Ion specificities of artificial macromolecules
Artificial macromolecules are well-defined synthetic polymers, with a relatively simple structure as compared to naturally occurring macromolecules. This review focuses on the ion specificities of artifical macromolecules. Ion specificities are influenced by solvent-mediated indirect ion–macromolecule interactions and also by direct ion–macromolecule interactions. In aqueous solutions, the role of water-mediated indirect ion–macromolecule interactions will be discussed. The addition of organic solvents to aqueous solutions significantly changes the ion specificities due to the formation of water–organic solvent complexes. For direct ion–macromolecule interactions, we will discuss specific ion-pairing interactions for charged macromolecules and specific ion–neutral site interactions for uncharged macromolecules. When the medium conditions change from dilute solutions to crowded environments, the ion specificities can be modified by either the volume exclusion effect, the variation of dielectric constant, or the interactions between ions, macromolecules, and crowding agents.