β-Cyclodextrin-Functionalized Cellulose Nanocrystals and Their Interactions with Surfactants.

β-cyclodextrin (β-CD) forms a host-guest inclusion complex with many organic and amphiphilic compounds found in pharmaceutical, textile, cosmetic, food, and personal care systems. Therefore, grafting of β-CD onto a cellulose nanocrystal (CNC) offers a possible strategy to use functionalized CNC to complex with surface-active molecules. We have successfully grafted β-CD onto CNCs in a stepwise manner using cyanuric chloride as the linker. The structure of β-CD-grafted CNC (CNC-CD) was characterized by UV-vis and Fourier-transform infrared spectroscopy, and the grafting ratio of β-CD was determined by the phenolphthalein inclusion protocol. Ionic surfactants induced the aggregation of CNC-CDs by forming inclusion complexes with β-CDs on the surface of CNC. The interactions of amphiphilic compounds with CNC-CD were examined by surface tensiometry, conductometric and potentiometric titration, and isothermal titration calorimetry. Mechanisms describing the complex formation between surfactants and CNC-CD were proposed, where an improved understanding of CD interactions with surfactants and lipids would enable better strategies for drug encapsulation and delivery with CDs.