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121.
We present a novel quantum-dynamics approach suitable for computing direct dissociation processes, including electronic transitions. This approach combines quantum trajectories in the Lagrangian reference frame with standard fixed-grid wave packets in order to overcome the limitations and difficulties of both techniques. As a model application, we consider the ultrafast photodissociation of H2 excited by a femtosecond extreme UV laser pulse. 相似文献
122.
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
123.
Alberto Fernández Jesús J. Fernández Margarita López-Torres José M. Vila 《Journal of organometallic chemistry》2005,690(16):3669-3679
Reaction of the ligand C6H5N(H)NCMe(C5H4N) (a) with palladium(II) acetate in toluene gave the mononuclear cyclometallated complex [Pd{C6H4N(H)NCMe(C5H4N)}(AcO)] (1a). Reaction of 1a with sodium chloride gave the analogous chlorine compound [Pd{C6H4N(H)NCMe(C5H4N)}(Cl)] (3a) which could also be prepared by reaction of a with lithium tetrachloropalladate and sodium acetate in methanol for 48 h; whereas shorter reaction times afforded the non-cyclometallated complex [Pd{C6H5N(H)NCMe(C5H4N)}(Cl)2] (2a). Reaction of the ligand 2-ClC6H4N(H)NCMe(C5H4N) · HCl (b), with palladium(II) acetate, or with lithium tetrachloropalladate and sodium acetate, yielded the cyclometallated complex [Pd2-ClC6H3N(H)NCMe(C5H4N)(Cl)] (1b). Treatment of 3a and 1b with silver trifluoromethanesulphonate (triflate) and triphenylphosphine in acetone gave the mononuclear complexes [Pd{2-RC6HnN(H)NCMe(C5H4N)}(PPh3)][CF3SO3], (R = H, n = 4, 4a; R = Cl, n = 3, 2b) with the ligand as C,N,N′ terdentate and substitution of chlorine by triphenylphosphine. Reaction of 3a and 1b with silver triflate and the tertiary diphosphine Ph2P(CH2)4PPh2 (dppb) in a 2:1 molar ratio gave the dinuclear cyclometallated complexes [{Pd[2-RC6H3N(H)NCMe(C5H4N)]}2(μ-Ph2P(CH2)4PPh2)][CF3SO3]2 (R = H, 5a; R = Cl, 3b) with a μ2-diphosphine bridging ligand. Similarly, treatment of 3a and 1b with silver triflate and the tertiary triphosphines MeC(CH2PPh2)3 (tripod) and (Ph2PCH2CH2)2PPh (triphos), in 3:1 molar ratio, gave the novel trinuclear complexes [{Pd[C6H4N(H)NCMe(C5H4N)]}3{μ3-MeC(CH2Ph2)3}][CF3SO3]3 (6a) and [{Pd[2-ClC6H3N(H)NCMe(C5H4N)]}3{μ3-(PPh2CH2CH2)2PPh}][CF3SO3] 3 (4b) regioselectively, with the phosphine as a μ3-bridging ligand. When the reaction between 3a and triphos was carried out in 1:1 molar ratio the mononuclear complex [Pd{C6H4N(H)NCMe(C5H4N)}{(PPh2CH2CH2)2PPh-P,P,P}][ClO4] (7a) was obtained. The crystal structures of 2b, 3a and 4a have been determined by X-ray crystallography. 相似文献
124.
Alberto Plaza Ciro Balestrieri Giuseppe Bifulco Arafa Hamed Sonia Piacente 《Tetrahedron》2005,61(31):7470-7480
Eight new 14,15-secopregnane glycosides, namely argelosides C-J, possessing two ketal functions involved in three five-membered rings, have been isolated from the hairy seeds of Solenostemma argel. Their structures have been established by MS and NMR experiments, combined with quantum mechanical calculations of the 13C chemical shifts for the interpretation of the experimental data. On the basis of the obtained results, the structures of argelosides A and B have been revised. Additionally, the effect of these compounds on the VEGF-induced in Kaposi's sarcoma cell proliferation was evaluated. Results indicated that all the compounds reduced the cell proliferation in a dose-dependent manner. 相似文献
125.
126.
Otón F Tárraga A Velasco MD Molina P 《Dalton transactions (Cambridge, England : 2003)》2005,(7):1159-1161
A ferrocene-based heteroditopic receptor containing urea and crown ether units shows electrochemical responses to dihydrogenphosphate and fluoride anions. K+ cations can only be detected in the presence of dihydrogenphosphate. 相似文献
127.
Lancelot N Elbayed K Raya J Piotto M Briand JP Formaggio F Toniolo C Bianco A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(6):1317-1323
A tetra- and a hepta-homopeptide from the C(alpha)-tetrasubstituted Aib (alpha-aminoisobutyric acid) residue were covalently linked to the POEPOP resin by the fragment-condensation approach. The conformational preferences of the two model peptides were determined for the first time on a solid support by means of high-resolution magic angle spinning NMR spectroscopy. The results obtained indicate that the Aib homopeptides adopt a regular 3(10)-helical structure even when they are covalently bound to a polymeric matrix, and thus confirm the remarkable conformational stability of the peptides rich in this amino acid. An ATR-FTIR spectroscopic investigation, performed in parallel, also confirmed that these polymer-bound peptides do indeed adopt a helical conformation. The results of this study open the possibility to exploit the peptide-resin conjugates based on C(alpha)-tetrasubstituted alpha-amino acids as helpful, structurally organized templates in molecular recognition studies or as catalysts in asymmetric synthesis. 相似文献
128.
Jos R. Ascenso Maria de Deus Carvalho Alberto R. Dias Carlos C. Romo Maria J. Calhorda Luis F. Veiros 《Journal of organometallic chemistry》1994,470(1-2):147-152
The metallocene thioether derivatives [Cp2M(MeSCH2CH2SMe)][PF6]2 (1, M = MO; 2, M = W), [Cp2Mo(SCH2CH2SMe)][PF6] (3) and [Cp2M(SCH2CH2S)] (4, M = Mo; 5, M = W) exhibit temperature-dependent fluxional behavior in solution, owing to the pyramidal sulfur inversion process. The activation energies for this process were determined from proton band-shape analysis in the cases of 1 (54.9 ± 2 kJ mol−1), 2 (51.2 ± 4.6 kJ mol−1) and 3 (30.0 ± 3.1 kJ mol−1). Extended Hückel calculations on related model complexes suggest that local inversion at the sulfur atoms, rather that an inversion of the complete S---C---C---S chain, is responsible for the observed fluxional behaviour. 相似文献
129.
Reactions of ligands 2-vinylpyridine 1, 4-vinylpyridine 2, 2-allylpyridine 3, 1-allylpyrazole 4, acrylonitrile 5 and allylcyanide 6 with the metallocene derivatives [Mo(η5-C5H5)2H3][PF6] 7, [Mo(η5-C5H5)2HI] 8, [W(η5-C5H5)2H3] [PF6] 9, [Mo(η5-C5H5)2H2] 10, [M(η5-C5H5)2Br2], M = Mo 11, M = W 12 are described. Reaction of 7 with 1, 8 with 1, 3 with 8 and 4 with 8 gave mixtures of metallocyle isomers resulting from coordination of the nitrogen atom to molybdenum followed by internal hydrometallation; reaction of 11 with 1 gave an olefinic π complex; reaction of either 9 or 11 with 1 gave intractable oils; reactions of 8 with 2, 11 with 5, 12 with 5, 11 with 6 and 12 with 6 yielded monosubstituted products in which the ligand is N-coordinated. 相似文献
130.
Domenici V Geppi M Veracini CA Zakharov AV 《The journal of physical chemistry. B》2005,109(39):18369-18377
In this work, the rotational-diffusion coefficients D(parallel) and D(perpendicular) for the ferroelectric smectogen (+)-(S)-4-[4'-(1-methylheptyloxy)] biphenyl 4-(10-undecenyloxy)benzoate have been studied by means of 2H NMR spectroscopy in the smectic C phase, using a new theoretical approach (Domenici,V.; Geppi, M.; Veracini, C. A. Chem. Phys. Lett. 2003, 382, 518). The analysis of spin-lattice relaxation times has been performed in terms of the diffusional constant and the activation energy of the internal and overall molecular-reorientational motions, and the results are compared to the smectic A (SmA) phase. Moreover, from the 2H NMR data in the SmA phase, the dielectric permittivity and the dielectric relaxation time functions are investigated using a theoretical approach. The longitudinal and transverse components of the real Rchigammaomega and imaginary chigammaomega (gamma = parallel, perpendicular) parts of the complex susceptibility tensor and the nematic-like rotational-viscosity coefficients, lambda2 and lambda5, are calculated. 相似文献