Molecular design and characterizations of new calixarene-based gelators of organic fluids

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Abstract
We have found that certain calix[n]arenes having long acyl groups at the p-positions (e.g., 5,11,17,23,29,35,41,47-octadodecanoylcalix[8]arene-49,50,51,52,53,54,55,56-octol: 28C12) act as excellent and unique gelators of various organic solvents (e.g., toluene, carbon tetrachloride, carbon disulfide, hexane, isopropanol, etc.). The sol–gel phase transition temperatures (Tgel) could be determined by the inverted test-tube method or by the DSC method. The change in the aggregation mode at the phase transition temperature was directly observable by an optical microscope: below Tgel., the fibrillar network (diameter ca. 1 µm) appeared whereas above Tgel, it ‘melted’ down. It was shown on the basis of these measurements that the sol-gel phase transition occurs reversibly. The spectroscopic studies using 1H NMR and IR spectroscopy and the comparative experiments using the analogues of 28C12(nine cyclic and six non-cyclic) established that the prerequisites for the formation of the stable organic gels are (i) the intermolecular CO ⋯ HO hygrogen-bonding interaction to form the three-dimensional network and (ii) the moderate affinity of gelators with solvent molecules. The results offer important strategies useful for the molecular design of new gelators of organic fluids.

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