Novel polydopamine-based composites with adjustable antioxidant activity

It is obtained here that dopamine and quercetin, not easily miscible compounds, can form stable quercetin – polydopamine (Q:PDA) composite systems under special conditions: oxidative polymerization of dopamine in the presence of quercetin in mixed water/ethanol solution at both, acidic and alkaline pH, by using NaIO4 as oxidant. The structure of the Q:PDA composites in bulk and as coating layers on SiO2 nanoparticles has been characterized by solid-state NMR spectroscopy, which directly confirms the incorporation of quercetin in the PDA matrix. Indirectly, it was also proved by HPTLC by monitoring quercetin released during Q:PDA disassembling in strongly acidic 0.1 M HCl solution. The morphology of Q:PDA coating layers has been characterized by AFM on glass substrates. It was found that, compared to PDA alone, layer thickness is increased in the presence of quercetin, reaching the highest value of about 190 nm for 1:1 quercetin/dopamine relative concentration, at pH 5.5 and 24 h deposition time. Sine quercetin is one of the most widely consumed natural antioxidant, and PDA has been reported with interesting antioxidant activity, the free radical scavenging properties of the Q:PDA composites was investigated. The free radicals bleaching activity was found dependent on the specific Q:PDA synthesis/deposition conditions, which might be of interest in biomedical applications that require adjustable antioxidant activity. [Display omitted] •Although not easily miscible, quercetin and polydopamine can form stable composite systems, Q:PDA.•Solid-state NMR and disassembling experiments suggest quercetin is bound non-covalently in Q:PDA composites.•The morphology and thicknesses of Q:PDA coatings have been characterized by AFM on glass substrates.•It was found an adjustable free radicals bleaching activity of Q:PDA, of potential interest for biomedical applications.