Characterization of macrocyclic host-guest systems by liquid-liquid extraction

Macrocyclic compounds have advanced the molecular recognition of many organic and inorganic guest molecules, utilizing in particular their high degree of pre-organization. This has led to a number of attractive applications, for example in sensor technology, selective separation processes, and the manufacture of advanced materials, right through to the development of artificial enzymes. Liquid-liquid extraction has accompanied these developments from the outset and has contributed, on the one hand, to a better understanding of the fundamentals of molecular recognition processes and, on the other hand, to the development of practical methods for the effective and selective separation of different guest molecules using macrocyclic compounds. Extraction offers the possibility to investigate host-guest systems where the reaction partners have very different solubility properties. The use of the radiotracer method in particular provides very reliable data with a high degree of accuracy. This approach yields highly accurate separation and selectivity factors, as well as information on the lipophilicity of host compounds and even thermodynamic parameters, which provide insight into the enthalpic and entropic contributions of the molecular recognition process. Graphical Abstract