Dramatically Increased Binding Constant of Water-Soluble Cyclodextrin Hyperbranched Polymers: Explored with Diffusion Ordered NMR Spectroscopy (DOSY)

We report that the polymerization of cyclodextrin (CD) with epichlorohydrin (ECH) dramatically increases the binding constant of CD to vanillin, from 55 to 8.4 × 103 M–1, by approximately 100 times, as determined by diffusion ordered spectroscopy (DOSY)–1H NMR. The binding constant increased with an increase of the ECH content of the polymer, although ECH polymers without CDs showed no affinity at all, suggesting that the hydrophobicity of the ECH network outside of CDs helps to enhance the binding. This increased binding constant allows CD–ECH polymers to increase the drug loading ratio, which may be one of the most critical issues for drug delivery systems.