毫米波回旋速调管磁控注入电子枪模拟计算

介绍了毫米波回旋速调管磁控注入电子枪的结构与特点。电子枪提供的电子束流性能直接影响到回旋速调管的总体参数,为保证整管的效率和输出功率,利用电子枪模拟程序对电子轨迹进行模拟计算,研究了电极形状、磁场分布以及电子轨迹与电子注参量的影响,并为磁控注入电子枪的设计提供了理论依据。     

Size and Structure of Empty and Filled Nanocontainer Based on Peptide Dendrimer with Histidine Spacers at Different pH

Novel peptide dendrimer with Lys-2His repeating units was recently synthesized, studied by NMR (Molecules, 2019, 24, 2481) and tested as a nanocontainer for siRNA delivery (Int. J. Mol. Sci., 2020, 21, 3138). Histidine amino acid residues were inserted in the spacers of this dendrimer. Increase of their charge with a pH decrease turns a surface-charged dendrimer into a volume-charged one and should change all properties. In this paper, the molecular dynamics simulation method was applied to compare the properties of the dendrimer in water with explicit counterions at two different pHs (at normal pH with neutral histidines and at low pH with fully protonated histidines) in a wide interval of temperatures. We obtained that the dendrimer at low pH has essentially larger size and size fluctuations. The electrostatic properties of the dendrimers are different but they are in good agreement with the theoretical soft sphere model and practically do not depend on temperature. We have shown that the effect of pairing of side imidazole groups is much stronger in the dendrimer with neutral histidines than in the dendrimer with protonated histidines. We also demonstrated that the capacity of a nanocontainer based on this dendrimer with protonated histidines is significantly larger than that of a nanocontainer with neutral histidines.     

BiGaIn2S6 – Synthese,Struktur und Eigenschaften

BiGaIn₂S₆ – Synthesis, Structure, and Properties The novel compound BiGaIn₂S₆ was obtained in the quaternary system Bi–Ga–In–S. BiGaIn₂S₆ forms red transparent platelets and exhibits a range of homogeneity between BiGa₁In₂S₆ and BiGa_0.8In_2.2S₆. The compound is a semiconductor with E_g(opt.) = 1.9 eV. – BiGaIn₂S₆ crystallizes monoclinically forming a new structure type (a = 1112.0 pm, b = 380.6 pm, c = 1228.0 pm, β = 116.30°, Z = 2, space group P2₁/m, no. 11). The S atoms form strongly corrugated 2 D fragments of the (hc)₂ sphere packing type. The In atoms occupy octahedral holes (d(In–S) = 262 pm) and the Ga atoms tetrahedral holes (d(Ga–S) = 234 pm) inside the 2 D-layers. The Bi atoms on the top of trigonal BiS₃ pyramids (d(Bi–S) = 265 pm) are at the periphery of the layers and have four additional S ligands from the neigbouring layer at much larger distances (d(Bi–S) = 319 pm). – The bonding of a Bi^III sulfide is analyzed for the first time by the Electron Localization Function (ELF).     

Flavin- and Deazaflavin-Containing Model Compounds Mimic the Energy Transfer Step in Type-II DNA-Photolyases

A distinct energy transfer between the deazaflavin and the flavin is observed in compounds that mimic the DNA repair function of DNA-photolase enzymes (see sketch). Studies on these models prove that the deazaflavin acts solely as photoantenna and suggest that the two cofactors have to be separated within the enzyme to suppress a competitive intercofactor electron transfer reaction.     

Controllable Intramolecular Motions That Generate Fluorescent Signals for a Metal Scorpionate Complex

Simply by changing the pH value, the side chain of complex 1 can be reversibly moved between two positions. Coordination to the metal center through the nitrogen atom of the side chain at moderate pH values is accompanied by a decrease in fluorescence intensity (from I_F=100% to I_F=60%). A further decrease is observed upon deprotonation of the bound water molecule at higher pH (I_F≤2%). Therefore, 1 can be seen as a molecular three-position switch.     

Bismut(II)-chalkogenometallate(III) Bi2M4X8, Verbindungen mit Bi24+-Hanteln (M = Al,Ga; X = S,Se)

Bismuth(II) Chalcogenometallates(III) Bi₂M₄X₈, Compounds with Bi₂⁴⁺ Dumbbells (M = Al, Ga and X = S, Se) The ternary bismuth(II) chalcogenometallates(III) Bi₂M₄X₈ (with M = Al, Ga and X = S, Se) were synthesized from the binary chalcogenides M₂X₃ and Bi₂X₃ and elementary bismuth. All compounds are diamagnetic semiconductors with E_g (opt.) = 1.8–2.7 eV. The phases (except Bi₂Al₄Se₈) are thermodynamically stable and decompose peritectically above 965–1020 K. Bi₂Al₄Se₈ is metastable below 825 K and is obtained only by rapid quenching from T > 825 K. The isotypic compounds crystallize in a new tetragonal tP28 structure type (P4/nnc). The characteristic unit is the hitherto unknown clustercation Bi₂⁴⁺, with the mean bond length d(Bi–Bi) = 314.2 pm, the Raman frequency 102 cm^–1 ≤ ν_s ≤ 108 cm^–1, and the mean force constant of f = 0.68 N · cm^–1. The Electron Localization Function, ELF, shows the covalent Bi–Bi bond, the lone electron pairs of the ψ-octahedrally coordinated Bi(II) cations, and the polar character of the Bi–X bonds.     

Einkristallstrukturaufklärung und elektronenmikroskopische Untersuchungen an einem neuen Uranniobat: γ-UNbO5

X-Ray Single Crystal and Electron Microscopic Investigations on a New Uranium Niobate: γ-UNbO₅ Black cuboid formed crystals of γ-UNbO₅ were obtained (at T₁) by chemical transport in a temperature gradient (T₂ → T₁; 1000 °C → 980 °C) using UNb₂O₇ as starting material (at T₂) and a combination of NbCl₅ and Cl₂ as transport agent. They were examined by X-rays and electron microscopy. The new modification of γ-UNbO₅ crystallizes orthorhombically (space group Pmma) with a = 7.492(3) Å, b = 4.124(4) Å and c = 6.434(4) Å. The compound is isostructural to UVO₅ and UMoO₅. The crystal structure shows parallel layers formed by edge sharing UO₇ and NbO₆ polyhedra. Polyhedra of neighbouring layers (distance = b) are mutually corner linked.     

碳纤维阴极发射均匀性的实验研究

 分别用自制浸渍碘化铯（CsI）针式环状碳纤维阴极和环状不锈钢阴极所产生的电子束轰击尼龙目击靶,研究碳纤维阴极发射均匀性。在碳纤维阴极电子束轰击的目击靶上得到了均匀的烧蚀痕迹,而不锈钢阴极电子束轰击的目击靶上烧蚀痕迹不均匀,表明碳纤维阴极发射电子束的均匀性优于不锈钢阴极。分析认为两阴极不同的发射机制及其所特有的材料性质和结构导致其发射电子束均匀性的差异。用光学显微镜和电子显微镜对不锈钢阴极尖端和碳纤维阴极尖端和侧面进行扫描,发现不锈钢阴极仅尖端处被烧蚀,而碳纤维阴极尖端和侧面都有烧蚀痕迹,验证了碳纤维阴极由场发射和表面闪络共同作用的发射机制的假设分析。     

Coordinative Approach to Mediated Electron Transfer: Ruthenium Complexed to Native Glucose Oxidase

Catalytically and electrocatalytically very active and stable are the complexes Ru(LL)-GO, which are extremely readily accessible from glucose oxidase (GO) and the Ru^II complexes cis-[Ru(LL)₂Cl₂] (LL=bpy, phen). These provide an unprecedentedly high amplification coefficient I/I_o (see cyclic voltammograms) even at high scan rates and, correspondingly, very high rates of intramolecular electron transfer.     

Decreased Electron Transfer Rates of Manganese Porphyrins with Conformational Distortion of the Macrocycle

Slow electron transfer to manganese(iii) porphyrins results when the macrocycle deviates from planarity. This was demonstrated by measuring the kinetics of homogeneous electron transfer from a series of semiquinone radical anions to synthetic manganese porphyrins (shown schematically; R¹=H, Cl, F; R²=H, F). Three of the four porphyrins studied have nonplanar macrocycles. These results could have implications for the role of manganese in biological electron transfer processes.