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31.
Marvin Ross 《高压研究》2013,33(5-6):649-657
Abstract Superfluid Helium (11) and liquid nitrogen are the only liquids which have been shown experimentally, to exhibit shock cooling. In the present paper we use the Landau model to demonstrate theoretically that the roton gap, which decreases with increasing density, plays the same role leading to shock cooling in liquid helium as the dissociation energy does in liquid nitrogen. 相似文献
32.
A. E. Legzdins B. E. McCarry C. H. Marvin D. W. Bryant 《International journal of environmental analytical chemistry》2013,93(2-4):79-94
Abstract A normal phase HPLC methodology using a semi-preparative polyaminocyano column in conjunction with a selection of short-term genotoxicity assays has been developed for bioassay-directed fractionation studies of complex environmental mixtures. To illustrate the effectiveness of this methodology, an organic extract prepared from respirable air particulate samples collected in Hamilton, Canada was separated into a non-polar aromatic fraction and a polar aromatic fraction using a combination of alumina and Sephadex LH20 chromatography. These fractions were evaluated for their genotoxic potential using the Salmonella/microsome (Ames) assay with six different strains of Salmonella. The non-polar aromatic fraction was analyzed by normal phase HPLC and the eluent was collected in one-minute subfractions; these subtractions were bioassayed in three different Salmonella strains (YG1021 -S9, YG1024 -S9 and YG1029 +S9) to afford three different mutation profiles of this sample. Some subfractions which exhibited high mutagenic responses were subjected to further chemical analyses using GC/MS in order to identify those compounds responsible for the genotoxic responses. The nitroarene compounds 2-nitrofluoranthene, 1-nitropyrene and 2-nitropyrene and higher molecular weight polycyclic aromatic hydrocarbons such as benzo[a]pyrene and indeno[l,2,3-cd]pyrene were identified and quantified in some of the biologically active subfractions. The normal phase gradient conditions afforded very reproducible retention times for a series of polycyclic aromatic standards with a broad range of compound polarities. In addition, polycyclic aromatic hydrocarbons (PAH) were observed to elute from the normal phase HPLC column in a series of peaks; successive peaks contained PAH of increasing molecular weight while any individual peak was shown to contain PAH of the same molecular weight. 相似文献
33.
Can a Six‐Letter Alphabet Increase the Likelihood of Photochemical Assault to the Genetic Code? 下载免费PDF全文
Brennan Ashwood Marvin Pollum Prof. Dr. Carlos E. Crespo‐Hernández 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(46):16648-16656
In 2014, two unnatural nucleosides, d5SICS and dNaM, were shown to selectively base pair and replicate with high fidelity in a modified strain of E. coli, thus effectively expanding its genetic alphabet from four to six letters. More recently, a significant reduction in cell proliferation was reported in cells cultured with d5SICS, and putatively with dNaM, upon exposure to brief periods of near‐visible radiation. The photosensitizing properties of the lowest‐energy excited triplet state of both d5SICS and dNaM were implicated in their cytotoxicity. Importantly, however, the excited‐state mechanisms by which near‐visible excitation populates the triplet states of d5SICS and dNaM are currently unknown. In this study, steady‐state and time‐resolved spectroscopies are combined with quantum‐chemical calculations in order to reveal the excited‐state relaxation mechanisms leading to efficient population of the triplet states in these unnatural nucleosides in solution. It is shown that excitation of d5SICS or dNaM with near‐visible light leads overwhelmingly to ultrafast population of their triplet states on the femtosecond time scale. The results presented in this work lend strong support to the proposal that photoexcitation of these unnatural nucleosides can accelerate oxidatively generated damage to DNA and other biomolecules within the cellular environment. 相似文献
34.
Ludwig Maier Marvin M. Crutchfield 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):45-51
Abstract Dedicated to Professor Martin Schmeisser on the occasion of his 65th birthday. Several phosphonic acids of the type H2O3PCH2OCHRCO2H, R = H, CH3, CO2H; [H2O3P(CH2)x]2 Y, x = 1, 2; Y = O, S; and [o-H2O3P(CH2)]2C6H4 have been synthesized and their capacity to chelate with calcium has been determined. 相似文献
35.
Marvin H. Caruthers Wolfgang Brill Douglas J. Dellinger 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):549-553
Abstract Methods for the rapid synthesis of DNA and RNA are described. The procedures involve using nucleoside phosphoramidites as synthons and silica as a polymeric support. Additionally, a novel reaction involving nucleoside O-alkyl methylphosphonothioates is described. 相似文献
36.
The asymmetric transfer hydrogenation of β-amido-α-keto esters providing the corresponding anti-β-amido-α-hydroxy esters via dynamic kinetic resolution is reported. The use of a commercially available, or simply prepared, chiral ruthenium catalyst results in good yields as well as high diastereoselectivities and enantioselectivities. 相似文献
37.
Tom Bettens Marvin Hoffmann Prof. Mercedes Alonso Em. Prof. Paul Geerlings Prof. Andreas Dreuw Prof. Frank De Proft 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(10):3397-3406
A hitherto unexplored class of molecules for molecular force probe applications are expanded porphyrins. This work proves that mechanical force is an effective stimulus to trigger the interconversion between Hückel and Möbius topologies in [28]hexaphyrin, making these expanded porphyrins suitable to act as conformational mechanophores operating at mild (sub-1 nN ) force conditions. A straightforward approach based on distance matrices is proposed for the selection of pulling scenarios that promote either the planar Hückel topology or the three lowest lying Möbius topologies. This approach is supported by quantum mechanochemical calculations. Force distribution analyses reveal that [28]hexaphyrin selectively allocates the external mechanical energy to molecular regions that trigger Hückel–Möbius interconversions, explaining why certain pulling scenarios favor the Hückel two-sided topology and others favor Möbius single-sided topologies. The meso-substitution pattern on [28]hexaphyrin determines whether the energy difference between the different topologies can be overcome by mechanical activation. 相似文献
38.
Dr. Ali Abdulkarim Marvin Nathusius Rainer Bäuerle Dr. Karl-Philipp Strunk Dr. Sebastian Beck Dr. Hans Joachim Räder Prof. Annemarie Pucci Dr. Christian Melzer Daniel Jänsch Dr. Jan Freudenberg Prof. Uwe H. F. Bunz Prof. Klaus Müllen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(1):281-288
The synthesis of unsubstituted oligo-para-phenylenes ( OPP ) exceeding para-hexaphenylene—in the literature often referred to as p-sexiphenyl—has long remained elusive due to their insolubility. We report the first preparation of unsubstituted para-nonaphenylenes ( 9PP s) by extending our precursor route to poly-para-phenylenes ( PPP ) to a discrete oligomer. Two geometric isomers of methoxylated syn- and anti-cyclohexadienylenes were synthesized, from which 9PP was obtained via thermal aromatization in thin films. 9PP was characterized via optical, infrared and solid-state 13C NMR spectroscopy as well as atomic force microscopy and mass spectrometry, and compared to polymeric analogues. Due to the lack of substitution, para-nonaphenylene, irrespective of the precursor isomer employed, displays pronounced aggregation in the solid state. Intermolecular excitonic coupling leads to formation of H-type aggregates, red-shifting emission of the films to greenish. 9PP allows to study the structure–property relationship of para-phenylene oligomers and polymers, especially since the optical properties of PPP depend on the molecular shape of the precursor. 相似文献
39.
Alena Shlyaykher Marvin Ehmann Dr. Antti J. Karttunen Dr. Frank Tambornino 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(54):13552-13557
The full series of quasibinary alkali-metal selenocyanates was synthesized either by oxidation of the respective cyanides (A=Li−Rb) or by metathesis (A=Cs). For Li[SeCN] only ball-milling and subsequent annealing led to the isolation of the quasibinary selenocyanate. Their structures were refined from single-crystal and powder X-ray data. The respective solid-state IR and Raman spectra were interpreted with the aid of solid-state quantum-mechanical calculations and DSC-TGA measurements allowed for extraction of melting points. Only for Li[SeCN] a possible phase transition was observed that is discussed on the basis of VT-PXRD experiments. It is also the only quasibinary selenocyanate to form a hydrate (Li[SeCN] ⋅ 2H2O). 相似文献
40.
Christoph M. Hendrich Sebastian Senn Lea Haas Marvin T. Hoffmann Dr. Ute Zschieschang Luca C. Greiner Dr. Frank Rominger Dr. Matthias Rudolph Dr. Hagen Klauk Prof. Dr. Andreas Dreuw Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(59):14778-14784
Herein, we describe a gold-catalyzed cascade cyclization of Boc-protected benzylamines bearing two tethered alkyne moieties in a domino reaction initiated by a 6-endo-dig cyclization. The reaction was screened intensively, and the scope was explored, resulting in nine new Boc-protected dihydrobenzo[c]phenanthridines with yields of up to 98 %; even a π-extension and two bidirectional approaches were successful. Furthermore, thermal cleavage of the Boc group and subsequent oxidation gave substituted benzo[c]phenanthridines in up to quantitative yields. Two bidirectional approaches under the optimized conditions were successful, and the resulting π-extended molecules were tested as organic semiconductors in organic thin-film transistors. 相似文献