Electron topological description

The inhibitor activity of compounds with respect to different enzymes is important in the design and screening of many pharmaceuticals. Many inhibitors have similar structural groups, yet have different activities, indicating the importance of electronic factors. The electron-topological description, as shown below, is much more specific with respect to the interaction of the molecules with the bioreceptor. 

One further theoretical method that merits consideration at this point is the topological theory of molecular structure exemplified by Bader (1985, 1990). In this method a topological description of the total electron density in the molecule is used. A major advantage of this method is that it allows the total interaction between various centres to be probed. Cremer et al. (1983) used the Bader method to examine the homotropylium cation [12] and concluded that it was indeed homoaromatic. 

The aim ofthe present study is double i) to show that BET can be used as a tool for analyzing the adiabatic PESs and localizing the diabatic crossings which govern the overall electron changes ii) to provide a topological description of the three-electron bonds. 

In the present paper, the electron-topological (FT) method in the QSAR problem is briefly reviewed. The main idea of this method is to describe the molecules in a more natural way by presenting their electronic and topological (geometric) properties on the same level. The emphasis is on electronic features because chemical interaction is electronic in nature, at least at its first stage. In the ET method, the molecules are described by a set of m square symmetrical ET matrices that contain n rt + l)/2 elements, n being the number of atoms in the molecule. This description of the molecule with m x n n+l)/2 numbers is... 

On the other hand, in the quantitative methods discussed above where the electronic parameters are included, the compounds under consideration are strongly limited by the requirement that they be similar in structure over the whole series. The purpose of the electron-topological QSAR method under consideration in this review is to overcome the shortcomings of the previous QSAR methods, which ignore (completely or partly) the role of electronic structure in the description of the molecules or consider only series of compounds with similar structures. 

Fourre et al found that their ELF-based topological description of the chemical bond provides a deeper insight into the bonding evolution upon excitation, ionization, and electron attachment in carbonyl and imine compounds than the classical MO point of view. The changes occurring in the valence basin... 

Throughout the studies discussed above, there has been a close interplay between structural measurements and development of theoretical models of molecular electronic structure. Lipscomb s contributions have included topological description of the boron hydrides and fundamental theory. Several coworkers contributed in this area, but most notable is the work with Roald Hoffmann, which changed the way chemists approach the theory of molecules of interesting complexity (see, e.g., the comments in (2(5)). The extended Huckel method was developed in the Lipscomb s group by several people, including especially L. L. Lohr, Jr., and Roald Hoffman (see Roald s recollections in Current Contents Citation Classic, May 8, 1989). Although the method probably contributed more to chemistry than any other method imtil very recently, Lipscomb recalled decades after he introduced it that this method received intense criticism, even denouncement. More exact theory led to the first correct calculation of the rotational barrier in ethane (with R. M. Pitzer in 1963). 

Topological indices are used to describe some components of connectivity. A more complete description is afforded by unidimensional codes (linear line notations) such as SMILES. Connectivity plus explicit attention to valence electrons is afforded by the electrotopological indices... 

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