Charged Partial Surface Area CPSA Descriptors

10 Charged Partial Surface Area (CPSA) Descriptors 

The CPSA descriptors (Stanton and Jurs 1990 Stanton et al. 1992) are calculated according to the size and electrical charge of the atomic spheres and are considered a measure of the polar interaction between molecules. Total surface, total positive 

---

Stanton and Jurs [3] developed a model for a more diverse set of compounds, including hydrocarbons, halogenated hydrocarbons, alkanols, ethers, ketones, and esters. The model has been evaluated with 31 compounds, using, among others, charge partial surface area (CPSA) descriptors ... 

Delgado reports a QSPR model [49] for the prediction of log(l/S) for a set of 50 chlorinated hydrocarbons including chlorinated benzenes, dibenzo-p-dioxins and PCBs. The model involves only two molecular descriptors, one geometry-dependent descriptor and one charged partial surface area (CPSA) descriptor. The geometric descriptor is the area of the shadow of the molecule projected on a plane defined by the X and Y axes XY shadow) the CPSA descriptor is the surface weighted atomic partial negative surface area (WNSA-3). The model has a squared correlation coefficient of 0.97 and standard deviation of 0.45 log units. 

Charged Partial Surface Area descriptors ( CPSA descriptors)... 

CPSA descriptors charged partial surface area descriptors... 

HB-CPSA descriptors hydrogen-bond charged partial surface area descriptors -> charged partial surface area descriptors... 

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. 

A set of thirty different descriptors [Stanton and Jurs, 1990] which combine shape and electronic information to characterize molecules and therefore encode features responsible for polar interactions between molecules. The molecule representation used for deriving CPSA descriptors views molecule atoms as hard spheres defined by the - van der Waals radius. The - solvent-accessible surface area SASA is used as the molecular surface area it is calculated using a sphere with a radius of 1.5 A to approximate the contact surface formed when a water molecule interacts with the considered molecule. Moreover, the contact surface where polar interactions can take place is characterized by a specific electronic distribution obtained by mapping atomic partial charges on the solvent-accessible surface. 

Let SAd and SAa be the solvent accessible surface areas of hydrogen-bonding donors (d) and acceptors (a), respectively, and Qa the corresponding partial atomic charges, SASA the molecular solvent-accessible surface area the HB-CPSA descriptors are then defined as follows (note that the two different symbols encountered in the literature for some are considered as synonymous). 

Examples of combined descriptors using products are the contributions SA , largely used in -> CPSA descriptors, where q and 5A are partial charges and atomic surface areas [Bakken and Jurs, 1999a]. 

Let SA+ and SAf be the surface area contributions of the ath positive and negative atoms, respectively qf and qf the partial atomic charges for the ath positive and negative atoms and and Of the total sum of partial positive and negative charges in the molecule, respectively. The CPSA descriptors are defined as the following ... 

---