Effect of Pr doping on magnetic and dielectric properties of Ni-Zn ferrites by “one-step synthesis”

Pr³⁺-doped Ni-Zn ferrites with a nominal composition of Ni_0.5Zn_0.5Pr_xFe_2−xO₄ (where x=0-0.08) were prepared by a one-step synthesis. The magnetic and dielectric properties of the as-prepared Ni-Zn ferrites were investigated. X-ray diffraction data indicated that, after doping, all samples consisted of the main spinel phase in combination of a small amount of a foreign PrFeO₃ phase. The lattice constants of the ferrites initially increased after Pr³⁺ doping, but then became smaller with additional Pr³⁺ doping. The addition of Pr³⁺ resulted in a reduction of grain size and an increase of density and densification of the as-prepared samples. Magnetic measurement revealed that the saturation magnetization of the as-prepared ferrites, M_s, decreased, while the coercivity, H_c, increased with increasing substitution level, x, and the Curie temperature, T_c, kept a rather high value, fluctuating between 308 and 320 °C. Both the real and imaginary parts of permeability of the ferrites decreased slightly after Pr³⁺ doping. However, the natural resonance frequency shifted towards higher frequency from 13.07 to 36.17 MHz after the addition of Pr³⁺, driving the magnetic permeability to much higher frequency, reaching the highest value (36.17 MHz) when x=0.04. Introduction of Pr³⁺ ions into the Ni-Zn ferrite reduced the values of the dielectric loss tangent, especially in the frequency range of 1-400 MHz. However, the magnitude of dielectric loss of the samples doped with different amounts of Pr³⁺ raised little.     

Mass Spectrometric Strategies to Improve the Identification of Pt(II)-Modification Sites on Peptides and Proteins

To further explore the binding chemistry of cisplatin (cis-Pt(NH₃)₂Cl₂) to peptides and also establish mass spectrometry (MS) strategies to quickly assign the platinum-binding sites, a series of peptides with potential cisplatin binding sites (Met(S), His(N), Cys(S), disulfide, carboxyl groups of Asp and Glu, and amine groups of Arg and Lys, were reacted with cisplatin, then analyzed by electron capture dissociation (ECD) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). Radical-mediated side-chain losses from the charge-reduced Pt-binding species (such as CH₃S^? or CH₃SH from Met, SH^? from Cys, CO₂ from Glu or Asp, and NH₂ ^? from amine groups) were found to be characteristic indicators for rapid and unambiguous localization of the Pt-binding sites to certain amino acid residues. The method was then successfully applied to interpret the top-down ECD spectrum of an inter-chain Pt-crosslinked insulin dimer, insulin?+?Pt(NH₃)₂?+?insulin (>10 kDa). In addition, ion mobility MS shows that Pt binds to multiple sites in Substance P, generating multiple conformers, which can be partially localized by collisionally activated dissociation (CAD). Platinum(II) (Pt(II)) was found to coordinate to amine groups of Arg and Lys, but not to disulfide bonds under the conditions used. The coordination of Pt to Arg or Lys appears to arise from the migration of Pt(II) from Met(S) as shown by monitoring the reaction products at different pH values by ECD. No direct binding of cisplatin to amine groups was observed at pH 3?~?10 unless Met residues were present in the sequence, but noncovalent interactions between cisplatin hydrolysis and amination [Pt(NH₃)₄]²⁺ products and these peptides were found regardless of pH.

Crystallization behavior and morphology of β‐nucleated isotactic polypropylene with different stereo‐defect distribution

Aiming at further investigating the combination effect of concentration of β‐nucleating agent (β‐NA) and stereo‐defect distribution on the crystallization behavior of β‐nucleated isotactic polypropylene (β‐iPP), in this study, the crystallization behavior and polymorphic morphology of twoβ‐iPP resins with nearly same average isotacticity (PP‐A and PP‐B) but different uniformities of stereo‐defect distribution were investigated by differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD) and polarized optical microscopy (POM). The results of DSC and WAXD showed that the addition of TMB‐5 increases the crystallization temperature and decreases the spherulite sizes of both PP‐A and PP‐B, and reduces their crystallization energy barriers as well; however, the polymorphic behaviors of PP‐A and PP‐B exhibit different dependence on the TMB‐5 concentration. For PP‐A with less uniform distribution of stereo‐defects, β‐phase can be observed only when the TMB‐5 concentration is no less than 0.1 wt.%, while for PP‐B with more uniform stereo‐defect distribution, addition of 0.01 wt.% TMB‐5 can induce the formation of β‐phase. Moreover, the analysis of POM indicated that the crystalline morphologies of both PP‐A and PP‐B change greatly with the TMB‐5 concentration, and the variation features of PP‐A and PP‐B are quite different from each other. PP‐B with more uniform stereo‐defect distribution was more favorable for the formation of large amount of β‐phase in the presence of wide concentration range of TMB‐5. The different polymorphic behaviors and their different dependences on the β‐NA concentration were related to the different uniformities of stereo‐defect distribution of the samples, since the distribution of stereo‐defects could restrain the regular insertion of molecular chains during crystallization and thus determine the tendency the α‐phase crystallization of the sample. Copyright © 2014 John Wiley & Sons, Ltd.     

Investigation on the dynamic crystallization and melting behavior of β‐nucleated isotactic polypropylene with different stereo‐defect distribution—the role of dual‐selective β‐nucleation agent

The selectivities of different β‐nucleating agents might be quite different from each other, which is important in determining the crystallization and properties of the obtained β‐isotactic polypropylene (β‐iPP). However, the relationship between molecular structure and dynamic crystallization behavior of β‐iPP nucleated by dual‐selective β‐nucleating agent (DS‐β‐NA) is still not clear. In this study, the dynamic crystallization and melting behavior of two β‐iPP with nearly same average isotacticity but different stereo‐defect distribution, nucleated by a DS‐β‐NA (N,N′‐dicyclohexyl‐2,6‐naphthalenedicarboxamide; trade name TMB‐5), were studied by differential scanning calorimetry, wide‐angle X‐ray diffraction, and scanning electronic microscopy. The results indicated that in the presence of TMB‐5, the dynamic crystallization and melting behavior of the samples are quite different because the joint effects of the dual selectivity of TMB‐5 and stereo‐defect distribution of the iPP under different cooling rates. Two important roles were observed: (i) slow cooling rate favors the formation of high β‐fraction; and (ii) high crystallization temperature favors the crystallization of α‐phase accelerated by TMB‐5. Generally, the dual selectivity of the DS‐β‐NA, the stereo‐defect distribution of iPP, and the cooling rate were important factors in determining the formation of β‐crystal. Copyright © 2013 John Wiley & Sons, Ltd.     

Solution Dependence of the Collisional Activation of Ubiquitin [M + 7H]7+ Ions

The solution dependence of gas-phase unfolding for ubiquitin [M + 7H]⁷⁺ ions has been studied by ion mobility spectrometry-mass spectrometry (IMS-MS). Different acidic water:methanol solutions are used to favor the native (N), more helical (A), or unfolded (U) solution states of ubiquitin. Unfolding of gas-phase ubiquitin ions is achieved by collisional heating and newly formed structures are examined by IMS. With an activation voltage of 100 V, a selected distribution of compact structures unfolds, forming three resolvable elongated states (E1-E3). The relative populations of these elongated structures depend strongly on the solution composition. Activation of compact ions from aqueous solutions known to favor N-state ubiquitin produces mostly the E1 type elongated state, whereas activation of compact ions from methanol containing solutions that populate A-state ubiquitin favors the E3 elongated state. Presumably, this difference arises because of differences in precursor ion structures emerging from solution. Thus, it appears that information about solution populations can be retained after ionization, selection, and activation to produce the elongated states. These data as well as others are discussed. Figure

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Diels–Alder/Oxidative Aromatization Approach towards the All‐Carbon DEF Tricyclic Skeleton of Daphenylline

Daphenylline is a recently isolated Daphniphyllum alkaloid with an unprecedented novel hexacyclic scaffold. In this study, the synthesis of the fused all‐carbon DEF tricyclic skeleton of daphenylline has been accomplished. Key steps of the reported sequence involve Evans asymmetric allylation, aldol condensation, Diels–Alder reaction, and oxidative aromatization reactions. The developed strategy might lead to the total synthesis of daphenylline.     

蟹状星云脉冲星的TeV γ射线周期发射

利用自行研制的两台大气切伦科夫望远镜(ACT2和ACT3),在1995年秋至1996年春的观测季节对蟹状星云脉冲星进行了168小时(ACT2)和126小时(ACT3)的跟踪观测.分析这些数据没有发现有月或天时间尺度稳定的33ms周期的TeVγ射线发射,但发现两段持续几十分钟的暴发样本具有33ms周期.     

利用真实气体效应提高激波阶跃压力

在本文中提出了在激波管中,利用真实气体效应来提高激波阶跃压力的新方法,该方法对获得阶跃特性好的高阶跃压力(例如,动压标定等)是非常好。它是借助在高压下计及分子之间作用力、分子体积效应和激励效应而获得压力增益。经分析和试验表明,该方法得到.阶跃压力是比理想气体高出30％,该方法在国内外尚未进行系统研究,是一个有发展前途的方法。     

限域于SBA-15孔道内的活性相聚集形态

针对Pd/SBA-15和MoO3/SBA-15两类催化剂样品,使用N2物理吸附手段对比研究了限域于介孔SBA-15分子筛孔道内活性相Pd与MoO3的聚集形态.结果表明,金属Pd以颗粒状形态分布在SBA-15分子筛孔道内,氧化物MoO3则以层状形态存在.并用高分辨透射电镜验证了此分析结果.     

Molecular Engineering of a Metal-Organic Polymer for Enhanced Electrochemical Nitrate-to-Ammonia Conversion and Zinc Nitrate Batteries

Metal–organic framework-based materials are promising single-site catalysts for electrocatalytic nitrate (NO₃⁻) reduction to value-added ammonia (NH₃) on account of well-defined structures and functional tunability but still lack a molecular-level understanding for designing the high-efficient catalysts. Here, we proposed a molecular engineering strategy to enhance electrochemical NO₃⁻-to-NH₃ conversion by introducing the carbonyl groups into 1,2,4,5-tetraaminobenzene (BTA) based metal-organic polymer to precisely modulate the electronic state of metal centers. Due to the electron-withdrawing properties of the carbonyl group, metal centers can be converted to an electron-deficient state, fascinating the NO₃⁻ adsorption and promoting continuous hydrogenation reactions to produce NH₃. Compared to CuBTA with a low NO₃⁻-to-NH₃ conversion efficiency of 85.1 %, quinone group functionalization endows the resulting copper tetraminobenzoquinone (CuTABQ) distinguished performance with a much higher NH₃ FE of 97.7 %. This molecular engineering strategy is also universal, as verified by the improved NO₃⁻-to-NH₃ conversion performance on different metal centers, including Co and Ni. Furthermore, the assembled rechargeable Zn−NO₃⁻ battery based on CuTABQ cathode can deliver a high power density of 12.3 mW cm⁻². This work provides advanced insights into the rational design of metal complex catalysts through the molecular-level regulation for NO₃⁻ electroreduction to value-added NH₃.