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RESEARCH PRODUCT

Ag5 nanoclusters with dual catalytic antiradical activities

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Silver nanoclusters of five atoms (Ag5) display outstanding catalytic activities for the deactivation of radicals. Using 2,2-diphenyl-1‑picrylhydrazyl (DPPH) radical as a model system, we observed a fast radical reduction to DPPH anions using only [Ag5] 3 to 4 orders of magnitude less than [DPPH]. Moreover, nanoclusters remain stable at the end of the reaction, and can deactivate again DPPH radicals at the same rate, indicating that they act as anti-radical catalysts. The radical scavenger catalytic activity of Ag5 proceeds selectively through the oxidation of methanol (used to dissolve the radical) to formaldehyde, which is supported by DFT calculations. The obtained catalytic rate constants are almost 2 orders of magnitude higher than oxidases, and more than 4 orders of magnitude larger than graphene quantum dots. We also show that Ag5 not only catalyze the reduction of radicals but also their oxidation, promoting the inhibition of the autoxidation mechanisms of hydrocarbon polymers, which are very sensitive to the presence of radicals. For this purpose, thin films of two industrially relevant polymers (polyisoprene and acrylonitrile–butadienestyrene copolymer), were exposed to standard simulated photo-ageing conditions in the presence of Ag5. Using Attenuated Total Reflection-FTIR and DFT modeling we observed that, although Ag5 nanoclusters, with ≈ 15% surface coverage, do not totally inhibit the oxidation, they favour a decomposition that yields inactive products, in contrast with the more detrimental ketone formation pathway. These results not only open new possibilities for developing a post-process inhibition of polymer degradation, for which nowadays there are no efficient procedures, but also, they could be used as very efficient dual-redox catalytic radical scavengers for different industrial or biomedical purposes This research was partially supported by the Consellería de Educación (Xunta de Galicia), Grants No. Grupos Ref. Comp. ED431C 2017/22, ED431C 2019/13 and AEMAT-ED431E2018/08 to M.A.L.Q. The European Union’s Horizon 2020 Research and Innovation Programme (Bac-To-Fuel) under Grant Agreement No. 825999 (M.A.L.Q.). The European Union H2020 project Nanorestart (646063), the Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2019-2022, ED431G 2019/03; Consolidación e estructuración ED431B 2018/16) and the European Union (European Regional Development Fund—ERDF) (M.L.). DB expresses gratitude for a postdoctoral grant from Xunta de Galicia, Spain (POS-A/2013/018) SI