Antioxidant Activity of SiO2@{Sericin} Hybrids: A Comparable OH-Radical and DPPH-Radical Scavenging Study.

Abstract

A new class of hybrid materials was developed via covalent grafting of sericin, a silk-derived protein, onto SiO2 particles to assess their antioxidant properties. Two variants of SiO2@sericin hybrids were synthesized, with 10% ({SiO2@sericin_10}) or 20% ({SiO2@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 {SiO2@sericin} hybrids exhibit significantly enhanced antioxidant activity compared with sericin in aqueous solution. Specifically, 1 g of the {SiO2@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 SiO2 surface is highly dependent on its loading concentration. At the high loading (20%), sericin forms a hermetic coating over the SiO2 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 {SiO2@sericin_20} quenches 202 μmol of DPPH radicals and 100 μmol of ●OH, which are smaller than the amount of {SiO2@sericin_10}. These findings reinforce our previous conclusion that covalent grafting of organic molecules bearing antioxidant functionalities onto SiO2 surfaces is an effective strategy to enhance radical scavenging efficiency, applicable to both hydroxyl-radical and DPPH (hydrogen atom transfer) quenching mechanisms.