双线性滞回结构滤波问题的分段线性化法

提出了一种双线性滞回特性的分段微分表达式，根据伊藤随机微分方程和连续Markov向量过程的理论，导出了无须进行积分计算的双线性滞回结构的分段线性滤波器，简化了计算．算例表明，该法比随机等效线性化法和数字模拟的结果更为吻合．     

Uranium versus Thorium: Synthesis and Reactivity of [η5-1,2,4-(Me3C)3C5H2]2U[η2-C2Ph2]

The synthesis, electronic structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Addition of diphenylacetylene (PhC≡CPh) to the uranium phosphinidene metallocene [η⁵-1,2,4-(Me₃C)₃C₅H₂]₂U=P-2,4,6-tBu₃C₆H₂ ( 1 ) yields the stable uranium metallacyclopropene, [η⁵-1,2,4-(Me₃C)₃C₅H₂]₂U[η²-C₂Ph₂] ( 2 ). Based on density functional theory (DFT) results the 5f orbital contributions to the bonding within the metallacyclopropene U-(η²-C=C) moiety increases significantly compared to the related Th^IV compound [η⁵-1,2,4-(Me₃C)₃C₅H₂]₂Th[η²-C₂Ph₂], which also results in more covalent bonds between the [η⁵-1,2,4-(Me₃C)₃C₅H₂]₂U²⁺ and [η²-C₂Ph₂]²⁻ fragments. Although the thorium and uranium complexes are structurally closely related, different reaction patterns are therefore observed. For example, 2 reacts as a masked synthon for the low-valent uranium(II) metallocene [η⁵-1,2,4-(Me₃C)₃C₅H₂]₂U^II when reacted with Ph₂E₂ (E=S, Se), alkynes and a variety of hetero-unsaturated molecules such as imines, ketazine, bipy, nitriles, organic azides, and azo derivatives. In contrast, five-membered metallaheterocycles are accessible when 2 is treated with isothiocyanate, aldehydes, and ketones.     

Bonding charge density from atomic perturbations

Charge transfer among individual atoms is the key concept in modern electronic theory of chemical bonding. In this work, we present a first‐principles approach to calculating the charge transfer. Based on the effects of perturbations of an individual atom or a group of atoms on the electron charge density, we determine unambiguously the amount of electron charge associated with a particular atom or a group of atoms. We computed the topological electron loss versus gain using ethylene, graphene, MgO, and SrTiO₃ as examples. Our results verify the nature of chemical bonds in these materials at the atomic level. © 2015 Wiley Periodicals, Inc.     

Chiral N,O‐Ligand/[Cu(OAc)2]‐Catalyzed Asymmetric Construction of 4‐Aminopyrrolidine Derivatives by 1,3‐Dipolar Cycloaddition of Azomethine Ylides with α‐Phthalimidoacrylates

A protocol to access useful 4‐aminopyrrolidine‐2,4‐dicarboxylate derivatives has been developed. A variety of chiral N,O‐ligands derived from 2,3‐dihydroimidazo[1,2‐a]pyridine motifs have been evaluated in the asymmetric 1,3‐dipolar cycloaddition of azomethine ylides to α‐phthalimidoacrylates. Reactions catalyzed by copper in combination with ligand 7‐Cl‐DHIPOH provided the highest level of stereoselectivity for the 1,3‐dipolar cycloaddition reaction. The reaction tolerates both β‐substituted and β‐unsubstituted α‐phthalimidoacrylate as dipolarophiles, affording the corresponding quaternary 4‐aminopyrrolidine cycloadducts with excellent diastereo‐ (>98:2 d.r.) and enantioselectivities (up to 97 % ee). Removal of the phthalimido protecting group can be accomplished by a simple NaBH₄ reduction. Theoretical calculations employing DFT methods show this cycloaddition reaction is likely to proceed through a stepwise mechanism and the stereochemistry was also theoretically rationalized.     

CH Bond Activation by Early Transition Metal Carbide Cluster Anion MoC3−

Although early transition metal (ETM) carbides can activate C?H bonds in condensed‐phase systems, the electronic‐level mechanism is unclear. Atomic clusters are ideal model systems for understanding the mechanisms of bond activation. For the first time, C?H activation of a simple alkane (ethane) by an ETM carbide cluster anion (MoC₃^?) under thermal‐collision conditions has been identified by using high‐resolution mass spectrometry, photoelectron imaging spectroscopy, and high‐level quantum chemical calculations. Dehydrogenation and ethene elimination were observed in the reaction of MoC₃^? with C₂H₆. The C?H activation follows a mechanism of oxidative addition that is much more favorable in the carbon‐stabilized low‐spin ground electronic state than in the high‐spin excited state. The reaction efficiency between the MoC₃^? anion and C₂H₆ is low (0.23±0.05) %. A comparison between the anionic and a highly efficient cationic reaction system (Pt⁺+C₂H₆) was made. It turned out that the potential‐energy surfaces for the entrance channels of the anionic and cationic reaction systems can be very different.     

Colorimetric and visual determination of adenosine triphosphate using a boronic acid as the recognition element,and based on the deaggregation of gold nanoparticles

The authors describe a new kind of adenosine triphosphate (ATP) assay. It is based on the use of gold nanoparticles (AuNPs) coated with 4-mercaptophenylboronic acid (MPBA) as the recognition element for ATP. MPBA has a specific affinity for AuNPs through Au-S interaction, and three boronic acid groups undergo condensation to form a boroxine ring. This induces the aggregation of AuNPs and a visible color change from red to blue. However, in the presence of ATP, the boronic acid group of MPBA preferentially binds to the 2’, 3’-hydroxy group of ATP to form a stable boronate ester. Hence, the aggregation of AuNPs is progressively decreased as the concentration of ATP increases, and the color change is increasingly reversed. The ratio of absorbance at 520 and 683 nm increases linearly in the 8 to 100 μM ATP concentration range, with a 0.12 μM limit of detection (at an S/N ratio of 3 σ). The colorimetric assay was successfully applied to the determination of ATP in T47D breast cancer cells and in cultured cells with added anticarcinogen.

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Graphical abstract Schematic of a colorimetric assay for the visualization and sensitive and selective detection of adenosine triphosphate (ATP) based on the use of gold nanoparticles (AuNPs) coated with 4-mercaptophenylboronic acid (MPBA). The assay was applied to the determination of ATP in T47D breast cancer cells and in cultured cells with added anticarcinogen.

     

Selective separation and determination of the synthetic colorants in beverages by magnetic solid‐phase dispersion extraction based on a Fe3O4/reduced graphene oxide nanocomposite followed by high‐performance liquid chromatography with diode array detection

A facile adsorbent, a nanocomposite of Fe₃O₄ and reduced graphene oxide, was fabricated for the selective separation and enrichment of synthetic aromatic azo colorants by magnetic solid‐phase dispersion extraction. The nanocomposite was synthesized in a one‐step reduction reaction and characterized by atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X‐ray diffraction and Brunauer–Emmett–Teller analysis. The colorants in beverages were quickly adsorbed onto the surface of the nanocomposite with strong π–π interactions between colorants and reduced graphene oxide, and separated with the assistance of an external magnetic field. Moreover, the four colorants in beverages were detected at different wavelengths by high performance liquid chromatography with diode array detection. A linear dependence of peak area was obtained over 0.05–10 μg/mL with the limits of detection of 10.02, 11.90, 10.41, 15.91 ng/mL for tartrazine, allure red, amaranth, and new coccine, respectively (signal to noise = 3). The recoveries for the spiked colorants were in the range of 88.95–95.89% with the relative standard deviation less than 2.66%. The results indicated that the nanocomposite of Fe₃O₄ and reduced graphene oxide could be used as an excellent selective adsorbent for aromatic compounds and has potential applications in sample pretreatment.     

Palladium‐Catalyzed Enantioselective CH Arylation for the Synthesis of P‐Stereogenic Compounds

A palladium‐catalyzed enantioselective C? H arylation of N‐(o‐bromoaryl)‐diarylphosphinic amides is described for the synthesis of phosphorus compounds bearing a P‐stereogenic center. The method provides good enantioselectivities and high yields. The products were readily transformed into P‐chiral biphenyl monophosphine ligands.     

Sub‐ppt Level Detection of Mercury(II) Based on Anodic Stripping Voltammetry with Prestripping Step at an In Situ Formed Bismuth Film Modified Glassy Carbon Electrode

Sensitive and selective detection of Hg²⁺ in solution is a challenging work. An anodic stripping voltammetry with prestripping step at an in situ formed bismuth film modified glassy carbon electrode was proposed for detection of mercury(II) in solution. This prestripping step was able to decrease the background and improve the signal‐to‐noise ratio and thus enhance the sensitivity. With this method, highly sensitive and selective detection of Hg²⁺ with a ppt‐level detection limit of 0.5 ng L^?1 could be achieved. Moreover, this method provides low interference, rapid and extreme simple and convenience, and hold great promise for in situ Hg²⁺ determination.     

Flow injection-chemiluminescence determination of phenol using potassium permanganate and formaldehyde system

It is found that phenol can react with potassium permanganate in the acidic medium and produce chemiluminescence, which is greatly enhanced by formaldehyde. The optimum conditions for this chemiluminescent reaction are in detail studied using a flow injection system. The experiments indicate that under optimum conditions, the chemiluminescence intensity is linearly related to the concentration of phenol in the range 5.0x10(-9) to 1.0x10(-6)gmL-1 with a detection limit (3sigma) of 3x10(-9)gmL-1. The relative standard deviation is 1.2% for 4.0x10(-7)gmL-1 phenol solution in 11 repeated measurements. This method has the advantages of simple operation, fast response and high sensitivity. The method is successfully applied to the determination of phenol in the waste water.