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121.
Saskia Mller Hans-Joachim Drexler Detlef Heller 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(10):1434-1438
The complexes {bis[(2‐diphenylphosphanyl)phenyl] ether‐κ2P,P′}(η4‐norbornadiene)rhodium(I) tetrafluoridoborate, [Rh(C7H8)(C36H28OP2)]BF4, and {bis[(2‐diphenylphosphanyl)phenyl] ether‐κ2P,P′}[η4‐(Z,Z)‐cycloocta‐1,5‐diene]rhodium(I) tetrafluoridoborate dichloromethane monosolvate, [Rh(C8H12)(C36H28OP2)]BF4·CH2Cl2, are applied as precatalysts in redox‐neutral atomic‐economic propargylic CH activation [Lumbroso et al. (2013). Angew. Chem. Int. Ed. 52 , 1890–1932]. In addition, the catalytically inactive pentacoordinated 18‐electron complex {bis[(2‐diphenylphosphanyl)phenyl] ether‐κ2P,P′}chlorido(η4‐norbornadiene)rhodium(I), [RhCl(C7H8)(C36H28OP2)], was synthesized, which can form in the presence of chloride in the reaction system. 相似文献
122.
The generation of vortical structures by a strong magnetic dipole field in a liquid metal duct flow is studied by means of three-dimensional direct numerical simulations. The dipole is considered as the paradigm for a magnetic obstacle which will deviate the streamlines due to Lorentz forces which act on the fluid elements. Our model uses the quasi-static approximation applicable in the limit of small magnetic Reynolds numbers. The analysis covers the stationary flow regime at smaller flow Reynolds numbers Re as well as the fully time-dependent regimes at higher values with a turbulent flow in the wake of the magnetic obstacle. We present a systematic study of these two basic flow regimes on Re and the Hartmann number Ha, a measure of the strength of the magnetic dipole field. Furthermore, three orientations of the dipole are compared, the streamwise, spanwise and wall-normal ones. The most efficient generation of turbulence at a fixed distance above the duct occurs for the spanwise orientation in which we can observe the formation of Hartmann layers at the top plate. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
123.
Niall M. McLoughlin Dr. Arne Kuepper Dr. Saskia Neubacher Prof. Dr. Tom N. Grossmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(40):10477-10483
Biomolecular assemblies composed of proteins and oligonucleotides play a central role in biological processes. While in nature, oligonucleotides and proteins usually assemble via non-covalent interactions, synthetic conjugates have been developed which covalently link both modalities. The resulting peptide-oligonucleotide conjugates have facilitated novel biological applications as well as the design of functional supramolecular systems and materials. However, despite the importance of concerted protein/oligonucleotide recognition in nature, conjugation approaches have barely utilized the synergistic recognition abilities of such complexes. Herein, the structure-based design of peptide-DNA conjugates that bind RNA through Watson-Crick base pairing combined with peptide-mediated major groove recognition is reported. Two distinct conjugate families with tunable binding characteristics have been designed to adjacently bind a particular RNA sequence. In the resulting ternary complex, their peptide elements are located in proximity, a feature that was used to enable an RNA-templated click reaction. The introduced structure-based design approach opens the door to novel functional biomolecular assemblies. 相似文献
124.
Methyl-branched fatty acids (MBFAs) are the dominant form of fatty acid found in many bacteria. They are also found at low
levels in a range of foodstuffs, where their presence has been linked to bacterial sources. In this study we evaluated the
potential of compound-specific isotope analysis to obtain insights into the stable carbon isotope ratios (δ13C values in ‰) of individual MBFAs and to compare them to the stable carbon isotope ratios of straight-chain fatty acids in
food. Due to their low abundance in foodstuffs, the MBFAs were enriched prior to gas chromatography coupled to isotope ratio
mass spectrometric (GC–IRMS) analysis. After transesterification, urea complexation was used to suppress the 16:0 and 18:0
methyl esters that were dominant in the samples. Following that, silver-ion high performance liquid chromatography was used
to separate the saturated from the unsaturated fatty acids. The resulting solutions of saturated fatty acids obtained from
suet, goat’s milk, butter, and human milk were studied by GC–IRMS. The δ13C values of fatty acids with 12–17 carbons ranged from −25.4‰ to −37.6‰. In all samples, MBFAs were most depleted in carbon-13,
followed by the odd-chain fatty acids 15:0 and 17:0. 14:0 and 16:0 contained the highest proportions of carbon-13. The results
from this study illustrate that MBFAs have distinctive δ13C values and must originate from other sources and/or from very different substrates. These measurements support the initial
hypothesis that δ13C values can be used to attribute MBFAs to particular sources. 相似文献
125.
Degen P Paulus M Maas M Kahner R Schmacke S Struth B Tolan M Rehage H 《Langmuir : the ACS journal of surfaces and colloids》2008,24(22):12958-12962
We studied the adsorption of gamma-Fe 2O 3 nanoparticles from an aqueous solution under different charged Langmuir monolayers (stearic acid, stearyl alcohol, and stearyl amine). The aqueous subphase was composed of a colloidal suspension of gamma-Fe 2O 3 nanoparticles. The average hydrodynamic diameter of the nanoparticles measured by dynamic light scattering measurements was 16 nm. The observed zeta potential of +40 mV (at pH 4) results in a long-term stability of the colloidal dispersion. The behavior of the different monolayer/nanoparticle composites were studied with surface pressure/area (pi/ A) isotherms. The adsorption of the nanoparticles under the different monolayers induced an expansion of the monolayers. These phenomena depended on the charge of the monolayers. After the Langmuir/Blodgett transfer on glass substrates, the nanoparticle/monolayer composite films were studied by means of UV-vis spectroscopy. The spectra pointed to increasing adsorption of the nanoparticles with increasing electronegativity of the monolayers. On the basis of these results, we studied the in situ adsorption of nanoparticles under the different monolayers by X-ray reflectivity measurements. Electron density profiles of the liquid/gas interfaces were obtained from the X-ray reflectivity data. The results gave clear evidence for the presence of electrostatic interaction between the differently charged monolayers and the positively charged nanoparticles. While the adsorption process was favored by the negatively charged stearic acid monolayer, the positively charged layer of stearyl amine prevented the formation of ultrathin nanoparticle layers. 相似文献
126.
Geels RB Calmat S Heck AJ van der Vies SM Heeren RM 《Rapid communications in mass spectrometry : RCM》2008,22(22):3633-3641
Many biological active proteins are assembled in protein complexes. Understanding the (dis)assembly of such complexes is therefore of major interest. Here we use mass spectrometry to monitor the disassembly induced by thermal activation of the heptameric co-chaperonins GroES and gp31. We use native electrospray ionization mass spectrometry (ESI-MS) on a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer to monitor the stoichiometry of the chaperonins. A thermally controlled electrospray setup was employed to analyze conformational and stoichiometric changes of the chaperonins at varying temperature. The native ESI-MS data agreed well with data obtained from fluorescence spectroscopy as the measured thermal dissociation temperatures of the complexes were in good agreement. Furthermore, we observed that thermal denaturing of GroES and gp31 proceeds via intermediate steps of all oligomeric forms, with no evidence of a transiently stable unfolded heptamer. We also evaluated the thermal dissociation of the chaperonins in the gas phase using infrared multiphoton dissociation (IRMPD) for thermal activation. Using gas-phase activation the smaller (2-4) oligomers were not detected, only down to the pentamer, whereafter the complex seemed to dissociate completely. These results demonstrate clearly that conformational changes of GroES and gp31 due to heating in solution and in the gas phase are significantly different. 相似文献
127.
The isotypic lithium rare‐earth oxonitridosilicates LiLn5Si4N10O (Ln = La, Pr) were synthesized at temperatures of 1200 °C in weld shut tantalum ampoules employing liquid lithium as flux. Thereby, a silicate substructure with a low degree of condensation was obtained. LiLa5Si4N10O crystallizes in space group P$\bar{1}$ [Z = 1, LiLa5Si4N10O: a = 5.7462(11), b = 6.5620(13), c = 8.3732(17) Å, α = 103.54(3), β = 107.77(3), γ = 94.30(3), wR2 = 0.0405, 1315 data, 96 parameters]. The nitridosilicate substructure consists of loop branched dreier single‐chains of vertex sharing SiN4 tetrahedra. Lattice energy calculations (MAPLE) and EDX measurements confirmed the electrostatic bonding interactions and the chemical compositions. The 7Li solid‐state MAS NMR investigation is reported. 相似文献
128.
Lupart S Gregori G Maier J Schnick W 《Journal of the American Chemical Society》2012,134(24):10132-10137
The isotypic layered oxonitridosilicates Li(14)Ln(5)[Si(11)N(19)O(5)]O(2)F(2) (Ln = Ce, Nd) have been synthesized using Li as fluxing agent and crystallize in the orthorhombic space group Pmmn (Z = 2, Li(14)Ce(5)[Si(11)N(19)O(5)]O(2)F(2): a = 17.178(3), b = 7.6500(15), c = 10.116(2) ?, R1 = 0.0409, wR2 = 0.0896; Li(14)Nd(5)[Si(11)N(19)O(5)]O(2)F(2): a = 17.126(2), b = 7.6155(15), c = 10.123(2) ?, R1 = 0.0419, wR2 = 0.0929). The silicate layers consist of dreier and sechser rings interconnected via common corners, yielding an unprecedented silicate substructure. A topostructural analysis indicates possible 1D ion migration pathways between five crystallographic independent Li positions. The specific Li-ionic conductivity and its temperature dependence were determined by impedance spectroscopy as well as DC polarization/depolarization measurements. The ionic conductivity is on the order of 5 × 10(-5) S/cm at 300 °C, while the activation energy is 0.69 eV. Further adjustments of the defect chemistry (e.g., through doping) can make these compounds interesting candidates for novel oxonitridosilicate based ion conductors. 相似文献
129.
Eight selected experiments intend at demonstrating synthesis, properties, function and application of nanomaterials. The reader should be stimulated to “Do‐it‐yourself” experiments at schools as well as at universities. In detail the experiments are: (1) Light scattering of suspensions, (2) Self‐made opals, (3) Quantum‐Size effects and red gold, (4) Surfaces and surface functionalization, (5) Pyrophoric iron, (6) Superparamagnetism and magnetic liquids, (7) TiO2 and dye‐sensitized solar cells as well as (8) Phosphors and luminescent biomarkers. All experiments are organized to allow for simple and fast implementation, although this implies a certain limitation regarding the quality of the material properties in detail. Altogether, the interest in nanosciences and nanotechnology should be aroused as well as the curiosity to learn even more. 相似文献
130.
Sandro Pagano Saskia Lupart Sebastian Schmiechen Prof. Dr. Wolfgang Schnick 《无机化学与普通化学杂志》2010,636(11):1907-1909
The isotypic nitridosilicates Li4Ca3Si2N6 and Li4Sr3Si2N6 were synthesized by reaction of strontium or calcium with Si(NH)2 and additional excess of Li3N in weld shut tantalum ampoules. The crystal structure, which has been solved by single‐crystal X‐ray diffraction (Li4Sr3Si2N6: C2/m, Z = 2, a = 6.1268(12), b = 9.6866(19), c = 6.2200(12) Å, β = 90.24(3)°, wR2 = 0.0903) is made up from isolated [Si2N6]10– ions and is isotypic to Li4Sr3Ge2N6. The bonding angels and distances within the edge‐sharing [Si2N6]10– double‐tetrahedra are strongly dependent on the lewis acidity of the counterions. This finding is discussed in relation to the compounds Ca5Si2N6 and Ba5Si2N6, which also exhibit isolated [Si2N6]10– ions. 相似文献