Abstract
To describe electrostatic potentials, new sets of fractional point charges are presented for medium-sized neurotransmitters; dopamine, gamma-aminobutyric acid (GABA) and acetylcholine. The charge set consists of the original STO-3G Mulliken net atomic charges and new additional charges. The new additional charge sets were determined to correct electrostatic potential (ESP) values on the van der Waals molecular surface based upon Mulliken net atomic charges from STO-3G calculation.
The additional charge sets were obtained first for a variety of small molecules (water, ammonia, methane, ethane, benzene, formic acid anion, acetic acid, methylammonium, trimethylammonium, tetramethylammonium, and methyl acetate). Lone-pair regions of oxygen and nitrogen atoms showed remarkable improvement. The new additional charge sets were transferred as they were to Mulliken net atomic charge sets of the larger neurotransmitter molecules.
The present method is useful for large molecules of the types often considered in the fields of biological and pharmaceutical sciences; the approach gives approximately the same qualities to classical fractional point charge ESP's as can be obtained with complex ab initio calculations.
