Theoretical Investigation of <i>N</i>-Nitrosodimethylamine Formation from Nitrosation of Trimethylamine

Tertiary amines have been demonstrated to be capable of undergoing nitrosative cleavage to produce carcinogenic N-nitrosamines. The reaction mechanism of the nitrosation of trimethylamine (TMA) to produce N-nitrosodimethylamine (NDMA) was investigated at the CBS-QB3 level of theory. The formation of NDMA from TMA was proposed to be initiated by the formation of an iminium ion, Me2N+CH2. Two different mechanisms (NOH elimination mechanism and oxidation abstraction mechanism) leading to Me2N+CH2 were investigated, and the oxidation abstraction mechanism was found to be mainly operative. This result indicates that the oxidation abstraction mechanism plays an important role in the nitrosation of both N,N-dialkyl aromatic and tertiary aliphatic amines. Starting from the iminium ion, two experimentally proposed mechanisms (pathways 1 and 2) and one new mechanism (pathway 3) were examined. Pathway 1 proposes that the iminium ion undergoes hydrolysis to give dimethylamine (DMA), which then can be further nitrosated to NDMA; pathway 2 proposes that the iminium ion reacts with NO2− and forms a neutral intermediate, which then collapses to NDMA. In pathway 3, the iminium ion reacts with N2O3 to give NDMA. Calculation results indicate that in aqueous solution pathway 1 is more feasible than pathways 2 and 3; moreover, the transformation from the iminium ion to NDMA is the rate-determining step. This work will be helpful to elucidate the formation mechanisms of the carcinogenic N-nitrosamines from the nitrosation of tertiary amines

Carbon Dioxide in the Nitrosation of Amine: Catalyst or Inhibitor?

Nitrosamines are a class of carcinogenic, mutagenic, and teratogenic compounds generally produced from the nitrosation of amine. This paper investigates the mechanism for the formation of nitrosodimethylamine (NDMA) from the nitrosation of dimethylamine (DMA) by four common nitrosating agents (NO2–, ONOO–, N2O3, and ONCl) in the absence and presence of CO2 using the DFT method. New insights are provided into the mechanism, emphasizing that the interactions of CO2 with amine and nitrosating agents are both potentially important in influencing the role of CO2 (catalyst or inhibitor). The role of CO2 as catalyst or inhibitor mainly depends on the nitrosating agents involved. That is, CO2 shows the catalytic effect when the weak nitrosating agent NO2– or ONOO– is involved, whereas it is an inhibitor in the nitrosation induced by the strong nitrosating agent N2O3 or ONCl. To conclude, CO2 serves as a “double-edged sword” in the nitrosation of amine. The findings will be helpful to expand our understanding of the pathophysiological and environmental significance of CO2 and to develop efficient methods to prevent the formation of carcinogenic nitrosamines

Reactions of Amine and Peroxynitrite: Evidence for Hydroxylation as Predominant Reaction and New Insight into the Modulation of CO₂

Peroxynitrite is related to numerous diseases including cardiovascular diseases, inflammation, and cancer. In order to expand the understanding for the toxicology of peroxynitrite in biological system, the reactions of amine (morpholine as a probe) with peroxynitrite and the modulation of CO₂ were investigated by using DFT methods. The results strongly indicate that the hydroxylation of amine by peroxynitrous acid ONOOH, which was previously overlooked by most studies, is predominant relative to the widely reported nitration and nitrosation in the absence of CO₂. The product <i>N</i>-hydroxylamine is proposed to be mainly generated via nonradical pathway (two-electron oxidation). The modulation of CO₂ exhibits two main functions: (1) inhibition of hydroxylation due to the promoted consumption of peroxynitrite via fast reaction of CO₂ with ONOO¯ to form ONOOCO₂¯; (2) dual effect (catalysis and inhibition) of CO₂ toward nitration and nitrosation. As a new insight, amine does react with CO₂ and produce inert amine carbamate R₂NCOO¯. This reaction has the potential to compete with the reaction of CO₂ and ONOO¯, which leads to inhibition of nitration and nitrosation. The concentration of CO₂ could be a critical factor determining the final effect, catalysis or inhibition. As a new finding, HCO₃¯ is probably an effective catalyst for the reaction of amine and CO₂. Moreover, further studies on how the different types of the amine might affect the outcome of the reactions would be an interesting topic

Additional file 1: of Is the presence of HCMV components in CNS tumors a glioma-specific phenomenon?

Table S1. Expression of HCMV proteins and DNA in glioma and non glial tumors of CNS. Figure S1. Nested PCR analysis of HCMV DNA from peripheral blood samples. No HCMV DNA was detected in benign meningioma (lane 1), malignant meningioma(lane 2), PRL pituitary adenoma(lane 3), GH pituitary adenoma(lane 4), ACTH pituitary adenoma(lane 5), cavernous hemangioma(lane 6) and metastatic carcinoma samples(lane 7) (DOCX 41 kb

Data_Sheet_1_Growth of Stipa breviflora does not respond to nitrogen addition because of its conservative nitrogen utilization.docx

Enhanced atmospheric nitrogen (N) deposition is threating species diversity in the desert steppe ecoregions. Needlegrass (Stipa breviflora) is the dominant specie in the desert steppe grasslands of China and southern Mongolia, and the response of S. brevifolia to N deposition is not well known. In this study, we conducted an experiment to determine the growth and N uptake of S. breviflora in response to several N addition rates. The results showed that N addition did not change plant growth, emergence rate, plant height, or biomass of S. breviflora, even at a N addition rate of 50 kg N ha−1 yr.−1 with sufficient soil moisture during a 120-day growth period. The absence of a N effect was due to the fact that N uptake in S. breviflora was not improved by N addition. These results indicated that S. breviflora is very conservative with respect to N utilization, which could possibly help it resist enhanced atmospheric N deposition. Moreover, conservative N utilization also enables S. breviflora to survive in N-limiting soils.</p

High-Performance Recovery of Vanadium(V) in Leaching/Aqueous Solution by a Reusable Reagent-Primary Amine N1519

Efficient extraction and stripping for recovering vanadium­(V) from the leaching/aqueous solution of chromium-bearing vanadium slag (V–Cr slag) are essential to the reuse of heavy metals. The performance characteristics of a new reagent, primary amine N1519, were first reported for extracting vanadium. With a phase ratio of organic to aqueous up to 1:1, 99.7% of vanadium­(V) can be effectively extracted from the leaching/aqueous solution, and powder of NH₄VO₃ was obtained through the stripping with ammonia. The new reagent can be recyclable in use for sustainable reuse after stripping. Different extraction conditions, e.g., the initial pH of the leaching/aqueous solution and the molar quantity of N1519 were investigated. The powder of vanadium-organic compounds (VOC) with N1519 formed in the process of extraction was obtained and purified through three-steps of solvent-out crystallizations. The hydrogen bond association mechanism of extraction was illustrated with the structure of VOC and the enthalpy change in extraction process. The fast extraction process and slow stripping procedure for recovering vanadium­(V) are suitable for use in annular centrifugal contactors with very short contact/resident times and mixed-settler extractors with very good mass transfer, respectively. The results offer significant advantages over conventional processes

A Cleaner Process for Selective Recovery of Valuable Metals from Electronic Waste of Complex Mixtures of End-of-Life Electronic Products

In recent years, recovery of metals from electronic waste within the European Union has become increasingly important due to potential supply risk of strategic raw material and environmental concerns. Electronic waste, especially a mixture of end-of-life electronic products from a variety of sources, is of inherently high complexity in composition, phase, and physiochemical properties. In this research, a closed-loop hydrometallurgical process was developed to recover valuable metals, i.e., copper and precious metals, from an industrially processed information and communication technology waste. A two-stage leaching design of this process was adopted in order to selectively extract copper and enrich precious metals. It was found that the recovery efficiency and extraction selectivity of copper both reached more than 95% by using ammonia-based leaching solutions. A new electrodeposition process has been proven feasible with 90% current efficiency during copper recovery, and the copper purity can reach 99.8 wt %. The residue from the first-stage leaching was screened into coarse and fine fractions. The coarse fraction was returned to be releached for further copper recovery. The fine fraction was treated in the second-stage leaching using sulfuric acid to further concentrate precious metals, which could achieve a 100% increase in their concentrations in the residue with negligible loss into the leaching solution. By a combination of different leaching steps and proper physical separation of light materials, this process can achieve closed-loop recycling of the waste with significant efficiency

Ultrafine WC_1–<i>x</i> Nanocrystals: An Efficient Cocatalyst for the Significant Enhancement of Photocatalytic Hydrogen Evolution on g‑C₃N₄

Developing noble metal-free, inexpensive, and highly active cocatalysts to increase the photocatalytic activity of photocatalysts and promote the practical application is significantly important. In this work, ultrafine carbon-deficient tungsten carbide (WC1–x) nanocrystals with an average size of 1.98 ± 0.29 nm are successfully prepared as cocatalysts to dramatically enhance the photocatalytic activity of graphitic carbon nitride (g-C3N4). The optimized system (WC1–xCN5) exhibits the best photocatalytic H2 production rate of 124.5 μmol h–1 (2490 μmol h–1 g–1), which is about 56 times that of bare g-C3N4. In this system, ultrafine WC1–x nanocrystals play a multifunctional role: effectively boosting the carrier separation and transfer and providing rich active sites for H2 production. Hence, the loading of WC1–x nanocrystals remarkably increases the photocatalytic H2 production activity of g-C3N4. This work demonstrates that ultrafine WC1–x nanocrystals have practical application potential to enhance photocatalytic H2 evolution of g-C3N4

Tooth Enamel Proteins Enamelin and Amelogenin Cooperate To Regulate the Growth Morphology of Octacalcium Phosphate Crystals

To examine the hypothetical cooperative role of enamelin and amelogenin in controlling the growth morphology of enamel crystals in the postsecretory stage, we applied a cation selective membrane system for the growth of octacalcium phosphate (OCP) in the truncated recombinant porcine amelogenin (rP148) with and without the 32 kDa enamelin fragment. Enamelin alone inhibited the growth in the c-axis direction more than rP148, yielding OCP crystals with the smallest aspect ratio of all conditions tested. When enamelin was added to the amelogenin “gel-like matrix”, the inhibitory action of the protein mixture on the growth of OCP in the c-axis direction was diminished, while that in the b-axis direction was increased. As a result, the length to width ratio (aspect ratio) of OCP crystal was markedly increased. Addition of enamelin to amelogenin enhanced the potential of amelogenin to stabilize the amorphous calcium phosphate (ACP) transient phase. The ratio of enamelin and amelogenin was crucial for stabilization of ACP and the growth of OCP crystals with larger aspect ratio. The cooperative regulatory action of enamelin and amelogenin was attained, presumably, through coassembling of enamelin and amelogenin. These results have important implications in understanding the growth mechanism of enamel crystals with large aspect ratio