Direct force measurement between cucurbit[6]uril and spermine using atomic force microscopy

The rupture forces of individual host-guest complexes between surface-confined cucurbit[6]uril (CB[6]) and spermine derivatives were measured directly by atomic force microscopy (AFM). While 1,2-dithiolane-attached spermine was immobilized on a gold-coated AFM tip, perallyloxyCB[6] was attached to an allyl-terminated self-assembled monolayer on a gold substrate by olefin metathesis reaction. A histogram and autocorrelation function analysis yielded a rupture force of approximately 120 pN, which is the highest value ever reported for a synthetic host-guest system.