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1.
J Obstet Gynaecol ; : 1-7, 2022 Jun 04.
Artigo em Inglês | MEDLINE | ID: mdl-35659173

RESUMO

6-Phosphofructo-2-kinase/fructose-2,6-biphosphatase 4 (PFKFB4) was reported to be necessary for tumour growth in several cancers. However, the function of PFKFB4 in cervical cancer has not been clearly elucidated. Bioinformatics analysis was applied to detect the expression of PFKFB4 in cervical cancer and the association with survival prognosis. The effect of PFKFB4 on cervical cancer cells growth, cycle, invasion, migration and glucose metabolism was investigated by loss-of-function approaches in vitro. The association between PFKFB4 and MEK/ERK/c-Myc pathway was identified by western blot assay. We found that PFKFB4 was highly expressed in cervical cancer samples and its overexpression led to a poor prognosis of cervical cancer patients. Knock down of PFKFB4 reduced cell growth, blocked cell cycle, inhibited cell invasion and migration, and blocked glucose metabolism in cervical cancer cells. Our findings afforded a theoretical basis for further research on the treatment of cervical cancer based on the control of PFKFB4 expression. Impact StatementWhat is already known on this subject? PFKFB4 was overexpressed in several kinds of cancers and its requirement for tumour growth has been confirmed in cancers such as glioma and breast cancer. However, the function of PFKFB4 in cervical cancer cells has not been clearly elucidated. A bioinformatics study showed that PFKFB4 was a member of a six-gene signature associated with glycolysis to predict the prognosis of patients with cervical cancer. However, the relationship between PFKFB4 and glucose metabolism in cervical cancer has not been revealed.What do the results of this study add? Our results showed that PFKFB4 was highly expressed in cervical cancer samples and its overexpression led to a poor prognosis of cervical cancer patients. Moreover, the administration of si-PFKFB4 significantly reduced cell growth ability, blocked cell cycle, restrained the mobility and suppressed the glucose metabolism in cervical cancer cells partially by inactivating MEK/ERK/c-Myc pathway.What are the implications of these findings for clinical practice and/or further research? Our findings afforded a theoretical basis for further research on the treatment of cervical cancer based on the control of PFKFB4 expression.

2.
Sci Total Environ ; 833: 155187, 2022 Aug 10.
Artigo em Inglês | MEDLINE | ID: mdl-35421464

RESUMO

Phosphorus (P) is an essential macronutrient for all living organisms. Despite a diversity of P compounds in the environment, orthophosphate is the most bioavailable form of P. Remineralization of complex P molecules (e.g., organic P and phosphoanhydrides) into orthophosphate is traditionally considered to be carried out primarily by enzymes. Natural minerals are recently viewed to be abiotic catalysts (as compared to the organic phosphatases) to facilitate the cleavage of terminal P-O-C/P bonds and remineralization of complex P compounds. However, quantitative comparison between biotic and abiotic remineralization pathways of complex P molecules is still missing, impeding our capability to assess the importance and contribution of abiotic P remineralization in the environment. This study compares the hydrolysis rates of six organic phosphates and three inorganic phosphoanhydrides by representative enzymes (acid and alkaline phosphatases) and natural oxide minerals (hematite, birnessite, and boehmite). The results show that enzymes and minerals have different substrate preferences. Specifically, alkaline phosphatase hydrolyzes phosphate monoesters faster than phosphoanhydrides, whereas acid phosphatase and minerals show higher hydrolysis rates toward phosphoanhydrides than phosphate monoesters. Although the hydrolysis rates by enzymes (~µM hr-1) are orders of magnitude higher than those by minerals (~µM d-1), normalization of the rates by the natural abundance of enzymes and minerals leads to comparable contributions of both processes in soils and sediments. These results highlight the significance of natural minerals in the remineralization of complex P compounds, a process that was traditionally overlooked but with important implications for constraining P biogeochemical cycling in the environment.


Assuntos
Fosfatos , Solo , Minerais/química , Organofosfatos , Fosfatos/análise , Monoéster Fosfórico Hidrolases
3.
Biophys J ; 121(4): 658-669, 2022 02 15.
Artigo em Inglês | MEDLINE | ID: mdl-35016860

RESUMO

DNA supercoils are generated in genome regulation processes such as transcription and replication and provide mechanical feedback to such processes. Under tension, a DNA supercoil can present a coexistence state of plectonemic and stretched phases. Experiments have revealed the dynamic behaviors of plectonemes, e.g., diffusion, nucleation, and hopping. To represent these dynamics with conformational changes, we demonstrated first the fast dynamics on the DNA to reach torque equilibrium within the plectonemic and stretched phases, and then identified the two-phase boundaries as collective slow variables to describe the essential dynamics. According to the timescale separation demonstrated here, we developed a two-phase model on the dynamics of DNA supercoiling, which can capture physiologically relevant events across timescales of several orders of magnitudes. In this model, we systematically characterized the slow dynamics between the two phases and compared the numerical results with those from the DNA polymer physics-based worm-like chain model. The supercoiling dynamics, including the nucleation, diffusion, and hopping of plectonemes, have been well represented and reproduced, using the two-phase dynamic model, at trivial computational costs. Our current developments, therefore, can be implemented to explore multiscale physical mechanisms of the DNA supercoiling-dependent physiological processes.


Assuntos
DNA Super-Helicoidal , Polímeros , DNA , Conformação de Ácido Nucleico , Física
4.
Sci Total Environ ; 803: 149918, 2022 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-34482133

RESUMO

Co-sorption of metal ions and anions/ligands at the mineral-water interface plays a critical role in regulating the mobility, transport, fate, and bioavailability of these components in natural environments. This review focuses on co-sorption of metal ions and naturally occurring anions/ligands on environmentally relevant minerals. The underlying mechanisms for their interfacial reactions are summarized and the environmental impacts are discussed. Co-sorption mechanisms of these components depend on a variety of factors, such as the identity and properties of minerals, pH, species and concentration of metal ions and anions/ligands, addition sequence of co-sorbed ions, and reaction time. The simultaneous presence of metal ions and anions/ligands alters the initial sorption behaviors with promotive or competitive effects. Promotive effects are mainly attributed to surface electrostatic interactions, ternary surface complexation, and surface precipitation, especially for the co-sorption systems of metal ions and inorganic anions on minerals. Competitive effects involve potential complexation of metal-anions/ligands in solution or their competition for surface adsorption sites. Organic ligands usually increase metal ion sorption on minerals at low pH via forming ternary surface complexes or surface precipitates, but inhibit metal ion sorption via the formation of aqueous complexes at high pH. The different mechanisms may act simultaneously during metal ion and anion/ligand co-sorption on minerals. Finally, the potential application for remediation of metal-contaminated sites is discussed based on the different co-sorption behaviors. Future challenges and topics are raised for metal-anion/ligand co-sorption research.


Assuntos
Metais , Minerais , Adsorção , Ânions , Concentração de Íons de Hidrogênio , Íons , Ligantes
5.
J Chem Phys ; 154(13): 134708, 2021 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-33832239

RESUMO

Elemental copper and potassium are immiscible under ambient conditions. It is known that pressure is a useful tool to promote the reaction between two different elements by modifying their electronic structure significantly. Here, we predict the formation of four K-Cu compounds (K3Cu2, K2Cu, K5Cu2, and K3Cu) under moderate pressure through unbiased structure search and first-principles calculations. Among all predicted structures, the simulated x-ray diffraction pattern of K3Cu2 perfectly matches a K-Cu compound synthesized in 2004. Further simulations indicate that the K-Cu compounds exhibit diverse structural features with novel forms of Cu aggregations, including Cu dimers, linear and zigzag Cu chains, and Cu-centered polyhedrons. Analysis of the electronic structure reveals that Cu atoms behave as anions to accept electrons from K atoms through fully filling 4s orbitals and partially extending 4p orbitals. Covalent Cu-Cu interaction is found in these compounds, which is associated with the sp hybridizations. These results provide insights into the understanding of the phase diversity of alkali/alkaline earth and metal systems.

6.
Small ; 16(48): e2004457, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-33155379

RESUMO

Nano heterostructures relying on their versatile construction and the breadth of combined functionality have shown great potential in energy storage fields. Herein, 2D sandwiched MoSe2 /TiO2- x /graphene nano heterostructures are designed by integrating structural and functional effects of each component, aiming to address the rate capability and cyclic stability of MoSe2 for sodium ion capacitors (SICs). These 2D nano heterostructures based on graphene platform can facilitate the interfacial electron transport, giving rise to fast reaction kinetics. Meanwhile, the 2D open structure induces a large extent of surface capacitive contribution, eventually leading to a high rate capability (415.2 mAh g-1 @ 5 A g-1 ). An ultrathin oxygen deficient TiO2- x layer sandwiched in these nano heterostructures provides a strong chemical-anchoring regarding the products generated during the sodiation/desodiation process, securing the entire cyclic stability. The associated sodiation/desodiation mechanism is revealed by operando and ex situ characterizations, which exhibits a strong solid electrolyte interphase (SEI) dependence. The simulations verify the dependent sodiation products and enhanced heterostructural chemical-anchoring. Assembled SICs based on these nano heterostructures anode exhibit high initial Coulombic efficiency, energy/power densities, and long cycle life, shedding new light on the design of nano heterostructure electrodes for high performance energy storage application.

7.
ACS Appl Mater Interfaces ; 12(26): 29218-29227, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32490658

RESUMO

Performance degradation of lithium/sodium-ion capacitors (LICs/SICs) mainly originates from anode pulverization, particularly the alloying and conversion types, and has spurred research for alternatives with an insertion mechanism. Three-dimensional (3D) topotactic host materials remain much unexplored compared to two-dimensional (2D) ones (graphite, etc.). Herein, vanadium monophosphide (VP) is designed as a 3D topotactic host anode. Ex situ electrochemical characterizations reveal that there are no phase changes during (de)intercalation, which follows the topotactic intercalation mechanism. Computational simulations also confirm the metallic feature and topotactic structure of VP with a spacious interstitial position for the accommodation of guest species. To boost the electrochemical performance, carbon nano-onions (CNOs) are coupled with 3D VP. Superior specific capacity and rate capability of VP-CNOs vs lithium/sodium can be delivered due to the fast ion diffusion nature. An exceptional capacity retention of above 86% is maintained after 20 000 cycles, benefitting from the topotactic intercalation process. The optimized LICs/SICs exhibit high energy/power densities and an ultrastable lifespan of 20 000 cycles, which outperform most of the state-of-the-art LICs and SICs, demonstrating the potential of VP-CNOs as insertion anodes. This exploration would draw attention with regard to insertion anodes with 3D topotactic host topology and provide new insights into anode selection for LICs/SICs.

8.
Environ Sci Technol ; 54(13): 8362-8372, 2020 07 07.
Artigo em Inglês | MEDLINE | ID: mdl-32539353

RESUMO

Anaerobic digestion (AD) with hydrothermal (HT) pretreatment is an emerging technology for enhanced resource recovery from sewage sludge. This study investigates the speciation of Fe, P, and S during sequential HT-AD treatment of sewage sludge using sequential chemical extraction, X-ray diffraction, and X-ray absorption spectroscopy. Results suggest strong correlations between Fe and P species as well as Fe and S species, affecting the solubility and bioavailability of each other. For instance, much vivianite formed in the hydrochars after HT treatment at low temperature, while more strengite precipitated at higher HT temperature. During the subsequent AD process, microbial reduction of strengite and other Fe(III) species led to the formation of more vivianite, with concurrent P release into the solution and adsorption onto other minerals. HT pretreatment of sewage sludge had a weak effect on the sulfidation of Fe during the AD process. This work has important implications for understanding the nutrient speciation and availability in sludge-derived hydrochars and AD solids. It also provides fundamental knowledge for the selection and optimization of HT pretreatment conditions for enhanced resource recovery through sequential HT-AD process.


Assuntos
Fósforo , Esgotos , Anaerobiose , Ferro , Enxofre , Eliminação de Resíduos Líquidos
9.
Sci Adv ; 6(23): eaba9206, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32537513

RESUMO

Group V elements in crystal structure isostructural to black phosphorus with unique puckered two-dimensional layers exhibit exciting physical and chemical phenomena. However, as the first element of group V, nitrogen has never been found in the black phosphorus structure. Here, we report the synthesis of the black phosphorus-structured nitrogen at 146 GPa and 2200 K. Metastable black phosphorus-structured nitrogen was retained after quenching it to room temperature under compression and characterized in situ during decompression to 48 GPa, using synchrotron x-ray diffraction and Raman spectroscopy. We show that the original molecular nitrogen is transformed into extended single-bonded structure through gauche and trans conformations. Raman spectroscopy shows that black phosphorus-structured nitrogen is strongly anisotropic and exhibits high Raman intensities in two A g normal modes. Synthesis of black phosphorus-structured nitrogen provides a firm base for exploring new type of high-energy-density nitrogen and a new direction of two-dimensional nitrogen.

10.
J Chem Phys ; 152(11): 114115, 2020 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-32199430

RESUMO

All-atom molecular dynamics (MD) simulations of bio-macromolecules can yield relatively accurate results while suffering from the limitation of insufficient conformational sampling. On the other hand, the coarse-grained (CG) MD simulations efficiently accelerate conformational changes in biomolecules but lose atomistic details and accuracy. Here, we propose a novel multiscale simulation method called the adaptively driving multiscale simulation (ADMS)-it efficiently accelerates biomolecular dynamics by adaptively driving virtual CG atoms on the fly while maintaining the atomistic details and focusing on important conformations of the original system with irrelevant conformations rarely sampled. Herein, the "adaptive driving" is based on the short-time-averaging response of the system (i.e., an approximate free energy surface of the original system), without requiring the construction of the CG force field. We apply the ADMS to two peptides (deca-alanine and Ace-GGPGGG-Nme) and one small protein (HP35) as illustrations. The simulations show that the ADMS not only efficiently captures important conformational states of biomolecules and drives fast interstate transitions but also yields, although it might be in part, reliable protein folding pathways. Remarkably, a ∼100-ns explicit-solvent ADMS trajectory of HP35 with three CG atoms realizes folding and unfolding repeatedly and captures the important states comparable to those from a 398-µs standard all-atom MD simulation.


Assuntos
Substâncias Macromoleculares/química , Modelos Químicos , Peptídeos/química , Conformação Molecular , Simulação de Dinâmica Molecular , Conformação Proteica
11.
Environ Sci Pollut Res Int ; 27(13): 14751-14762, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32052339

RESUMO

The widespread use of zinc oxide nanoparticles (ZnO NPs), the second most produced nanomaterial, inevitably leads to their release into the environment. In this study, dissolution and transformation of ZnO NPs in the presence of δ-MnO2, an abundant and ubiquitous manganese (Mn) oxide mineral, was investigated via a suite of techniques covering bulk to molecular scales. Dissolution kinetics indicated that the presence of δ-MnO2 significantly affected ZnO NP dissolution rate/trend and equilibrium Zn2+ concentration, which were found to be mainly dependent on the concentration and mass ratio of ZnO NPs and δ-MnO2. Approximately 300 mg ZnO NPs per g δ-MnO2 was expected for ZnO NP uptake at pH 7.0 via ZnO NP dissolution and surface Zn2+ adsorption. X-ray diffraction (XRD), ζ potential, high-resolution transmission electron microscopy (HR-TEM), and Zn K-edge X-ray absorption spectroscopy (XAS) results revealed that when the mole content of ZnO NPs was less than the total adsorption sites of δ-MnO2 surface, ZnO NPs were completely dissolved and adsorbed on δ-MnO2 surface in the form of inner-sphere complexes. A fraction of ZnO NPs persisted when the mole ratio of ZnO to δ-MnO2 further increased. These results suggest that the transformation and fate of ZnO NPs is affected by environment-relevant minerals such as Mn oxides due to their huge capacity of fixing dissolved metal cations at the surface or interlayer structure.


Assuntos
Nanopartículas , Óxido de Zinco , Compostos de Manganês , Óxidos , Solubilidade
12.
Math Biosci Eng ; 16(5): 4936-4946, 2019 05 31.
Artigo em Inglês | MEDLINE | ID: mdl-31499698

RESUMO

In this paper, a class of discrete Hopfield-type neural networks with time delays is consid-ered. Sufficient and necessary conditions for global attractivity and stability of the equilibrium of the discrete Hopfield-type neural networks are given by using a class of n-dimensional nonlinear algebraic equations and M-matrix theory.

13.
Dalton Trans ; 48(38): 14299-14305, 2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31453996

RESUMO

A thorough structural exploration was performed for MgB6 combining the global structure searching method with first-principles calculations. Besides the known Cmcm phase, new phases, i.e. I4/mmm, C2/m-I, C2/m-II and P21/m, were predicted to be stable in the pressure range of 18-100 GPa. Unexpectedly, Cmcm-MgB6 was found to be a semiconductor with an indirect band gap of 0.38 eV with the HSE06 functional, in good agreement with the experimental finding. I4/mmm-MgB6 stabilized above 18 GPa exhibits semimetallic behaviour with a topological node-line near the Fermi level. Consequently, C2/m-I MgB6 with a sandwich structure similar to MgB2 is predicted to be a superconductor with a critical temperature (Tc) of 9.5 K. By analysing the electronic structure, the intriguing semiconductor-semimetal-superconductor transition may be ascribed to the delocalization of more B-p electrons in the boron sublattice. The novel functions uncovered for MgB6 may inspire more efforts to discover materials with intriguing properties.

14.
Environ Sci Technol ; 53(16): 9542-9552, 2019 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-31313918

RESUMO

The geochemical behaviors of phosphate-containing species at mineral-water interfaces are of fundamental importance for controlling phosphorus mobility, fate, and bioavailability. This study investigates the sorption and hydrolysis of polyphosphate (a group of important long-chained phosphate molecules) on aluminum oxides in the presence of divalent metal cations (Ca2+, Cu2+, Mg2+, Mn2+, and Zn2+) at pH 6-8. γ-Al2O3 with three particle sizes (5, 35, and 70 nm) was used as an analogue of natural aluminum oxides to investigate the particle size effect. All metal cations enhanced polyphosphate hydrolysis at different levels, with Ca2+ showing the most significant enhancement, and the difference in the enhancement might be due to the intrinsic affinity of metal cations to polyphosphate. In the presence of Ca2+, the hydrolysis rate decreased with increasing mineral particle size. Solid-state 31P nuclear magnetic resonance spectroscopy (NMR) revealed the main surface P species to be amorphous calcium phosphate precipitates, phosphate groups in polyphosphate that formed direct bonds with the mineral surface as inner-sphere complexes, and phosphate groups in polyphosphate that were not directly bonded to the mineral surfaces. Our results reveal the critical roles of mineral-water interface processes and divalent metal cations on controlling polyphosphate speciation and transformation and phosphorus cycling.


Assuntos
Óxido de Alumínio , Polifosfatos , Adsorção , Alumínio , Hidrólise , Metais
15.
Sci Total Environ ; 650(Pt 2): 1980-1987, 2019 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-30290340

RESUMO

Zinc and aluminum layered double hydroxides (Zn-Al LDH) are a common group of major Zn species in various Zn-contaminated soil/sediment environments, yet their formation pathways and underlying mechanisms under varied conditions are not well understood. This study investigated the formation of Zn-Al LDHs through the direct interaction of two solid substrates, ZnO nanoparticles (NPs) and a representative Al oxide, γ-Al2O3. Batch experiments and complementary microscopic and spectroscopic analyses were conducted to elucidate the reaction kinetics and mechanisms, as well as the morphologic and structural evolution of the products. Dissolved Zn and Al concentrations decreased significantly in a dual solid system compared to a single solid system. A bulk Zn-Al LDH phase was found to form under a wide pH range (6.5-9.5). Aside from Zn-Al LDH, γ-Al2O3 was the main remaining solid phase at pH 6.5, whereas ZnO NPs were the main residual solid phases at pH 9.5. Formation of amorphous Zn(OH)2 was also observed at both pH values, likely due to Zn2+ release at low pH and Al(OH)4- adsorption at high pH. It is proposed that the formation of Zn-Al LDH occurs via a dissolution-sorption-coprecipitation process, where the solubility of ZnO NPs or γ-Al2O3 solid phases determines the reaction pathways and kinetics under varied pH conditions. The results from this work revealed the transformation mechanisms for ZnO NPs under conditions from weakly acidic to alkaline pH with highly available Al particles and shed light on the environmental fate of ZnO NPs in Zn or ZnO NP contaminated environments.

16.
Adv Sci (Weinh) ; 5(11): 1800666, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30479920

RESUMO

The discovery of electrides, in particular, inorganic electrides where electrons substitute anions, has inspired striking interests in the systems that exhibit unusual electronic and catalytic properties. So far, however, the experimental studies of such systems are largely restricted to ambient conditions, unable to understand their interactions between electron localizations and geometrical modifications under external stimuli, e.g., pressure. Here, pressure-induced structural and electronic evolutions of Ca2N by in situ synchrotron X-ray diffraction and electrical resistance measurements, and density functional theory calculations with particle swarm optimization algorithms are reported. Experiments and computation are combined to reveal that under compression, Ca2N undergoes structural transforms from R 3 ¯ m symmetry to I 4 ¯ 2d phase via an intermediate Fd 3 ¯ m phase, and then to Cc phase, accompanied by the reductions of electronic dimensionality from 2D, 1D to 0D. Electrical resistance measurements support a metal-to-semiconductor transition in Ca2N because of the reorganizations of confined electrons under pressure, also validated by the calculation. The results demonstrate unexplored experimental evidence for a pressure-induced metal-to-semiconductor switching in Ca2N and offer a possible strategy for producing new electrides under moderate pressure.

17.
Inorg Chem ; 57(15): 9385-9392, 2018 Aug 06.
Artigo em Inglês | MEDLINE | ID: mdl-30024155

RESUMO

Transition-metal (TM) phosphides attract increasing attention with applications for energy conversion and storage, due to their outstanding physical, chemical, and electronic properties. The 3d transition metal tetraphosphides (TMP4, TM = V, Cr, Mn, and Fe) possess multiple allotropies and rich electronic properties. Here, we perform the investigations of the structural, electronic, and elastic properties for 3d-TMP4 (TM = V, Cr, Mn, and Fe) using density functional theory (DFT) calculations. These compounds are featured with alternating buckled phosphorus sheets with ten-numbered phosphorus rings and varied transition-metal layers. Hybrid DFT calculations reveal that TMP4 compounds exhibit a wide range of electrical properties, ranging from metallic behavior for VP4 to semiconducting behavior for CrP4 with the narrow direct band gap of 0.63 eV to enlarged semiconducting MnP4 and FeP4 with band gap of 1.6-2.1 eV. The bonding analysis indicates that P-P and TM-P covalent interactions dominate in the phosphorus sheets and TMP6 octahedrons, which are responsible for the structural and electronic diversity.

18.
Huan Jing Ke Xue ; 39(6): 2982-2990, 2018 Jun 08.
Artigo em Chinês | MEDLINE | ID: mdl-29965658

RESUMO

With the rapid development of nanotechnology, the environmental behavior and ecological effect of nanoparticles (NPs) are receiving more and more attention. As an important environmental component, metal oxide NPs occur widely in nature, such as in water bodies, air, soils, and sediments. They have a large surface area and high surface activity, allowing them to control and affect the speciation, migration, transformation, and bioavailability of some contaminants and nutrients in the environment. The nano-size is a unique property of nanoparticles. The size of particles regulates and determines the structure and physicochemical properties of nano-oxides, which greatly affects interfacial reactions with the relevant elements and environmental geochemical behaviors. The effects of NPs size on the environmental geochemical behaviors, such as adsorption, (reductive) dissolution, (catalytic) oxidation, aggregation and transport, are briefly summarized, and the mechanism of the size effect is discussed. Finally, hot spots for future research of metal oxide nanoparticles related to size effects in the environment are proposed.

19.
Geochem Trans ; 19(1): 12, 2018 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-29934914

RESUMO

Recently, the wide application of CuO nanoparticles (NPs) in engineering field inevitably leads to its release into various geologic settings, which has aroused great concern about the geochemical behaviors of CuO NPs due to its high surface reactivity and impact on the fate of co-existing contaminants. However, the redox transformation of pollutants mediated by CuO NPs and the underlying mechanism still remain poorly understood. Here, we studied the interaction of CuO NPs with As(III), and explored the reaction pathways using batch experiments and multiple spectroscopic techniques. The results of in situ quick scanning X-ray absorption spectroscopy (Q-XAS) analysis verified that CuO NPs is capable of catalytically oxidize As(III) under dark conditions efficiently at a wide range of pHs. As(III) was firstly adsorbed on CuO NPs surface and then gradually oxidized to As(V) with dissolved O2 as the terminal electron acceptor. As(III) adsorption increased to the maximum at a pH close to PZC of CuO NPs (~ pH 9.2), and then sharply decreased with increasing pH, while the oxidation capacity monotonically increased with pH. X-ray photoelectron spectroscopy and electron paramagnetic resonance characterization of samples from batch experiments indicated that two pathways may be involved in As(III) catalytic oxidation: (1) direct electron transfer from As(III) to Cu(II), followed by concomitant re-oxidation of the produced Cu(I) by dissolved O2 back to Cu(II) on CuO NPs surface, and (2) As(III) oxidation by reactive oxygen species (ROS) produced from the above Cu(I) oxygenation process. These observations facilitate a better understanding of the surface catalytic property of CuO NPs and its interaction with As(III) and other elements with variable valence in geochemical environments.

20.
Environ Sci Technol ; 52(3): 1183-1190, 2018 02 06.
Artigo em Inglês | MEDLINE | ID: mdl-29359927

RESUMO

Polyphosphates are a group of phosphorus (P) containing molecules that are produced by a wide range of microorganisms and human activities. Although polyphosphates are ubiquitous in aquatic environments and are of environmental significance, little is known about their transformation and cycling. This study characterized the polyphopshate-hydrolysis mechanisms of several representative phosphatase enzymes and evaluated the effects of polyphosphate chain length, light condition, and calcium (Ca2+). 31P nuclear magnetic resonance (NMR) spectroscopy was used to monitor the dynamic changes of P molecular configuration during polyphosphate hydrolysis and suggested a terminal-only degradation pathway by the enzymes. Such mechanism enabled the quantification of the hydrolysis rates by measuring orthophosphate production over time. At the same initial concentration of polyphosphate molecules, the hydrolysis rates were independent of chain length. The hydrolysis of polyphosphate was also unaffected by light condition, but was reduced by the presence of Ca2+. The released orthophosphates formed Ca-phosphate precipitates in the presence of Ca2+, likely in amorphous phases. Results from this study lay the foundation for better understanding the chemical processes governing polyphosphate transport and transformation in various environmental settings.


Assuntos
Monoéster Fosfórico Hidrolases , Polifosfatos , Hidrólise , Espectroscopia de Ressonância Magnética , Fósforo
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