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71.
Nikola Peřinka Markéta Držková Milena Hajná Bohumil Jašúrek Petra Šulcová Tomáš Syrový Marie Kaplanová Jaroslav Stejskal 《Journal of Thermal Analysis and Calorimetry》2014,116(2):589-595
The polyaniline dispersions stabilized with poly(N-vinylpyrrolidone) (PANI/PVP) were synthesized by oxidative polymerization with different mass ratios of PANI and PVP and different molar concentrations of the components in the polymerization mixture. The composite powders prepared from colloidal PANI/PVP dispersions were characterized by thermogravimetry and differential thermal analysis. The change in the ratio of PANI and PVP as well as the starting molar concentrations of aniline hydrochloride and oxidant has influence on the resulting properties of the dispersions. Concerning the doping, the results show that PANI/PVP powders are stable up to approximately 160 °C. Degradation of polymer chains starts at temperatures above 250 °C. The PANI/PVP composite powders with lower content of PANI exhibit slightly higher thermal stability. Further, colloidal PANI/PVP dispersions were screen-printed on aluminum foil for infrared spectroscopic characterization and on poly(ethylene terephthalate) foil for electrical measurements. The sheet resistance of printed layers measured by two-point probe was of the order of tens to thousands of kΩ sq?1. The influence of both the change in the composition and the drying temperature is discussed. 相似文献
72.
Dr. Jamie Hicks Dr. Petra Vasko Andreas Heilmann Prof. Jose M. Goicoechea Prof. Simon Aldridge 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20556-20560
The reactivity of the electron-rich anionic AlI aluminyl compound K2[(NON)Al]2 (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) towards mono- and disubstituted arenes is reported. C−H activation chemistry with n-butylbenzene gives exclusively the product of activation at the arene meta position. Mechanistically, this transformation proceeds in a single step via a concerted Meisenheimer-type transition state. Selectivity is therefore based on similar electronic factors to classical SNAr chemistry, which implies the destabilisation of transition states featuring electron-donating groups in either ortho or para positions. In the cases of toluene and the three isomers of xylene, benzylic C−H activation is also possible, with the product(s) formed reflecting the feasibility (or otherwise) of competing arene C−H activation at a site which is neither ortho nor para to a methyl substituent. 相似文献
73.
Jixin Qiao Petra Lagerkvist Ilia Rodushkin Susanna Salminen-Paatero Per Roos Syverin Lierhagen Karl Andreas Jensen Emma Engstrom Yann Lahaye Lindis Skipperud 《Journal of Radioanalytical and Nuclear Chemistry》2018,315(3):565-580
Inductively coupled plasma mass spectrometry (ICP-MS) techniques are widely used for determination of long-lived radionuclides and their isotopic ratios in the nuclear fields. Uranium (U) and Plutonium (Pu) isotopes have been determined by many researchers with ICP-MS due to its relatively high sensitivity and short measurement time. In this work, an inter-laboratory comparison exercise among the Nordic countries was performed, focusing on the measurement of U and Pu isotopes in certified reference materials by ICP-MS. The performance and characters of different ICP-MS instruments are evaluated and discussed in this paper. 相似文献
74.
Iain L. Marr Petra Kluge Laura Main Vincent Margerin Cyrille Lescop 《Mikrochimica acta》1995,119(3-4):219-232
Three sets of samples have been investigated in some detail. One set is from a river polluted by mine workings, containing substantial levels of Fe, Mn,Cu, Zn and Ni with traces of many other metals. The second set consists of typical estuarine sediments contaminated from a wide range of industrial sources, and the third set consists of oily drilling cuttings from the sea bottom in the vicinity of a North Sea oil production platform.These samples have been subjected to treatment 1) with EDTA at two different pH's (extracts) 2) with HNO3/H2O2 3) with HNO3/HCl and 4) with HNO3/HCl/HF (digests). EDTA recoveries, compared toaqua regia digests, are often very reproducible, not dependent on pH, and usually significantly low. Nitric/peroxide andaqua regia digests often give very close results suggesting that these are meaningful values indicating the maximum levels of polluting metals in the sediments. However, the triple acid digest with HF does sometimes give higher values (and reasonable agreement for CRM's such as MESS-1) but with poorer reproducibility. 相似文献
75.
76.
Lenka Kulhánková Jonáš Tokarský Petra Vilímová Pavlína Peikertová Oldřich Motyka 《Chemical Papers》2017,71(2):317-327
Preparation method of polyaniline/montmorillonite (PANI/MMT) nanocomposite in the form of thin layer deposited on various substrates is optimized in this work to obtain high electrical conductivity. Simple method (i.e. polymerization of anilinium sulfate in the presence of MMT) has been used for the preparation and following four conditions were varied: preparation temperature (T = 10 or 20 °C), preparation time (t = 4 or 6 h), size fraction of MMT (p < 1 or 5 µm), and type of substrate (microscope glass slides, silica glass slides, polyester foils). Therefore, 24 samples were prepared, characterized and their electrical conductivity was compared. Raman spectroscopy and scanning electron microscopy were used for the characterization of the structure of samples. Thickness of layers was measured using atomic force microscopy. Based on the comparison of samples and with respect to the aim of obtaining high electrical conductivity, it was found that the most suitable substrate is polyester foil and preparation conditions are T = 20 °C, t = 6 h, p < 5 µm. To obtain highly conductive layers on glass substrates (although less conductive than layers on foil), preparation time have to be shortened to 4 h. 相似文献
77.
Dipl.‐Chem. Alexander Rupp Dr. Nataliya Roznyatovskaya Dr. Harald Scherer Dr. Witali Beichel Petra Klose Carola Sturm Dr. Anke Hoffmann Dr. Jens Tübke Prof. Dr. Thorsten Koslowski Prof. Dr. Ingo Krossing 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(31):9794-9804
Several, partly new, ionic liquids (ILs) containing imidazolium and ammonium cations as well as the medium‐sized [NTf2]? (0.230 nm3; Tf=CF3SO3?) and the large [Al(hfip)4]? (0.581 nm3; hfip=OC(H)(CF3)2) anions were synthesized and characterized. Their temperature‐dependent viscosities and conductivities between 25 and 80 °C showed typical Vogel–Fulcher–Tammann (VFT) behavior. Ion‐specific self‐diffusion constants were measured at room temperature by pulsed‐gradient stimulated‐echo (PGSTE) NMR experiments. In general, self‐diffusion constants of both cations and anions in [Al(hfip)4]?‐based ILs were higher than in [NTf2]?‐based ILs. Ionicities were calculated from self‐diffusion constants and measured bulk conductivities, and showed that [Al(hfip)4]?‐based ILs yield higher ionicities than their [NTf2]? analogues, the former of which reach values of virtually 100 % in some cases.From these observations it was concluded that [Al(hfip)4]?‐based ILs come close to systems without any interactions, and this hypothesis is underlined with a Hirshfeld analysis. Additionally, a robust, modified Marcus theory quantitatively accounted for the differences between the two anions and yielded a minimum of the activation energy for ion movement at an anion diameter of slightly greater than 1 nm, which fits almost perfectly the size of [Al(hfip)4]?. Shallow Coulomb potential wells are responsible for the high mobility of ILs with such anions. 相似文献
78.
Leva S Lichte A Burmeister J Muhn P Jahnke B Fesser D Erfurth J Burgstaller P Klussmann S 《Chemistry & biology》2002,9(3):351-359
Mirror-image oligonucleotide ligands (Spiegelmers) that bind to the pharmacologically relevant target gonadotropin-releasing hormone I (GnRH) with high affinity and high specificity have been identified using the Spiegelmer technology. GnRH is a decapeptide that plays an important role in mammalian reproduction and sexual maturation and is associated with several benign and malignant diseases. First, aptamers that bind to D-GnRH with dissociation constants of 50-100 nM were isolated out of RNA and DNA libraries. The respective enantiomers of the DNA and RNA aptamers were synthesized, and their binding to L-GnRH was shown. These Spiegelmers bind to L-GnRH with similar affinity to that of the corresponding aptamers that bind to D-GnRH. We further demonstrated dose-dependent inhibition of GnRH-induced Ca(2+) release in Chinese hamster ovary cells that were stably transfected with the human GnRH receptor. 相似文献
79.
[reaction: see text] A new method for the synthesis of 2',3'-dideoxynucleoside analogues has been developed. An electrochemical activation of 2-substituted furans is followed by the coupling with a pyrimidine or purine base. This gives planar furyl nucleosides as key intermediates, which are hydrogenated cis-selectively to give the corresponding beta-2',3'-dideoxynucleosides as racemic mixtures. An enzymatic kinetic resolution gives rise to beta-D- and beta-L-configured derivatives in high optical purity. This is exemplified by the synthesis of beta-D- and beta-L-3'-deoxythymidine. 相似文献
80.
C. M. Dion P. Sjölund S. J.H. Petra S. Jonsell M. Nylén L. Sanchez-Palencia A. Kastberg 《The European physical journal. Special topics》2008,159(1):11-17
We study a Brownian motor, based on cold atoms in optical lattices, where atomic motion can be induced in a controlled manner
in an arbitrary direction, by rectification of isotropic random fluctuations. In contrast with ratchet mechanisms, our Brownian
motor operates in a potential that is spatially and temporally symmetric, in apparent contradiction to the Curie principle.
Simulations, based on the Fokker-Planck equation, allow us to gain knowledge on the qualitative behaviour of our Brownian
motor. Studies of Brownian motors, and in particular ones with unique control properties, are of fundamental interest because
of the role they play in protein motors and their potential applications in nanotechnology. In particular, our system opens
the way to the study of quantum Brownian motors. 相似文献