The Structures and Thermodynamics of Complexes between Water‐Soluble Calix[4]arenes and Dipyridinium Ions

Abstract

Three crystalline complexes were prepared by the inclusion complexation of p‐sulfonatothiacalix[4]arene (TCAS) and p‐sulfonatocalix[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 so‐called 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Sulfonate···Pyridinium Supramolecular Synthon: A Robust Interaction Utilized to Design Molecular Assemblies

“…Besides strength and directionality, the defining criterion for a robust supramolecular synthon is its frequency of occurrence. Although reported few and far between, − sulfonate···pyridinium interactions are not categorized as robust supramolecular synthons. , Our recent account of supramolecular assemblies based on this synthon indicated its facile manifestation . Molecular salts 1 – 6 further indicate persistent sulfonate···pyridinium synthon formation, even in the presence of other possible competing interactions.…”

“…It was also observed that in addition to thermal and chemical stability, proton transfer leads to incipience of color in the products of colorless pristine formers. These results prompted us to further investigate the sparsely reported sulfonate···pyrdinium synthon. − In addition to fewer hits than for the corresponding carboxylic acid···pyridine synthon, our CCDC search indicated a large tendency for proton transfer of the sulfonic proton to pyridyl nitrogen, i.e., salt formation in the sulfonic acid pyridine-based synthon, Chart . Here, we report a series of supramolecular aggregates utilizing aryl-sulfonic acid and various pyridyl derivatives (Chart ), as a case for consideration of sulfonate···pyridinium interaction as a robust supramolecular synthon.…”

Molecular Recognition in Water Using Macrocyclic Synthetic Receptors

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Study of ionic surfactants interactions with carboxylated single-walled carbon nanotubes by using ion-selective electrodes

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