Organic Letters
Letter
R2 was more vulnerable to Lewis acid (MII) assisted imine
hydrolysis. NDI 1 did not display any NMR changes indicative of
anion/NDI interaction (Figure S8), confirming that the anion/
NDI interaction in R3 was indeed facilitated by the cation-
induced folding and electrostatic interaction.
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In summary, we have designed and synthesized two NDI-based
ditopic receptors and demonstrated how a key structural
difference led to dramatically different cation, anion, and ion-
pair recognition behaviors. The tridentate receptor R3 undergoes
MII-induced folding into a ‘U’ conformation, leading to the
formation of ion-pair complexes, in which two interlocked R3
molecules bind a metal ion with their linkers and anions with the
NDI units. The entire process can be reversed with a strong
chelator, making R3 a reusable ion-pair receptor. By contrast,
bidentate R2undergoes ZnII mediated iminehydrolysis, revealing
the importance of the central pyridine ring on the entire ion-pair
recognition process. To our knowledge, R3 represents the first
NDI-based ion-pair receptor, which captures guest cation and
anion simultaneously under allosteric regulation, as the cation-
induced folding and dimerization enabled anion binding at a
differentlocation. Infuture, thecation-inducedfoldingofbis-NDI
receptors could also be exploited for neutral guest recognition,40
sensing, and electron transfer processes. These prospects are
currently under investigation in our laboratory.
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2011, 47, 8112.
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ASSOCIATED CONTENT
* Supporting Information
TheSupportingInformationisavailablefreeofchargeontheACS
■
S
Experimental details, synthesis of receptors, additional
NMR and MALDI-MS data (PDF)
(29) Guha, S.; Goodson, F. S.; Corson, L. J.; Saha, S. J. Am. Chem. Soc.
2012, 134, 13679.
(30) Goodson, F. S.; Panda, D. K.; Ray, S.; Mitra, A.; Guha, S.; Saha, S.
Org. Biomol. Chem. 2013, 11, 4797.
(31) Li, C.-Z.; Chueh, C.-C.; Ding, F.; Yip, H.-L.; Liang, P.-W.; Li, X.;
Jen, A. K.-Y. Adv. Mater. 2013, 25, 4425−4430.
(32) Hogg, L.; Leigh, D. A.; Lusby, P. J.; Morelli, A.; Parsons, S.; Wong,
J. K. Y. Angew. Chem. 2004, 43, 1218.
AUTHOR INFORMATION
■
Corresponding Author
ORCID
(33) Legrand, Y.-M.; Dumitru, F.; Lee, A. V. D.; Barboiu, M. Supramol.
Chem. 2009, 21, 230.
Notes
(34) The MALDI-TOF analysis revealed [R3·MII·R3·X−] ion-pair
complexes containing only one anion, although two X− anions are
needed to balance the overall charges. It is plausible that one of them is
lost during the ionization yielding the charged entities that are only
detected by MALDI. Furthermore, the 1H NMR spectra of the
complexes clearly suggest that all four NDI units in the interlocked
ion-pair complexes are located in the same environment, which is
possible when both pairs of parallel NDI arms sandwich a charge diffuse
anion, as predicted by the energy minimized computational model.
(35) Ulrich, S.; Lehn, J.-M. Chem. - Eur. J. 2009, 15, 5640.
(36) Ulrich, S.; Petitjean, A.; Lehn, J.-M. Eur. J. Inorg. Chem. 2010, 2010,
1913.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Science Foundation
(AwardNo. 1660329). Authorsacknowledge thecontributions of
Drs. Christian Hubley (USACE) and late Atanu Mitra.
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