Synthesis and characterization of water-soluble β-cyclodextrin polymers via thiol-maleimide 'click' chemistry

Water-soluble beta-cyclodextrin polymers (beta-CDPs) employing thiolated beta-cyclodextrin (beta-CD-(SH)7) and maleimide-functionalized hydroxypropyl-beta-cyclodextrin (HPCD-AMI) were successfully synthesized in aqueous solution via thiol-maleimide 'click' chemistry. The intermediate and final synthesized beta-CDPs were characterized by Fourier transform infrared spectroscopy (FT-IR), H-1 nuclear magnetic resonance (H-1 NMR), Matrix-assisted laser desorption ionization-time of flight mass spectroscopy (MALDI-TOF), size exclusion chromatography (SEC), X-ray powder diffractometer (XRD), and thermalgravimetric analysis (TGA). It was found that the Mw of beta-CDPs increased with both feed ratio of HPCD-AMI/beta-CD-(SH) 7 and reaction temperature. Moreover, the H-1 NMR indicated that beta-CDPs prepared at elevated temperature have higher degree of thiol-maleimide reaction compared to that prepared at room temperature, thereby leading to more compact star-like branched structure. Phase solubility study showed that the affinity of curcumin with beta-CDPs was significantly higher than that with the native beta-CD and HP beta-CD. The increase of Mw resulted in an increased or decreased complex-forming capacity, depending on the microstructure of beta-CDPs. Besides, the release behavior study confirmed that beta-CDPs exhibited excellent sustained-release ability for curcumin. These results suggest that the prepared beta-CDPs can be a promising candidate in drug delivery and pharmaceutical application.