Disruption of the E. coli LptC dimerization interface and characterization of lipopolysaccharide and LptA binding to monomeric LptC

Lipopolysaccharide (LPS) is an essential element of nearly all Gram‐negative bacterial outer membranes and serves to protect the cell from adverse environmental stresses. Seven members of the lipopolysaccharide transport (Lpt) protein family function together to transport LPS from the inner membrane (IM) to the outer leaflet of the outer membrane of bacteria such as Escherichia coli. Each of these proteins has a solved crystal structure, including LptC, which is a largely periplasmic protein that is associated with the IM LptB₂FG complex and anchored to the membrane by an N‐terminal helix. LptC directly binds LPS and is hypothesized to be involved in the transfer of LPS to another periplasmic protein, LptA. Purified and in solution, LptC forms a dimer. Here, point mutations designed to disrupt formation of the dimer are characterized using site‐directed spin labeling double electron electron resonance (DEER) spectroscopy, light scattering, circular dichroism, and computational modeling. The computational studies reveal the molecular interactions that drive dimerization of LptC and elucidate how the disruptive mutations change this interaction, while the DEER and light scattering studies identify which mutants disrupt the dimer. And, using electron paramagnetic resonance spectroscopy and comparing the results to the previous quantitative characterization of the interactions between dimeric LptC and LPS and LptA, the functional consequences of monomeric LptC were also determined. These results indicate that disruption of the dimer does not affect LPS or LptA binding and that monomeric LptC binds LPS and LptA at levels similar to dimeric LptC.     

城市绿地对热岛效应缓解作用研究——以保定市中心城区为例

随着中国城镇化建设的进行,城市热岛效应逐渐成为城市发展的显著问题之一,而城市绿地能有效地缓解城市热岛效应,在城市规划中,可以通过对城市绿地进行合理布局,从而减缓城市热岛效应的影响。本文采用遥感数据反演的方法,综合应用地理信息系统（GIS）和遥感（RS）技术,得到不同时期保定市中心城区地表温度和植被覆盖度的时空演变图,分析近10年的时空演变规律,并用网格法对植被覆盖度与地表温度之间的耦合关系进行研究,得出研究区内的植被覆盖度每增加10%,其地表的平均温度可减少0.9℃~1.3℃。选取研究区域内的8个城市绿地,利用缓冲区分析的方法,定量研究城市绿地面积与其降温范围之间的关系,结合保定市热岛效应集中区域及周边土地利用现状,提出增加城市绿地的可能位置,为城市绿地布局提供科学依据。     

Efficient Solar‐Driven Water Oxidation over Perovskite‐Type BaNbO2N Photoanodes Absorbing Visible Light up to 740 nm

Photoelectrochemical water splitting using semiconductors absorbing a wide range of visible light is a potentially attractive means of harvesting large portions of the solar spectrum. However, this is also very challenging because narrowing the semiconductor band gap lowers the driving force for photoreactions. Herein, a highly active perovskite BaNbO₂N exhibiting photoexcitation up to 740 nm for water oxidation is reported. The synthesis route, consisting of moderate nitridation and subsequent annealing in inert Ar flow, enhances the crystallinity of the BaNbO₂N surface without inducing the reduction of the Nb species. As a result, a particulate BaNbO₂N photoanode exhibits a photocurrent of 5.2 mA cm^?2 at 1.23 V_RHE under simulated solar irradiation, which is the highest yet reported for an oxynitride responsive at wavelengths above 600 nm. Suppressing the reduction of B‐site cations during the synthesis of perovskite AB(O,N)₃, which otherwise results in surface defects or impurities, is critical for achieving high water oxidation activity.     

Multiple Cases of Efficient Nonfullerene Ternary Organic Solar Cells Enabled by an Effective Morphology Control Method

Ternary organic solar cells (OSCs) have attracted much research attention, as they can maintain the simplicity of the single‐junction device architecture while broadening the absorption range of OSCs. However, one main challenge that limits the development of ternary OSCs is the difficulty in controlling the morphology of ternary OSCs. In this paper, an effective approach to control the morphology is presented that leads to multiple cases of efficient nonfullerene ternary OSCs with efficiencies of up to 11.2%. This approach is based on a donor polymer with strong temperature dependent aggregation properties processed from hot solutions without any solvent additives and a pair of small molecular acceptors (SMAs) that have similar surface tensions and thus low propensity to form discrete phases. Such a ternary blend exhibits a simplified bulk‐heterojunction morphology that is similar to the morphology of previously reported binary blends. As a result, an almost linear relationship between V_OC and film composition is observed for all nonfullerene ternary devices. Meanwhile, by carefully designing a control system with a large interfacial tension, a different phase separation and V_OC dependence is demonstrated. This morphology control approach can be applicable to more material systems and accelerates the development of the ternary OSC field.     

解脂耶氏酵母细胞表面展示乳糖水解酶高效水解乳糖

乳糖是婴幼儿获取能量的重要碳源之一,但乳糖需要在乳糖酶的作用下水解成半乳糖与葡萄糖后才能被吸收。缺少乳糖分解酶的婴幼儿在摄入含乳糖的食品后,未被消化的乳糖会直接进入大肠,刺激大肠蠕动加快,造成一系列不适应症状即乳糖不耐症,我国属于乳糖不耐症高发国家。因此,解决乳糖的体外水解问题对减轻该症状有重要的意义。研究通过将β-半乳糖苷酶(也称为乳糖水解酶)表面展示在食品安全微生物解脂耶氏酵母(Yarrowia lipolytica)细胞表面,通过培养获得该酵母,然后直接利用酵母细胞来水解乳糖生成半乳糖与葡萄糖。采用该工程酵母细胞(HCY10),能在24小时内完全水解50g/L的乳糖,生成半乳糖与葡萄糖。该方法具有高效、简便的优点,能为乳糖的高效水解提供一条新的途径。     

Review on Challenges and Recent Advances in the Electrochemical Performance of High Capacity Li‐ and Mn‐Rich Cathode Materials for Li‐Ion Batteries

Li and Mn‐rich layered oxides, xLi₂MnO₃·(1–x)LiMO₂ (M=Ni, Mn, Co), are promising cathode materials for Li‐ion batteries because of their high specific capacity that can exceed 250 mA h g^?1. However, these materials suffer from high 1^st cycle irreversible capacity, gradual capacity fading, low rate capability, a substantial charge‐discharge voltage hysteresis, and a large average discharge voltage decay during cycling. The latter detrimental phenomenon is ascribed to irreversible structural transformations upon cycling of these cathodes related to potentials ≥4.5 V required for their charging. Transition metal inactivation along with impedance increase and partial layered‐to‐spinel transformation during cycling are possible reasons for the detrimental voltage fade. Doping of Li, Mn‐rich materials by Na, Mg, Al, Fe, Co, Ru, etc. is useful for stabilizing capacity and mitigating the discharge‐voltage decay of xLi₂MnO₃·(1–x)LiMO₂ electrodes. Surface modifications by thin coatings of Al₂O₃, V₂O₅, AlF₃, AlPO₄, etc. or by gas treatment (for instance, by NH₃) can also enhance voltage and capacity stability during cycling. This paper describes the recent literature results and ongoing efforts from our groups to improve the performance of Li, Mn‐rich materials. Focus is also on preparation of cobalt‐free cathodes, which are integrated layered‐spinel materials with high reversible capacity and stable performance.     

Mechanism of ammonium adsorption from wastewater by modified bentonite and optimization by response surface

Three modified bentonites, dry alkali modification, thermal modification, and acid modification, were prepared and characterized by XRD and FTIR. Batch experiments were performed to evaluate their efficiency as adsorbent for ammonium removal. Multi-variables interaction effects were evaluated by Response Surface Methodology. The results showed that the adsorption efficiency of ammonium by dry alkali modification bentonite was the best in three modified methods; the next was that of thermal modification. The crystalline structure of bentonite was significantly changed with dry alkali modification. Na₂SiO₃ and Na₂AlSi₃O₈(OH) were achieved by bentonite with powder NaOH modification. The increase in the mole ratio of exchangeable cations indicated that the adsorption efficiency of ammonium increased; while the layer spacing of bentonite expanded with the amount of the adsorbed water and hydrated water increased by thermal modification. In multi-variables interaction effects (holding time, calcination temperature, pH, dosage), the most significant factors were calcination temperature and dosage.     

Tree ring responses to climate variability of xerophytic thickets from South Soalara,Madagascar

Xerophytic thickets occur along the southwestern part of Madagascar. Although providing a wide variety of resources and services to the local population, this particular vegetation is subjected to deforestation. This study focuses on linking dendroclimatology and dendroecology by examining the spatial and temporal variability of the ecological growth conditions. Information from tree rings was retrieved, on one hand, to identify the problem of the limiting effects of past climate on growth and, on the other hand, to show how local environment takes part in the growth pattern of South Soalara species, in the southwestern part of Madagascar. Methods and principles of dendrochronology were applied on nine species belonging to seven botanical families. A total of 42 stem discs from 3 to 5 trees per species were collected at 30 cm height. All discs exhibited visible tree rings, but anatomical distinctness varied between species. This study highlighted the annual formation of tree rings through successful crossdating techniques. Then, from the nine constructed chronologies, species were grouped into three clusters. Analysis between precipitation and radial growth showed that the response to climate occurred mainly in rainy season. Large-scale climatic drivers such as sea surface temperature (SST¹) of ENSO² regions revealed a teleconnection with tree growth in cluster 1. Mean radial increments were computed from the measured tree ring width and varied from 0.66 to 1.98 mm year⁻¹, showing that those species are slow-growing. All species were recorded as having a certain dendrochronological potential, which was ranked as useful for Rhizogum madagascariense and Terminalia gracilipes, poor for Gyrocarpus americanus and problematic for the other species. It is recommended to increase the number of wood samples and to provide more knowledge on the characteristics of the species in order to improve the quality of the chronology and the climatic signal on tree rings.     

Sequence analysis of sub-genotype D hepatitis B surface antigens isolated from Jeddah,Saudi Arabia

Little is known about the prevalence of HBV genotypes/sub-genotypes in Jeddah province, although the hepatitis B virus (HBV) was identified as the most predominant type of hepatitis in Saudi Arabia. To characterize HBV genotypes/sub-genotypes, serum samples from 15 patients with chronic HBV were collected and subjected to HBsAg gene amplification and sequence analysis. Phylogenetic analysis of the HBsAg gene sequences revealed that 11 (48%) isolates belonged to HBV/D while 4 (18%) were associated with HBV/C. Notably, a HBV/D sub-genotype phylogenetic tree identified that eight current isolates (72%) belonged to HBV/D1, whereas three isolates (28%) appeared to be more closely related to HBV/D5, although they formed a novel cluster supported by a branch with 99% bootstrap value. Isolates belonging to D1 were grouped in one branch and seemed to be more closely related to various strains isolated from different countries. For further determination of whether the three current isolates belonged to HBV/D5 or represented a novel sub-genotype, HBV/DA, whole HBV genome sequences would be required. In the present study, we verified that HBV/D1 is the most prevalent HBV sub-genotype in Jeddah, and identified novel variant mutations suggesting that an additional sub-genotype designated HBV/DA should be proposed. Overall, the results of the present HBsAg sequence analyses provide us with insights regarding the nucleotide differences between the present HBsAg/D isolates identified in the populace of Jeddah, Saudi Arabia and those previously isolated worldwide. Additional studies with large numbers of subjects in other areas might lead to the discovery of the specific HBV strain genotypes or even additional new sub-genotypes that are circulating in Saudi Arabia.     

Traveling behavior of a termite in tunnels with different curvatures and base surface roughness

This study focused on understanding the termite traveling behavior. Artificial tunnels with different curvatures and base surface roughness were constructed. Each tunnel was 50 mm in length, with widths of W (W = 2, 3, or 4 mm). The distance between the two ends of the tunnel was D (D = 20, 30, 40, or 50 mm). A higher value of D means a lower curvature. The roughness, R (R = 60, 120, 240 and ∞), was generated by uniformly sanding the substrate with a sanding machine. A higher R value means a finer base surface. The symbol ∞ represents a smooth surface. Time (τ) taken by a termite to pass through the tunnel was measured. τ was longer in tunnels with a smooth surface compared with the tunnels with a rough surface. When W = 2, there was no effect of the roughness on speed. This is because the narrow tunnel width diluted the effects of the smoothness of the surface. When W = 3, τ was statistically shorter for R = 240, than for R = 60 and 120. This suggests that an appropriate surface roughness could positively contribute to the traveling speed.