(168g) Adsorption, Stabilization and Recovery of Polyphenolic Flavonoids By TiO2 Functionalized Mesoporous Silica Nanoparticles

Flavonoids such as quercetin and its derivatives, which are normally isolated from plants, are antioxidants with medicinal and therapeutic applications for the treatment of cancer, cardiovascular disease and other conditions because they act against tumors, inflammation, and reactive oxygen species. At the same time, because they are photoactive compounds, flavonoids are highly susceptible to degradation and activity loss after extraction from biological sources. Therefore, methods are needed to retain the activity of flavonoids during physicochemical processes and storage. A possible material of interest for binding, protection and release of a wide variety of compounds are engineered silica particles. Porous silica nanoparticles are of interest for the recovery, and more recently, the delivery of therapeutics. Recent progress in metal oxide chemistry allows the synthesis of silica nanoparticles of controlled size, pore properties, and surface functionalization. Titania (TiO₂) dispersed in mesoporous silica nanoparticles (MSNP) is hypothesized to have the potential to act as a high surface area adsorbent for quercetin due to its ability to bind dienols through chelation.

Here, the adsorption of quercetin and rutin (0.05-10 mg/ml in ethanol) is investigated on MSNPs (165 nm diameter) that are functionalized with submonolayer coverage (7-85%) of TiO₂. The amount of flavonoid adsorbed onto the particles was found to be a strong function of titania grafting density on the silica surface. As a function of quercetin concentration, strong binding occurs at low solution concentration followed by a gradual approach to saturation at higher concentration. Nanoparticles with approximately 60% of monolayer coverage of titania adsorb 230 mg quercetin/gram silica, which is more than 100 times the capacity of nonporous particles with similar titania coverage. The flavonoid recovery from nanoparticles was also investigated using biocompatible ethanolic citric acid solution (20% w/v) and a five step multistage desorption process were able to recover more than 90% of the bound flavonoids cumulatively. The radical scavenging activity (RSA) of recovered and particle bound quercetin were measured and most of the RSA was retained after binding quercetin, and after recovery of bound quercetin into solution. The materials developed here have the potential to be used to strongly and directly bind flavonoids and related secondary metabolites from plant cells, and will serve as a synthetic platform to isolate, recover, and potentially deliver these compounds in biological systems.