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排序方式: 共有62条查询结果,搜索用时 15 毫秒
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Kevin E. Riley Jane S. Murray Jindřich Fanfrlík Jan Řezáč Ricardo J. Solá Monica C. Concha Felix M. Ramos Peter Politzer 《Journal of molecular modeling》2013,19(11):4651-4659
In a previous study we investigated the effects of aromatic fluorine substitution on the strengths of the halogen bonds in halobenzene…acetone complexes (halo?=?chloro, bromo, and iodo). In this work, we have examined the origins of these halogen bonds (excluding the iodo systems), more specifically, the relative contributions of electrostatic and dispersion forces in these interactions and how these contributions change when halogen σ-holes are modified. These studies have been carried out using density functional symmetry adapted perturbation theory (DFT-SAPT) and through analyses of intermolecular correlation energies and molecular electrostatic potentials. It is found that electrostatic and dispersion contributions to attraction in halogen bonds vary from complex to complex, but are generally quite similar in magnitude. Not surprisingly, increasing the size and positive nature of a halogen’s σ-hole dramatically enhances the strength of the electrostatic component of the halogen bonding interaction. Not so obviously, halogens with larger, more positive σ-holes tend to exhibit weaker dispersion interactions, which is attributable to the lower local polarizabilities of the larger σ-holes. Figure
In this work we investigate the roles played by electrostatic and dispersion forces in stabilizing halogen bonding interactions. 相似文献
3.
Riley KE Murray JS Fanfrlík J Rezáč J Solá RJ Concha MC Ramos FM Politzer P 《Journal of molecular modeling》2011,17(12):3309-3318
In the past several years, halogen bonds have been shown to be relevant in crystal engineering and biomedical applications.
One of the reasons for the utility of these types of noncovalent interactions in the development of, for example, pharmaceutical
ligands is that their strengths and geometric properties are very tunable. That is, substitution of atoms or chemical groups
in the vicinity of a halogen can have a very strong effect on the strength of the halogen bond. In this study we investigate
halogen-bonding interactions involving aromatically-bound halogens (Cl, Br, and I) and a carbonyl oxygen. The properties of
these halogen bonds are modulated by substitution of aromatic hydrogens with fluorines, which are very electronegative. It
is found that these types of substitutions have dramatic effects on the strengths of the halogen bonds, leading to interactions
that can be up to 100% stronger. Very good correlations are obtained between the interaction energies and the magnitudes of
the positive electrostatic potentials (σ-holes) on the halogens. Interestingly, it is seen that the substitution of fluorines
in systems containing smaller halogens results in electrostatic potentials resembling those of systems with larger halogens,
with correspondingly stronger interaction energies. It is also shown that aromatic fluorine substitutions affect the optimal
geometries of the halogen-bonded complexes, often as the result of secondary interactions. 相似文献
4.
We have extended an earlier study, in which we characterized in detail the electrostatic potentials on the inner and outer surfaces of a group of carbon and BxNx model nanotubes, to include several additional ones with smaller diameters plus a new category, C2xBxNx. The statistical features of the surface potentials are presented and analyzed for a total of 19 tubes as well as fullerene and a small model graphene. The potentials on the surfaces of the carbon systems are relatively weak and rather bland; they are much stronger and more variable for the BxNx and C2xBxNx. A qualitative correlation with free energies of solvation indicates that the latter two categories should have considerably greater water solubilities. The inner surfaces are generally more positive than the corresponding outer ones, while both positive and negative potentials are strengthened by increasing curvature. The outsides of BxNx tubes have characteristic patterns of alternating positive and negative regions, while the insides are strongly positive. In the closed C2xBxNx systems, half of the C–C bonds are double-bond-like and have negative potentials above them; the adjacent rows of boron and nitrogens show the usual BxNx pattern. When the C2xBxNx tubes are open, with hydrogens at the ends, the surface potentials are dominated by the B+–H– and N––H+ linkages.Figure Calculated electrostatic potential on the molecular surface of closed (6,0) B48N48; a is an outside view, while b shows the interior. Color ranges, in kcal mol–1: red, greater than 20; yellow, between 20 and 0; green, between 0 and –10; blue, between –10 and –20; purple, more negative than –20 相似文献
5.
Hennemann M Murray JS Politzer P Riley KE Clark T 《Journal of molecular modeling》2012,18(6):2461-2469
The strong collinear polarizability of the A-H bond in A-H···B hydrogen bonds is shown to lead to an enhanced σ-hole on the donor hydrogen atom and hence to stronger hydrogen bonding. This effect helps to explain the directionality of hydrogen bonds, the well known cooperative effect in hydrogen bonding, and the occurrence of blue-shifting. The latter results when significant additional electron density is shifted into the A-H bonding region by the polarization effect. The shift in the A-H stretching frequency is shown to depend essentially linearly on the calculated atomic charge on the donor hydrogen for all donors in which A belongs to the same row of the periodic table. A further result of the polarization effect, which is also expected for other σ-hole bonds, is that the strength of the non-covalent interaction depends strongly on external electric fields. 相似文献
6.
G. Politzer 《Development genes and evolution》1953,146(3):403-406
Ohne Zusammenfassung 相似文献
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Alejandro Toro-Labbé Soledad Gutiérrez-Oliva Jane S. Murray Peter Politzer 《Journal of molecular modeling》2009,15(6):707-710
The reaction force F(R) and the position-dependent reaction force constant κF(R) are defined by F(R)=-∂V(R)/∂R and κ(R)=∂2V(R)/∂R2, where V(R) is the potential energy of a reacting system along a coordinate R. The minima and maxima of F(R) provide a natural division of the process into several regions. Those in which F(R) is increasing are where the most dramatic changes in electronic properties take place, and where the system goes from activated
reactants (at the force minimum) to activated products (at the force maximum). κ(R) is negative throughout such a region. We summarize evidence supporting the idea that a reaction should be viewed as going
through a transition region rather than through a single point transition state. A similar conclusion has come out of transition state spectroscopy. We describe this region as a chemically-active, or electronically-intensive,
stage of the reaction, while the ones that precede and follow it are structurally-intensive. Finally, we briefly address the
time dependence of the reaction force and the reaction force constant. 相似文献