The structures and thermodynamics of complexes between water-soluble calix[4]arenes and dipyridinium ions
Three crystalline complexes were prepared by the inclusion complexation of p-sulfonatothiacalix[4]arene (TCAS) and psulfonatocalix[ 4]arene (CAS) with 2,2 -dipyridinium (2-DP...
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Main Authors: | , , , , |
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Format: | Article |
Published: |
2011
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Subjects: | |
Online Access: | https://hdl.handle.net/10356/92322 http://hdl.handle.net/10220/6944 |
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Institution: | Nanyang Technological University |
Summary: | Three crystalline complexes were prepared by the inclusion
complexation of p-sulfonatothiacalix[4]arene (TCAS) and psulfonatocalix[
4]arene (CAS) with 2,2 -dipyridinium (2-DPD;
(complexes 1 and 2, respectively), and TCAS with 4,4'-dipyridinium
(4-DPD; complex 3). The crystal structures show
that the calixarenes in 1 and 2 maintain their original cone
conformation, with shallow inclusion of 2-DPD, and assemble
themselves into bi-layer arrangements. However, the cone
shape of TCAS in 3 is disrupted by 4-DPD to assume the socalled
1,2-alternate conformation in the solid state, which is
similar to the 1,3-alternate case of CAS stabilized by 4-DPD
(4). The thermodynamics of this inclusion complexation were
further investigated by microcalorimetric titration in aqueous
solution. The obtained results indicated that the molecular
binding ability and selectivity of TCAS/CAS with DPDs is
entirely controlled by enthalpy gains accompanied by a
smaller negative entropic change; these are discussed from the viewpoint of electrostatic, hydrogen-bonding, π-stacking,
and van der Waals interactions, size/shape-fit, and a desolvation
effect between host and guest. The molecular selectivity
for the inclusion complexation of 2-DPD with CAS was found
to be nine times greater than that of 4-DPD with CAS. Combining
the present crystal structures and thermodynamic
parameters revealed that the position of the nitrogen atoms
in the DPDs is the crucial factor for controlling the binding
modes, molecular selectivity, conformational features, and
assembly behavior of the host upon complexation with
TCAS/CAS. This will help us to design large molecular
assemblies possessing highly supramolecular architectures
based on calixarenes by controlling exactly the guest
molecules. |
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