No abstract available

[en] Highlights: • 55% of oxalate-containing particles were internally mixed with metals. • Enhanced oxalate production might be due to increased aqueous phase reactions. • The complexation with metals also contributed to the enrichment of oxalate. • The efficient photolysis of oxalate was observed in the metal particles. Recently, internal mixing states of oxalate with metals in single particles have been reported from field studies, yet the role of metals in the formation processes of oxalate remains unclear due to the diversity of chemical components and complex atmospheric environment. In this study, the mixing states of oxalate with five metals, including zinc (Zn), copper (Cu), lead (Pb), vanadium (V) and iron (Fe) were investigated in Guangzhou, China. It was found that 55% of oxalate-containing particles were internally mixed with these metals. The number fraction of oxalate in the metal-containing particles ranged from 5.4–26%, which is much higher than that in the total detected particles (4.0%), indicating significant enrichment of oxalate in the metal-containing particles. Enhanced oxalate production was found in the Fe- and V-containing particles based on distinctly higher relative peak area (RPA) ratios of oxalate to its precursors compared to the total particles, possibly due to enhanced aqueous phase reactions in the Fe- and V-containing particles. However, enrichment of oxalate in the Zn-, Pb-, and Cu-containing particles was possibly associated with complexation of gas phase oxalic acid with the metals, as indicated by the small increase in RPA ratios in these particles. On the other hand, the internal mixing of oxalate with metals was found to provide a way of efficient photolysis of oxalate-metal complexes, which led to a decrease in oxalate after sunrise in the metal-containing particles. In this study, the enhanced mixing states of oxalate with metals have revealed the important role of metals in the production and degradation of oxalate, providing insights for the evaluation of metals in the formation processes of organic aerosol in field studies, which is beneficial to the further study of air pollution in metal emission areas.

[en] The inhibiting powers towards positronium formation of H₂C₂O₄, HC₂O₄^-, C₂O₄^2- and mixtures of these solutes in aqueous solutions have been measured. Whereas complete inhibition can be observed in solutions of the first two solutes, C₂O₄^2- yields only a limited decrease in the intensity of positronium. These results are discussed in terms of the spur model and of hot positron or positronium reactions. (author)

[en] Neptunium (IV) oxalate was precipitated using a two-stage precipitation system. A series of precipitation experiments was used to identify the significant process variables affecting precipitate characteristics. Process variables tested were input concentrations, solubility conditions in the first stage precipitator, precipitation temperatures, and residence time in the first stage precipitator. A procedure has been demonstrated that produces neptunium (IV) oxalate particles that filter well and readily calcine to the oxide

[en] The inhibiting powers towards positronium formation of H₂C₂O₄, HC₂O₄^-, C₂O₄^-- and mixtures of these solutes in aqueous solutions have been measured. Whereas complete inhibition can be observed in solutions of the first two solutes, C₂O₄^-- yields only a limited decrease in the intensity of positronium. These results are discussed in terms of the spur model and of hot positron or positronium

[en] Rare earth oxalates precipitation is extendedly used in hydrometallurgical processes related to rare earth recycling methods and treatment of radioactive liquid wastes, where rare earth elements are separated from other fission products. For a deeper comprehension of this reactive precipitation process, the thermodynamic modeling of the oxalate-rare earth systems in nitric acid aqueous media is presented for neodymium and cerium systems, due to their distinctive relevance among the rare earth elements. A Pitzer model was selected for the modeling, which was developed using the implementation present within PHREEQC software. Calculations were launched through a COM interface with Matlab (R) and PHREEQC database was complemented by adjustment of the individual Pitzer coefficients for each species interaction to experimental data reported in literature and own experimental water activity measurements required to complete the study. The implemented model is able to accurately predict oxalate-rare earth solubility in a wide range of rare earth and nitric acid concentrations up to > 10 m. (authors)

[en] A method for the precipitation of plutonium(IV) oxalate from homogeneous solutions using diethyl oxalate is reported. The precipitate obtained is crystalline and easily filterable with yields in the range of 92-98% for precipitations involving a few mg to g quantities of plutonium. Decontamination factors for common impurities such as U(VI), Am(III) and Fe(III) were determined. TGA and chemical analysis of the compound indicate its composition as Pu(Csub(2)Osub(4))sub(2).6Hsub(2)O. Data are obtained on the solubility of the oxalate in nitric acid and in mixtures of nitric acid and oxalic acid of varying concentrations. Green PuOsub(2) obtained by calcination of the oxalate has specifications within the recommended values for trace foreign substances such as chlorine, fluorine, carbon and nitrogen. (author)

[en] Ethylene Glycol (CAS RN 107-21-1) can to cause kidney toxicity via the formation of calcium oxalate crystals in a variety of species including humans. Numerous repeated dose studies conducted in rats have indicated that male rats are more susceptible than female rats. Furthermore, subchronic and chronic studies using different dietary exposure regimens have indicated that male Wistar rats may be more sensitive to renal toxicity than male F344 rats. This study was, therefore, conducted to compare the toxicity of ethylene glycol in the two strains of rats under identical exposure conditions and to evaluate the potential contribution of toxicokinetic differences to strain sensitivity. Ethylene glycol was mixed in the diet at concentrations to deliver constant target dosage levels of 0, 50, 150, 500, or 1000 mg/kg/day for 16 weeks to groups of 10 male Wistar and 10 male F-344 rats based upon weekly group mean body weights and feed consumption. Kidneys were examined histologically for calcium oxalate crystals and pathology. Samples of blood, urine and kidneys from satellite animals exposed to 0, 150, 500, or 1000 mg/kg/day for 1 or 16 weeks were analyzed for ethylene glycol, glycolic acid and oxalic acid. Treatment of Wistar rats at 1000 mg/kg/day resulted in the death of 2 rats; in addition, at 500 and 1000 mg/kg/day, group mean body weights were decreased compared to control throughout the 16 weeks. In F-344 rats exposed at 1000 mg/kg/day and in Wistar rats at 500 and 1000 mg/kg/day, there were lower urine specific gravities, higher urine volumes, and increased absolute and relative kidney weights. In both strains of rats treated at 500 and 1000 mg/kg/day, some or all treated animals had increased calcium oxalate crystals in the kidney tubules and crystal nephropathy. The effect was more severe in Wistar rats than in F-344 rats. Accumulation of oxalic acid in the kidneys of both strains of rats were consistent with the dose- and strain-dependent toxicity. As the nephrotoxicity progressed over the 16 weeks, the clearance of ethylene glycol and its metabolites decreased, exacerbating the toxicity. Benchmark dose analysis indicated a BMDL05 for kidney toxicity in Wistar rats of 71.5 mg/kg/day; nearly four-fold lower than in F-344 rats (285 mg/kg/day). This study confirms that the Wistar rat is more sensitive to ethylene glycol-induced renal toxicity than the F344 rat and indicates that metabolism plays a role in the strain differences

[en] We have developed molecular switching system triggered by oxalate anion operating on platinum square planar coordination plane by controlling well-known alkyl inversion process on nitrogens. This work shows that oxalate anion disturbs the thermodynamic equilibrium between syn and aniti conformer and induces the syn conformer to be produced in excess. Thus oxalate may be regarded as a trigger that bring about the conformational change of complex 1. This behavior might be exploited to develop sensors for the kidney stone disease-related oxalate anions. A molecular conformational switching has been of growing interest in association with molecular electronics, machines and sensors. External stimuli such as a transition metal, light, a redox reaction, pH variation and guest molecules were used to control the thermodynamic equilibrium between the conformers. For example, complexation with lewis acid, TiCl₄, changes the conformation of arene-dicarboxamide from syn to anti atropisomer. The specially designed ligand is programmed to have syn conformer by the application of the transition metal complex PdCl₂(PhCN)₂. N-Alkyl-substituted-ethylenediamine complexes of platinum(II) are well known to adopt syn and anti conformers which are inter-converted fast in aqueous solutions. We have been interested in developing a conformational switching system by exploiting this behavior, thus designed complex with two uryl groups which are well known to bind carboxylates. We speculated that the thermodynamic ratio of syn to anti conformer of would be influenced by a suitable dicarboxylate anion such as oxalate which is a biologically important anion

[en] The degradation and transformation of p-nitrophenol (PNP) was evaluated with as-prepared iron oxides (γ-FeOOH, Fe₃O₄, and α-Fe₂O₃) as catalyst. Results showed that α-Fe₂O₃ exhibited higher catalytic activity than the other two samples for reduction transformation and oxidative degradation of PNP. α-Fe₂O₃ showed higher surface-bound Fe(II) contents in the presence of oxalic acid and stronger affinity to PNP, leading to an increase in PNP reductive transformation. And α-Fe₂O₃ could effectively adsorb visible light and hinder the recombination of charge carriers, resulting in higher oxidative degradation activity. p-Aminophenol (PAP), as the main reduction transformation product of PNP, could be removed further by oxidative degradation in the reaction system itself. A possible mechanism was suggested for the comprehensive effect of PNP degradation during the reaction process.