High-performance liquid chromatographic study of the interactions between immobilized beta-cyclodextrin polymers and hydrophobically end-capped polyethylene glycols.

The formation of inclusion complexes between polyethylene glycols (PEGs) bearing hydrophobic ends (naphtyl and phenyladamantyl) and beta-cyclodextrin polymers (poly beta-CD) immobilized onto silica particles was studied by high-performance liquid chromatography (HPLC). It was shown that hydrophobic interactions were involved in the retention mechanism of these compounds, since retention volumes decreased when organic solvents were added to the mobile phase while it was the contrary in the presence of salts. Moreover, the association could be reversed by adding a competitor (hydroxypropyl beta-cyclodextrin) to the mobile phase. A theoretical model permitted the evaluation of affinity constants of 1:1 complexes formed between the modified PEGs and the immobilized poly beta-CD which depended on the type of hydrophobic groups grafted to the PEG.