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Now showing items 145 - 160 of 446

  • Degumming raw silk by a halotolerant metalloprotease isolated from metabolites of Vibrio sp. LA-05

    Zhang, Hong   Li, Hui   Liu, Haoran   Lang, Dietmar A.   Xu, Hai   Zhu, Hu  

    The crude sample of a halotolerant metalloprotease produced by Vibrio sp. LA-05 was systematically investigated as a silk degumming agent. The experimental results showed that the required time, when the sericin was completely eliminated, varied with the incubation temperatures. The sericin was almost completely removed when raw silk was co-incubated with the crude protease solution (490 U/mL) at 45 degrees C for 3 h. The results of SEM, thermal analyses, tensile properties and regenerated silk fibroin indicated that the properties of silk fibre de gummed with crude protease were superior to those of the traditional Na2CO3 method. Furthermore, SDS-PAGE analyses revealed that the sericin could be hydrolyzed into small peptides by protease during the degumming process. Sericin proteolysis product (SPP) recovered from the protease degumming solution displayed dose dependent ABTS(center dot+) scavenging activity and ferric ion reducing capacity. The antioxidant activity of SPP was significantly better than that of sericin recovered from the Na2CO3 degumming solution. The findings in this study suggest that this halotolerant metalloprotease may be developed to an eco-friendly, energy- and resource-saving silk degumming agent.
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  • Synthesis of gamma-MnOOH nanorods and their isomorphous transformation into beta-MnO2 and alpha-Mn2O3 nanorods

    Zhou, Fu   Zhao, Xuemei   Yuan, Cunguang   Xu, Hai  

    gamma-MnOOH nanorods with different diameters were synthesized by a simple one-step polymer-assisted hydrothermal method using 50% (wt.%) Mn(NO3)(2) solution and PEG-10000 as reagents. The diameters of as-synthesized gamma-MnOOH nanorods were well controlled by simply varying the volume of the 50% Mn(NO3)(2) solution. The calcination behavior of the as-synthesized gamma-MnOOH nanorods was studied. Nanorods of beta-MnO2 and alpha-Mn2O3 were synthesized by calcination at 350 and 600 degrees C for 1 h respectively.
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  • Interfacial assembly of lipopeptide surfactants on octyltrimethoxysilane-modified silica surface.

    Wang, Jiqian   Jia, Donghui   Tao, Kai   Wang, Chengdong   Zhao, Xiubo   Yaseen, Mohammed   Xu, Hai   Que, Guohe   Webster, John R P   Lu, Jian R  

    The adsorption of a series of cationic lipopeptide surfactants, C14Kn (where C14 denotes the myristic acyl chain and Kn represents n number of lysine residues) at the hydrophobic solid/water interface has been studied using spectroscopic ellipsometry (SE) and neutron reflection (NR). The hydrophobic C8 surface was prepared by grafting a monolayer of octyltrimethoxysilane on the silicon surface. SE was used to follow the dynamic adsorption from these lipopeptide surfactants and the amount was found to undergo a fast increase within the first 2-3 min, followed by a much slower process tending to equilibration in the subsequent 15-20 min. Lipopetide surfactants with n =3D 1-4 showed similar dynamic features, indicating that the interaction between the acyl chain and the C8 surface is the main driving force for adsorption. The saturation adsorption amount of C14Kn at the C8/water interface was found to be inversely related to the increasing number of Lys residues in the head group due to the increase of steric hindrance and electrostatic repulsion between the head groups. Solution concentration had a significant effect on the initial adsorption rate, similar to the feature observed from nonionic surfactants CmEn. The structure of the adsorbed layers was studied by NR in conjunction with isotopic contrasts. The layer formed by the head groups of C14K1 was 10 A thick, and those formed by C14K2, C14K3 and C14K4 head groups were all about 13 A thick. In contrast, the thicknesses of the layers formed by hydrophobic tails of C14K1, C14K2 C14K3, and C14K4 were found to be 17, 13, 10, and 10 A, respectively, resulting in the steady increase of area per molecule at the interface from 29 =C2=B1 2 A(2) for C14K1 to 65 =C2=B1 2 A(2) for C14K4. Thus, with an increase in the head group length, the molecules in the adsorbed layer tended to lie down upon adsorption. =20
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  • Thermo-responsive behavior of borinic acid polymers:experimental and molecular dynamics studies

    Wan, Wen-Ming   Zhou, Peng   Cheng, Fei   Sun, Xiao-Li   Lv, Xin-Hu   Li, Kang-Kang   Xu, Hai   Sun, Miao   Jaekle, Frieder  

    The thermo-responsive properties of borinic acid polymers were investigated by experimental and molecular dynamics simulation studies. The homopolymer poly(styrylphenyl(tri-iso-propylphenyl)borinic acid) (PBA) exhibits an upper critical solution temperature (UCST) in polar organic solvents that is tunable over a wide temperature range by addition of small amounts of H2O. The UCST of a 1 mg mL(-1) PBA solution in DMSO can be adjusted from 20 to 100 degrees C by varying the H2O content from similar to 0-2.5%, in DMF from 0 to 100 degrees C (similar to 3-17% H2O content), and in THF from 0 to 60 degrees C (similar to 4-19% H2O). The UCST increases almost linearly from the freezing point of the solvent with higher freezing point to the boiling point of the solvent with the lower boiling point. The mechanistic aspects of this process were investigated by molecular dynamics simulations. The latter indicate rapid and strong hydrogen-bond formation between BOH moieties and H2O molecules, which serve as crosslinkers to form an insoluble network. Our results suggest that borinic acid-containing polymers are promising as new "smart" materials, which display thermo-responsive properties that are tunable over a wide temperature range.
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  • A New Photoresponsive Bis (Crown Ether) for Extraction of Metal Ions

    Liang, Yong   Wang, Xiang   Zhao, Siqi   He, Piao   Luo, Ting   Jiang, Jinzhi   Liang, Wenjie   Cai, Jianfeng   Xu, Hai  

    A new photoresponsive bis (crown ether) 1 was synthesized from carboxylic crown ethers and 4,4 ' - hydroxy azobenzene, and its ability for the extraction of alkali metal, alkaline earth metal, and partial transition metal ions was also studied. Intriguingly, our results showed that the extraction rate of metal ions by compound 1 after light irradiation was generally more efficient than in the ambient light. Particularly, compound 1 displayed excellent selectivity for Sr2+ under UV light irradiation, as a result of the formation of a sandwich complex with metal ions, suggesting its promising potential application to selectively extract strontium ions.
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  • Right-Handed Helical Foldamers Consisting of De Novo D-AApeptides

    Teng, Peng   Ma, Ning   Cerrato, Darrell Cole   She, Fengyu   Odom, Timothy   Wang, Xiang   Ming, Li June   van der Vaart, Arjan   Wojtas, Lukasz   Xu, Hai   Cai, Jianfeng  

    New types of foldamer scaffolds are formidably challenging to design and synthesize, yet highly desirable as structural mimics of peptides/proteins with a wide repertoire of functions. In particular, the development of peptidomimetic helical foldamers holds promise for new biomaterials, catalysts, and drug molecules. Unnatural l-sulfono-gamma-AApeptides were recently developed and shown to have potential applications in both biomedical and material sciences. However, d-sulfono-gamma-AApeptides, the enantiomers of l-sulfono-gamma-AApeptides, have never been studied due to the lack of high-resolution three-dimensional structures to guide structure-based design. Herein, we report the first synthesis and X-ray crystal structures of a series of 2:1 l-amino acid/d-sulfono-gamma-AApeptide hybrid foldamers, and elucidate their folded conformation at the atomic level. Single-crystal X-ray crystallography indicates that this class of oligomers folds into well-defined right-handed helices with unique helical parameters. The helical structures were consistent with data obtained from solution 2D NMR, CD studies, and molecular dynamics simulations. Our findings are expected to inspire the structure-based design of this type of unique folding biopolymers for biomaterials and biomedical applications.
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  • Interaction between Surfactants and SiO2 Nanoparticles in Multiphase Foam and Its Plugging Ability

    Wang, Jiqian   Xue, Guobin   Tian, Baoxue   Li, Songyan   Chen, Kai   Wang, Dong   Sun, Yawei   Xu, Hai   Petkov, Jordan T.   Li, Zhaomin  

    To improve the stability of foam fluids, SiO2 nanoparticles and trace amount of Gemini cationic surfactant were combined with the main foaming agent, nonionic surfactant, to form a tricomponent multiphase foam. The stability of the multiphase foam was assessed through two parameters of half-life time and dilational modulus. The Interaction between surfactants and nanoparticles were studied though surface tension, adsorption amount, and C potential measurement. The effects of saline ions and temperature on foam stability were also investigated. The plugging ability of the tricomponent multiphase foam was assessed using a sandpack model. The optimized tricomponent multiphase foam was 10 times more stable than corresponding foam without nanoparticles in terms of half-life time and also resisted to saline and temperature to a certain degree because the adsorption of nanoparticles at the interface improved the mechanic strength of foam film. The tricomponent multiphase foam showed more excellent plugging ability in porous media than foam without nanoparticles during flooding. The adsorption of cationic surfactant not only changed the surface hydrophobicity of the SiO2 nanoparticles, but also promoted the adsorption of APG molecules. Combined the results of Gemini C12C3C12Br2 replaced by CTAB or SDS, and C12C3C12Br2/SiO2 replaced by pretreated partially hydrophobic SiO2 nanoparticle (H15), it is deduced that the in situ surface modification by cationic adsorption to a suitable hydrophobicity was a key step in multiphase stability. Compared with the pretreated partially hydrophobic SiO2 nanoparticle, more SiO2 nanoparticles were distributed at the air/liquid interface and utilized effectively in the tricomponent multiphase foam.
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  • Quantifying the dependence of cyanobacterial growth to nutrient for the eutrophication management of temperate-subtropical shallow lakes

    Zou, Wei   Zhu, Guangwei   Cai, Yongjiu   Xu, Hai   Zhu, Mengyuan   Gong, Zhijun   Zhang, Yunlin   Qin, Boqiang  

    The increasing global occurrence of cyanobacterial blooms, attributed primarily to human-induced nutrient enrichment, significantly degrades freshwater ecosystems and poses serious risks to human health. The current study examined environmental variables and cyanobacterial biovolume (B-c(yano)) of 28 shallow lakes in the eastern China plains during the spring and summer of 2018. We used a 95% quantile regression model to explore season-specific response of B-c(yano) to total nitrogen (TN), or total phosphorus (TP), and robust linear relationships were observed between log(B-c(yano) +0.001) and log(TN), or log(TP) in both spring and summer periods. Based on these regressions, regional-scale and season-specific TN and TP thresholds are proposed for these lakes to ensure the safety for recreational waters and drinking water source. However, actual B-c(yano) for a given concentration of TN (or TP) for many observations were considerably lower than the results of the 95% regression model predict, indicating that other factors significantly modulated nutrient limitation of B-c(yano). Generalized additive model and quantile regression model were used together to explore potentially significant modulating factors, of which lake retention time, macrophytes cover and N: P ratio were identified as most important. Thus, it is necessary to develop type-specific nutrient thresholds with the consideration of these significant modulating factors. Furthermore, nutrient-B-c(yano) relationships of our studied lakes with lake retention time>100 days and no macrophyte were further explored and nutrient thresholds of this lake type were proposed. Nutrient thresholds proposed in this study may play an essential role in achieving a cost-effective eutrophication management for shallow lakes both in the eastern China plains and elsewhere with similar climatic background. On a broader scale, the approaches and findings of this study may provide valuable reference to formulate reasonable nutrient reduction targets for other ecoregions with different climatic conditions. (C) 2020 Elsevier Ltd. All rights reserved.
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  • Automation of the bao steel works hot strip mill : D. Lindhoff, Xu Hai Hong, Wang Wen Rui, Zhang Jian Ping, pp 133–139

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  • Steering graphene quantum dots in living cells:lighting up the nucleolus

    Wang, Xiaojuan   Wang, Yanan   He, Hua   Chen, Xin   Sun, Xing   Sun, Yawei   Zhou, Guangjun   Xu, Hai   Huang, Fang  

    The nucleolus is an important subnuclear structure and there are very few dyes available in the market for nucleolar imaging. Subcellular organelles delivery presents a common stumbling block for many nanomaterial-based applications, including intracellular structure fluorescence staining. We now introduce a novel luminescent graphene quantum dot (nGQD), which is able to selectively light up the nucleoli of living cells, to address these challenges. Investigations on subcellular localization of different GQDs have demonstrated that the positively charged surface and the ultra-small size are the key parameters for nucleoli-rich distribution of nanomaterials, which is of importance for transferring this strategy to other nanoparticles. The novel nGQD has great potential to be applied as a nucleolar stain or an efficient gene/drug carrier.
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  • Solubilization and Stabilization of Isolated Photosystem I Complex with Lipopeptide Detergents

    Wang, Xiaoqiang   Huang, Guihong   Yu, Daoyong   Ge, Baosheng   Wang, Jiqian   Xu, Fengxi   Huang, Fang   Xu, Hai   Lu, Jian R.  

    It is difficult to maintain a target membrane protein in a soluble and functional form in aqueous solution without biological membranes. Use of surfactants can improve solubility, but it remains challenging to identify adequate surfactants that can improve solubility without damaging their native structures and biological functions. Here we report the use of a new class of lipopeptides to solubilize photosystem I (PS-I), a well known membrane protein complex. Changes in the molecular structure of these surfactants affected their amphiphilicity and the goal of this work was to exploit a delicate balance between detergency and biomimetic performance in PS-I solubilization via their binding capacity. Meanwhile, the effects of these surfactants on the thermal and structural stability and functionality of PS-I in aqueous solution were investigated by circular dichroism, fluorescence spectroscopy, SDS-PAGE analysis and O-2 uptake measurements, respectively. Our studies showed that the solubility of PS-I depended on both the polarity and charge in the hydrophilic head of the lipopeptides and the length of its hydrophobic tail. The best performing lipopeptides in favour of PS-I solubility turned out to be C14DK and C16DK, which were comparable to the optimal amphiphilicity of the conventional chemical surfactants tested. Lipopeptides showed obvious advantages in enhancing PS-I thermostability over sugar surfactant DDM and some full peptide amphiphiles reported previously. Fluorescence spectroscopy along with SDS-PAGE analysis demonstrated that lipopeptides did not undermine the polypeptide composition and conformation of PS-I after solubilization; instead they showed better performance in improving the structural stability and integrity of this multi-subunit membrane protein than conventional detergents. Furthermore, O-2 uptake measurements indicated that PS-I solubilized with lipopeptides maintained its functionality. The underlying mechanism for the favorable actions of lipopeptide in PS-I solubilization and stabilization is discussed.
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  • Controlling harmful cyanobacterial blooms in a hyper-eutrophic lake (Lake Taihu, China): The need for a dual nutrient (N & P) management strategy

    Paerl, Hans W.   Xu, Hai   McCarthy, Mark J.   Zhu, Guangwei   Qin, Boqiang   Li, Yiping   Gardner, Wayne S.  

    Harmful cyanobacterial blooms, reflecting advanced eutrophication, are spreading globally and threaten the sustainability of freshwater ecosystems. Increasingly, non-nitrogen (N(2))-fixing cyanobacteria (e.g., Microcystis) dominate such blooms, indicating that both excessive nitrogen (N) and phosphorus (P) loads may be responsible for their proliferation. Traditionally, watershed nutrient management efforts to control these blooms have focused on reducing P inputs. However, N loading has increased dramatically in many watersheds, promoting blooms of non-N(2) fixers, and altering lake nutrient budgets and cycling characteristics. We examined this proliferating water quality problem in Lake Taihu, China's 3rd largest freshwater lake. This shallow, hyper-eutrophic lake has changed from bloom-free to bloom-plagued conditions over the past 3 decades. Toxic Microcystis spp. blooms threaten the use of the lake for drinking water, fisheries and recreational purposes. Nutrient addition bioassays indicated that the lake shifts from P limitation in winter-spring to N limitation in cyanobacteria-dominated summer and fall months. Combined N and P additions led to maximum stimulation of growth. Despite summer N limitation and P availability, non-N(2) fixing blooms prevailed. Nitrogen cycling studies, combined with N input estimates, indicate that Microcystis thrives on both newly supplied and previously-loaded N sources to maintain its dominance. Denitrification did not relieve the lake of excessive N inputs. Results point to the need to reduce both N and P inputs for long-term eutrophication and cyanobacterial bloom control in this hyper-eutrophic system. (C) 2010 Elsevier Ltd. All rights reserved.
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  • Preparation of porous silica ceramics with relatively high strength by a TBA-based gel-casting method

    Xu, Hai   Liu, Jiachen   Du, Haiyan   Guo, Anran   Hou, Zhenguang  

    Porous silica ceramics with relatively high mechanical strength can be successfully fabricated via a novel tert-butyl alcohol-based gel-casting method. The microstructure similar to stone arch bridges and the sintering neck can be easily observed clue to the evaporation of tert-butyl alcohol (TBA) during the drying process. The porosity of samples with different solid loading sintered at 1150 degrees C varied within the range of 56.4% and 70.1%, as the bulk density from 0.67 to 1.04 g/cm(3). The compressive strength of sintered silica ceramics increased from 4.32 MPa to 8.82 MPa, which was attributed to the 3D-framework structure and the connection of silica particles. By setting the solid loading (15 wt.%) and changing the sintering temperature from 1050 to 1200 C, the porosity of the sintered samples varied within the range of 51% and 72.4%, as the bulk density remarkably varied from 0.59 to 1.18 g/cm(3) and pore sizes from 3.31 to 2.89 nm. (C) 2011 Elsevier B.V. All rights reserved.
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  • Spatial and temporal variations of Rb/Sr ratios of the bulk surface sediments in Lake Qinghai.

    Xu, Hai   Liu, Bin   Wu, Feng  

    The Rb/Sr ratios of lake sediments have been suggested as indicators of weathering intensity by increasing work. However, the geochemistry of Rb/Sr ratios of lake sediments is variable between different lakes. In this study, we investigated the spatial and temporal patterns of Rb/Sr ratios, as well as those of other major elements in surface sediments of Lake Qinghai. We find that the spatial pattern of Rb/Sr ratios of the bulk sediments correlates well with that of the mass accumulation rate, and those of the terrigenous fractions, e.g., SiO2, Ti, and Fe. The temporal variations of Rb/Sr ratios also synchronize with those of SiO2, Ti, and Fe of each individual core. These suggest that Rb/Sr ratios of the surface sediments are closely related to terrigenous input from the catchment. Two out of eight cores show similar trends between Rb/Sr ratios and precipitation indices on decadal scales; however, the other cores do not show such relationship. The result of this study suggests that physical weathering and chemical weathering in Lake Qinghai catchment have opposite influence on Rb/Sr ratios of the bulk sediments, and they compete in dominating the Rb/Sr ratios of lake sediments on different spatial and temporal scales. Therefore, it is necessary to study the geochemistry of Rb/Sr ratio of lake sediments (especially that on short term timescales) particularly before it is used as an indicator of weathering intensity of the catchment.
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  • Chemical Vapor Deposition of Large-Size Monolayer MoSe2 Crystals on Molten Glass

    Chen, Jianyi   Zhao, Xiaoxu   Tan, Sherman J. R.   Xu, Hai   Wu, Bo   Liu, Bo   Fu, Deyi   Fu, Wei   Geng, Dechao   Liu, Yanpeng   Liu, Wei   Tang, Wei   Li, Linjun   Zhou, Wu   Sum, Tze Chien   Loh, Kian Ping  

    We report the fast growth of high-quality millimeter-size monolayer MoSe2 crystals on molten glass using an ambient pressure CVD system. We found that the isotropic surface of molten glass suppresses nucleation events and greatly improves the growth of large crystalline domains. Triangular monolayer MoSe2 crystals with sizes reaching 2.5 mm, and with a room-temperature carrier mobility up to 95 cm2(/)(V.s), can be synthesized in 5 min. The method can also be used to synthesize millimeter-size monolayer MoS2 crystals. Our results demonstrate that "liquid-state" glass is a highly promising substrate for the low-cost growth of high-quality large-size 2D transition metal dichalcogenides (TMDs).
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  • Arid Central Asia saw mid-Holocene drought

    Xu, Hai   Zhou, Kang'en   Lan, Jianghu   Zhang, Guilin   Zhou, Xinying  

    The mid-Holocene hydroclimates and the forcing mechanisms over arid Central Asia (ACA) are hotly debated in the context of global climate change. It is widely assumed that ACA Holocene precipitation broadly followed and/or was out-of-phase with Northern Hemisphere solar insolation. However, here we show a broadly antiphase relationship between Holocene boreal solar insolation and ACA hydroclimatic trend revealed from a well-dated peat core (at the Big Black peatland; BBP) in northwestern China, southern Altai Mountains. Multiple-proxies, including peat development rate, pollen assemblages, and peat cellulose isotopic records, show wet conditions during the early and late Holocene, but drought condition during the midHolocene. This hydroclimatic pattern is similar to those extracted from other peatlands nearby and those inferred from sedimentary records in lakes in adjacent regions. The trend of delta O-18 in BBP peat cellulose is similar to that of a stalagmite in northern Xinjiang, both of which record the Holocene atmospheric precipitation delta O-18 trend over ACA areas and possibly suggest a changing proportion of glacier meltwater supply. We speculate that the mid-Holocene drought over ACA could be ascribed to: (1) the northward movement of the westerlies, such that when the westerlies moved northward under warm conditions, less water vapor was transported to ACA, and vice versa, and (2) increased evaporation under mid-Holocene warm conditions. The data from this study and the potential mechanisms suggest that drier conditions are expected over ACA areas under a continuous global warming expectation.
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