Mapping the Internal Recognition Surface of an Octanuclear Coordination Cage Using Guest Libraries

Turega, Simon M.; Cullen, William; Whitehead, M. A.; Hunter, Christopher A.; Ward, Michael D.

doi:10.1021/ja504269m

Cited by 113 publications

(157 citation statements)

References 129 publications

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“…Previously, we have established that for a range of cyclic ketones from cyclopentanone to cycloundecanone where steric problems on guest binding in H w did not arise (all guest volumes ≤Rebek's 55 % volume limit),21 a linear increase of around 5 kJ mol −1 in the free energy of binding for each additional CH 2 group was observed which is consistent with expectations based on the increased hydrophobic surface area of the guest 12. These guests therefore provide an ideal starting point to probe the incremental effects associated with stepwise, predictable increases in the hydrophobic surface area of the guest.…”

Section: Resultssupporting

confidence: 88%

“…Apart from this expected effect however, the value of −Δ G for guest binding increased by ca. 5 kJ mol −1 per additional methylene group, exactly as we observed with the cyclic ketone series 12. Most importantly for this work, the temperature dependent studies of binding demonstrated the same two key points as were observed using the ketone series.…”

Section: Resultssupporting

confidence: 83%

“…Our coefficient of 5 kJ mol −1 per CH 2 group12 is close to this, affording favourable enthalpy contributions to binding of up to 50 kJ mol −1 for the hydrocarbon component of cycloundecanone, for example, which optimally fills the cavity;12 this Δ H value is of a magnitude consistent with formation of an additional five hydrogen bonds when all ten water molecules are liberated by this guest.…”

Section: Resultssupporting

confidence: 58%

“…We can imagine that displacing the first water molecule from a cluster of ten, and transferring it to the bulk solution, results in a change in hydrogen‐bonding that is not the same as would arise from displacement of the fifth, or tenth, water molecule. As the guests in Scheme 1 fall within a fairly narrow size range (between 31 and 43 % of the cavity volume),11, 12 it is reasonable that the incremental effect of the extra methylene group in each pairwise comparison is similar in each case.…”

Section: Resultsmentioning

confidence: 99%

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Binding of Hydrophobic Guests in a Coordination Cage Cavity is Driven by Liberation of “High‐Energy” Water

Metherell

Cullen

Williams

et al. 2017

Chemistry A European J

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The cavity of an M8L12 cubic coordination cage can accommodate a cluster of ten water molecules in which the average number of hydrogen bonds per water molecule is 0.5 H‐bonds less than it would be in the bulk solution. The presence of these “hydrogen‐bond frustrated” or “high‐energy” water molecules in the cavity results in the hydrophobic effect associated with guest binding being predominantly enthalpy‐based, as these water molecules can improve their hydrogen‐bonding environment on release. This contrasts with the classical form of the hydrophobic effect in which the favourable entropy change associated with release of ordered molecules from hydrophobic surfaces dominates. For several guests Van't Hoff plots showed that the free energy of binding in water is primarily enthalpy driven. For five homologous pairs of guests related by the presence or absence of a CH2 group, the incremental changes to ΔH and TΔS for guest binding—that is, ΔΔH and TΔΔS, the difference in contributions arising from the CH2 group—are consistently 5(±1) kJ mol−1 for ΔΔH and 0(±1) kJ mol−1 for TΔΔS. This systematic dominance of ΔH in the binding of hydrophobic guests is consistent with the view that guest binding is dominated by release of “high energy” water molecules into a more favourable solvation environment, as has been demonstrated recently for some members of the cucurbituril family.

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Section: Resultssupporting

confidence: 88%

Section: Resultssupporting

confidence: 83%

Section: Resultssupporting

confidence: 58%

Section: Resultsmentioning

confidence: 99%

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Binding of Hydrophobic Guests in a Coordination Cage Cavity is Driven by Liberation of “High‐Energy” Water

Metherell

Cullen

Williams

et al. 2017

Chemistry A European J

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“…Binding of guest molecules by container compounds is often dependent on the volume of the host. Recognition of long-chain, linear hydrocarbons by biological receptors and synthetic supramolecular hosts generally involves ∼55% volume occupancy and relatively low surface complementarity (14)(15)(16). Cavitands with a depth of 1 nm are readily prepared and bind medium-chain n-alkanes, from octane (C 8 ) to decane (C 10 ).…”

mentioning

confidence: 99%

Recognition and sequestration of ω-fatty acids by a cavitand receptor

Mosca

Ajami

Rebek

2015

Proc. Natl. Acad. Sci. U.S.A.

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One of the largest driving forces for molecular association in aqueous solution is the hydrophobic effect, and many synthetic receptors with hydrophobic interiors have been devised for molecular recognition studies in water. Attempts to create the longer, narrower cavities appropriate for long-chain fatty acids have been thwarted by solvophobic collapse of the synthetic receptors, giving structures that have no internal spaces. The collapse generally involves the stacking of aromatic panels onto themselves. We describe here the synthesis and application of a deep cavitand receptor featuring "prestacked" aromatic panels at the upper rim of the binding pocket. The cavitand remains open and readily sequesters biologically relevant long-chain molecules-unsaturated ω-3, -6, and -9 fatty acids and derivatives such as anandamide-from aqueous media. The cavitand exists in isomeric forms with different stacking geometries and n-alkanes were used to characterize the binding modes and conformational properties. Long alkyl chains are accommodated in inverted J-shaped conformations. An analogous cavitand with electron-rich aromatic walls was prepared and comparative binding experiments indicated the role of intramolecular stacking in the binding properties of these deep container molecules. (1) and other open-ended host structures (2, 3) that more or less fold around their guest targets. As initially encountered by Cram et al. (4), deep cavitands are dynamic and interconvert between two conformations in organic media: a receptive "vase" form and the unreceptive "kite" form as its dimeric "velcrand" (Fig. 1) (4-8). Stacking of aromatic surfaces in the velcrand buries one face of each kite and is driven by a generalized solvophobic effect. The vase can be rigidified by covalent bonds (9-13) but in water the dynamic cavitands collapse into velcrands through the more specific hydrophobic effect. The presence of appropriate guests shifts the equilibrium to the vase conformation: The guest must fit into, fill, and solvate the cavitand host's hydrophobic interior. Binding of guest molecules by container compounds is often dependent on the volume of the host. Recognition of long-chain, linear hydrocarbons by biological receptors and synthetic supramolecular hosts generally involves ∼55% volume occupancy and relatively low surface complementarity (14-16). Cavitands with a depth of 1 nm are readily prepared and bind medium-chain n-alkanes, from octane (C 8 ) to decane (C 10 ). Longer alkanes such as tetradecane (C 14 ) often induce the formation of dimeric, capsule-like assemblies in which the alkyls assume compressed conformations involving folding and coiling (17, 18). Common, long-chain fatty acids bearing saturated or unsaturated alkyl chains are not readily accommodated in dimeric capsules (19,20) or in the vase forms of typical cavitands. Here, we report a deeper cavitand with a longer, narrower cavity that readily sequesters physiologically relevant fatty acids and derivatives from aqueous media. ResultsSynthesis and Characte...

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Coordination Compounds

McConnell

Lehr

2019

Supramolecular Chemistry in Water

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Mapping the Internal Recognition Surface of an Octanuclear Coordination Cage Using Guest Libraries

Cited by 113 publications

References 129 publications

Binding of Hydrophobic Guests in a Coordination Cage Cavity is Driven by Liberation of “High‐Energy” Water

Binding of Hydrophobic Guests in a Coordination Cage Cavity is Driven by Liberation of “High‐Energy” Water

Recognition and sequestration of ω-fatty acids by a cavitand receptor

Coordination Compounds

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