Computer-Aided Design of Nanoceria Structures as Enzyme Mimetic Agents: The Role of Bodily Electrolytes on Maximizing Their Activity

Abstract

Nanoceria, typically used for 'clean air' catalytic converter technologies, is the same material that could also be used as a nanomedicine. Specifically, nanoceria, which can capture, store and release oxygen, for oxidative/reductive reactions, can also be used to control oxygen content in cellular environments; as a 'nanozyme', nanoceria mimics enzymes by acting as an antioxidant agent. The computational design procedures for predicting active materials for catalytic converters can therefore be used to design active ceria nanozymes. Crucially, the ceria nanomedicine is not a molecule; rather it is a crystal and exploits its unique crystal properties.Here, we use ab initio and classical computer modelling, together with experiment, to design structures for nanoceria that maximises its nanozymetic activity. We predict that the nanomaterial should have (truncated) polyhedral or cuboidal morphologies to expose (active)CeO2 {100} surfaces. It should also contain oxygen vacancies and surface -OH species. We also show that the surface structures strongly affects the biological activity of nanoceria.Analogous to catalyst poisoning, phosphorus 'poisoning' -the interaction of nanoceria with phosphate, a common bodily electrolyteemanates from phosphate ions binding strongly to CeO2{100} surfaces, inhibiting oxygen capture and release and hence its ability to act as an nanozyme. Conversely, phosphate interaction with {111} surfaces is weak and therefore these surfaces protect the nanozyme against poisoning.The atom-level understanding presented here also illuminates catalytic processes and poisoning in 'clean-air' or fuel-cell technologies because the mechanism underpinning and exploited in each technologyoxygen capture, storage and releaseis identical.

Antioxidant Enzyme-Mimetic Activity and Neuroprotective Effects of Cerium Oxide Nanoparticles Stabilized with Various Ratios of Citric Acid and EDTA

“…Cerium can reversibly bind oxygen and shift between oxidation states Ce 4+ and Ce 3+ , giving the nanoparticle a regenerative capacity to act cyclically as a superoxide dismutase mimetic, which is associated with higher Ce 3+ concentrations, and a catalase mimetic, which is associated with higher Ce 4+ concentrations, depending on the particle size and redox environment [19,20]. Particle size plays a role in the ratio of Ce 3+ and Ce 4+ present in CeNPs in that as particle size decreases, Ce 3+ content increases while Ce 4+ declines [23,70,71,72,73]. Different analytical methods used to assess the Ce 3+ concentration of CeNPs have yielded varying results.…”

“…Much has been written about the effect of phosphate on the catalytic activity of CeNPs [90,91]. Phosphate ions poison superoxide dismutase-mimetic activity of CeNPs [73], and phosphate is present in virtually all physiological solutions in low, millimolar concentrations. Phosphate diminishes superoxide dismutase-mimetic activity by binding to the surface of the CeNP crystals at the sites of oxygen vacancies, and there is a direct relationship between the Ce 3+ concentration and the number of oxygen vacancies, as noted above.…”

Nanostructured Ceria: Biomolecular Templates and (Bio)applications

“…However, it was found that phosphate anions can strongly bind to (100) surfaces, inhibiting the oxygen capture and release, hence poisoning the ceria nanozyme. By contrast, the phosphate interaction with (111) surfaces is weaker, therefore these surfaces protect the ceria nanostructure against passivation [29]. 111), (110), and (100) surfaces.…”

“…Ce (IV) is white, Ce (III) is blue, and oxygen is red. Reprinted with permission from [ 29 ], Copyright © 2021, American Chemical Society.…”

Influence of Carbon Dioxide on the Energetics of Cerium Oxide Surfaces and Nanoparticle Morphology

“…This is in agreement with previous computational work. 41,47,48 The surface energy for the reduced surface was calculated according to…”