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排序方式: 共有92条查询结果,搜索用时 15 毫秒
31.
Dr. Lorena Herkert Dr. Philipp Selter Dr. Constantin G. Daniliuc Nils Bäumer Dr. Jasnamol P. Palakkal Prof. Dr. Gustavo Fernández Prof. Dr. Michael Ryan Hansen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(14):4617-4626
Understanding the relationship between molecular design and packing modes constitutes one of the major challenges in self-assembly and is essential for the preparation of functional materials. Herein, we have achieved high precision control over the supramolecular packing of amphiphilic PtII complexes by systematic variation of the hydrophilic side-chain length. A novel approach of general applicability based on complementary X-ray diffraction and solid-state NMR spectroscopy has allowed us to establish a clear correlation between molecular features and supramolecular ordering. Systematically increasing the side-chain length gradually increases the steric demand and reduces the extent of aromatic interactions, thereby inducing a gradual shift in the molecular packing from parallel to a long-slipped organization. Notably, our findings highlight the necessity of advanced solid-state NMR techniques to gain structural information for supramolecular systems where single-crystal growth is not possible. Our work further demonstrates a new molecular design strategy to modulate aromatic interaction strengths and packing arrangements that could be useful for the engineering of functional materials based on PtII and aromatic molecules. 相似文献
32.
Ilse Oberbumer Ernst Grell Fritz Raschdorf Wilhelm J. Richter 《Helvetica chimica acta》1982,65(7):2280-2287
Virginiamycin S5 and viridogrisein II were isolated by liquid chromatography from the crude antibiotics virginiamycin and viridogrisein, respectively. Their structures were elucidated by amino-acid analysis and mass spectrometry. 相似文献
33.
L. Sydow S. Vohl S. Lemaître H. Patberg R. Reckenfelderbäumer H. Paetz gen. Schieck W. Glöckle D. Hüber H. Witała 《Few-Body Systems》1998,25(1-3):133-155
The polarization-transfer coefficients K
, K
and K
, K
have been measured in the elastic scattering reactions D(, )p and D(, )d at MeV, respectively. They are compared to solutions of the three-nucleon Faddeev equations obtained with the recent nucleon-nucleon
interactions AV18, CD Bonn, NijmI and II. Effects of the Tucson-Melbourne three-nucleon force, adjusted separately to reproduce
the triton binding energy for each of these potentials, are studied. Both and exhibit a scaling behaviour with the triton binding energy. For and the various predictions with two-nucleon forces only agree practically with each other but spread after inclusion of the
three-nucleon force. The agreement of theory and data is fair but the neglect of the proton-proton Coulomb force precludes
a final conclusion.
Received July 28, 1997; revised February 3, 1998; accepted for publication March 11, 1998 相似文献
34.
Nils Bumer Kalathil K. Kartha Stefan Buss Ivn Maisuls Jasnamol P. Palakkal Cristian A. Strassert Gustavo Fernndez 《Chemical science》2021,12(14):5236
Herein, we exploit coordination geometry as a new tool to regulate the non-covalent interactions, photophysical properties and energy landscape of supramolecular polymers. To this end, we have designed two self-assembled Pt(ii) complexes 1 and 2 that feature an identical aromatic surface, but differ in the coordination and molecular geometry (linear vs. V-shaped) as a result of judicious ligand choice (monodentate pyridine vs. bidentate bipyridine). Even though both complexes form cooperative supramolecular polymers in methylcyclohexane, their supramolecular and photophysical behaviour differ significantly: while the high preorganization of the bipyridine-based complex 1 enables an H-type 1D stacking with short Pt⋯Pt contacts via a two-step consecutive process, the existence of increased steric effects for the pyridyl-based derivative 2 hinders the formation of metal–metal contacts and induces a single aggregation process into large bundles of fibers. Ultimately, this fine control of Pt⋯Pt distances leads to tuneable luminescence—red for 1vs. blue for 2, which highlights the relevance of coordination geometry for the development of functional supramolecular materials.In this article, we exploit coordination geometry as a new tool to control the energy landscape and photophysical properties (red vs. blue luminescence) of supramolecular polymers. 相似文献
35.
Tobias Nowitzki Holger Borchert Dr. Birte Jürgens Thomas Risse Dr. Volkmar Zielasek Dr. Marcus Bäumer Prof. Dr. 《Chemphyschem》2008,9(5):729-739
Bimetallic nanoparticles often turn out to be superior to the corresponding monometallic systems with respect to their catalytic properties. To study such effects for the methanol decomposition reaction, model catalysts were prepared by physical vapor deposition of Pd and Co under ultrahigh‐vacuum (UHV) conditions. Monometallic Pd and Co particles as well as CoPd core–shell particles were generated on an epitaxial alumina film grown on NiAl(110). The interaction with methanol is examined by temperature‐programmed desorption of methanol and carbon monoxide and by X‐ray photoelectron spectroscopy. The decomposition of methanol proceeds in two reaction pathways independent of the particle composition: complete dehydrogenation towards carbon monoxide and hydrogen, and C? O bond scission yielding carbon deposits. Pd is the most active material studied here. The relative importance of the two channels varies for the different particle systems: on Pd dehydrogenation is preferred, whereas the C? O bond cleavage is more pronounced on Co. The bimetallic clusters show a moderate performance for both pathways. Carbon deposition poisons the model catalysts by blocking the adsorption sites for methoxide, which is the first intermediate product during methanol decomposition. In particular on Co, large amounts of carbon deposits can also be caused by dissociation of the final product of the dehydrogenation pathway, carbon monoxide. A comparison with the results of methanol decomposition on Co, Pd, and CoPd catalysts in continuous‐flow reactors demonstrates that the findings of the present UHV study are relevant for catalytic performance under high‐pressure conditions. 相似文献
36.
37.
C. Aumann V. Schenke P. Krüger und J. Hasenbäumer 《Fresenius' Journal of Analytical Chemistry》1909,48(7-8):504-506
Ohne Zusammenfassung 相似文献
38.
Marvin Hartwig Zoellner Peter Zaumseil Henrik Wilkens Sebastian Gevers Joachim Wollschläger Marcus Bäumer Ya-Hong Xie Gang Niu Thomas Schroeder 《Journal of Crystal Growth》2012,355(1):159-165
Epitaxial oxide thin film layers are of interest for model catalytic studies. We report the growth of Ce1?xPrxO2?δ mixed oxide layers of different stoichiometries (x=0–1) and oxygen deficiency (δ>0) on Si(111) by co-evaporating molecular beam epitaxy. The main objective is to identify the crystal phases and to investigate the correlation between compositions and crystal structures. X-ray photoemission spectroscopy was performed to quantify the stoichiometries. An extensive laboratory and synchrotron based X-ray diffraction analysis was carried out to determine the vertical and lateral lattice orientations and the strain status of the layers. The study revealed that single crystalline Ce1?xPrxO2?δ/Si(111) heterostructures can be epitaxially grown on Si(111) for model catalytic studies. In addition to the structure–stoichiometry relationship typical to mixed oxide bulk powders, we identified a hexagonal mixed Ce–Pr oxide thin film phase not yet reported in bulk studies. 相似文献
39.
40.
The annihilation of the nematic hedgehog and anti-hedgehog within an infinite cylinder of radius R is studied. The semi-microscopic lattice-type model and Brownian molecular dynamics are used. We distinguish among the i)
early pre-collision, ii) late pre-collision, iii) early post-collision, and iv) late post-collision stages. In the pre-collision stage our results agree qualitatively with the existing experimental observations and also continuum-type simulations. The
core of each defect exhibits a ring-like structure, where the ring axis is set perpendicular to the cylinder symmetry axis. For ξ(0)d/(2R) > 1 the interaction between defects is negligible, where ξ(0)d describes the initial separation of defects. Consequently, the defects annihilate within the simulation time window for ξ(0)d/(2R) < 1. For close enough defects their separation scales as ξd
(tc - t)0.4±0.1, where tc stands for the collision time. In elastically anisotropic medium the hedgehog is faster than the anti-hedgehog. In the early pre-collision stage the defects can be treated as point-like particles, possessing inherent core structure, that interact via the nematic director field. In the late pre-collision stage the cores reflect the interaction between defects. After the collision a charge-less ring structure is first formed. In the early post-collision stage the ring adopts an essentially untwisted circular structure of the radius ξr. In the late post-collision stage we observe two qualitatively different scenarios. For μ = ξr/R < μc ∼ 0.25 the ring collapses leading to the escaped radial equilibrium structure. For μ > μc the chargeless ring triggers the nucleation growth into the planar polar structure with line defects. 相似文献