Electrostatic descriptors

In addition to the steric and electrostatic descriptors, it was proposed to use other 3D molecular fields characterized by the sampling over the rectangular grid - in particular, the hydrophobic field/molecular lipophilic potential (MLP), ° hydrogen bonding and quantum-chemical parameters, e.g., orbital densities.Descriptor selection techniques are often recommended to enhance the stability, predictivity and interpretability of the CoMFA models. ... 

Electrostatic descriptors, in particular, effective atomic charge Q estimated using the electronegativity equalization approach and absolute charge Qa. 

Fi ire 2.5. Process of steric and electrostatic descriptor generation in CoMFA. Note that this process results in a familiar QSAR table (cf Fig. 2.2). PLS is used as a standard analytical technique in CoMFA. 

Kroemer, R.T., Hecht, P. and Liedl, K.R. (1996). Different Electrostatic Descriptors in Comparative Molecular Field Analysis A Comparison of Molecular Electrostatic and Coulomb Potentials. J. Comput. Chem., 17,1296-1308. 

Many molecular properties, especially those measured in condensed media, depend on intermolecular interactions. The main term of such interactions is, in most cases, the electrostatic attraction or repulsion between the molecules or their different parts. Consequently, the respective electrostatic descriptors characterizing a molecule would... 

Electrostatic descriptors Net atomic charge on atom A (Mulliken charge)... 

Commonly, the minimum (most negative) and maximum (most positive) partial charges in the molecule or the minimum and maximum partial charges for particular types of atoms (e.g., C, O, etc.) have been used as electrostatic descriptors in the... 

A special class of electrostatic descriptors [charged partial surface area (abbreviated as CPSA) descriptors] has been proposed by Jurs et al. [28-30] in terms of the surface area of the whole molecule or its fragments and in terms of the charge distribution in the molecule. These descriptors, listed in the table, should account for the polar interactions between molecules. 

Rice BM, Byrd EF (2013) Evaluation of electrostatic descriptors for crystalline density. Langmuir... 

In the above formula, D denotes that the summation goes over aU hydrogen donor surfaces, qo is the partial charge on H-bonding donor atoms, Sd is the solvent-accessible surface area of H-bonding donor atoms, and Stot is the total solvent-accessible molecular surface area. The electrostatic descriptors have intuitive interpretations. Their inclusion in QSAR models makes easy and clear analysis of the phenomenon under investigation. 

Descriptors used in the present study are calculated from the information about the connections between the atoms, from atomic 3-D coordinates, and from information about atomic electronic properties. In this work were used (i) graph theoretical (topological descriptors), (ii) geometric descriptors, (iii) electrostatic descriptors, (iv) 3-D descriptors for spectrum-like representation, and (v) density of states spectra. We elaborate on topological descriptors adopted in this particular work in view of a multitude of topological indices available and, in this way. 

Electrostatic Descriptors and Choice ci Partial Atomic Charges... 

A difficult issue with CoMFA entails electrostatic fields calculated inside a particular molecule, because very small changes in location of a lattice point can make a dramatic difference in the potential. Keep in mind that the receptor could not occupy this position. In the default setting in SYBYL CoMFA, any electrostatic energy inside a molecule is assigned to the mean of the noncutoff values of molecules for which this point is outside the molecule. In other implementations, the electrostatic energies are calculated only outside the union volume of the superimposed molecules.[n some CoMFA studies, however, better results were achieved without any steric-based deletion of electrostatic descriptors.20.21... 

CoMMA uses 13 descriptors of shape and electrostatic properties. The pure shape descriptors are the three principal moments of inertia, and the two pure electrostatic descriptors are the magnitude of the dipole moment and the magnitude of the principal quadrupole moment. To complement these, six additional descriptors that relate shape and charge are calculated the dipolar components as well as the magnitudes of the components of displacement between the center of mass and the center of dipole along the three principal axes of inertia. Last, quadrupolar components are calculated with respect to a translated initial reference frame whose origin coincides with the center of dipole. 

Gonz ilez-Diaz, H., Molina, R., Uriarte, E. (2004). Markov entropy backbone electrostatic descriptors for predicting proteins biological activity. Bioorganic Medicinal Chemistry Letters, 14, 4691. 

VAMP can be used with Tsar to provide quantum mechanically calculated descriptors for QSAR. Apart from molecular properties such as dipole, quadrupole, and octupole moments, ionization potential, electron affinity, polarizability (calculated as a default in VAMP by a variational method), etc., atomic properties such as Coulson-, Mulliken-, or MEP-derived charges, chemical shifts and atomic dipoles and quadrupoles, VAMP can also calculate surface electrostatic descriptors introduced by Politzer, and is useful for QSARs and QSPRs involving intermolecular interactions. Many of these descriptors can be exported directly into Tsar for analysis by classical regression techniques or artificial neural nets. ... 

The steric field descriptors explained 42.7 % of the variance, while the electrostatic descriptors explained 57.3 %. 

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