Carboxylic acids accelerate acidic environment-mediated nanoceria dissolution

Abstract

Ligands that accelerate nanoceria dissolution may greatly affect its fate and effects. This project identified carboxylic acids that contribute to nanoceria dissolution in aqueous, acidic environments. Nanoceria has commercial and potential therapeutic applications. It biotransforms in vivo. Citric acid is commonly used to stabilize nanoceria during synthesis and in aqueous dispersions. In this study, citrate-stabilized nanoceria dispersions (~ 4 nm average primary particle size) were placed in dialysis cassettes whose membranes would pass cerium salts but not nanoceria particles. The cassettes were immersed in isoosmotic baths containing carboxylic acids at pH 4.5 at 37 °C, or select agents. Cerium atom material balances were conducted for the cassette and bath by sampling of each chamber and cerium quantitation by inductively coupled plasma mass spectrometry. Samples were also collected for high-resolution transmission electron microscopy observation of nanoceria size (cassette). In carboxylic acid solutions, nanoceria dissolution increased cerium concentration in the bath and decreased the nanoceria primary particle size in the cassette. In solutions of citric, malic, and lactic acid, and in the ammonium ion, ~ 15 nm nanoceria agglomerates persisted. With other carboxylic acids, nanoceria agglomerates grew to ~ 1 micron. Nanoceria particles were stable in solutions containing citrate (pH 7.4), water, or horseradish peroxidase i.e., the dissolution half-lives were very high. Extending these findings to in vivo and environmental systems, one would expect acidic environments containing carboxylic acids to degrade nanoceria by dissolution; two examples would be phagolysosomes and in the plant rhizosphere.

Surface-controlled dissolution rates: a case study of nanoceria in carboxylic acid solutions

“…Carboxylic acids that complex with nanoceria surfaces are known to stabilize their dispersions. In related work, Yokel and co-workers 74 (see Fig. 6 of this reference) have shown that lactic, malic, and succinic acids reduce agglomeration of nanoceria, while the rest of the carboxylic acids do not inhibit agglomeration.…”

“…Synthesis reproducibility with respect to nanoparticle size was good: Masui et al 45 reported an average nanoceria particle size of 3.9 nm (equivalent to a surface area of 211 m 2 /g) while this lab produced average nanoceria particle sizes of 4.24 nm (equivalent to a surface area of 196 m 2 /g). At this particle size, there is a mixture of Ce 3+ and Ce 4+ on the nanoceria surfaces 74 . Figures 2a and 2b show nanoceria samples at t = 0 and t = 7 weeks, respectively.…”

“…Thus, there is good correspondence between the nanoceria size predicted by the surface-controlled dissolution model and the ECD particle size as estimated from the particle area distribution. Additional TEM images of the nanoceria at several time points and for all carboxylic acids in the study can be found in Figure 6 of Yokel et al 74…”

“…Yokel et al 74 provided descriptive interpretations on the differential effects of carboxylic acids on nanoceria dissolution, which are relevant to in vivo and environmental systems. EELS plots in this reference (Fig.…”

2D Gadolinium Oxide Nanoplates as T1 Magnetic Resonance Imaging Contrast Agents

“…Samples were placed in dialysis membranes which allowed the passage of free Gadolinium into the dialysate but retained intact nanocrystals. [104,105] After three days of equilibration at a 1:1000 volume ratio, Gadolinium concentrations in both the dialysate and sample were determined by ICP-MS (Figure S10, Supporting Information). No Gadolinium was detected in the dialysate of nanoplate samples except for the most acidic case (pH = 2) and we can conclude that at least 97% of the Gadolinium remained in a nanoparticle form.…”