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51.
F. Bartumeus P. Fernández M. G.E. da Luz J. Catalan R. V. Solé S. A. Levin 《The European physical journal. Special topics》2008,157(1):157-166
Rate limitation due to encounters is fundamental to many ecological
interactions. Since encounter rate governs reaction rates, and thus,
dynamics of systems, it deserves systematic study. In classical
population biology, ecological dynamics rely on the assumption of
perfectly mixed interacting entities (e.g., individuals, populations,
etc.) in a spaceless world. The so-called mean field assumption
assumes that encounter rates are driven exclusively by changes in the
density of the interacting entities and not on how they are
distributed or move in space. Therefore, the mean field assumption
does not give any insight into relevant spatiotemporal statistical
properties produced by the trajectories of moving entities through
space. In the present study, we develop spatially explicit
simulations of random walking particles (i.e., Lévy walkers) to
evaluate encounter rate constraints beyond the mean field
assumption. We show that encounter rate fluctuations are driven not
only by physical aspects such as the size or the velocity of the
interacting particles, but also by different motion patterns. In
particular, superdiffusion phenomena might be relevant at low
densities and/or low spatial dimensionality. Finally, we discuss
potential adaptive responses of living organisms that may allow
individuals to control how they diffuse through space and/or the
spatial dimensions employed in the exploration process. 相似文献
52.
Serrano I López MI Ferrer Í Poater A Parella T Fontrodona X Solà M Llobet A Rodríguez M Romero I 《Inorganic chemistry》2011,50(13):6044-6054
The synthesis of a family of new Ru complexes containing the facial tridentate ligand with general formula [Ru(II)(T)(D)(X)](n+) (T = trispyrazolylmethane (tpm); D = ((4S,4'S)-(-)-4,4',5,5'-tetrahydro-4,4'-bis(1-methylethyl)-2,2'-bioxazole) (iPr-box-C) or N-(1-hydroxy-3-methylbutan-(2S)-(-)-2-yl)-(4S)-(-)-4-isopropyl-4,5-dihydrooxazole-2-carbimidate (iPr-box-O); X = Cl, H(2)O) has been described. All complexes have been spectroscopically characterized in solution through (1)H NMR and UV-vis techniques, and the redox properties of complexes have also been studied by means of cyclic voltammetry (CV). Furthermore, the chloro complexes presented here have been characterized in the solid state through monocrystal X-ray diffraction analysis. The oxazolinic iPr-box-C ligand undergoes a Ru-assisted hydrolysis reaction generating the corresponding amidate anionic ligand iPr-box-O, that keeps coordinated to the Ru metal center and that produces a strong σ-donation effect over it. The reactivity of the Ru-OH(2) complexes described in this paper together with other similar ones, previously synthesized by us, has been tested with regard to the epoxidation of different olefins. Complexes [Ru(II)(R-box-C)(tpm)OH(2)](BF(4))(2), R = Bz, 3'c/iPr, 3c, show high stereoselectivity in the epoxidation of cis-β-methylstyrene, with the exclusive formation of the cis-epoxide. However, there is a significant difference in regioselectivity between the two catalysts in the epoxidation of 4-vinylcyclohexene; complex 3'c leads to the regioselective oxidation at the ring alkene position, whereas complex 3c leads to the oxidation at the terminal position. Computational calculations indicate only small energy differences between the two possible products of 4-vinylcyclohexene epoxidation, but the energy barriers for the interaction of the catalytic systems with the alkene groups of 4-vinylcyclohexene agree with the reactivity differences found for the two catalysts having isopropyl or benzyl as substituent of the oxazole ligand. Computed local Fukui functions help to explain the observed reactivity trends. 相似文献
53.
Gold(I)‐Catalyzed N‐Desulfonylative Amination versus N‐to‐O 1,5‐Sulfonyl Migration: A Versatile Approach to 1‐Azabicycloalkanes 下载免费PDF全文
Solène Miaskiewicz Boris Gaillard Dr. Nicolas Kern Prof. Dr. Jean‐Marc Weibel Prof. Dr. Patrick Pale Dr. Aurélien Blanc 《Angewandte Chemie (International ed. in English)》2016,55(31):9088-9092
Valuable 1‐azabicycloalkane derivatives have been synthesized through a novel gold(I)‐catalyzed desulfonylative cyclization strategy. An ammoniumation reaction of ynones substituted at the 1‐position with an N‐sulfonyl azacycle took place in the presence of a gold cation by intramolecular cyclization of the disubstituted sulfonamide moiety onto the triple bond. Depending on the size of the heterocyclic ring and substitution of the substrates, two unprecedented forms of nucleophilic attack on the sulfonyl group were exploited, that is, a N‐desulfonylation in the presence of an external protic O nucleophile (37–87 %, 10 examples) and a unique N‐to‐O 1,5‐sulfonyl migration (60–98 %, 9 examples). 相似文献
54.
Marc Garcia‐Borràs Dr. Josep M. Luis Prof. Dr. Marcel Swart Prof. Dr. Miquel Solà 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(14):4468-4479
One of the most important reactions in fullerene chemistry is the Diels–Alder (DA) reaction. In two previous experimental studies, the DA cycloaddition reactions of cyclopentadiene (Cp) and 1,2,3,4,5‐pentamethylcyclopentadiene (Cp*) with La@C2v‐C82 were investigated. The attack of Cp was proposed to occur on bond 19 , whereas that of Cp* was confirmed by X‐ray analysis to be over bond o . Moreover, the stabilities of the Cp and Cp* adducts were found to be significantly different, that is, the decomposition of La@C2v‐C82Cp was one order of magnitude faster than that of La@C2v‐C82Cp*. Herein, we computationally analyze these DA cycloadditions with two main goals: First, to compute the thermodynamics and kinetics of the cycloadditions of Cp and Cp* to different bonds of La@C2v‐C82 to assess and compare the regioselectivity of these two reactions. Second, to understand the origin of the different thermal stabilities of the La@C82Cp and La@C82Cp* adducts. Our results show that the regioselectivity of the two DA cycloadditions is the same, with preferred attack on bond o . This result corrects the previous assumption of the regioselectivity of the Cp attack that was made based only on the shape of the La@C82 singly occupied molecular orbital. In addition, we show that the higher stability of the La@C82Cp* adduct is not due to the electronic effects of the methyl groups on the Cp ring, as previously suggested, but to higher long‐range dispersion interactions in the Cp* case, which enhance the stabilization of the reactant complex, transition state, and products with respect to the separated reactants. This stabilization for the La@C82Cp* case decreases the Gibbs reaction energy, thus allowing competition between the direct and retro reactions and making dissociation more difficult. 相似文献
55.
To obtain a state-of-the-art benchmark potential energy surface (PES) for the archetypal oxidative addition of the methane C-H bond to the palladium atom, we have explored this PES using a hierarchical series of ab initio methods (Hartree-Fock, second-order M?ller-Plesset perturbation theory, fourth-order M?ller-Plesset perturbation theory with single, double and quadruple excitations, coupled cluster theory with single and double excitations (CCSD), and with triple excitations treated perturbatively [CCSD(T)]) and hybrid density functional theory using the B3LYP functional, in combination with a hierarchical series of ten Gaussian-type basis sets, up to g polarization. Relativistic effects are taken into account either through a relativistic effective core potential for palladium or through a full four-component all-electron approach. Counterpoise corrected relative energies of stationary points are converged to within 0.1-0.2 kcal/mol as a function of the basis-set size. Our best estimate of kinetic and thermodynamic parameters is -8.1 (-8.3) kcal/mol for the formation of the reactant complex, 5.8 (3.1) kcal/mol for the activation energy relative to the separate reactants, and 0.8 (-1.2) kcal/mol for the reaction energy (zero-point vibrational energy-corrected values in parentheses). This agrees well with available experimental data. Our work highlights the importance of sufficient higher angular momentum polarization functions, f and g, for correctly describing metal-d-electron correlation and, thus, for obtaining reliable relative energies. We show that standard basis sets, such as LANL2DZ+1f for palladium, are not sufficiently polarized for this purpose and lead to erroneous CCSD(T) results. B3LYP is associated with smaller basis set superposition errors and shows faster convergence with basis-set size but yields relative energies (in particular, a reaction barrier) that are ca. 3.5 kcal/mol higher than the corresponding CCSD(T) values. 相似文献
56.
57.
Solène Morand Prof. Philippe Jubault Prof. Jean-Philippe Bouillon Dr. Samuel Couve-Bonnaire 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(69):17273-17292
gem-Heteroatom-substituted fluoroalkenes have received little attention despite their great potential in medicinal chemistry or in fine chemistry. Indeed, due to the electronic and steric similarity between the fluoroalkene moiety and the amide bond as well as the high strength of the carbon-fluorine bond, these gem-heteroatom-substituted fluoroalkenes could be envisioned as stable mimics of various important organic functions, such as phosphates, carbamates, S-thiocarbamates and ureas. We present herein an overview describing the syntheses over the last decade of heteroatom-substituted fluoroalkenes in geminal position. This review will be divided into several sections covering each the common following heteroatom: oxygen-, nitrogen-, sulfur-, phosphorus-, boron- and silicon-substituted fluoroalkenes. 相似文献
58.
Tom Schoonjans Antonio Brunetti Bruno Golosio Manuel Sanchez del Rio Vicente Armando Solé Claudio Ferrero Laszlo Vincze 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(11-12):776-784
This work presents the recent developments of xraylib, an ANSI C library that provides convenient access to a large number of X-ray related databases, with a focus on quantitative X-ray fluorescence applications. The enhancements include improved X-ray fluorescence production cross sections that take into account cascade effects and M-lines, as well as revised line energies, atomic level widths, Compton broadening profiles etc. A full overview of the complete application programming interface is presented. 相似文献
59.
60.
Over the past 50 years, pentafluorobenzaldehyde has received much attention due to its unique chemical and physical properties as well as its real or potential applications in chemistry of porphyrines, additives, drug delivery and in analytical chemistry. Pentafluorobenzaldehyde is multifunctional aromatic compound containing five atoms of fluorine and one aldehydic function. That is why it can provide nucleophilic substitutions of all or some atoms of fluorine, nucleophilic additions of aldehydic function, “haloform reaction” and some cyclization reactions. This year, it is being the 50th year, since the first synthesis of this compound was published. 相似文献