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61.
Konrad Kowalski Anne VessièresSiden Top Gérard Jaouen Janusz Zakrzewski 《Tetrahedron letters》2003,44(13):2749-2751
A synthetic pathway giving access to diphenyl ethylene organometallic derivatives possessing the ferrocifen precursor skeleton modified in the Cp′ ring is described. It relies on reaction of the (η5-propionylcyclopentadienyl) (η6-benzene)iron(II) salt 7 with substituted cyclopentadienyl anions or their heteroanalogs followed by the McMurry coupling reaction with 4,4′-dihydroxybenzophenone. Using this approach pentamethylcyclopentadienyl and 3,4-dimethylphospholyl analogs of ferrocifen precursor (10 and 11) have been synthesized. Even with the presence of the bulky and containing phosphorus η5-ligands these compounds are still recognized by the two subtypes of estrogen receptor(ERα and ERβ). 相似文献
62.
Non-aqueous capillary electrophoresis of the positional isomers of a sulfated monosaccharide 总被引:2,自引:0,他引:2
Descroix S Varenne A Goasdoue N Abian J Carrascal M Daniel R Gareil P 《Journal of chromatography. A》2003,987(1-2):467-476
A non-aqueous capillary electrophoresis (NACE) method coupled to indirect absorbance detection has been developed for the separation of the three positional isomers of monosulfated fucose. The optimized electrolyte was composed of 12 mM ethanolamine, 2 mM trimesic acid buffer in a methanol-ethanol (1:1, v/v) mixture. As the retained electrolyte entails no separating agent other than the pH buffer, the NACE separation of the positional isomers has been ascribed mainly to selective ion-pairing with the electrolyte counter-ion and the possibility of a selective solvation effect in the alcohol mixture. In the absence of pure isomeric standards, peak identification was completed by MS and NMR spectroscopy and selective enzymatic desulfation. This method should be of interest for the structure elucidation of monosulfated fucose-based polysaccharides and for the screening of sulfoesterase of unknown activity. 相似文献
63.
ULTRAVIOLET LIGHT-INDUCED FREE RADICAL FORMATION IN SKIN: AN ELECTRON PARAMAGNETIC RESONANCE STUDY 总被引:7,自引:0,他引:7
It has been suggested that ultraviolet light induces free radical formation in skin, leading to photoaging and cancer. We have demonstrated by electron paramagnetic resonance that the ascorbate free radical is naturally present in unexposed skin at a very low steady state level. When a section of SKH-1 hairless mouse skin in an EPR cavity is exposed to UV light (4,500 J m−2 −1, Xe lamp, 305 nm cutoff and IR filters), the ascorbate free radical signal intensity increases. These results indicate that UV light increases free radical oxidative stress, consistent with ascorbate's role as the terminal, small-molecule antioxidant. The initial radicals produced by UV light would have very short lifetimes at room temperature; thus, we have applied EPR spin trapping techniques to detect these radicals. Using α-[4-pyridyl 1-oxide]-N- tert -butyl nitrone (POBN), we have for the first time spin trapped a UV light-produced carbon-centered free radical from intact skin. The EPR spectra exhibited hyperfine splittings that are characteristic of POBN/alkyl radicals, aN = 15.56 G and aH = 2.70 G, possibly generated from membrane lipids as a result of β-scission of lipid alkoxyl radicals. Iron can act as a catalyst for free radical oxidative reactions; chronic exposure of skin to UV radiation causes increased iron deposition. Using our spin trapping system, we have shown that topical application of the iron-chelator, Desferal, to a section of skin reduces the UV light-induced POBN adduct radical signal. These results provide direct evidence for free radical generation and a role for iron in UV light-induced dermatopathology. We suggest that iron chelators can serve as photoprotective agents by preventing these oxidations. 相似文献
64.
Ab initio SCF computations on the intrinsic preferences of the H+, CH
3
+
and C2H
5
+
cations towards the two principal sites of protonation or alkylation on cytosine, N3 or O2, show that this preference undergoes a continuous modification with the increase in size and complexity of the cation. N3 is the preferred site of fixation of H+, O2 the preferred site of C2H
5
+
, while CH
3
+
has no marked preference. The exchange repulsion term of the binding energy appears responsible for the preference of C2H
5
+
for O2.This work was supported by the Ligue Francaise contre le Cancer and the National Foundation for Cancer Research (USA) 相似文献
65.
Graff JN McElhaney AE Basu P Gruhn NE Chang CS Enemark JH 《Inorganic chemistry》2002,41(10):2642-2647
Complexes of the form (Tp*)MoOCl(p-OC(6)H(4)X) and (Tp*)MoO(p-OC(6)H(4)X)(2) (Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate and X = OEt, OMe, Et, Me, H, F, Cl, Br, I, and CN) were examined by electrochemical techniques and gas-phase photoelectron spectroscopy to probe the effect of the remote substituent (X) on electron-transfer reactions at the oxomolybdenum core. Cyclic voltammetry revealed that all of these neutral Mo(V) compounds undergo a quasireversible one-electron oxidation (Mo(VI)/Mo(V)) and a quasireversible one-electron reduction (Mo(V)/Mo(IV)) at potentials that linearly depend on the electronic influence (Hammett sigma(p) parameter) of X. The first ionization energies for (Tp*)MoO(p-OC(6)H(4)X)(2) (X = OEt, OMe, H, F, and CN) were determined by photoelectron spectroscopy. A nearly linear correlation was found for the Mo(VI)/Mo(V) oxidation potentials in solution and the gas-phase ionization energies. Calculated heterogeneous electron-transfer rate constants show a slight systematic dependence on the substituent. 相似文献
66.
Vonderheide AP Meija J Tepperman K Puga A Pinhas AR States JC Caruso JA 《Journal of chromatography. A》2004,1024(1-2):129-137
High-performance chelation ion chromatography (HPCIC) was employed to retain cationic Cr(III) on an anion-exchange column and hence allow the separation of the two most prevalent forms of chromium, Cr(II) and Cr(VI). A mobile phase of nitric acid was utilized at pH = 1.5; additionally, 2,6-pyridinedicarboxylic acid was used at a concentration of 6 mM. Additives with different structural characteristics were used in an effort to elucidate retention mechanisms. Inductively-coupled plasma mass spectrometry was used for chromium detection. A collision cell was utilized to reduce chloride-based polyatomic ions that may interfere with the detection of Cr(III), and a detection limit study yielded levels in the low part-per-billion range. The newly developed method was applied to the chromatographic analysis of samples of an incubation medium containing Cr(VI) incubated with cell nuclei. 相似文献
67.
Azioune A Slimane AB Hamou LA Pleuvy A Chehimi MM Perruchot C Armes SP 《Langmuir : the ACS journal of surfaces and colloids》2004,20(8):3350-3356
Novel ester-functionalized polypyrrole-silica nanocomposite particles were prepared by oxidative copolymerization of pyrrole and N-succinimidyl ester pyrrole (50/50% initial concentrations), using FeCl3 in the presence of ultrafine silica nanoparticles (20 nm diameter). The N-succinimidyl ester pyrrole monomer was prepared in aqueous solution using 1-(2-carboxyethylpyrrole) and N-hydroxysuccinimide in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide. The resulting nanocomposites (N-succinimidyl ester polypyrrole-silica) are raspberry-shaped agglomerates of silica sol particles "glued" together by the insoluble poly(pyrrole-co-N-succinimidyl pyrrole). The N-succinimidyl ester polypyrrole-silica particles were characterized in terms of their size, density, copolymer content, and polydispersity. Scanning electron microscopy and disk centrifuge sedimentometry confirmed that the nanocomposite particles had narrow size distributions. X-ray photoelectron spectroscopy analysis indicated a silica-rich surface and a high surface concentration of N-succinimidyl ester groups. These nanoparticles exhibited good long-term dispersion stability. The chemical stability of the ester functions in aqueous media after several weeks of storage was monitored by FTIR spectroscopy. The functionalized nanocomposites were tested as bioadsorbents of human serum albumin (HSA). The very high amount of immobilized HSA determined by UV-visible spectroscopy is believed to be due to covalent binding. Incubation of the HSA-grafted nanocomposite with anti-HSA resulted in immediate flocculation, an indication that they are alternative candidates for visual diagnostic assays. 相似文献
68.
Anne Astier Jean-Claude Daran Yves Jeannin Catherine Rigault 《Journal of organometallic chemistry》1983,241(1):53-68
Syntheses and single-crystal X-ray diffraction studies have been completed on two cycloruthenapentadienyl (CO)6Ru2L2 derivatives, with L = CH2OHC = CCH2OH and C2H5C=CCH2CH2OH respectively. Crystal data are as follows: for [(CO)3RuC4(CH2OH)4]Ru(CO)3·H2O, P21/c, a 13.72(1), b 9.501(4), c 14.86(1) Å, β 101.10(6)°, Rw = 0.052 for 1911 reflections; for [(CO)3RuC4(CH2CH2OH)2(C2H5)2]Ru(CO)3, P21/c, a 9.191(3), b 16.732(4), c 14.903(3) Å, β 113.61(4)°, Rw = 0.042 for 2865 reflections. Both compounds are built up from binuclear units, each unit being regarded as a Ru(CO)3 fragment π-bonded to a cycloruthenapentadienyl ring. The molecular parameters are compared with those of known cyclometallapentadienyl complexes of transition metals. The presence of a semi-bridging CO group is discussed. 相似文献
69.
Laurent Griffe Dr. Mary Poupot Dr. Patrice Marchand Dr. Alexandrine Maraval Dr. Cédric‐Olivier Turrin Dr. Olivier Rolland Pascal Métivier Dr. Gérard Bacquet Dr. Jean‐Jacques Fournié Dr. Anne‐Marie Caminade Dr. Rémy Poupot Dr. Jean‐Pierre Majoral Dr. 《Angewandte Chemie (International ed. in English)》2007,46(14):2334-2334