Quantum-chemical calculations of the charge distribution in ionic surfactants

The charge distribution in common ionic surfactant molecules is estimated u sing quantum chemical methods. Calculations are compared for four widely ac cepted semiempirical methods (MINDO/3, AM1, PM3, and MNDO/d). The atomic pa rtial charges are calculated for surfactants with linear alkyl tails and co mmon headgroups, including anionic (sulfate, sulfonate, carboxylate), catio nic (trimethylammonium, pyridinium), and amphoteric (betaine, dimethylamine oxide) classes. The headgroup charges are shown to distribute to the rest of the molecule, with significant partial charge on the a-methylene group ( 3 -40%) and a partial charge on the remaining alkyl tail (4-11%). The parti al charge distribution influences surfactant self-assembly and physical pro perties.