Self-assembly of janus cyclodextrins at the air-water interface and in organic solvents

The self-organization of various amphiphilic cyclodextrins is reported at the air-water interface as well as in organic solvents. These rather rigid molecules expose different molecular surfaces to the external medium according to the nature of the environment, and consequently several types of association are observed. At the air-water interface, stable mono- and multilayers are formed whose behavior can be related to the molecular structure of the amphiphilic compounds. In apolar aromatic solvents, such as benzene or toluene, dimerization occurs as shown by vapour pressure osmometry (VPO), H-1 NMR spectroscopy and (HC)-H-1-C-13 heteronuclear NOE measurements. Such a feature is absent in organic solvents that compete for the formation of hydrogen bonds. The consequences of these results concerning the use of cyclodextrin derivatives as calibration standards for the determination of molecular weights are discussed.