QUANTUM CHEMICAL STUDY OF SOLVENT EFFECTS ON BIOMOLECULES - APPLICATION OF THE VIRTUAL CHARGE MODEL AND THE SELF-CONSISTENT REACTION FIELD-THEORY OF SOLVENT EFFECT TO GAMMA-AMINO BUTYRIC-ACID, BETA-ALANINE AND GLYCINE

The faithfulness of the self-consistent reaction field theory and the virtual charge model to represent solvent polarization effects on biomolecules has been examined. Both theories have been implemented within the CNDO/2 MO scheme and subsequently applied to the study of the above mentioned molecules. The results herein reported allow for a rather adequate description of the physicochemical behaviour of these systems. In particular the interconversion process between the non-zwitterionic and the zwitterionic species appears to be essentially due to medium polarization forces. A molecular mechanism already advanced to explain the neurophysiological activity of GABA is substantiated by this study; moreover, a new mechanistic source for this activity is conjectured. From the methodological viewpoint the SCRF theory is given a new solute-solvent f-parameter which permits to introduce the concept of electrostriction into the quantum chemical data analysis. The cross study with the VCM has allowed for the establishment of a relationship between f and the solvent dielectric constant. The polarity scale nature of this mapping is established. © 1979.