无光滤波六倍频微波信号产生的系统设计

基于两个级联偏振调制器,提出了一种高频谱纯度、稳定的六倍频微波信号产生方法。该方法通过适当调整偏振片的偏振方向、射频驱动信号电压和相位,实现无光滤波器条件下、任何波段六倍频微波信号的产生。利用Optisystem平台搭建的仿真系统,以S波段4 GHz信号为例,验证了该设计系统产生的六倍频信号质量,并分析了非理想射频驱动电压和相位对六倍频信号质量的影响,结果表明：该设计系统能产生最大光边带抑制比、射频无杂散抑制比分别为21.3,15.2 dB的六倍频微波信号;且非理想驱动电压和相位差的偏离应控制在理想值5%的范围之内。     

氢氧化铝/环氧树脂复合材料的电荷衰减特性

环氧树脂电气绝缘性能优良, 但是其在脉冲功率设备中充当绝缘子时, 表面容易带电且不易衰减, 当表面电荷集聚到一定的程度会造成局部放电甚至发展为沿面闪络。为了提高环氧树脂的沿面闪络性能, 用中心粒径为1 m的氢氧化铝(ATH)无机填料来改善环氧树脂复合材料的表面性能。分别制备了ATH填料质量分数为0%(纯环氧) , 20%, 40%, 60%, 80%和100%的ATH/环氧树脂复合材料试样。用电声脉冲法研究了ATH填料对环氧树脂复合材料电荷衰减性能的影响, 对比了试样直流极化场强为10 kV/mm和30 kV/mm的试验结果。结果表明：ATH/环氧树脂复合材料电荷的衰减常数不仅与填料的质量分数有关, 而且与试样的带电量有关。     

热稳定单原子催化剂的理性构筑:从原子级结构到实际应用

80%以上的工业生产过程涉及催化,如化工生产、能源转换、制药和废物处理等等.催化剂的使用显著提高了生产效率,降低了生产成本,为国民经济、地球环境和人类文明的可持续发展做出了很大贡献.为了满足日益增长的生产需求和最大的经济效益,开发高效、稳定、低成本的新型催化剂已成为当务之急.金属中心负载在载体上的负载型金属催化剂因其较好的催化活性和相对较低的金属用量而受到广泛关注.研究发现,负载型结构可增强传热和传质并增加活性金属中心的分散度,从而影响催化性能.此外,负载金属的颗粒尺寸对催化剂的性能有很大影响.迄今为止,科学家们一直在通过减小金属颗粒尺寸和提高原子利用效率来提高催化剂的活性.原子级尺寸的颗粒通常表现出与大尺寸颗粒显着不同的物理和化学性质,而当活性位点的尺寸缩小到单个原子时,单原子催化剂的概念应运而生.对于单原子催化剂,金属原子中心通过配位被载体中的缺陷锚定,从而调整金属原子的电子云分布.这种配位调整使得单原子催化剂拥有与传统催化剂不同的性能.作为催化领域的新前沿,单原子催化剂已经在许多催化反应中表现出前所未有的活性和选择性.然而,许多报道的单原子催化剂在高温环境或长期催化应用中容易受到奥斯特瓦尔德熟化过程的影响,从而导致催化剂烧结和失活.而烧结的原因在于金属原子和载体之间较弱的相互作用.失活催化剂的再生和回收将大大增加工业生产的时间和经济成本.因此,开发具有优异热稳定性的单原子催化剂以满足工业需求是十分必要的.本综述首先总结了近年来关于热稳定型单原子催化剂合成方法的基础研究,并从原子尺度上分析了这些方法所构建的金属中心的结构形态和配位环境.此外,结合近些年的研究中新的表征技术与理论计算手段解释了热稳定性的来源.重点讨论了热稳定单原子催化剂的实际催化应用.分析了热稳定单原子催化剂在热催化应用中的独特作用机理、并尝试为确定催化过程中真正的活性中心以及通过原子级调控手段进行高活性热稳定单原子催化剂的合成提供理论指导.最后总结了热稳定单原子催化剂发展的主要问题,并简要分析了单原子催化领域的研究挑战和发展前景.     

Purification Process and In Vitro and In Vivo Bioactivity Evaluation of Pectolinarin and Linarin from Cirsium japonicum

Pectolinarin and linarin are two major flavone O-glycosides of Cirsium japonicum, which has been used for thousands of years in traditional Chinese medicine. Pharmacological research on pectolinarin and linarin is meaningful and necessary. Here, a process for the purification of pectolinarin and linarin from C. japonicum was established using macroporous resin enrichment followed by prep-HPLC separation. The results show the purity of pectolinarin and linarin reached 97.39% and 96.65%, respectively. The in vitro bioactivities result shows the ORAC values of pectolinarin and linarin are 4543 and 1441 µmol TE/g, respectively, meanwhile their inhibition rate of BSA-MGO-derived AGEs is 63.58% and 19.31% at 2 mg/mL, which is 56.03% and 30.73% in the BSA-fructose system, respectively. The COX-2 inhibition rate at 50 µg/mL of linarin and pectolinarin reached 55.35% and 40.40%, respectively. Furthermore, the in vivo bioassay combining of histopathologic evaluation and biochemical analysis of liver glutamic oxaloacetic transaminase, serum creatinine and TNF-α show pectolinarin can alleviate lipopolysaccharide (LPS)-induced acute liver and kidney injury in mice. Metabolomics analysis shows that pectolinarin attenuates LPS-challenged liver and kidney stress through regulating the arachidonic acid metabolism and glutathione synthesis pathways. Collectively, our work presents a solid process for pectolinarin and linarin purification and has discovered a promising natural therapeutic agent—pectolinarin.     

Non-Covalent Dimer as Donor Chromophore for Constructing Artificial Light-Harvesting System in Water

Dynamic emissive materials in aqueous media have received much attention owing to their ease of preparation, tunable luminescence and environmental friendliness. However, hydrophobic fluorophores usually suffer from aggregation-caused quenching in water. In this work, we constructed an artificial light-harvesting system by using a non-covalent aggregation-induced emission dimer as antenna and energy donor. The dimer is quadruple hydrogen bonded from a ureidopyrimidinone derivative (M) containing a tetraphenylethylene group. The dispersed nano-assemblies based on the dimer in aqueous media were fabricated with the help of surfactant. By loading a hydrophobic acceptor molecule DBT into the nano-assemblies, man-made light-harvesting nanoparticles were fabricated, showing considerable energy transfer efficiency and a relatively high antenna effect. Additionally, the fluorescence color of the system can be gradually tuned by varying the content of the acceptors. This study provides a general way for the construction of an aqueous light-harvesting system based on a supramolecular dimer, which is important for potential application in luminescent materials.     

Efficient Degradation of Tetracycline Antibiotics by Engineered Myoglobin with High Peroxidase Activity

Tetracyclines are one class of widely used antibiotics. Meanwhile, due to abuse and improper disposal, they are often detected in wastewater, which causes a series of environmental problems and poses a threat to human health and safety. As an efficient and environmentally friendly method, enzymatic catalysis has attracted much attention. In previous studies, we have designed an efficient peroxidase (F43Y/P88W/F138W Mb, termed YWW Mb) based on the protein scaffold of myoglobin (Mb), an O₂ carrier, by modifying the heme active center and introducing two Trp residues. In this study, we further applied it to degrade the tetracycline antibiotics. Both UV-Vis and HPLC studies showed that the triple mutant YWW Mb was able to catalyze the degradation of tetracycline, oxytetracycline, doxycycline, and chlortetracycline effectively, with a degradation rate of ~100%, ~98%, ~94%, and ~90%, respectively, within 5 min by using H₂O₂ as an oxidant. These activities are much higher than those of wild-type Mb and other heme enzymes such as manganese peroxidase. As further analyzed by UPLC-ESI-MS, we identified multiple degradation products and thus proposed possible degradation mechanisms. In addition, the toxicity of the products was analyzed by using in vitro antibacterial experiments of E. coli. Therefore, this study indicates that the engineered heme enzyme has potential applications for environmental remediation by degradation of tetracycline antibiotics.     

Ultrabright AIEdots with tunable narrow emission for multiplexed fluorescence imaging

AIEgen doped fluorescent nanodots (AIEdots) have attracted lots of attention, due to their superior characteristics as fluorescent probes, such as excellent photostability, large Stokes shift, high brightness and tunable emission. Unfortunately, most of the currently available AIEdots exhibit broad emission bandwidth, which limits their applications in multiplexed fluorescence imaging and detection. In this work, the strategy of designing and fabricating narrow emissive AIEdots (NE-AIEdots) with tunable wavelengths was presented by constructing a light-harvesting system with high energy transfer efficiency. Efficient intra-particle energy transfer from highly doped AIEgens, serving as the light-harvesting antenna, to the lightly doped narrow emissive fluorophore, resulted in high brightness and narrow emission. The emission band of NE-AIEdots with the full-width-at-half-maximum varied from 18 to 36 nm was 3–6.3 times narrower than that of traditional AIEdots. The single-particle brightness of NE-AIEdots was over 5-times that of commercial quantum dots under the same excitation and collection conditions. Taking advantage of the superior performance of these NE-AIEdots, multiplexed fluorescence imaging of lymph nodes in living mice was realized, which supported the future applications of NE-AIEdots for in vivo multiplexed labeling and clinical surgery.

AIEdots with high brightness and narrow emission bandwidth were developed for multiplexed in vitro and in vivo fluorescence imaging.     

New lead-iodide formates with a strong second-harmonic generation response and suitable birefringence obtained by the substitution strategy

Nonlinear optical (NLO) crystals featuring a strong second-harmonic generation (SHG) response and suitable birefringence to achieve phase-matching are in urgent demand in industrial and commercial applications. Based on the substitution strategy, two new NLO lead-iodide formates, K₂[PbI₂(HCOO)₂] and Rb₂[PbI₂(HCOO)₂], have been successfully synthesized using a moderate mixed-solvothermal method. K₂[PbI₂(HCOO)₂] and Rb₂[PbI₂(HCOO)₂] exhibit strong phase-matching SHG responses of 8 and 6.8 × KDP, respectively, a suitable birefringence and transparent window covering most of the visible light and mid-IR region. Crystal structures and theoretical calculations unveil that the origins of the strong SHG response and suitable birefringence can be credibly attributed to the oriented arrangement of the highly distorted [PbI₂O₄] hexa-coordinated polyhedra, which are consistent in their local dipole moments, as well. This research provides a new strategy to explore high-performance NLO crystals.

K₂[PbI₂(HCOO)₂] and Rb₂[PbI₂(HCOO)₂] with highly distorted [PbI₂O₄] polyhedra in an oriented arrangement exhibit a very strong phase-matching SHG response, suitable birefringence, wide transparent windows and good thermal stability.     

A vending machine for drug-like molecules – automated synthesis of virtual screening hits

As a result of high false positive rates in virtual screening campaigns, prospective hits must be synthesised for validation. When done manually, this is a time consuming and laborious process. Large “on-demand” virtual libraries (>7 × 10¹² members), suitable for preparation using capsule-based automated synthesis and commercial building blocks, were evaluated to determine their structural novelty. One sub-library, constructed from iSnAP capsules, aldehydes and amines, contains unique scaffolds with drug-like physicochemical properties. Virtual screening hits from this iSnAP library were prepared in an automated fashion for evaluation against Aedes aegypti and Phytophthora infestans. In comparison to manual workflows, this approach provided a 10-fold improvement in user efficiency. A streamlined method of relative stereochemical assignment was also devised to augment the rapid synthesis. User efficiency was further improved to 100-fold by downscaling and parallelising capsule-based chemistry on 96-well plates equipped with filter bases. This work demonstrates that automated synthesis consoles can enable the rapid and reliable preparation of attractive virtual screening hits from large virtual libraries.

A compact and operationally simple automation technology can prepare virtual screening hits from a large on-demand library of drug-like molecules.     

大气光学湍流估算模式及其相似性函数

地表热通量和水汽通量对全球气候变化和大气环流有着重要而广泛的影响,而Monin-Obukhov(M-O)相似性函数在计算近地层热通量和水汽通量的过程中扮演着重要的角色;同时M-O相似性函数是大气光学湍流估算模式中不可或缺的因子。通过对合肥西郊35 m铁塔上气象数据的分析,利用非线性最小二乘法拟合得到了一套全新的M-O相似性函数。将之与前人提出的相似性函数作对比,展现出了较好的一致性。同时,该函数大气光学湍流的估算模式中,估算值与实测值具有较好的吻合度。分析结果表明：在稳定条件和非常不稳定条件下,可以认为温度相似性函数等于湿度相似性函数,在弱不稳定条件下两者不再满足这种相似性。