Confinement of Amino Acids in Tetra-<i>p</i>-Sulfonated Calix[4]arene Bilayers

Supramolecular complexes of tetra-p-sulfonated calix[4]arene and racemic (alanine, histidine, and phenylalanine) and chiral ((S)-alanine, (S)-histidine, and (S)-tyrosine) amino acids have been isolated in the solid state and their molecular structures elucidated by X-ray diffraction studies. For alanine, histidine, and phenylalanine, racemic pairs of molecules are confined in capsules of tetra-p-sulfonated calix[4]arene in an overall bilayer arrangement. The (S)-amino acid isomers for alanine and histidine, however, formed 1:1 complexes within the bilayer arrangement found for many tetra-p-sulfonated calix[4]arene complexes. For (S)-tyrosine, a π-stacked chiral pair of isomers was encapsulated by tetra-p-sulfonated calix[4]arene.