Chloride capture using a C–H hydrogen-bonding cage

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Science  12 Jul 2019:
Vol. 365, Issue 6449, pp. 159-161
DOI: 10.1126/science.aaw5145

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  • RE: Chloride capture using only C-H hydrogen bonding

    While the authors describe a remarkable cage molecule capable of extremely high affinity binding of chloride ion in which the chloride makes only contacts with hydrogens of C-H bonds, I find it misleading to imply that chloride binding and selectivity is due only to C-H hydrogen bonding. For some reason, the authors do not mention in this paper that a triazole group has a dipole moment of about 5 Debeye with its positive end aligned with the C-H bond vector, as they discussed in an earlier paper describing a chloride binding macrocyclic receptor based on triazoles (Angew. Chemie. Int. Ed., 2008, 2649-2652). So while the chloride is making contact with C-H's, which determine the size and selectivity of the cavity, it is the 6 dipoles pointing at the chloride anion which stabilize it. Had the cage been made with double bonds instead of triazoles, I doubt if chloride would have bound.

    Competing Interests: None declared.