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Open AccessArticle

Interactions of Small-Molecule Guests with Interior and Exterior Surfaces of a Coordination Cage Host

1
Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK
2
Department of Chemistry, University of Sheffield, Western Bank, Sheffield S3 7HF, UK
*
Author to whom correspondence should be addressed.
Chemistry 2020, 2(2), 510-524; https://doi.org/10.3390/chemistry2020031
Received: 15 May 2020 / Revised: 29 May 2020 / Accepted: 1 June 2020 / Published: 2 June 2020
(This article belongs to the Section Supramolecular Chemistry)
Coordination cages are well-known to act as molecular containers that can bind small-molecule guests in their cavity. Such cavity binding is associated with interactions of the guests with the surrounding set of surfaces that define the cavity; a guest that is a good fit for the cavity will have many favourable interactions with the interior surfaces of the host. As cages have exterior as well as interior surfaces, possibilities also exist for ‘guests’ that are not well-bound in the cavity to interact with the exterior surface of the cage where spatial constraints are fewer. In this paper, we report a combined solid-state and solution study using an octanuclear cubic M8L12 coordination cage which illustrates the occurrence of both types of interaction. Firstly, crystallographic studies show that a range of guests bind inside the cavity (either singly or in stacked pairs) and/or interact with the cage exterior surface, depending on their size. Secondly, fluorescence titrations in aqueous solution show how some flexible aromatic disulfides show two separate types of interaction with the cage, having different spectroscopic consequences; we ascribe this to separate interactions with the exterior surface and the interior surface of the host cage with the former having a higher binding constant. Overall, it is clear that the idea of host/guest interactions in molecular containers needs to take more account of external surface interactions as well as the obvious cavity-based binding. View Full-Text
Keywords: coordination cage; host-guest chemistry; fluorescence; crystal structures; supramolecular chemistry coordination cage; host-guest chemistry; fluorescence; crystal structures; supramolecular chemistry
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Taylor, C.G.P.; Train, J.S.; Ward, M.D. Interactions of Small-Molecule Guests with Interior and Exterior Surfaces of a Coordination Cage Host. Chemistry 2020, 2, 510-524.

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