25,27-Bis(ethoxycarbonylmethoxy)-26,28-bis(2-pyridylmethoxy)-5,11,17,23-tetra-tert-butylcalixarene with a 1,3-alternate conformation (1,3-alternate-2) has been synthesized. Dynamic 1H NMR spectroscopy has established that the conformation is immobilized (i.e., the oxygen-through-the-annulus rotation is inhibited). The single crystal was grown from acetonitrile and analysed by X-ray crystallography. It was found that the structural characteristics of a 1,3-alternate conformation are (i) the four phenyl rings are more or less parallel to each other, the dihedral angles between the four phenyl rings and the mean plane of the four methylene groups being 93.5, 100.4, 101.4 and 106.1°, (ii) the ArCH2Ar bond angles are more expanded than those for other conformations and (iii) 1,3-alternate-2 in solution adopts C2 symmetry whereas in the solid state it is less symmetrical because of the unsymmetrical orientation of the ester and the pyridyl substituents. This is a rare example of the X-ray crystallographic analysis of 1,3-alternate calixarenes.
A novel calixarene amphiphilic molecule, denoted by CCaL3, was synthesized and found to form a spherical micelle consisting of 12 molecules at low pH in aqueous solution. Furthermore, uniform Au nanoparticles with 2.0 nm in diameter were synthesized in aqueous solution on the template consisting of the four cysteines of the upper rim of CCaL3. Asymmetric field flow fractionation coupled with light scattering showed that there was no dispersity in the CCaL3 micellar aggregation number. When AuCl4– ions were added into the CCaL3 micelle solution, induced circular dichroism (ICD) appeared, indicating appearance of the structural chirality of the CCaL3/AuCl4– complex. A combination of electron microscopy and small-angle X-ray scattering showed that helically coiled bilayer sheets were formed upon addition of AuCl4–. Subsequent reduction with the amine of cysteine moieties led to uniform Au nanoparticles formation with 2.0 nm in diameter on the micellar plate surface. The nanoparticle size was almost equal to the size of cavity constructed by the four cysteines on the calixarene upper rim, indicating that the growth of Au nanoparticles was spatially controlled by the host–guest interaction between the cysteines and Au.