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41.
The tellurium(II) dithiolates Te[SCH2CH2C(O)OCH3]2, ( 1 ), Te[SCH2CH2CH2SC(O)CH3]2, ( 2 ), and Te[SCH2CH2CH2CH2SC(O)CH3]2, ( 3 ) were synthesized from Te(StBu)2 and the corresponding thiol. All compounds are sensitive toward higher temperatures and light and decompose to elemental tellurium and the disulfide. In the solid state, the Te atom of 1 exhibits the novel Te(S2Te2) coordination mode. Additionally to the two Te—S bonds, each Te atom forms two long Te···Te contacts to neighboring molecules, leading to a coordination number of four and a distorted sawhorse configuration. No intramolecular Te···O interactions are present in the solid state, in accordance with ab initio calculations (MP2/ecp‐basis) for the isolated molecule. 125Te NMR shifts of all compounds lay within a narrow range and close to the respective shift of other Te(SCH2R)2 compounds. VT 125Te NMR spectra gave no hint to donor acceptor interactions in solution for any of the compounds and thus corroborate results from IR‐spectroscopy, ab initio geometry optimizations, and thermochemical calculations. 相似文献
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Johann Sjuts PD Dr 《ZDM》2005,37(5):424-430
Can the describable complexity of test problems concerning mathematical thinking and the empirical results of their dealing with be put into a relation? Can graded test problems be constructed which lead to results which can basically be predicted? Empirical studies give interesting and helpful answers which lead to didactically important consequences, just like the evaluation of the PISA results. 相似文献
44.
Stephan Berner Andreas B. Schmidt Mirko Zimmermann Dr. Andrey N. Pravdivtsev Dr. Stefan Glöggler Prof. Dr. Dr. h.c. Jürgen Hennig PD Dr. Dominik von Elverfeldt Prof. Dr. Jan-Bernd Hövener 《ChemistryOpen》2019,8(6):728-736
The signal enhancement provided by the hyperpolarization of nuclear spins of biological molecules is a highly promising technique for diagnostic imaging. To date, most 13C-contrast agents had to be polarized in an extra, complex or cost intensive polarizer. Recently, the in situ hyperpolarization of a 13C contrast agent to >20 % was demonstrated without a polarizer but within the bore of an MRI system. This approach addresses some of the challenges of MRI with hyperpolarized tracers, i. e. elevated cost, long production times, and loss of polarization during transfer to the detection site. Here, we demonstrate the first hyperpolarization of a biomolecule in aqueous solution in the bore of an MRI at field strength of 7 T within seconds. The 13C nucleus of 1-13C, 2,3-2H2-succinate was polarized to 11 % corresponding to a signal enhancement of approximately 18.000. Interesting effects during the process of the hydrogenation reaction which lead to a significant loss of polarization have been observed. 相似文献
45.
We present the theoretical basis for a profound upgrade of the method of absorbance band fitting (“band deconvolution”), which requires only minute changes in the code of corresponding spectrometer software. This upgrade is based on a (re-)connection of the damped harmonic oscillator model (“Lorentz oscillator”) and the Lorentz profile used for band fitting. Based on this reconnection, we provide a proper extension to multiple oscillators. As a result, band fitting allows directly obtaining all oscillator parameters with very good accuracy, at least for the not too strong oscillators present in organic and biological matter. Accordingly, this could be the initial spark to open the way to a long-awaited paradigm shift in infrared spectroscopy: Away from a mere oscillator position-based, towards an also intensity-based quantitative interpretation of spectra. As an extra, absorbance band fitting (“Poor Man's Dispersion Analysis”), allows to obtain the index of refraction function in one go. 相似文献
46.
PD Dr. Thomas G. Mayerhöfer Dr. Andrei V. Pipa Prof. Dr. Jürgen Popp 《Chemphyschem》2019,20(21):2748-2753
As derived by Max Planck in 1903 from dispersion theory, Beer's law has a fundamental limitation. The concentration dependence of absorbance can deviate from linearity, even in the absence of any interactions or instrumental nonlinearities. Integrated absorbance, not peak absorbance, depends linearly on concentration. The numerical integration of the absorbance leads to maximum deviations from linearity of less than 0.1 %. This deviation is a consequence of a sum rule that was derived from the Kramers-Kronig relations at a time when the fundamental limitation of Beer's law was no longer mentioned in the literature. This sum rule also links concentration to (classical) oscillator strengths and thereby enables the use of dispersion analysis to determine the concentration directly from transmittance and reflectance measurements. Thus, concentration analysis of complex samples, such as layered and/or anisotropic materials, in which Beer's law cannot be applied, can be achieved using dispersion analysis. 相似文献
47.
Daniel Duvinage Dr. Lorraine A. Malaspina PD Dr. Simon Grabowsky Dr. Stefan Mebs Prof. Dr. Jens Beckmann 《欧洲无机化学杂志》2023,26(1):e202200482
In a combined experimental and computational study, the molecular and electronic structures of the divalent bis(m-terphenyl)element cations [(2,6-Mes2C6H3)2E]+ of group 13 ( 1 , E=B; 2 , E=Al; 3 , E=Ga; 4 , E=In; 5 , E=Tl) were investigated. The preparation and characterization of 2 , 3 and 5 were previously reported by Wehmschulte's (Organometallics 2004 , 23, 1965–1967; J. Am. Chem. Soc. 2003 , 125, 1470–1471) and our groups (Organometallics 2009 , 28, 6893–6901). The indinium ion 4 was prepared and fully characterized for the first time. Attempts to prepare the borinium ion 1 by fluoride or hydride abstraction were unsuccessful. The electronic structures of 1 – 5 and the stabilization by the bulky m-terphenyl substituents were analyzed using quantum chemical calculations and compared to the divalent bis(m-terphenyl)pnictogenium ions [(2,6-Mes2C6H3)2E]+ of group 15 ( 6 , E=P; 7 , E=As; 8 , E=Sb; 9 , E=Bi) previously investigated by our group (Angew. Chem. Int. Ed. 2018 , 57, 10080–10084). The calculated fluoride ion affinities (FIA) of 1–9 are higher than that of SbF5, which classifies them as Lewis superacids. 相似文献
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Tim Tichter Jonathan Schneider PD Dr. Dirk Andrae Marcus Gebhard Prof. Dr. Christina Roth 《Chemphyschem》2020,21(5):428-441
An algorithm for the simulation and evaluation of cyclic voltammetry (CV) at macroporous electrodes such as felts, foams, and layered structures is presented. By considering 1D, 2D, and 3D arrays of electrode sheets, cylindrical microelectrodes, hollow-cylindrical microelectrodes, and hollow-spherical microelectrodes the internal diffusion domains of the macroporous structures are approximated. A universal algorithm providing the time-dependent surface concentrations of the electrochemically active species, required for simulating cyclic voltammetry responses of the individual planar, cylindrical, and spherical microelectrodes, is presented as well. An essential ingredient of the algorithm, which is based on Laplace integral transformation techniques, is the use of a modified Talbot contour for the inverse Laplace transformation. It is demonstrated that first-order homogeneous chemical kinetics preceding and/or following the electrochemical reaction and electrochemically active species with non-equal diffusion coefficients can be included in all diffusion models as well. The proposed theory is supported by experimental data acquired for a reference reaction, the oxidation of [Fe(CN)6]4− at platinum electrodes as well as for a technically relevant reaction, the oxidation of VO2+ at carbon felt electrodes. Based on our calculation strategy, we provide a powerful open source tool for simulating and evaluating CV data implemented into a Python graphical user interface (GUI). 相似文献
49.
Barrett AG Braddock DC de Koning PD White AJ Williams DJ 《The Journal of organic chemistry》2000,65(2):375-380
The double allylboration of aldehydes using 1, 3-bis(diisopinocampheylboryl)-2-methylenepropanes (R,R)-3 and (S, S)-3 under Brown's salt-free conditions provides C(2)-symmetric 3-methylenepentane-1,5-diols 1 in excellent enantiomeric excess. The absolute stereochemistry of the products was confirmed by a single-crystal X-ray study of bis-Mosher ester 6g. Desymmetrization and further functionalization of diol 1a were achieved by treatment of the bis-BOC carbonate 13 with IBr in toluene at -80 degrees C to give cyclic iodocarbonate 14 as a single diastereomer. This methodology is also applicable in natural product synthesis; enantiomerically pure spiroketals 1,7-dioxaspiro[5.5]undecanes 18 and 25, the latter representing an expedient synthesis of the AB ring system of the spongistatins 20, were easily accessed from simple starting materials in excellent yields and selectivities. 相似文献
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Roberto Menzel Eric Täuscher Dieter Weiß PD Dr. Rainer Beckert Prof. Dr. Helmar Görls 《无机化学与普通化学杂志》2010,636(7):1380-1385
Herein the syntheses of three novel ligands, in which an azaheterocycle is connected with a thiazole subunit: 4‐methoxy‐5‐methyl‐2‐pyridine‐2‐yl‐1,3‐thiazole ( 1 ), 4‐methoxy‐5‐methyl‐2‐pyrimidine‐2‐yl‐1,3‐thiazole ( 2 ) and 4‐methoxy‐5‐phenyl‐2‐pyridine‐2‐yl‐1,3‐thiazole ( 3 ) are reported. Because these ligands are cyclic versions of 1,4‐diazadienes, they offer good prerequisites for the synthesis of metal complexes and were employed as chelating ligands. Three novel heteroleptic cationic complexes of the type Ru(bpy)2( L ), with bpy = 2,2′‐bipyridine were successfully synthesised. The RuII complexes as well as the ligands were characterised by means of mass spectrometry, NMR, UV/Vis and IR spectroscopy and elemental analysis. Furthermore, an X‐ray structure of Ru(bpy)2 2 (PF6), as far as we know the first example where a thiazole is directly connected to a RuII core, is presented in this paper. 相似文献