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51.
Campbell R Carrella LM Clegg W Mulvey RE Rentschler E Robertson SD Russo L 《Inorganic chemistry》2011,50(10):4656-4659
One of the milestone structures in the development of transition-metal complexes with metal-metal bonds of multiple bond order was the lithium methylchromate dimer Me(8)Cr(2)[Li(donor)](4) (donor = THF or Et(2)O). Using a simple salt metathesis reaction mixing this compound with sodium tert-butoxide, the sodium congener Me(8)Cr(2)[Na(OEt(2))](4) has been synthesized as a green crystalline compound and isolated in 51% yield. Its solid-state structure was determined by single-crystal X-ray diffraction. Exhibiting exact crystallographic C(4h) symmetry, this heavier alkali-metal chromate structure is also dimeric, formally comprising a (Me(8)Cr(4))(4-) tetranionic core with four peripheral Na(+) cations carrying supporting ether ligands. Its salient feature is the long Cr···Cr distance of 3.263(2) ?, which is remarkably elongated compared to that in the lithium THF-solvated congener [1.968(2) ?]. With respect to the methyl C atoms, the Cr coordination is distorted-square-planar. Each Na(+) interacts with four methyl C atoms, and there are also some short Na···H(C) contacts. Unlike for lithium chromate, no NMR spectroscopic data could be obtained for sodium chromate. The paramagnetic character of sodium chromate was confirmed by variable-temperature magnetization measurements, which indicated antiferromagnetic behavior. 相似文献
52.
Qiang Liu Hubert Meissel Ilia Sadykov Simon Jones Nick Van Dijk Przemyslaw Rzepka Luca Artiglia Marco Ranocchiari Jeroen A. van Bokhoven 《Helvetica chimica acta》2021,104(7):e2100082
Stability studies on supported metal nanoparticles are essential for gaining insight into the design and optimization of high-performance materials. In this work, the dissolutions of Pt-based catalysts in HBr/Br2 mixture of various concentration regimes were studied and correlated with material structural properties. The dissolution of metal nanoparticles was enhanced by adding Br2 to the HBr solution. Comparing with commercial Pt/C catalyst, the well-alloyed PtIr/C catalyst was observed to exhibit high resistance towards dissolution. In addition, regulating the accessibility of the metal sites to dissolution-inducing species contributed to the marked stability of the nanoparticles in HBr/Br2 solutions, as shown for the surface-modified PtIr/C catalysts with organic diamine molecules. 相似文献
53.
A one-pot synthesis of poly-substituted tetramic acids and of their six-membered ring analogs have been obtained in one step by reaction of N-Boc dipeptides, activated as their O-succinimidyl esters (Boc-AA-AA-OSu), with the sodium anion of dibenzyl malonate. The adducts spontaneously cyclize to form five or six-member rings. To check whether this class of compounds may be used to promote reverse-turn conformations, one adduct was further derivatized. The formation of a hydrogen bond between the NH–Boc and the carbonyl at C2 of the heterocycle is highlighted, upon analysis of the product by IR, 1H NMR, and MD techniques, thus suggesting that these compounds are good candidates to promote reverse-turn conformations or other secondary structures and may be used for the formation of new foldamers. 相似文献
54.
Amorati R Ferroni F Lucarini M Pedulli GF Valgimigli L 《The Journal of organic chemistry》2002,67(26):9295-9303
A systematic investigation is reported on the regeneration of alpha-tocopherol (alpha-TOH) in homogeneous solution by coantioxidants in order to better understand the mechanism and the factors responsible for the effectiveness of this process. The current availability of thermochemical data concerning the reactants involved in the regeneration reactions, as well as a large number of the kinetic constants for the various reactions involved, allowed us to rationalize the experimental observations collected so far. Three limiting cases have been considered. The first case is that of a coantioxidant irreversibly regenerating alpha-TOH, where the effectiveness of the recycling process depends on the magnitude of the rate constant k(r). The second case is that of a coantioxidant reversibly recycling alpha-TOH, where regeneration can only be observed if the bond dissociation enthalpy value of the coantioxidant is lower or at least close to that of the O-H bond of alpha-tocopherol. The third case is that of a catechol derivative (chosen as a model compound for polyphenolic antioxidants), where recycling of alpha-TOH is feasible even though the BDE value is significantly higher than that of vitamin E. In this case, the driving force for the recycling process is the removal of the semiquinone radical from the catechol derivative by the alpha-tocopheroxyl radical, which makes the regeneration of alpha-TOH practically irreversible. 相似文献
55.
Luca Beverina Dr. 《Chemphyschem》2010,11(10):2075-2077
56.
Dr. Daniele Paderni Dr. Eleonora Macedi Dr. Larisa Lvova Dr. Gianluca Ambrosi Prof. Mauro Formica Prof. Luca Giorgi Prof. Roberto Paolesse Prof. Vieri Fusi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(49):e202201062
A new series of ligands containing the 2-(2-hydroxy-3- naphthyl)-4-methylbenzoxazole (HNBO) fluorophore showed selectivity for Mg2+ ions, without the interference of Ca2+. The most promising representative L3 resulted the best performing sensor for Mg2+ both in solution and embedded in an all-solid-state optode, especially towards real samples of drinkable water. 相似文献
57.
A Stable Porphyrin Functionalized Graphite Electrode Used at the Oxygen Evolution Reaction Potential
Gianlorenzo Bussetti Roberto Bernasconi Claudia Filoni Luca Magagnin Alberto Bossi Franco Ciccacci Lamberto Duò 《Electroanalysis》2022,34(7):1227-1236
Many researches have been devoted to rechargeable power generators that can store (but also release) energy. This availability is ensured through (e. g.) the oxygen evolution reaction (OER). However, (i) large values of the overpotentials and (ii) a progressive detriment of the anode (graphite) electrode limit the ultimate device. In view of enhancing the electrode performances, graphite was protected by following different strategies, which oblige to follow precise preparation protocols. Here, we prove that a thin layer of free-base porphyrin molecules is able to protect the underneath graphite electrode from detriment even if many (about 100) electrochemical cycles are performed. 相似文献
58.
The formation of a line of equally spaced particles at the centerline of a microchannel, referred as “particle ordering,” is desired in several microfluidic applications. Recent experiments and simulations highlighted the capability of viscoelastic fluids to form a row of particles characterized by a preferential spacing. When dealing with non-Newtonian fluids in microfluidics, the adherence condition of the liquid at the channel wall may be violated and the liquid can slip over the surface, possibly affecting the ordering efficiency. In this work, we investigate the effect of wall slip on the ordering of particles suspended in a viscoelastic liquid by numerical simulations. The dynamics of a triplet of particles in an infinite cylindrical channel is first addressed by solving the fluid and particle governing equations. The relative velocities computed for the three-particle system are used to predict the dynamics of a train of particles flowing in a long microchannel. The distributions of the interparticle spacing evaluated at different slip coefficients, linear particle concentrations, and distances from the channel inlet show that wall slip slows down the self-assembly mechanism. For strong slipping surfaces, no significant change of the initial microstructure is observed at low particle concentrations, whereas strings of particles in contact form at higher concentrations. The detrimental effect of wall slip on viscoelastic ordering suggests care when designing microdevices, especially in case of hydrophobic surfaces that may enhance the slipping phenomenon. 相似文献
59.
Marcos Juanes Rizalina Tama Saragi Cristbal Prez Luca Evangelisti Lourdes Enríquez Martín Jaraíz Alberto Lesarri 《Molecules (Basel, Switzerland)》2022,27(8)
Weakly-bound intermolecular clusters constitute reductionist physical models for non-covalent interactions. Here we report the observation of the monomer, the dimer and the monohydrate of 2-adamantanol, a secondary alcohol with a bulky ten-carbon aliphatic skeleton. The molecular species were generated in a supersonic jet expansion and characterized using broadband chirped-pulse microwave spectroscopy in the 2–8 GHz frequency region. Two different gauche-gauche O-H···O hydrogen-bonded isomers were observed for the dimer of 2-adamantanol, while a single isomer was observed for the monomer and the monohydrate. The experimental rotational parameters were compared with molecular orbital calculations using density functional theory (B3LYP-D3(BJ), B2PLYP-D3(BJ), CAM-B3LYP-D3(BJ), ωB97XD), additionally providing energetic and electron density characterization. The shallow potential energy surface makes the dimer an interesting case study to benchmark dispersion-corrected computational methods and conformational search procedures. 相似文献
60.
Ana Cristina Gmez-Herrero Carlos Snchez-Snchez Frdric Chrioux Jose Ignacio Martínez Jos Abad Luca Floreano Alberto Verdini Albano Cossaro Estelle Mazaleyrat Valrie Guisset Philippe David Simone Lisi Jos Angel Martín Gago Johann Coraux 《Chemical science》2021,12(6):2257
Catechols are ubiquitous substances often acting as antioxidants, thus of importance in a variety of biological processes. The Fenton and Haber–Weiss processes are thought to transform these molecules into aggressive reactive oxygen species (ROS), a source of oxidative stress and possibly inducing degenerative diseases. Here, using model conditions (ultrahigh vacuum and single crystals), we unveil another process capable of converting catechols into ROSs, namely an intramolecular redox reaction catalysed by a Cu surface. We focus on a tri-catechol, the hexahydroxytriphenylene molecule, and show that this antioxidant is thereby transformed into a semiquinone, as an intermediate product, and then into an even stronger oxidant, a quinone, as final product. We argue that the transformations occur via two intramolecular redox reactions: since the Cu surface cannot oxidise the molecules, the starting catechol and the semiquinone forms each are, at the same time, self-oxidised and self-reduced. Thanks to these reactions, the quinone and semiquinone are able to interact with the substrate by readily accepting electrons donated by the substrate. Our combined experimental surface science and ab initio analysis highlights the key role played by metal nanoparticles in the development of degenerative diseases.An antioxidant catechol transforms following intramolecular redox reactions into highly reactive oxygen species, a semiquinone and a quinone, on copper. 相似文献