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排序方式: 共有57条查询结果,搜索用时 31 毫秒
31.
Hocek M Stepnicka P Ludvík J Císarová I Votruba I Reha D Hobza P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(8):2058-2066
Palladium-catalyzed Sonogashira cross-coupling reactions of halopurines 9-benzyl-6-chloropurine (2 a), 9-benzyl-8-bromoadenine (2 b), and 9-benzyl-2-chloroadenine (2 c) with ethynylferrocene (1) gave the corresponding (ferrocenylethynyl)purines 3 a-c in moderate to good yields. Catalytic hydrogenation of these alkynes over Pd/C afforded the respective saturated [2-(ferrocenyl)ethyl]purines 4 a-c. The crystal structures 3 a, 3 b, 4 a and 4 b as determined by X-ray diffraction show interesting solid-state interactions, markedly different for purines 3 a and 4 a on one hand and adenines 3 b and 4 b that possess a free amino group on the other. Electrochemistry of electrochemically labelled purines 3 and 4 has been studied by voltammetry and cyclic voltammetry on platinum disc electrode and the experimental oxidation potentials were confirmed and explained by ionization potentials from theoretical DFT calculations. Several compounds of this series exhibited a considerable cytostatic effect. 相似文献
32.
A synthesis of ethene and ethyne derivatives carrying the anionic -C(BCH3)11- substituent on one or both carbon atoms is described. Two-electron oxidation of the dianions yielded the stable and isolable electroneutral title biradicals. 相似文献
33.
Klíma J Frias-Ferrer A González-García J Ludvík J Sáez V Iniesta J 《Ultrasonics sonochemistry》2007,14(1):19-28
The intensity distribution of the ultrasonic energy is, after the frequency, the most significant parameter to characterize ultrasonic fields in any sonochemical experiment. Whereas in the case of low intensity ultrasound the measurement of intensity and its distribution is well solved, in the case of high intensity (when cavitation takes place) the measurement is much more complicated. That is why the predicting the acoustic pressure distribution within the cell is desirable. A numerical solution of the wave equation gave the distribution of intensity within the cell. The calculations together with experimental verification have shown that the whole reactor behaves like a resonator and the energy distribution depends strongly on its shape. The agreement between computational simulations and experiments allowed optimisation of the shape of the sonochemical reactor. The optimal geometry resulted in a strong increase in intensity along a large part of the cell. The advantages of such optimised geometry are (i) the ultrasonic power necessary for obtaining cavitation is low; (ii) low power delivered to the system results in only weak heating, consequently, no cooling is necessary and (iii) the "active volume" is large, i.e. the fraction of the reactor volume with high intensity is large and is not limited to a vicinity close to the horn tip. 相似文献
34.
Róbert Obertík Dr. Josef Chudoba Dr. Jiří Šturala Dr. Ján Tarábek Dr. Lucie Ludvíková Dr. Tomáš Slanina Prof. Dr. Burkhard König Prof. Dr. Radek Cibulka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(67):e202202487
Catalyst recovery is an integral part of photoredox catalysis. It is often solved by adding another component-a sacrificial agent-whose role is to convert the catalyst back into its original oxidation state. However, an additive may cause a side reaction thus decreasing the selectivity and overall efficiency. Herein, we present a novel approach towards chemoselective photooxidation reactions based on suitable solvent-acetonitrile acting simultaneously as an electron acceptor for catalyst recovery, and on anaerobic conditions. This is allowed by the unique properties of the catalyst, 7,8-dimethoxy-3-methyl-5-phenyl-5-deazaflavinium chloride existing in both strongly oxidizing and reducing forms, whose strength is increased by excitation with visible light. Usefulness of this system is demonstrated in chemoselective dehydrogenations of 4-methoxy- and 4-chlorobenzyl alcohols to aldehydes without over-oxidation to benzoic acids achieving yields up to 70 %. 4-Substituted 1-phenylethanols were oxidized to ketones with yields 80–100 % and, moreover, with yields 31-98 % in the presence of benzylic methyl group, diphenylmethane or thioanisole which are readily oxidized in the presence of oxygen but these were untouched with our system. Mechanistic studies based on UV-Vis spectro-electrochemistry, EPR and time-resolved spectroscopy measurements showed that the process involving an electron release from an excited deazaflavin radical to acetonitrile under formation of solvated electron is crucial for the catalyst recovery. 相似文献
35.
Oxides of transition metals could be suitable alternatives to catalysts based on noble metals in the oxidation processes used
for the abatement of volatile organic compounds. Mixed oxides of transition metals can exhibit good efficiency and thermal
stability, as well as being inexpensive. In this work, oxide catalysts containing various combinations of Cu, Co, Ni, Mn,
and Al, grained or supported on oxidised aluminium foil Al2O3/Al, were studied in terms of their chemical and physical properties, including their chemical composition, porous structure,
phase composition, reducibility, and activity in total ethanol oxidation. Ternary co-precipitated catalysts in the form of
grains obtained from layered double hydroxide-like precursors were highly active, especially those containing manganese. Deposition
of the selected precursors on an anodised aluminium foil-support afforded less active catalysts, mainly because the required
metal molar ratios were not achieved, and insufficient amounts of metals were deposited. However, by controlling the preparation
conditions (pH), higher loading of active components and higher catalytic activity were obtained. 相似文献
36.
Ludmila Šimková Jiří Klíma Petr Sazama Jiří Ludvík 《Journal of Solid State Electrochemistry》2011,15(10):2133-2139
Redox properties of 2,2-dinitroethene-1,1-diamine (FOX-7) were electrochemically investigated by DC polarography, cyclic voltammetry
and preparative electrolyses, and electroreduction products were analysed. The polarographic reduction of FOX-7 in aqueous
buffered solutions exhibited a total sum of limiting currents corresponding to the expected 18 electrons. This result fits
well with the chemical reduction of this energetic material resulting in ethan-1,2-diamine. Exhaustive electrolysis, however,
did not yield this product and the passed charge for total degradation of this compound corresponds only to 4–7 F. As the
main products, gaseous N2, N2O, NO and NH3 were proved by combination EC–GC–MS and, besides that, nitrite anions and ammonia ions were identified by other methods.
All these observations suggest that instead of electrochemical reduction, an electrochemically initiated degradation process
accompanying the exhaustive electrolysis occurs. This seems to be analogous to the chain of reactions during explosion, which
are slowed down by a very low concentration and cooled by the solvent. 相似文献
37.
Koláčná Lucie Klíma Jiří Polák Peter Tobrman Tomáš Liška Alan Ludvík Jiří 《Journal of Solid State Electrochemistry》2022,26(2):503-514
Journal of Solid State Electrochemistry - A series of nine precursors for pyrene-based biodegradable organic (semi)conductors having tetrasubstituted double bond as a central organic core and... 相似文献
38.
Liška Alan Flídrová Karolína Lhoták Pavel Ludvík Jiří 《Monatshefte für Chemie / Chemical Monthly》2015,146(5):857-862
Monatshefte für Chemie - Chemical Monthly - A newly synthesized series of mono- and di-, nitro- or nitrosocalix[4]arenes has been investigated electrochemically. It was shown that besides the... 相似文献
39.
Prof. Jiří Kulhánek Prof. Filip Bureš Prof. Oldřich Pytela Dr. Tomáš Mikysek Prof. Jiří Ludvík 《化学:亚洲杂志》2011,6(6):1604-1612
Eleven new, stable, push–pull systems that feature 4,5‐bis[4‐(N,N‐dimethylamino)phenyl]imidazole and 4,5‐dicyanoimidazole as the donor and acceptor moieties and the systematically extended and varied π‐linker were prepared and investigated. Evaluation of the measured UV/Vis spectra, electrochemical data (cyclic voltammetry (CV), rotating‐disc voltammetry (RDV), and polarography) and calculated β and γ polarizabilities showed efficient charge transfer (CT) in biimidazole‐type chromophores. Push–pull system 27 , which features a planar thiophene‐derived π‐linker, was revealed to be the most efficient chromophore within the studied series. This chromophore possessed the most bathochromically shifted CT band, the lowest electrochemical gap, and highest β and γ polarizabilities. The CT transition was most significantly affected by structural features such as π‐linker length, planarity, conjugating arrangement, and the presence of olefinic/acetylenic or 1,4‐phenylene/thiophene subunits in the π‐linker. 相似文献
40.
Ludv Stahre 《Fresenius' Journal of Analytical Chemistry》1897,36(1):195
Ohne Zusammenfassung 相似文献