution (the SH2 process is clearly demonstrated by density functional theory calculations and ESR experiments), which converts the peroxyls into new efficient initiating radicals. The photochemical in situ incorporation of Ti NPs has never previously been reported. The synthesis of metal nanoparticles by a SH2 approach instead of the reduction of a metal salt appears to be a promising original method.
104.
We investigate anomalous reaction kinetics related to segregation in the one-dimensional reaction-diffusion system A + B → C. It is well known that spatial fluctuations in the species concentrations cause a breakdown of the mean-field behavior at low concentration values. The scaling of the average concentration with time changes from the mean-field t(-1) to the anomalous t(-1/4) behavior. Using a stochastic modeling approach, the reaction-diffusion system can be fully characterized by the multi-point probability distribution function (PDF) of the species concentrations. Its evolution is governed by a Fokker-Planck equation with moving boundaries, which are determined by the positivity of the species concentrations. The concentration PDF is in general non-Gaussian. As long as the concentration fluctuations are small compared to the mean, the PDF can be approximated by a Gaussian distribution. This behavior breaks down in the fluctuation dominated regime, for which anomalous reaction kinetics are observed. We show that the transition from mean field to anomalous reaction kinetics is intimately linked to the evolution of the concentration PDF from a Gaussian to non-Gaussian shape. This establishes a direct relationship between anomalous reaction kinetics, incomplete mixing and the non-Gaussian nature of the concentration PDF. 相似文献
105.
Aurélie Periat Alexandre Grand‐Guillaume Perrenoud Davy Guillarme 《Journal of separation science》2013,36(19):3141-3151
The goal of this study was to compare the performance of three separation techniques for the analysis of 57 hydrophilic compounds. RPLC, hydrophilic interaction liquid chromatography (HILIC) and subcritical fluid chromatography (SFC) were tested. The comparison was based on the retention, selectivity, peak shape (asymmetry and peak width) and MS sensitivity. As expected, RPLC had some obvious limitations for such classes of compounds, and on average the %ACN required to elute these hydrophilic substances was 4, 7, and 11% ACN at pH 3, 6, and 9, respectively. However, a hybrid polar‐embedded C18 phase with an appropriate mobile phase could represent a viable strategy for hydrophilic basic compounds with log D greater than –2 on average. HILIC and SFC were found to be more appropriate for analyzing a large majority of these hydrophilic analytes (~60 and 70% of compounds eluted during the gradient in HILIC and SFC), while maintaining good MS sensitivity. Finally, this work demonstrated the complementarity of the three analytical techniques and showed that the selection of a suitable strategy should mostly be based on physicochemical properties of the analytes (pKa, log D, H‐bonding capability, etc.). 相似文献
106.
Dr. Davy Sinnaeve Julian Ilgen Dr. Maria Enrica Di Pietro Johann J. Primozic Dr. Volker Schmidts Prof. Dr. Christina M. Thiele Prof. Dr. Burkhard Luy 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(13):5354-5358
Residual dipolar couplings (RDCs) are amongst the most powerful NMR parameters for organic structure elucidation. In order to maximize their effectiveness in increasingly complex cases such as flexible compounds, a maximum of RDCs between nuclei sampling a large distribution of orientations is needed, including sign information. For this, the easily accessible one-bond 1H–13C RDCs alone often fall short. Long-range 1H–1H RDCs are both abundant and typically sample highly complementary orientations, but accessing them in a sign-sensitive way has been severely obstructed due to the overflow of 1H–1H couplings. Here, we present a generally applicable strategy that allows the measurement of a large number of 1H–1H RDCs, including their signs, which is based on a combination of an improved PSYCHEDELIC method and a new selective constant-time β-COSY experiment. The potential of 1H–1H RDCs to better determine molecular alignment and to discriminate between enantiomers and diastereomers is demonstrated. 相似文献
107.
Kohei Iwai Dr. Hiroshi Yamagishi Colin Herzberger Yuji Sato Prof. Hayato Tsuji Prof. Ken Albrecht Kimihisa Yamamoto Dr. Fumio Sasaki Dr. Hiroyasu Sato Aswin Asaithambi Prof. Axel Lorke Prof. Yohei Yamamoto 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(31):12774-12779
Microcrystallites are promising minute mirrorless laser sources. A variety of luminescent organic compounds have been exploited along this line, but dendrimers have been inapplicable owing to their fragility and extremely poor crystallinity. Now, a dendrimer family that overcomes these difficulties is presented. First-, second-, and third-generation carbazole (Cz) dendrimers with a carbon-bridged oligo(phenylenevinylene) (COPV2) core (GnCOPV2, n=1–3) assemble to form microcrystals. The COPV2 cores align uni/bidirectionally in the crystals while the Cz units in G2- and G3COPV2 align omnidirectionally. The dendrons work as light-harvesting antennas that absorb non-polarized light and transfer it to the COPV2 core, from which a polarized luminescence radiates. Furthermore, these crystals act as laser resonators, where the lasing thresholds are strongly coupled with the crystal morphology and the orientation of COPV2, which is in contrast with the conventional amorphous dendrimers. 相似文献
108.
Marina Lučić Dr. Dimitri A. Svistunenko Prof. Michael T. Wilson Dr. Amanda K. Chaplin Bradley Davy Dr. Ali Ebrahim Dr. Danny Axford Dr. Takehiko Tosha Dr. Hiroshi Sugimoto Dr. Shigeki Owada Dr. Florian S. N. Dworkowski Dr. Ivo Tews Dr. Robin L. Owen Dr. Michael A. Hough Dr. Jonathan A. R. Worrall 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(48):21840-21846
Obtaining structures of intact redox states of metal centers derived from zero dose X-ray crystallography can advance our mechanistic understanding of metalloenzymes. In dye-decolorising heme peroxidases (DyPs), controversy exists regarding the mechanistic role of the distal heme residues aspartate and arginine in the heterolysis of peroxide to form the catalytic intermediate compound I (FeIV=O and a porphyrin cation radical). Using serial femtosecond X-ray crystallography (SFX), we have determined the pristine structures of the FeIII and FeIV=O redox states of a B-type DyP. These structures reveal a water-free distal heme site that, together with the presence of an asparagine, imply the use of the distal arginine as a catalytic base. A combination of mutagenesis and kinetic studies corroborate such a role. Our SFX approach thus provides unique insight into how the distal heme site of DyPs can be tuned to select aspartate or arginine for the rate enhancement of peroxide heterolysis. 相似文献
109.
E. Davy 《Fresenius' Journal of Analytical Chemistry》1882,21(1):580
Ohne Zusammenfassung 相似文献
110.
H. G. Dekay C. B. Jordans M. D. Evans E. D. Davy und J. Opieska-Blauth 《Fresenius' Journal of Analytical Chemistry》1937,110(1-2):78-79
Ohne Zusammenfassung 相似文献