Antioxidant Activity of SiO<sub>2</sub>@{Sericin} Hybrids: A Comparable OH-Radical and DPPH-Radical Scavenging Study
Annita Theofanous, George Theofilou, Yiannis Deligiannakis, Maria Louloudi
Abstract
High Resolution Image Download MS PowerPoint Slide A new class of hybrid materials was developed via covalent grafting of sericin, a silk-derived protein, onto SiO 2 particles to assess their antioxidant properties. Two variants of SiO 2 @sericin hybrids were synthesized, with 10% ({SiO 2 @sericin_10}) or 20% ({SiO 2 @sericin_20}) sericin loadings. An in tandem analysis of their antioxidant efficiency was performed against OH and DPPH radicals. The experimental results demonstrate that the {SiO 2 @sericin} hybrids exhibit significantly enhanced antioxidant activity compared with sericin in aqueous solution. Specifically, 1 g of the {SiO 2 @sericin_10} hybrid quenches 308 μmol of DPPH radicals and 120 μmol of ● OH, whereas aqueous sericin in solution quenched only 85 μmol of DPPH and 53 μmol of ● OH. IR, Raman, BET, and DLS data collectively indicate that the interfacial topography of sericin on the SiO 2 surface is highly dependent on its loading concentration. At the high loading (20%), sericin forms a hermetic coating over the SiO 2 nanoparticles, resulting in steric hindrance that restricts the accessibility of antioxidant functional groups. In contrast, at the optimized 10% loading, a greater proportion of sericin’s antioxidant moieties remains accessible for radical scavenging. This interfacial topography effect is reflected in the antioxidant’s activity. One gram of {SiO 2 @sericin_20} quenches 202 μmol of DPPH radicals and 100 μmol of ● OH, which are smaller than the amount of {SiO 2 @sericin_10}. These findings reinforce our previous conclusion that covalent grafting of organic molecules bearing antioxidant functionalities onto SiO 2 surfaces is an effective strategy to enhance radical scavenging efficiency, applicable to both hydroxyl-radical and DPPH (hydrogen atom transfer) quenching mechanisms.