181 PPT3

Study Notes

Molecular Descriptors in Quantitative Structure-Activity Relationships

Log P, a measure of lipophilicity, is often estimated using the logarithm of the partition coefficient between n-octanol and water.
Log P can be estimated using an additive scheme or a fragment-based approach, where correction factors account for interactions between fragments.
Molar refractivity, a measure of steric bulk, is calculated using the refractive index, density, and molecular weight, and accounts for the polarizability of the molecule.
Topological indices are single-valued descriptors that characterize molecular structures based on size, branching, and shape, such as the Wiener Index.
Molecular connectivity indices, introduced by Randic ́ and developed by Kier and Hall, are based on the degree of each atom and the connectivity of bonds in the molecule.
Chi molecular connectivity indices, introduced by Kier and Hall, are sequential indices that sum the atomic delta values over bond paths of different lengths.
Valence delta values for atoms are defined in terms of the number of sigma electrons, hydrogen atoms, and valence electrons, and can differentiate between different types of atoms.
The chi indices for the various isomers of hexane involve summations over sequences of bonds of different lengths.
Kappa shape indices, designed to characterize molecular shape, involve comparing a molecule with extreme shapes that are possible for a given number of atoms.
The first-order kappa index involves a count over single bond fragments and is determined by the number of edges in the completely connected graph and the number of bonds in the linear molecule.
The second-order kappa index is determined by the count of two-bond paths and involves the number of bonds in the molecule for which the shape index is being calculated.
The kappa indices themselves do not include any information about the identity of the atoms.