To finalize a scheme intended to calculate directly approximate charge distributions for proteins, parameters for a modified PEOE method are obtained for both ionic and aromatic functional groups. For ionic groups, the electrostatic potentials of several ionic molecules (computed with the 6-31G** basis set) are used as constraints; for aromatic groups, the experimental gas-phase dipole and quadrupole moments of several aromatic molecules are used as constraints. The electrostatic potentials calculated with the modified PEOE point charges of ionic molecules are quite close to the ab initio electrostatic potential surfaces, and the dipole and quadrupole moments calculated with the modified PEOE charges of aromatic molecules agree well with experimental data. The method enables the charge distribution, described as a set of atom-centered monopoles, to be calculated directly. This avoids assumptions concerning transferability of charges from small model compounds and describes in an approximate fashion the redistribution of charge upon assembly of amino acid residues into polypeptide molecules. The computational requirements for the procedure are negligible.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry