3D-ordered macroporous N-doped carbon encapsulating Fe-N alloy derived from a single-source metal-organic framework for superior oxygen reduction reaction

Fe-N compounds with excellent electrocatalytic oxygen reduction activity are considered to be one of the most promising non-precious metal materials for fuel cells.Fe-N compounds with excellent electrocatalytic oxygen reduction activity are considered to be one of the most promising non-precious metal materials for fuel cells,which focuses on the Fe-N4 single-atom catalysts and the iron nitride materials(such as Fe2N and Fe3N).A hybridized catalyst having a hierarchical porous structure with regular macropores could enable the desired mass transfer efficiency in the catalytic process.In this study,we have constructed a new type of hybrid catalyst having iron and iron-nitrogen alloy nanoparticles(Fe-N austenite,termed as Fe-NA)embedded in the three-dimensional ordered macroporous N-doped carbon(3DOM Fe/Fe-NA@NC)by direct pyrolysis of single-source dicyandiamide-based iron metal-organic frameworks.The as-synthesized composites preserve the hierarchical porous carbon framework with ordered macropores and high specific surface area,incorporating the uniformly dispersed iron/iron-nitrogen austenite nanoparticles.Thereby,the striking architectural configuration embedded with highly active catalytic species delivers a superior oxygen reduction activity with a half-wave potential of 0.88 V and a subsequent superior Zn-air battery performance with high open-circuit voltage and continuous stability as compared to those using a commercial 20%Pt/C catalyst.

Design of the Metal Precursors Molecular Structures in Impregnating Solutions for Preparation of Efficient Ni Mo/Al_2O_3 Hydrodesulfurization Catalysts

The molecular structures of metal precursors in the impregnating solution were designed so as to prepare efficient Ni Mo/Al_2O_3 hydrodesulfurization(HDS) catalysts. At first, five typical impregnating solutions were designed; the existing metal precursors, such as [Mo4(citrate)2O11]^(4-)-like, [P2Mo18O62]^(6-)-like and [P2Mo5O23]^(6-)-like species in the solutions were confirmed by laser Raman spectroscopy(LRS). The UV-Vis spectra results indicated that the solutions containing both phosphoric acid and citric acid could change the existing form of nickel species. Five corresponding Ni Mo/Al_2O_3 catalysts were prepared by the incipient wetness impregnation method. The LRS analysis results of dried catalysts showed that the above metal precursors could be partly retained on alumina support after impregnation and drying, although the interface reaction between different metal precursors and alumina support unavoidably took place. Then the catalysts were sulfided and characterized by N2 physisorption, TEM and XPS analyses. The results showed that different metal precursors in impregnating solution could mainly result in the difference in both the morphology of(Ni)Mo S2 slabs and the promoting effect of Ni species. The catalyst prepared mainly with [P2Mo5O23]^(6-)-like species used as precursors exhibited worse dispersion of(Ni)Mo S2 slabs and lower ratio of Ni–Mo–S active phases than the one with [Mo4(citrate)2O11]^(4-)-like species. Promisingly, the catalyst prepared with co-existing [Mo4(citrate)2O11]^(4-)-like, [P2Mo18O62]^(6-)-like and [P2Mo5O23]^(6-)-like species showed better hydrodesulfurization activity for 4,6-DMDBT thanks to its more well-dispersed Ni–Mo–S active phases.

Electrocatalytic water oxidation by a nickel oxide film derived from a molecular precursor

In this study,we fabricated a NiOx film by electrodeposition of an ethanediamine nickel complex precursor(pH=11)on a fluorine‐doped tin oxide substrate.The resulting film is robust and exhibits high catalytic activity for electrochemical water oxidation.Water oxidation is initiated with an overpotential of375mV(1mA/cm2)and a steady current density of8.5mA/cm2is maintained for at least10h at1.3V versus the normal hydrogen electrode.Kinetic analysis reveals that there is a2e?/3H+pre‐equilibrium process before the chemical rate‐determining step.The low‐cost preparation,robustness,and longevity make this catalyst competitive for applications in solar energy conversion and storage.

Effects of post-mortem aging process on characteristic water-soluble taste-active precursors in yellow-feathered broilers

Chilled chicken has become the mainstream of chicken consumption.In order to explore the effect of post-mortem aging on water-soluble flavor precursors of chicken,pH,adenosine triphosphate(ATP)degradation,flavor nucleosides,free amino acids and water-soluble low molecular weight peptides were determined using Qingyuan partridge yellow-feathered broilers as material during 0-4℃ post-mortem aging in 48 h.The results showed that the pH value fell to the limit pH 5.64(4 h)in chicken breast and 6.21(3 h)in thigh.Regardless of chicken breast or thigh,ATP dropped rapidly within 3 h.It was found that the K-value in chicken thigh was the lowest at 2 h indicating the freshness was the best.Considering the equivalent umami concentration(EUC),the value at 3 h and 4 h was relatively high,but the corresponding electronic tongue umami value was not high,which further showed that the water-soluble low molecular taste peptide played an important role on the post-mortem aging process.Combined with cluster analysis and partial least squares discriminant analysis(PLS-DA),it was preliminarily inferred that the optimal time for chilled chicken during 0-4℃ post-mortem aging was 2 h,which could provide a theoretical basis for the further processing of fresh chicken.

Bi_(2)S_(3)Nanorods Hosted on rGO Sheets from Pyrolysis of Molecular Precursors for Efficient Li-Ion Storage

Bismuth-based compounds with high capacity and durability are still challenging in Li-ion batteries(LIBs).In this article,Bi_(2)S_(3)nanorods hosted on reduced graphene oxide nanosheets(Bi_(2)S_(3)/rGO,BSG)are successfully prepared using molecular precursor pyrolysis strategy.1D nanorod architecture possesses preeminent kinetic characteristics,shortening the ion diffusion path and increasing the contact area between electrode and electrolyte.The large specific surface area and charge polarization of rGO at the interface promote charge transfer.The capacity of material(BSG-400)reaches 558.4 m Ah g^(-1)at 0.2 A g^(-1)after 200 cycles.The anode properties of the composite outperform those of pristine Bi_(2)S_(3).The introduction of graphene enables the interfacial interaction between rGO and Bi_(2)S_(3).The closely contact interface improves the conductivity and lithium storage performances of Bi_(2)S_(3).The regulatory effect of rGO on the electronic density of states and band gap of Bi_(2)S_(3)has been demonstrated by theoretical calculation.The synthetic approach has the advantages of universality,simple operation procedure,and strong repeatability.This research provides some ideas for the preparation of other metal sulfides/rGO nanomaterials and their application in battery research.

Molecular composition of low-temperature oxidation products of the heavy oil

Low-temperature oxidation(LTO)is the main reaction that affects fuel formation in the in-situ combustion process,which has important significance for the subsequent combustion propulsion and the successful extraction of crude oil.In this study,heavy oil was subjected to LTO reactions at different temperatures.Three types of reaction products with varying oxidation depths were characterized in terms of the number of oxygen atoms and the polarity of the molecule to reveal the low-temperature oxidation process of the heavy oil.Ketone compounds and acid polyoxides in the oil phase and deep oxidation products with a higher number of oxygen atoms in the coke were identified with increasing oxidation depth.The experimental results showed that the oxidation reaction of the heavy oil changed from kinetic-controlled to diffusion-controlled in the open oxidation system of the heavy oil as the oxidation depth increased.The oxidation reaction of the oil phase reached a maximum and stable value in oxygen content.The molecular compositions of the ketone compound and acid polyoxide did not change significantly with further increase in reaction temperature.The molecular compositions of the deep oxidation products with a higher number of oxygen atoms in the coke phase changed significantly.The coke precursor molecules with a lower oxygen content and condensation degree participated in the coke formation,and the oxidation reaction pathway and the complexity of the oxidation product component also increased.

Emerging structures and dynamic mechanisms ofγ-secretase for Alzheimer’s disease

γ-Secretase,called“the proteasome of the membrane,”is a membrane-embedded protease complex that cleaves 150+peptide substrates with central roles in biology and medicine,including amyloid precursor protein and the Notch family of cell-surface receptors.Mutations inγ-secretase and amyloid precursor protein lead to early-onset familial Alzheimer’s disease.γ-Secretase has thus served as a critical drug target for treating familial Alzheimer’s disease and the more common late-onset Alzheimer’s disease as well.However,critical gaps remain in understanding the mechanisms of processive proteolysis of substrates,the effects of familial Alzheimer’s disease mutations,and allosteric modulation of substrate cleavage byγ-secretase.In this review,we focus on recent studies of structural dynamic mechanisms ofγ-secretase.Different mechanisms,including the“Fit-Stay-Trim,”“Sliding-Unwinding,”and“Tilting-Unwinding,”have been proposed for substrate proteolysis of amyloid precursor protein byγ-secretase based on all-atom molecular dynamics simulations.While an incorrect registry of the Notch1 substrate was identified in the cryo-electron microscopy structure of Notch1-boundγ-secretase,molecular dynamics simulations on a resolved model of Notch1-boundγ-secretase that was reconstructed using the amyloid precursor protein-boundγ-secretase as a template successfully capturedγ-secretase activation for proper cleavages of both wildtype and mutant Notch,being consistent with biochemical experimental findings.The approach could be potentially applied to decipher the processing mechanisms of various substrates byγ-secretase.In addition,controversy over the effects of familial Alzheimer’s disease mutations,particularly the issue of whether they stabilize or destabilizeγ-secretase-substrate complexes,is discussed.Finally,an outlook is provided for future studies ofγ-secretase,including pathways of substrate binding and product release,effects of modulators on familial Alzheimer’s disease mutations of theγ-secretase-substrate complexes.Comprehensive understanding of the functional mechanisms ofγ-secretase will greatly facilitate the rational design of effective drug molecules for treating familial Alzheimer’s disease and perhaps Alzheimer’s disease in general.

仿突变生物合成调控对土曲霉C23-3次生代谢产物的影响

【目的】丁内酯I是土曲霉(Aspergillus terreus)产生的一种具有多样生物活性的小分子天然产物,对其结构多样性拓展的探索具有重要意义。以一株高产丁内酯I的海洋来源土曲霉C23-3作为基础菌株,研究丁内酯前体小分子类似物和前体合成酶抑制剂对其次生代谢的影响。【方法】以海水马铃薯液体培养基为基础培养基,以3种前体小分子类似物和3种对羟基苯丙酮酸的合成酶抑制剂作为化学诱导剂,在静置发酵条件下进行菌株的化学调控培养。采用高效液相色谱、高效液相色谱-离子阱质谱联用及基于质谱的分子网络和数据库挖掘分析次生代谢产物的产量和多样性。【结果】多数前体小分子类似物和合成酶抑制剂对丁内酯I产量均有不同程度抑制,而高浓度的前体小分子类似物3,4-二羟基苯丙酮酸、两种合成酶抑制剂联用及这三者的联用表现出了较强的抑制效果;并且在丁内酯I的合成受到强烈抑制条件下,丁内酯类、土震素类、洛伐他汀类等多类次生代谢产物的合成也下降,但一种环肽类化合物产量超过10倍的大幅提升,可能是菌体对作为群体感应信号及全局性转录因子lae A诱导子的丁内酯I合成受到压制胁迫的一种应激反应,具体机制有待深入研究。【结论】丁内酯I的前体确为对羟基苯丙酮酸,3,4-二羟基苯丙酮酸及对羟基苯丙酮酸合成酶抑制剂可用作抑制丁内酯I合成的小分子工具,以用于仿突变生物合成的进一步探索以获得多样化丁内酯衍生物,也可诱导产生环肽类化合物。

Pathological,molecular,and clinical characteristics of cholangiocarcinoma:A comprehensive review

Cholangiocarcinomas are a heterogeneous group of highly aggressive cancers that may arise anywhere within the biliary tree.There is a wide geographical variation with regards to its incidence,and risk-factor associations which may include liver fluke infection,primary sclerosing cholangitis,and hepatolithiasis amongst others.These tumours are classified into intrahepatic,perihilar and distal based on their anatomical location.Morphologically,intrahepatic cholangiocarcinomas are further sub-classified into small and large duct variants.Perihilar and distal cholangiocarcinomas are usually mucin-producing tubular adenocarcinomas.Cholangiocarcinomas develop through a multistep carcinogenesis and are preceded by dysplastic and in situ lesions.While clinical characteristics and management of these tumours have been extensively elucidated in literature,their ultra-structure and tumour biology remain relatively unknown.This review focuses on the current knowledge of pathological characteristics,molecular alterations of cholangiocarcinoma,and its precursor lesions(including biliary intraepithelial neoplasia,intraductal papillary neoplasms of the bile duct,intraductal tubulopapillary neoplasms and mucinous cystic neoplasm).

含氟-硅聚合物海洋防污涂层材料设计研究新进展

海洋生物污损是人类致力于解决的一个难题,具有绿色环保、广谱性和长效性等特点的海洋防污涂料的研究和应用成为涂料领域的发展方向之一,其中含氟-硅聚合物海洋防污涂层材料的设计及应用受到广泛关注。本文首先对从2016年至今海洋防污涂料领域的一些综述进行简要介绍,然后着重对氟-硅聚合物、氟-硅前驱物、有机-无机纳米复合技术在含氟-硅聚合物海洋防污涂层材料设计研究中的应用最新进展进行了评述,并对其未来发展方向进行了展望。

Conclusive Growth of CdTe Nanorods by Solvothermal Decomposition Using Single Source Precursors

CdTe nanorods are synthesized by solvothermal decomposition, using single source molecular precursors (SSMP) cadmium (II), complex of bis-(aminopropyl telluride) (SSMP-I) and cadmium (II) bis-(isopropyl telluro) propane (SSMP-II) and quinoline as solvent at relatively low temperature (210°C). As synthesized nanomaterials are structurally characterized by XRD and SEM, SEM micrographs revealed formation of rod shapes structures whose dimensions change with the source precursor molecule. The average crystallite size estimated from XRD data is 29.78 and 28.94 nm respectively using Precursors I and II. The average size of nanorods is 1.237 μm and 0.15μm respectively, estimated from SEM micrographs. These are much larger than the average crystallite size estimated from XRD data. This is attributed to the agglomeration of nanocrystallites as quinoline is not a good capping agent.

水对聚丙烯腈溶液热致变凝胶化的微观促进机理研究

使用分子动力学模拟作为研究方法,从微观层面上研究了聚丙烯腈(PAN)/二甲基亚砜(DMSO)/水(H2O)混合溶液的热致变凝胶化过程,并明确了水的微观促进机理。结果表明,模拟计算得到的含水量为4%(质量分数,下同)的三元体系的凝胶点温度在332.75 K附近,与文献报道的实验结果吻合;水会增加PAN分子链的振动幅度,增加氰基之间发生交联作用的概率,从而促进PAN溶液快速发生凝胶化转变;在一定的范围内,含水量越大,PAN的振动幅度越大;水减少了PAN周围DMSO分子的数量,增强PAN分子链的聚集程度,导致氰基之间更容易发生交联作用。

ZrC-ZrB_2-SiC ceramic nanocomposites derived from a novel single-source precursor with high ceramic yield

For the first time, ZrC-ZrB_2-SiC ceramic nanocomposites were successfully prepared by a single-source-precursor route, with allylhydridopolycarbosilane(AHPCS),triethylamine borane(TEAB),and bis(cyclopentadienyl) zirconium dichloride(Cp_2 ZrCl_2) as starting materials. The polymer-to-ceramic transformation and thermal behavior of obtained single-source precursor were characterized by means of Fourier transform infrared spectroscopy(FT-IR) and thermal gravimetric analysis(TGA). The results show that the precursor possesses a high ceramic yield about 85% at 1000 ℃.The phase composition and microstructure of formed ZrC-ZrB_2-SiC ceramics were investigated by means of X-ray diffraction(XRD) and high resolution transmission electron microscopy(HRTEM).Meanwhile, the weight loss and chemical composition of the resultant ZrC-ZrB_2-SiC nanocomposites were investigated after annealing at high temperature up to 1800 ℃. High temperature behavior with respect to decomposition as well as crystallization shows a promising high temperature stability of the formed ZrC-ZrB_2-SiC nanocomposites.

Lithographic patterning of ferromagnetic FePt nanoparticles from a single-source bimetallic precursor containing hemiphasmidic structure for magnetic data recording media

Patterning of L10 FePt nanoparticles(NPs) with high coercivity offers a promising route to develop bit-patterned media(BPM) for the next generation magnetic data recording system, but the synthesis of monodisperse FePt NPs and mass production of their nanopatterns has been a longstanding challenge. Here, highly efficient nanoimprint lithography was applied for large-scale universal patterning, which was achieved by imprinting the solution of a single-source bimetallic precursor. The rigid coplanar metallic cores and the surrounding flexible tails in the bimetallic complex permit the spontaneous molecular arrangements to form the highly ordered negative morphology replicated from the soft template.In-situ pyrolysis study was then investigated by one-pot pyrolysis of the precursor under an Ar/H2 atmosphere, and the resultant NPs were fully characterized to identify the phase,morphology and magnetic properties. Finally, highly-ordered patterns on certain substrates were preserved perfectly after pyrolysis and could be potentially utilized in magnetic data recording media.

水合三氯乙醛前体物的分子量分布和荧光特性

运用超滤分离技术将水合三氯乙醛前体物含量最高的夏季水样中溶解性有机物分为四个部分,采用三维激发-发射矩阵荧光光谱对不同分子量有机物组分进行表征,并对20种氨基酸、牛血清白蛋白等模式化合物进行氯化试验,以找出水合三氯乙醛的主要前体物成分。结果表明MW<1 k Da的水合三氯乙醛生成势含量最高,为24.81μg/L,其次为10 k Da<MW<0.45μm(17.49μg/L)、3 k Da<MW<10 k Da(8.16μg/L)和1 k Da<MW<3 k Da(5.50μg/L),其中MW<1 k Da和10 k Da<MW<0.45μm两部分有机物占水合三氯乙醛前体物含量的75.55%。三维激发-发射矩阵荧光光谱结果表明水合三氯乙醛的主要前体物可能为类芳香性蛋白质和类微生物代谢产物等物质而非类富里酸和类腐殖酸。丙氨酸、天冬酰胺、天冬氨酸、半胱氨酸、组氨酸、苏氨酸、色氨酸、酪氨酸、牛血清白蛋白、鲱鱼精DNA等模式化合物是水合三氯乙醛主要前体物,其水合三氯乙醛生成量均大于30μg/mg C。

MCM-36分子筛的合成及其苯与丙烯烷基化性能研究

分别从MCM-22和MCM-49前驱体出发合成了MCM-36分子筛,在液-固固定床反应器上对MCM-36分子筛的苯与丙烯液相烷基化反应性能进行了评价.由MCM-22前驱体出发合成的MCM-36(A)结晶度良好,比MCM-22具有更高比表面积和介孔孔容,酸量明显下降.由MCM-49前驱体出发合成的MCM-36(B)的比表面积和介孔孔容增加,小角XRD特征衍射峰强度低于MCM-36(A),与MCM-49相比酸量下降幅度较小.在苯与丙烯液相烷基化反应中MCM-36(A)的活性与MCM-22相当,丙烯的转化率大于99.5%,异丙苯的选择性比MCM-22提高了7%.MCM-36(B)的反应活性高于MCM-36(A),而异丙苯的选择性低于MCM-36(A).MCM-36分子筛上苯与丙烯液相烷基化反应活性的提高归因于有效酸性位的增加,异丙苯选择性的提高则主要归因于B酸量的降低.

低分子量聚碳硅烷制备3D-Cf/SiC复合材料

研究了低分子量聚碳硅烷(PCS)通过先驱体浸渍裂解(PIP)工艺制备Cf/SiC复合材料.分析表明:PCS的数均分子量为400,活性较强,陶瓷化产率为70%左右,在1200℃基本转化为微晶态的β-SiC.分别通过3种不同升温速率制备了3D-Cf/SiC复合材料试样,其弯曲强度分别为745.2 MPa、686.7 MPa和762.5 MPa,明显高于文献报道3D-Cf/SiC复合材料弯曲强度300～500 MPa的水平.试样断口的SEM照片均显示长的纤维拔出,有良好的增韧效果,低分子量PCS裂解得到的基体比较致密.实验结果说明,低分子量PCS适合于制备3D-Cf/SiC复合材料,并且提高升温裂解速率对材料性能影响很小.

聚硼硅氮烷陶瓷前驱体分子结构设计和合成

聚硼硅氮烷是制备高性能硅硼碳氮(SiBCN)复相陶瓷的主要聚合物前驱体,在耐高温、抗氧化高性能陶瓷领域中具有重要的研究价值。本文分4个方面,即基于硼吖嗪的聚硼硅氮烷、侧基含有环硼氮烷或单硼烷的聚硼硅氮烷、基于多官能硼烷构筑的聚硅氮烷和含硼聚硅基碳化二亚胺,从聚硼硅氮烷分子结构设计、改性、合成及在多维尺寸材料中初步应用的角度综述了该领域国内外研究的新进展,指出了聚硼硅氮烷陶瓷前驱体设计合成研究发展中值得关注的新方向。

不同分子质量区间腐殖酸的氯化反应特性研究

以自配的腐殖酸水样为研究对象，投加次氯酸钠对其进行消毒，考察了消毒过程中三卤甲烷、卤乙酸的生成量及DOC、UV254、A410、A465/A656的变化情况。结果表明，分子质量为50—100ku的腐殖酸为生成三卤甲烷和卤乙酸的最主要前体物；消毒反应后，各分子质量区间腐殖酸的DOC、UV254和A410都有不同程度的下降，且对小分子质量腐殖酸的DOC、UV254和A410的去除率高于对大分子质量腐殖酸的；A465／A656的变化表明消毒过程中腐殖酸的分子质量呈下降趋势。

珠江源水中THMFP的分子质量分布及其特征研究

以珠江广州段水源水为研究对象，采用超滤分离方法将其中的有机物分成分子质量不同的几种形态，考察了各分子质量组分在DOC、UV、THMFP等方面的差异。结果表明：①分子质量在3～10ku间的有机物是珠江广州段源水中最主要的THMs前驱物；②分子质量最小（〈1ku）的组分，尽管SUVA值最低，THMs生成能力（THMFP／DOC）却最强；③经超滤分离有机物量的损失很少，但紫外吸收明显减弱，THMs生成量也随之减少。