Reduction-Driven 3D to 2D Transformation of Cu Nanoparticles.

The interaction between metal and metal oxides at the nanoscale is of uttermost importance in several fields, thus its enhancement is highly desirable. In catalysis, the performance of the nanoparticles is dependent on a wide range of properties, including its shape that is commonly considered stable during the catalytic reaction. In this study, highly reducible CeO2-x nanoparticles are synthesized aiming to provide Cu/CeO2-x nanoparticles, which are classically active catalysts for the CO oxidation reaction. It is observed that the Cu nanoparticles shape changes during reduction treatment (prior to the CO oxidation reaction) from a nearly spherical 3D to a planar 2D shape, then enhances the Cu-CeO2-x interaction. The spread of the Cu nanoparticles over the CeO2-x surface during the reduction treatment occurs due to the minimization of the total system energy. The shape change is accompanied by migration of O atoms from CeO2 surface to the border of the Cu nanoparticles and the change from the Cu0 to Cu+1 state. The spreading of the Cu nanoparticles influences on the reactivity results toward the CO oxidation reaction since it changes the local atomic order around Cu atoms. The results show a timely contribution for enhancing the interaction between metal and metal oxide.

Artificial cerium-based proenzymes confined in lyotropic liquid crystals: synthetic strategy and on-demand activation.

Inorganic nanoparticles that mimic the activity of enzymes are promising systems for biomedical applications. However, they cannot distinguish between healthy and damaged tissues, which could cause undesired effects. Natural enzymes avoid this drawback via activation triggered by specific biochemical events in the body. Inspired by this strategy, we proposed an artificial cerium-based proenzyme system that could be activated to a superoxide dismutase-like form using H2O2 as the trigger. To achieve this goal, an innovative and easy strategy to synthesize Ce(OH)3 nanoparticles as artificial proenzymes was developed using a lyotropic liquid crystal composed of phytantriol, which was essential to maintain their stability at physiological pH. The transmission electron microscopy measurements showed that the Ce(OH)3 nanoparticles were as small as 2 nm. The nanoparticles were fitted into the tiny aqueous channels of the liquid crystal matrix, which presented a Pn3m space group. X-ray absorption near edge structure measurements were used to determine the Ce(iii) fraction of the proenzyme-like nanoparticles, which was around 85%. The Ce(iii) fraction dramatically dropped to around 5% after contact with H2O2 because of the conversion of Ce(OH)3 to CeO(2-x) nanoparticles. The CeO(2-x) nanoparticles showed superoxide dismutase-like activity in contrast to the inactive Ce(OH)3 form. The proof of concept presented in this work opens up new possibilities for using nanoparticles as artificial proenzymes that are activated by a biochemical trigger in vivo.