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251.
Looser V Langenegger SM Häner R Hartig JS 《Chemical communications (Cambridge, England)》2007,(42):4357-4359
Highly active variants of minimal hammerhead ribozymes are generated by the replacement of substantial parts of stem-loop structures with pyrene building blocks. 相似文献
252.
253.
Hebben N Himmel HJ Eickerling G Herrmann C Reiher M Herz V Presnitz M Scherer W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(36):10078-10087
In this article we analyze in detail the electronic properties of the D(3h)-symmetric tris(ethylene) complexes of nickel, palladium, and platinum ([M(C(2)H(4))(3)] M=Ni, Pd, Pt). In the case of [Pd(C(2)H(4))(3)] the analysis is based on new experimental IR and Raman spectra for the matrix-isolated molecules and in all cases on the results of quantum-chemical (DFT) calculations. The experimental spectra collected for [Pd(C(2)H(4))(3)] provide evidence for several previously unobserved vibrational modes, including the in-phase and out-of-phase nu(C-C) and delta(CH(2)) modes, and the in-phase nu(M-C) mode. Special consideration is given to possible inter-ligand interactions. The interaction force constant f(CC,CC) between two C(2)H(4) ligands can be directly estimated from the spectra, and its very small value (0.002 N m(-1)) indicates the absence of any significant inter-ligand interaction. An analysis of the topology of the theoretical electron density distribution, rho(r), and the corresponding Laplacian, nabla(2)rho(r), for [Pd(C(2)H(4))(3)] and its lighter and heavier homologues [Ni(C(2)H(4))(3)] and [Pt(C(2)H(4))(3)], respectively, is in full agreement with the conclusions drawn from the experimental results. The combined experimental and quantum-chemical results provide detailed insights in the electronic properties of these prototypical ethylene complexes. 相似文献
254.
[Tetrakis(acetonitrile)‐dibromo‐nickel(II)]‐di‐acetonitrile was obtained from a solution of nickel(II) dibromide in acetonitrile at 258 K. The crystal structure [monoclinic, P21/n (no.14), a = 1005.5(5), b = 831.3(5) , c = 1131.7(5) pm, β = 106.263(5)°, V = 908.1(8)·106 pm3, Z = 2, R1 for 1580 reflections with I0>2σ(I0): 0.0505] contains sixfold coordinated NiII atoms. Two trans coordinating bromide anions and four equatorial acetonitrile molecules form an elongated octahedron around the central NiII atom. [Ni(CH3CN)4Br2] octahedra are connected via hydrogen bonds to neighboring octahedra as well as to solvate acetonitrile molecules. 相似文献
255.
Synthesis and Crystal Structure of Cs3AuO2 Bright orange single crystals of Cs3AuO2, sensitive to moisture and atmosphere, are obtained by reacting CsAu with a 1 : 1 molar mixture of Cs2O and CsO2 (CsAu : Cs2O : CsO2 = 3 : 2 : 2) in sealed silver crucibles under argon atmosphere at 380 °C for a period of 6 days. The crystal structure (Pearsoncode mP72, P21/n, a = 1019.6(3), b = 1984.3(7), c = 1028.5(4) pm, β = 93.96(1)°, Z = 12, 2562 reflections mit Io > 2σ(I), R1 = 0.0662, wR2 = 0.1660) is characterized by the presence of dumb‐bell‐shaped [O–Au–O]‐moieties (d(Au–O) = 200,8(2) pm), a common feature of oxoaurates(I). 相似文献
256.
Verena Petzet Christof Büskens Hans Josef Pesch Andrey Prikhodovsky Victor Karkhin Vasily Ploshikhin 《PAMM》2004,4(1):580-581
Hot cracking is one of the big problems in laser beam welding. By multi‐beam welding, first suggested in the 70‐s (cf. [1], [4]), hot cracking can be avoided. Hereby two additional laser beams are employed. These beams generate a compression which compensate for the critical tensile strain in the solid‐liquid region of the weld induced by the main laser beam. However, hot cracking can only be prevented if the positions, sizes, and powers of the additional laser beams are suitably chosen, i.e. are optimized. Non‐optimal values can even enhance hot cracking. Until now these quantities have been found either by trial and error or by prescribing them intuitively. In the present paper a constrained nonlinear programming problem is formulated to solve the problem of hot crack initiation by minimizing the accumulated transverse strain, i.e. the opening displacement, in the solid‐liquid region. This approach is based on the so‐called strip expansion technique, cf. [2]. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
257.
Verena Schultz-Coulon Elisabeth Irran Bernd Putz Wolfgang Schnick 《无机化学与普通化学杂志》1999,625(7):1086-1092
β-SrNH and β-SrND – Synthesis and Crystal Structure Determination by X-Ray and Neutron Powder Diffraction By reaction of strontium with NH3 in a flow tube at 750 °C a novel modification of strontium imide, β-SrNH, was obtained as a dark yellow powder. According to X-ray powder diffractometry und crystal structure determination by direct methods β-SrNH and β-SrND adopt a highly distorted variant of the NaCl type of structure (Pnma, a = 757.70(1), b = 392.260(4), c = 569.652(9) pm, Z = 4, wRp = 0.098, Rp = 0.075, RF = 0.044). Temperature dependent neutron powder diffraction of β-SrND revealed the position of the D atoms which in contrast to α-SrND are crystallographically ordered. At higher temperatures β-SrNH transforms to α-SrNH. 相似文献
258.
259.
Verena Wiedemair Kathrin Gruber Nataly Knpfle Katrin E. Bach 《Molecules (Basel, Switzerland)》2022,27(6)
Hemp and hemp seed press cake—a by-product of hemp oil production—are high-protein, gluten-free raw materials that are often used to enhance the nutritional value of breads. The addition of hemp materials, however, often negatively impacts the technological parameters of breads. Consequently, this study investigated whether and how much the addition of various by-products of hemp seed press cakes to wheat bread mixtures adversely affects the texture and colour profile. The texture profile and colour were determined using a texture analyser and tristimulus measurements. The particle size of raw materials was also measured. Principal component analysis was then used to visualise the correlation between all measured values as well as nutritional parameters. The results showed that the addition of only 1% of some hemp raw materials caused significant technological changes (p > 0.05). Hemp raw materials increased bread hardness and decreased elasticity. The colour of breads containing 1% hemp was also visibly darker than the reference bread. The addition of more hemp led to further darkening and the deterioration of the technological parameters of the products. Consequently, while various hemp materials have high nutritional value, a balance with sensory properties, e.g., textural and colour, has to be reached. 相似文献
260.