Nanostructured Oxide-Based Systems for the pH-Triggered Release of Cinnamaldehyde

Cinnamaldehyde is a natural product with antibacterial, antifungal, and anti-inflammatory properties, poorly stable in environmental conditions. Systems for the controlled release of cinnamaldehyde are of great interest to the food and pharmaceutical industries. Here, a new oxide-based construct for the release of cinnamaldehyde catalyzed by acidic pH was obtained by a facile grafting method based on amino-silane linkers and imine chemistry. The grafting procedure led to a loading of ca. 5 molecules/nm2, determined on oxide powders with CHN and TGA measurements. The covalent grafting of cinnamaldehyde, demonstrated by FTIR analyses, preserved the molecule stability, simplifying storage. Release tests were performed at different pH values (between 5.0 and 7.4). Thanks to imine chemistry, a fast cinnamaldehyde (CIN) release was observed in a pH 5.0 environment. Using 1 mg/mL suspensions, CIN concentrations within the range adopted in the food industry were obtained (12.4 ppm). The grafting procedure was also performed on a porous film based on a photocatalytic oxide, demonstrating the versatility of this method, adaptable to both powders and macroscopic materials. By taking advantage of the photoactivity of the oxide, regeneration of the fouled film was achieved upon UV irradiation for 1 h, opening the door to reusable devices for the controlled release of cinnamaldehyde.