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Complexation of yellow diaminoazobenzenes 1 and 3 inside cucurbit7uril (CB7) results in the formation of purple-colored CB7.cis-1.2H+ and CB7.cis-3.2H+ complexes, respectively. The high binding affinity and selectivity displayed by CB7 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 cucurbitnuril molecular containers. The remarkable yellow to purple color change was utilized in the construction of an indicator displacement assay for biologically active amines 4-10. This indicator displacement assay is capable of quantifying the pseudoephedrine (5) content in Sudafed tablets over the 5-350 microM range.
Wu et al. (Tue,) studied this question.
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