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61.
Although reliable determination of the molecular dipole moment from experimental charge density analyses on molecular crystals is a challenging undertaking, these values are becoming increasingly common experimental results. We collate all known experimental determinations and use this database to identify broad trends in the dipole moment enhancements implied by these measurements as well as outliers for which enhancements are pronounced. Compelling evidence emerges that molecular dipole moments from X-ray diffraction data can provide a wealth of information on the change in the molecular charge distribution that results from crystal formation. Most importantly, these experiments are unrivalled in their potential to provide this information in such detail and deserve to be exploited to a much greater extent. The considerable number of experimental determinations now available has enabled us to pinpoint those studies that merit further attention, either because they point unequivocally to a considerable enhancement in the crystal (of 50 % or more), or because the experimental determinations suggest enhancements of 100 % or more--much larger than independent theoretical estimates. In both cases further detailed experimental and theoretical studies are indicated. 相似文献
62.
Birger Jansson 《BIT Numerical Mathematics》1964,4(4):205-212
A method which transforms two random variables having rectangular distributions into a pair of bivariate normal deviates with prescribed covariance matrix is described. The same transformation is used for integrating the bivariate normal distribution over areas which are the intersection of the domain outside an equiprobability ellipse and a sector determined by two lines through the point of gravity of the normal distribution. 相似文献
63.
Lundwall M Pokapanich W Bergersen H Lindblad A Rander T Ohrwall G Tchaplyguine M Barth S Hergenhahn U Svensson S Björneholm O 《The Journal of chemical physics》2007,126(21):214706
Clusters formed by a coexpansion process of argon and neon have been studied using synchrotron radiation. Electrons from interatomic Coulombic decay as well as ultraviolet and x-ray photoelectron spectroscopy were used to determine the heterogeneous nature of the clusters and the cluster structure. Binary clusters of argon and neon produced by coexpansion are shown to exhibit a core-shell structure placing argon in the core and neon in the outer shells. Furthermore, the authors show that 2 ML of neon on the argon core is sufficient for neon valence band formation resembling the neon solid. For 1 ML of neon the authors observe a bandwidth narrowing to about half of the bulk value. 相似文献
64.
Diana Jæger Bradley S. Simpson Chi P. Ndi Anna K. Jäger Christoph Crocoll Birger Lindberg Møller 《Natural product research》2018,32(5):576-581
Acacia ligulata A.Cunn. ex Benth. (Fabaceae: Mimosoideae) is a native Australian plant used traditionally by Australian Aboriginal groups. This study was undertaken to investigate the bioactivity of A. ligulata extracts and to evaluate their chemical composition. Potential antibacterial, cytotoxic and enzyme inhibitory effects relevant to traditional medicinal and food uses of the species were examined and LC-MS/MS was performed to investigate the chemical composition. Antibacterial activity was observed for bark and leaf extracts with an MIC for the bark extract of 62.5 μg/mL against Streptococcus pyogenes. Pod extracts showed cytotoxic effects against cancer cells, with the highest activity against melanoma SK-MEL28 cells with IC50 values between 40.8 and 80.6 μg/mL. Further, the leaf and pod extracts also inhibited α-amylase EC-3.2.1.1 and α-glucosidase EC-3.2.1.20 with IC50 values between 9.7–34.8 and 12.6–64.3 μg/mL, respectively. The LC-MS/MS profiling indicated that several different saponins were present in the active extracts. 相似文献
65.
Kartik Chandra Mondal Sudipta Roy Birger Dittrich Bholanath Maity Sayan Dutta Debasis Koley Suresh Kumar Vasa Rasmus Linser Sebastian Dechert Herbert W. Roesky 《Chemical science》2015,6(9):5230-5234
Silicondiselenide is a semiconductor and exists as an insoluble polymer (SiSe2)n which is prepared by reacting elemental silicon with selenium powder in the temperature range of 400–850 °C. Herein, we report on the synthesis, isolation, and characterization of carbene stabilized molecular silicondiselenide in the form of (cAAC)2Si2Se4 (3) [cAAC = cyclic alkyl(amino)carbene]. 3 is synthesized via reaction of diatomic silicon(0) compound (cAAC)2Si2 (2) with black selenium powder at –78 °C to room temperature. The intensely orange colored compound 3 is soluble in polar organic solvents and stable at room temperature for a month under an inert atmosphere. 3 decomposes above 245 °C. The molecular structure of 3 has been confirmed by X-ray single crystal diffraction. It is also characterized by UV-vis, IR, Raman spectroscopy and mass spectrometry. The stability, bonding, and electron density distributions of 3 have been studied by theoretical calculations. 相似文献
66.
Dr. Kartik Chandra Mondal Dr. Sudipta Roy Dr. Susmita De Dr. Pattiyil Parameswaran Dr. Birger Dittrich Dr. Fabian Ehret Prof. Dr. Wolfgang Kaim Prof. Dr. Herbert W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(37):11646-11649
Compound (Me2‐cAAC:)2Co0 ( 2 ; Me2‐cAAC:=cyclic (alkyl) amino carbene; :C(CH2)(CMe2)2N‐2,6‐iPr2C6H3) was synthesized by the reduction of the precursor (Me2‐cAAC:)2CoICl ( 1 ) with KC8 in THF. The cyclic voltammogram of 1 exhibited one‐electron reduction, which suggests that synthesis of a bent 2‐metallaallene ( 2 ) from 1 should be possible. Compound 2 contains one cobalt atom in the formal oxidation state zero, which is stabilized by two Me2‐cAAC: ligands. Bond lengths from X‐ray diffraction are 1.871(2) and 1.877(2) Å with a C‐Co‐C bond angle of 170.12(8)°. The EPR spectrum of 2 exhibited a broad resonance attributed to the unique quasi‐linear structure, which favors near degeneracy and gives rise to very rapid relaxation conditions. The cAAC?Co bond in 2 can be considered as a typical Dewar–Chatt–Duncanson type of bonding, which in turn retains 2.5 electron pairs on the Co atom as nonbonding electrons. 相似文献
67.
Lundwall M Lindblad A Bergersen H Rander T Ohrwall G Tchaplyguine M Svensson S Björneholm O 《The Journal of chemical physics》2006,125(1):014305
Argon clusters have been doped with krypton atoms in a pick-up setup and investigated by means of ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS). The width of the krypton surface feature in the XPS spectra from mixed krypton/argon clusters has been studied and found to be narrower than in the case of homogeneous krypton clusters. By considering known spectral broadening mechanisms of the cluster features and the electron binding energy shift of the cluster surface feature relative to the atomic signal, we conclude that krypton ad-atoms preferentially occupy high-coordination surface sites on the argon host-cluster. 相似文献
68.
Ghadwal RS Azhakar R Pröpper K Holstein JJ Dittrich B Roesky HW 《Inorganic chemistry》2011,50(17):8502-8508
Reactions of N-heterocyclic carbene stabilized dichlorosilylene IPr·SiCl(2) (1) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with (η(5)-C(5)H(5))V(CO)(4), (η(5)-C(5)H(5))Co(CO)(2), and Fe(2)(CO)(9) afford dichlorosilylene complexes IPr·SiCl(2)·V(CO)(3)(η(5)-C(5)H(5)) (2), IPr·SiCl(2)·Co(CO)(η(5)-C(5)H(5)) (3), and IPr·SiCl(2)·Fe(CO)(4) (4), respectively. Complexes 2-4 are stable under an inert atmosphere, are soluble in common organic solvents, and have been characterized by elemental analysis and multinuclear ((1)H, (13)C, and (29)Si) NMR spectroscopy. Molecular structures of 2-4 have been determined by single crystal X-ray crystallographic studies and refined with nonspherical scattering factors. 相似文献
69.
70.
Müller M Steinmüller B Daoulas KCh Ramírez-Hernández A de Pablo JJ 《Physical chemistry chemical physics : PCCP》2011,13(22):10491-10502
The ability of soft, coarse-grained models to describe the narrow interface of a nearly incompressible polymer melt in contact with a solid is explored by numerical self-consistent field calculations and Monte-Carlo simulations. We investigate the effect of the discreteness of the bead-spring architecture by quantitatively comparing the results of a bead-spring model with different number of beads, N, but identical end-to-end distance, R(e), and a continuous Gaussian-thread model. If the width, ξ, of the narrow polymer-solid contact is smaller or comparable to the length of a statistical segment, b=R(e)/√N-1, strong differences in the interface tension and the density profiles between the two models are observed, and strategies for compensating the discrete nature of the bead-spring model are investigated. Compensating the discretization of the chain contour in the bead-spring model by applying an external segment-solid potential, we simultaneously adjust the interface tension and the density profile to the predictions of the Gaussian-thread model. We suggest that the geometry of the polymer-solid contact and the interface tension are relevant characteristics that a coarse-grained model of polymer-solid contacts must reproduce in order to establish a quantitative relationship to an experimental system. 相似文献