Chapter 3: Synthetic Receptors for Alkali Metal Cations

This chapter describes the development of neutral host molecules that bind seemingly featureless, spherical alkali metal cations. This work evolved into the broad field of supramolecular chemistry. Crown ethers, cryptands, spherands, and cavitands were the genesis of the field. Variants of each of these structural types were developed to enhance selectivity, to permit on–off switching, to foster ion transport or to permit real-time detection of a guest ion. The principles and structures have now been incorporated into a range of sensors applicable in the biological context and as biomimetics—compounds that imitate the functions of natural cation binding peptides and proteins.