A reference scale of cucurbit[7]uril binding affinities.

The accurate determination of ultra-high binding affinities in supramolecular host-guest chemistry is a challenging endeavour because direct binding titrations are generally limited to affinities <106 M-1 due to sensitivity constraints of common titration methods. To determine higher affinities, competitive titrations are usually performed, in which one compound with a well established binding affinity serves as a reference. Herein, we propose a reference scale for such competitive titrations with the host cucurbit[7]uril (CB7) comprising binding affinities in the range from 103 to 1015 M-1. The suggested reference compounds are commercially available and will aid in the future determination of CB7 binding affinities for stimuli-responsive host-guest systems.