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521.
We have made the first detailed measurements of a diffusive supersonic radiation wave in the laboratory. A 10 mg/cm(3) SiO2 foam is radiatively heated by the x-ray flux from a laser-irradiated hohlraum. The resulting radiation wave propagates axially through the optically thick foam and is measured via time-resolved x-ray imaging as it breaks out the far end. The data show that the radiation wave breaks out at the center prior to breaking out at the edges, indicating a significant curvature in the radiation front. This curvature is primarily due to energy loss into the walls surrounding the foam. 相似文献
522.
P. Mohr 《The European Physical Journal A - Hadrons and Nuclei》2007,34(1):23-28
α-decay half-lives for 104, 105, 106Te and 108, 109, 110Xe close above the doubly-magic 100Sn are calculated from systematic double-folding potentials. The derived α preformation factors are compared to results for
212, 213, 214Po and 216, 217, 218Rn above the doubly-magic 208Pb. α-decay energies of Q
α = 5.42±0.07MeV and 4.65±0.15MeV are predicted for 104Te and 108Xe; the corresponding half-lives are T
1/2 ≈ 5ns for 104Te and of the order of 60μs for 108Xe. Additionally, the properties of rotational bands in 104Te are analyzed, and the first excited 2+ state in 104Te is predicted at E
x = 650±40keV; it decays preferentially by γ emission with a reduced transition strength of 10 Weisskopf units to the ground
state of 104Te and with a minor branch by α emission to the ground state of 100Sn. 相似文献
523.
Stahl J Mohr W de Quadras L Peters TB Bohling JC Martín-Alvarez JM Owen GR Hampel F Gladysz JA 《Journal of the American Chemical Society》2007,129(26):8282-8295
Reactions of trans,trans-(C6F5)(p-tol3P)2Pt(CC)4Pt(Pp-tol3)2(C6F5) and diphosphines Ar2P(CH2)mPAr2 yield trans,trans-(C6F5)(Ar2P(CH2)mPAr2)Pt(CC)4Pt(Ar2P(CH2)mPAr2)(C6F5), in which the platinum atoms are spanned via an sp and two sp3 carbon chains (Ar/m = 3, Ph/14, 87%; 4, p-tol/14, 91%; 5, p-C6H4-t-Bu/14, 77%; 7, Ph/10, 80%; 8, Ph/11, 80%; 9, Ph/12, 36%; only oligomers form for m > 14). Crystal structures of 3-5 show that the sp3 chains adopt chiral double-helical conformations that shield the sp chain at approximately the van der Waals distance, with both enantiomers in the unit cell. The platinum square planes define angles of 196.6 degrees -189.9 degrees or more than a half twist. Crystal structures of 7-9, which have shorter sp3 chains, exhibit nonhelical conformations. Reaction of the corresponding Pt(CC)6Pt complex and Ph2P(CH2)18PPh2 gives an analogous adduct (27%). The crystal structure shows two independent molecules, one helical and the other not. Low-temperature NMR data suggest that the enantiomeric helical conformations of 3-5 rapidly interconvert in solution. Cyclic voltammograms of 3-5 show more reversible oxidations than model compounds lacking bridging sp3 chains. These are the only double-helical molecules that do not feature bonding interactions between the helix strands, or covalent bonds to templates dispersed throughout the strands, or any type of encoding. The driving force for helix formation is analyzed. 相似文献
524.
525.
The morphology of organic monolithic stationary phases based on poly(styrene-divinylbenzene) was modified by changing the
ratio of monomers to microporogen in order to make them also suitable for small molecule separations. The morphology of the
columns was characterized by high-resolution scanning electron micrography, showing larger primary globules and larger macropores,
as well as no mesopores >20 nm in the monolithic skeleton. The permeability of the modified monoliths was approximately three
times higher than that of columns which have been optimized for large molecule separations, enabling operation of a 30 cm
long column at pressures below 250 bar. In the isocratic separation of dansylated amino acids, plate counts of 50000–107000 m−1 were achievable, which are equivalent to efficiencies obtained with 3.1 μm porous particles. The separation performance for
small molecules in gradient elution was investigated using mixtures of dansylated amino acids, β-lactam antibiotics, and thyroid
hormones. Finally, the modified monolithic capillary columns also proved to be highly efficient in the separation of biopolymers
such as peptides and proteins, enabling peak width at half height of 3–8 s and peak capacities of 110–180 in 15–30 min gradient
runs. 相似文献
526.
Behenna DC Mohr JT Sherden NH Marinescu SC Harned AM Tani K Seto M Ma S Novák Z Krout MR McFadden RM Roizen JL Enquist JA White DE Levine SR Petrova KV Iwashita A Virgil SC Stoltz BM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(50):14199-14223
α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center. 相似文献
527.
The Pendellösung — length L is experimentally determined for wedge-shaped specimens of GaAs for (220)-diffraction and the Laue case for Kα1-wave length of Ag and Mo and calculated using equations of dynamical theory of X-ray diffraction. The agreement of values is well. The dislocation contrast in the topography is dependent on specimen thickness. The wedge-shaped specimens permit exact determination of the critical specimen thickness d0 for the contrast change between extinction and anomal absorption and the determination of favourable thickness of specimens in the range of the extinction contrast. 相似文献
528.
529.
Ronja Rabea Paschke Swantje Mohr Dr. Sascha Lange Prof. Dr. Adam Lange Dr. Jacek Kozuch 《Angewandte Chemie (International ed. in English)》2023,62(47):e202309069
Viroporins are small ion channels in membranes of enveloped viruses that play key roles during viral life cycles. To use viroporins as drug targets against viral infection requires in-depth mechanistic understanding and, with that, methods that enable investigations under in situ conditions. Here, we apply surface-enhanced infrared absorption (SEIRA) spectroscopy to Influenza A M2 reconstituted within a solid-supported membrane, to shed light on the mechanics of its viroporin function. M2 is a paradigm of pH-activated proton channels and controls the proton flux into the viral interior during viral infection. We use SEIRA to track the large-scale reorientation of M2’s transmembrane α-helices in situ during pH-activated channel opening. We quantify this event as a helical tilt from 26° to 40° by correlating the experimental results with solid-state nuclear magnetic resonance-informed computational spectroscopy. This mechanical motion is impeded upon addition of the inhibitor rimantadine, giving a direct spectroscopic marker to test antiviral activity. The presented approach provides a spectroscopic tool to quantify large-scale structural changes and to track the function and inhibition of the growing number of viroporins from pathogenic viruses in future studies. 相似文献
530.