Synthesis of chitosan 6-OH immobilized cyclodextrin derivates via click chemistry

The synthesis of chitosan 6-OH immobilized cyclodextrin (CTS-6-CD) via click chemistry was investigated. After protecting the 2-NH₂ group of chitosan by forming a Schiff base (BCTS) with benzaldehyde, the protected chitosan C₆-OH p-toluenesulfonate (BCTS-6-OTs) was generated by treating with p-toluenesulfonyl chloride. Afterwards, nucleophilic substitution of the sulfonate with NaN₃ furnished the Schiff base protected chitosan C₆-N₃ (BCTS-6-N₃). On the other hand, alkynylic β-cyclodextrin (CD-OPg) was obtained by alkynylation of β-cyclodextrin (β-CD). With these two substrates in hand, β-CD was immobilized at the Schiff base protected chitosan 6-OH position via click chemistry between CD-OPg and BCTS-6-N₃ to afford BCTS-6-CD, and then chitosan 6-OH immobilized cyclodextrin derivates (CTS-6-CD) was obtained by deprotecting the Schiff base of BCTS-6-CD. The structures of these products were characterized by FTIR, and their crystal properties and thermal stabilities were studied by XRD and TG respectively. By using UV spectroscopy to determine the immobilized amount, we also investigated the effect of the click reaction conditions on the immobilized loading of the synthesized BCTS-6-CD. It was found that the immobilized loading was 197.61 μmol·g^-1 in the BCTS-6-CD that was synthesized under the optimum conditions, and it went up to 223.17 μmol·g^-1 in CTS-6-CD by deprotecting the Schiff base group.