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51.
A detailed in situ 13C and 1H NMR spectroscopic characterization of the following families of alkylperoxo complexes of titanium is presented: Ti(η2-OOtBu)n(OiPr)4−n, where n = 1–4; binuclear complexes [(iPrO)3Ti(μ-OiPr)2Ti(OiPr)2(η2-OOtBu)] and [(η2-OOtBu)(iPrO)2Ti(μ-OiPr)2Ti(OiPr)2(η2-OOtBu)]; complexes with β-diketonato ligands: Ti(LL)2(OEt)(η2-OOtBu), Ti(LL)2(OiPr)(η2-OOtBu), Ti(LL)2(η2-OOtBu)2, Ti(LL)2(OtBu)(η1-OOtBu), where HLL = acetylacetone, dipivaloylmethane. These alkylperoxo complexes could not be isolated due to their instability and were studied in situ at low temperatures. Whereas the side-on (η2) coordination mode of tert-butylperoxo ligand is generally preferable, the end-on (η1) coordination caused by spatial hindrance from surrounding bulky ligands is found in two cases. The quantitative data on the reactivity of alkylperoxo complexes found towards sulfides and alkenes were obtained. The system TiO(acac)2/tBuOOH in C6H6 was reinvestigated using 13C and 1H NMR spectroscopy. The structure of the complex Ti(acac)2{CH3C(O)(OOtBu)COO} actually formed in this system was elucidated. Four types of titanium(IV) alkylperoxo complexes were detected in the Sharpless–Katsuki catalytic system using 13C NMR spectroscopy. 相似文献
52.
借助于紫外-可见吸收光谱法、荧光光谱法以及停流-荧光光谱法研究了盐酸胍(GdmHcl)诱导人血红蛋白的去折叠过程。实验发现,盐酸胍诱导的血红蛋白去折叠有两个不同的过程,即随着GdmHcl浓度增加到1.0 mol·L-1左右时,血红蛋白亚基发生解聚,形成中间态;持续增加其浓度时,各亚基发生内部去折叠,最终导致血红素发生崩解。加入还原剂(β-巯基乙醇)对血红蛋白亚基解聚、血红素崩解有协同作用且直接引起亚基和全分子同步变构。血红蛋白去折叠过程从“三态模型”转变为“二态模型”。 相似文献
53.
Nathan Kornblum 《Angewandte Chemie (International ed. in English)》1975,14(11):734-745
A new type of substition process at a saturated carbon atom is described. These reactions, which proceed via a chain sequence in which radical anions and free radicals are intermediates, are noteworthy for providing novel and powerful means of synthesis: they occur readily under mild conditions, they give excellent yields of pure products, and, in contrast to SN2 displacements, they are rather insensitive to steric hindrance. As a consequence, radical anion processes are especially valuable for the preparation of highly branched structures. Many inorganic and organic anions readily enter into these displacements and, indeed, amines are also effective. Systems which undergo substitutions via this electron transfer mechanism include benzylic, cumylic, strictly aliphatic, and heterocyclic molecules. It is of interest that a number of groups which do not behave as leaving groups in SN2 displacements are readily displaced at room temperature from a satureted carbon atom via the radical anion-free radical pathway, e.g., nitro, azide, sulfone, and ether groups. 相似文献
54.
Abhishek KalerVachan Singh Meena Manpreet SinghBrahmam Pujala Asit K. ChakrabortiUttam Chand Banerjee 《Tetrahedron letters》2011,52(41):5355-5358
A novel biocatalytic method for the enantioselective synthesis of (R)-bromo-3-[4-(2-methoxy-ethyl) phenoxy]-2-propanol [(R)-BMEPP], a precursor for the synthesis of (S)-metoprolol, an anti hypertensive drug is described. We have developed kinetic resolution of rac-BMEPP by transesterification using Candida rugosa lipase and vinyl acetate as the acyl donor affording the product with excellent conversion (49%) and ee (>99%). Various reaction parameters (source of enzyme, reaction media, and concentration of substrate and acylating agent) for the enzymatic kinetic resolution have been reported. 相似文献
55.
M.Sc. Beatrice Battistella M.Sc. Linda Iffland-Mühlhaus B.Sc. Maximillian Schütze Dr. Beatrice Cula Dr. Uwe Kuhlmann Prof. Dr. Holger Dau Prof. Dr. Peter Hildebrandt Dr. Thomas Lohmiller Dr. Stefan Mebs Prof. Dr. Ulf-Peter Apfel Prof. Dr. Kallol Ray 《Angewandte Chemie (International ed. in English)》2023,62(6):e202214074
In many metalloenzymes, sulfur-containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S-ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four-nitrogen bound [Co(cyclam)]2+ ( 1 ; cyclam=1,5,8,11-tetraaza-cyclotetradecane) and the S-containing analog [Co(S2N2-cyclam)]2+ ( 2 ; S2N2-cyclam=1,8-dithia-5,11-diaza-cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the CoII centers in 1 and 2 point to the involvement of sulfur in the O2 reduction process as the key for the improved catalytic ORR capabilities of 2 . 相似文献
56.
Dr. Suiqin Li Dr. Shibin Wang Dr. Jiahui He Kai Li Yinjie Xu Mengxin Wang Shuying Zhao Yuhang Wang Prof. Xiaonian Li Prof. Xing Zhong Prof. Jianguo Wang 《Angewandte Chemie (International ed. in English)》2023,62(30):e202306553
Replacing the oxygen evolution reaction (OER) with the thermodynamically favorable electrooxidation of organics is considered a promising approach for the simultaneous production of hydrogen (H2) and high-value chemicals. However, exploring and optimizing efficient electrocatalysts remains a challenge for large-scale production of value-added steroid carbonyl and H2. Herein, Cr-NiO/GF and Cr-Ni3N/GF (GF: graphite felt) electrocatalysts were designed as anode and cathode for the production of steroid carbonyls and H2, respectively. The cooperative Cr-NiO and ACT (4-acetamido-2,2,6,6-tetramethyl-1-piperidine-N-oxyl) electrocatalyst can be extended to the electrooxidation of a series of steroid alcohols to the corresponding aldehydes. Additionally, Cr-Ni3N displays superior electrocatalytic activity for hydrogen evolution reaction (HER), with a low overpotential of 35 mV to deliver 10 mA cm−2. Furthermore, the system coupled with anodic electrooxidation of sterol and cathodic HER exhibited excellent performance with high space-time yield of 48.85 kg m−3 h−1 for steroid carbonyl and 1.82 L h−1 for H2 generation in a two-layer stacked flow cell. Density Functional Theory (DFT) calculations indicated that Cr doping effectively stabilizes ACTH on the NiO surface, and ACTH molecule could be captured via the ketonic oxygen interaction with Cr, resulting in excellent electrocatalytic activity. This work develops a novel approach to the rational design of efficient electrocatalysts for the simultaneous production of H2 and large-scale value-added pharmaceutical carbonyl intermediates. 相似文献
57.
Dr. Hemlata Agarwala Xiaoyu Chen Julien R. Lyonnet Dr. Ben A. Johnson Prof. Dr. Mårten Ahlquist Prof. Dr. Sascha Ott 《Angewandte Chemie (International ed. in English)》2023,62(17):e202218728
Molecular electrocatalysts for CO2-to-CO conversion often operate at large overpotentials, due to the large barrier for C−O bond cleavage. Illustrated with ruthenium polypyridyl catalysts, we herein propose a mechanistic route that involves one metal center that acts as both Lewis base and Lewis acid at different stages of the catalytic cycle, by density functional theory in corroboration with experimental FTIR. The nucleophilic character of the Ru center manifests itself in the initial attack on CO2 to form [ Ru -CO2]0, while its electrophilic character allows for the formation of a 5-membered metallacyclic intermediate, [ Ru -CO2CO2]0,c, by addition of a second CO2 molecule and intramolecular cyclization. The calculated activation barrier for C−O bond cleavage via the metallacycle is decreased by 34.9 kcal mol−1 as compared to the non-cyclic adduct in the two electron reduced state of complex 1 . Such metallacyclic intermediates in electrocatalytic CO2 reduction offer a new design feature that can be implemented consciously in future catalyst designs. 相似文献
58.
The sonochemical degradation of ethyl paraben (EP), a representative of the parabens family, was investigated. Experiments were conducted at constant ultrasound frequency of 20 kHz and liquid bulk temperature of 30 °C in the following range of experimental conditions: EP concentration 250–1250 μg/L, ultrasound (US) density 20–60 W/L, reaction time up to 120 min, initial pH 3–8 and sodium persulfate 0–100 mg/L, either in ultrapure water or secondary treated wastewater.A factorial design methodology was adopted to elucidate the statistically important effects and their interactions and a full empirical model comprising seventeen terms was originally developed. Omitting several terms of lower significance, a reduced model that can reliably simulate the process was finally proposed; this includes EP concentration, reaction time, power density and initial pH, as well as the interactions (EP concentration) × (US density), (EP concentration) × (pHo) and (EP concentration) × (time).Experiments at an increased EP concentration of 3.5 mg/L were also performed to identify degradation by-products. LC–TOF–MS analysis revealed that EP sonochemical degradation occurs through dealkylation of the ethyl chain to form methyl paraben, while successive hydroxylation of the aromatic ring yields 4-hydroxybenzoic, 2,4-dihydroxybenzoic and 3,4-dihydroxybenzoic acids. By-products are less toxic to bacterium V. fischeri than the parent compound. 相似文献
59.
A novel one-step sample preparation technique called ultrasound-assisted matrix solid-phase dispersive liquid extraction was developed. After sample matrices being dispersed, target analytes were extracted into acid solutions and fat and lipin were dissolved in n-hexane while the interfering components were retained by dispersing sorbent. The extraction process could be rapidly accomplished within 9 min with high sample throughput under the synergistic effects of vibration, ultrasound action and heating. The extraction efficiency of approach was demonstrated for the determination of intermediates in commercial hair dyes with ion chromatography. Linearity ranges of 0.2–100 mg L−1 and detection limits varying from 0.019 to 0.048 mg L−1 were achieved. The recoveries ranged from 85.7 to 107.0% with the relative standard deviations (RSDs) of 0.31–3.7%. These results showed that the method was simple, time-saving, reliable and suitable for the routine analysis of intermediates in large numbers of hair dyes. 相似文献
60.
Hans‐Friedrich Klein Annette Kuhn Prof. Dr. Norbert Kuhn Prof. Dr. Stefan Laufer Markus Ströbele 《无机化学与普通化学杂志》2012,638(11):1784-1786
Triphenylphosphine reacts with thionyl chloride to give [Ph3PCl]Cl, Ph3PO and Ph3PS the formation of the anions S(O)Cl and SCl being discussed; the crystal structure of [Ph3PCl]Cl · S(O)Cl2 is reported. 相似文献