Tuning the enzyme-like activities of cerium oxide nanoparticles using a triethyl phosphite ligand

Yadav N. Patel V. McCourt L. Ruppert M. Miller M. Inerbaev T. Mahasivam S. Bansal V. Vinu A. Singh S. Karakoti A.
22 April 2022 Royal Society of Chemistry

Biomaterials Science
2022 #10 Issue 12 3245 - 3258 pp.

Cerium oxide nanoparticles (CeNPs) exhibit excellent in vitro and in vivo antioxidant properties, determined by the redox switching of surface cerium ions between their two oxidation states (Ce³⁺ and Ce⁴⁺). It is known that ligands such as triethyl phosphite (TEP) can tune the redox behavior of CeNPs and change their biological enzyme-mimetic activities; however, the corresponding mechanism for such a behavior is completely unknown. Herein, we have studied the effect of TEP in promoting the SOD-enzyme-like activity in CeNPs with high and low Ce³⁺/Ce⁴⁺ ratio, which were synthesized by wet chemical and thermal hydrolysis methods, respectively, and incubated with varying concentrations of TEP. X-ray diffraction, UV-visible, photoluminescence, X-ray photoelectron spectroscopy, and Raman spectroscopy combined with DFT calculations were used to investigate the interaction of TEP on the surface of CeNPs. We observed a clear correlation between TEP concentration and the formation of surface oxygen vacancies. XPS analysis confirmed the increase in Ce³⁺ concentration after interaction with TEP. Moreover, we show that TEPs influence depends on the surface Ce³⁺/Ce⁴⁺ ratio. The superoxide dismutase-, catalase-, and oxidase-like activities of CeNPs with high Ce³⁺/Ce⁴⁺ ratio are not affected by TEP interaction, whereas catalase- and oxidase-like activities of CeNPs with low Ce³⁺/Ce⁴⁺ ratio decrease and the SOD-like activity is found to increase upon incubation with different concentrations of TEP. We also demonstrate that TEP interaction does not affect the regeneration of the CeNP surface, while the DFT calculations show that TEP facilitates the formation of defects on the surface of stoichiometric cerium oxide by reducing the oxygen vacancy formation energy. CeNPs with low Ce³⁺/Ce⁴⁺ ratio incubated with TEP also exhibited good antibacterial activity as compared to the CeNPs or TEP alone.

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Nanomaterials and Toxicology Laboratory, Division of Biological and Life Sciences, School of Arts and Sciences, Ahmedabad University, Ahmedabad, 380009, India
Global Innovative Center for Advanced Nanomaterials, The School of Engineering, College of Engineering, Science and Environment, The University of Newcastle, Callaghan, 2308, Australia
School of Engineering, College of Engineering, Science and Environment, The University of Newcastle, Callaghan, 2308, Australia
School of Environmental and Life Sciences, College of Engineering, Science and Environment, The University of Newcastle, Callaghan, 2308, Australia
L. N. Gumilyov Eurasian National University, Nur-Sultan, 010008, Kazakhstan
Ian Potter NanoBioSensing Facility, NanoBiotechnology Research Laboratory, School of Science, RMIT University, Melbourne, 3001, VIC, Australia
National Institute of Animal Biotechnology, Telangana, Hyderabad, India
Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 630090, Russian Federation

Nanomaterials and Toxicology Laboratory
Global Innovative Center for Advanced Nanomaterials
School of Engineering
School of Environmental and Life Sciences
L. N. Gumilyov Eurasian National University
Ian Potter NanoBioSensing Facility
National Institute of Animal Biotechnology
Sobolev Institute of Geology and Mineralogy

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