Amphiphilic O-functionalized calix[4]resocinarenes with tunable structural behavior

Abstract

Novel amphiphilic calix[4]resorcinarenes oxyethylated at the upper rim and alkylated at the lower rim (CR–C_nH_2n+1, here n is the number of carbon atoms in the alkyl substituent; n = 2,5,7,8,9,11) were synthesized, and their association behavior in water-organic solvents was explored. Surface properties and the association behavior of CRs were shown to be strongly controlled by their structure and the nature of the co-solvent. Solely CR–C₅H₁₁ demonstrates surface activity in the mixed water–DMF and water–DMSO solutions, while no surface activity occurs in the water–THF mixture. The DLS measurements revealed a very low concentration threshold of the aggregation (around 0.01 mM) for the CR series including surface inactive compounds. In water–DMF and water–DMSO solutions the CRs of low hydrophobicity were shown to associate through an open model with the formation of large aggregates of 300–400 nm, while more hydrophobic CRs can associate through a closed model and form rather small micelle-like aggregates of 10 to 20 nm.