Frank Biedermann, Chapter 2 in Supramolecular Chemistry in Water, 2019 Wiley-VCH Verlag GmbH & Co. KGaA.
The guideline and the benchmark for water?compatible host systems is, as so often in supramolecular chemistry, Nature. Proteins, for example, achieve impressive binding affinities in water by burying the substrate in a structurally well?defined cleft or cavity inside the protein structure. The reduced conformational flexibility of macrocycles and the defined size and shape of their cavity facilitates the rationalization of experimental binding trends and the theoretical modeling of host?guest complexes. The chapter describes macrocycles that selectively bind charged guests in aqueous media. It focuses on macrocyclic hosts that bind both non?charged and charged organic guests and for which the hydrophobic effect appears to play an important role. The chapter also discusses selected classes of macrocycles for organic guests and some of their properties. When choosing a suitable water?compatible host for a specific supramolecular application in mind, the following key features are worth considering: guest binding affinity and selectivity; availability/scalability; functionality; solubility; and biocompatibility/toxicity.