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1.
Dr. Gabriel Menendez Rodriguez Dr. Francesco Zaccaria Leonardo Tensi Prof. Cristiano Zuccaccia Prof. Paola Belanzoni Prof. Alceo Macchioni 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(6):2050-2064
The degradation pathways of highly active [Cp*Ir(κ2-N,N-R-pica)Cl] catalysts (pica=picolinamidate; 1 R=H, 2 R=Me) for formic acid (FA) dehydrogenation were investigated by NMR spectroscopy and DFT calculations. Under acidic conditions (1 equiv. of HNO3), 2 undergoes partial protonation of the amide moiety, inducing rapid κ2-N,N to κ2-N,O ligand isomerization. Consistently, DFT modeling on the simpler complex 1 showed that the κ2-N,N key intermediate of FA dehydrogenation ( INH ), bearing a N-protonated pica, can easily transform into the κ2-N,O analogue ( INH2 ; ΔG≠≈11 kcal mol−1, ΔG ≈−5 kcal mol−1). Intramolecular hydrogen liberation from INH2 is predicted to be rather prohibitive (ΔG≠≈26 kcal mol−1, ΔG≈23 kcal mol−1), indicating that FA dehydrogenation should involve mostly κ2-N,N intermediates, at least at relatively high pH. Under FA dehydrogenation conditions, 2 was progressively consumed, and the vast majority of the Ir centers (58 %) were eventually found in the form of Cp*-complexes with a pyridine-amine ligand. This likely derived from hydrogenation of the pyridine-carboxiamide via a hemiaminal intermediate, which could also be detected. Clear evidence for ligand hydrogenation being the main degradation pathway also for 1 was obtained, as further confirmed by spectroscopic and catalytic tests on the independently synthesized degradation product 1 c . DFT calculations confirmed that this side reaction is kinetically and thermodynamically accessible. 相似文献
2.
M. Cristelli V. Alfi L. Pietronero A. Zaccaria 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,73(1):41-49
We introduce a microscopic model for the dynamics of the order book to study how the lack of liquidity influences price fluctuations. We use the average density of the stored orders (granularity g) as a proxy for liquidity. This leads to a Price Impact Surface which depends on both volume ω and g. The dependence on the volume (averaged over the granularity) of the Price Impact Surface is found to be a concave power law function 〈φ(ω,g)〉g~ωδ with δ≈0.59. Instead the dependence on the granularity is φ(ω,g|ω)~gα with α≈-1, showing a divergence of price fluctuations in the limit g→0. Moreover, even in intermediate situations of finite liquidity, this effect can be very large and it is a natural candidate for understanding the origin of large price fluctuations. 相似文献
3.
H. Zhao R. Proietti Zaccaria P. Verma J. Song H. Sun 《Applied physics. B, Lasers and optics》2010,100(3):499-503
We have studied the extent of the single-mode operation regime for high symmetric index-guiding quasicrystal fibers by analyzing
the validity of the effective V parameter, which is used to determine the single-mode cutoff for photonic crystal fibers. We demonstrate that this parameter
can also be applied, without any approximations, to a high symmetric 12-fold Stampfli quasicrystal made of silica. We explain
this result in terms of both intrinsic-quasicrystal defect and photonic crystal constituent units. We also analyze the extent
of the second-order mode operation to further confirm the cutoff between the single- and multimode operations. 相似文献
4.
Matúš Durec Francesco Zaccaria Dr. Célia Fonseca Guerra Prof. Dr. Radek Marek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(31):10912-10922
Repetitive guanine‐rich nucleic acid sequences play a crucial role in maintaining genome stability and the cell life cycle and represent potential targets for regulatory drugs. Recently, it has been demonstrated that guanine‐based ligands with a porphyrin core can be used as markers of G‐quadruplex assemblies in cell tissues. Herein, model systems of guanine‐based ligands are explored by DFT methods. The energies of formation of modified guanine tetrads and those of modified tetrads stacked on the top of natural guanine tetrads have been calculated. The interaction energy has been decomposed into contributions from hydrogen bonding, stacking, and ion coordination and a twist–rise potential energy scan has been performed to find the individual local minima. Energy decomposition analysis reveals the impact of various substituents (F, Cl, Br, I, Me, NMe2) on individual energy terms. In addition, cooperative reinforcement in forming the modified and stacked tetrads, as well as the frontier orbitals participating in the hydrogen‐bonding framework involving the HOMO–LUMO gap between the occupied σHOMO on the proton‐accepting C=O and =N? groups and unoccupied σLUMO on the N?H groups, has been studied. The investigated systems are demonstrated to have a potential in ligand development, mainly due to stacking enhancement compared with natural guanine, which is used as a reference. 相似文献
5.
Vincenzo Piccialli Sabrina Zaccaria Roberto Centore Angela Tuzi Nicola Borbone Giorgia Oliviero Stefano D’Errico Valentina D’Atri 《Journal of chemical crystallography》2012,42(4):360-365
Abstract
The conformational arrangement of an all-threo bis-THF diol compound, synthesized through the RuO4-catalysed oxidative bis-cyclization of farnesyl acetate, was determined via crystallographic analysis and detailed 2D-NMR solution studies. The bis-THF compound crystallizes in the orthorhombic Pbca space group, with unit cell parameters a = 10.496(1), b = 17.974(1), c = 19.777(2) ?, Z = 8. The final refinement converged to R 1 = 0.0484 for 4714 independent observed reflections having I > 2σ(I). There is a good agreement between the solution molecular conformation determined by 2D-NMR and the X-ray molecular conformation. The molecule adopts a folded, horse shoe-type conformation both in solution and in the crystal, that suggests aptitude to coordinate cations. Additionally, in the crystals, the molecular conformation is stabilized by intramolecular and intermolecular H-bonding. 相似文献6.
Q Gao C Zaccaria M Tontini L Poletti P Costantino L Lay 《Organic & biomolecular chemistry》2012,10(33):6673-6681
The Gram-negative encapsulated bacterium Neisseria meningitidis type A (MenA) is a major cause of meningitis in developing countries, especially in the sub-Saharan region of Africa. The development and manufacture of an efficient glycoconjugate vaccine against MenA is greatly hampered by the poor hydrolytic stability of its capsular polysaccharide, consisting of (1→6)-linked 2-acetamido-2-deoxy-α-d-mannopyranosyl phosphate repeating units. The replacement of the ring oxygen with a methylene group to get a carbocyclic analogue leads to the loss of the acetalic character of the phosphodiester and consequently to the enhancement of its chemical stability. Here we report the synthesis of oligomers (mono-, di- and trisaccharide) of carba-N-acetylmannosamine-1-O-phosphate as candidates for stabilized analogues of the corresponding fragments of MenA capsular polysaccharide. Each of the synthesized compounds contains a phosphodiester-linked aminopropyl spacer at its reducing end to allow for protein conjugation. The inhibition abilities of the synthetic molecules were investigated by a competitive ELISA assay, showing that only the carba-disaccharide is recognized by a polyclonal anti-MenA serum with an affinity similar to a native MenA oligosaccharide with average polymerization degree of 3. 相似文献
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8.
Cavicchia Carlo Vichi Maurizio Zaccaria Giorgia 《Advances in Data Analysis and Classification》2020,14(4):837-853
Advances in Data Analysis and Classification - Many relevant multidimensional phenomena are defined by nested latent concepts, which can be represented by a tree-structure supposing a hierarchical... 相似文献
9.
Vincenzo Piccialli Sabrina Zaccaria Giorgia Oliviero Akseli Hemminki Valentina Romano Roberto Centore 《Tetrahedron》2010,66(48):9370-9378
Four novel C30 polyether bis-spiroketals, displaying selective inhibition of the BT474 breast-derived cancer cell line, have been obtained from squalene through an unprecedented one-step, RuO4-catalysed, cascade process characterised by a tandem oxidative pentacyclization/double oxidative spiroketalization sequence. Preliminary studies indicate that the Ru-mediated spiroketalization steps proceed with retention of configuration at the forming spirocentres. A similarity with the oxidative behaviour of PCC has been disclosed. 相似文献
10.
M. Fiorentino P. Maddalena M. A. Man’ko V. I. Man’ko A. Porzio R. Romano S. Solimeno F. Zaccaria 《Journal of Russian Laser Research》1998,19(4):311-339
The sensitivity of an interferometric gravitational wave (GW) antenna operating above a few hundred Hertz is shot-noise limited. Sub-shot-noise sensitivity can be achieved by superimposing squeezed light on the laser field. The benefits of this approach are reduced in nonideal interferometers having fringe visibility less than unity, as pointed out by Gea-Banacloche and Leuchs and recently discussed by Chickarmane. Here, we consider an interferometer described by a set of coefficients Vl(k), Vsq(k), Vlsq(k) depending on the misalignment, mismatching, and aberrations of the optical systems, as well as on the asymmetry of the beam splitter and the two-arm losses. Due to the presence of terms proportional to the product of laser times squeezed fields, we have taken into account the amplitude fluctuations of al. A simple model of the squeezed vacuum light, produced by a degenerate optical parametric oscillator (OPO), is used for calculating the dependence of the spectral density of the output of a GW antenna on the fluctuations of the OPO-cavity resonance frequency, the pump amplitude fluctuation, and the nonlinear-crystal-temperature drift. A set of figures ηsq± and rlsq±(2) are introduced for describing the effects of the amplitude fluctuations and the relative line width γla on the spectral density of the quadrature phase operator X = alasq+ h.c. 相似文献