Thermal polymorphic transformation of p-tert-butylcalix[4] arene derivatives bearing amino acid substituents

Studies were made on the polymorphism of p-tert-butylcalix[4]arene derivati ves having amino acid groups on the lower rim to stabilize their hydrophili c pseudocavity by circular intramolecular hydrogen bonding. The calixarenes exhibit a polymorphic transformation upon heating in the solid state. This transformation is controlled by the thermal history of solids, accompanyin g the change on the conformation of the calixarene skeleton and also the ch ange of hydrogen bonding in the hydrophilic pseudocavity.