Tuning the interactions in cyclodextrin polymer nanoassemblies

The aim of this paper was to study the associations between a neutral β-cyclodextrin polymer and amphiphilic dextrans substituted with two kinds of groups able to make inclusion complexes with β-cyclodextrin. The first kind of substituent is purely hydrophobic (dodecyl C₁₂ or adamantyl Ada groups) and the second one, cyclohexancarboxylic acid group CHX, brings pH-dependent charge density on the dextran chains. Synthesis and characterization of the di-substituted dextrans have been detailed in a first part where it has been shown that the incorporation of CHX groups (up to 7 mol.%) did not modify the self assembling properties of the amphiphilic dextrans. Affinity of the amphiphilic dextrans for β-cyclodextrin polymer has been studied by different methods including isothermal titration calorimetry, dynamic light scattering and zeta potential. An original pH sensitive behaviour has been obtained for polymer–polymer associations at low concentrations. Nanoassemblies are formed at pH around 4 which are destabilized at lower pH and swollen into soluble aggregates at higher pH. The nanoassemblies formed at pH 4 have also been evidenced by transmission electron microscopy and have revealed a spherical shape of few hundred nanometers.