Atom-typeE-State index

The E-state indices may define chemical spaces that are relevant in similarity/ diversity search in chemical databases. This similarity search is based on atom-type E-state indices computed for the query molecule [55]. Each E-state index is converted to a z score, Z =(% -p )/0 , where is the ith E-state atomic index, p is its mean and O is its standard deviation in the entire database. The similarity was computed with the EucHdean distance and with the cosine index and the database used was the Pomona MedChem database, which contains 21000 chemicals. Tests performed for the antiinflamatory drug prednisone and the antimalarial dmg mefloquine as query molecules demonstrated that the chemicals space defined by E-state indices is efficient in identifying similar compounds from drug and drug-tike databases. 

The data containing 324 descriptor values of 88 molecules was given as an input to VSMP program, to build models based on three and four descriptors, keeping the interdescriptor correlation below 0.75. The best three-descriptors model, Eq. 80, was based on descriptors 254 (atomic type E-state index), 311 (AlogP98), and 320 (2D Van der Waals surface area) with a correlation coefficient, r, of 0.8425, and the cross-validated correlation coefficient, q, of 0.8239. The correlation coefficients of the other two VSMP models, Eqs. 81 and 82 were 0.8411 and 0.8329, respectively. Significantly, the descriptors 254 and 311 were selected in all the best three-descriptors models of VSMP. The three descriptors, in the models 80, 81, and 82 were 320, 144 (Kappa shape index of order 1), and 30 (topological Xu index), respectively. 

These topological indexes, based on the molecular connectivity approach, include three types the ""Xr molecular connectivity chi indexes that characterize the structural attributes of molecules, the ""k kappa indexes of molecular shape, and the topological equivalence state T values that individually characterize atoms and groups in the molecular skeleton and are used primarily to determine chemically equivalent atoms within a molecule. A further development of this approach has led to the electrotopological state atom indexes, which will not be discussed here but will be presented elsewhere. Molecular connectivity chi indexes are discussed in the first part of this paper along with illustrative applications. Then kappa shape indexes are discussed. The topological state index is discussed in the final section. 

The definition of these 30 indices is shown in Tables 7.1 and 7.2, where the A index encodes the number of electronegative atoms ( ea), while the E index encodes the sum of the S-State index for the electronegative atoms, N, 0, F, Cl, Br is the average value for a specific type of atom, sulphur has not been considered as an electronegative atom). The rescaling procedure brings about... 

E-State descriptors of potential internal hydrogen bond strength (7 = 2-10) Electrotopological state index values for atoms types ... 

In Section 3.1., we shall show that the dynamic model leads to an unambiguous determination of the type of nonbonded interactions involved while the static model may lead to erroneous predictions as a result of an ambiguous definition of the nature of a nonbonded interaction. The superiority of the dynamic model is due to the fact that nonbonded interactions affect bonded interactions and, thus, the change in an overall overlap population rather than the change of a specific overlap population between nonbonded atoms or groups is the most appropriate index of a nonbonded interaction. Accordingly, we shall employ the dynamic model in all subsequent discussions of molecular structure, unless otherwise stated. 

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