Spontaneous Aryldiazonium Grafting for the Preparation of Functional Cyclodextrin-Modified Materials

A mild and efficient surface modification protocol for the preparation of β-cyclodextrin (βCD) modified surfaces through aryldiazonium-mediated grafting is reported. Monosubstituted 6-O-aminophenol-β-cyclodextrin (amβCD) was synthesized through a three-step protocol. This compound was found to form supramolecular aggregates in aqueous solutions at relatively low concentrations via cavity-directed self-assembly. Disruption of these supramolecular structures through judicious choice of solvent was found to be essential for the formation of the reactive aryldiazonium species from the amino-phenolic precursor and for spontaneous surface grafting from aqueous solutions. Cyclodextrin thin films were prepared on carbon macroscopic substrates and electrodes and were characterized via infrared reflectance absorption spectroscopy (IRRAS), cyclic voltammetry, and water contact angle measurements. Protein adsorption studies demonstrated that βCD adlayers reduced nonspecific protein adsorption. βCD moieties in adlayers can be used nonetheless for specific host-guest complexation and are grafted at the surface with monolayer coverage (1.2 × 10^-10 mol cm^-2) as demonstrated via experiments using ferrocene, a redox probe. Finally, cyclodextrin covalent immobilization was demonstrated also on stainless steel and polyamide samples, two substrates with wide ranging technological applications.