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Issue 19, 2013
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Subtle “supramolecular buttressing effects” in Cucurbit[7]uril/guest assemblies

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Abstract

Biphenyl derivatives bearing a dimethylsulfonium group at position 3 and three different substituents at position 4 (H, F and CH3) have been prepared as probes to test the validity of the “supramolecular buttressing” concept. We define the latter as the alteration, by a neighboring unit, of a substituent effect on intermolecular recognition. In this case, the 4-substituents exert some pressure on the 3-dimethylsulfonium groups and control the ratio of their syn and anti conformations. As free species, biphenyls bearing 4-H and 4-F substituents are present as approximately equimolar mixtures of syn and anti-conformers, while the biphenyl scaffold with a 4-CH3 group adopts the anti-conformation exclusively. The 3-dimethylsulfonium substituents then interact with one of the carbonylated portals of Cucurbit[7]uril (CB[7]), and their conformations affect the position of the guests inside the cavity of the macrocycle, thereby validating our “supramolecular buttressing” model. Surprisingly however, binding affinities towards CB[7] are barely affected by the nature of the 4-substituents and the conformations of the neighboring sulfonium groups, despite very different electronic densities presented to the CB[7] portal in their syn or anti conformations. Solvation was found to dramatically smoothen host–guest Columbic interactions, although the latter remain important in the recognition process. Replacing the positively charged 3-dimethylsulfonium unit with an isopropyl substituent decreases the affinity of the biphenyl guest by 1000-fold.

Graphical abstract: Subtle “supramolecular buttressing effects” in Cucurbit[7]uril/guest assemblies

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Publication details

The article was received on 03 Feb 2013, accepted on 26 Mar 2013 and first published on 27 Mar 2013


Article type: Paper
DOI: 10.1039/C3OB40250A
Citation: Org. Biomol. Chem., 2013,11, 3116-3127

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    Subtle “supramolecular buttressing effects” in Cucurbit[7]uril/guest assemblies

    R. Joseph and E. Masson, Org. Biomol. Chem., 2013, 11, 3116
    DOI: 10.1039/C3OB40250A

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