Confined micro-environment of micelles regulates their interaction with anions

Ion interactions with supramolecular assemblies underlie their applications in the areas of drug delivery, ion recognition, and conduction. The current challenge remains in directly characterizing the interaction of ions with supramolecular assemblies at the nanoscale. Here, we demonstrate that the micro-environment of neutral polymer micelles regulates its interaction with anions by combining element-sensitive anomalous small angle X-ray scattering (ASAXS) and theoretical calculations. ASAXS and molecular dynamics simulations reveal that monovalent ReO4− is located preferentially in the outer shell of the micelle, while the more strongly hydrated divalent SeO42– is excluded from the micelle. However, DFT calculations show that the more highly charged SeO42– should have stronger affinity for an isolated polymer chain than ReO4−. These results suggest that the confined environment created by polymer self-assembly modulates the contribution of hydrophobic and electrostatic interactions to the binding of anions with polymers. The present work sheds light on the role of crowded environments in the interaction of anions with polymers in supramolecular assemblies and offers valuable insights to optimize the design of supramolecular systems.