Assessment of the chemical and enantiomeric purity of organic reference materials

This review evaluates commonly used methodologies for assessing the chemical purity of organic reference materials. Direct assay of the principal component can be established by methodologies such as gas chromatography, liquid chromatography (LC), quantitative nuclear magnetic resonance (NMR), elemental analysis and titrimetry. Measurements of detectable impurity components mainly include determination of water or moisture content, and analysis of residual solvents, and organic and inorganic impurities. To complete assessment of chemical purity, it is necessary to determine the enantiomeric purity of chiral organic reference materials. Promising methodologies for analysis include LC with chiral stationary phases, capillary electrophoresis using chiral selectors, and NMR with chemical-shift reagents.     

Axial ligand influence on geometries, charge distributions and electronic structures of iron tetraazamacrocycle [FeTIM(X)(Y)] complexes assessed by Density Functional Theory

We employed the Density Functional Theory along with small basis sets, B3LYP/LANL2DZ, for the study of FeTIM complexes with different pairs of axial ligands (CO, H₂O, NH₃, imidazole and CH₃CN). These calculations did not result in relevant changes of molecular quantities as bond lengths, vibrational frequencies and electronic populations supporting any significant back-donation to the carbonyl or acetonitrile axial ligands. Moreover, a back-donation mechanism to the macrocycle cannot be used to explain the observed changes in molecular properties along these complexes with CO or CH₃CN. This work also indicates that complexes with CO show smaller binding energies and are less stable than complexes with CH₃CN. Further, the electronic band with the largest intensity in the visible region (or close to this region) is associated to the transition from an occupied 3d orbital on iron to an empty π^∗ orbital located at the macrocycle. The energy of this Metal-to-Ligand Charge Transfer (MLCT) transition shows a linear relation to the total charge of the macrocycle in these complexes as given by Mulliken or Natural Population Analysis (NPA) formalisms. Finally, the macrocycle total charge seems to be influenced by the field induced by the axial ligands.     

Recent progress in transition metal catalysed hydrofunctionalisation of less activated olefins

The electrophilic activation(C-H activation) of alkenes by transition metal catalysts is a fundamental step in a rapidly growing number of catalytic processes since it would provide simple, clean, and economic methods for making controlled and selectively functionalized organic moieties directly from simple olefins. Also catalytic activation of C-H bonds leading to useful organic reactions such as new C-C, C-N and C-O bond formation is of considerable interest for the chemical and pharmaceutical industries and remained a long-term challenge to chemists. A substantial progress has made in the last decade in this area. Contrary to traditional belief, it is nowadays possible to control the regiochemistry of various additions of nucleophiles to alkenes by the choice of transition metal catalysts. Atom economy, an inevitable factor of current research also can be accomplished in these reactions. Developments in this area of selective hydrofunctionalisation of alkenes by taking into consideration of the mechanistic aspects and the role of organometallic catalyst or active species formed during the reaction on the outcome of the reactions are reviewed.     

Transition metal alkylidene complexes. Pathways in their formation and tautomerization between bis-alkylidenes and alkyl alkylidynes

Studies from authors’ group (at the University of Tennessee) on alkylidene complexes and α-H migration in alkyl alkylidyne complexes, leading to unusual tautomerization equilibria between bis-alkylidenes and alkyl alkylidynes, are reviewed. Preparation of silyl alkylidene complexes (Me₃ECH₂)₂Ta(CHEMe₃)(SiR₃) [R₃ = (SiMe₃)₃, E = C, 3a, Si, 3b; R₃ = Bu^tPh₂, E = C, 4a, Si, 4b] and the pathway in the formation of 3b are discussed first. Pathways in the formation of archetypical Schrock-type alkyl alkylidenes (Me₃ECH₂)₃TaCHEMe₃ (E = C, 5a; Si, 5b), including the work using Ta(CD₂CMe₃)₅ (21-d₁₀) to confirm that it is the precursor to (Me₃CCD₂)₃TaCDCMe₃ (5a-d₇), are then considered. Tautomerization of silyl alkylidyne (Me₃CCH₂)₂W(CCMe₃)(SiBu^tPh₂) (6a) with bis-alkylidene (Me₃CCH₂)W(CHCMe₃)₂(SiBu^tPh₂) (6b) as well as (Me₃SiCH₂)₃W(CSiMe₃)(PR₃) [R₃ = Me₃, 7a; Me₂Ph, 8a; Me₂(CH₂)₂PMe₂ (DMPE-P), 9a] with (Me₃SiCH₂)₂W(CHSiMe₃)₂(PR₃) (R₃ = Me₃, 7b; Me₂Ph, 8b; DMPE-P, 9b) [P refers to a dangling P atom in Me₂P(CH₂)₂PMe₂] is covered next. Finally the conversion of the tungsten phosphine tautomerization mixtures to alkyl alkylidene alkylidyne (Me₃SiCH₂)W(CHSiMe₃)(CSiMe₃)(PR₃)₂ [(PR₃)₂ = (PMe₃)₂, 10; (PMe₂Ph)₂, 11; DMPE, 12], including its pathway, is presented.     

Z-Selective hydroamidation of terminal alkynes with secondary amides and imides catalyzed by a Ru/Yb-system

A catalyst system formed in situ from bis(2-methallyl)cycloocta-1,5-diene-ruthenium(II) [(cod)Ru(met)₂], 1,4-bis(dicyclohexylphosphino)butane (dcypb) and ytterbium(III) triflate hydrate (Yb(OTf)₃) was found to catalyze the addition of nitrogen nucleophiles to terminal alkynes under mild conditions to stereoselectively form the Z-enamide or Z-enimide products. Various secondary amides and imides could be added across the triple bond of a range of aliphatic and aromatic alkynes. The new bimetallic catalyst system sets new standards with regard to scope and selectivity for the synthesis of Z-configured anti-Markovnikov enamides.     

Synthesis, luminescence properties of a novel aromatic carboxylic acid (L) and corresponding Eu(III) and Tb(III) compounds as well as the binding characteristics of L with bovine serum albumin (BSA)

A novel polyamino polycarboxylic pyridine derivative ligand, N,N,N¹,N¹-(2,6-bis((3-(aminoethyl)-5-methyl-1H-pyrazol-1-yl)methyl)pyridine)hexakis(acetic acid) (L), was designed and synthesized with the motive that it is able to sensitize the emission of lanthanides. Its corresponding Eu(III) and Tb(III) complexes Na₄EuLCl₃·3H₂O and Na₄TbLCl₃·5H₂O were successfully prepared. The ligand and the complexes were characterized by elemental analysis, IR, MS, NMR and TG-DTA. The luminescence properties of the compounds in solid state were investigated; each complex had very narrow emission bands and strong luminescence intensity up to about 10,000. The TG-DTA studies showed that the initial decomposition temperature of both complexes was over 250 °C, elucidating the complexes had a high thermal stability. Meanwhile, the comparison with similar complexes suggested that the ligand with more coordination sites possessed more efficient antenna effect. To explore the potential medicinal value of L, the binding interaction of L and bovine serum albumin (BSA) was carried out by fluorescence spectrum. The studies indicated that the reaction between L and BSA was a static quenching procedure. The binding site number n and binding constant Ka were calculated according to the double logarithm regression equation. The thermodynamic parameters showed the Van der Waals and hydrogen bond interactions were the mainly impulse to the reaction.     

A New Electrochemical Biosensor for Determination of Hydrogen Peroxide in Food Based on Well‐Dispersive Gold Nanoparticles on Graphene Oxide

Herein, we describe a new method for the detection of hydrogen peroxide (H₂O₂) in food by using an electrochemical biosensor. Initially, ultrafine gold nanoparticles dispersed on graphene oxide (AuNP‐GO) were synthesized by the redox reaction between AuCl₄^? and GO, and thionine‐catalase conjugates were then assembled onto the AuNP‐GO surface on a glassy carbon electrode. With the aid of the AuNP‐GO, the as‐prepared biosensor exhibited good electrocatalytic efficiency toward the reduction of H₂O₂ in pH 5.8 acetic acid buffer. Under optimal conditions, the dynamic responses of the biosensor toward H₂O₂ were achieved in the range from 0.1 µM to 2.3 mM, and the detection limit (LOD) was 0.01 µM at 3s_B. The Michaelis–Menten constant was measured to be 0.98 mM. In addition, the repeatability, reproducibility, selectivity and stability of the biosensor were investigated and evaluated in detail. Finally, the method was applied for sensing H₂O₂ in spiked or naturally contaminated samples including sterilized milk, apple juices, watermelon juice, coconut milk, and mango juice, receiving good correspondence with the results from the permanganate titration method. The disposable biosensor could offer a great potential for rapid, cost‐effective and on‐field analysis of H₂O₂ in foodstuff.     

空穴掺杂铱氧化物Srn+1IrnO3n+1 (n=1,2)的角分辨光电子能谱研究

近年来, 与铜氧化物高温超导体具有类似电子结构的5d 轨道 Ruddlesden-Popper 类型铱氧化物由于体系中库伦排斥和自旋轨道耦合之间的合作效应被人们广泛探究. 其中, 金属绝缘体转变的关键影响因素是该方向的核心研究问题, 该结果对推进掺杂莫特绝缘体体系的研究具有重要作用. 因为铱氧化物与铜氧化物在单能带哈伯德模型的次 近 邻 跃 迁 项 具 有 不 同 符 号, 因 此 空 穴 掺 杂 铱 氧 化 物 类 比 电 子 掺 杂 铜 氧 化 物. 我 们 将 空 穴 掺 杂Ruddlesden-Popper 类型铱氧 化 物 系 统 依 据 几 种 不 同 的 掺 杂 元 素 进 行 分 类, 分 别 介 绍 其 角 分 辨 光 电 子 能 谱(ARPES) 探测到的电子结构, 对其中金属绝缘体转变类型进行了总结, 并对该领域中的未来研究方向做出了展望.     

A dual-mode biosensor for salivary cortisol with antibody-aptamer sandwich pattern and enzyme catalytic amplification

Journal of Solid State Electrochemistry - A split-type and dual-mode (photoelectrochemical and electrochemical, PEC and EC) biosensor was developed for non-invasive and sensitive detection of...