Air, aqueous and thermal stabilities of Ce3+ ions in cerium oxide nanoparticle layers with substrates

Selective inhibition of partial EMT-induced tumour cell growth by cerium valence states of extracellular ceria nanoparticles for anticancer treatment

Targeting specific tumour cells and their microenvironments is essential for enhancing the efficacy of chemotherapy and reducing its side effects. A partial epithelial-to-mesenchymal transition state (pEMT, with a hybrid epithelial/mesenchymal phenotype) in tumour cells is an attractive targeting for anticancer treatment because it potentially provides maximal stemness and metastasis relevant to malignant cancer stem cell-like features. However, treatment strategies to target pEMT in tumour cells remain a challenge. This study demonstrates that extracellular cerium oxide nanoparticles (CNPs) selectively inhibit the growth of pEMT-induced tumour cells, without affecting full epithelial tumour cells. Herein, highly concentrated Ce3+ and Ce4+ ions are formed on CNP-layered poly-L-lactic acid surfaces. Cell cultures of pEMT-induced and uninduced lung cancer cell lines on the CNP-layered substrates allow the effect of extracellular CNPs on tumour cell growth to be investigated. The extracellular CNPs with dominant Ce3+ and Ce4+ ions were able to trap pEMT-induced tumour cells in a growth-arrested quiescent/dormant or cytostatic state without generating redox-related reactive oxygen species (ROS), i.e. non-redox mechanisms. The dominant Ce3+ state provided highly efficient growth inhibition of the pEMT-induced tumour cells. In contrast, the dominant Ce4+ state showed highly selective and appropriate growth regulation of normal and tumour cells, including a mesenchymal phenotype. Furthermore, Ce4+-CNPs readily adsorbed serum-derived fibronectin and laminin. Cerium valence-specific proteins adsorbed on CNPs may influence receptor-mediated cell-CNP interactions, leading to tumour cell growth inhibition. These findings provide new perspectives for pEMT-targeting anticancer treatments based on the unique biointerface of extracellular CNPs with different Ce valence states.

Effect of Surface Treatment of Nanocrystalline CeO2 on Its Dephosphorylation Activity and Adsorption of Inorganic Phosphates

The surface of nanocrystalline cerium oxide (CeO2) was treated with various chemical agents by a simple postmodification method at 25 °C and atmospheric pressure. Hydrogen peroxide, ammonium persulfate, deionized water, ascorbic acid, and ortho-phosphoric acid were used in order to study and evaluate their effect on surface materials, such as surface area, crystallite size, number of surface hydroxyl groups, particle morphology, and Ce3+/Ce4+ ratio. Paraoxon-methyl (PO) decomposition and inorganic phosphate adsorption were used to evaluate the effect of surface treatment on catalytic and adsorption properties. CeO2 surface was studied by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and acid-base titration. While the treatment procedure affected the number of surface hydroxyl groups and the amount of bulk surface oxygen vacancies, only negligible changes were observed in the Ce3+/Ce4+ ratio. Interestingly, surface treatment affected the ability to decompose PO, but only a small effect on inorganic phosphate adsorption was observed, indicating the robustness of CeO2 for the latter. A mechanism for possible interaction of the used chemicals with the CeO2 surface was proposed.

Synthesis Attempt and Structural Studies of Novel A2CeWO6 Double Perovskites (A2+ = Ba, Ca) in and outside of Ambient Conditions

This comprehensive work showcases two novel, rock-salt-type minerals in the form of amphoteric cerium-tungstate double perovskite and ilmenite powders created via a high-temperature solid-state reaction in inert gases. The presented studies have fundamental meaning and will mainly focus on a detailed synthesis description of undoped structures, researching their possible polymorphism in various conditions and hinting at some nontrivial physicochemical properties like charge transfer for upcoming optical studies after eventual doping with selectively chosen rare-earth ions. The formerly mentioned, targeted A₂BB'X₆ group of compounds contains mainly divalent alkali cations in the form of ^XIIA = Ba²⁺, Ca²⁺ sharing, here, oxygen-arranged clusters (^IIX = O^2-) with purposely selected central ions from f-block ^VIB = Ce^4/3+ and d-block ^VIB' = W^4/5/6+ since together they often possess some exotic properties that could be tuned and implemented into futuristic equipment like sensors or energy converters. Techniques like powder XRD, XPS, XAS, EPR, Raman, and FTIR spectroscopies alongside DSC and TG were involved with an intent to thoroughly describe any possible changes within these materials. Mainly, to have a full prospect of any desirable or undesirable phenomena before diving into more complicated subjects like: energy or charge transfer in low temperatures; to reveal whether or not the huge angular tilting generates large enough dislocations within the material's unit cell to change its initial properties; or if temperature and pressure stimuli are responsible for any phase transitions and eventual, irreversible decomposition.

Tunable phosphate-mediated stability of Ce3+ ions in cerium oxide nanoparticles for enhanced switching efficiency of their anti/pro-oxidant activities

Switching of the Ce3+/Ce4+ oxidation states in cerium oxide nanoparticles (CNPs) provides various superior nanozyme activities. However, nanozymes lack a switch to reversibly regulate the multi-nanozyme capacity depending on physiological/pathological environments, e.g. different pH and H2O2 levels. Furthermore, highly concentrated Ce3+ ions with abundant oxygen vacancies (Vo) in CNPs have the potential to enhance their catalytic activities, but the phosphate anions (P) adsorbed on Ce3+ ions block their several catalytic activities. This study, therefore, demonstrates that the tunable P-mediated stability of Ce3+ ions involves the superoxide dismutase (SOD) mimetic activity of CNPs, and leads to enhanced switching efficiency of their anti/pro-oxidant activities. Herein, highly concentrated Ce3+ ions in Vo-CNP layers (Vo-CNPLs) were fabricated, and the threshold conditions necessary to alter the stability of Ce3+ ions treated with P were explored by X-ray photoelectron spectroscopy. P-adsorbed Ce3+ ions (P-Ce3+) in Vo-CNPLs were efficiently destabilized in H2O2 solution (pH 5-6) rather than in HCl and HNO3 solutions (pH 3), and the presence of H2O2 readily released P from Ce3+ sites. Indeed, though P-Ce3+ temporarily arrested the SOD mimetic activity to generate H2O2 (linked to anti-oxidant activity) at physiological pH, they did enable the initiation of SOD mimetic activity (pro-oxidant activity) even at pH 5 close to biologically-appropriate acid conditions, e.g. in lysosome/endosome/tumor-microenvironments. These findings suggest that P-Ce3+ ions enhance the switching efficiency of their anti/pro-oxidant activities. Thus, P-mediated switches could be utilized to achieve a better understanding of the nanozyme switching-mechanisms, and for the design of multi-functional nanozymes for enhancing therapeutic efficacy.

One-pot synthesis of cerium and praseodymium co-doped carbon quantum dots as enhanced antioxidant for hydroxyl radical scavenging

The antioxidant activity of ceria nanoparticles is tightly regulated by size distribution and heteroatom doping. Inspired by this rule, cerium and praseodymium codoped carbon quantum dots (Ce/Pr-CQDs) were synthesized through the one-pot hydrothermal carbonization method. Taking intrinsic advantage of CQDs, the resultant Ce/Pr-CQDs exhibited uniform and ultra-small morphology with an average size of 2.8 nm, which led to an increased proportion of Ce³⁺. In addition, the doping of Pr into Ce-CQDs improved the redox properties. As we expected, the Ce/Pr-CQDs possessed enhanced hydroxyl radical scavenging properties compared with the cerium-doped carbon quantum dots (Ce-CQDs). Furthermore, Ce/Pr-CQDs with favorable biocompatibility and negligible cytotoxicity are readily internalized into cytoplasm, decreasing the level of reactive oxygen species (ROS). Taken together, the resultant Ce/Pr-CQDs displayed great potential for applications relating to oxidative-stress-associated disease.

A new solvothermal method for the synthesis of size-controlled YAG:Ce single-nanocrystals

This modified solvothermal method, combined with in situ photoluminescence measurements, allows the synthesis of well-crystallized size-controlled YAG:Ce nanocrystals.