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1.
Water Sci Technol ; 80(3): 563-574, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31596267

RESUMO

This study was conducted to evaluate the influence of chloride ions (Cl-) on organic contaminants decolorization by the Fe0-activated persulfate process (PS/Fe0), as well as the generation of transformation products. Orange II (OII) was chosen as the target pollution. The results indicated that Cl- influenced the OII decolorization by PS/Fe0 system, resulting in the generation of chlorine-containing by-products. OII containing Cl- solution can be efficiently decolorized by PS/Fe0 process, and the decolorization efficiencies changed depending on Cl- concentration due to the reaction between Cl- and sulfate radicals (SO4-•). The operating cost for 94% color and 64% chemical oxygen demand (COD) removal of the OII dye was estimated at 0.73 USD/m3. The chlorine-containing by-products, such as chlorobenzene, 3,5-dichloro-benzene-1,2-diol, and 2,3-dichloro-2,3-dihydro-1,4-naphthoquinone, were generated during the reaction. The results further indicated that increasing both PS concentration and temperature enhanced OII decolorization and reduced the generation of chlorine-containing intermediates. The addition of ultrasound can further decrease the generation of chlorine-containing intermediates under high-temperature conditions. The proposed pathways of decolorization of OII containing Cl- also indicated that SO4-• dominated the OII degradation, while the presence of Cl- led to the generation of chlorine-containing intermediates.


Assuntos
Cloretos , Modelos Químicos , Sulfatos , Cor , Ferro/química , Oxirredução
2.
J Chem Phys ; 151(12): 124706, 2019 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-31575160

RESUMO

Most theories of the binding of molecules to surfaces or for the association between molecules treat the binding species as structureless entities and neglect their rigidity and the changes in their stiffness induced by the binding process. The binding species are also taken to be "ideal," meaning that the existence of van der Waals interactions and changes in these interactions upon molecular binding are also neglected. An understanding of the thermodynamics of these multifunctional molecular binding processes has recently come into focus in the context of the molecular binding of complex molecules, such as dendrimers and DNA grafted nanoparticles, to surfaces where the degree of binding cooperativity and selectivity, as well as the location of the binding transition, are found to be sensitive to the number of binding units constrained to a larger scale polymeric scaffold. We address the fundamental problem of molecular binding by extending classical Langmuir theory to describe the particular example of the reversible binding of semiflexible polymer chains to a solid substrate under melt conditions. The polymer chains are assumed to have a variable number N of binding units (segments) and to exhibit variable bending energies and van der Waals interactions in the bulk and on the surface, in addition to strong directional interactions with the surface. The resulting generalized Langmuir theory is applied to the examination of the influence of the chain connectivity of ideal polymers on the surface coverage Θ, transition binding temperature T1/2 at which Θ = 1/2, and on the derivative |dΘ/dT|T=T1/2 and the constant volume specific heat of binding, Cv bind, measures of the cooperativity and "sharpness" of the binding transition, respectively. Paper II is devoted to the impact of the van der Waals attractive interactions and chain stiffness on the reversible binding of nonideal polymer chains to a solid surface, including the enthalpy-entropy compensation phenomenon observed experimentally in many molecular and particle binding processes.


Assuntos
Modelos Químicos , Polímeros/química , Adsorção , Congelamento , Termodinâmica
3.
J Chem Phys ; 151(12): 125101, 2019 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-31575173

RESUMO

Gene regulation is one of the most important fundamental biological processes in living cells. It involves multiple protein molecules that locate specific sites on DNA and assemble gene initiation or gene repression multimolecular complexes. While the protein search dynamics for DNA targets has been intensively investigated, the role of intermolecular interactions during the genetic activation or repression remains not well quantified. Here, we present a simple one-dimensional model of target search for two interacting molecules that can reversibly form a dimer molecular complex, which also participates in the search process. In addition, the proteins have finite residence times on specific target sites, and the gene is activated or repressed when both proteins are simultaneously present at the target. The model is analyzed using first-passage analytical calculations and Monte Carlo computer simulations. It is shown that the search dynamics exhibit a complex behavior depending on the strength of intermolecular interactions and on the target residence times. We also found that the search time shows a nonmonotonic behavior as a function of the dissociation rate for the molecular complex. Physical-chemical arguments to explain these observations are presented. Our theoretical approach highlights the importance of molecular interactions in the complex process of gene activation/repression by multiple transcription factor proteins.


Assuntos
DNA/química , Modelos Químicos , Simulação por Computador , DNA/genética , DNA/metabolismo , Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Cinética , Método de Monte Carlo , Proteína Supressora de Tumor p53/química , Proteína Supressora de Tumor p53/genética , Proteína Supressora de Tumor p53/metabolismo
4.
J Chem Phys ; 151(12): 124104, 2019 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-31575184

RESUMO

An interfacial regularized Stokeslet scheme is presented to predict the motion of solid bodies (e.g., proteins or gel-phase domains) embedded within flowing lipid bilayer membranes. The approach provides a numerical route to calculate velocities and angular velocities in complex flow fields that are not amenable to simple Faxén-like approximations. Additionally, when applied to shearing motions, the calculations yield predictions for the effective surface viscosity of dilute rigid-body-laden membranes. In the case of cylindrical proteins, effective viscosity calculations are compared to two prior analytical predictions from the literature. Effective viscosity predictions for a dilute suspension of rod-shaped objects in the membrane are also presented.


Assuntos
Bicamadas Lipídicas/química , Modelos Químicos , Fenômenos Biomecânicos , Proteínas de Membrana/química , Torque , Viscosidade
5.
J Chem Phys ; 151(12): 125102, 2019 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-31575191

RESUMO

We present an analytical model for the role of hydrogen bonding on the spin-orbit coupling of a model DNA molecule. Here, we analyze in detail the electric fields due to the polarization of the hydrogen bond on the DNA base pairs and derive, within a tight binding analytical band folding approach, an intrinsic Rashba coupling which should dictate the order of the spin active effects in the chiral-induced spin selectivity effect. The coupling found is ten times larger than the intrinsic coupling estimated previously and points out to the predominant role of hydrogen bonding in addition to chirality in the case of biological molecules. We expect similar dominant effects in oligopeptides, where the chiral structure is supported by hydrogen-bonding and bears on orbital carrying transport electrons.


Assuntos
DNA/química , Modelos Químicos , Transporte de Elétrons , Ligações de Hidrogênio , Oligopeptídeos/química
6.
J Chem Phys ; 151(12): 124905, 2019 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-31575216

RESUMO

The von Willebrand Factor (vWF) is a large blood glycoprotein that aids in hemostasis. Within each vWF monomer, the A2 domain hosts a cleavage site for enzyme ADAMTS13, which regulates the size of vWF multimers. This cleavage site can only be exposed when an A2 domain unfolds, and the unfolding reaction energy landscape is highly sensitive to the force conditions on the domain. Based on previous optical tweezer experimental results, we advance here a new activated A2 monomer model (AA2MM) for coarse-grained modeling of vWF that accurately represents the force-based probabilistic change between the unfolded/refolded states. A system of springs is employed to mimic the complex mechanical response of vWF monomers subject to pulling forces. AA2MM was validated by comparing monomer scale simulation results to data from prior pulling experiments on vWF monomer fragments. The model was further validated by comparing multimer scale Brownian dynamics simulation results to experiments using microfluidic chamber microscopy to visualize tethered vWF proteins subject to flow. The A2 domain unfolding reaction was studied in bulk flow simulations (pure shear and elongation flow), giving evidence that elongational flow drives the vWF size regulation process in blood. The mechanoreactive, coarse-grained AA2MM accurately describes the complex mechanical coupling between human blood flow conditions and vWF protein reactivity.


Assuntos
Modelos Químicos , Fator de von Willebrand/química , Proteína ADAMTS13/sangue , Proteína ADAMTS13/química , Fenômenos Biomecânicos , Simulação por Computador , Humanos , Domínios Proteicos , Desdobramento de Proteína
7.
J Environ Sci (China) ; 85: 119-128, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31471018

RESUMO

A novel struvite crystallization method induced by bioelectrochemical acidolysis of magnesia (MgO) was investigated to recover phosphorus (P) from aqueous solution using a dual-chamber microbial electrolysis cell (DMEC). Magnesium ion (Mg2+) in the anolyte was firstly confirmed to automatically migrate from the anode chamber to the cathode chamber, and then react with ammonium (NH4+) and phosphate (PO43-) in the catholyte to form struvite. Recovery efficiency of 17.8%-60.2% was obtained with the various N/P ratios in the catholyte. When MgO (low solubility under alkali conditions) was added into the anolyte, the bioelectrochemical acidolysis of MgO naturally took place and the released Mg2+ induced struvite crystallization in the cathode chamber for P recovery likewise. Besides, there was a strong linear positive correlation between the recovery efficiency and the MgO dosage (R2 = 0.935), applied voltage (R2 = 0.969) and N/P ratio (R2 = 0.905). Increasing the applied voltage was found to enhance the P recovery via promoting the MgO acidolysis and the released Mg2+ migration, while increasing the N/P ratio in the catholyte enhanced the P recovery via promoting the struvite crystallization. Moreover, the electrochemical performance of the system was promoted due to more stable anolyte pH and lower pH gradient between the two chambers. Current density was promoted by 10%, while the COD removal efficiency was improved from 78.2% to 91.8% in the anode chamber.


Assuntos
Modelos Químicos , Fósforo/química , Estruvita/química , Óxido de Magnésio , Água
8.
J Environ Sci (China) ; 85: 177-188, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31471025

RESUMO

The effect of preparation parameters on the performance of zeolite for ammonium (20-300 mg N/L) adsorption from simulated wastewater is reported. It was found that the ratios of Na2O/SiO2 and Si/Al had a more important influence than crystallization time on zeolite adsorption properties. Relatively low Na2O/SiO2 ratios were beneficial for fabrication of zeolites with high proportions of micropore area and volume, which led to the surface adsorption mechanism being dominated by surface free energy and pore effects. However, with decreasing Si/Al ratios, the effect of ion-exchange was more prominent due to the high negative surface potential of zeolite. In addition, the concentration of weak acid sites on the zeolites was increased with lower ratios of Na2O/SiO2 and Si/Al, which may promote ammonium removal. Therefore, the most effective zeolite for ammonium removal, which was fabricated at Na2O/SiO2 = 1.375, Si/Al = 4 and crystallization time of 48 hr, exhibited the cooperative effects of adsorption, ion-exchange and a large amount of weak acid sites. The maximum ammonium adsorption capacity (35.06 ±â€¯0.98 mg/g) and the removal efficiency (94.44% ±â€¯4.00%) were obtained at the dosage of 4.0 g/L zeolite NaX at ammonium concentrations of 300 mg N/L and 20 mg N/L, respectively. The Freundlich isotherm and pseudo-first-order kinetics models provided excellent fitting for the ammonium adsorption process. In addition, zeolite NaX showed about 1.23-3.2 times the ammonium adsorption capacity of clinoptilolite. The stable and efficient reusability of zeolite NaX after five regeneration cycles demonstrated that this adsorbent has considerable potential for practical industrial applications.


Assuntos
Compostos de Amônio/química , Modelos Químicos , Zeolitas/química , Adsorção
9.
J Environ Sci (China) ; 85: 56-65, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31471031

RESUMO

In this study, greatly enhanced Mn(II) adsorption was achieved by as-synthesized diethylenetriaminepentaacetate acid intercalated Mg/Al layered double hydroxides (LDHs-DTPA). The adsorption capacity of LDHs-DTPA was 83.5 mg/g, which is much higher than that of LDHs-EDTA (44.4 mg/g), LDHs-Oxalate (21.6 mg/g) and LDHs (28.8 mg/g). The adsorption data of aqueous Mn(II) using LDHs-DTPA could be well described by the pseudo-second order kinetics and Langmuir isotherm model. Thermodynamics study results also showed that the adsorption process of Mn(II) by LDHs-DTPA was exothermic as indicated by the negative ΔH value. Furthermore, based on the structural, morphological and thermostable features, as well as FT-IR and XPS characterizations of LDHs-DTPA and the pristine LDHs, the adsorption mechanism of Mn(II) was proposed. The carboxyl groups of DTPA were proposed to be the main binding sites for Mn(II), and the hydroxyl groups of LDHs also played a minor role in the adsorption process. Among the three common regeneration reagents, 0.1 mol/L Na2CO3 was the best for reusing LDHs-DTPA in Mn(II) adsorption. Besides, the Mn(II) adsorption performance could be hindered in the presence of typical inorganic ions, especially cations. Further specific modifications of LDHs-DTPA are suggested to get more selective adsorption of Mn(II) in practical applications.


Assuntos
Manganês/química , Ácido Pentético/química , Poluentes Químicos da Água/química , Hidróxidos , Modelos Químicos
10.
J Environ Sci (China) ; 85: 74-81, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31471033

RESUMO

A column leaching experiment was used to investigate the efficacy of amendments on their ability to remove alkaline anions and metal ions from bauxite residue leachates. Treatments included, simulated acid rain (AR), phosphogypsum + vermicompost (PVC), phosphogypsum + vermicompost + simulated acid rain (PVA), and biosolids + microorganisms (BSM) together with controls (CK). Results indicated that amendment could effectively reduce the leachate pH and EC values, neutralize OH-, CO32-, HCO3-, and water soluble alkali, and suppress arsenic (As) content. Correlation analysis revealed significant linear correlations with pH and concentrations of OH-, CO32-, HCO3-, water-soluble alkali, and metal ions. BSM treatment showed optimum results with neutralizing anions (OH-, CO32-, and HCO3-), water soluble alkali, and removal of metal ions (Al, As, B, Mo, V, and Na), which was attributed to neutralization from the generation of small molecular organic acids and organic matter during microbial metabolism. BSM treatment reduced alkaline anions and metal ions based on neutralization reactions in bauxite residue leachate, which reduced the potential pollution effects from leachates on the soil surrounding bauxite residue disposal areas.


Assuntos
Óxido de Alumínio/química , Metais/química , Modelos Químicos , Poluentes do Solo/química , Ânions
11.
Phys Chem Chem Phys ; 21(36): 19944-19950, 2019 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-31475699

RESUMO

In this manuscript the ability of closo-carboranes to establish CHπ and BHπ interactions with several aromatic moieties exhibiting different electronic natures has been evaluated at the PBE0-D3/def2-TZVP level of theory. We have used the three closo isomers (ortho-, meta-, and para-) and benzene, trifluorobenzene and hexafluorobenzene as aromatic systems. Furthermore, we have used Bader's theory of "atoms in molecules" to further describe and characterize the noncovalent interactions described herein from a charge-density perspective. Finally, several biological examples retrieved from the PDB are also included, highlighting the impact of these interactions in the binding affinity of boron tracedrugs.


Assuntos
Compostos de Boro/química , Modelos Químicos , Cristalização , Tetra-Hidrofolato Desidrogenase/química , Tetra-Hidrofolato Desidrogenase/metabolismo , Vitamina D/química , Vitamina D/metabolismo , Raios X
12.
Phys Chem Chem Phys ; 21(36): 20083-20094, 2019 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-31482893

RESUMO

The formation of amyloid aggregates is the hallmark of many protein misfolding diseases, including Type-II diabetes mellitus, which is caused by the fibrillation of amylin protein. It is established that nano-sized ligands such as curcumin, resveratrol and graphene quantum dots can modify protein aggregation rates. In this article, we report a comparative study of these ligands to estimate their protein aggregation rates and fluorescence quenching using various experimental techniques. Through light scattering experiments, the RH of bare amylin was found to increase at a rate of 43% per day, whereas in the presence of the ligands in different molar ratios (A1C10, A1R10 and A1GQDs20), the sizes of the complexes were found to grow at rates of 7%, 8% and 13% per day, respectively. We observed fluorescence quenching using photoluminescence experiments for all three protein-ligand complexes. The protein aggregation rate and fluorescence quenching exhibited a concentration-dependent competitive role in the inhibition process. Interestingly, for graphene quantum dots, the protein aggregation rate is more affected at lower concentrations, while fluorescence quenching dominates at higher concentrations; this is in contrast to curcumin and resveratrol, where fluorescence quenching dominates at all concentrations of the ligands in the complex. The FTIR data showed appreciable conversion of ß-sheets into less aggregation-prone secondary structures for all three amylin-ligand ratios; however, the inhibition performance of curcumin overshadowed those of the other two inhibitors. The inhibition behavior of these three ligands was corroborated by analysis of analytical and high-resolution TEM images of the fibrils.


Assuntos
Modelos Químicos , Agregação Patológica de Proteínas , Fluorescência , Polipeptídeo Amiloide das Ilhotas Pancreáticas/antagonistas & inibidores , Polipeptídeo Amiloide das Ilhotas Pancreáticas/metabolismo , Polipeptídeo Amiloide das Ilhotas Pancreáticas/ultraestrutura , Microscopia Eletrônica de Transmissão
13.
Phys Chem Chem Phys ; 21(37): 20840-20848, 2019 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-31517382

RESUMO

The room temperature pump-probe X-ray free electron laser (XFEL) measurements used for serial femtosecond crystallography provide remarkable information about the structures of the catalytic (S-state) intermediates of the oxygen-evolution reaction of photosystem II. However, mixed populations of these intermediates and moderate resolution limit the interpretation of the data from current experiments. The S3 XFEL structures show extra density near the OEC that may correspond to a water/hydroxide molecule. However, in the latest structure, this additional oxygen is 2.08 Šfrom the Oε2 of D1-E189, which is closer than the sum of the van der Waals radii of the two oxygens. Here, we use Boltzmann statistics and Monte Carlo sampling to provide a model for the S2-to-S3 state transition, allowing structural changes and the insertion of an additional water/hydroxide. Based on our model, water/hydroxide addition to the oxygen-evolving complex (OEC) is not thermodynamically favorable in the S2g = 2 state, but it is in the S2g = 4.1 redox isomer. Thus, formation of the S3 state starts by a transition from the S2g = 2 to the S2g = 4.1 structure. Then, electrostatic interactions support protonation of D1-H190 and deprotonation of the Ca2+-ligated water (W3) with proton loss to the lumen. The W3 hydroxide moves toward Mn4, completing the coordination shell of Mn4 and favoring its oxidation to Mn(iv) in the S3 state. In addition, binding an additional hydroxide to Mn1 leads to a conformational change of D1-E189 in the S2g = 4.1 and S3 structures. In the S3 state a fraction of D1-E189 release from Mn1 and bind a proton.


Assuntos
Modelos Químicos , Oxigênio/química , Complexo de Proteína do Fotossistema II/química , Termodinâmica
14.
Phys Chem Chem Phys ; 21(37): 20606-20612, 2019 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-31528919

RESUMO

In this work, the interaction between an Auramine O (AuO) fluorescent molecular rotor and natural DNA, its thermodynamic aspects and the resulting variation of the optical properties upon binding are addressed by a combined spectroscopic (UV-vis and fluorescence) and computational approach. DNA binding causes a shift in the maximum of absorption from 432 nm to 444 nm, a decrease of the extinction coefficient and a dramatic enhancement of fluorescence emission, these results being in agreement with intercalation into the polynucleotide helix. Intercalation is indeed confirmed by the thermodynamic parameters for the binding reaction (in particular, the highly negative ΔH). Theoretical modelling at the TD-DFT level was done on a simplified model system consisting of the AuO molecule intercalated between two DNA base pairs. The evolution of the calculated vertical transitions quantitatively reproduces the experimentally observed hypo- and bathochromic shifts, thus confirming the intercalation hypothesis.


Assuntos
Benzofenoneídio/química , DNA/química , Modelos Químicos , Análise Espectral , Fluorescência , Simulação de Dinâmica Molecular
15.
Ying Yong Sheng Tai Xue Bao ; 30(9): 2999-3009, 2019 Sep.
Artigo em Chinês | MEDLINE | ID: mdl-31529875

RESUMO

Two typical soil profiles of sand dune (mixed sandy loam with sandy soil; uniform sandy soil) were selected from the arid region on the edge of the Badain Jaran desert to analyze soil physical characteristics. The effects of soil physical characteristics on capillary rise were monitored and simulated. The relationship between two typical soil profiles of sand dune and capillary rise were investigated to reveal the interactive processes among groundwater, capillary water, and soil water. Results showed that capillary rise was mainly affected by soil bulk density and soil clay content in the arid-desert area. The capillary rise could reach to 152 cm above shallow layer in the profile of mixed sandy loam with sandy soils, and 120 cm in the profile of sandy soil, respectively. Soil water distribution driven by the capillary rise was more uniform in the profile of sandy soil. Soil water content showed a diminishing trend from the groundwater to the maximum distance of capillary rise. In contrast, soil water distribution was markedly varied in the profile of mixed sandy loam with sandy soil. The process of capillary movement could be well simulated with Hydrus-3D model. Soil structure above the groundwater was the critical factor, which could affect the capillary rise and soil water distribution. However, the effects of soil in-season evaporation and plant root uptake on capillary rise movement need to be explored in further studies.


Assuntos
Água Subterrânea/química , Solo/química , Clima Desértico , Modelos Químicos , Estações do Ano , Água
16.
Phys Chem Chem Phys ; 21(37): 20628-20640, 2019 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-31495862

RESUMO

Methionine synthase (MetH) is a methylcobalamin (MeCbl)-dependent mammalian enzyme which plays a critical role in carrying out the transfer of a methyl group from methyl tetrahydrofolate to homocysteine to generate methionine and tetrahydrofolate. This catalytic cycle proceeds via cleavage of a Co-C bond which is formally heterolytic. This cleavage results in a structural change in the MeCbl cofactor bound to an enzyme. Unlike the native catalysis, upon photoexcitation, the Co-C bond in MeCbl-bound MetH generates the Co(ii)/CH3 radical pairs (RPs). Protein residues of the cap domain, particularly phenylalanine708 (F708) and leucine 715 (L715), which surrounds the upper face of the MeCbl cofactor, inhibit the photolysis of MeCbl by caging the CH3 radical and inducing the geminate recombination of the Co(ii)/CH3 RP. A molecular-level understanding of these effects requires a detailed investigation of the low-lying electronic states. Toward this, we have mutated the F708 residue with alanine (A708) and constructed the potential energy surfaces (PESs) for the low-lying S1 electronic state using a combined quantum mechanics/molecular mechanics (QM/MM) approach. The S1 PESs for the wild-type (WT) and mutant enzymes are the result of crossing of two electronic states, namely metal-to-ligand charge transfer (MLCT) and ligand field (LF) states, indicated by a seam. It is shown that the topologies of the S1 PESs are significantly modulated by introducing a mutation at the F708 position. Specifically, for the WT enzyme, the energy barrier of photoreaction and the energy difference between MLCT and LF minima are markedly higher than those of its mutant counterpart. Moreover, mutation influences the photoactivation of the Co-C bond in enzyme-bound MeCbl by decreasing the rate of geminate recombination and altering the rate of radical pair formation. This theoretical insight was also compared with transient absorption spectroscopic (TAS) studies which are in good agreement with the present findings.


Assuntos
5-Metiltetra-Hidrofolato-Homocisteína S-Metiltransferase/genética , Carbono/química , Cobalto/química , Vitamina B 12/análogos & derivados , 5-Metiltetra-Hidrofolato-Homocisteína S-Metiltransferase/metabolismo , Modelos Químicos , Estrutura Molecular , Mutação/genética , Fotólise , Domínios Proteicos/genética , Vitamina B 12/metabolismo
17.
J Environ Radioact ; 208-209: 106040, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31518883

RESUMO

Because of the Fukushima Dai-ichi Nuclear Power Plant accident, forest ecosystems in wide areas were contaminated with 137Cs. It is important to characterize the behavior of 137Cs after its deposition onto forest surface environments for evaluating and preventing long-term radiation risks. In the present study, 137Cs vertical distributions in the soil profile were observed repeatedly at five forest sites with different vegetation types for 4.4 years after the accident in 2011, and 137Cs migration in the organic layer and mineral soil was analyzed based on a comparison of models and observations. Cesium-137 migration from the organic layer to the underlying mineral soil was represented by a two-component exponential model. Cesium-137 migration from the organic layer was faster than that observed in European forests, suggesting that the mobility and bioavailability of 137Cs could be suppressed rapidly in Japanese forests. At all sites, 137Cs transfer in mineral soil could be reproduced by a simple diffusion equation model with continuous 137Cs supply from the organic layer. The diffusion coefficients of 137Cs in the mineral soil were estimated to be 0.042-0.55 cm2 y-1, which were roughly comparable with those of European forest soils affected by the Chernobyl Nuclear Power Plant accident. Model predictions using the determined model parameters indicated that 10 years after the accident, more than 70% of the deposited 137Cs will migrate to the mineral soil but only less than 10% of the total 137Cs inventory will penetrate deeper than 10 cm in the mineral soil across all sites. The results of the present study suggest that the 137Cs deposited onto Japanese forest ecosystems will be retained in the surface layers of mineral soil for a long time.


Assuntos
Radioisótopos de Césio/análise , Florestas , Acidente Nuclear de Fukushima , Monitoramento de Radiação , Poluentes Radioativos do Solo/análise , Japão , Modelos Químicos , Solo
18.
Water Sci Technol ; 80(1): 11-24, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31461418

RESUMO

This paper aims to assess the performance of a distributed hydrological model for simulating the transport of various heavy metals in rivers, to enhance and support environmental monitoring strategies for rivers in developing countries. In this context, we evaluated the performance of the Geophysical flow Circulation (GeoCIRC) model based on Object-Oriented Design (OOD) for the simulation of contamination from multiple heavy metals (Pb, Hg, Cr, and Zn) in Harrach River in Algeria. The results of the case study were in good agreement with the observations. Methodology for the assessment of data quality control and the improvement of monitoring procedures was proposed by using the hydrological model to simulate different scenarios. The GeoCIRC-model-based OOD allowed the prediction of the concentrations of heavy metals with minimal input data. Also, various heavy metals could be numerically treated simultaneously because the OOD increases the model's flexibility to allow the handling of many transportable materials. Therefore, the GeoCIRC model is a powerful tool for the monitoring of environmental contamination in rivers by various heavy metals.


Assuntos
Monitoramento Ambiental , Metais Pesados/análise , Poluentes Químicos da Água/análise , Argélia , China , Sedimentos Geológicos , Modelos Químicos , Medição de Risco , Rios
19.
Water Sci Technol ; 80(1): 98-108, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31461426

RESUMO

The sorption of Cu ions on pure fly ash-based geopolymer, fly ash-based geopolymer with Pb ions addition (modified) and zeolite NaX was studied. Taguchi's approach was applied to determine the impact of solute concentration (c), temperature (T), mixing time (t) and sorbent type (S) on the sorption of Cu ions onto different sorbents under batch conditions. Optimum experimental conditions and influence of controllable factors were determined using the larger-the-better approach. The influence in descending order is c > S > t > T, for both removal and loading. Also, the impact of sorbent type and solute concentration on the process equilibrium was examined. The equilibrium amount of Cu retained on the sorbents in equilibrium (qe) was as follows: pure geopolymer - 1.169 mmol g-1, modified geopolymer - 1.186 mmol g-1, and zeolite NaX - 1.695 mmol g-1. The experimental data were modelled using Jovanovic, Khan, Baudu, and Fritz-Schlünder isotherm models and their goodness of fit were compared. The Baudu isotherm model was the most useful in predicting the equilibrium of Cu sorption on pure and modified geopolymer. Goodness of fit of the selected isotherm models for the sorption of Cu ions on zeolite NaX was in the order: Fritz-Schlünder > Khan > Jovanovic > Baudu.


Assuntos
Cobre/química , Zeolitas , Adsorção , Concentração de Íons de Hidrogênio , Íons , Cinética , Modelos Químicos
20.
Phys Chem Chem Phys ; 21(35): 18850-18865, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31432055

RESUMO

Proton detected solid-state NMR under fast magic-angle-spinning (MAS) conditions is currently redefining the applications of solid-state NMR, in particular in structural biology. Understanding the contributions to the spectral linewidth is thereby of paramount importance. When disregarding the sample-dependent inhomogeneous contributions, the NMR proton linewidth is defined by homogeneous broadening, which has incoherent and coherent contributions. Understanding and disentangling these different contributions in multi-spin systems like proteins is still an open issue. The coherent contribution is mainly caused by the dipolar interaction under MAS and is determined by the molecular structure and the proton chemical shifts. Numerical simulation approaches based on numerically exact direct integration of the Liouville-von Neumann equation can give valuable information about the lineshape, but are limited to small spin systems (<12 spins). We present an alternative simulation method for the coherent contributions based on the rapid and partially analytic calculation of the second moments of large spin systems. We first validate the method on a simple system by predicting the 19F linewidth in CaF2 under MAS. We compare simulation results to experimental data for microcrystalline ubiquitin (deuterated 100% back-exchanged at 110 kHz and fully-protonated at 125 kHz). Our results quantitatively explain the observed linewidth per-residue basis for the vast majority of residues.


Assuntos
Simulação por Computador , Modelos Químicos , Proteínas/química , Ressonância Magnética Nuclear Biomolecular , Prótons
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