SELF-ASSEMBLY OF TETRACATIONIC AMPHIPHILES BEARING A CALIX[4]ARENE CORE - CORRELATION BETWEEN THE CORE STRUCTURE AND THE AGGREGATION PROPERTIES

Water-soluble, conformationally-immobilized calix[4]arenes (1 and 2(n)) with cone and 1,3-alternate conformations have been synthesized: at the para-position of each phenyl unit 1 has a Me(3)N(+)CH(2) group and 2(n) has a Me(3)N(+)[CH2]nOCH2 group. Examinations with surface tension, fluorescence and dynamic light-scattering established that in water cone-1 aggregates into small micellar particles whereas such molecular aggregates are not detected for 1,3-alternate-1. In 2(n) both the cone and 1,3-alternate isomers formed aggregates in water but the cone isomers always gave CAC (critical aggregation concentration) values lower than the 1,3-alternate isomers. These results consistently indicate that the cone 2(n) isomers with a cone-shaped hydrophobic surface are more cohesive intermolecularly than the 1,3-alternate 2(n) isomers with a cylindrical hydrophobic surface. From the molecular shape one can expect that the cone isomers favourably form a globular micelle whereas the 1,3-alternate isomers favourably form a two-dimensional lamella. This was evidenced by the fact that 1,3-alternate-2(n) can form stable vesicular aggregates detectable by an electron microscope whereas cone-2(n) cannot form such stable aggregates. These results demonstrate that the aggregation properties of calix[4]arene-containing amphiphiles can be controlled by the conformational structure difference in the calix[4]arene core.