(405a) Ceria Nanoparticle Dissolution and Stability in Acidic Aqueous Environments

Ceria (cerium oxide) nanomaterials, or nanoceria, have many applications such as acting as a redox catalysis and in catalyst supports, solid oxide fuel cells, sintering additives, heat resistant alloy coatings, and as UV absorbents and superconducting materials. The cerium atoms on the surface of nanoceria can store or release oxygen, cycling between Ce³⁺ and Ce⁴⁺, and can therefore relieve oxidative stress within the body. As an anti-oxidant, nanoceria has to potential to reduce nausea and bacterial reproduction, stimulate the immune system to assist in fighting infection and disease, and prevent cancerous tumor growth. Nanoceria dissolution is present in acidic environments in vivo. In order to accurately define the fate of nanoceria in vivo, nanoceria dissolution or stabilization is observed in vitro using acidic aqueous environments.

Nanoceria stabilization is a known problem even during its synthesis; in fact, a carboxylic acid, citric acid, is used in many synthesis protocols. Citric acid adsorbs onto nanoceria surfaces, capping particle formation and creating stable dispersions with extended shelf lives. For example, citric acid surface coatings prolong nanoceria’s residence time within the blood stream. Dynamic light scattering (DLS) was utilized to determine the hydrodynamic diameter of nanoceria in aqueous solutions as a measure of dispersion stability. Nanoceria is shown to agglomerate in the presence of some carboxylic acids over a time scale of up to 28 weeks, and degrade in others, at pH of 4.5 (representing that of phagolysosomes). Sixteen carboxylic acids were tested: citric, glutaric, tricarballylic, 2-hydroxybutyric, 3-hydroxybutyric, adipic, malic, acetic, pimelic, succinic, lactic, tartronic, isocitric, tartaric, dihydroxymalonic, and glyceric acid. Each acid is introduced as 0.11M, into pH 4.5 iso-osmotic solutions. Controls such as ammonium nitrate, sodium nitrate, and water are also tested to assess their effects on nanoceria dissolution and stabilization.

To further test stability, nanoceria suspensions are subjected to light versus dark milieu. Light induced nanoceria agglomeration in some, but not all ligands, and is likely to be a result of UV irradiation. Light initiates free radicals generated from the ceria nanoparticles. Some of the ligands completely dissolved the nanoceria when exposed to light. Citric, malic, and lactic acids form coordination complexes with cerium on the surface of the ceria nanoparticle that can inhibit agglomeration. This approach identifies key functional groups required to prevent nanoceria agglomeration. The impact of each ligand on nanoceria are analyzed and will ultimately describe the fate of nanoceria in vivo.

Supported by NIH Grant 1R01GM109195.