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Crystallographic observation of 'induced fit' in a cryptophane host-guest model system.

Taratula O, Hill PA, Khan NS, Carroll PJ, Dmochowski IJ - Nat Commun (2010)

Bottom Line: Cryptophane-A, comprised of two cyclotriguaiacylenes joined by three ethylene linkers, is a prototypal organic host molecule that binds reversibly to neutral small molecules via London forces.Of note are trifunctionalized, water-soluble cryptophane-A derivatives, which exhibit exceptional affinity for xenon in aqueous solution.Cryptophane internal volume varied by more than 20% across this series, which exemplifies 'induced fit' in a model host-guest system.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104, USA.

ABSTRACT
Cryptophane-A, comprised of two cyclotriguaiacylenes joined by three ethylene linkers, is a prototypal organic host molecule that binds reversibly to neutral small molecules via London forces. Of note are trifunctionalized, water-soluble cryptophane-A derivatives, which exhibit exceptional affinity for xenon in aqueous solution. In this paper, we report high-resolution X-ray structures of cryptophane-A and trifunctionalized derivatives in crown-crown and crown-saddle conformations, as well as in complexes with water, methanol, xenon or chloroform. Cryptophane internal volume varied by more than 20% across this series, which exemplifies 'induced fit' in a model host-guest system.

No MeSH data available.


Related in: MedlinePlus

Ethylenedioxy linker of cryptophane-A. Both anti and gauche conformations are observed in all crystal structures of cryptophane host–guest complexes.
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f5: Ethylenedioxy linker of cryptophane-A. Both anti and gauche conformations are observed in all crystal structures of cryptophane host–guest complexes.

Mentions: In this crystallographic study, we also examined geometrical parameters of the ethylenedioxy linkers that changed during the guest-binding process. In contrast with previous solution spectroscopic studies92526, ethylenedioxy linkers exhibited mixed anti and gauche conformations in the solid state. This determination was based on measured dihedral angles (Θ1, Θ2, Θ3) for all three linkers from the perspective of the 'north' pole of the cryptophane, as defined by CTG with allyl substituents (Fig. 5). By increasing the guest volume from MeOH to CDCl3, the most dramatic change was observed for the linker labelled O(5)-C(51)H2-C(52)H2-O(6): the conformation changed from gauche to anti with the dihedral angle decreasing from 74.5° to −171.7° (Table 2). Such linker transformations allow the increased vertical distance between CTG units observed for chloroform encapsulation (Supplementary Table S2), and also allow the cavity to expand horizontally upon binding this largest guest. The superimposition of cryptophane structures with different sized guests, in addition to calculated internal volumes and dihedral angles, indicate how cryptophane-A can accommodate guests of varied shape and size.


Crystallographic observation of 'induced fit' in a cryptophane host-guest model system.

Taratula O, Hill PA, Khan NS, Carroll PJ, Dmochowski IJ - Nat Commun (2010)

Ethylenedioxy linker of cryptophane-A. Both anti and gauche conformations are observed in all crystal structures of cryptophane host–guest complexes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3105606&req=5

f5: Ethylenedioxy linker of cryptophane-A. Both anti and gauche conformations are observed in all crystal structures of cryptophane host–guest complexes.
Mentions: In this crystallographic study, we also examined geometrical parameters of the ethylenedioxy linkers that changed during the guest-binding process. In contrast with previous solution spectroscopic studies92526, ethylenedioxy linkers exhibited mixed anti and gauche conformations in the solid state. This determination was based on measured dihedral angles (Θ1, Θ2, Θ3) for all three linkers from the perspective of the 'north' pole of the cryptophane, as defined by CTG with allyl substituents (Fig. 5). By increasing the guest volume from MeOH to CDCl3, the most dramatic change was observed for the linker labelled O(5)-C(51)H2-C(52)H2-O(6): the conformation changed from gauche to anti with the dihedral angle decreasing from 74.5° to −171.7° (Table 2). Such linker transformations allow the increased vertical distance between CTG units observed for chloroform encapsulation (Supplementary Table S2), and also allow the cavity to expand horizontally upon binding this largest guest. The superimposition of cryptophane structures with different sized guests, in addition to calculated internal volumes and dihedral angles, indicate how cryptophane-A can accommodate guests of varied shape and size.

Bottom Line: Cryptophane-A, comprised of two cyclotriguaiacylenes joined by three ethylene linkers, is a prototypal organic host molecule that binds reversibly to neutral small molecules via London forces.Of note are trifunctionalized, water-soluble cryptophane-A derivatives, which exhibit exceptional affinity for xenon in aqueous solution.Cryptophane internal volume varied by more than 20% across this series, which exemplifies 'induced fit' in a model host-guest system.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104, USA.

ABSTRACT
Cryptophane-A, comprised of two cyclotriguaiacylenes joined by three ethylene linkers, is a prototypal organic host molecule that binds reversibly to neutral small molecules via London forces. Of note are trifunctionalized, water-soluble cryptophane-A derivatives, which exhibit exceptional affinity for xenon in aqueous solution. In this paper, we report high-resolution X-ray structures of cryptophane-A and trifunctionalized derivatives in crown-crown and crown-saddle conformations, as well as in complexes with water, methanol, xenon or chloroform. Cryptophane internal volume varied by more than 20% across this series, which exemplifies 'induced fit' in a model host-guest system.

No MeSH data available.


Related in: MedlinePlus