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•The adsorption properties of zeolites under a wide range of H2O content were studied.•Hierarchical zeolites were successfully obtained by alkali treatment.•The adsorption and ...desorption performance were both improved for various VOCs.•This paper provided an effective example for more efficient use of zeolite.
Zeolites have been widely used in the adsorption and removal of volatile organic compounds (VOCs). In this study, we investigated the adsorption properties of 9 commercial zeolites and MCM-41 mesoporous silica for p-xylene. And then zeolites with hierarchical structures were prepared by alkali (0.1–0.8 mol•L−1 mixed alkali solution) modification and their adsorption and desorption properties were investigated for various VOCs. The structure of these materials was thoroughly characterized, and the relationship between the adsorption capacity and physical parameters was investigated. It was found that the pore diameter and Si/Al ratio were the most important parameters for p-xylene adsorption under humid conditions, which should be optimized simultaneously to achieve satisfactory adsorption capacity. And the best adsorption capacity could reach approximately 100 mg•g−1 in humid conditions. Meanwhile, enhancing the diffusion of the VOC molecules in microporous zeolites with micron crystals through the manufacture of hierarchical structure was also important. The adsorption capacity of the modified zeolites increased by more than 25%, and the desorption temperature decreased. It showed that the alkali modification not only improved the utilization efficiency of the adsorption sites, but also facilitated desorption, which is crucial for adsorbing materials.
A novel coronavirus severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) outbreak has caused a global coronavirus disease 2019 (COVID-19) pandemic, resulting in tens of thousands of ...infections and thousands of deaths worldwide. The RNA-dependent RNA polymerase (RdRp), also named nsp12 is the central component of coronaviral replication and transcription machinery, and it appears to be a primary target for the antiviral drug remdesivir. We report the cryo-electron microscopy structure of COVID-19 virus full-length nsp12 in complex with cofactors nsp7 and nsp8 at 2.9-angstrom resolution. In addition to the conserved architecture of the polymerase core of the viral polymerase family, nsp12 possesses a newly identified β-hairpin domain at its N terminus. A comparative analysis model shows how remdesivir binds to this polymerase. The structure provides a basis for the design of new antiviral therapeutics that target viral RdRp.
Recent research has demonstrated that black carbons catalyze the transformation of a range of nitrated explosives sorbed to the carbon surfaces in the presence of sulfides. Although surface ...oxygenated functional groups, particularly quinones, and electrical conductivity have both been hypothesized to promote these reactions, the importance of these properties has not been tested. In this work, the importance of electrical conductivity was addressed by producing chars of increasing electrical conductivity via pyrolysis of wood shavings at increasing temperature. The reactivity of chars with respect to transformation of the explosive RDX in the presence of sulfides correlated with electrical conductivity. Oxygenated functional groups were apparently not involved, as demonstrated by the elimination of reactivity of an activated carbon after ozone treatment or sorption of model quinones to the activated carbon surface. Although RDX transformation correlated with char electrical conductivity, no RDX transformation was observed when RDX was physically separated from sulfides but electrically connected through an electrochemical cell. RDX transformation occurred in the presence of a surface-associated sulfur species. The correlation with char electrical conductivity suggests that sulfides are oxidized on carbon surfaces to products that serve as potent nucleophiles promoting RDX transformation.
Nucleotide analog inhibitors, including broad-spectrum remdesivir and favipiravir, have shown promise in in vitro assays and some clinical studies for COVID-19 treatment, this despite an incomplete ...mechanistic understanding of the viral RNA-dependent RNA polymerase nsp12 drug interactions. Here, we examine the molecular basis of SARS-CoV-2 RNA replication by determining the cryo-EM structures of the stalled pre- and post- translocated polymerase complexes. Compared with the apo complex, the structures show notable structural rearrangements happening to nsp12 and its co-factors nsp7 and nsp8 to accommodate the nucleic acid, whereas there are highly conserved residues in nsp12, positioning the template and primer for an in-line attack on the incoming nucleotide. Furthermore, we investigate the inhibition mechanism of the triphosphate metabolite of remdesivir through structural and kinetic analyses. A transition model from the nsp7-nsp8 hexadecameric primase complex to the nsp12-nsp7-nsp8 polymerase complex is also proposed to provide clues for the understanding of the coronavirus transcription and replication machinery.
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•Structures of SARS-CoV-2 RNA polymerase in complexes with RNA revealed•Conformational changes in nsp8 and its interaction with the exiting RNA are observed•Incorporation and delayed-chain-termination mechanism of remdesivir is elucidated•Transition model from primase complex to polymerase complex is proposed
Cryo-EM structures of the SARS-CoV-2 RNA polymerase in complexes with RNA, before and after RNA translocation, reveals structural rearrangements that the RNA-dependent RNA polymerase (RdRp) nsp12 and its co-factors (nsp7 and nsp8) undergo to accommodate nucleic acid binding. Further insights into how the complex is inhibited by remdesivir, and into the primase to polymerase transition, are also presented.
•Research progress of CCUS in the iron and steel industry were reviewed.•The maturity and applicability of various technologies were further analyzed.•Four kinds of coupling schemes were proposed for ...CCUS in the iron and steel industry.
The iron and steel industry is a dominant carbon emission source in China. CCUS is an important potential technology for large-scale carbon reduction. However, due to the characteristics of multi-point source emissions of the iron and steel industry, the application is still in its infancy. Here, the research progresses of CCUS technology in the iron and steel industry are systematically reviewed, including the projects and novel materials. The maturity and applicability of various technologies were further analyzed by considering the CO2 emission characteristics of different steel-making processes. Finally, four kinds of integrated schemes of CCUS in the iron and steel industry were proposed, including “synergistic chemical utilization of hydrogen resource and CO2”, “steel slag mineralization and carbon fixation in coordination with solid waste disposal”, “microalgae biological carbon fixation collaborative wastewater treatment”, and “CO2 geological utilization and storage”. The applicability of the proposed integrated schemes were further analyzed based on the regional distribution of iron and steel enterprises in China. The results of this work were aimed at facilitating the application of CCUS in the iron and steel industry in China.
Protein phosphatase 2A (PP2A) is a principal Ser/Thr phosphatase, the deregulation of which is associated with multiple human cancers, Alzheimer's disease and increased susceptibility to pathogen ...infections. How PP2A is structurally organized and functionally regulated remains unclear. Here we report the crystal structure of an AB'C heterotrimeric PP2A holoenzyme. The structure reveals that the HEAT repeats of the scaffold A subunit form a horseshoe-shaped fold, holding the catalytic C and regulatory B' subunits together on the same side. The regulatory B' subunit forms pseudo-HEAT repeats and interacts with the C subunit near the active site, thereby defining substrate specificity. The methylated carboxy-terminal tail of the C subunit interacts with a highly negatively charged region at the interface between A and B' subunits, suggesting that the C-terminal carboxyl methylation of the C subunit promotes B' subunit recruitment by neutralizing charge repulsion. Together, our structural results establish a crucial foundation for understanding PP2A assembly, substrate recruitment and regulation.
This article investigates practical tracking joint with obstacle‐avoidance for a class of uncertain robotic systems. The remarkable features are revealed from two aspects. First, more serious system ...uncertainties are allowed than the related literature due to the presence of unknown system matrices and mismatched disturbance in the investigated system. Second, only coarse conditions are required on reference trajectory and obstacles since their time derivatives are not necessarily to be available for feedback but those of the related literature muse be, while the reference trajectory is only required to be first rather than second order continuously differentiable. For this, a secure adaptive control framework is established by incorporating adaptive dynamic compensation mechanism into the backstepping procedure with the smart choice of adaptive law and the skillful injection of a barrier function. Consequently, a state‐feedback controller is explicitly designed which guarantees the obstacle‐avoidance of the robotic system while all the signals of the resulting closed‐loop system are bounded with system output practically tracking the reference trajectory. Finally, simulation results are provided for two specified robot systems to validate the effectiveness of the theoretical results.
A secure adaptive control framework is established to design a state‐feedback controller which guarantees the obstacle‐avoidance of the robotic system, while all the signals of the resulting closed‐ loop system are bounded with system output practically tracking the reference trajectory.
Fly ash is a potential alternative to activated carbon for mercury adsorption. The effects of physicochemical properties on the mercury adsorption performance of three fly ash samples were ...investigated. X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, and other methods were used to characterize the samples. Results indicate that mercury adsorption on fly ash is primarily physisorption and chemisorption. High specific surface areas and small pore diameters are beneficial to efficient mercury removal. Incompletely burned carbon is also an important factor for the improvement of mercury removal efficiency, in particular. The C-M bond, which is formed by the reaction of C and Ti, Si and other elements, may improve mercury oxidation. The samples modified with CuBr2 , CuCl 2 and FeCl3 showed excellent performance for Hg removal, because the chlorine in metal chlorides acts as an oxidant that promotes the conversion of elemental mercury （Hg0） into its oxidized form （Hg2＋）. Cu2＋ and Fe3＋ can also promote Hg 0 oxidation as catalysts. HCl and O2 promote the adsorption of Hg by modified fly ash, whereas SO2 inhibits the Hg adsorption because of competitive adsorption for active sites. Fly ash samples modified with CuBr2 , CuCl2 and FeCl3 are therefore promising materials for controlling mercury emissions.
Plastic mulch films (PMFs) are widely used to improve crop quality and quantity. Although they provide a range of benefits, they degrade into widespread microplastics (MPs), which can cause an ...unavoidable risk of environmental problems. The residue of PMFs is a significant source of MPs in soils, which can then spread into various ecosystems and be easily absorbed by organisms due to their small size, and subsequently transported through food chain. Notably, MPs have been found in the human placenta, stool and blood, raising an urgent reminder of the potential dangers of MPs to human health. This review summarizes recent studies concerning the effects of MPs on the reproductive system in soil invertebrates, aquatic animals and rodents of both sexes and the mechanisms by which MPs affect the animal reproductive system. The studies on females demonstrated that MPs decrease oocyte quantity and quality, and induce ovary fibrosis, pyroptosis and apoptosis of granulosa cells. In addition, disrupted integrity of the blood-testis barrier, damaged spermatogenesis and compromised sperm quality have been shown in most studies on male animals. The studies on the mechanisms of these effects have provided evidence that MPs act on the animal reproductive system through reactive oxygen species-related mechanisms by initiating the Wnt/β-Catenin and NLRP3/Caspase-1 pathways in females, and the Nrf2/HO-1/NF-κB, p38 MAPK and MAPK/Nrf2 pathways in males. Taken together, these studies reveal the reproductive toxicity of MPs from PMF on animals and serve as a reminder to properly dispose of PMF waste.
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•MPs from plastic mulch films decrease the offspring production of soil fauna.•MPs induce lower percentage of pregnant and number of embryos because of the decreased ovarian capacity and oocytes quality.•MPs cause testicular toxicity and affect sperm quality with abnormal hormone level.•Transgenerational effects are detected in the soil fauna and aquatic animals induced by MPs.•MPs affect animal reproductive system by activating reactive oxygen species related signaling pathways.
The computational design of transmembrane proteins with more than one membrane-spanning region remains a major challenge. We report the design of transmembrane monomers, homodimers, trimers, and ...tetramers with 76 to 215 residue subunits containing two to four membrane-spanning regions and up to 860 total residues that adopt the target oligomerization state in detergent solution. The designed proteins localize to the plasma membrane in bacteria and in mammalian cells, and magnetic tweezer unfolding experiments in the membrane indicate that they are very stable. Crystal structures of the designed dimer and tetramer-a rocket-shaped structure with a wide cytoplasmic base that funnels into eight transmembrane helices-are very close to the design models. Our results pave the way for the design of multispan membrane proteins with new functions.
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