Photoactivable alizarin and eugenol-based materials for antibacterial applications

Abstract

We report herein the design of a new visible-light epoxy-based alizarin photosensitizer (AE) of iodonium salt (Iod) for the cationic polymerization (CP) of epoxidized eugenol monomers under visible-light irradiation. The combination of AE and Iod demonstrates highly efficient photoinitiating properties under air. As highlighted by fluorescence, laser flash photolysis (LFP) and electron paramagnetic resonance spin-trapping (ESR ST) experiments, AE acts as an electron donating molecule, and reacts with Iod under light exposure through its excited singlet and triplet states via a photoinduced electron transfer reaction, producing thus protonic acids, H+, able to initiate CP. Also, we demonstrate by EPR ST that the addition of diepoxy eugenol monomer may lead to the formation of reactive radical species which may be oxidized by Iod to form cationic species. Thus, new bio-based and photoactivable materials were designed by cationic photopolymerization with the use of alizarin-based photosensitizer and eugenol derived monomers. By tuning the weight proportion of eugenol derived epoxy monomers (mono- (EE) and di-epoxidized (EdE) eugenol), we can modulate the thermal and mechanical properties of the resulting materials. The new AE-based materials have demonstrated two interesting properties: first, the presence of EE in the polymer network has considerably decreased the number of colony forming units (CFUs) at the surface of materials whatever the bacterial strains used, and these samples demonstrate photoactivable properties as they produce, under visible-light irradiation, singlet oxygen, a biocide agent against bacteria. Interestingly, the irradiation of the AE/Iod/EE(50)/EdE(50) materials lead to a tremendous decrease of the number of E. coli and S. aureus CFUs at their surface. A reduction by 100% of the bacterial adhesion is observed upon visible-light exposure.