Nonclassical Recrystallization

Applications in the fields of materials science and nanotechnology increasingly demand monodisperse nanoparticles in size and shape. Up to now, no general purification procedure exists to thoroughly narrow the size and shape distributions of nanoparticles. Here, we show by analytical ultracentrifugation (AUC) as an absolute and quantitative high-resolution method that multiple recrystallizations of nanocrystals to mesocrystals is a very efficient tool to generate nanocrystals with an excellent and so-far unsurpassed size-distribution (PDI_c=1.0001) and shape. Similar to the crystallization of molecular building blocks, nonclassical recrystallization removes “colloidal” impurities (i.e., nanoparticles, which are different in shape and size from the majority) by assembling them into a mesocrystal. In the case of nanocrystals, this assembly can be size- and shape-selective, since mesocrystals show both long-range packing ordering and preferable crystallographic orientation of nanocrystals. Besides the generation of highly monodisperse nanoparticles, these findings provide highly relevant insights into the crystallization of mesocrystals.     

Effects of oxidation pretreatment temperature on Kovar used as CO_2 reforming catalyst

The effect of oxidation pretreatment temperature(500 ~ 1 000 ℃) on the catalytic activity of Kovar applied on hydrocarbon CO2reforming was examined. Catalytic performance evaluation using tetradecane at 800 ℃ with 70 μmol/s CO2revealed 700 and 1 000 ℃ as the best pre-oxidation temperature in producing CO and H2,respectively. XRD and SEM-EDX analyses showed that a separate metal oxide layer composed of iron oxide(Fe2O3and F3O4),nickel,cobalt,and possibly their respective oxides started to form when oxidation was conducted at 700 ℃ or higher.The presence of iron enhanced the stability of nickel in the structure while the compact structure of Fe3O4resulted into the formation of a thick and rigid metal oxide layer on the surface of the Kovar tube. The strong physical bond between the metal oxide layer and Kovar tube provided the catalyst good mechanical strength and consequently good catalytic activity.     

Determination of bis-carboxyethyl germanium sesquioxide by gas chromatography with microwave-induced plasma-atomic emission detection after derivatization with alkyl chloroformates

Organic germanium compounds, especially Ge-132, more corrctly denoted as bis-beta-carboxyethyl germanium sesquioxide ([Ge(=O)CH₂CH₂CO₂H]₂O), are of continued interest as they are said to promote health and display anticancer activity. Although these beneficial effects have never been substantiated by comprehensive clinical studies, this drug can still be obtained through various sources and is usually marketed as a nutritional supplementation rather than an anticancer medication. As the quality standards under which this drug is produced are unknown, the need for an effective quality control of these products arises. To date, Ge-132 is considered generally as a safe compound for application in contrast to inorganic germanium which demonstrates severe renal toxicity. In this paper, a new approach to the determination of Ge-132, based on derivatization by ethyl chloroformate reagent (ECF), in the presence of ethanol and pyridine in the mixture, and subsequent analysis by gas chromatography coupled with microwave-induced plasma-atomic emission detection (GC-MIP-AED), is reported. Reaction conditions of the derivatization procedure were optimized with particular respect to the reagent (ECF) and catalyst (pyridine) concentrations. The proposed method is capable of distinguishing Ge-132 from inorganic germanium. The derivatization procedure was also tested with the use of methyl chloroformate (MCF) as alternative reagent, providing interesting additional information about the nature of the final product and the proposed reaction scheme. Among the two types of chloroformates, i.e., MCF and ECF, the latter proved to be more suitable for the proposed method, providing a calibration curve of superior sensitivity and linearity compared with the one obtained with MCF. The method was applied successfully in three real samples, two food supplements, and one commercially available fertilizer. The analysis of the Ge-132 derivative showed good linearity in the concentration of 1–250 mg L^?1 (r ²?=?0.9986) and a satisfactory precision (RSD?=?6.8 %), which qualifies the proposed method for the speciation analysis of Ge in various matrices.     

Electrochemical determination of acetaminophen at a carbon electrode modified in the presence of β-cyclodextrin: role of the activated glassy carbon and the electropolymerised β-cyclodextrin

Acetaminophen is a well-known drug commonly used to provide pain relief, but it can also lead to acute liver failure at high concentrations. Therefore, there is considerable interest in monitoring its concentrations. Sensitive and selective acetaminophen electrochemical sensors were designed by cycling a glassy carbon electrode (GCE) to high potentials in the presence of β-CD in a phosphate electrolyte, or by simply activating the GCE electrode in the phosphate solution. Using cyclic voltammetry, adsorption-like voltammograms were recorded. The acetaminophen oxidation product, N-acetyl benzoquinone imine, was protected from hydrolysis, and this was attributed to the adsorption of acetaminophen at the modified GCE. The rate constants for the oxidation of acetaminophen were estimated as 4.3 × 10^–3 cm² s^–1 and 3.4 × 10^–3 cm² s^–1 for the β-CD-modified and -activated electrodes, respectively. Using differential pulse voltammetry, the limit of detection was calculated as 9.7 × 10^–8 M with a linear concentration range extending from 0.1 to 80 μM. Furthermore, good selectivity was achieved in the presence of caffeine, ascorbic acid and aspirin, enabling the determination of acetaminophen in a commercial tablet. Similar electrochemical data were obtained for both the β-CD-modified and activated GCE surfaces, suggesting that the enhanced detection of acetaminophen is connected mainly to the activation and oxidation of the GCE. Using SEM, EDX and FTIR, no evidence was obtained to indicate that the β-CD was electropolymerised at the GCE.

     

Design,Synthesis, and Validation of a Novel [11C]Promethazine PET Probe for Imaging Abeta Using Autoradiography

Promethazine, an antihistamine drug used in the clinical treatment of nausea, has been demonstrated the ability to bind Abeta in a transgenic mouse model of Alzheimer’s disease. However, so far, all of the studies were performed in vitro using extracted tissues. In this work, we report the design and synthesis of a novel [¹¹C]promethazine PET radioligand for future in vivo studies. The [¹¹C]promethazine was isolated by RP-HPLC with radiochemical purity >95% and molar activity of 48 TBq/mmol. The specificity of the probe was demonstrated using human hippocampal tissues via autoradiography.     

A paradigm shift in rate determining step from single electron transfer between phenylsulfinylacetic acids and iron(III) polypyridyl complexes to nucleophilic attack of water to the produced sulfoxide radical cation: a non‐linear Hammett

Mechanism of oxidative decarboxylation of phenylsulfinylacetic acids (PSAAs) by iron(III) polypyridyl complexes in aqueous acetonitrile medium has been investigated spectrophotometrically. An initial intermediate formation between PSAA and [Fe(NN)₃]³⁺ is confirmed from the observed Michaelis–Menten kinetics and fractional order dependence on PSAA. Significant rate retardation with concentration of [Fe(NN)₃]³⁺ is rationalized on the basis of coordination of a water molecule at the carbon atom adjacent to the ring nitrogen of the metal polypyridyl complexes by nucleophilic attack at higher concentrations. Electron‐withdrawing and electron‐releasing substituents in PSAA facilitate the reaction and Hammett correlation gives an upward ‘V’ shaped curve. The apparent upward curvature is rationalized based on the change in the rate determining step from electron transfer to nucleophilic attack, by changing the substituents from electron‐releasing to electron‐withdrawing groups. Electron‐releasing substituents in PSAA accelerate the electron transfer from PSAA to the complex and also stabilize the intermediate through resonance interaction leading to negative reaction constants (ρ). Conversely, electron‐withdrawing groups, while retarding the electron transfer exert an accelerating effect on the nucleophilic attack of H₂O which leading to low magnitude of ρ⁺ compared to high ρ^? values of electron‐releasing groups. Marcus theory is applied, and a fair agreement is seen with the experimental values. Copyright © 2016 John Wiley & Sons, Ltd.     

Longitudinal-transverse separations of deep-inelastic structure functions at low Q2 for hydrogen and deuterium

We report on a study of the longitudinal to transverse cross section ratio, R=sigmaL/sigmaT, at low values of x and Q2, as determined from inclusive inelastic electron-hydrogen and electron-deuterium scattering data from Jefferson Laboratory Hall C spanning the four-momentum transfer range 0.06相似文献