In PIBSI, the deposit-DCA interaction comes primarily from non-covalent NH-π interactions between the polyamine groups and the aromatic deposit. On the other hand, the larger number of polar moieties in the betaine head-group underpins the improved performance of the zwitterionic surfactant. The presence of the alcohol group allows to leverage similar non-covalent forces as in the case of PIBSI, based on OH-π interactions. The phenyl group in the zwitterionic surfactant also has π-π interactions with the circumovalene deposit. 101 Most importantly, the quarternary ammonium cation enables cation-π interactions, while the carboxylate anion results in ion-dipole or anion-π interactions. The standard OPLS-AA parametrisation underestimates the strength of cation-π interactions, which leads to an adsorption free energy for the zwitterionic surfactant on circumovalene from iso-octane that is around one third lower than when the π-electrons are explicitly represented using the IFF framework. This is similar to the underestimation in the adsorption energy for the tetramethylammonium (TMA) cation-benzene system reported previously with OPLS-AA. On the other hand, the adsorption free energy for PIBSI is identical for the standard OPLS-AA parameterisation and IFF with explicit π-electrons.