Intramolecular Hydrogen Bonding in DIBMA Model Compounds

The structure of model compounds for the amphiphilic copolymer poly(diisobutylene-alt-maleic acid), DIBMA, is investigated with (gas phase) B3LYP/6-31G** and PM7 calculations. It is found that in the monoprotonated state of the repeating unit strong (about 70 kJ mol⁻¹) ionic hydrogen bonds are formed within the hydrogen succinate rings, which impart partial structural rigidity on the backbone of the copolymer. Based on literature pK_a values of the first and second deprotonation step of the succinic acid units, it is argued that the ionic hydrogen bonds are likely to be present in aqueous solution as well. The main chain conformation depends strongly on the stereochemical configuration of the carbon atoms in the hydrogen succinate rings. The possible consequences of the hydrogen bonding for the mechanism of membrane solubilization by maleic acid-based amphiphilic copolymers are discussed.