Modulating the Catalytic Activity of Cerium Oxide Nanoparticles with the Anion of the Precursor Salt

Abstract

In this work, we tested our hypothesis that surface chemistry and antioxidant properties of cerium nanoparticles (CNPs) are affected by presence of counterions. We first employed various precursor cerium (III) (Ce(III)) salts with different counterions (acetate, nitrate, chloride, sulfate) to synthesize CNPs following the same wet chemical methodology. Electron spin resonance (ESR) studies provided evidence for the formation of radicals from counterions (e.g., NO3•2− from reduction of NO3− in CNPs synthesized from Ce(III) nitrate). Physicochemical properties of these CNPs, e.g., dispersion stability, hydrodynamic size, signature surface chemistry, SOD-mimetic activity, and oxidation potentials were found to be significantly affected by the anions of the precursor salts. CNPs synthesized from Ce(III) nitrate and Ce(III) chloride exhibited higher extent of SOD-mimetic activities. Therefore, these CNPs were studied extensively employing in-situ UV-Visible spectroelectrochemistry and changing the counterion concentrations affected the oxidation potentials of these CNPs. Thus, the physicochemical and antioxidant properties of CNPs can be modulated by anions of the precursor. Furthermore, our ESR studies present evidence of the formation of guanine cation radical (G•+) in 5′-dGMP via UV-photoionization at 77 K in the presence of CNPs synthesized from Ce(III) nitrate and chloride and CNPs act as the scavenger of radiation-produced electrons.

The Rational Design and Biological Mechanisms of Nanoradiosensitizers

“…Cerium oxide NPs increased ROS production in pancreatic cancer cells, resulting in the activation of thioredoxin 1 (TRX1)-apoptosis signaling kinase 1 (ASK1)-c-Jun terminal kinase (JNK) (TRX1-ASK1-JNK) redox-sensing pathway and apoptosis [48]. In contrast, another work showed that cerium nanoparticles (CNPs) exhibited higher SOD-mimetic activity, which could be modulated by the change in the anion of the precursor salt [55]. CuO NPs (5.4 nm) significantly increased oxidative stress levels, resulting in radiosensitization effects in MCF-7 cells and U14 tumor-bearing nude mice [49].…”

Effect of Cerium Precursor in the Synthesis of Ce-MCM-41 and in the Efficiency for Liquid-Phase Oxidation of Benzyl Alcohol

“…However, metal precursor salts in the synthesis gel could cause changes in the assembly of CTA + molecules, leading to less organized materials when compared to Si-MCM-41. As Barkam and co-workers [52] demonstrated, even the use of different anions for the same metal precursor can extensively affect the physicochemical properties of particles in solution [52].…”

“…As for Ce-MCM-NO 3 , part of the cerium added in the synthetic medium does not react with silicate oligomers and precipitates to form non-framework [Ce(OH) 3 ], which converts completely to CeO 2 after calcination. Such a hypothesis is scarcely pointed out to explain the difference in the reactivity of cerium precursors in the synthesis of oxides, but there is an extensive literature regarding the differences in the use of precursors that leads to singular microstructural properties of these materials [52,76,77]. These works clearly suggest that the anions in cerium precursors have major roles in defining the properties of the final cerium-based materials more than just the mere electrostatic counterparts in the synthetic medium.…”

Importance of sample preparation on reliable surface characterisation of nano‐objects: ISO standard 20579‐4

“…Many of these complications can be summarized as follows: (1) synthesis processes are often highly sensitive to subtle variations in unexpected ways and not easily reproducible and (2) nano‐objects are unstable, easily damaged during handling, storage, and analysis, and frequently change as a function of time or environment . Seemingly minor variations in synthesis, age or source of precursor chemicals, processing, or storage have been found to produce nano‐objects with significantly different properties or lifetimes …”

“…1,9,19 Seemingly minor variations in synthesis, age or source of precursor chemicals, processing, or storage have been found to produce nanoobjects with significantly different properties or lifetimes. [20][21][22][23] The significant impact of seemingly minor changes in sample preparation on properties, along with the ease of sample transformation due to environmental changes, complicates the ability of experiments to be reproduced. This sensitivity highlights the importance of knowledge of sample history and appropriate characterization in providing important information about a sample and the impacts of analysis.…”