Decomposition of water by cerium oxide of δ-phase

Reduced cerium dioxide (CeO_2?x) can reduce water, producing hydrogen at ?298 K. Kinetic studies were focused on the stoichiometric reaction of δ-phase cerium oxide (CeO_1.818) with water vapor. Different activation energies of 18.1 and 33.4 kJ mol^?1 were observed for the reactions at the temperature ranges above and below ca. 453 K, respectively. Rate equations observed in the two temperature ranges were also different. These results strongly suggest that the rate-determining steps are different between the two temperature ranges. Rapid oxygen exchange observed between H₂¹⁸O and lattice oxygen in cerium oxide of δ- phase at ? 298 K indicated that neither the adsorption of water molecules not the diffusion of oxygen ions in the bulk of the oxide can be the rate-determining step. H₂D₂ exchange occurred rapidly at 373 K compared to the rate of water decomposition, suggesting that the recombination of hydrogen atoms on the surface is not rate- determining either. A tentative reaction mechanism was proposed to explain the results of the kinetic studies. The rate-determining step at high temperatures (>453 K) is the reduction of OH^? by the six-coordinated Ce³⁺ which is present in the nonstoichiometric cerium oxide, while that at low temperatures (<453 K) is the subsequent reduction of H⁺ by the seven-coordinated Ce³⁺.     

Enhanced photocatalytic activity of ceria-doped zinc oxide under UV illumination prepared via chemical precipitation

Transition metal oxide has emerged as one of the most potential candidates for environment remediation by utilizing solar energy through photocatalysis. This study compares the optical characteristics of zinc oxide (ZnO) and ceria-doped zinc oxide (CeZnO) nanoparticles synthesized through a facile chemical precipitation method without using any assistant catalyst. The present work investigates the consequences of ceria (cerium dioxide, CeO₂) intrusion on the photocatalytic activity of ZnO nanoparticles using methylene blue (MB) as a probe pollutant. The CeZnO showed an increase in photoactivity when compared to ZnO nanoparticles for degradation of MB in an aqueous solution under ultraviolet (UV) irradiance. The resulting heterojunction between ZnO and that of ceria enhances the charge separation efficiency showing a strong correlation between ZnO and CeO₂ heterojunction on the charge transfer mechanism across the interface.     

The uptake of manganese ions and the apparent thermal transition of the erythrocyte membranes

The nuclear magnetic resonance manganese doping technique is currently used for the determination of the water diffusional exchange time through human erythrocyte membranes. An apparent thermal transition at 26 degrees C was noticed at 18-30 mM manganese doping in the suspending solution. An analysis in terms of a two-phase nuclear spin exchanging system revealed that apparent thermal transitions are expected to occur in the upper and lower temperature regions. They represent a shift from intermediate exchange rates where water diffusion through the membrane is dominant to either fast or slow exchange rates where proton relaxation is the controlling process. The lower temperature apparent transition may be altered by the intracellular manganese concentration; the lower the Mn2+ concentration the lower the transition. Also according to this interpretation only a fraction of the erythrocytes are significantly permeated by Mn2+. The upper transition depends on the Mn2+ concentration in the extracellular volume; it decreases with decreasing Mn2+ concentration.     

CeO2 nanoparticles synthesized through green chemistry are biocompatible: In vitro and in vivo assessment

Widespread use of cerium oxide (CeO₂) nanoparticles (NPs) is found in almost all areas of research due to their distinctive properties. CeO₂ NPs synthesized via green chemistry have been characterized for antioxidant, phytochemical, and biological potential. Physical characterization through scanning electron microscopy, XRD, and TGA showed that the NPs are circular in shape, 20‐25 nm in size, and stable in a wide range of temperature. NPs display significant antioxidant (32.7% free radical scavenging activity) and antileishmanial (IC₅₀ 48 µg mL^?1) properties. In vitro toxicity tested against lymphocytes verified that NPs are biocompatible (99.38% viability of lymphocytes at 2.5 μg mL^?1). In vivo toxicity experiments showed no harmful effects on rat serum chemistry and histology of various organs and did not even change the concentration of antioxidative enzymes, total protein contents, lipid peroxidation, and nitrosative stress. These observations are in line with the statement that plant‐based synthesis of CeO₂ NPs lessens or nullifies in vitro and in vivo toxicity and hence CeO₂ NPs are regarded as a safe and biocompatible material to be used in drug delivery.     

Antibacterial Activity of Polymer Coated Cerium Oxide Nanoparticles

Cerium oxide nanoparticles have found numerous applications in the biomedical industry due to their strong antioxidant properties. In the current study, we report the influence of nine different physical and chemical parameters: pH, aeration and, concentrations of MgSO₄, CaCl₂, KCl, natural organic matter, fructose, nanoparticles and Escherichia coli, on the antibacterial activity of dextran coated cerium oxide nanoparticles. A least-squares quadratic regression model was developed to understand the collective influence of the tested parameters on the anti-bacterial activity and subsequently a computer-based, interactive visualization tool was developed. The visualization allows us to elucidate the effect of each of the parameters in combination with other parameters, on the antibacterial activity of nanoparticles. The results indicate that the toxicity of CeO₂ NPs depend on the physical and chemical environment; and in a majority of the possible combinations of the nine parameters, non-lethal to the bacteria. In fact, the cerium oxide nanoparticles can decrease the anti-bacterial activity exerted by magnesium and potassium salts.     

Oxygen isotope analysis of bacterial and fungal manganese oxidation

The ability of micro‐organisms to oxidize manganese (Mn) from Mn(II) to Mn(III/IV) oxides transcends boundaries of biological clade or domain. Many bacteria and fungi oxidize Mn(II) to Mn(III/IV) oxides directly through enzymatic activity or indirectly through the production of reactive oxygen species. Here, we determine the oxygen isotope fractionation factors associated with Mn(II) oxidation via various biotic (bacteria and fungi) and abiotic Mn(II) reaction pathways. As oxygen in Mn(III/IV) oxides may be derived from precursor water and molecular oxygen, we use a twofold approach to determine the isotope fractionation with respect to each oxygen source. Using both ¹⁸O‐labeled water and closed‐system Rayleigh distillation approaches, we constrain the kinetic isotope fractionation factors associated with O atom incorporation during Mn(II) oxidation to ?17.3‰ to ?25.9‰ for O₂ and ?1.9‰ to +1.8‰ for water. Results demonstrate that stable oxygen isotopes of Mn(III/IV) oxides have potential to distinguish between two main classes of biotic Mn(II) oxidation: direct enzymatic oxidation in which O₂ is the oxidant and indirect enzymatic oxidation in which superoxide is the oxidant. The fraction of Mn(III/IV) oxide‐associated oxygen derived from water varies significantly (38%–62%) among these bio‐oxides with only weak relationship to Mn oxidation state, suggesting Mn(III) disproportionation may account for differences in the fraction of mineral‐bound oxygen from water and O₂. Additionally, direct incorporation of molecular O₂ suggests that Mn(III/IV) oxides contain a yet untapped proxy of of environmental O₂, a parameter reflecting the integrated influence of global respiration, photorespiration, and several other biogeochemical reactions of global significance.     

Saccharose complexes of manganese in different oxidation states

The interaction between saccharose and manganese in different oxidation states was studied in alkaline media by polarographic, potentiometric, ESR spectroscopic and UV-Vis spectrophotometric methods. The results showed that stable manganese(II) and manganese(III) complexes and a complex of manganese(II,III) in a mixed oxidation state were formed with the composition [Mn^IIL(OH)₂], [Mn₂^IIIL₂(OH)₈]²⁻ and [Mn^IIMn^IIIL₂(OH)₆]⁻, respectively. The manganese(II)-saccharose complex was shown to dimerize in alkaline media. The stability constants of the Mn(II,III) and Mn(III) complexes were determined. The oxidation of the manganese(II)-saccharose complex by a stoichiometric amount of K₃ [FeCN]₆ resulted in the formation of the manganese(III) and manganese(IV) complexes. However, oxidation by molecular oxygen only yielded the manganese(III) complex which reduced spontaneously in inert atmosphere to the mixed valence Mn(II,III) complex. The latter was able to be oxidized again by oxygen to the Mn(III) complex. This process proved to be reversible and could be repeated several times.     

Mesoproterozoic surface oxygenation accompanied major sedimentary manganese deposition at 1.4 and 1.1 Ga

Manganese (Mn) oxidation in marine environments requires oxygen (O₂) or other reactive oxygen species in the water column, and widespread Mn oxide deposition in ancient sedimentary rocks has long been used as a proxy for oxidation. The oxygenation of Earth's atmosphere and oceans across the Archean-Proterozoic boundary are associated with massive Mn deposits, whereas the interval from 1.8–1.0 Ga is generally believed to be a time of low atmospheric oxygen with an apparent hiatus in sedimentary Mn deposition. Here, we report geochemical and mineralogical analyses from 1.1 Ga manganiferous marine-shelf siltstones from the Bangemall Supergroup, Western Australia, which underlie recently discovered economically significant manganese deposits. Layers bearing Mn carbonate microspheres, comparable with major global Mn deposits, reveal that intense periods of sedimentary Mn deposition occurred in the late Mesoproterozoic. Iron geochemical data suggest anoxic-ferruginous seafloor conditions at the onset of Mn deposition, followed by oxic conditions in the water column as Mn deposition persisted and eventually ceased. These data imply there was spatially widespread surface oxygenation ~1.1 Ga with sufficiently oxic conditions in shelf environments to oxidize marine Mn(II). Comparable large stratiform Mn carbonate deposits also occur in ~1.4 Ga marine siltstones hosted in underlying sedimentary units. These deposits are greater or at least commensurate in scale (tonnage) to those that followed the major oxygenation transitions from the Neoproterozoic. Such a period of sedimentary manganogenesis is inconsistent with a model of persistently low O₂ throughout the entirety of the Mesoproterozoic and provides robust evidence for dynamic redox changes in the mid to late Mesoproterozoic.     

Reconstitution of the Mn-depleted photosystem 2 by using some manganese complexes

Restoration of electron flow and oxygen-evolution quantity of Mn-depleted photosystem 2 (PS2) was performed with using synthetic manganese complexes Mn(im)₆Cl₂, Mn(im)₂Cl₂, Mn(5-Clsalgy)₂, and Mn(salgy)₂ instead of original manganese cluster for reconstruction of electron transport and oxygen evolution.     

A colorimetric detection of dopamine in urine and serum based on the CeO2@ZIF-8/Cu-CDs laccase-like nanozyme activity

This study reports a sensitive and selective colorimetric approach for the analysis of dopamine (DA) based on CeO₂@ZIF-8/Cu-CDs laccase-like nanozymes activity. The CeO₂@ZIF-8/Cu-CDs was synthesized using cerium oxide (CeO₂) and copper-doped carbon dots (Cu-CDs) with 2-methylimidazole by a facilely hydrothermal approach. The CeO₂@ZIF-8/Cu-CDs exhibited excellent laccase-like nanozymes activity and can oxidize the colorless substrate (DA) to red product with 4-aminoantipyrine as the chromogenic agent. The Michaelis–Menten constant (K_m) and the maximal velocity (V_max) of CeO₂@ZIF-8/Cu-CDs are 0.20 mM and 1.48 μM/min, respectively. The detection method has a linear range of 0.05–7.5 μg/mL and a detection limit as low as 8.5 ng/mL with good reproducibility. The developed colorimetric sensor was applied to rapid and precise quantitative evaluation of DA levels in serum and urine samples. This study presents a new approach for detecting biological molecules by utilizing the controlled regulation of nanozymes' laccase-like activity.     

The effect of manganese nanoparticles on performance,redox reactions and epigenetic changes in turkey tissues

The hypothesis of the research was the assumption, that manganese nanoparticles can affect the body in the same way as macromolecules. Their smaller size and greater biological reactivity will potentially allow the Mn addition to the diet to be reduced and, consequently, less excretion of this element into the environment. The aim of the study was to determine whether the use of Mn nanoparticles would make it possible to reduce the level of this micronutrient added to turkey diets without adversely affecting redox reactions in cells and epigenetic changes. The experiment was conducted on six groups with 10 replications, in a two-factor design with three dosages of manganese: 100, 50 and 10 mg/kg, and two sources: manganese oxide (MnO) and manganese nanoparticles (NP-Mn₂O₃). Markers of oxidative stress determined in the blood, that is, the concentration of lipid hydroperoxides, malondialdehyde, protein carbonyl derivatives, 3-nitrotyrosine, 8-hydroxydeoxyguanosine, total glutathione, superoxide dismutase, glutathione peroxidase, catalase, ceruloplasmin, total antioxidant status, albumin and vitamin C content. The level of epigenetic changes in the blood was determined by analysing global DNA methylation. In the experiment, in which the diet of turkeys was supplemented with two forms of Mn (MnO or NP-Mn₂O₃) at three dosages: 100, 50 and 10 mg/kg, the 10 mg/kg dose, especially in the form of NP-Mn₂O₃, induced lipid oxidation reactions to the greatest extent. Irrespective of the dosage of Mn in the turkey diet, Mn in the form of NP-Mn₂O₃ was found to reduce protein nitration more than Mn in the form of MnO. Reducing the Mn dosage in the diet from 100 to 50 mg/kg and then to 10 mg/kg is unfavourable because proportionally increases protein and DNA oxidation in cells, decreases the activity of antioxidant enzymes, and increases the level of glutathione. Reducing the dosage from 100 to 10 mg/kg increases global DNA methylation. The reduction of the Mn level, regardless of the form used, is disadvantageous, because it weakens the defense of the antioxidant system, which consequently can induce oxidative processes in the cells. Although Mn in the form of NP-Mn₂O₃ reduce protein nitration better than in MnO form, the use of manganese nanoparticles in turkey feeding (even in lower doses) requires further study.     

Theoretical guidance and experimental confirmation on catalytic tendency of M-CeO2 (M = Zr,Mn, Ru or Cu) for NH3-SCR of NO

Abstract

Herein, we demonstrate that the degrees of catalytic performance of M-CeO₂-based catalysts (M=Mn, Cu, Ru or Zr) for an ammonia selective catalytic reduction (NH₃-SCR) of nitric-oxide (NO) can be estimated using three theoretical terms; (i) an oxygen vacancy formation energy of a catalyst, (ii) an adsorption energy of NO and (iii) an adsorption energy of NH₃. Those terms predict the trend of the catalytic performance as the order; Mn–CeO₂ > Cu–CeO₂ > Ru–CeO₂ > Zr–CeO₂ > CeO₂. To verify the theoretical prediction, the catalysts were synthesized and tested their performances on the NH₃-SCR of NO reaction. The normalized NO conversion rates at low temperatures (100–200 °C) were measured for Mn–CeO₂, Cu–CeO₂, Ru–CeO₂, Zr–CeO₂ and CeO₂ as 2.61–7.46, 1.30–6.82, 0.73–3.02, 0.81–3.31 and 1.55–2.33 mol s^?1 m^?2, respectively. In addition, a concept of a structure-activity relationship analysis shows a strong relationship between theoretical and experimental results. Consequently, an application of predicting the catalytic performance of catalysts from theoretical calculations prior the catalyst synthesis is useful in catalyst design and screening that can reduce time and cost.     

The Effects of Cerium Valence States at Cerium Oxide Coatings on the Responses of Bone Mesenchymal Stem Cells and Macrophages

Ideal orthopedic coatings should trigger good osteogenic response and limited inflammatory response. The cerium valence states in ceria are associated with their anti-oxidative activity and anti-inflammatory property. In the study, we prepared two kinds of plasma sprayed CeO₂ coatings with different Ce⁴⁺ concentrations to investigate the effects of Ce valence states on the response of bone mesenchymal stem cells (BMSCs) and macrophage RAW264.7. Both the coatings (CeO₂-A and CeO₂-B) were characterized via XRD, SEM, and X-ray photoelectron spectroscopy. The CeO₂ coatings enhanced osteogenic behaviors of BMSCs in terms of cellular proliferation, alkaline phosphatase (ALP) activity and calcium deposition activity in comparison with the Ti substrate. In particular, the CeO₂-B coating (higher Ce⁴⁺ concentration) elicited greater effects than the CeO₂-A coating (higher Ce³⁺ concentration). RT-PCR and western blot results suggested that the CeO₂-B coating promoted BMSCs osteogenic differentiation through the SMAD-dependent BMP signaling pathway, which activated Runx2 expression and subsequently enhanced the expression of ALP and OCN. With respect to either CeO₂-A coating or Ti substrate, the CeO₂-B coating exerted greater effects on the macrophages, increasing the anti-inflammatory cytokines (IL-10 and IL-1ra) expression and suppressing the expression of the pro-inflammatory cytokines (TNF-α and IL-6) and ROS production. Furthermore, it also upregulated the expression of osteoinductive molecules (TGF-β1 and BMP2) in the macrophages. The regulation of cerium valence states at plasma sprayed ceria coatings can be a valuable strategy to improve osteogenic properties and alleviate inflammatory response.     

Microbial Communities Promoting Mn(II) Oxidation in Ashumet Pond,a Historically Polluted Freshwater Pond Undergoing Remediation

An extensive culture-dependent and -independent study was conducted to identify microorganisms contributing to the biogeochemical cycling of manganese (Mn) in Ashumet Pond, a freshwater pond in Massachusetts currently undergoing remediation. A variety of bacteria (including Gamma-, Beta-, and Alpha-proteobacteria, Firmicutes, and Bacteroides) and Ascoymete fungi were isolated from the pond that promote Mn(II) oxidation and subsequent formation of Mn(III/IV) oxide minerals. Targeted-amplicon pyrosequencing of the bacterial and fungal communities associated with Mn oxide-encrusted samples show a highly diverse microbial community, of which the cultured phylotypes represent a minor proportion. This suggests a larger community, not identified through culturing, contributes to Mn oxide formation within the Pond.     

氧化铈纳米颗粒种子引发对盐胁迫下辣椒种子萌发及幼苗生长的影响

氧化铈纳米颗粒(CeO₂NP_S),因具有较强的自由基清除能力和抗氧化酶特性,已被证明可提高植物的耐盐性,但其对辣椒种子引发作用和机制尚不明确。为揭示CeO₂NP_S种子引发处理辣椒对盐胁迫下的萌发及幼苗生长的影响,以辣椒品种(Capsicum annuum)茂蔬360为试验材料,设置了7个CeO₂NP_S浓度(0、0.05、0.1、0.2、0.3、0.4、0.5 mmol·L^-1),以未引发处理组为对照,研究不同浓度CeO₂NP_S种子引发处理后对盐胁迫下辣椒种子萌发、幼苗生物量和生理生化指标的影响。结果表明:(1)0.5 mmol·L^-1 CeO₂NP_S种子引发处理后的种子,其可溶性蛋白质、脯氨酸含量和过氧化氢酶(CAT)活性、抗坏血酸(AsA)含量和AsA/DHA比值显著提高,超氧阴离子(O₂^-)含量显著降低; 盐胁迫下,该处理种子的发芽率、发芽势、发芽指数、活力指数最大。(2)0.4 mmol·L^-1 CeO₂NP_S种子引发处理的幼苗在盐胁迫下的鲜重、干重和根长最大,幼苗的可溶性蛋白质、AsA含量和AsA/DHA比值均显著提高。综上认为,CeO₂NP_S引发处理不仅可通过降低种子水势、促进贮藏物质代谢和提高抗氧化能力提高种子在盐胁迫下的发芽率,还可在苗期通过增强蛋白合成和抗坏血酸-谷胱甘肽循环(AsA-GSH)促进盐胁迫下幼苗的生长。     

Cerium oxide nanoparticles as potential antibiotic adjuvant. Effects of CeO2 nanoparticles on bacterial outer membrane permeability

BackgroundTherapeutic options against Multi Drug Resistant (MDR) pathogens are limited and the overall strategy would be the development of adjuvants able to enhance the activity of therapeutically available antibiotics. Non-specific outer membrane permeabilizer, like metal-oxide nanoparticles, can be used to increase the activity of antibiotics in drug-resistant pathogens. The study aims to investigate the effect of cerium oxide nanoparticles (CeO₂ NPs) on bacterial outer membrane permeability and their application in increasing the antibacterial activity of antibiotics against MDR pathogens.MethodsThe ability of CeO₂ NPs to permeabilize Gram-negative bacterial outer membrane was investigated by calcein-loaded liposomes. The extent of the damage was evaluated using lipid vesicles loaded with FITC-dextran probes. The effect on bacterial outer membrane was evaluated by measuring the coefficient of permeability at increasing concentrations of CeO₂ NPs. The interaction between CeO₂ NPs and beta-lactams was evaluated by chequerboard assay against a Klebsiella pneumoniae clinical isolate expressing high levels of resistance against those antibiotics.ResultsCalcein leakage increases as NPs concentrations increase while no leakage was observed in FITC-dextran loaded liposomes. In Escherichia coli the outer membrane permeability coefficient increases in presence of CeO₂ NPs. The antibacterial activity of beta-lactam antibiotics against K. pneumoniae was enhanced when combined with NPs.ConclusionsCeO₂ NPs increases the effectiveness of antimicrobials which activity is compromised by drug resistance mechanisms. The synergistic effect is the result of the interaction of NPs with the bacterial outer membrane. The low toxicity of CeO₂ NPs makes them attractive as antibiotic adjuvants against MDR pathogens.     

Rapid loss of structural motifs in the manganese complex of oxygenic photosynthesis by X-ray irradiation at 10-300 K

Structural changes upon photoreduction caused by x-ray irradiation of the water-oxidizing tetramanganese complex of photosystem II were investigated by x-ray absorption spectroscopy at the manganese K-edge. Photoreduction was directly proportional to the x-ray dose. It was faster in the higher oxidized S2 state than in S1; seemingly the oxidizing potential of the metal site governs the rate. X-ray irradiation of the S1 state at 15 K initially caused single-electron reduction to S0* accompanied by the conversion of one di-mu-oxo bridge between manganese atoms, previously separated by approximately 2.7 A, to a mono-mu-oxo motif. Thereafter, manganese photoreduction was 100 times slower, and the biphasic increase in its rate between 10 and 300 K with a breakpoint at approximately 200 K suggests that protein dynamics is rate-limiting the radical chemistry. For photoreduction at similar x-ray doses as applied in protein crystallography, halfway to the final Mn(II)4 state the complete loss of inter-manganese distances <3 A was observed, even at 10 K, because of the destruction of mu-oxo bridges between manganese ions. These results put into question some structural attributions from recent protein crystallography data on photosystem II. It is proposed to employ controlled x-ray photoreduction in metalloprotein research for: (i) population of distinct reduced states, (ii) estimating the redox potential of buried metal centers, and (iii) research on protein dynamics.     

Various physicochemical and surface properties controlling the bioactivity of cerium oxide nanoparticles

Amidst numerous emerging nanoparticles, cerium oxide nanoparticles (CNPs) possess fascinating pharmacological potential as they can be used as a therapeutic for various oxidative stress-associated chronic diseases such as cancer, inflammation and neurodegeneration due to unique redox cycling between Ce³⁺ and Ce⁴⁺ oxidation states on their surface. Lattice defects generated by the formation of Ce³⁺ ions and compensation by oxygen vacancies on CNPs surface has led to switching between CeO₂ and CeO_2–x during redox reactions making CNPs a lucrative catalytic nanoparticle capable of mimicking key natural antioxidant enzymes such as superoxide dismutase and catalase. Eventually, most of the reactive oxygen species and nitrogen species in biological system are scavenged by CNPs via an auto-regenerative mechanism in which a minimum dose can exhibit catalytic activity for a longer duration. Due to the controversial outcomes on CNPs toxicity, considerable attention has recently been drawn towards establishing relationships between the physicochemical properties of CNPs obtained by different synthesis methods and biological effects ranging from toxicity to therapeutics. Unlike non-redox active nanoparticles, variations in physicochemical properties and the surface properties of CNPs obtained from different synthesis methods can significantly affect their biological activity (inactive, antioxidant, or pro-oxidant). Moreover, these properties can influence the biological identity, cellular interactions, cellular uptake, biodistribution, and therapeutic efficiency. This review aims to highlight the critical role of various physicochemical and the surface properties of CNPs controlling their biological activity based on 165 cited references.