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排序方式: 共有628条查询结果,搜索用时 328 毫秒
121.
Dr. Camille Lecourt Sabrina Dhambri Khalil Yamani Dr. Guillaume Boissonnat Dr. Simon Specklin Dr. Etienne Fleury Karim Hammad Eric Auclair Serge Sablé Dr. Antonio Grondin Dr. Paola B. Arimondo Dr. François Sautel Dr. Georges Massiot Dr. Christophe Meyer Prof. Dr. Janine Cossy Dr. Geoffroy Sorin Dr. Marie-Isabelle Lannou Prof. Dr. Janick Ardisson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(11):2745-2749
A strategy for the assembly of the entire carbon backbone of a stereoisomer of the antitumor marine natural product hemicalide has been investigated. The devised convergent approach relies on Horner–Wadsworth–Emmons and Julia–Kocienski olefination reactions for the construction of the C6=C7 and C34=C35 double bonds, respectively, an aldol reaction to create the C27−C28 bond, and a Suzuki–Miyaura cross-coupling as the endgame to form the C15−C16 bond. 相似文献
122.
Sabrina Moret Susi Cherubin Maria Teresa Rodriguez-Estrada Giovanni Lercker 《Journal of separation science》1994,17(12):827-830
This work suggests an HPLC method for qualitative and quantitative determination of Nε(2-amino-2-carboxyethyl)-L -lysine (LAL). LAL was released from total hydrolysates of various proteins of animal origin and derivatized with dansyl chloride. The performance of two different columns, Spherisorb 3S TG and μ-Bondapack C18, was compared; better resolution and quantitative response were obtained with the former. The mobile phase was a mixture of 0.01 M phosphate buffer (pH 7) and acetonitrile. Linear response and quantitative repeatability were tested for both detectors used (UV-Vis set at 254 nm; fluorimetric set at λex(max) = 360 nm and λem(max) = 525 nm). For LAL standard the minimum detectable amount was 0.05 ng, whereas for LAL in actual samples the amount was 0.5 ng (40 μg/g of analyzed proteins). Good analytical repeatability was obtained, resulting in CV % of 4.7 and 3.8 for UV and fluorimetric detectors, respectively. LAL recovery was determined using both detectors; the values obtained were 94 % (fluorimetric) and 92 % (UV). Greater noise levels were observed with the fluorimetric detector and its higher sensitivity could not, therefore, be fully utilized. The highest amounts of LAL were found in the casein (2816 μg/g) and cooked albumin (615 μg/g) samples. 相似文献
123.
The 1,3‐dipolar cycloaddition reactions of 2‐diazocyclohexane‐1,3‐dione ( 7a ; Table 1) and of alkyl diazopyruvates ( 11a – e ; Table 3) to 2,3‐dihydrofuran and other enol ethers have been investigated in the presence of chiral transition metal catalysts. With RhII catalysts, the cycloadditions were not enantioselective, but those catalyzed by [RuIICl2( 1a )] and [RuIICl2( 1b )] proceeded with enantioselectivities of up to 58% and 74% ee, respectively, when diazopyruvates 11 were used as substrates. The phenyliodonium ylide 7c yielded the adduct 8a in lower yield and poorer selectivity than the corresponding diazo precursor 7a (Table 2) upon decomposition with [Ru(pybox)] catalysts. This suggests that ylide decomposition by RuII catalysts, contrary to that of the corresponding diazo precursors, does not lead to Ru‐carbene complexes as reactive intermediates. Our method represents the first reproducible, enantioselective 1,3‐cycloaddition of these types of substrates. 相似文献
124.
Mikhail Agrachev Wenwen Fei Sabrina Antonello Sara Bonacchi Tiziano Dainese Alfonso Zoleo Marco Ruzzi Flavio Maran 《Chemical science》2020,11(13):3427
Singlet oxygen, 1O2, can be generated by molecules that upon photoexcitation enable the 3O2 → 1O2 transition. We used a series of atomically precise Au24M(SR)18 clusters, with different R groups and doping metal atoms M. Upon nanosecond photoexcitation of the cluster, 1O2 was efficiently generated. Detection was carried out by time-resolved electron paramagnetic resonance (TREPR) spectroscopy. The resulting TREPR transient yielded the 1O2 lifetime as a function of the nature of the cluster. We found that: these clusters indeed generate 1O2 by forming a triplet state; a more positive oxidation potential of the molecular cluster corresponds to a longer 1O2 lifetime; proper design of the cluster yields results analogous to those of a well-known reference photosensitizer, although more effectively. Comprehensive kinetic analysis provided important insights into the mechanism and driving-force dependence of the quenching of 1O2 by gold nanoclusters. Understanding on a molecular basis why these molecules may perform so well in 1O2 photosensitization is instrumental to controlling their performance.Atomically precise Au24M(SR)18 clusters were used as singlet-oxygen photosensitizers. Comprehensive kinetic analysis provided insights into the mechanism and driving-force dependence of the quenching of 1O2 by gold nanoclusters. 相似文献
125.
Bitan G Tarus B Vollers SS Lashuel HA Condron MM Straub JE Teplow DB 《Journal of the American Chemical Society》2003,125(50):15359-15365
Aberrant protein oligomerization is an important pathogenetic process in vivo. In Alzheimer's disease (AD), the amyloid beta-protein (Abeta) forms neurotoxic oligomers. The predominant in vivo Abeta alloforms, Abeta40 and Abeta42, have distinct oligomerization pathways. Abeta42 monomers oligomerize into pentamer/hexamer units (paranuclei) which self-associate to form larger oligomers. Abeta40 does not form these paranuclei, a fact which may explain the particularly strong linkage of Abeta42 with AD. Here, we sought to determine the structural elements controlling paranucleus formation as a first step toward the development of strategies for treating AD. Because oxidation of Met(35) is associated with altered Abeta assembly, we examined the role of Met(35) in controlling Abeta oligomerization. Oxidation of Met(35) in Abeta42 blocked paranucleus formation and produced oligomers indistinguishable in size and morphology from those produced by Abeta40. Systematic structural alterations of the C(gamma)(35)-substituent group revealed that its electronic nature, rather than its size (van der Waals volume), was the factor controlling oligomerization pathway choice. Preventing assembly of toxic Abeta42 paranuclei through selective oxidation of Met(35) thus represents a potential therapeutic approach for AD. 相似文献
126.
Agnese Abate Elisabetta Brenna Giovanni Fronza Claudio Fuganti Sabrina Ronzani Stefano Serra 《Helvetica chimica acta》2003,86(3):592-606
The enantiomerically enriched diastereoisomers of the chiral 1,3‐dioxane odorants Floropal® ( 1 ) and Magnolan® ( 2 ) were prepared by an enzyme‐mediated approach. Their olfactory properties were evaluated to investigate differences in the odor perception for the stereoisomers. 相似文献
127.
Erich Kleinpeter Sabrina Klod Mária Šamaliková Zora Šusteková 《Journal of Molecular Structure》2003,645(1):17-27
The characteristic vibrations (νCO and νCC) of a large number of hydantoin derivatives are reported. Especially the very fine correlations νCO(sym) versus νCO(asym) (r2=0.985) but also successful correlations of the vibration wave numbers to HAMMETT's substituent constants and some other experimental parameters (pKs, OxPot, RedPot) as well, corroborate reassignments of previously obtained results [Monatsh. Chem. 92 (1961) 361] and prove the doublet obtained in the region of the CO stretching vibrations to be the symmetrical and anti-symmetrical vibrational modes of a mechanically coupled system of two quasi-symmetrical CO bonds. 相似文献
128.
A practical approach to assessment of sampling uncertainty 总被引:1,自引:0,他引:1
Paolo de Zorzi Maria Belli Sabrina Barbizzi Sandro Menegon Andrea Deluisa 《Accreditation and quality assurance》2002,7(5):182-188
The paper reports the approach followed in the SOILSAMP project, funded by the National Environmental Protection Agency (ANPA)of
Italy. SOILSAMP is aimed at assessing uncertainties associated with soil sampling in agricultural, semi-natural, urban, and
industrial environments. The uncertainty assessment is based on a bottom-up approach, according to the Guide to the Expression
of Uncertainty in Measurement published by the International Organization for Standardization (ISO). A designated agricultural
area, which has been characterized in terms of elemental spatial distribution, will be used in future as a reference site
for soil sampling intercomparison exercises.
Received: 19 November 2001 Accepted: 6 January 2002 相似文献
129.
Dipl.-Ing. Sabrina D. Püschmann Philipp Frühwirt Michael Pillinger Andreas Knöchl Marlene Mikusch Dr. Judith Radebner Dr. Ana Torvisco Prof. Roland C. Fischer Prof. Norbert Moszner Prof. Dr. Georg Gescheidt Dr. Michael Haas 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(10):3338-3347
Tetraacylgermanes are known as highly efficient photoinitiators. Herein, the synthesis of mixed tetraacylgermanes 4 a – c and 6 a – e with a nonsymmetric substitution pattern is presented. Germenolates are crucial intermediates of these new synthetic protocols. The synthesized compounds show increased solubility compared with symmetrically substituted tetraacylgermanes 1 a – d . Moreover, these mixed derivatives reveal broadened n–π* absorption bands, which enhance their photoactivity. Higher absorption of these new compounds at wavelengths above 450 nm causes efficient photobleaching when using an LED emitting at 470 nm. The quantum yields are in the range of 0.15–0.57, depending on the nature of the aroyl substituents. On the basis of these properties, mixed-functionalized tetraacylgermanes serve as ideal photoinitiators in various applications, especially in those requiring high penetration depth. The synthesized compounds were characterized by elemental analysis, IR spectroscopy, NMR and CIDNP spectroscopy, UV/Vis spectroscopy, photolysis experiments, and X-ray crystallography. The CIDNP data suggest that the germyl radicals generated from the new tetraacylgermanes preferentially add to the tail of the monomer butyl acrylate. In the case of 6 a – e only the mesitoyl groups are cleaved off, whereas for 4 a – c both the mesitoyl and the aroyl group are subject to α-cleavage. 相似文献
130.
Sabrina M. Nobre Mauro N. Muniz Marcus Seferin Wagner M. da Silva Adriano L. Monteiro 《应用有机金属化学》2011,25(4):289-293
We have developed a sequential and selective Pd‐catalyzed double‐Heck arylation of ethylene that results in non‐symmetrical nitro‐stilbene analogs of trans‐resveratrol at excellent yields. A catalytic system consisting of Pd(OAc)2 and P(o‐tolyl)3 permitted us to carry out the two consecutive Heck arylations without losing activity from the first to the second Heck reaction. After the first Heck arylation of ethylene, no isolation or additional catalyst loading is required for the second Heck arylation reaction. This protocol was applied to the synthesis of methylated trans‐resveratrol, which was obtained at a 65% overall yield. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献