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排序方式: 共有117条查询结果,搜索用时 46 毫秒
1.
The 1,3-dipolar cycloadditions of C-glycosyl nitrile oxides and acetylenes to an alkyne and an azide, respectively, bearing a masked glycinyl moiety furnished disubstituted isoxazoles and triazoles. Unveiling the glycinyl group in these cycloadducts afforded C-glycosyl alpha-amino acids in which the two bioactive entities were tethered through rigid five-membered heterocycles. Optimized entries to the same compounds involved the use of unmasked but protected alkyne- and azide-containing amino acids as the partners of 1,3-dipolar cycloadditions. 相似文献
2.
3.
P. Espeau B. Nicolaï R. Céolin M. -A. Perrin L. Zaske J. Giovannini F. Leveiller 《Journal of Thermal Analysis and Calorimetry》2007,90(2):341-342
Investigation into the thermal behavior of orthorhombic Forms I and II of spironolactone, by means of differential scanning
calorimetry and high-resolution X-ray powder diffraction, showed that Form I melts then recrystallizes into Form II at 373–393
K, i.e. in the temperature range within which high resolution X-ray powder diffration showed that Form I transforms into Form II.
Refinements of the lattice parameters of the two forms indicated that Form I is denser than Form II in the range from 298
K up to the temperature at which it melts. 相似文献
4.
Jessica Walkenhorst Umberto De Giovannini Alberto Castro Angel Rubio 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(5):128
Recent advances in laser technology allow us to follow electronic motion at its natural time-scale with ultra-fast time resolution, leading the way towards attosecond physics experiments of extreme precision. In this work, we assess the use of tailored pumps in order to enhance (or reduce) some given features of the probe absorption (for example, absorption in the visible range of otherwise transparent samples). This type of manipulation of the system response could be helpful for its full characterization, since it would allow us to visualize transitions that are dark when using unshaped pulses. In order to investigate these possibilities, we perform first a theoretical analysis of the non-equilibrium response function in this context, aided by one simple numerical model of the hydrogen atom. Then, we proceed to investigate the feasibility of using time-dependent density-functional theory as a means to implement, theoretically, this absorption-optimization idea, for more complex atoms or molecules. We conclude that the proposed idea could in principle be brought to the laboratory: tailored pump pulses can excite systems into light-absorbing states. However, we also highlight the severe numerical and theoretical difficulties posed by the problem: large-scale non-equilibrium quantum dynamics are cumbersome, even with TDDFT, and the shortcomings of state-of-the-art TDDFT functionals may still be serious for these out-of-equilibrium situations. 相似文献
5.
Olga Bortolini Dr. Alberto Cavazzini Pier Paolo Giovannini Roberto Greco Nicola Marchetti Dr. Alessandro Massi Luisa Pasti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(24):7802-7808
The heterogeneous proline‐catalyzed aldol reaction was investigated under continuous‐flow conditions by means of a packed‐bed microreactor. Reaction‐progress kinetic analysis (RPKA) was used in combination with nonlinear chromatography for the interpretation, under synthetically relevant conditions, of important mechanistic aspects of the heterogeneous catalytic process at a molecular level. The information gathered by RPKA and nonlinear chromatography proved to be highly complementary and allowed for the assessment of optimal operating variables. In particular, the determination of the rate‐determining step was pivotal for optimizing the feed composition. On the other hand, the competitive product inhibition was responsible for the unexpected decrease in the reaction yield following an apparently obvious variation in the feed composition. The study was facilitated by a suitable 2D instrumental arrangement for simultaneous flow reaction and online flow‐injection analysis. 相似文献
6.
F. Becattini A. Giovannini S. Lupia 《Zeitschrift fur Physik C Particles and Fields》1996,72(3):491-496
Predictions of a thermodynamical model of hadron production for multiplicity distribution ine + e ? annihilations at LEP and PEP-PETRA centre of mass energies are shown. The production process is described as a two-step process in which primary hadrons emitted from the thermal source decay into final observable particles. The final charged tracks multiplicity distributions turn out to be of Negative Binomial type and are in quite good agreement with experimental observations. The average number of clans calculated from fitted Negative Binomial coincides with the average number of primary hadrons predicted by the thermodynamical model, suggesting that clans should be identified with primary hadrons. 相似文献
7.
Alessandro Massi Alberto CavazziniOmar Pandoli Valentina CostaLuisa Pasti Pier Paolo Giovannini 《Tetrahedron letters》2011,52(5):619-622
The activity and stability under flow conditions of covalently and non-covalently silica supported proline and proline-like organocatalysts is herein described. The slow aldol reaction of cyclohexanone with p-nitro benzaldehyde and the fast α-amination of isovaleraldehyde with dibenzyl azodicarboxylate have been selected as model reactions for this study. Prospects and limitations of the disclosed continuous-flow organocatalytic approach are widely discussed. 相似文献
8.
Tacchi S Montoncello F Madami M Gubbiotti G Carlotti G Giovannini L Zivieri R Nizzoli F Jain S Adeyeye AO Singh N 《Physical review letters》2011,107(12):127204
The dispersion curves of collective spin-wave excitations in a magnonic crystal consisting of a square array of interacting saturated nanodisks have been measured by Brillouin light scattering along the four principal directions of the first Brillouin zone. The experimental data are successfully compared to calculations of the band diagram and of the Brillouin light scattering cross section, performed through the dynamical matrix method extended to include the dipolar interaction between the disks. We found that the fourfold symmetry of the geometrical lattice is reduced by the application of the external field and therefore equivalent directions of the first Brillouin zone are characterized by different dispersion relations of collective spin waves. The dispersion relations are explained through the introduction of a bidimensional effective wave vector that characterizes each mode in this magnonic metamaterial. 相似文献
9.
P. Solokha M. Giovannini N.R. Lee-Hone D.H. Ryan 《Journal of solid state chemistry》2011,184(9):2498-2505
The crystal structure of the ternary intermetallic compound Yb3Pd2Sn2 has been determined ab initio from powder X-ray diffraction data. The compound crystallizes as a new structure type in the orthorhombic space group Pbcm and lattice constants a=0.58262(3), b=1.68393(8), c=1.38735(7) nm. Yb3Pd2Sn2 is composed of a complex ∞[Pd2Sn2]δ− polyanionic network in which the Yb ions are embedded. A comparison between this structure and those of Eu3Pd2Sn2 and Ca3Pd2Sn2, other novel polar intermetallic compounds, was made. DC susceptibility and 170Yb Mössbauer spectroscopic measurements indicate a close-to divalent Yb behavior. Moreover, a hybridization between 4f and conduction electrons is suggested by electronic structure calculations and heat capacity measurements. 相似文献
10.
Bortolini O Fantin G Fogagnolo M Giovannini PP Massi A Pacifico S 《Organic & biomolecular chemistry》2011,9(24):8437-8444
An efficient method for the N-heterocyclic carbene (NHC)-catalyzed conjugate addition of acetyl anions to various α,β-unsaturated acceptors (Stetter reaction) has been optimized by using 2,3-butandione (biacetyl) as an alternative surrogate of acetaldehyde. The disclosed procedure proved to be compatible with microwave dielectric heating for reaction time reduction and with the use of different linear α-diketones as acyl anion donors (e.g. 3,4-hexanedione for propionyl anion additions). Moreover, the unprecedented umpolung reactivity of cyclic α-diketones in the atom economic nucleophilic acylation of chalcones is herein presented. Mechanistic aspects of the thiazolium-based catalysis involving linear and cyclic α-diketone substrates are also discussed. 相似文献