Adsorption characterization of various modified β-cyclodextrins onto TEMPO-oxidized cellulose nanofibril membranes and cryogels

TEMPO-Oxidized cellulose nanofibrils (toCNF), in the form of highly entangled network such as membrane or cryogels, have proven to be of interest for various applications, including drug release or purification by pollutant adsorption. β-Cyclodextrins (β-CDs) have the ability to form inclusion complexes with large amount of hydrophobic molecules, and are considered as a promising way to bring new functionalities to these materials, by reducing drug burst release effect or improving the pollutant adsorption properties. The study of the adsorption β-CDs onto toCNF is then crucial to design toCNF/β-CDs materials, but is very complex due to the chemical proximity between these compounds. In this study, we develop toCNF cryogels containing various types of β-CDs derivatives by physical adsorption. Different protocols for analyzing the interactions between these compounds, such as Isothermal Titration Calorimetry (ITC), Quartz-Crystal Microbalance with dissipation monitoring (QCM-d) and a Phenolphthalein-based protocol (PhP protocol) have been performed. Adsorption between β-CD and toCNF was proven at two different temperatures with ITC. QCM-d measurements allowed measuring adsorption of different β-CDs derivatives onto toCNF, with higher adsorption measured for the modified β-CDs, and with estimated binding capacity ranging from 13.4 to 47.6 μmol/g toCNF. PhP protocol allowed us to monitor the amount of β-CDs released in aqueous environment, highlighting a lower release for modified β-CDs onto toCNF, and the results were consistent with the estimated binding capacity. This quantification of the binding adsorption capacity of various β-CDs is key results for optimizing the design of toCNF/β-CDs materials.