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991.
We generalize here the splitting approach to the long range (Coulomb) interaction for the three body scattering problem. With this approach, the exterior complex rotation technique can be applied for systems with asymptotic Coulomb interaction. We illustrate the method with calculations of the electron scattering on the hydrogen atom and positive helium ion in the frame of the Temkin–Poet model. 相似文献
992.
Outstanding Chiroptical Properties: A Signature of Enantiomerically Pure Alleno–Acetylenic Macrocycles and Monodisperse Acyclic Oligomers
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Etienne J. Donckele Dr. Ori Gidron Dr. Nils Trapp Prof. Dr. Francois Diederich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(31):9558-9566
A second series of shape‐persistent alleno–acetylenic macrocycles and monodisperse acyclic oligomers with conformationally less flexible backbones were synthesized in enantiomerically pure form by short, high‐yielding routes starting from optically active 1,3‐diethynylallenes. All seven stereoisomers—two pairs of enantiomers and three achiral stereoisomers—in the macrocyclic series were separated and configurationally assigned. The electronic circular dichroism (ECD) spectra of the D2‐symmetric, (P,P,P,P)‐ and (M,M,M,M)‐configured macrocycles display remarkably intense chiroptical responses. A strong amplification of chirality is observed in the acyclic oligomeric series. Their preference for helical secondary structures of one handedness was supported by X‐ray analysis and computational studies. This new set of data provides proof that outstanding ECD responses are a hallmark of alleno–acetylenic macrocyclic and acyclic oligomeric chromophores. 相似文献
993.
Carbon-coated Na3V2(PO4)3 (NVP) was prepared by a standard sol–gel procedure. The apparent diffusion coefficients of sodium ions in the rhombohedral NVP have been determined by different techniques such as galvanostatic intermittent titration technique (GITT) and cyclic voltammetry (CV). It was found that the apparent diffusion coefficients range from 6?×?10?13 cm2 s?1 to 2?×?10?15 cm2 s-1. These sodium ion apparent diffusion coefficients follow a similar trend as observed for lithium ions in the closely related monoclinic modification of Li3V2(PO4)3, demonstrating a minimum at the potential where the ion extraction/insertion occurs. 相似文献
994.
Charge‐Scaling Effect in Ionic Liquids from the Charge‐Density Analysis of N,N′‐Dimethylimidazolium Methylsulfate
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Dr. Witali Beichel Dr. Nils Trapp Dipl.‐Phys. Christoph Hauf Dipl.‐Ing. Oliver Kohler Dr. Georg Eickerling Prof. Dr. Wolfgang Scherer Prof. Dr. Ingo Krossing 《Angewandte Chemie (International ed. in English)》2014,53(12):3143-3146
The charge scaling effect in ionic liquids was explored on the basis of experimental and theoretical charge‐density analyses of [C1MIM][C1SO4] employing the quantum theory of atoms in molecules (QTAIM) approach. Integrated QTAIM charges of the experimental (calculated) charge density of the cation and anion resulted in non‐integer values of ±0.90 (±0.87) e. Efficient charge transfer along the bond paths of the hydrogen bonds between the imidazolium ring and the anion was considered as the origin of these reduced charges. In addition, a detailed QTAIM analysis of the bonding situation in the [C1SO4]? anion revealed the presence of negative πO→σ*S‐O hyperconjugation. 相似文献
995.
Przemyslaw Gawel Cagatay Dengiz Dr. Aaron D. Finke Dr. Nils Trapp Prof. Dr. Corinne Boudon Dr. Jean‐Paul Gisselbrecht Prof. Dr. François Diederich 《Angewandte Chemie (International ed. in English)》2014,53(17):4341-4345
A versatile, two‐step synthesis of highly substituted, cyano‐functionalized diaryltetracenes has been developed, starting from easily accessible tetraaryl[3]cumulenes. This unprecedented transformation is initiated by [2+2] cycloaddition of tetracyanoethylene (TCNE) to the proacetylenic central double bond of the cumulenes to give an intermediate zwitterion, which after an electrocyclization cascade and dehydrogenation yields 5,5,11,11‐tetracyano‐5,11‐dihydrotetracenes in a one‐pot procedure. A subsequent copper‐assisted decyanation/aromatization provided the target 5,11‐dicyano‐6,12‐diaryltetracene derivatives. All of the postulated structures were confirmed by X‐ray crystallography. The new chromophores are thermally highly stable and feature promising fluorescence properties for potential use in optoelectronic devices. They are selective chemosensors for CuI ions, which coordinate to one of the CN substituents and form a 1:1 complex with an association constant of Ka=1.5×105 L mol?1 at 298 K. 相似文献
996.
Substitution‐Controlled Excited State Processes in Heteroleptic Copper(I) Photosensitizers Used in Hydrogen Evolving Systems
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Dr. Stefanie Tschierlei Dr. Michael Karnahl Dr. Nils Rockstroh Dr. Henrik Junge Prof. Dr. Matthias Beller Prof. Dr. Stefan Lochbrunner 《Chemphyschem》2014,15(17):3709-3713
Four different heteroleptic [Cu(N^N)(P^P)]PF6 complexes, which combine classical bidentate diimine ligands and sterically demanding diphosphine ligands, are studied by a combination of ultrafast time‐resolved spectroscopy and quantum chemical calculations. The light‐induced excited state processes, accompanied by a structural change, are discussed with respect to the application of these complexes as a new class of noble‐metal‐free photosensitizers in proton reducing systems. In particular, the influence of different substituents in the ligand backbone on the photophysical properties is highlighted. 相似文献
997.
Popov J Vobornik D Coban O Keating E Miller D Francis J Petersen NO Johnston LJ 《Langmuir : the ACS journal of surfaces and colloids》2008,24(23):13502-13508
The incorporation of ceramide in phase-separated monolayers of ternary lipid mixtures has been studied by a combination of atomic force microscopy (AFM), fluorescence, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Replacement of a fraction of the sphingomyelin by ceramide in DOPC/SM/cholesterol monolayers leads to changes in the SM-cholesterol-rich liquid-ordered domains. AFM shows the formation of heterogeneous domains with small raised islands that are assigned to a ceramide-rich gel phase. ToF-SIMS provides conclusive evidence for the localization of SM and ceramide in ordered domains and shows that ceramide is heterogeneously distributed in small islands throughout the domains. The results indicate the utility of combining AFM and ToF-SIMS for understanding compositions of phase-separated membranes. 相似文献
998.
A solid-phase synthesized propargyl derivative of the neuropeptide leucine-enkephalin (Enk) reacts rapidly and quantitatively with Co(2)(CO)(8) to give the Co(2)(CO)(6)-alkyne labeled peptide , which is the first organometallic peptide bioconjugate to show significant toxicity against two different tumor cell lines. 相似文献
999.
Gasser G Hüsken N Köster SD Metzler-Nolte N 《Chemical communications (Cambridge, England)》2008,(31):3675-3677
The facile side-specific insertion, on the solid phase, of one or two ferrocene moieties into peptide nucleic acid (PNA) oligomers by click chemistry is presented. 相似文献
1000.
Banás P Rulísek L Hánosová V Svozil D Walter NG Sponer J Otyepka M 《The journal of physical chemistry. B》2008,112(35):11177-11187
The hepatitis delta virus (HDV) ribozyme is an RNA motif embedded in human pathogenic HDV RNA. Previous experimental studies have established that the active-site nucleotide C75 is essential for self-cleavage of the ribozyme, although its exact catalytic role in the process remains debated. Structural data from X-ray crystallography generally indicate that C75 acts as the general base that initiates catalysis by deprotonating the 2'-OH nucleophile at the cleavage site, while a hydrated magnesium ion likely protonates the 5'-oxygen leaving group. In contrast, some mechanistic studies support the role of C75 acting as general acid and thus being protonated before the reaction. We report combined quantum chemical/molecular mechanical calculations for the C75 general base pathway, utilizing the available structural data for the wild type HDV genomic ribozyme as a starting point. Several starting configurations differing in magnesium ion placement were considered and both one-dimensional and two-dimensional potential energy surface scans were used to explore plausible reaction paths. Our calculations show that C75 is readily capable of acting as the general base, in concert with the hydrated magnesium ion as the general acid. We identify a most likely position for the magnesium ion, which also suggests it acts as a Lewis acid. The calculated energy barrier of the proposed mechanism, approximately 20 kcal/mol, would lower the reaction barrier by approximately 15 kcal/mol compared with the uncatalyzed reaction and is in good agreement with experimental data. 相似文献