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 tensi on, fluorescence and dynamic light-scattering established that in wate r cone-1 aggregates into small micellar particles whereas such molecul ar aggregates are not detected for 1,3-alternate-1. In 2(n) both the c one and 1,3-alternate isomers formed aggregates in water but the cone isomers always gave CAC (critical aggregation concentration) values lo wer than the 1,3-alternate isomers. These results consistently indicat e that the cone 2(n) isomers with a cone-shaped hydrophobic surface ar e more cohesive intermolecularly than the 1,3-alternate 2(n) isomers w ith a cylindrical hydrophobic surface. From the molecular shape one ca n expect that the cone isomers favourably form a globular micelle wher eas the 1,3-alternate isomers favourably form a two-dimensional lamell a. This was evidenced by the fact that 1,3-alternate-2(n) can form sta ble vesicular aggregates detectable by an electron microscope whereas cone-2(n) cannot form such stable aggregates. These results demonstrat e that the aggregation properties of calix[4]arene-containing amphiphi les can be controlled by the conformational structure difference in th e calix[4]arene core.