Littérature scientifique sur le sujet « Mo/Cu CODH »

Heavy metal abundance and potential environmental risks are reported for surface sediments (n = 21) from the Port of Koper area, Republic of Slovenia. The enrichment factor (EF) indicates minor enrichment in arsenic (As), cadmium (Cd), copper (Cu), molybdenum (Mo), lead (Pb), antimony (Sb), and zinc (Zn), moderately to severely enriched with nickel (Ni). The trace metal chemistries, in the context of sediment quality guidelines (SQG), imply adverse threshold effect concentrations (TEC) and probable effect concentrations (PEC), for Ni only. Sediment sequential leaching experiments demonstrated that the majority of heavy metals were of natural lithogenic origin and low bioavailability. The heavy metals’ potential for “Risk Assessment Code” values exhibited no or low anthropogenic environmental burden, with the exception of Mo.

This paper focuses on researching the scientific problem of deep extraction and inference of favorable geological and geochemical information about mineralization at depth, based on which a deep mineral resources prediction model is established and machine learning approaches are used to carry out deep quantitative mineral resources prediction. The main contents include: (i) discussing the method of 3D geochemical anomaly extraction under the multi-fractal content-volume (C-V) models, extracting the 12 element anomalies and constructing a 3D geochemical anomaly data volume model for laying the data foundation for researching geochemical element distribution and association; (ii) extracting the element association characteristics of primary geochemical halos and inferring deep metallogenic factors based on compositional data analysis (CoDA), including quantitatively extracting the geochemical element associations corresponding to ore-bearing structures (Sb-Hg) based on a data-driven CoDA framework, quantitatively identifying the front halo element association (As-Sb-Hg), near-ore halo element association (Au-Ag-Cu-Pb-Zn) and tail halo element association (W-Mo-Co-Bi), which provide quantitative indicators for the primary haloes’ structural analysis at depth; (iii) establishing a deep geological and geochemical mineral resources prediction model, which is constructed by five quantitative mineralization indicators as input variables: fracture buffer zone, element association (Sb-Hg) of ore-bearing structures, metallogenic element Au anomaly, near-ore halo element association Au-Ag-Cu-Pb-Zn and the ratio of front halo to tail halo (As-Sb-Hg)/(W-Mo-Bi); and (iv) three-dimensional MPM based on the maximum entropy model (MaxEnt) and Gaussian mixture model (GMM), and delineating exploration targets at depth. The results show that the C-V model can identify the geological element distribution and the CoDA method can extract geochemical element associations in 3D space reliably, and the machine learning methods of MaxEnt and GMM have high performance in 3D MPM.

Trace elements in soils might cause contamination and ecological risks to the environment with increasing anthropogenic disturbance. This study investigated the distribution, speciation, risks and possible sources of 28 target trace elements in soils of the northeastern Qinghai–Tibet Plateau. The average concentrations of trace elements in soils of the study area ranged from 0.25 (Hg) to 697.38 mg kg−1 (Cr). The residual fraction was the dominant host of V, Cr, Cu, Sn, Sb Hg and REEs, while Co, Ni, Zn, Mo, Cd and Pb had large proportions in the non-residual fractions. Risk assessment code analysis showed that Cd should be recognized as a priority pollutant in the study area. Correlation analysis indicated that Pb, Cu, Zn, Cd and Sn might originate from the same or similar source. The 206Pb/207Pb and 208Pb/206Pb ratios of the soils were in the range of 1.166–1.224 and 2.031–2.122, respectively. The anthropogenic Pb contribution proportion was in the range of 0–53.92% for the study area. The anthropogenic Pb contribution was higher in the areas with more intensive anthropogenic activities. Heavy metals and excessive anthropogenic disturbance should be effectively controlled in the northeastern Qinghai–Tibet Plateau to maintain the ecological sustainability and human health of this fragile area.

AbstractThe interaction of femtosecond laser with initially cold solid metallic targets (Al, Au, Cu, Mo, Ni) was investigated in a wide range of laser intensity with focus on the laser energy absorption efficiency. Our developed simulation code (FEMTO-2D) is based on two-temperature model in two-dimensional configuration, where the temperature-dependent optical and thermodynamic properties of the target material were considered. The role of the collisional processes in the ultrashort pulse laser–matter interaction has been carefully analyzed throughout the process of material transition from the cold solid state into the dense plasma state during the pulse. We have compared the simulation predictions of the laser pulse absorption with temperature-dependent reflectivity and optical penetration depth to the case of constant optical parameters. By considering the effect of the temporal and spatial (radial) distribution of the laser intensity on the light absorption efficiency, we obtained a good agreement between the simulated results and available experimental data. The appropriate model for temperature-dependent optical parameters defining the laser absorption efficiency will allow more accurate simulation of the target thermal response in the applications where it is critical, such as prediction of the material damage threshold, laser ablation threshold, and the ablation profile.

Abstract Ten new Agricultural/Food Reference Materials — Bovine Muscle Powder (National Institute of Standards and Technology [NIST], code NIST RM 8414), Whole Egg Powder (NIST RM 8415), Microcrystalline Cellulose (NIST RM 8416), Wheat Gluten (NIST RM 8418), Corn Starch (NIST RM 8432), Corn Bran (NIST RM 8433), Whole Milk Powder (NIST RM 8435), Durum Wheat Flour (NIST RM 8436), Hard Red Spring Wheat Flour (NIST RM 8437) and Soft Winter Wheat Flour (NIST RM 8438) — were prepared by application of milling, irradiation, sieving, blending, and packaging procedures. Excellent material homogeneity was found for virtually all major, minor, and trace elements of interest. The reference materials were characterized with respect to elemental composition via an extensive international, interlaboratory characterization (certification) campaign. Chemical analyses conducted in 73 cooperating laboratories applying 13 major classes of independently different analytical methods led to 278 concentration values for 34 nutritionally, toxicologically, and environmentally pertinent elements. A total of 213 best-estimate and 65 informational concentration values are available for Al, As, B, Ba, Br, Ca, Cd, CI, Co, Cr, Cs, Cu, F, Fe, Hg, I, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, Rb, S, Sb, Se, Sr, Ti, V, W, and Zn. These products make a substantial contribution to the existing world repertoire of biological reference materials with respect to natural matrix and elemental composition. They are expected to be useful to analysts for quality control of analytical data. Applications include evaluations of analytical methods and instruments used in nutritional, toxicological, monitory, regulatory, environmental, agricultural, and other investigations. These products are available to the analytical community from the Standard Reference Materials Program, NIST, Gaithersburg, MD.

Abstract. This paper presents a new sampling head design and the method used to evaluate it. The elemental composition of aerosols collected by two different sampling devices in a semi-arid region of Tunisia is compared by means of compositional perturbation vectors and biplots. This set of underused mathematical tools belongs to a family of statistics created specifically to deal with compositional data. The two sampling devices operate at a flow rate in the range of 1 m3 h−1, with a cut-off diameter of 10 µm. The first device is a low-cost laboratory-made system, where the largest particles are removed by gravitational settling in a vertical tube. This new system will be compared to the second device, a brand-new standard commercial PM10 sampling head, where size segregation is achieved by particle impaction on a metal surface. A total of 44 elements (including rare earth elements, REEs, together with Al, As, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Rb, S, Sc, Se, Sr, Ti, Tl, U, V, Zn, and Zr) were analysed in 16 paired samples, collected during a 2-week field campaign in Tunisian dry lands, close to source areas, with high levels of large particles. The contrasting meteorological conditions encountered during the field campaign allowed a broad range of aerosol compositions to be collected, with very different aerosol mass concentrations. The compositional data analysis (CoDA) tools show that no compositional differences were observed between samples collected simultaneously by the two devices. The mass concentration of the particles collected was estimated through chemical analysis. Results for the two sampling devices were very similar to those obtained from an online aerosol weighing system, TEOM (tapered element oscillating microbalance), installed next to them. These results suggest that the commercial PM10 impactor head can therefore be replaced by the decanter, without any measurable bias, for the determination of chemical composition and for further assessment of PM10 concentrations in source regions.

Abstract RA825 is a Ni-Fe-Cr-Mo-Cu-Ti alloy with good aqueous corrosion resistance to reducing acids. Applications include the handling of phosphoric and sulfuric acid. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on corrosion resistance as well as heat treating and joining. Filing Code: Ni-563. Producer or source: Rolled Alloys.

I processi di produzione e consumo negli ecosistemi del suolo contribuiscono ai cicli biochimici globali di molti gas in tracce (CH4, CO, H2, N2O e NO) che sono rilevanti per la chimica atmosferica e il clima. Tali piccole molecole di gas svolgono ruoli diversi nel metabolismo dei microrganismi posti nel suolo che si basano su metalloenzimi specifici per la loro trasformazione. Tra questi, è stato dimostrato che i metalloenzimi a base di molibdeno sono cruciali in tale contesto. In particolare, è stato riportato che un molibdoenzima specifico è coinvolto nell'ossidazione della CO atmosferica. MoCu CO deidrogenasi (MoCu CODH) è un enzima presente nei carbossidobatteri aerobici, come Oligotropha carbossidovorans, che rappresentano uno dei componenti essenziali nel consumo biogeochimico di monossido di carbonio (CO). Essi infatti contribuiscono al mantenimento della concentrazione subtossica di CO nella bassa atmosfera elaborandone circa 2 × 108 tonnellate all'anno. Questa metalloproteina batterica catalizza l'ossidazione della CO a CO2, mentre può anche scindere H2 in due protoni e due elettroni. Tali reazioni vengono eseguite grazie a un sito attivo unico composto da due metalli, uno ione rame e uno molibdeno, legati tra loro tramite un atomo di zolfo. Nonostante siano stati condotti ampi studi teorici e sperimentali su questo enzima, diversi aspetti relativi alla sua reattività non sono stati ancora chiariti. Nella presente tesi ci siamo concentrati sulla descrizione in silico di MoCu CODH al fine di approfondire la comprensione dei meccanismi di reazione catalizzati dall'enzima. Per fare ciò, nel quadro della teoria del funzionale della densità (DFT), abbiamo applicato modelli di diverse dimensioni per ottenere una descrizione accurata del sistema. Nel contesto della catalisi dell'ossidazione della CO, abbiamo evidenziato che se un intermedio simile al tiocarbonato si forma lungo il percorso catalitico, non rappresenta una specie limitante la velocità nel panorama energetico enzimatico, a differenza di quanto proposto in base ai risultati di precedenti studi teorici. Inoltre, siamo stati in grado di suggerire un meccanismo catalitico alternativo per l'ossidazione della CO che coinvolge il ruolo diretto di una molecola d'acqua, attivata dal sito attivo circostante. Per quanto riguarda l'attività idrogenasica di MoCu CODH, sono stati presentati due meccanismi plausibili per la scissione di H2. Per la prima volta abbiamo suggerito che il sito attivo MoCu CODH possa essere visto come Frustrated Lewis Pairs (FLP) e abbiamo proposto un meccanismo tipo FLP per l'ossidazione del diidrogeno. In alternativa, un evento di protonazione, quale la protonazione del residuo di cisteina coordinata allo ione rame prima del legame di H2 al sito attivo, si è rivelato necessario per presentare un canale reattivo plausibile.
Production and consumption processes in soil ecosystems contribute to the global bio­chemical cycles of many trace gases (CH4, CO, H2, N2O and NO) that are relevant for atmospheric chemistry and climate. Such small gas molecules play different role into the metabolism of microorganisms placed in soil that rely on specific metalloen­zymes for their transformation. Among these, molybdenum-­based metalloenzymes were evidenced to be crucial in such context. In particular, a specific molybdoen­zyme was reported to be involved in atmospheric CO oxidation. MoCu CO dehy­drogenases (MoCu CODH) is an enzyme found in aerobic carboxido­bacteria, such as Oligotropha carboxidovorans which represent one of the essential components in the biogeochemical carbon monoxide (CO) consumption. In fact, they contribute to maintenance of sub­toxic concentration of CO in the lower atmosphere by processing approximately 2×108 tons of it annually. This bacterial metalloprotein catalyses the oxidation of CO to CO2, while it can also split H2 in two protons and two electrons. Such reactions are performed thanks to a unique active site composed of two metals, a copper ion and a molybdenum one, linked together through a sulphur atom. Despite extended theoretical and experimental studies had been carried out concerning this enzyme, several aspects related to its reactivity have not been unravelled.In the present thesis, we focused on the in silico description of MoCu CODH in order to deepen the understanding of the reaction mechanisms catalysed by the enzyme. To do so, in the framework of density functional theory (DFT), we applied models of different sizes to obtain an accurate description of the system. In the context of CO oxidation catalysis, we evidenced that if a previously proposed thiocarbonate ­like intermediate is formed along the catalytic path, it does not repre­sent a rate ­limiting species on the enzymatic energy landscape, differently from results of previous theoretical studies. Moreover, we were able to suggest an alternative cat­alytic mechanism for the oxidation of CO that involves the direct role of a water molecule, activated by the sourrounding active site. As for the MoCu CODH hydrogenase activity, two plausible mechanisms for the splitting of H2 were presented. For the first time we suggested that the MoCu CODH active site may be viewed as a Frustrated Lewis Pair (FLP), and we proposed a FLP­-like mechanism for oxidation of the dihydrogen. Alternatively, a protonation event–e.g. Cu­-bound cysteine residue protonation – prior to binding of H2 to the active site proved to be necessary to present a plausible reactive channel.