Cucurbit[7]uril Complexation Drives Thermal trans-cis-Azobenzene Isomerization and Enables Colorimetric Amine Detection

Complexation of yellow diaminoazobenzenes 1 and 3 inside cucurbit[7]uril (CB[7]) results in the forination of purple-colored CB[7]center dot cis-3 center dot 2H(+) and CB[7]center dot cis-3 center dot 2H(+) complexes, respectively. The high binding affinity and selectivity displayed by CB 7 toward 1 and 3 pays the > 10 kcal mol(-1) thermodynamic cost for this isomerization. We investigated the behavior of these complexes as a function of pH and observed large pK(a) shifts and high pH responsiveness, which are characteristic Of cucurbit[n]uril molecular containers. The remarkable yellow to Purple color change Was utilized ill file construction of an indicator displacement assay for biologically active airlines 4-10. This indicator displacement assay is capable of quantifying the pseudoephedrine (5) content in Sudafed tablets over the 5-350 mu M range.