| 1. |
- Bjelic, Sinisa, et al.
(författare)
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Exploration of Alternate Catalytic Mechanisms and Optimization Strategies for Retroaldolase Design
- 2014
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Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 426:1, s. 256-271
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Tidskriftsartikel (refereegranskat)abstract
- Designed retroaldolases have utilized a nucleophilic lysine to promote carbon-carbon bond cleavage of β-hydroxy-ketones via a covalent Schiff base intermediate. Previous computational designs have incorporated a water molecule to facilitate formation and breakdown of the carbinolamine intermediate to give the Schiff base and to function as a general acid/base. Here we investigate an alternative active-site design in which the catalytic water molecule was replaced by the side chain of a glutamic acid. Five out of seven designs expressed solubly and exhibited catalytic efficiencies similar to previously designed retroaldolases for the conversion of 4-hydroxy-4-(6-methoxy-2-naphthyl)-2-butanone to 6-methoxy-2-naphthaldehyde and acetone. After one round of site-directed saturation mutagenesis, improved variants of the two best designs, RA114 and RA117, exhibited among the highest kcat (>10(-3)s(-1)) and kcat/KM (11-25M(-1)s(-1)) values observed for retroaldolase designs prior to comprehensive directed evolution. In both cases, the >10(5)-fold rate accelerations that were achieved are within 1-3 orders of magnitude of the rate enhancements reported for the best catalysts for related reactions, including catalytic antibodies (kcat/kuncat=10(6) to 10(8)) and an extensively evolved computational design (kcat/kuncat>10(7)). The catalytic sites, revealed by X-ray structures of optimized versions of the two active designs, are in close agreement with the design models except for the catalytic lysine in RA114. We further improved the variants by computational remodeling of the loops and yeast display selection for reactivity of the catalytic lysine with a diketone probe, obtaining an additional order of magnitude enhancement in activity with both approaches.
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| 2. |
- Hou, Xiao-Qing, et al.
(författare)
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Functional Evolution of a Bark Beetle Odorant Receptor Clade Detecting Monoterpenoids of Different Ecological Origins
- 2021
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Ingår i: Molecular biology and evolution. - : Oxford University Press. - 0737-4038 .- 1537-1719. ; 38:11, s. 4934-4947
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Tidskriftsartikel (refereegranskat)abstract
- Insects detect odors using an array of odorant receptors (ORs), which may expand through gene duplication. How and which new functions may evolve among related ORs within a species remain poorly investigated. We addressed this question by functionally characterizing ORs from the Eurasian spruce bark beetle Ips typographus, in which physiological and behavioral responses to pheromones, volatiles from host and nonhost trees, and fungal symbionts are well described. In contrast, knowledge of OR function is restricted to two receptors detecting the pheromone compounds (S)-(-)-ipsenol (ItypOR46) and (R)-(-)-ipsdienol (ItypOR49). These receptors belong to an Ips-specific OR-lineage comprising seven ItypORs. To gain insight into the functional evolution of related ORs, we characterized the five remaining ORs in this Glade using Xenopus oocytes. Two receptors responded primarily to the host tree monoterpenes (+)-3-carene (ItypOR25) and p-cymene (ItypOR27). Two receptors responded to oxygenated monoterpenoids produced in larger relative amounts by the beetle-associated fungi, with ItypOR23 specific for (+)-trans-(1R, 4S)-4-thujanol, and ItypOR29 responding to (+)-isopinocamphone and similar ketones. ItypOR28 responded to the pheromone E-myrcenol from the competitor Ips duplicatus. Overall, the OR responses match well with those of previously characterized olfactory sensory neuron classes except that neurons detecting E-myrcenol have not been identified. The characterized ORs are under strong purifying selection and demonstrate a shared functional property in that they all primarily respond to monoterpenoids. The variation in functional groups among OR ligands and their diverse ecological origins suggest that neofunctionalization has occurred early in the evolution of this OR-lineage following gene duplication.
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| 3. |
- Li, Zichuan, et al.
(författare)
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Impacts of silicon on biogeochemical cycles of carbon and nutrients in croplands
- 2018
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Ingår i: Journal of Integrative Agriculture. - : Elsevier. - 2095-3119. ; 17:10, s. 2182-2195
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Forskningsöversikt (refereegranskat)abstract
- Crop harvesting and residue removal from croplands often result in imbalanced biogeochemical cycles of carbon and nutrients in croplands, putting forward an austere challenge to sustainable agricultural production. As a beneficial element, silicon(Si) has multiple eco-physiological functions, which could help crops to acclimatize their unfavorable habitats. Although many studies have reported that the application of Si can alleviate multiple abiotic and biotic stresses and increase biomass accumulation, the effects of Si on carbon immobilization and nutrients uptake into plants in croplands have not yet been explored. This review focused on Si-associated regulation of plant carbon accumulation, lignin biosynthesis, and nutrients uptake, which are important for biogeochemical cycles of carbon and nutrients in croplands. The tradeoff analysis the supply of bioavailable Si can enhance plant net photosynthetic rate and biomass carbon production (especially root biomass input to soil organic carbon pool), but reduce shoot lignin biosynthesis. Besides, the application of Si could improve uptake of most nutrients under deficient conditions, but restricts excess uptake when they are supplied in surplus amounts. Nevertheless, Si application to crops may enhance the uptake of nitrogen and iron when they are supplied in deficient to luxurious amounts, while potassium uptake enhanced by Si application is often involved in alleviating salt stress and inhibiting excess sodium uptake in plants. More importantly, the amount of Si accumulated in plant positively correlates with nutrients release during the decay of crop biomass, but negatively correlates with straw decomposability due to the reduced lignin synthesis. The Si-mediated plant growth and litter decomposition collectively suggest that Si cycling in croplands plays important roles in biogeochemical cycles of carbon and nutrients. Hence, scientific Si management in croplands will be helpful for maintaining sustainable development of agriculture.
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| 4. |
- Lin, Ci, et al.
(författare)
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Improving photocatalytic hydrogen generation of g-C3N4 via efficient charge separation imposed by Bi2O2Se nanosheets
- 2024
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- Enabling highly efficient photocatalytic hydrogen production from solar-driven water splitting is of immense potential and environmental significance. However, the crucial issue of the low utilization efficiency of photogenerated charges in most photocatalysts, such as polymeric graphitic carbon nitride, g-C3N4 (CN), hampers the overall photocatalytic activity and hinders practical applications. To surmount this parasitic phenomenon, we develop a heterojunction-based strategy that improves the charge separation efficiency in CN. The heterostructure is constructed between thermally exfoliated CN and liquid phase exfoliated Bi2O2Se (BOS) via a solution-phase, electrostatically driven self-assembly process. The properly aligned band positions between the two components create a built-in electric field, which endows the composite with an enhanced charge separation efficiency. The optimized Pt-deposited heterostructure photocatalyst exhibits a hydrogen production rate of 6481 μmol h−1 g−1, and an apparent quantum efficiency of 11.65% at 420 nm, compared to those of Pt-deposited ECN (4595 μmol h−1 g−1, 6.64 %). We validate the efficient charge separation effect and the prolonged lifetime of photogenerated carriers in the heterostructure using a series of comprehensive characterizations across multiple timescales, thus, elucidating the origin of the observed photocatalytic activity. This demonstration offers valuable insights into improving the utilization efficiency of photogenerated charges for photocatalysis by heterostructure engineering with materials of distinct electronic configurations.
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| 5. |
- Sun, Yuanhao, et al.
(författare)
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Pollen-based reconstruction of total land-cover change over the Holocene in the temperate steppe region of China : An attempt to quantify the cover of vegetation and bare ground in the past using a novel approach
- 2022
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Ingår i: Catena (Cremlingen. Print). - : Elsevier. - 0341-8162 .- 1872-6887. ; 214
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Tidskriftsartikel (refereegranskat)abstract
- Fossil pollen data are essential for reconstructing ancient vegetation and land-cover changes. Sugita's REVEALS model is the best method to estimate regional plant cover (in percentage cover) using pollen data from lakes. Such reconstructions imply that the sum of all plants' cover is 100%. However, land cover is not always represented by vegetation alone, the area of bare ground can be significant in many types of biomes, e.g., in alpine or steppe regions. Here we define "total land cover " as the sum of vegetation cover (VegC) and bare ground (BareC). In this study, we use the relationship between tree pollen percentages and both tree cover (TreeC) and VegC (=TreeC + herb cover (HerbC)) based on a dataset of modern pollen assemblages and related total land cover. This relationship is applied to estimate past "actual " vegetation cover (a-VegC) from fossil pollen percentages using the Modern Analogue Technique (MAT). The REVEALS (RV) model can then be applied to the same fossil pollen records to estimate regional cover of individual plant taxa (RV PlantC; e.g., RV PinusC, etc.), total tree cover (RV-TreeC) and total herb cover (RV-HerbC). These cover values can then be converted into RV aPlantC, RV a-TreeC and RV a-HerbC using the MAT-reconstructed a-VegC (e.g., RV PinusC x MAT a-VegC = RV aPinusC; RV-TreeC x MAT a-VegC = RV a-TreeC, etc.). The results of leave-one-out cross-validation indicates that the MAT reconstructions using the modern pollen assemblages provide values of a-TreeC, a-HerbC and BareC mostly very similar to the modern vegetation data. We further tested the method using pollen assemblages from lake surface sediments of 11 lakes and the results also suggest a good performance of MAT-based reconstruction. We then applied the proposed method (MAT-REVEALS) to four Holocene pollen records available from the study area to evaluate the feasibility of the strategy to reconstruct past actual plant cover. The results suggest that the method provides plausible estimates of vegetation cover for the sub-regions within the study area. The results from Lake Daihai over the last 10,000 years BP are interpreted and discussed in more details to evaluate the effects of possible departures from the approach assumptions.
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| 6. |
- Wan, Qiuchi, et al.
(författare)
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Evaluating quantitative pollen representation of vegetation in the tropics : A case study on the Hainan Island, tropical China
- 2020
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Ingår i: Ecological Indicators. - : Elsevier. - 1470-160X .- 1872-7034. ; 114, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- Complex pollen-vegetation relationships in tropical environments have long been a challenge for the interpretation of pollen spectra in terms of vegetation cover. Here, we test the application of the widely-used Extended R-Value (ERV) model in the tropical secondary and planted woodlands of the Hainan Island (China) to estimate relative pollen productivities (RPPs) for common plant taxa occurring as pollen in surface and fossil samples of the region. We collected pollen (soil samples) and related vegetation data within 1500 m radius at 23 random distributed sites within an area of 50 km x 100 km. We found a large difference between the modern pollen assemblages and the related vegetation composition in terms of number and dominance of taxa. We tested the three existing ERV sub-models and three methods to distance-weight vegetation cover, i.e. 1/d, the Prentice's model (using a Gaussian Plume dispersal model, GPM), and the Lagrangian stochastic dispersal model (LSM). The LSM appears to be inappropriate for our dataset. The combination of ERV sub-model 2 and Prentice's model using nine anemophilous and zoophilous (or with "messy" pollination syndrome) taxa was found to provide the best results. The relevant source area of pollen (RSAP) of the soil samples was estimated to ca. 1000-1500 m. The ranking of RPPs is as follows: Castanopsis-Lithocarpus (19.44 +/- 0.17) Asteraceae (8.74 +/- 0.05) > Moraceae (6.52 +/- 0.08) > Euphorbiaceae (5.22 +/- 0.1) > Papilionaceae (2.66 +/- 0.05) > Mallotus-Macaranga (2.21 +/- 0.08) > Anacardiaceae (1.77 +/- 0.04) > Rubiaceae (1.29 +/- 0.02) > Poaceae (=1). Violation of the ERV model assumptions of anemophily and stationarity of vegetation composition influenced the performance of the ERV analysis in this study and implied careful evaluation of the results. Nevertheless, the obtained RPPs are considered reliable and will allow to quantify the relative cover of the nine plant taxa in the past. Further studies of this kind will be worthwhile to obtain additional RPP values for a larger number of tropical taxa, even though quantification of past plant cover in the tropics will remain a challenge. The numerous zoophilous taxa may either be absent of the pollen record, or exhibit pollen-vegetation relationships for which the ERV-model is not successful in estimating RPPs. These plant taxa will require other approaches for their quantification in the past.
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| 7. |
- Xiao, Zefang, et al.
(författare)
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Effects of chemical modification with glutaraldehyde on the weathering performance of Scots pine sapwood
- 2012
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Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 46:4, s. 749-767
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Tidskriftsartikel (refereegranskat)abstract
- Scots pine sapwood was treated with glutaraldehyde (GA) in aqueous solution using magnesium chloride as a catalyst in order to evaluate the durability towards weathering. Infrared spectroscopy suggested that GA treatment increased the photo-stability of lignin during artificial weathering of micro-veneers in a QUV over 168 h; photo-protection increased with increasing GA concentration. In comparison with the unmodified controls, GA-modified pine micro-veneer strips exhibited a lower tensile strength loss measured in a zero-span mode in the course of weathering. During 18 months of outdoor exposure, GA-modified pine wood boards exhibited a lower moisture content and water uptake than the unmodified ones. GA treatment also clearly restricted the penetration of blue stain fungi into deeper layers of wood. On the macroscopic scale, the surface of the GA-modified boards was significantly smoother due to less erosion, cracking and minor peeling of tracheids. Scanning electron microscopy further revealed that individual tracheids were detached from the cell compound and then washed away from the unmodified wood surface, whereas tracheids on surfaces of GA-modified wood remained in the tissue compound but displayed many axial and transversal cracks.
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| 8. |
- Xie, S., et al.
(författare)
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A re-assessment of metal pollution in the Dexing mining area in Jiangxi province, China : current status, hydro-geochemical controls, and effectiveness of remediation practices
- 2022
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Ingår i: International Journal of Environmental Science and Technology. - : Springer Nature. - 1735-1472 .- 1735-2630. ; 19, s. 10707-10722
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Tidskriftsartikel (refereegranskat)abstract
- This study re-assess the environmental impacts of the Dexing copper mine (the largest open-pit copper mine in Asia) on the Lean river and its two tributaries (the Dawu river and Jishui river) in the Jiangxi province, China, with particular focus on metal pollution as well as the effectiveness and side-effects of remediation activities. Results show that the Dawu river and its mixing zone with the Lean river were still heavily influenced by acid mine drainage (AMD) and loaded with elevated levels of metals, in particular Mn, Ni, and Al whose concentrations were frequently above the health-based guideline values. Manganese and Ni in the AMD-impacted waters were predicted to occur as free ions or sulfate and carbonate complexes, and thus highly-toxic to living organisms. Although Al in the AMD-impacted waters was predicted to exist largely as colloidal hydroxides with low bioavailability, abundant formation of such nano-sized particles could impair the respiratory and circulatory systems of aquatic macro-invertebrates. The integration and comparison of the results from the current and previous studies show that the concentrations of several metals (Cu, Zn, and Cd) in the Dawu river decreased significantly after 2011-2012, during which several remediation practices were implemented (e.g., AMD neutralization, excavation of contaminated sediments in impounded rivers, and rehabilitation of mine tailings and open-pit slopes). This provides evidence that these remediation practices have effectively limited the dispersion of metals from the mining area. However, AMD neutralization greatly enhanced the release of sulfate, making the mining area an even more important sulfate source.
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| 9. |
- Xu, Bing, et al.
(författare)
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Financial support for micro and small enterprises : Economic benefit or social responsibility?
- 2020
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Ingår i: Journal of Business Research. - : Elsevier. - 0148-2963 .- 1873-7978. ; 115, s. 266-271
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Tidskriftsartikel (refereegranskat)abstract
- Regarding the financial support provided to micro and small enterprises (MSEs), deciding whether to prioritize economic benefit or social responsibility is a crucial policy choice, especially in developing countries. This paper establishes a new research framework for density of enterprise output value and wages conditional on loans to balance economic benefit (sales revenue) and social responsibility (employee payroll). Using data on 9125 Chinese enterprises from January 2015 to December 2017, this paper shows that loans have a range effect on sales revenue and employee payroll, which ascends gradually to a plateau and eventually descends. Based on this finding, this paper proposes a reallocation scheme. With total loans unchanged, fixed sales revenue can increase employee payroll by 3.8%. Similarly, fixed employee payroll can increase sales revenue by 5.2%. This study not only provides empirical evidence for financially supporting MSEs, but also provides alternative decision support for policy design.
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| 10. |
- Xu, Jingzhe, et al.
(författare)
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Geochemistry of soils derived from black shales in the Ganziping mine area, western Hunan, China
- 2013
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 70:1, s. 175-190
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Tidskriftsartikel (refereegranskat)abstract
- The geochemistry of major and trace elements (including heavy metals and rare earth elements) of the fresh and weathered black shales, and the soils derived from black shales in the Ganziping mine area in western Hunan province (China) were studied using the following techniques: X-ray fluorescence (XRF), inductively coupled plasma mass spectrometer (ICP-MS) and X-ray diffraction (XRD). The results show that the black-shale soils are significantly enriched with Al2O3 and Fe2O3, and depleted of mobile elements CaO, Na2O and K2O. The soils are also highly enriched with heavy metals U, V, Ni, Ba, Cu, Zn and Pb, that may cause potential heavy-metal contamination of the soils. Composition of the soils is homogeneous compared to the weathered black shales, for which the concentrations of major elements except CaO and Na2O, and trace elements except heavy metals (U, V, Ni, Ba, Cu, Zn and Pb) as well as the mobile Sr, show lower variations than in the weathered black shales. Ratios of Zr/Hf, Ta/Nb, Y/Ho, Nd/Sm, and Ti/(Ti + Zr), of the soils are also less variable, with values constantly similar to that of the fresh and weathered black shales correspondingly. Thus, components of the soils are believed to be contributed from the parent black shales through weathering and pedogenesis. It is concluded that the soils were formed by at least two stages of geochemical processes: the early stage of chemical differentiation and the later stage of chemical homogenization. The chemical differentiation that was taken during black-shale weathering might have caused the depletion of CaO and Na2O, and the enrichment of Al2O3 and Fe2O3; while the chemical homogenization that was taken during pedogenesis led to the depletion of SiO2 and K2O, and to the further enrichment of Al2O3 and Fe2O3. The heavy-metal enrichment (contamination) of the soils was then genetically related to the enrichment of Al2O3 and Fe2O3 in the soils.
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