Geological evidence of extensive N-fixation by volcanic lightning during very large explosive eruptions.

Most of the nitrogen (N) accessible for life is trapped in dinitrogen (N2), the most stable atmospheric molecule. In order to be metabolized by living organisms, N2 has to be converted into biologically assimilable forms, so-called fixed N. Nowadays, nearly all the N-fixation is achieved through biological and anthropogenic processes. However, in early prebiotic environments of the Earth, N-fixation must have occurred via natural abiotic processes. One of the most invoked processes is electrical discharges, including from thunderstorms and lightning associated with volcanic eruptions. Despite the frequent occurrence of volcanic lightning during explosive eruptions and convincing laboratory experimentation, no evidence of substantial N-fixation has been found in any geological archive. Here, we report on the discovery of a significant amount of nitrate in volcanic deposits from Neogene caldera-forming eruptions, which are well correlated with the concentrations of species directly emitted by volcanoes (sulfur, chlorine). The multi-isotopic composition (δ18O, Δ17O) of the nitrates reveals that they originate from the atmospheric oxidation of nitrogen oxides formed by volcanic lightning. According to these first geological volcanic nitrate archive, we estimate that, on average, about 60 Tg of N can be fixed during a large explosive event. Our findings hint at a unique role potentially played by subaerial explosive eruptions in supplying essential ingredients for the emergence of life on Earth.

Chemical and ultramorphologic effects of ethylenediaminetetraacetic acid and sodium hypochlorite in young and old root canal dentin.

OBJECTIVES: The objectives of this study were to evaluate and compare the time-dependent chemical and ultramorphologic effects of ethylenediaminetetraacetic acid (EDTA) and sodium hypochlorite (NaOCl) in young and old dentin. METHODS: Sixty-four teeth scheduled for extraction were collected from young (<30 years) and old (>60 years) patients. In 48 teeth, the dentin was reduced to a powder state and treated with EDTA or EDTA + NaOCl for 1 and 10 minutes, respectively. X-ray diffraction analysis was used to determine the changes in the composition of dentin through dissolution of hydroxyapatite (HAp). In the remaining teeth (n = 16), the root canals were prepared, bisected, and subjected to the same time-dependent treatment regimens. The changes in the number and area of dentinal tubules were calculated by image analysis. The data were analyzed statistically by paired t test and one-way analysis of variance, followed by Tukey honestly significant difference test at P = .05. RESULTS: In both young and old dentin, EDTA significantly decreased the HAp intensity at 1 and 10 minutes, whereas EDTA + NaOCl only decreased that of old dentin at 10 minutes. Pair-wise comparisons revealed that in old dentin, the reduction in HAp intensity after treatment with EDTA and EDTA + NaOCl was significantly greater at 10 minutes than at 1 minute, whereas in young dentin, a significant decrease was only observed in the EDTA/10-minute subgroup. Compared with their 1-minute counterparts, 10-minute treatment with EDTA + NaOCl significantly increased the tubular diameter and tubular area of old dentin. In young dentin, the tubular area and diameter values were not affected by treatment time (P > .05). CONCLUSIONS: In young root dentin, 10-minute treatment with EDTA + NaOCl does not significantly alter the chemical and ultramorphologic structure and thus appears to be unnecessary. In old dentin, extended treatment time with EDTA + NaOCl should be avoided owing to excessive demineralization and erosion. In both types of dentin, EDTA was not effective in complete removal of the smear layer.

Bioinorganic magnetic core-shell nanocomposites carrying antiarthritic agents: intercalation of ibuprofen and glucuronic acid into Mg-Al-layered double hydroxides supported on magnesium ferrite.

This paper describes the synthesis and characterization of a composite constituted by an antiarthritic agent (AA) intercalated into a layered double hydroxide (LDH) supported on magnesium ferrite. Core-shell nanocomposites were prepared by depositing Mg-Al-NO(3)-LDH on a MgFe(2)O(4) core prepared by calcination of a nonstoichiometric Mg-Fe-CO(3)-LDH. Intercalation of ibuprofen and glucuronate anions was performed by ion-exchange with nitrate ions. The structural characteristics of the obtained products were investigated by powder X-ray diffraction, element chemical analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Morphologies of the nanocomposite particles were examined by scanning electron microscopy and transmission electron microscopy. The products were shown to intercalate substantial amounts of AA with enhanced thermal stabilities. Room-temperature magnetic measurements by vibrating sample magnetometry revealed that the products show soft ferromagnetic properties suitable for potential utilization in magnetic arthritis therapy.