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61.
Homothetic solutions of the n-body problem can be seen as heteroclinic orbits when the dynamical variables are changed via the McGehee blow-up and the time is suitably scaled. Transversality of the invariant asymptotic manifolds which contain the heteroclinic orbits is related to some structural stability. We fully characterize the cases in which such transversality is obtained for the n-body problem in any dimension. 相似文献
62.
The essentially non-oscillatory (ENO)-wavelet transform developed by Chan and Zhou (SIAM J. Numer. Anal. 40(4), 1369–1404, 2002) is based on a combination of the Daubechies-2p wavelet transform and the ENO technique. It uses extrapolation methods to compute the scaling coefficients without differencing function values across jumps and obtains a multiresolution framework (essentially) free of edge artifacts. In this work, we present a different way to compute the ENO-DB2p wavelet transform of Chan and Zhou which allows us to simplify the process and easily generalize it to other families of orthonormal wavelets. 相似文献
63.
Dr. Barbara Müller Dr. Wei‐Zheng Shen Dr. Pablo J. Sanz Miguel Dr. Francisca M. Albertí Dr. Tushar van der Wijst Dr. Marc Noguera Dr. Luis Rodríguez‐Santiago Prof. Mariona Sodupe Prof. Bernhard Lippert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(36):9970-9983
The preparation and X‐ray crystal structure analysis of {trans‐[Pt(MeNH2)2(9‐MeG‐N1)2]} ? {3 K2[Pt(CN)4]} ? 6 H2O ( 3 a ) (with 9‐MeG being the anion of 9‐methylguanine, 9‐MeGH) are reported. The title compound was obtained by treating [Pt(dien)(9‐MeGH‐N7)]2+ ( 1 ; dien=diethylenetriamine) with trans‐[Pt(MeNH2)2(H2O)2]2+ at pH 9.6, 60 °C, and subsequent removal of the [(dien)PtII] entities by treatment with an excess amount of KCN, which converts the latter to [Pt(CN)4]2?. Cocrystallization of K2[Pt(CN)4] with trans‐[Pt(MeNH2)2(9‐MeG‐N1)2] is a consequence of the increase in basicity of the guanine ligand following its deprotonation and Pt coordination at N1. This increase in basicity is reflected in the pKa values of trans‐[Pt(MeNH2)2(9‐MeGH‐N1)2]2+ (4.4±0.1 and 3.3±0.4). The crystal structure of 3 a reveals rare (N7,O6 chelate) and unconventional (N2,C2,N3) binding patterns of K+ to the guaninato ligands. DFT calculations confirm that K+ binding to the sugar edge of guanine for a N1‐platinated guanine anion is a realistic option, thus ruling against a simple packing effect in the solid‐state structure of 3 a . The linkage isomer of 3 a , trans‐[Pt(MeNH2)2(9‐MeG‐N7)2] ( 6 a ) has likewise been isolated, and its acid–base properties determined. Compound 6 a is more basic than 3 a by more than 4 log units. Binding of metal entities to the N7 positions of 9‐MeG in 3 a has been studied in detail for [(NH3)3PtII], trans‐[(NH3)2PtII], and [(en)PdII] (en=ethylenediamine) by using 1H NMR spectroscopy. Without exception, binding of the second metal takes place at N7, but formation of a molecular guanine square with trans‐[(Me2NH2)PtII] cross‐linking N1 positions and trans‐[(NH3)2PtII] cross‐linking N7 positions could not be confirmed unambiguously, despite the fact that calculations are fully consistent with its existence. 相似文献
64.
Pelayo Camps Carles GaldeanoDiego Muñoz-Torrero Jordi RullTeresa Calvet Mercè Font-Bardia 《Tetrahedron: Asymmetry》2011,22(7):745-751
The enantioselective synthesis of the title compound, its conversion into a thiourea-type organocatalyst and the behavior of this organocatalyst in several enantioselective Michael reactions are described. 相似文献
65.
Calero C Faraudo J Bastos-González D 《Journal of the American Chemical Society》2011,133(38):15025-15035
Here we study experimentally and by simulations the interaction of monovalent organic and inorganic anions with hydrophobic and hydrophilic colloids. In the case of hydrophobic colloids, our experiments show that charge inversion is induced by chaotropic inorganic monovalent ions but it is not induced by kosmotropic inorganic anions. For organic anions, giant charge inversion is observed at very low electrolyte concentrations. In addition, charge inversion disappears for both organic and inorganic ions when turning to hydrophilic colloids. These results provide an experimental evidence for the hydrophobic effect as the driving force for both ion specific effects and charge inversion. In the case of organic anions, our molecular dynamics (MD) simulations with full atomic detail show explicitly how the large adsorption free energies found for hydrophobic colloids are transformed into large repulsive barriers for hydrophilic colloids. Simulations confirm that solvation free energy (and hence the hydrophobic effect) is responsible for the build up of a Stern layer of adsorbed ions and charge inversion in hydrophobic colloids and it is also the mechanism preventing charge inversion in hydrophilic colloids. Overall, our experimental and simulation results suggest that the interaction of monovalent ions with interfaces is dominated by solvation thermodynamics, that is, the chaotropic/kosmotropic character of ions and the hydrophobic/hydrophilic character of surfaces. 相似文献
66.
Harrison JA Kartha KP Fournier EJ Lowary TL Malet C Nilsson UJ Hindsgaul O Schenkman S Naismith JH Field RA 《Organic & biomolecular chemistry》2011,9(5):1653-1660
Systematically modified octyl galactosides and octyl N-acetyllactosamines were assessed as inhibitors of, and substrates for, T. cruzi trans-sialidase (TcTS) in the context of exploring its acceptor substrate binding site. These studies show that TcTS, which catalyses the α-(2→3)-sialylation of non-reducing terminal β-galactose residues, is largely intolerant of substitution of the galactose 2 and 4 positions whereas substitution of the galactose 6 position is well tolerated. Further studies show that even the addition of a bulky sugar residue (glucose, galactose) does not impact negatively on TcTS binding and turnover, which highlights the potential of 'internal' 6-substituted galactose residues to serve as TcTS acceptor substrates. Results from screening a 93-membered thiogalactoside library highlight a number of structural features (notably imidazoles and indoles) that are worthy of further investigation in the context of TcTS inhibitor development. 相似文献
67.
Miquel Grau-Sánchez Àngela Grau Miquel Noguera 《Journal of Computational and Applied Mathematics》2011,235(6):1739-1743
The development of an inverse first-order divided difference operator for functions of several variables, as well as a direct computation of the local order of convergence of an iterative method is presented. A generalized algorithm of the secant method for solving a system of nonlinear equations is studied and the maximum computational efficiency is computed. Furthermore, a sequence that approximates the order of convergence is generated for the examples and it confirms in a numerical way that the order of the methods is well deduced. 相似文献
68.
Raducan M Rodríguez-Escrich C Cambeiro XC Escudero-Adán EC Pericàs MA Echavarren AM 《Chemical communications (Cambridge, England)》2011,47(17):4893-4895
[Au(tmbn)(2)](SbF(6)) is the first gold(I) complex supported by two nitrile ligands that is indefinitely stable at room temperature. This is a highly versatile precatalyst that can be used for the preparation of active and robust solid-supported gold(I) catalysts. 相似文献
69.
70.