Preparation and Properties of Supramolecular Aggregation of Dual-Sensitive Cyclodextrins

Abstract

Polymer inclusion complexes with supramolecular structures formed between various polymers and cyclodextrins (CDs) have been attracted increasing attention. The stimuli-responsive supramolecules including pH, temperature, light, and magnetic fields as “smart” soft materials have been found promising in bioapplications, because they could respond environmental changes and self-induce structural transformations. Thus, to design and achieve responsive supramolecule is of significance not only to scientific research but also to potential applications. In this report, light and temperature dual-sensitive supramolecules were prepared by host-guest interaction between light-sensitive cyclodextrin derivatives and temperature-sensitive polymers. Light-sensitive 4-hydroxycinnamic acid modified β-cyclodextrin (4HCA-CD) was prepared firstly as host compound. Then, two adamantanes (ADs) terminated temperature-sensitive AD-poly(N-isopropylacrylamide)-AD polymer (AD-PNIPAM-AD) was prepared by reversible addition fragmentation chain transfer polymerization (RAFT) using two ADs terminated compound as chain transfer agent. The structures of 4HCA-CD and AD-PNIPAM-AD were confirmed by FT-IR and H NMR spectra. Molecular weight and its distribution of AD-PNIPAM-AD were determined by GPC. The 4HCA-CD/AD-PNIPAM-AD complex was prepared by mixing 4HCA-CD and AD-PNIPAM-AD, and was confirmed by 2D NMR spectrum and GPC. With UV irradiation, the absorbance of cinnamate group at 290 nm by ultraviolet visible spectrophotometer (UV-vis) spectra reduced, and the molecular weight of the complex increased about twice. These results suggested that the 4HCA-CD/AD-PNIPAM-AD complex had light-sensitivity. Moreover, the complex showed thermo-sensitivity, and the lower critical solution temperature (LCST) of the obtained host-guest inclusion complexation was 34 °C. Up to LCST, the complex solution produced floccules. Below to LCST, the floccules disappeared and homogeneous solution recovered. The 4HCA-CD/AD-PNIPAM-AD complex could self-assemble into supramolecular aggregation by adding additional water into the complex solution in DMF. Interestingly, the size of the formed aggregation reduced after increasing the temperature up to LCST, possibly due to hydrophilic and hydrophobic transformation and re-assembly of the aggregations. Furthermore, the size could be recycled to the original size by decreasing temperature lower than LCST.