A quantum mechanical study of the ionic interactions in model compounds of polyelectrolite–surfactant complexes derived from polypeptides

A quantum mechanical study on the interactions of alkyltrimethylammonium–acetate (with alkyl=methyl, ethyl, propyl and butyl), methylammonium–methyl sulfate and methylammonium–acetate ion pairs in the gas phase and in solution is presented. These are model complexes for the ionic interactions of self-assembled polyelectrolite–surfactant complexes derived from polypeptides. Two different solvents (water and chloroform) were used to analyze the effects of varying the dielectric constant of the surrounding media on the ionic interactions. The stability of the methylammonium–methyl sulfate and methylammonium–acetate ion pairs was compared to that of the corresponding non-ionic hydrogen-bonded forms.