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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

Side (a) and (b) top views of two superimposed crystal structures of triallyl cryptophane (2). 2 is shown encapsulating MeOH (grey) and CDCl3 (pink). Guests, hydrogens and side chains were removed for easier viewing.
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f4: Side (a) and (b) top views of two superimposed crystal structures of triallyl cryptophane (2). 2 is shown encapsulating MeOH (grey) and CDCl3 (pink). Guests, hydrogens and side chains were removed for easier viewing.

Mentions: Overlaid structures of 2, complexed with MeOH and CDCl3 (Fig. 4), provide clear indication that the internal volume of cryptophane-A is controlled by the three O-CH2-CH2-O linkers connecting the CTG units. We used CrystMol 2.1 (ref. 38) to superimpose the carbon backbone structures of 2 with bound MeOH and CDCl3, as these guests produced the largest difference in host cavity volume (Table 1). The superimposed cryptophane structures show the smaller 2-MeOH structure (Fig. 4, grey carbon backbone) residing mostly inside the pink carbon backbone representing 2-CDCl3. The structures can be aligned such that one of the ethylenedioxy linkers (labelled O(2)-C(46)H2-C(47)H2-O(3)) is almost unchanged. However, linker O(8)-C(56)H2-C(57)H2-O(9) in the 2-CDCl3 complex is partly expanded such that the O(8)-O(8) and C(56)-C(56) distances between the two structures differ by 0.56 and 0.65 Å, respectively. An even more pronounced change is seen for the third linker, (O(5)-C(51)H2-C(52)H2-O(6)); O(6)-O(6) and C(52)-C(52) distances differ by 0.89 and 1.06 Å (Fig. 4, Supplementary Table S2). These data show that cryptophane-A can expand both horizontally and vertically upon binding the larger chloroform guest, moving the CTG units farther apart by as much as 0.4 Å.


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)

Side (a) and (b) top views of two superimposed crystal structures of triallyl cryptophane (2). 2 is shown encapsulating MeOH (grey) and CDCl3 (pink). Guests, hydrogens and side chains were removed for easier viewing.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Side (a) and (b) top views of two superimposed crystal structures of triallyl cryptophane (2). 2 is shown encapsulating MeOH (grey) and CDCl3 (pink). Guests, hydrogens and side chains were removed for easier viewing.
Mentions: Overlaid structures of 2, complexed with MeOH and CDCl3 (Fig. 4), provide clear indication that the internal volume of cryptophane-A is controlled by the three O-CH2-CH2-O linkers connecting the CTG units. We used CrystMol 2.1 (ref. 38) to superimpose the carbon backbone structures of 2 with bound MeOH and CDCl3, as these guests produced the largest difference in host cavity volume (Table 1). The superimposed cryptophane structures show the smaller 2-MeOH structure (Fig. 4, grey carbon backbone) residing mostly inside the pink carbon backbone representing 2-CDCl3. The structures can be aligned such that one of the ethylenedioxy linkers (labelled O(2)-C(46)H2-C(47)H2-O(3)) is almost unchanged. However, linker O(8)-C(56)H2-C(57)H2-O(9) in the 2-CDCl3 complex is partly expanded such that the O(8)-O(8) and C(56)-C(56) distances between the two structures differ by 0.56 and 0.65 Å, respectively. An even more pronounced change is seen for the third linker, (O(5)-C(51)H2-C(52)H2-O(6)); O(6)-O(6) and C(52)-C(52) distances differ by 0.89 and 1.06 Å (Fig. 4, Supplementary Table S2). These data show that cryptophane-A can expand both horizontally and vertically upon binding the larger chloroform guest, moving the CTG units farther apart by as much as 0.4 Å.

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