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91.
Dahle J Noordhuis P Stokke T Svendsrud DH Kvam E 《Photochemistry and photobiology》2005,81(1):114-119
We previously reported that approximately 10% of V79 Chinese hamster fibroblast populations clonally derived from single cells immediately after irradiation with either ultraviolet B (UV-B, 290-320 nm, mainly 311 nm) or ultraviolet A (UV-A, 320-400 nm, mainly 350-390 nm) radiation exhibit genomic instability. The instability is revealed by relatively high mutation frequencies in the hypoxanthine phosphoribosyl transferase (hprt) gene up to 23 cell generations after irradiation. These delayed mutant clones exhibited higher levels of oxidative stress than normal cells. Therefore, persistently increased oxidative stress has been proposed as a mechanism for UV-induced genomic instability. This study investigates whether this mechanism is reflected in the deletion spectrum of delayed mutant clones. Eighty-eight percent of the delayed mutant clones derived from UV-A-irradiated populations were found to have total deletion of the hprt gene. Correspondingly, 81% of UV-A-induced early mutations (i.e. detected shortly after irradiation) also had total deletions. Among delayed UV-B-induced mutant clones, 23% had total deletions and 8% had deletion of one exon, whereas all early UV-B events were either point mutations or small deletions or insertions. In conclusion, the multiplex polymerase chain reaction deletion screen showed that there were explicit differences in the occurrence of large gene alterations between early and delayed mutations induced by UV-B radiation. For UV-A radiation the deletion spectra were similar for delayed and early mutations. UV-A radiation is, in contrast to UV-B radiation, only weakly absorbed by DNA and probably induces mutation almost solely via production of reactive oxygen species. Therefore, the present results support the hypothesis that persistent increase in oxidative stress is involved in the mechanism of UV-induced genomic instability. 相似文献
92.
Phenols were converted to their magnesium salts with the MgCl2-Et3N base system and subsequently reacted with Eschenmoser's salt, affording N,N-dimethyl substituted benzylamines in high to excellent yields. A series of mono N-substituted benzylamines were prepared in one-pot syntheses by ortho-formylation of phenols to corresponding salicylaldehydes, which in turn reacted with amines to imines. The imines were subsequently reduced to mono N-substituted benzylamines. Some of these benzylamines were further converted, without work-up, to mono N-substituted dihydro-2H-1,3-benzoxazines. 相似文献
93.
Radovan Bast Dr. Andreas Heßelmann Dr. Paweł Sałek Dr. Trygve Helgaker Prof. Dr. Trond Saue Dr. 《Chemphyschem》2008,9(3):445-453
We test the performance of four‐component relativistic density functional theory by calculating the static and frequency‐dependent electric dipole–dipole polarizabilities of all (ground‐state) closed‐shell atoms up to Ra. We consider 12 nonrelativistic functionals, including three asymptotically shape‐corrected functionals, by using two smooth interpolation schemes introduced by the Baerends group: the gradient‐regulated asymptotic connection (GRAC) procedure and the statistical averaging of (model) orbital potentials (SAOP). Basis sets of doubly augmented triple‐zeta quality are used. The results are compared to experimental data or to accurate ab initio results. The reference static electric dipole polarizability of palladium has been obtained by finite‐field calculations using the coupled‐cluster singles, doubles, and perturbative triples method within this work. The best overall performance is obtained using hybrid functionals and their GRAC shape‐corrected versions. The performance of SAOP is among the best for nonhybrid functionals for Group 18 atoms but its precision degrades when considering the full set of atoms. In general, we find that conclusions based on results obtained for the rare‐gas atoms are not necessarily representative of the complete set of atoms. GRAC cannot be used with effective core potentials since the asymptotic correction is switched on in the core region. 相似文献
94.
Trond Digernes 《P-Adic Numbers, Ultrametric Analysis, and Applications》2018,10(4):253-266
We give a review of finite approximations of quantum systems, both in an Archimedean and a non-Archimedean setting. Proofs will generally be omitted. In the Appendix we present some numerical results. 相似文献
95.
Zhe
Li James E. McClure Jill Middleton Trond Varslot Adrian P. Sheppard 《国际流体数值方法杂志》2020,92(9):1162-1197
Digital images of porous media often include features approaching the image resolution length scale. The behavior of numerical methods at low resolution is therefore important even for well-resolved systems. We study the behavior of the Shan-Chen (SC) and Rothman-Keller (RK) multicomponent lattice-Boltzmann models in situations where the fluid-fluid interfacial radius of curvature and/or the feature size of the medium approaches the discrete unit size of the computational grid. Various simple, small-scale test geometries are considered, and a drainage test is also performed in a Bentheimer sandstone sample. We find that both RK and SC models show very high ultimate limits: in ideal conditions the models can simulate static fluid configuration with acceptable accuracy in tubes as small as three lattice units across for RK model (six lattice units for SC model) and with an interfacial radius of curvature of two lattice units for RK and SC models. However, the stability of the models is affected when operating in these extreme discrete limits: in certain circumstances the models exhibit behaviors ranging from loss of accuracy to numerical instability. We discuss the circumstances where these behaviors occur and the ramifications for larger-scale fluid displacement simulations in porous media, along with strategies to mitigate the most severe effects. Overall we find that the RK model, with modern enhancements, exhibits fewer instabilities and is more suitable for systems of low fluid-fluid miscibility. The shortcomings of the SC model seem to arise predominantly from the high, strongly pressure-dependent miscibility of the two fluid components. 相似文献
96.
Trond R. Henninen Marta Bon Feng Wang Daniele Passerone Rolf Erni 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(2):849-855
Little is known about metallic clusters consisting merely of a dozen of atoms or even less, despite of their importance in catalysis and crystal nucleation. Scanning transmission electron microscopy (STEM) provides direct atomic structure information but has inherently suffered from limited time resolution. We employ fast dynamic STEM combined with a spatio-temporal image denoising algorithm to explore the structure and stability of Pt clusters on carbon, which represents a highly relevant catalysis system. At room temperature, dynamic amorphous 2D structures are found, while above ≈300 °C, the clusters transform into a crystalline state. Our experimental and theoretical data reveal an unexpected strong trend of the crystalline clusters to exhibit the face-centered cubic, bulk structure of Pt with cuboidal geometries being most prominent. 相似文献
97.
Brautaset T Bruheim P Sletta H Hagen L Ellingsen TE Strøm AR Valla S Zotchev SB 《Chemistry & biology》2002,9(3):367-373
Genetic manipulation of the polyketide synthase (PKS) gene nysC involved in the biosynthesis of the tetraene antifungal antibiotic nystatin yielded a recombinant strain producing hexaene nystatin derivatives. Analysis of one such compound, S48HX, by LC-MS/MS suggested that it comprises a 36-membered macrolactone ring completely decorated by the post-PKS modification enzymes. Further characterization by bioassay has shown that S48HX exhibits antifungal activity. Genetic analysis of the hexaene-producing mutant revealed an in-frame deletion within the nysC gene via recombination between two homologous ketoreductase domain-encoding sequences. Apparently, this event resulted in the elimination of one complete module from NysC PKS, subsequently leading to the production of the nystatin derivative with a contracted macrolactone ring. These results represent the first example of manipulation of a PKS gene for the biosynthesis of a polyene antibiotic. 相似文献
98.
Cover Picture: Total Synthesis of the Anti‐inflammatory and Pro‐resolving Lipid Mediator MaR1n−3 DPA Utilizing an sp3–sp3 Negishi Cross‐Coupling Reaction (Chem. Eur. J. 45/2014) 下载免费PDF全文
99.
Gard Gjessing Lars-Inge Gammelster Johnsen Simen Gjelseth Antonsen Jens M. J. Nolse Yngve Stenstrm Trond Vidar Hansen 《Molecules (Basel, Switzerland)》2022,27(7)
Monohydroxylated polyunsaturated fatty acids belonging to the oxylipin class of natural products are present in marine and terrestrial sources as well as in the human body. Due to their biological activities and role in diverse biosynthetic pathways, oxylipins biosynthesized from eicosapentaenoic acid and arachidonic acid have attracted great interest from the scientific community. One example is 3-hydroxyeicosapentaenoic acid where the absolute configuration at C-3 has only been tentatively assigned. In this paper, studies on acetate type aldol reactions that enabled the preparation of 3-(R)-hydroxyeicosapentaenoic acid (3R-HETE, 2) and its enantiomer are presented. 相似文献
100.
[reaction: see text] 3,5-Disubstituted isoxazoles are obtained in good yields by a convenient one-pot, three-step procedure utilizing a regioselective copper(I)-catalyzed cycloaddition reaction between in situ generated nitrile oxides and terminal acetylenes. Most functional groups do not interfere with the reaction, which can be performed in aqueous solvents without protection from oxygen. Since all reagents are used in stoichiometric amounts, formation of byproducts is minimized. 相似文献