Inclusion of antioxidants in MCM-41: physico-chemical properties and activity

Flavonoids have great potential against oxidative stress, an important biochemical process involving highly reactive oxygen or nitrogen species that can lead to the oxidation of lipids, proteins or nucleic acids and contribute to cellular dysfunction. Quercetin, in particular, satisfies the proposed criteria for effective radical scavenging, since the o-dihydroxy-structure in the central ring confers high stability to the radical form and participates in electronic delocalization. The therapeutic usefulness is limited by the unfavourable physico-chemical properties: poor water solubility and low thermal and photostability. One recently proposed method to solve these drawbacks consists in the inclusion of antioxidants in supramolecular structures (phospholipids, cyclodextrins, etc.), which should also allow controlled release for topical treatments. In this work, we have studied the inclusion of quercetin and Trolox (a water soluble analog of vitamin E often employed as a benchmark for its antioxidant activity) in MCM-41 mesoporous silica. In vitro tests showed a slower release of the antioxidants after inclusion, in agreement with an increase of photostability under UVB irradiation; a certain radical scavenging activity was also observed. The influence of the preparative methods and the differences between the two antioxidants are discussed in terms of the hydrophilic/hydrophobic interaction with the silica surface.