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31.
Indira Fabre Niklas von Wolff Dr. Gaëtan Le Duc Dr. Emmanuel Ferrer Flegeau Dr. Christian Bruneau Prof. Pierre H. Dixneuf Dr. Anny Jutand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(23):7595-7604
The activation of the C? H bond of 1‐phenylpyrazole ( 2 ) and 2‐phenyl‐2‐oxazoline ( 3 ) by [Ru(OAc)2(p‐cymene)] is an autocatalytic process catalyzed by the co‐product HOAc. The reactions are indeed faster in the presence of acetic acid and water but slower in the presence of a base K2CO3. A reactivity order is established in the absence of additives: 2‐phenylpyridine>2‐phenyl‐2‐oxazoline>1‐phenylpyrazole (at RT). The accelerating effect of added acetate ions reveals an intermolecular deprotonation after C? H bond activation by a cationic RuII center (SE3 mechanism). The reactions of 1‐phenylpyrazole and 2‐phenyl‐2‐oxazoline first lead to the neutral cyclometalated complexes A2 and A3 ligated by one acetate. The latter dissociate to the cationic complexes B2 + and B3 + , respectively, and acetate. A slow incorporation of one or two D atoms into 2 , 3 , and 2‐phenylpyridine ( 1 ) was observed in the presence of deuterated acetic acid. The “reversibility” of the C? H bond activation/deprotonation takes place from the cationic complexes B n + (n=1–3). They are also involved in oxidative additions to PhI, which are rate‐determining and lead to the mono‐ and bis‐phenylated products at high temperatures. A general mechanism is proposed for the arylation of arenes 1–3 catalyzed by [Ru(OAc)2(p‐cymene)]. In contrast, the reaction of Pd(OAc)2 with 2‐phenylpyridine ( 1 ), is much faster: Pd(OAc)2>[Ru(OAc)2(p‐cymene)]. Since the kinetics is not affected by added acetates, the reaction proceeds through a CMD mechanism assisted by a ligated acetate (intramolecular process) and is irreversible. A bis‐cyclometalated PdII^PdII dimer D′1 is formed whose bielectronic electrochemical oxidation leads to a [PdIII^PdIII]2+ dimer, in agreement with the result of a reported chemical oxidation used in arene functionalizations catalyzed by Pd(OAc)2. 相似文献
32.
Anny Leudjo Taka Elvis Fosso-Kankeu Xavier Yangkou Mbianda Michael Klink Eliazer Bobby Naidoo 《Molecules (Basel, Switzerland)》2021,26(13)
A multifunctional nanobiocomposite polymer was developed in this study through a cross-linking polymerization of cyclodextrin with phosphorylated multi-walled carbon nanotubes followed by sol-gel to incorporate TiO2 and Ag nanoparticles. This work’s novelty was to prove that the developed nanobiocomposite polymer is a potential filter nanosponge capable of removing organic, inorganic, and microorganisms’ pollutants from wastewater samples. The synthesized multifunctional nanobiocomposite polymer was characterized using a range of spectroscopy and electron microscopy techniques. Fourier-transform infrared (FTIR) confirmed the presence of oxygen-containing groups on the developed nanobiocomposite polymer and carbamate linkage (NH(CO)) distinctive peak at around 1645 cm−1, which is evidence that the polymerization reaction was successful. The scanning electron microscopy (SEM) image shows that the developed nanobiocomposite polymer has a rough surface. The Dubinin–Radushkevich and the pseudo-second-order kinetic models best described the adsorption mechanism of Co2+ and TCE’s onto pMWCNT/CD/TiO2-Ag. The efficacy of the developed nanobiocomposite polymer to act as disinfectant material in an environmental media (e.g., sewage wastewater sample) compared to the enriched media (e.g., nutrient Muller Hinton broth) was investigated. From the results obtained, in an environmental media, pMWCNT/CD/TiO2-Ag nanobiocomposite polymer can alter the bacteria’s metabolic process by inhibiting the growth and killing the bacteria, whereas, in enriched media, the bacteria’s growth was retarded. 相似文献
33.
The mechanism of the reaction of trans-[ArPdX(PPh(3))(2)] (Ar=p-Z-C(6)H(4); Z=CN, F, H; X=I, Br, Cl) with Ar'B(OH)(2) (Ar'=p-Z'-C(6)H(4); Z'=CN, H, OMe) has been established in DMF in the presence of the base OH(-) in the context of real palladium-catalyzed Suzuki-Miyaura reactions. The formation of the cross-coupling product ArAr' and [Pd(0)(PPh(3))(3)] has been followed through the application of electrochemical techniques. Kinetic data have been obtained for the first time, with determination of the observed rate constant, k(obs), of the overall reaction. trans-[ArPdX(PPh(3))(2)] is not reactive in the absence of the base. The base OH(-) plays three roles. It favors the reaction: 1) by formation of trans-[ArPd(OH)(PPh(3))(2)], a key complex which, in contrast to trans-[ArPdX(PPh(3))(2)], reacts with Ar'B(OH)(2) (rate-determining transmetalation), and 2) by unexpected promotion of the reductive elimination from the intermediate trans-[ArPdAr'(PPh(3))(2)], which generates ArAr' and a Pd(0) species. Conversely, the base OH(-) disfavors the reaction by formation of the unreactive anionic Ar'B(OH)(3)(-). As a consequence of these antagonistic effects of OH(-), the overall reactivity is controlled by the concentration of OH(-) and passes through a maximum as the concentration of OH(-) is increased. Therefore, the base favors the rate-determining transmetalation and unexpectedly also the reductive elimination. 相似文献
34.
Julien Henri Laetitia Minder Kevin Mohanasundaram Sbastien Dilly Anne Goupil-Lamy Carmelo Di Primo Anny Slama Schwok 《Molecules (Basel, Switzerland)》2022,27(22)
This work identifies new ligands of the nucleoprotein N of SARS-CoV-2 by in silico screening, which used a new model of N, built from an Alphafold model refined by molecular dynamic simulations. The ligands were neuropeptides, such as substance P (1-7) and enkephalin, bound at a large site of the C-terminal or associated with the N-terminal β−sheet. The BA4 and BA5 Omicron variants of N also exhibited a large site as in wt N, and an increased flexibility of the BA5 variant, enabling substance P binding. The binding sites of some ligands deduced from modeling in wt N were assessed by mutation studies in surface plasmon resonance experiments. Dynamic light scattering showed that the ligands impeded RNA binding to N, which likely inhibited replication. We suggest that the physiological role of these neuropeptides in neurotransmission, pain and vasodilation for cholecystokinin and substance P could be altered by binding to N. We speculate that N may link between viral replication and multiple pathways leading to long COVID-19 symptoms. Therefore, N may constitute a “danger hub” that needs to be inhibited, even at high cost for the host. Antivirals targeted to N may therefore reduce the risk of brain fog and stroke, and improve patients’ health. 相似文献
35.
Daniel B. Yarosh Jeannie Kibitel Stephen E. Ullrich Tae-Heung Kim Honnavara N. Ananthaswamy Paul Krien Anny Fourtanier Margaret L. Kripke 《Photochemistry and photobiology》1999,69(5):571-574
Exposure to sunlight can result in a number of harmful effects, including sunburn, erythema, premature aging of the skin, immune suppression and skin cancer. Studies designed to understand the underlying mechanisms often depend upon the use of artificial sources of UV radiation. Unfortunately, conclusions from different laboratories using different lamps often conflict, and it is entirely possible that the different spectra of sunlights used in each may be a source of conflict. To minimize confounding variables, we employed two of the more commonly used UV light sources, fluorescent sunlamps, such as the FS-40 and Kodacel-filtered FS-40 sunlamps, and a xenon arc solar simulator and compared, in one series of standardized experiments, the effects of each light source on DNA damage, urocanic acid isomerization and edema formation. The dose-response curves, calculated by linear regression or curve fitting were compared. The data indicate that DNA damage and urocanic acid isomerization were more sensitive to shorter wavelengths of UV than longer wavelengths, and the biological endpoint of edema most closely correlated with the induction of DNA damage. The results emphasize the dominance of shorter wavelengths within the UV spectrum in damaging biological tissues, even when the solar simulator, which contains significant amounts of UVA, was used and demonstrate that each light source has a characteristic pattern of induction of biochemical and biological endpoints. 相似文献
36.
Dr. Simon Wagschal Dr. Luca Alessandro Perego Alexandre Simon Aida Franco-Espejo Chanelle Tocqueville Dr. Jennifer Albaneze-Walker Dr. Anny Jutand Dr. Laurence Grimaud 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(28):6980-6987
Understanding the nature of the intermediate species operating within a palladium catalytic cycle is crucial for developing efficient cross-coupling reactions. Even though the XPhos/Pd(OAc)2 catalytic system has found numerous applications, the nature of the active catalytic species remains elusive. A Pd0 complex ligated to XPhos has been detected and characterized in situ for the first time using cyclic voltammetry and NMR techniques. In the presence of XPhos, Pd(OAc)2 initially associates with the ligand to form a complex in solution, which has been characterized as PdII(OAc)2(XPhos). This PdII center is then reduced to the Pd0(XPhos)2 species by an intramolecular process. This study also sheds light on the formation of PdI–PdI dimers. Finally, a kinetic study probes a dissociative mechanism for the oxidative addition with aryl halides involving Pd0(XPhos) as the reactive species in equilibrium with the unreactive Pd0(XPhos)2. Remarkably, the reportedly poorly reactive PhCl reacts at room temperature in the oxidative addition, which confirms the crucial role of the XPhos ligand in the activation of aryl chlorides. 相似文献
37.
Verbeeck S Meyers C Franck P Jutand A Maes BU 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(43):12831-12837
Halide anions can increase or decrease the transmetallation rate of the Stille reaction through in situ halide metathesis. Although the influence of the halogen present in oxidative addition complexes on the transmetallation rate with organostannanes was already known, the application of in situ halide metathesis to accelerate cross-coupling reactions with organometallic reagents is not described in the literature yet. In addition a second unprecedented role of halides was discovered. Halide anions stabilize the [Pd(0)(L)(2)] catalyst in Stille reactions, by means of [Pd(0)X(L)(2)](-) formation (X=Cl, I), hereby preventing its leaching from the catalytic cycle. Both arene (iodobenzene) and azaheteroarene (2-halopyridine, halopyrazine, 2-halopyrimidine) substrates were used. 相似文献
38.
Adamo C Amatore C Ciofini I Jutand A Lakmini H 《Journal of the American Chemical Society》2006,128(21):6829-6836
The mechanism of the palladium-catalyzed homocoupling of arylboronic acids ArB(OH)(2) (Ar = 4-Z-C(6)H(4) with Z = MeO, H, CN) in the presence of dioxygen, leading to symmetrical biaryls, has been fully elucidated. The peroxo complex (eta(2)-O(2))PdL(2) (L = PPh(3)), generated in the reaction of dioxygen with the Pd(0) catalyst, was found to play a crucial role. Indeed, it reacts with the arylboronic acid to generate an adduct (coordination of one oxygen atom of the peroxo complex to the oxophilic boron atom of the arylboronic acid) characterized by (31)P NMR spectroscopy and ab initio calculations. This adduct reacts with a second molecule of arylboronic acid to generate trans-ArPd(OH)L(2) complexes. A transmetalation by the arylboronic acid gives trans-ArPdArL(2) complexes. The biaryl is then released in a reductive elimination. This reaction is at the origin of the formation of biaryls as byproducts in palladium-catalyzed Suzuki-Miyaura reactions when they are not conducted under oxygen-free atmosphere. 相似文献
39.
Activation of Aryl and Heteroaryl Halides by an Iron(I) Complex Generated in the Reduction of [Fe(acac)3] by PhMgBr: Electron Transfer versus Oxidative Addition 下载免费PDF全文
Dr. Guillaume Lefèvre Dr. Anny Jutand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(16):4796-4805
The mechanism of the reactions of aryl/heteroaryl halides with aryl Grignard reagents catalyzed by [FeIII(acac)3] (acac=acetylacetonate) has been investigated. It is shown that in the presence of excess PhMgBr, [FeIII(acac)3] affords two reduced complexes: [PhFeII(acac)(thf)n] (n=1 or 2) (characterized by 1H NMR and cyclic voltammetry) and [PhFeI(acac)(thf)]? (characterized by cyclic voltammetry, 1H NMR, EPR and DFT). Whereas [PhFeII(acac)(thf)n] does not react with any of the investigated aryl or heteroaryl halides, the FeI complex [PhFeI(acac)(thf)]? reacts with ArX (Ar=Ph, 4‐tolyl; X=I, Br) through an inner‐sphere monoelectronic reduction (promoted by halogen bonding) to afford the corresponding arene ArH together with the Grignard homocoupling product PhPh. In contrast, [PhFeI(acac)(thf)]? reacts with a heteroaryl chloride (2‐chloropyridine) to afford the cross‐coupling product (2‐phenylpyridine) through an oxidative addition/reductive elimination sequence. The mechanism of the reaction of [PhFeI(acac)(thf)]? with the aryl and heteroaryl halides has been explored on the basis of DFT calculations. 相似文献
40.