Cucurbit[7]uril-Tetramethylrhodamine Conjugate for Direct Sensing and Cellular Imaging

Andrew T. Bockus, Lauren C. Smith, Amy G. Grice, Omar A. Ali, Carolyn C. Young, William Mobley, Ashley Leek, James L. Roberts, Brittany Vinciguerra, Lyle Isaacs, Adam R. Urbach

Research output: Contribution to journalArticlepeer-review

61 Scopus citations


This paper describes the design and synthesis of a conjugate (Q7R) comprising the synthetic host cucurbit[7]uril (Q7) linked to the fluorescent dye tetramethylrhodamine (TMR), and the characterization of its optical and guest-binding properties as well as its cellular uptake. Q7R was synthesized in two steps from monofunctionalized azidobutyl-Q7 and NHS-activated TMR. The fluorescence of Q7R is quenched upon guest binding, and this observable was used to determine equilibrium dissociation constant (Kd) values. Unexpectedly, the Kd values for guests binding to Q7R and to unmodified Q7 were essentially identical. Therefore, Q7R can directly report binding to Q7 without an energetic penalty due to the conjugated fluorophore. This result demonstrates a potentially general strategy for the design of single-component host-indicator conjugates that respond sensitively to analytes without perturbing the binding properties of the host. The unique properties of Q7R enabled measurement of Kd values across 3 orders of magnitude and at concentrations as low as 0.7 nM. This result is particularly relevant given the unmatched range of guests and binding affinities demonstrated for Q7. Confocal fluorescence microscopy of live and fixed HT22 neurons revealed the cellular uptake of Q7R and its punctate localization in the cytoplasm. Q7R did not alter cell growth at concentrations up to 2.2 μM over 4 days. These experiments demonstrate the feasibility of Q7R as a direct sensor for guest binding and as a cell-permeable compound for imaging applications.

Original languageEnglish (US)
Pages (from-to)16549-16552
Number of pages4
JournalJournal of the American Chemical Society
Issue number50
StatePublished - Dec 21 2016
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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