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21.
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Andrea Hartwig Leon Mullenders Monika Asmu? Heike Dally M. Hartmann 《Fresenius' Journal of Analytical Chemistry》1998,361(4):377-380
Based on pronounced enhancing effects in combination with other DNA-damaging agents the potentials of Ni(II), Cd(II) and
As(III) to interfere with DNA repair processes in HeLa cells was investigated. With respect to oxidative DNA damage, Ni(II)
and Cd(II) induced DNA strand breaks starting at concentrations of 250 μM and 5 μM, respectively. The induction of oxidative
DNA base modifications like 8-hydroxyguanine was restricted to the cytotoxic concentration of 750 μM Ni(II) and not observed
after treatment with Cd(II). In contrast, the removal of oxidative DNA base modifications was inhibited at concentrations
as low as 50 μM Ni(II) and 0.5 μM Cd(II). Regarding nucleotide excision repair, Ni(II) and Cd(II) disturbed the DNA-protein
interactions involved in the damage recognition step when applying HeLa nuclear protein extracts and a UV-damaged oligonucleotide,
while As(III) inhibited the actual incision event. In the case of Ni(II) and Cd(II), this effect was reversible by the addition
of Mg(II) and Zn(II), respectively. Furthermore, Cd(II) inactivated the isolated bacterial Fpg protein, most likely by the
displacement of Zn(II) from its zinc finger structure. Since DNA is continuously damaged by exogenous and endogenous sources,
an impaired repair capacity might well account for the carcinogenic action of the metal compounds.
Received: 30 July 1997 / Revised: 6 October 1997 / Accepted: 10 October 1997 相似文献
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Zusammenfassung Die optisch aktiven Methylcymantren-- und--carbonsäuren bekannter Absolutkonfiguration wurden auf dem Weg: COClCON3NH2Hal in die entsprechenden Chlor-, Brom- und Jod-methylcymantrene umgewandelt, und dieORD der genannten Verbindungen sowie die Drehungen der Methylcymantrenylisocyanate (dargestellt aus den Aziden) gemessen. In den Halogen-methylcymantrenen liegen optisch aktive Metallocene vor, bei denen der Beitrag zur Drehung nur aus der Atomchiralität stammen kann, während bei den anderen Methylcymantrenderivaten auch die Konformationschiralität einen Beitrag leistet. Entsprechend sind die [M]D-Werte der Halogen-methylcymantrene proportional den Polarisierbarkeiten von Hal. DieNMR-Daten der neuen Cymantrenderivate werden mitgeteilt und kurz diskutiert.
Mit 3 Abbildungen
16. Mitt.:H. Falk undK. Schlögl, Mh. Chem.99, 578 (1968).
a) 3. Mitt.:Heike Gowal undK. Schlögl, Mh. Chem.99, 267 (1968); b) 2. Mitt.:Heike Gowal undK. Schlögl, Mh. Chem.98, 2302 (1967); c) 1. Mitt.:S. G. Cottis, H. Falk undK. Schlögl, Tetrahedron Letters [London]1965, 2857. 相似文献
The optically active methylcymantrene-- and--carboxylic acids of known absolute configuration were converted into the corresponding chloro, bromo and iodo methylcymantrenesvia their chlorides, azides and amines. TheORD of these cymantrene derivatives as well as the rotations of methylcymantrenyl isocyanates (prepared from the azides) are reported. The halogen methylcymantrenes represent optically active metallocenes, in which the contribution to the optical rotations originates only from atomic chirality, whilst in the case of the other methylcymantrene derivatives the conformational chirality also contributes. Correspondingly, the [M]D values of the halogen methylcymantrenes are proportional to the polarizibilities of Hal. TheNMR data of the new cymantrene derivatives are reported and briefly discussed.
Mit 3 Abbildungen
16. Mitt.:H. Falk undK. Schlögl, Mh. Chem.99, 578 (1968).
a) 3. Mitt.:Heike Gowal undK. Schlögl, Mh. Chem.99, 267 (1968); b) 2. Mitt.:Heike Gowal undK. Schlögl, Mh. Chem.98, 2302 (1967); c) 1. Mitt.:S. G. Cottis, H. Falk undK. Schlögl, Tetrahedron Letters [London]1965, 2857. 相似文献
26.
The possibility of lasing without inversion on the 1079.8 nm line of a HeNe laser is investigated. It is shown that a modified double- scheme can be realized by use of the 877.9 nm line for introducing Zeeman coherence. It is shown experimentally that Zeeman coherence can enforce laser action, even if the inversion is below threshold. A different choice of the polarization of the driving beam can result in suppression of laser action above threshold. The underlying mechanisms are examined. On the 611.8 nm line, laser action below threshold inversion is obtained with the driving beam tuned to 824.9 nm (up-conversion). 相似文献
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Schmidt R Blaich T Elze TW Emling H Freiesleben H Grimm K Henning W Holzmann R Keller JG Klingler H Kulessa R Kratz JV Lambrecht D Lange JS Leifels Y Lubkiewicz E Moore EF Wajda E Prokopowicz W Schütter C Spies H Stelzer K Stroth J Walus W Wollersheim HJ Zinser M Zude E 《Physical review letters》1993,70(12):1767-1770
29.
S. F. Bureiko N. S. Golubev G. S. Denisov I. Ya. Lange 《Reaction Kinetics and Catalysis Letters》1977,7(2):139-144
The kinetic isotope effect in proton exchange between methanol and water in CCl4 solution was studied by1H and2H NMR and kinetic IR spectroscopy. The exchange rate increases in the series CD3OH+H2O3OD+H2O3OD+D2O. It has been concluded that the limiting step of the reaction involves the formation of an H-bonded cyclic intermediate.
1H 2H - CCl4. , CD3OH+H2O相似文献3OD+H2O 3OD+D2O. , - -.
30.
Asymmetric induction was achieved in the photoaddition of 3-methyl-2-cyclohexenone to optically active enoates 1a–c and the absolute configuration of the major adduct was determined. 相似文献