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81.
Mark D. Struble Courtney Kelly Maxime A. Siegler Thomas Lectka 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(34):9070-9074
Reported herein is the synthesis of a molecule containing an unusually strong hydrogen bond between an OH donor and a covalent F acceptor, a heretofore somewhat ill‐defined if not controversial interaction. This unique hydrogen bond is to a large extent a product of the tight framework of the rigid caged system. Remarkably, the interaction shows little to no perceptible shift in the OH stretch of the IR spectrum relative to appropriate nonhydrogen‐bound standards in fairly non‐interactive solvents. This fascinating example of what has been termed a virtual “no‐shift” hydrogen bond is investigated through NMR (coupling constants, isotopic chemical shift perturbations, proton exchange rates) and IR studies which all tell a consistent story. 相似文献
82.
Occurrence of betablockers in effluents of wastewater treatment plants from the Lyon area (France) and risk assessment for the downstream rivers 总被引:1,自引:0,他引:1
Five betablockers (oxprenolol, metoprolol, propranolol, bisoprolol, betaxolol) were analysed in effluents collected over a 3-month period from wastewater treatment plants (WTP) from the Lyon area in France. The analytical protocol consisted of solid phase extraction of the dissolved aqueous phase on HLB cartridges and analysis by gas chromatography coupled with mass detection (GC-MS) after derivatization. Concentrations of metoprolol, propranolol and bisoprolol varied from 45 to 2838 ng/L whereas oxprenolol and betaxolol were never detected in these effluent samples. A high variability of betablockers concentrations and fluxes was observed between WTP effluents and within each WTP over the time period studied. Considering a flux per person for a dry weather period, Fontaine plant was pointed out as the less efficient WTP, which might be explained by its type of treatment (biological aerated filters). But we need additional analysis of effluent and influent waters to confirm this hypothesis. A tentative approach of local environmental risk assessment of propranolol based on the calculation of PEC/PNEC (predicted environmental concentration/predicted non effect concentration) ratio approach lead us to conclude on a negligible risk for the downstream rivers (Rhône river at Ternay and Saône river at Couzon Mt d’Or). 相似文献
83.
In addition to the need for functional models of cytochrome c oxidase, structural models are still required for a better understanding of the small reorganizations occurring during the catalytic cycle. An efficient synthetic approach has been designed to prepare several phenanthroline-strapped porphyrins, two of them bearing two pendant imidazoles. These built-in bases are both potentially able to act as axial bases for the metalloporphyrin and as complementary ligands for copper if necessary. Diamagnetic zinc(II) was used to demonstrate that the distal/proximal selectivity demonstrated by exogenic bases binding studies can be extended to the coordination of iron(III). Combination of EPR and paramagnetic 1H NMR shows that the imidazole binding on the zinc species can be further extended to the iron(III) species in dilute conditions. 相似文献
84.
Vitale M Lecourt T Sheldon CG Aggarwal VK 《Journal of the American Chemical Society》2006,128(8):2524-2525
The reaction of lithiated trimethylsilyldiazomethane (LTMSD) with aldehydes and subsequent quenching with TMSCl furnished relatively stable alpha-silylated diazocompounds. Upon treatment of the alpha-silylated diazocompounds with Rh2(OAc)4 in refluxing toluene, alpha-silyl silyl enol ethers were formed from unbranched and branched aliphatic aldehydes through predominantly 1,2-migration of the C-H bond. In contrast, treatment of the alpha-silylated diazocompounds with Rh2(tfa)4 at room temperature gave alpha-silyl silyl enol ethers through exclusive and unusual 1,2-migration of the C-C bond. The origin of the selectivity observed from the two catalysts is discussed in relation to early and late transition states. 相似文献
85.
In this paper, we present and apply a computer-assisted method to study steady states of a triangular cross-diffusion system. Our approach consist in an a posteriori validation procedure, that is based on using a fixed point argument around a numerically computed solution, in the spirit of the Newton–Kantorovich theorem. It allows to prove the existence of various non homogeneous steady states for different parameter values. In some situations, we obtain as many as 13 coexisting steady states. We also apply the a posteriori validation procedure to study the linear stability of the obtained steady states, proving that many of them are in fact unstable. 相似文献
86.
87.
88.
A stereocontrolled total synthesis of (+)-longicin, a representative of the class of mono-THF-acetogenins, is described. The strategy involves the utilization of d- and l-glutamic acids as chirons that correspond to two five-carbon segments harboring stereogenic centers at C4 and at C17 of the C(32) polyketide-derived natural product. The use of Grubbs' RCM reaction as a novel "chain elongation" strategy for the synthesis of acetogenin-type structures and a new protocol for butenolide incorporation are also described. [structure: see text] 相似文献
89.
Maxime D. Crozet 《Tetrahedron letters》2006,47(39):7061-7065
A new simple, rapid and high yielding synthesis of various 6-aryl-2-arylsulfonylmethyl-3-nitroimidazo[1,2-a]pyridines by Suzuki cross-coupling reaction is described using microwave irradiation in aqueous medium without organic co-solvent in the presence of tetrabutylammonium bromide. 相似文献
90.
Wise CA Paris M Morar B Wang W Kalaydjieva L Bittles AH 《Rapid communications in mass spectrometry : RCM》2003,17(11):1195-1202
Analysis of single nucleotide polymorphisms (SNPs) has become an increasingly important area of research, with numerous applications in medical genetics, population genetics, forensic science, and agricultural biotechnology. Large-scale SNP analyses require the development of methodologies that are economical, flexible, accurate and capable of automation. Primer extension in conjunction with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) is currently emerging as a potential method for high-throughput SNP genotyping. We have evaluated a number of published primer extension methods and refined a simple and robust protocol to analyze human autosomal disease-causing mutations and population genetic markers on the Y-chromosome. Twelve different variant sites were examined, and homozygotes, heterozygotes and hemizygotes were accurately typed. A 100% concordance was observed between SNP genotypes obtained using the MALDI-TOFMS technique and alternative genotyping methods, such as restriction fragment length polymorphism (RFLP) assays and denaturing high-performance liquid chromatography (DHPLC). Since multiple polymorphisms can be detected in single reactions, the method provides a cost-effective approach for SNP analysis. The protocol is also extremely flexible (able to accommodate new markers) and can be adapted to a number of platforms without the use of commercial kits. 相似文献