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981.
Makogon O Flyunt R Tobien T Naumov S Bonifacić M 《The journal of physical chemistry. A》2008,112(26):5908-5916
Using pulse radiolysis and steady-state gamma-radiolysis techniques, it has been established that, in air-saturated aqueous solutions, peroxyl radicals CH 2HalOO (*) (Hal = halogen) derived from CH 2Cl 2 and CH 2Br 2 react with dimethyl selenide (Me 2Se), with k on the order of 7 x 10 (7) M (-1) s (-1), to form HCO 2H, CH 2O, CO 2, and CO as final products. An overall two-electron oxidation process leads directly to dimethyl selenoxide (Me 2SeO), along with oxyl radical CH 2HalO (*). The latter subsequently oxidizes another Me 2Se molecule by a much faster one-electron transfer mechanism, leading to the formation of equal yields of CH 2O and the dimer radical cation (Me 2Se) 2 (*+). In absolute terms, these yields amount to 18% and 28% of the CH 2ClO (*) and CH 2BrO (*) yields, respectively, at 1 mM Me 2Se. In competition, CH 2HalO (*) rearranges into (*)CH(OH)Hal. These C-centered radicals react further via two pathways: (a) Addition of an oxygen molecule leads to the corresponding peroxyl radicals, that is, species prone to decomposition into H (+)/O 2 (*-) and formylhalide, HC(O)Hal, which further degrades mostly to H (+)/Hal (-) and CO. (b) Elimination of HHal yields the formyl radical H-C(*)=O with a rate constant of about 6 x 10 (5) s (-1) for Hal = Cl. In an air-saturated solution, the predominant reaction pathway of the H-C(*)=O radical is addition of oxygen. The formylperoxyl radical HC(O)OO (*) thus formed reacts with Me 2Se via an overall two-electron transfer mechanism, giving additional Me 2SeO and formyloxyl radicals HC(O)O(*). The latter rearrange via a 1,2 H-atom shift into (*)C(O)OH, which reacts with O2 to give CO2 and O2(*)(-). The minor fraction of H-C(*)=O undergoes hydration, with an estimated rate constant of k approximately 2 x 10(5) s(-1). The resulting HC(*)(OH)2 radical, upon reaction with O2, yields HCO 2H and H (+)/O2(*-). Some of the conclusions about the reactions of halogenated alkoxyl radicals are supported by quantum chemical calculations [B3LYP/6-31G(d,p)] taking into account the influence of water as a dielectric continuum [by the self-consistent reaction field polarized continuum model (SCRF=PCM) technique]. Based on detailed product studies, mechanisms are proposed for the free-radical degradation of CH 2Cl 2 and CH 2Br 2 in the presence of oxygen and an electron donor (namely, Me 2Se in this study), and properties of the reactive intermediates are discussed. 相似文献
982.
983.
Sergeant CD Ott I Sniady A Meneni S Gust R Rheingold AL Dembinski R 《Organic & biomolecular chemistry》2008,6(1):73-80
Reactions of 5-alkynyl-2'-deoxyuridines with dicobalt octacarbonyl Co2(CO)8 in THF at room temperature gave hexacarbonyl dicobalt nucleoside complexes (77-93%). The metallo-nucleosides were characterized, including an X-ray structure of a 1-cyclohexanol derivative. In crystalline form, the Co-Co bond is perpendicular to the plane of the uracil base, which is found in the anti position. The level of growth inhibition of MCF-7 and MDA-MB-231 human breast cancer cell lines was examined and compared to results obtained with the alkynyl nucleoside precursors. The cobalt compounds displayed good antiproliferative activities with IC50 values in the range of 5-50 microM. Interestingly, the coordination of the dicobalt carbonyl moiety to 5-alkynyl-2'-deoxyuridines led to a significant increase in the cytotoxic potency for alkyl/aryl substituents at the non-nucleoside side of the alkyne, but in the case of hydrogen (terminal alkyne) or a silyl group, a decrease of the cytotoxic effect was observed. As demonstrated using examples for an active and a low active target compound, the cytotoxicity was significantly influenced by the uptake into the tumor cells and the biodistribution into the nuclei. 相似文献
984.
Albert T. H. Bartholomäus Dávid Roman Walid K. Al-Jammal Prof. Dr. Ivan Vilotijević Prof. Dr. Christine Beemelmanns 《European journal of organic chemistry》2023,26(18):e202300177
The formation of C−C bonds via the allylation of carbonyl compounds has been widely applied in total syntheses. Amongst the many possible strategies, the Barbier-type allylation in aqueous media has received only moderate attention over the last decades despite its mild reaction conditions. In this study, we investigated the indium (In0) and zinc (Zn0) mediated Barbier allylation reaction to efficiently synthesize base-labile 3-methylene-5-hydroxy containing building blocks for natural product total synthesis. As model study we selected the allylation of lipidic undecanal with ethyl 3-(bromomethyl)but-3-enoate in the presence of either Zn0 or In0 and investigated the effects of additives on yields and selectivities. We then applied the optimized reaction conditions to sterically demanding allyl bromides and functionalized aromatic aldehydes yielding eleven new homoallylic alcohols, one of which was further transformed via oxidation and reduction sequences. 相似文献
985.
A new synthetic approach is suggested for preparation of layered rare-earth oxide compounds containing [Ln2O2] slices and molecular anion sheets (CO32-, SO42-, and CrO42-). It is based on exchange reactions of rare-earth oxychlorides, [Ln2O2]Cl2, and alkali carbonates, sulfates, or chromates. Five new rare-earth oxychromates [Ln2O2]CrO4 (Ln=Pr-Gd) have been prepared which adopt a new, probably layered, structure type. In addition, significantly easier and more efficient synthetic pathways were found to the known compounds [Ln2O2]K2(CO3)2 and [La2O2]CrO4. The structure of the latter compound has been determined from neutron powder diffraction data. Factors affecting reaction pathways and products are discussed, as well as prospects for applying the approach to more complex layered compounds. 相似文献
986.
An Improved Protocol for Synthesis of 3‐Substituted 5‐Arylidene‐2‐thiohydantoins: Two‐step Procedure Alternative to Classical Methods 下载免费PDF全文
Olga Yu Kuznetsova Roman L. Antipin Anna V. Udina Olga O. Krasnovskaya Elena K. Beloglazkina Vladimir I. Terenin Victor E. Koteliansky Nikolay V. Zyk Alexander G. Majouga 《Journal of heterocyclic chemistry》2016,53(5):1570-1577
A novel method for the direct synthesis of 5‐arylidene‐2‐thiohydantoins from thioureas and aromatic aldehydes in the presence of base in ethanol was developed. Application of this efficient method allowed preparing thiohydantoins, which are difficult to synthesis by traditional methods. 相似文献
987.
Free-solution IEF of protein digests was studied in a newly introduced MicroRotofortrade mark multicompartment electrolyzer. The fractionation was performed in a cylindrical separation chamber divided into ten compartments with or without the addition of carrier ampholytes. In the case of autofocusing mode of operation, the tryptic digest itself served as the mixture of ampholytes leading to the separation of the peptides with well-defined pI's. The focusing process was monitored visually using colored pI markers. The resulting fractions from both modes of the separation were analyzed by CE and electrospray-TOF mass spectrometer using electrospray tips microfabricated in polyimide. Additional experiments, aiming at visualization of the mass flux within the focusing compartments were performed using isotachophoretic migration of color cationic tracers. The study considered the autofocusing of both the peptides with well-defined narrow pI's as well as those showing negligible net charge in a broader pH range. Although not all peptides in the protein digests have well-defined pI's the autofocusing process can preseparate many of them leading to higher S/N in the ESI-MS signals and improved protein sequence coverage. 相似文献
988.
Dmitrii P. Krut’ko Roman S. Kirsanov Sergey A. Belov Maxim V. Borzov Andrei V. Churakov Judith A.K. Howard 《Polyhedron》2007
Treatment of decamethylzirconocene dichloride (η5-Cp∗)2ZrCl2 with amalgamated magnesium in pyridine results in formation of the o-C–H bond activation product [η5-C5Me5]2ZrH[η2-κC,N-C5H4N] (1). X-ray diffraction analysis (solid state) and NMR spectroscopy data (solutions) reveal the lateral positioning of the nitrogen atom in 1. At elevated temperatures, complex 1 smoothly rearranges into its isomer 2 with medial positioning of the N-atom. The parameters of equilibrium between 1 and 2 were measured at different temperatures. A reaction of 1 or a mixture of 1 and 2 (ca. 1:10) with CDCl3 smoothly and under mild conditions leads to one and the same η2-pyridyl chloride complex [η5-C5Me5]2ZrCl[η2-κC,N-C5H4N] (3) with medial positioning of the N-atom. The thermodynamic and mechanistic concepts of the paper are discussed with application of the DFT computational data. 相似文献
989.
Colorimetric detection and fingerprinting of bacteria by glass-supported lipid/polydiacetylene films
Scindia Y Silbert L Volinsky R Kolusheva S Jelinek R 《Langmuir : the ACS journal of surfaces and colloids》2007,23(8):4682-4687
Glass-supported films of lipids and polydiacetylene were applied for visual detection and colorimetric fingerprinting of bacteria. The sensor films comprise polydiacetylene domains serving as the chromatic reporter interspersed within lipid monolayers that function as a biomimetic membrane platform. The detection schemes are based on either visible blue-red transitions or fluorescence transformations of polydiacetylene, induced by amphiphilic molecules secreted by proliferating bacteria. An important feature of the new film platform is the feasibility of either naked-eye detection of bacteria or color analysis using conventional scanners. Furthermore, we find that the degrees of bacterially induced color transformations depend both on the bacterial strains examined and the lipid compositions of the films. Accordingly, bacterial fingerprinting can be achieved through pattern recognition obtained by recording the chromatic transformations in an array of lipid/PDA films having different lipid components. 相似文献
990.
Zubatyuk RI Volovenko YM Shishkin OV Gorb L Leszczynski J 《The Journal of organic chemistry》2007,72(3):725-735
The contribution of aromaticity and intramolecular hydrogen bonding to relative stability, for a set of (1H-azahetero-2-ylidene)-acetaldehyde and 2-azahetero-2-yl-ethanol tautomeric pairs, has been investigated by means of quantum chemical DFT and ab initio methods up to the MP4(SDTQ)/AUG-cc-pVDZ and MP2/AUG-cc-pVTZ levels of theory. It is found that the relative energy of the tautomers is governed by the change in the degree of heterocycle aromaticity upon intramolecular hydrogen transfer. An analysis of geometrical parameters of a hydrogen-bonded system reveals a clear relationship between the aromaticity of the heterocycle, the conjugation in a resonant spacer, and the strengths of the intramolecular hydrogen bonds. This allows the conclusion to be drawn that intramolecular N-H...O and O-H...N hydrogen bonds formed are found to be resonance-assisted and their strength is dependent on the pi-donating/accepting properties of the heterocycle. On the basis of the results of the calculations, a simple model describing the mechanism of resonance assistance of hydrogen bonding has been suggested. 相似文献