Crystal Structure of Metal-Dependent Allantoinase from Escherichia coli

Allantoinase acts as a key enzyme for the biogenesis and degradation of ureides by catalyzing the conversion of (S)-allantoin into allantoate, the final step in the ureide pathway. Despite limited sequence similarity, biochemical studies of the enzyme suggested that allantoinase belongs to the amidohydrolase family. In this study, the crystal structure of allantoinase from Escherichia coli was determined at 2.1 Å resolution. The enzyme consists of a homotetramer in which each monomer contains two domains: a pseudo-triosephosphate-isomerase barrel and a β-sheet. Analogous to other enzymes in the amidohydrolase family, allantoinase retains a binuclear metal center in the active site, embedded within the barrel fold. Structural analyses demonstrated that the metal ions in the active site ligate one hydroxide and six residues that are conserved among allantoinases from other organisms. Functional analyses showed that the presence of zinc in the metal center is essential for catalysis and enantioselectivity of substrate. Both the metal center and active site residues Asn94 and Ser317 play crucial roles in dictating enzyme activity. These structural and functional features are distinctively different from those of the metal-independent allantoinase, which was very recently identified.     

Prospective Life Cycle Assessment of Epitaxial Graphene Production at Different Manufacturing Scales and Maturity

Epitaxial growth is a potential production process for the new material graphene, where it is grown on silicon carbide (SiC) wafers at high temperatures. We provide first estimates of the life cycle cumulative energy demand, climate change, terrestrial acidification, and eco‐toxicity of this production. For this purpose, we applied prospective life cycle assessment (LCA) for three production scenarios (lab, pilot, and an industrial scenario), which reflect different production scales and technological maturity. The functional unit was one square centimeter of graphene. Results show that the three scenarios have similar impacts, which goes against previous studies that have suggested a decrease with larger production scale and technological maturity. The reason for this result is the dominance of electricity use in the SiC wafer production for all impacts (>99% in the worst case, >76% in the best case). Only when assuming thinner SiC wafers in the industrial scenario is there a reduction in impacts by around a factor of 10. A surface‐area–based comparison to the life cycle energy use of graphene produced by chemical vapor deposition showed that epitaxial graphene was considerably more energy intensive—approximately a factor of 1,000. We recommend producers of epitaxial graphene to investigate the feasibility of thinner SiC wafers and use electricity based on wind, solar, or hydropower. The main methodological recommendation from the study is to achieve a temporal robustness of LCA studies of emerging technologies, which includes the consideration of different background systems and differences in production scale and technological maturity.     

Very High Surface Capacity Observed Using Si Negative Electrodes Embedded in Copper Foam as 3D Current Collectors

Cu foam is evaluated as a replacement for metal foil current collectors to create 3D composite electrodes with the objective to produce Si‐based anodes with high loadings. The electrodes are prepared by casting the slurry into the porosity of the foam. With such a design, the loading and the surface capacity can reach values as high as 10 mg cm^?2 and 10 mAh cm^?2. Compared to the common 2D design, the 3D copper framework shows a great advantage in the cycle life (more than 400 cycles at a Si loading of 10 mg cm^?2 with commercial micrometric particles) and power performance. The thinness of the composite coating on the foam walls favors a better preservation of the electronic wiring upon cycling and fast lithium ion diffusion. A higher coulombic efficiency in half cells with lithium metal as the counter electrode is achieved by using carbon nanofibers (CNF) rather than carbon black (CB). The possibility to reach, in practice, higher surface capacity could allow a significant increase in both the volumetric and gravimetric energy densities by 23% and 19%, respectively, for the Cu foam‐silicon//LiFePO₄ stack compared to the graphite/LiFePO₄ stack of traditional design.     

Uptake and Toxicity of Arsenic,Copper, and Silicon in Azolla caroliniana and Lemna minor

Here we report on the analysis of two aquatic plant species, Azolla caroliniana and Lemna minor, with respect to tolerance and uptake of co-occurring arsenic, copper, and silicon for use in engineered wetlands. Plants were cultured in nutrient solution that was amended with arsenic (0 or 20 μM), copper (2 or 78 μM), and silicon (0 or 1.8 mM) either singly or in combination. We hypothesized that arsenic and copper would negatively affect the uptake of metals, growth, and pigmentation and that silicon would mitigate those stresses. Tolerance was assessed by measuring growth of biomass and concentrations of chlorophyll and anthocyanins. Both plant species accumulated arsenic, copper, and silicon; L. minor generally had higher levels on a per biomass basis. Arsenic negatively impacted A. caroliniana, causing a 30% decrease in biomass production and an increase in the concentration of anthocyanin. Copper negatively impacted L. minor, causing a 60% decrease in biomass production and a 45% decrease in chlorophyll content. Silicon augmented the impact of arsenic on biomass production in A. caroliniana but mitigated the effect of copper on L. minor. Our results suggest that mixtures of plant species may be needed to maximize uptake of multiple contaminants in engineered wetlands.     

施硅提高水稻叶片对紫外线胁迫的抗性

采用加硅与缺硅营养液培养的方法,首次研究证明硅能提高水稻(Oryza sativa L.)叶片抗紫外线胁迫的能力.结果表明,在紫外胁迫条件下,缺硅水稻叶片表面出现明显的棕色伤害斑点,而加硅叶片未出现伤害症状.硅在水稻表皮细胞壁及细胞内部的积累明显促进了紫外吸收物质在表皮细胞中的聚集,使表皮中可溶性酚类物质含量提高17%,不溶性紫外吸收物质的含量增加65%左右.荧光显微镜观察表明,在表皮细胞外壁或胞内沉积的水合二氧化硅固体中包含着大量不溶性的酚类化合物,它们与可溶性酚类物质一起在叶片的上、下表皮细胞中形成了吸收紫外线的屏障.     

喷施硅对蒙古黄芪抗氧化酶活性以及产量和品质的影响北大核心CSCD

以蒙古黄芪为试验材料,设置大田随机区组试验,研究苗期、开花期和根茎伸长期叶面喷施不同浓度硅(500、1000、2000和4000 mg/L)对蒙古黄芪生长发育、抗氧化酶活性、药材产量和品质的影响,并检测施硅对黄芪白粉病、根腐病的防治效果,以揭示硅对增强黄芪抗病性、提升品质和产量的影响机理,为生产中蒙古黄芪的高效栽培提供理论依据。结果表明:(1)在不同生育时期,喷施不同浓度硅能增加蒙古黄芪株高、茎粗、株幅和叶绿素含量,促进蒙古黄芪生长,并以2000 mg/L硅处理效果较佳。(2)不同生育时期喷施硅能提高蒙古黄芪叶片SOD、CAT、POD和APX等抗氧化酶活性,降低MDA含量,以开花期、根茎伸长期2000 mg/L硅处理较佳。(3)施硅能有效降低蒙古黄芪白粉病、根腐病的病情指数,当施硅浓度为2000 mg/L时防效均达到最高,并分别达到47.05%和39.08%。(4)施硅处理能有效提高蒙古黄芪单株干、鲜生物量、产量以及可溶性浸出物和黄芪甲苷含量等品质指标,并在2000 mg/L硅浓度处理下均达到最佳水平,此时可溶性浸出物和黄芪甲苷含量分别比对照显著提高了16.48%和31.96%。研究发现,叶面喷施适宜浓度硅可显著增强蒙古黄芪对白粉病、根腐病的抗性,促进植株生长,进而显著提高药材产量,改善药材品质,并以硅浓度为2000 mg/L时效果最佳。     

UNCOUPLING OF SILICON COMPARED WITH CARBON AND NITROGEN METABOLISMS AND THE ROLE OF THE CELL CYCLE IN CONTINUOUS CULTURES OF THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE) UNDER LIGHT,NITROGEN, AND PHOSPHORUS CONTROL1

The elemental composition and the cell cycle stages of the marine diatom Thalassiosira pseudonana Hasle and Heimdal were studied in continuous cultures over a range of different light‐ (E), nitrogen‐ (N), and phosphorus‐ (P) limited growth rates. In all growth conditions investigated, the decrease in the growth rate was linked with a higher relative contribution of the G2+M phase. The other phases of the cell cycle, G1 and S, showed different patterns, depending on the type of limitation. All experiments showed a highly significant increase in the amount of biogenic silica per cell and per cell surface with decreasing growth rates. At low growth rates, the G2+M elongation allowed an increase of the silicification of the cells. This pattern could be explained by the major uptake of silicon during the G2+M phase and by the independence of this process on the requirements of the other elements. This was illustrated by the elemental ratios Si/C and Si/N that increased from 2‐ to 6‐fold, depending of the type of limitation, whereas the C/N ratio decreased by 10% (E limitation) or increased by 50% (P limitation). The variations of the ratios clearly demonstrate the uncoupling of the Si metabolism compared with the C and N metabolisms. This uncoupling enabled us to explain that in any of the growth condition investigated, the silicification of the cells increased at low growth rates, whereas carbon and nitrogen cellular content are differently regulated, depending of the growth conditions.     

Designing Active and Stable Silicon Photocathodes for Solar Hydrogen Production Using Molybdenum Sulfide Nanomaterials

Silicon is a promising photocathode for tandem photoelectrochemical water splitting devices, but efficient catalysis and long term stability remain key challenges. Here, it is demonstrated that with appropriately engineered interfaces, molybdenum sulfide nanomaterials can provide both corrosion protection and catalytic activity in silicon photocathodes. Using a thin MoS₂ surface protecting layer, MoS₂‐n⁺p Si electrodes that show no loss in performance after 100 h of operation are created. Transmission electron microscopy measurements show the atomic structure of the device surface and reveal the characteristics of the MoS₂ layer that provide both catalytic activity and excellent stability. In spite of a low concentration of exposed catalytically active sites, these electrodes possess the best performance of any precious metal‐free silicon photocathodes with demonstrated long term stability to date. To further improve efficiency, a second molybdenum sulfide nanomaterial, highly catalytically active [Mo₃S₁₃]^2? clusters, is incorporated. These photocathodes offer a promising pathway towards sustainable hydrogen production.     

Corrugation Enabled Asymmetrically Ultrastretchable (95%) Monocrystalline Silicon Solar Cells with High Efficiency (19%)

Stretchable solar cells are of growing interest due their key role in realizing many applications such as wearables and biomedical devices. Ultrastretchability, high energy‐efficiency, biocompatibility, and mechanical resilience are essential characteristics of such energy harvesting devices. Here, the development of wafer‐scale monocrystalline silicon solar cells with world‐record ultrastretchability (95%) and efficiency (19%) is demonstrated using a laser‐patterning based corrugation technique. The demonstrated approach transforms interdigitated back contacts (IBC) based rigid solar cells into mechanically reliable but ultrastretchable cells with negligible degradation in the electric performance in terms of current density, open‐circuit voltage, and fill factor. The corrugation method is based on the creation of alternating grooves resulting in silicon islands with different shapes. The stretchability is achieved by orthogonally aligning the active silicon islands to the applied tensile stress and using a biocompatible elastomer (Ecoflex) as a stretchable substrate. The resulting mechanics ensure that the brittle silicon areas do not experience significant mechanical stresses upon asymmetrical stretching. Different patterns are studied including linear, diamond, and triangular patterns, each of which results in a different stretchability and loss of active silicon area. Finally, finite element method based simulation is conducted to study the generated deformation in the different patterned solar cells.