The first synthetic ion channel was constructed by partial substitution on the primary rim of β-cyclodextrin. Other substituted β-cyclodextrins have since been reported, including thiol-modified cyclodextrins, an anion-selective oligobutylene channel, and various poly-ethyleneoxide linked starburst oligomers.  Structure-activity relationships for a large suite of cyclodextrin "half-channels" prepared by "click"-chemistry has been recently reported.