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1.
Br J Anaesth ; 125(5): 773-778, 2020 11.
Artigo em Inglês | MEDLINE | ID: mdl-32859360

RESUMO

BACKGROUND: Increasing fresh gas flow (FGF) to a circle breathing system reduces carbon dioxide (CO2) absorbent consumption. We assessed the environmental and economic impacts of this trade-off between gas flow and absorbent consumption when no inhalational anaesthetic agent is used. METHODS: A test lung with fixed CO2 inflow was ventilated via a circle breathing system of an anaesthetic machine (Dräger Primus or GE Aisys CS2) using an FGF of 1, 2, 4, or 6 L min-1. We recorded the time to exhaustion of the CO2 absorbent canister, defined as when inspired partial pressure of CO2 exceeded 0.3 kPa. For each FGF, we calculated the economic costs and the environmental impact associated with the manufacture of the CO2 absorbent canister and the supply of medical air and oxygen. Environmental impact was measured in 100 yr global-warming potential, analysed using a life cycle assessment 'cradle to grave' approach. RESULTS: Increasing FGF from 1 to 6 L min-1 was associated with up to 93% reduction in the combined running cost with minimal net change to the 100 yr global-warming potential. Most of the reduction in cost occurred between 4 and 6 L min-1. Removing the CO2 absorbent from the circle system, and further increasing FGF to control CO2 rebreathing, afforded minimal further economic benefit, but more than doubled the global-warming potential. CONCLUSIONS: In the absence of inhalational anaesthetic agents, increasing FGF to 6 L min-1 reduces running cost compared with lower FGFs, with minimal impact to the environment.


Assuntos
Anestésicos Inalatórios/química , Dióxido de Carbono/química , Poluição Ambiental/análise , Gases/química , Anestesia com Circuito Fechado , Anestesia por Inalação , Anestésicos Inalatórios/economia , Poluição Ambiental/economia , Poluição Ambiental/prevenção & controle , Gases/economia , Aquecimento Global , Humanos , Pulmão/fisiologia , Modelos Anatômicos , Respiração Artificial , Hidróxido de Sódio
2.
J Chromatogr A ; 1626: 461389, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797860

RESUMO

The reliable measurement of very volatile organic compounds (VVOC) in indoor air by use of thermal desorption gas chromatography (TD-GC) in order to include them into evaluation schemes for building products even nowadays is a great challenge. For capturing these small molecules with carbon numbers ranging from C1C6, strong adsorbents are needed. In the present study, recovery rates of nine suitable adsorbents of the groups of porous polymers, graphitised carbon blacks (GCB) and carbon molecular sieves (CMS) are tested against a complex test gas standard containing 29 VVOC. By consideration of the recovery and the relative humidity (50% RH), combinations of the GCB Carbograph 5TD, the two CMS Carboxen 1003 and Carbosieve SII as well as the porous polymer Tenax® GR were identified to be potentially suitable for sampling the majority of the VVOC out of the gas mix. The results reveal a better performance of the adsorbents in combination than being used alone, particularly under humid sampling conditions. The recovery rates of the chosen compounds on each adsorbent should be in the range of 80-120%.


Assuntos
Poluição do Ar em Ambientes Fechados/análise , Cromatografia Gasosa-Espectrometria de Massas/métodos , Compostos Orgânicos Voláteis/análise , Adsorção , Carbono/química , Gases/química , Umidade , Polímeros/química , Temperatura
3.
PLoS One ; 15(8): e0236802, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32785277

RESUMO

The static mechanical properties of coal rock show anisotropism, which makes the permeability have anisotropic characteristics partly. The dynamic impact mechanical characteristics of structural anisotropic coal under low and medium strain rates were studied by using self-made vertical Split Hopkinson Bar (SHPB) equipment. The peak stress, the strain rate, dynamic elastic modulus and failure characteristics of raw coal with three coring directions were analyzed under the influence of five impact loads and structural anisotropy. The peak stress increases linearly with impact load, and the maximum strain rate and the dynamic elastic modulus increase exponentially with impact load. The coal samples display anisotropic mechanical characteristics. The values of maximum strain rate, peak stress and dynamic elastic modulus are ranked with directions by the perpendicular to bedding direction (Z direction), the parallel to bedding direction (X direction), and the oblique 45° to bedding direction (Y direction). Dynamic mechanical properties of structural anisotropic coal provide a theoretical basis for gas seepage in far-blasting field.


Assuntos
Carvão Mineral/análise , Módulo de Elasticidade , Gases/química , Estresse Mecânico
4.
Anal Chem ; 92(16): 10930-10934, 2020 08 18.
Artigo em Inglês | MEDLINE | ID: mdl-32678978

RESUMO

The emergence and rapid proliferation of the novel coronavirus (SARS-CoV-2) resulted in a global pandemic, with over 6,000,000 cases and nearly 400,000 deaths reported worldwide by the end of May 2020. A rush to find a cure prompted re-evaluation of a range of existing therapeutics vis-à-vis their potential role in treating COVID-19, placing a premium on analytical tools capable of supporting such efforts. Native mass spectrometry (MS) has long been a tool of choice in supporting the mechanistic studies of drug/therapeutic target interactions, but its applications remain limited in the cases that involve systems with a high level of structural heterogeneity. Both SARS-CoV-2 spike protein (S-protein), a critical element of the viral entry to the host cell, and ACE2, its docking site on the host cell surface, are extensively glycosylated, making them challenging targets for native MS. However, supplementing native MS with a gas-phase ion manipulation technique (limited charge reduction) allows meaningful information to be obtained on the noncovalent complexes formed by ACE2 and the receptor-binding domain (RBD) of the S-protein. Using this technique in combination with molecular modeling also allows the role of heparin in destabilizing the ACE2/RBD association to be studied, providing critical information for understanding the molecular mechanism of its interference with the virus docking to the host cell receptor. Both short (pentasaccharide) and relatively long (eicosasaccharide) heparin oligomers form 1:1 complexes with RBD, indicating the presence of a single binding site. This association alters the protein conformation (to maximize the contiguous patch of the positive charge on the RBD surface), resulting in a notable decrease in its ability to associate with ACE2. The destabilizing effect of heparin is more pronounced in the case of the longer chains due to the electrostatic repulsion between the low-pI ACE2 and the heparin segments not accommodated on the RBD surface. In addition to providing important mechanistic information on attenuation of the ACE2/RBD association by heparin, the study demonstrates the yet untapped potential of native MS coupled to gas-phase ion chemistry as a means of facilitating rational repurposing of the existing medicines for treating COVID-19.


Assuntos
Infecções por Coronavirus/patologia , Heparina/metabolismo , Espectrometria de Massas/métodos , Peptidil Dipeptidase A/metabolismo , Pneumonia Viral/patologia , Betacoronavirus/isolamento & purificação , Betacoronavirus/metabolismo , Sítios de Ligação , Infecções por Coronavirus/tratamento farmacológico , Infecções por Coronavirus/virologia , Gases/química , Heparina/farmacologia , Heparina/uso terapêutico , Humanos , Simulação de Dinâmica Molecular , Pandemias , Peptidil Dipeptidase A/química , Peptidil Dipeptidase A/genética , Pneumonia Viral/tratamento farmacológico , Pneumonia Viral/virologia , Ligação Proteica , Domínios Proteicos , Proteínas Recombinantes/biossíntese , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação , Glicoproteína da Espícula de Coronavírus/química , Glicoproteína da Espícula de Coronavírus/metabolismo , Internalização do Vírus/efeitos dos fármacos
5.
J Vis Exp ; (160)2020 06 25.
Artigo em Inglês | MEDLINE | ID: mdl-32658181

RESUMO

This protocol demonstrates a method for graphene-assisted quick growth and coalescence of AlN on nano-pattened sapphire substrate (NPSS). Graphene layers are directly grown on NPSS using catalyst-free atmospheric-pressure chemical vapor deposition (APCVD). By applying nitrogen reactive ion etching (RIE) plasma treatment, defects are introduced into the graphene film to enhance chemical reactivity. During metal-organic chemical vapor deposition (MOCVD) growth of AlN, this N-plasma treated graphene buffer enables AlN quick growth, and coalescence on NPSS is confirmed by cross-sectional scanning electron microscopy (SEM). The high quality of AlN on graphene-NPSS is then evaluated by X-ray rocking curves (XRCs) with narrow (0002) and (10-12) full width at half-maximum (FWHM) as 267.2 arcsec and 503.4 arcsec, respectively. Compared to bare NPSS, AlN growth on graphene-NPSS shows significant reduction of residual stress from 0.87 GPa to 0.25 Gpa, based on Raman measurements. Followed by AlGaN multiple quantum wells (MQWS) growth on graphene-NPSS, AlGaN-based deep ultraviolet light-emitting-diodes (DUV LEDs) are fabricated. The fabricated DUV-LEDs also demonstrate obvious, enhanced luminescence performance. This work provides a new solution for the growth of high quality AlN and fabrication of high performance DUV-LEDs using a shorter process and less costs.


Assuntos
Óxido de Alumínio/química , Grafite/química , Nanoestruturas/química , Semicondutores , Raios Ultravioleta , Compostos de Alumínio/química , Catálise , Gálio/química , Gases/química , Luminescência , Volatilização
6.
Phys Chem Chem Phys ; 22(19): 11095-11100, 2020 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-32373846

RESUMO

Förster Resonance Energy Transfer (FRET) between a photoexcited and a ground-state dye is dictated by how far apart the two dyes are compared to the Förster distance. While there is a significant number of studies on the process for biomacromolecules in solution, there are only a few reports on gas-phase FRET. Here we report on a simple gas-phase model system, synthesized with the rhodamine 575 (R575+) and rhodamine 640 (R640+) FRET pair and a covalent linker with four methylenes, R575+-(CH2)4-R640+. Each dye carries a positive charge which allows for mass-spectroscopy experiments. We have recorded gas-phase dispersed fluorescence spectra of the mass-selected dications excited at different wavelengths using the homebuilt LUNA (LUminescence iNstrument in Aarhus) setup and find in all cases that emission is exclusively from the R640+ acceptor dye. The linker does not interfere electronically with the dyes and simply acts as a spacer. We can therefore establish the direct effect of the interaction between the two dyes when it comes to emission band maximum. Indeed, we find that R640+ experiences a significant shift in its maximum from 560 ± 1 nm for the monomer cation to 577 ± 2 nm in the presence of R575+, independent of initial excitation of R575+ or R640+. This redshift is ascribed to the large polarizability along the long axis of the xanthene core structure, and that this polarizability is larger in the excited state than in the ground state. Experiments were also done on a triply charged 11-mer peptide labelled with the same two dyes, R575+-(Gly-Gln)5-Lys-R640+ + H+ (Gly = glycine, Gln = glutamine, and Lys = lysine) where the extra positive charge is located on the peptide. Again a redshifted emission spectrum of the donor is observed with maximum at 582 ± 2 nm. Our work clearly demonstrates strong sensitivity of the photophysics of one dye to the nearby environment, and that caution is needed when using the energy transfer efficiency to infer dye-dye separations in gas-phase experiments.


Assuntos
Corantes Fluorescentes/química , Gases/química , Rodaminas/química , Transferência Ressonante de Energia de Fluorescência/métodos , Corantes Fluorescentes/efeitos da radiação , Gases/efeitos da radiação , Luz , Estrutura Molecular , Oligopeptídeos/química , Rodaminas/efeitos da radiação , Eletricidade Estática
7.
Chemosphere ; 253: 126734, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32302909

RESUMO

A bioscrubbing process named SONOVA has been developed, tested and assessed herein to valorize flue gases containing SOx. The process consists in a first scrubbing stage, to absorb and oxidize SO2 to sulfate, followed by a two-step biological stage. It consists of (1) an up-flow anaerobic sludge (UASB) reactor to reduce sulfate to sulfide with crude glycerol and (2) a continuous stirred tank reactor (CSTR) to partially oxidize sulfide to elemental sulfur (S0). SONOVA integrates the reutilization of resources, using the effluent of the biological stage as a sorbent agent and the residual heat of flue gases to dry the product. S0 is then obtained as a value-added product, which nowadays is produced from fossil fuels. In this research, SO2 concentrations up to 4000 ppmv were absorbed in 2 s of gas contact time in the spray-scrubber with removal efficiencies above 80%. The UASB reduced up to 9.3 kg S-Sulfate m-3 d-1 with sulfide productivities of 6 kg S m-3 d-1 at an hydraulic retention time (HRT) as low as 2 h. Finally, CSTR was fed with the UASB effluent and operated at HRT ranging from 12 h to 4 h without biomass wash-out. Sulfide was fully oxidized to S0 with a productivity of 2.3 kg S m-3 d-1 at the lowest HRT tested. Overall, this research has explored not only maximum capabilities of each SONOVA stage but has also assessed the interactions between the different units, which opens up the possibility of recovering S0 from harmful SOx emissions, optimizing resources utilization and costs.


Assuntos
Reatores Biológicos/microbiologia , Esgotos/química , Óxidos de Enxofre/isolamento & purificação , Enxofre/isolamento & purificação , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias/química , Adsorção , Anaerobiose , Biomassa , Estudos de Viabilidade , Gases/química , Esgotos/microbiologia , Águas Residuárias/microbiologia
8.
PLoS One ; 15(4): e0227582, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32302306

RESUMO

Molecular hydrogen is thought to have an inhibitory effect on oxidative stress, thereby attenuating the onset and progression of various diseases including cardiovascular disease; however, few reports have assessed the preventive effect of constitutive inhalation of hydrogen gas on of vascular remodeling. Here, we investigated the effect of constitutive inhalation of hydrogen gas on vascular neointima formation using a cuff-induced vascular injury mouse model. After constitutive inhalation of compressed hydrogen gas (O2 21%, N2 77.7%, hydrogen 1.3%) or compressed air only (O2 21%, N2 79%) by C57BL/6 mice for 2 weeks from 8 weeks of age in a closed chamber, inflammatory cuff injury was induced by polyethylene cuff placement around the femoral artery under anesthesia, and hydrogen gas administration was continued until sampling of the femoral artery. Neointima formation, accompanied by an increase in cell proliferation, was significantly attenuated in the hydrogen group compared with the control group. NADPH oxidase NOX1 downregulation in response to cuff injury was shown in the hydrogen group, but the expression levels of NADPH oxidase subunits, p40phox and p47phox, did not differ significantly between the hydrogen and control groups. Although the increase in superoxide anion production did not significantly differ between the hydrogen and control groups, DNA damage was decreased as a result of reduction of reactive oxygen species such as hydroxyl radical (⋅OH) and peroxynitrite (ONOO-) in the hydrogen group. These results demonstrate that constitutive inhalation of hydrogen gas attenuates vascular remodeling partly via reduction of oxidative stress, suggesting that constitutive inhalation of hydrogen gas at a safe concentration in the living environment could be an effective strategy for prevention of vascular diseases such as atherosclerosis.


Assuntos
Hidrogênio/administração & dosagem , Isquemia Miocárdica/prevenção & controle , Neointima/prevenção & controle , Remodelação Vascular/efeitos dos fármacos , Lesões do Sistema Vascular/complicações , Administração por Inalação , Animais , Dano ao DNA/efeitos dos fármacos , Modelos Animais de Doenças , Regulação para Baixo/efeitos dos fármacos , Gases/administração & dosagem , Gases/química , Humanos , Radical Hidroxila/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Isquemia Miocárdica/patologia , NADPH Oxidase 1/metabolismo , Neointima/etiologia , Neointima/patologia , Nitrogênio/administração & dosagem , Estresse Oxidativo/efeitos dos fármacos , Oxigênio/administração & dosagem , Ácido Peroxinitroso/metabolismo
9.
J Phys Chem A ; 124(20): 4150-4159, 2020 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-32348131

RESUMO

The emergence of life on the prebiotic Earth must have involved the formation of polypeptides, yet the polymerization of amino acids is thermodynamically unfavorable under biologically relevant aqueous conditions because amino acids are zwitterions in solution and because of the production of a water molecule through a condensation reaction. Many mechanisms for overcoming this thermodynamic unfavorability have been proposed, but the role of gas phase water clusters has not been investigated. We present the thermodynamics of the water-mediated gas phase dimerization reaction of glycine as a model for the atmospheric polymerization of amino acids prior to the emergence of biological machinery. We hypothesize that atmospheric aerosols may have played a major role in the prebiotic formation of peptide bonds by providing the thermodynamic driving force to facilitate increasingly stable linear oligopeptides. In addition, we hypothesize that small aerosols orient amino acids on their surfaces, thus providing the correct molecular orientations to funnel the reaction pathways of peptides through transition states that lead eventually to polypeptide products. Using density functional theory and a thorough configurational sampling technique, we show that the thermodynamic spontaneity of the linear dimerization of glycine in the gas phase can be driven by the addition of individual water molecules.


Assuntos
Evolução Química , Gases/química , Origem da Vida , Peptídeos/química , Água/química , Sítios de Ligação , Dimerização , Glicina/química , Cinética , Modelos Moleculares , Prebióticos , Termodinâmica
10.
J Food Sci ; 85(5): 1536-1541, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32249415

RESUMO

The aim of this study was to investigate the influence of surface hydrophobicity and roughness of carrier materials on the inactivation of bacterial spores with gaseous hydrogen peroxide whereas condensate formation is prevented. Spores of Bacillus subtilis and Bacillus atrophaeus were applied either as single spore culture or as a mixed spore population to simulate natural contamination with microorganisms of different characteristics. Inactivation with gaseous hydrogen peroxide was carried out at 5200 ppm hydrogen peroxide without condensate formation. The inactivation results of B. subtilis and B. atrophaeus spores on carrier materials with varying surface hydrophobicity differed significantly. However, inactivation of the mixed spore populations resulted in similar resistance compared to the single spore batches. The results of this study indicate that surface hydrophobicity most probably has an impact on the inactivation with gaseous hydrogen peroxide whereas surface roughness only plays a minor role.


Assuntos
Bacillus subtilis/efeitos dos fármacos , Peróxido de Hidrogênio/química , Peróxido de Hidrogênio/farmacologia , Esporos Bacterianos/química , Bacillus/efeitos dos fármacos , Bacillus/crescimento & desenvolvimento , Bacillus subtilis/crescimento & desenvolvimento , Bacillus subtilis/fisiologia , Gases/química , Gases/farmacologia , Interações Hidrofóbicas e Hidrofílicas , Solo/química , Microbiologia do Solo , Esporos Bacterianos/efeitos dos fármacos , Esporos Bacterianos/crescimento & desenvolvimento , Propriedades de Superfície , Volatilização
11.
Food Chem ; 318: 126473, 2020 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-32143131

RESUMO

In this work is presented the development of a method for As and Se determination in crude palm oil samples by hydride generation atomic fluorescence spectrometry and Hg by cold vapor atomic fluorescence spectrometry after ultrasound-assisted emulsification and extraction induced by emulsion breaking (EIEB). The optimization of the method was carried out by multivariate designs. The developed method has presented limits of quantification (LOQ) of 0.72, 0.12, and 1.5 µg L-1 for As, Hg, and Se, respectively. The precisions of the proposed method expressed as repeatability were 0.92, 2.2, and 3.7% RSD for 2 µg L-1 (n = 10) of As, Hg and Se, respectively. The developed methodology was applied in palm oil samples collected in the Bahia State. Concentrations (µg L-1) found in the samples were between

Assuntos
Arsênico/análise , Emulsões/química , Análise de Alimentos/métodos , Mercúrio/análise , Óleo de Palmeira/análise , Selênio/análise , Fracionamento Químico/métodos , Análise de Alimentos/estatística & dados numéricos , Contaminação de Alimentos , Gases/química , Limite de Detecção , Análise Multivariada , Óleo de Palmeira/química , Espectrometria de Fluorescência/métodos , Espectrofotometria Atômica/métodos
12.
J Vis Exp ; (157)2020 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-32176215

RESUMO

Desalination through direct contact membrane distillation (DCMD) exploits water-repellent membranes to robustly separate counterflowing streams of hot and salty seawater from cold and pure water, thus allowing only pure water vapor to pass through. To achieve this feat, commercial DCMD membranes are derived from or coated with water-repellent perfluorocarbons such as polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF). However, the use of perfluorocarbons is limiting due to their high cost, non-biodegradability, and vulnerability to harsh operational conditions. Unveiled here is a new class of membranes referred to as gas-entrapping membranes (GEMs) that can robustly entrap air upon immersion in water. GEMs achieve this function by their microstructure rather than their chemical make-up. This work demonstrates a proof-of-concept for GEMs using intrinsically wetting SiO2/Si/SiO2 wafers as the model system; the contact angle of water on SiO2 is θo ≈ 40°. Silica-GEMs had 300 µm-long cylindrical pores whose diameters at the (2 µm-long) inlet and outlet regions were significantly smaller; this geometrically discontinuous structure, with 90° turns at the inlets and outlets, is known as the "reentrant microtexture". The microfabrication protocol for silica-GEMs entails designing, photolithography, chrome sputtering, and isotropic and anisotropic etching. Despite the water loving nature of silica, water does not intrude silica-GEMs on submersion. In fact, they robustly entrap air underwater and keep it intact even after six weeks (>106 seconds). On the other hand, silica membranes with simple cylindrical pores spontaneously imbibe water (< 1 s). These findings highlight the potential of the GEMs architecture for separation processes. While the choice of SiO2/Si/SiO2 wafers for GEMs is limited to demonstrating the proof-of-concept, it is expected that the protocols and concepts presented here will advance the rational design of scalable GEMs using inexpensive common materials for desalination and beyond.


Assuntos
Gases/química , Membranas Artificiais , Dióxido de Silício/química , Silício/química , Purificação da Água , Água/química , Ar , Destilação , Porosidade , Impressão , Água do Mar , Silanos/química
13.
Soft Matter ; 16(12): 3082-3087, 2020 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-32140697

RESUMO

Controlling the surface area, pore size and pore volume of microcapsules is crucial for modulating their activity in applications including catalytic reactions, delivery strategies or even cell culture assays, yet remains challenging to achieve using conventional bulk techniques. Here we describe a microfluidics-based approach for the formation of monodisperse silica-coated micron-scale porous capsules of controllable sizes. Our method involves the generation of gas-in water-in oil emulsions, and the subsequent rapid precipitation of silica which forms around the encapsulated gas bubbles resulting in hollow silica capsules with tunable pore sizes. We demonstrate that by varying the gas phase pressure, we can control both the diameter of the bubbles formed and the number of internal bubbles enclosed within the silica microcapsule. Moreover, we further demonstrate, using optical and electron microscopy, that these silica capsules remain stable under particle drying. Such a systematic manner of producing silica-coated microbubbles and porous microparticles thus represents an attractive class of biocompatible material for biomedical and pharmaceutical related applications.


Assuntos
Cápsulas/química , Emulsões/química , Óleos/química , Dióxido de Silício/química , Água/química , Materiais Biocompatíveis/química , Composição de Medicamentos/instrumentação , Desenho de Equipamento , Gases/química , Microbolhas , Porosidade
14.
J Environ Radioact ; 214-215: 106183, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32063288

RESUMO

Extensive vadose zone metals and organic contamination remains at many former industrial and defense manufacturing sites, and effective remedial solutions are needed to slow or prevent its migration to groundwater. In this study, the application of gaseous substrates to stimulate microbial respiratory reduction of comingled radioisotopes and nitrate under unsaturated conditions was examined for possible application at the Hanford Site, a former nuclear production facility in southeastern WA, USA. First, screening studies were performed to qualitatively measure the sediment respiratory response to 14 gaseous or volatile organic substrates at two moisture contents, 4% and 8%. Volatile substrates produced the strongest respiratory response, among them were butyrate, pentane, butyl acetate. Ethane and butane were the most effective gaseous substrates but only at 8% water content. Hanford sediment from two waste sites with distinctive chemistries were wetted to 7% moisture content, packed into columns, and treated with ethane or butane. After 4 weeks, columns were then leached to quantify retardation in the mobility of aqueous contaminant concentrations compared to no gas control columns. Treatment with both gases resulted in >80% removal of Cr from the aqueous phase. However, NO3 concentration and a waste sites exposure history to NO3 had a major effect on U and Tc reduction. Incomplete nitrate reduction outcompeted U and Tc in waste site sediments having limited prior exposure to NO3. Conversely, waste site sediments co-contaminated with NO3 were able to achieve highly reduced conditions resulting in complete denitrification of NO3, and delayed leaching of U and Tc. This implied effective reduction of both contaminants to less mobile species. This study demonstrates that unsaturated vadose sediments at Hanford waste sites have the capacity for a sustained respiratory response to gaseous substrate injection, which could potentially be deployed as part of an overall strategy to reduce the flux of long-lived radionuclides to groundwater at Hanford and other legacy waste sites.


Assuntos
Gases/química , Monitoramento de Radiação , Sedimentos Geológicos , Água Subterrânea , Radioisótopos , Poluentes Radioativos da Água
15.
Phys Chem Chem Phys ; 22(9): 5057-5069, 2020 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-32073000

RESUMO

Graph theory-based reaction pathway searches (ACE-Reaction program) and density functional theory calculations were performed to shed light on the mechanisms for the production of [an + H]+, xn+, yn+, zn+, and [yn + 2H]+ fragments formed in free radical-initiated peptide sequencing (FRIPS) mass spectrometry measurements of a small model system of glycine-glycine-arginine (GGR). In particular, the graph theory-based searches, which are rarely applied to gas-phase reaction studies, allowed us to investigate reaction mechanisms in an exhaustive manner without resorting to chemical intuition. As expected, radical-driven reaction pathways were favorable over charge-driven reaction pathways in terms of kinetics and thermodynamics. Charge- and radical-driven pathways for the formation of [yn + 2H]+ fragments were carefully compared, and it was revealed that the [yn + 2H]+ fragments observed in our FRIPS MS spectra originated from the radical-driven pathway, which is in contrast to the general expectation. The acquired understanding of the FRIPS fragmentation mechanism is expected to aid in the interpretation of FRIPS MS spectra. It should be emphasized that graph theory-based searches are powerful and effective methods for studying reaction mechanisms, including gas-phase reactions in mass spectrometry.


Assuntos
Teoria da Densidade Funcional , Radicais Livres/química , Oligopeptídeos/química , Análise de Sequência de Proteína/métodos , Sequência de Aminoácidos , Óxidos N-Cíclicos/química , Gases/química , Cinética , Espectrometria de Massas , Simulação de Dinâmica Molecular , Termodinâmica
16.
Chemosphere ; 249: 126164, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32065997

RESUMO

This study attempted to investigate the effect of impregnation sequence of the Pd/Ce/γ-Al2O3 sorbents on Hg0 removal. To this end, five kinds of sorbents were prepared and tested in simulated coal derived fuel gas (N2-H2-CO-H2S-Hg), including Pd/γ-Al2O3, Ce/γ-Al2O3 and three kinds of Pd-based sorbents with Ce impregnation on γ-Al2O3 substrate. The tests were conducted at 250 and 300 °C respectively. According to the results, bimetallic Ce-Pd/γ-Al2O3 sorbent prepared by simultaneously impregnating Pd and Ce showed much higher and more stable removal efficiency of Hg0 than the other three kinds of sorbents. The Hg0 removal efficiency of Ce-Pd/γ-Al2O3 sorbent reached above 98% within 480 min at 250 °C and 91% within 200 min at 300 °C. Characterization results indicated that the sorbent Ce-Pd/γ-Al2O3 prepared by the co-impregnation method had bigger specific surface area (216.6 m2/g) than the other three kinds of Pd-based sorbents. The content Pd and Ce on the sorbent Ce-Pd/γ-Al2O3 surface is 0.21% and 0.61%, which proved higher than that of the other three kinds of Pd-based sorbents, and observation from STEM-XEDS maps showed it demonstrated the highest dispersion. It is found that Ce is likely to promote the dispersion of Pd on the support surface during the preparation of the sorbent under the co-impregnation method. Meanwhile, Ce enhanced the H2S resistance of the sorbent. Thereby, Ce-Pd/γ-Al2O3 sorbent is found to have the optimal performance of mercury removal. In this study, the Hg0 removal mechanism of the Pd/Ce/γ-Al2O3 sorbents in the simulated coal derived fuel gas was also elaborated.


Assuntos
Poluentes Atmosféricos/química , Carvão Mineral/análise , Combustíveis Fósseis/análise , Mercúrio/química , Adsorção , Gases/química , Mercúrio/análise
17.
PLoS One ; 15(2): e0228955, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32106248

RESUMO

This paper discusses the optimal control of pressure using the zero-gradient control (ZGC) approach. It is applied for the first time in the study to control the optimal pressure of hydrogen natural gas mixture in an inclined pipeline. The solution to the flow problem is first validated with existing results using the Taylor series approximation, regression analysis and the Runge-Kutta method combined. The optimal pressure is then determined using ZGC where the optimal set points are calculated without having to solve the non-linear system of equations associated with the standard optimization problem. It is shown that the mass ratio is the more effective parameter compared to the initial pressure in controlling the maximum variation of pressure in a gas pipeline.


Assuntos
Gases/química , Gás Natural/análise , Algoritmos , Simulação por Computador , Hidrogênio , Manometria/métodos , Pressão
18.
J Chromatogr A ; 1618: 460938, 2020 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-32081486

RESUMO

This work presents and evaluates an algorithmic approach to deconvolving the elution profiles of chemical components of vapor mixtures that have been sampled and desorbed from a novel preconcentrator based on highly ordered silicon nanowire arrays. The arrays provide a medium for both preconcentration and partial chromatographic resolution, which is then further leveraged with multichannel detection. Here, mixtures of nitro aromatic vapors are sampled and then thermally desorbed from the device, at which point they are detected by a conventional mass selective detector. The overlapping elution profiles observed from the array are sequentially extracted using a chemometric analysis approach based on evolving factor analysis and multivariate curve resolution by alternating least squares, enabling qualitative and quantitative analysis of individual components without target analyte libraries or complete chromatographic separation. This work examines the analytical capabilities conferred to multichannel detection by silicon nanowire array pre-concentration and partial separation and discusses the technique's limitations, illustrated by both experimental and simulated data.


Assuntos
Cromatografia , Nanofios , Silício/química , Algoritmos , Gases/química , Análise dos Mínimos Quadrados , Espectrometria de Massas , Temperatura
19.
J Phys Chem Lett ; 11(5): 1636-1643, 2020 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-32013435

RESUMO

High efficiency of light harvesting in photosynthetic pigment-protein complexes is governed by evolutionary-perfected protein-assisted tuning of individual pigment properties and interpigment interactions. Due to the large number of spectrally overlapping pigments in a typical photosynthetic complex, experimental methods often fail to unambiguously identify individual chromophore properties. Here, we report a first-principles-based modeling protocol capable of predicting properties of pigments in protein environment to a high precision. The technique was applied to successfully uncover electronic properties of the Fenna-Matthews-Olson (FMO) pigment-protein complex. Each of the three subunits of the FMO complex contains eight strongly coupled bacteriochlorophyll a (BChl a) pigments. The excitonic structure of FMO can be described by an electronic Hamiltonian containing excitation (site) energies of BChl a pigments and electronic couplings between them. Several such Hamiltonians have been developed in the past based on the information from various spectroscopic measurements of FMO; however, fine details of the excitonic structure and energy transfer in FMO, especially assignments of short-lived high-energy sites, remain elusive. Utilizing polarizable embedding quantum mechanics/molecular mechanics with the effective fragment potentials, we computed the electronic Hamiltonian of FMO that is in general agreement with previously reported empirical Hamiltonians and quantitatively reproduces experimental absorption and circular dichroism spectra of the FMO protein. The developed computational protocol is sufficiently simple and can be utilized for predictive modeling of other wild-type and mutated photosynthetic pigment-protein complexes.


Assuntos
Proteínas de Bactérias/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Simulação de Dinâmica Molecular , Teoria Quântica , Proteínas de Bactérias/química , Bacterioclorofila A/química , Bacterioclorofila A/metabolismo , Chlorobi/metabolismo , Dicroísmo Circular , Transferência de Energia , Gases/química , Complexos de Proteínas Captadores de Luz/química , Fotossíntese
20.
Chemphyschem ; 21(6): 525-530, 2020 03 17.
Artigo em Inglês | MEDLINE | ID: mdl-32012435

RESUMO

Four conformers of the non-proteinogenic α-amino acid isovaline, vaporized by laser ablation, are characterized by Fourier-transform microwave techniques in a supersonic expansion. The comparison between the experimental rotational and 14 N nuclear quadrupole coupling constants and the ab initio calculated ones provides conclusive evidence for the identification of the conformers. The most stable species is stabilized by an N-H⋅⋅⋅O =C intramolecular hydrogen bond and a cis-COOH interaction, whereas the higher-energy conformers exhibit an N⋅⋅⋅H-O intramolecular hydrogen bond and trans-COOH, as in other aliphatic amino acids. The spectroscopic data herein reported can be used for the astrophysical purpose in a possible detection of isovaline in space.


Assuntos
Gases/química , Valina/química , Ligação de Hidrogênio , Conformação Molecular
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