Ionic Ce Research Articles

Toxicity of ceria nanoparticles to the regeneration of freshwater planarian Dugesia japonica: The role of biotransformation

Cerium oxide nanoparticles (n-CeO2) have wide applications ranging from industrial to consumer products, which would inevitably lead to their release into the environment. Despite the toxicity of n-CeO2 on aquatic organisms has been largely reported, research on developing organisms is still lacking. In this study, we investigate the toxic effects of n-CeO2 on the stem cells, tissue- and neuro-regeneration, using freshwater planarian Dugesia japonica as a model. Effects of bulk sized (μ-) CeO2 and ionic Ce (Ce3+) were compared with that of n-CeO2 to explore the origin of the toxic effects of n-CeO2. No overt toxicity was observed in μ-CeO2 treatment. n-CeO2 not only impaired the homeostasis of normal planarians, but also inhibited the regeneration processes of regenerated planarians, demonstrated by the inhibited blastema growth, disturbed antioxidant defense system at molecular levels, elevated DNA-damage and decreased stem cell proliferation. Regenerating organisms are more susceptible to n-CeO2 than the normal ones. Ce3+ exhibited significantly higher toxicity than n-CeO2, even though the total Ce uptake is 0.2 % less in Ce3+ than in n-CeO2 treated in planarian. X-ray absorption near edge spectroscopy (XANES) analysis revealed that 12.8 % of n-CeO2 (5.95 mg/kg Ce per planarian) was transformed to Ce3+ after interaction with planarian, suggesting that biotransformation at the nano-bio interface might play an important role in the observed toxicity. Since the biotransformation of n-CeO2 is a slow process, it may cause long-term chronic toxicity to planarians due to the slow while sustained release of toxic Ce3+ ions.

An integrated ICP-MS-based analytical approach to fractionate and characterize ionic and nanoparticulate Ce species.

Cerium dioxide nanoparticles (CeO2 NPs) are widely used in various fields, leading to concern about their effect on human health. When conducting in vivo investigations of CeO2 NPs, the challenge is to fractionate ionic Ce and CeO2 NPs and to characterize CeO2 NPs without changing their properties/state. To meet this challenge, we developed an integrated inductively coupled plasma-mass spectrometry (ICP-MS)-based analytical approach in which ultrafiltration is used to fractionate ionic and nanoparticulate Ce species while CeO2 NPs are characterized by single particle-ICP-MS (sp-ICP-MS). We used this technique to compare the effects of two sample pretreatment methods, alkaline and enzymatic pretreatments, on ionic Ce and CeO2 NPs. Results showed that enzymatic pretreatment was more efficient in extracting ionic Ce or CeO2 NPs from animal tissues. Moreover, results further showed that the properties/states of all ionic and nanoparticulate Ce species were well preserved. The rates of recovery of both species were over 85%; the size distribution of CeO2 NPs was comparable to that of original NPs. We then applied this analytical approach, including the enzymatic pretreatment and ICP-MS-based analytical techniques, to investigate the bioaccumulation and biotransformation of CeO2 NPs in mice. It was found that the thymus acts as a "holding station" in CeO2 NP translocation in vivo. CeO2 NP biotransformation was reported to be organ-specific. This is the first study to evaluate the impact of enzymatic and alkaline pretreatment on Ce species, namely ionic Ce and CeO2 NPs. This integrated ICP-MS-based analytical approach enables us to conduct in vivo biotransformation investigations of CeO2 NPs.

Distinguishing the effects of Ce nanoparticles from their dissolution products: identification of transcriptomic biomarkers that are specific for ionic Ce inChlamydomonas reinhardtii

AbstractCerium (Ce) is a rare earth element that is incorporated in numerous consumer products, either in its cationic form or as engineered nanoparticles (ENPs). Given the propensity of small oxide particles to dissolve, it is unclear whether biological responses induced by ENPs will be due to the nanoparticles themselves or rather due to their dissolution. This study provides the foundation for the development of transcriptomic biomarkers that are specific for ionic Ce in the freshwater alga, Chlamydomonas reinhardtii, exposed either to ionic Ce or to two different types of small Ce ENPs (uncoated, ∼10 nm, or citrate-coated, ∼4 nm). Quantitative reverse transcription PCR was used to analyse mRNA levels of four ionic Ce-specific genes (Cre17g.737300, MMP6, GTR12, and HSP22E) that were previously identified by whole transcriptome analysis in addition to two oxidative stress biomarkers (APX1 and GPX5). Expression was characterized for exposures to 0.03–3 µM Ce, for 60–360 min and for pH 5.0–8.0. Near-linear concentration–response curves were obtained for the ionic Ce and as a function of exposure time. Some variability in the transcriptomic response was observed as a function of pH, which was attributed to the formation of metastable Ce species in solution. Oxidative stress biomarkers analysed at transcriptomic and cellular levels confirmed that different effects were induced for dissolved Ce in comparison to Ce ENPs. The measured expression levels confirmed that changes in Ce speciation and the dissolution of Ce ENPs greatly influence Ce bioavailability.

Ce4+ doping to modulate electrochemical and radiative-charge-transfer behaviors of CsPbBr3 perovskite nanocrystals

Tunable morphology and radiative charge transfer of perovskite nanocrystals (PNCs) were achieved by heterovalently doping CsPbBr 3 PNCs with Ce(IV) cation in a hot-injection and doping-in-growth combined way. Ce(IV)-doping could bring out a new tetragonal CsPb 2 Br 5 phase within the parent PNCs, and transform cubic CsPbBr 3 PNCs to Ce 4+ -doped CsPbBr 3 PNCs with a dot-shaped morphology of smaller size. Ce 4+ -doped CsPbBr 3 PNCs exhibited enhanced absorption and electrochemical oxidative response as well as decreased photoluminescence and electrochemiluminescence than the parent CsPbBr 3 PNCs. Processing Ce 4+ -doped CsPbBr 3 PNCs with NH 3 •H 2 O could eliminate the effects of ionic Ce(IV) dopants via forming CeO 2 , and enable CsPbBr 3 -CeO 2 hybrids to directionally grow to columnar-morphology with partially restored photoluminescence and electrochemiluminescence. • Ce 4+ -doping could transform cubic CsPbBr 3 PNCs to a dot-shaped morphology of smaller size. • Ce 4+ -doping enable CsPbBr 3 PNCs with enhanced electrochemical and decreased light-emitting responses. • NH 3 •H 2 O could eliminate the effects of ionic Ce(IV) dopants via forming CeO 2 .

Biological impacts of Ce nanoparticles with different surface coatings as revealed by RNA-Seq in Chlamydomonas reinhardtii

In order to better understand the risks of engineered nanoparticles (ENPs), it is necessary to determine their fate and biological effects under realistic exposure scenarios (e.g. low ENP concentrations). RNA-Seq was deployed to characterize the relative biological impacts of three small Ce ENPs (i.e. nominal size <20 nm, 70 μg L−1 Ce), with different coating properties (i.e. uncoated, citrate or poly-acrylic acid coated), towards a unicellular freshwater microalga, Chlamydomonas reinhardtii. After 2 h exposition at pH 7.0, distinct differences in transcriptomic effects were observed when comparing ionic Ce and Ce ENPs. Notably, Ce ENPs specifically modulated mRNA levels of genes related to the ubiquitin-proteasome system and to flagella structure. Compared to control conditions, transcriptomic effects induced by the citrate coated Ce ENPs were rather limited, as only 23 genes were differentially expressed by this treatment (Log2FC > |1.0|, padj < 0.001); compared to uncoated Ce ENPs (688); polyacrylic coated Ce ENPs (315) or a similar concentration of ionic Ce (138). Somewhat surprisingly, similar changes in the algal transcriptomes were observed for treatments with poly-acrylic acid coated Ce ENPs (mainly Ce(III), little dissolution) and uncoated Ce ENPs (mainly Ce(IV) atoms, largely agglomerated) (Log2FC > |1.0|, padj < 0.001). For the moderate exposure concentrations examined here, toxicity appeared to be minimal for both ionic Ce and Ce ENPs. Nonetheless, an important number of genes could not be assigned to a biological pathway. The study gives important insights with respect to the role of particle surface coatings on biological effects, the mechanisms of interaction of Ce ENP with a green alga, in addition to identifying several useful transcriptomic biomarkers of Ce ENP exposure.

Structural and electronic properties of bastnaesite and implications for surface reactions in flotation

The structural and electronic properties of bastnaesite were studied by using the first-principles method based on the density functional theory (DFT). The geometry structure of bastnaesite was first optimized, and then the Mulliken populations, electron density and density of states were calculated and further analyzed in detail. The calculation results reveal that it mainly ruptures along the ionic Ce–O and Ce–F bonds during the cleavage of bastnaesite, leaving ≡Ce+, ≡F– and ≡CO3– dangling bonds exposed on the cleavage surface of bastnaesite. Combined with contact angle measurement, surface complexation theory and XPS analysis, the implications of structural and electronic properties on bastnaesite flotation reactions were studied. The hydration of exposed strong ionic bond on cleavage surface results in hydrophilic surface. According to surface complexation theory, the formed surface groups are ≡CeOH0, ≡CO3H0 and ≡FH0 groups. The investigated metal ions and flotation reagents complex with surface ≡CeOH0 groups, while ≡CO3H0 and ≡FH0 groups are not involved in the complexation. The high activity of Ce atoms facilitates these surface reactions.

The Effect of Ce-doping Molar Concentration with Silica Xerogel on the Materials Optical Properties

Ionic cerium-doped pure silica glass with high photoluminescence, has been prepared using the sol–gel technique and densification of the porous xerogel under inert and air atmosphere.The present study shows the effect of densification atmosphere and molar concentrations on the optical properties of ionic cerium-activated silica glasses.Moreover, the PL intensity increased with increasing the molar concentration of ionic Ce+3.The PL is composed of two sub-bandsascribable to tetragonal distortion of the matrix and spin–orbit coupling but these sub-bands arecloser to each other when the core rod is densified under inert atmosphere.

Elucidating the mechanisms for plant uptake and in-planta speciation of cerium in radish (Raphanus sativus L.) treated with cerium oxide nanoparticles

Even though the plant uptake of cerium oxide nanoparticles (CeO2 NPs) has been reported, the mechanisms remain unknown. This study aimed to provide new insights into CeO2 NPs plant uptake through two objectives: (1) to investigate whether CeO2 NPs dissolute before their plant uptake and (2) to determine the in-planta speciation of Ce. Bench scale experiments were conducted by growing radish in solutions containing 10mg elemental Ce/L of bulk CeO2 particles, CeO2 NPs or ionic Ce. Transmission electron microscope and inductively coupled plasma-mass spectrometry (ICP-MS) analysis suggested that one pathway for CeO2 NPs uptake was through direct uptake of intact CeO2 NPs. More importantly, our results confirmed that part of the particulate CeO2 was transformed into ionic Ce on the root surface before they were taken up by plants. Ionic Ce uptake and transport was a primary mechanism for Ce accumulation in plant shoots. This study further demonstrated that enhanced CeO2 dissolution on root surface was due to the organic acids with lower molecular weight (e.g. succinic acid) in radish root exudates. Large particles composed of high contents of P and Ce were detected in radish roots treated only with ionic Ce, suggesting the formation of CePO4 particles. In summary, the results indicated that CeO2 NPs was taken up by radish as both intact nanoparticles and dissolved ions. Inside plant tissues, Ce is present as a cocktail of CeO2 NPs, dissolved Ce and Ce salt (e.g. CePO4) and the specific combination of Ce species is tissue dependent.

Particle-specific toxicity and bioavailability of cerium oxide (CeO2) nanoparticles to Arabidopsis thaliana

The use of manufactured cerium oxide nanoparticles (CeO2-NPs) in consumer products has increased markedly over the past decade, and their release into natural ecosystems is unavoidable. This study investigated the phytotoxicity and uptake of CeO2-NPs in Arabidopsis thaliana grown in an agar medium. Although low concentrations of CeO2-NPs had stimulatory effects on plant growth, at higher concentrations, CeO2-NPs reduced growth and had adverse effects on the antioxidant systems and photosystem. Importantly, the toxicity resulted from the nanoparticles per se, rather than from the dissolved Ce ions. CeO2-NPs were taken up and subsequently translocated to shoot tissues, and transmission electron microscopy (TEM) showed the presence of a large number of needle-like particle aggregations in the intercellular regions and the cytoplasm of leaf cells. The up-translocation factor to shoots was independent of the concentrations of Ce in the roots and the supplied forms of Ce (i.e. CeO2-NPs, CeO2-bulk, and ionic Ce), suggesting that endocytosis is likely to be a general mechanism responsible for the translocation of these Ce compounds. These findings provide important information regarding the toxicity and uptake of CeO2-NPs in plants, which needs to be considered in environmental risk assessment for the safe use and disposal of CeO2-NPs.

First principles investigation of the crystal and electronic structures of CeNCl and “CeNF”

Based on DFT energy discrimination and detailed electronic and bonding properties, it is shown that the hitherto unexplored cerium nitride fluoride can be obtained in rhombohedral ThNF structure whereas actual CeNCl is confirmed in the early determination with PbFCl-like structure. The respectively adopted 3D and 2D like structures are assigned to the major role played by the F polarizability, four times smaller than Cl. In their ground state both compounds are found small gap insulators with 1.9 eV (CeNCl), 1.8 eV (CeNF) compared to insulating isoelectronic cerine CeO2 with 2.2 eV band gap. The bonding shows balance between covalence brought by Ce–N bond versus ionic Ce–F(Cl) bonding and d(Ce–N) < d(Ce–F(Cl)) distances. Synthesis routes for CeNF are proposed.

CePS4 Electronic Structure and Optical Properties

The structure of CePS4 has been determined from single-crystal X-ray diffraction data (I41/acd space group, a = b = 10.9228(3) Å, c = 19.3998(6) Å, V = 2314.5(2) Å3, Z = 16). The refinement, conducted from 547 independent reflections (I > 3σ(I) and 30 variables) led to RF (%) = 1.83 and RwF (%) = 2.36. Diffuse reflectance spectra of CePS4 and of the La1-xCexPS4 series indicated that the electronic absorption mechanism in CePS4, a 4f1 → 5d0 transition on the CeIII ions, is the same as in γ-Ce2S3, with only the band gap width being modified. To this transition corresponds an absorption threshold responsible for the yellow hue of the thiophosphate at about 2.5 eV. Band structure calculation (TB-LMTO-ASA) confirms the experimental evidence of the CeIII 4f1 → 5d0 transition. Comparisons between CePS4 and γ-Ce2S3 through their electronic localized functions revealed the inductive effect of the P−S covalent bonding on the Ce−S bond, with the resulting increase of the CeIII 4f1 → 5d0 transition in the thiophosphate as compared to the sulfide. This increase is ascribed, in part, to a lowering of the 4f block because of the decreased screening effect of the more ionic Ce−S bonding in CePS4.

Ionic and covalent bonds in CeO 2 crystal

We have performed cluster calculations in a study of the bonding nature in the CeO 2 crystal using the relativistic discrete-variational Xα method. The electron charge distribution of CeO 2 is compared with those of ZrO 2 and CaF 2. The charge density in the metal atomic region indicates stronger covalency for CeO 2 than that in Zr for ZrO 2. The repulsion between the metal and oxygen ionic cores is, however, strong and superior to the covalent interaction, and thus the ionic character determines the static bonding nature in the CeO 2 crystal. A population analysis shows that the mixed interaction due to the independent ionic and covalent contributions arises from the ionic Ce 5s, 5p and covalent Ce 4f, 5d orbitals which are proximate to each other in the bond region.