共查询到20条相似文献,搜索用时 15 毫秒
1.
Sebastian Barata-Vallejo Konrad Skotnicki Carla Ferreri Bronislaw Marciniak Krzysztof Bobrowski Chryssostomos Chatgilialoglu 《Molecules (Basel, Switzerland)》2021,26(18)
The conversion of ribonucleosides to 2′-deoxyribonucleosides is catalyzed by ribonucleoside reductase enzymes in nature. One of the key steps in this complex radical mechanism is the reduction of the 3′-ketodeoxynucleotide by a pair of cysteine residues, providing the electrons via a disulfide radical anion (RSSR•−) in the active site of the enzyme. In the present study, the bioinspired conversion of ketones to corresponding alcohols was achieved by the intermediacy of disulfide radical anion of cysteine (CysSSCys)•− in water. High concentration of cysteine and pH 10.6 are necessary for high-yielding reactions. The photoinitiated radical chain reaction includes the one-electron reduction of carbonyl moiety by disulfide radical anion, protonation of the resulting ketyl radical anion by water, and H-atom abstraction from CysSH. The (CysSSCys)•− transient species generated by ionizing radiation in aqueous solutions allowed the measurement of kinetic data with ketones by pulse radiolysis. By measuring the rate of the decay of (CysSSCys)•− at λmax = 420 nm at various concentrations of ketones, we found the rate constants of three cyclic ketones to be in the range of 104–105 M−1s−1 at ~22 °C. 相似文献
2.
The highly selective nitrogen donor ligands CyMe4BTBP and CyMe4BTPhen where γ–irradiated under identical experimental conditions in 1–octanol with and without contact to nitric acid solution. Subsequently, solvent extraction experiments were carried out to evaluate the stability of the extractants against γ–radiation monitoring Am(III) and Eu(III) distribution ratios. Generally, decreasing distribution ratios with increasing absorbed dose were detected for both molecules. Furthermore, qualitative mass spectrometric analyses were performed and ligand concentrations were determined by HPLC-DAD after irradiation to investigate the radiolysis mechanism. An exponential decrease with increasing absorbed dose was observed for both ligands with a faster rate for CyMe4BTPhen. Main radiolysis products indicated the addition of one or more diluent molecules (1–octanol) to the ligand via prior production of α-hydroxyoctyl radicals from diluent radiolysis. The addition of nitric acid during the irradiation lead to a remarkable stabilization of the system, as the extraction of Am(III) and Eu(III) did not change significantly over the whole examined dose range. Quantification of the remaining ligand concentration on the other hand showed decreasing concentrations with increasing absorbed dose. The stabilization of D values is therefore explained by the formation of 1–octanol addition products which are also able to extract the studied metal ions. 相似文献
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K. Indira Priyadarsini B. Mishra D. K. Maity Hari Mohan 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):985-988
Abstract Reactions of oxidizing radicals like hydroxyl (·OH) radical, specific electron transfer agents like N 3 ·, and I 2 ?. radicals were studied with selenourea (SeU) and compared with thiourea (ThU) using pulse radiolysis technique in microsecond time scales. Both the compounds efficiently react with ·OH radicals, however, SeU undergoes easier oxidation by secondary oxidants as compared to ThU. The results were supported by cyclic voltammetry studies. The radical cations of both SeU and ThU formed on oxidation undergo dimerization with the parent molecule to form two-centered three-electron-hemi bonded radical cations absorbing at 410 and 400 nm respectively with the stabilization energies of 21.1 and 20.5 kcal/mol for SeU and ThU, respectively. Preliminary studies indicated that at low concentration of SeU, the dimerization is prevented and the oxidation reaction produced metallic Se nanoparticles. 相似文献
5.
Richard D. Bowen Dudley H. Williams Helmut Schwarz 《Angewandte Chemie (International ed. in English)》1979,18(6):451-461
Organic ions decompose in the field-free regions of a mass spectrometer after a relatively well-defined lifetime (t ≈ 10?5s). This lifetime is very long compared with the time-scale of molecular bond vibrations and consequently the excess internal energy (“non fixed” energy) present in the transition state for dissociation is comparable with that found in solution experiments. In general, only the energetically most favorable decay routes are able to compete. Moreover, information concerning kinetic energy release (T) accompanying unimolecular decomposition may be obtained from a consideration of the metastable peak for the process; these extremely valuable data are inaccessible to solution experiments because of the effects of collisions. The chemistry of ions may therefore be investigated conveniently by generating the ions of interest in a mass spectrometer and analyzing the reactions which occur in metastable transitions. 相似文献
6.
脑神经退行性疾病中的有机化学-朊病毒(疯牛病)中的蛋白物理有机化学和自由基化学 总被引:5,自引:0,他引:5
杨池明 《高等学校化学学报》2002,23(2):243-250
通过关于“普里昂”蛋白病毒疾病的已有临床、医学生理、免疫和化学等方面的现象,讨论了朊病毒当中的部分蛋白氧化损伤和蛋白自由基化学本质。 相似文献
7.
Marco Werr Dr. Elisabeth Kaifer Prof. Hubert Wadepohl Prof. Hans-Jörg Himmel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(56):12981-12990
Molecular organic radicals have been intensively studied in the last decades, due to their interesting optical, magnetic and redox properties. Here we report the synthesis and characterisation of persistent organic radicals from one-electron oxidation of redox-active azines (RAAs), composed of two guanidinyl or related groups. By connecting two different groups together, asymmetric compounds result. In this way a series of compounds with varying redox potential is obtained that could be oxidised reversibly to the mono- and the dicationic charge states. The accessible redox states were fully determined by chemical redox reactions. The standard Gibbs free energy change for disproportionation of the radical monocation into the dication and the neutral molecule in solution, estimated from cyclovoltammetric measurements, varies between 43 and 71 kJ mol−1. While the neutral RAAs absorb predominately UV light, the radical monocations display strong absorptions covering almost the entire visible region and extending for some compounds into the NIR region. A detailed analysis of this highly reversible electrochromism is presented, and the fast switching characteristics are demonstrated in an electrochromic test device. 相似文献
8.
Xuanyu Zhang Rui You Zeyue Wei Xiao Jiang Jiuzhong Yang Yang Pan Peiwen Wu Qingdong Jia Zhenghong Bao Lei Bai Mingzhou Jin Bobby Sumpter Victor Fung Weixin Huang Zili Wu 《Angewandte Chemie (International ed. in English)》2020,59(21):8042-8046
Although hexagonal boron nitride (h‐BN) has recently been identified as a highly efficient catalyst for the oxidative dehydrogenation of propane (ODHP) reaction, the reaction mechanisms, especially regarding radical chemistry of this system, remain elusive. Now, the first direct experimental evidence of gas‐phase methyl radicals (CH3.) in the ODHP reaction over boron‐based catalysts is achieved by using online synchrotron vacuum ultraviolet photoionization mass spectroscopy (SVUV‐PIMS), which uncovers the existence of gas‐phase radical pathways. Combined with density functional theory (DFT) calculations, the results demonstrate that propene is mainly generated on the catalyst surface from the C?H activation of propane, while C2 and C1 products can be formed via both surface‐mediated and gas‐phase pathways. These observations provide new insights towards understanding the ODHP reaction mechanisms over boron‐based catalysts. 相似文献
9.
The pulse radiolysis technique has been employed to investigate the reaction of DNA-minor-groove ligand bisbenzimidazole Hoechst
33258 with pyrimidine and purine nucleotide-derived radicals. Formation of an N-centred Hoechst-33258 radical is observed.
Bimolecular rate constants and the yields of Hoechst-33258 radical have been evaluated. While the rate constant for the reaction
of pyrimidine-derived radicals with Hoechst-33258 remained the same (1–2) × 109 dm3 mol−1 s−1, the yields of the Hoechst-33258 radical varied from 25% (5′-cytidine monophosphate) to 75% (5′-guanosine monophosphate)
under anoxic conditions. The rate constant values for the reaction of purine-derived radicals with Hoechst-33258, under oxic
and anoxic conditions, remained the same whereas with pyrimidine-derived radicals, the rate constant value under oxic conditions
was about two orders of magnitude lower than under anoxic conditions. The difference in the yields of Hoechst-33258 radical
with various nucleotide-derived radicals suggest the formation of different types of radicals and that the reaction mainly
occurs by electron transfer from Hoechst-33258 to the nucleotide radicals. 相似文献
10.
A new method for determination of fatty acid amides in polyethylene packaging film was developed using gas chromatography/mass spectrometry (GC/MS). Liquid extraction, Soxhlet extraction ultrasonic-assisted extraction and pressurized solvent extraction (PSE) methods were compared and the results showed that pressurized solvent extraction was the best for extracting these compounds. After extraction, solvent was blown by nitrogen and a trifluoroethyl derivation step was carried out. The derivative compounds were identified and quantified by GC/MS using an HP-Innowax column. The retention times were 6.20 min for derivative hexadecanoamide, 8.56 min for derivative octadecanamide, 8.84 min for derivative oleamide and 13.68 min for derivative erucamide, respectively. The detection limits were 61.0 ng g−1, 74.0 ng g−1, 103.0 ng g−1, and 105.0 ng g−1, respectively, and the linearity were good. The proposed method was applied satisfactorily to determine these chemicals in different types of polyethylene samples. 相似文献
11.
Comprehensive Study of the Organic‐Solvent‐Free CDI‐Mediated Acylation of Various Nucleophiles by Mechanochemistry 下载免费PDF全文
Dr. Thomas‐Xavier Métro Dr. Julien Bonnamour Thomas Reidon Anthony Duprez Jordi Sarpoulet Prof. Dr. Jean Martinez Dr. Frédéric Lamaty 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(36):12787-12796
Acylation reactions are ubiquitous in the synthesis of natural products and biologically active compounds. Unfortunately, these reactions often require the use of large quantities of volatile and/or toxic solvents, either for the reaction, purification or isolation of the products. Herein we describe and discuss the possibility of completely eliminating the use of organic solvents for the synthesis, purification and isolation of products resulting from the acylation of amines and other nucleophiles. Thus, utilisation of N,N′‐carbonyldiimidazole (CDI) allows efficient coupling between carboxylic acids and various nucleophiles under solvent‐free mechanical agitation, and water‐assisted grinding enables both the purification and isolation of pure products. Critical parameters such as the physical state and water solubility of the products, milling material, type of agitation (vibratory or planetary) as well as contamination from wear are analysed and discussed. In addition, original organic‐solvent‐free conditions are proposed to overcome the limitations of this approach. The calculations of various green metrics are included, highlighting the particularly low environmental impact of this strategy. 相似文献
12.
Julia E. Fleckenstein Konrad Koszinowski Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(46):12745-12753
Solutions of butylzinc iodide in tetrahydrofuran, acetonitrile, and N,N‐dimethylformamide were analyzed by electrospray ionization mass spectrometry. In all cases, microsolvated butylzinc cations [ZnBu(solvent)n]+, n=1–3, were detected. The parallel observation of the butylzincate anion [ZnBuI2]? suggests that these ions result from disproportionation of neutral butylzinc iodide in solution. In the presence of simple bidentate ligands (1,2‐dimethoxyethane, N,N‐dimethyl‐2‐methoxyethylamine, and N,N,N′,N′‐tetramethylethylenediamine), chelate complexes of the type [ZnBu(ligand)]+ form quite readily. The relative stabilities of these complexes were probed by competition experiments and analysis of their unimolecular gas‐phase reactivity. Fragmentation of mass‐selected [ZnBu(ligand)]+ leads to the elimination of butene and formation of [ZnH(ligand)]+. In marked contrast, the microsolvated cations [ZnBu(solvent)n]+ lose the attached solvent molecules upon gas‐phase fragmentation to produce bare [ZnBu]+, which subsequently dissociates into [C4H9]+ and Zn. This difference in reactivity resembles the situation in organozinc solution chemistry, in which chelating ligands are needed to activate dialkylzinc compounds for the nucleophilic addition to aldehydes. 相似文献
13.
Radical Hydrodeiodination of Aryl,Alkenyl, Alkynyl,and Alkyl Iodides with an Alcoholate as Organic Chain Reductant through Electron Catalysis 下载免费PDF全文
Abhishek Dewanji Dr. Christian Mück‐Lichtenfeld Prof. Dr. Armido Studer 《Angewandte Chemie (International ed. in English)》2016,55(23):6749-6752
A simple and efficient method for radical hydrodeiodination is reported. The novel approach uses electron catalysis. In situ generated Na‐alcoholates are introduced as radical chain reducing reagents and reactions work with O2 as cheap initiator. Hydrodeiodination works on aryl, alkenyl, alkynyl iodides and a tert‐alkyl iodide also gets reduced applying the method. Albeit less general, the method is also applicable to the reduction of aryl bromides. The novel reagent is successfully used to conduct typical reductive radical cyclization reactions and mechanistic studies are reported. 相似文献
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Dr. Goedele Roos Prof. Frank De Proft Prof. Paul Geerlings 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(16):5050-5060
The effect of non‐polar and polar ligands and of monovalent cations on the one‐electron reduction potential of the thiyl radical and the disulfide bond was evaluated. The reduction potentials E° for the CH3S.–n L/CH3S?–n L and CH3SSCH3–L/CH3SSCH3.?–L redox couples were calculated at the B3LYP, M06‐2X and MP2 levels of theory, with n=1, 2 and L=CH4, C2H4, H2O, CH3OH, NH3, CH3COOH, CH3CONH2, NH4+, Na+, K+ and Li+. Non‐polar ligands decrease the E° value of the thiyl radical and disulfide bond, while neutral polar ligands favour electron uptake. Charged polar ligands and cations favour electron capture by the thiyl radical while disfavouring electron uptake by the disulfide bond. Thus, the same type of ligand can have a different effect on E° depending on the redox couple. Therefore, properties of an isolated ligand cannot uniquely determine E°. The ligand effects on E° are discussed in terms of the vertical electron affinity and reorganization energy, as well as molecular orbital theory. For a given redox couple, the ligand type influences the nature of the anion formed upon electron capture and the corresponding reorganization process towards the reduced geometry. 相似文献
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Unexpected Chemistry from the Reaction of Naphthyl and Acetylene at Combustion‐Like Temperatures 下载免费PDF全文
Dr. Dorian S. N. Parker Prof. Dr. Ralf. I. Kaiser Dr. Biswajit Bandyopadhyay Dr. Oleg Kostko Dr. Tyler P. Troy Dr. Musahid Ahmed 《Angewandte Chemie (International ed. in English)》2015,54(18):5421-5424
The hydrogen abstraction/acetylene addition (HACA) mechanism has long been viewed as a key route to aromatic ring growth of polycyclic aromatic hydrocarbons (PAHs) in combustion systems. However, doubt has been drawn on the ubiquity of the mechanism by recent electronic structure calculations which predict that the HACA mechanism starting from the naphthyl radical preferentially forms acenaphthylene, thereby blocking cyclization to a third six‐membered ring. Here, by probing the products formed in the reaction of 1‐ and 2‐naphthyl radicals in excess acetylene under combustion‐like conditions with the help of photoionization mass spectrometry, we provide experimental evidence that this reaction produces 1‐ and 2‐ethynylnaphthalenes (C12H8), acenaphthylene (C12H8) and diethynylnaphthalenes (C14H8). Importantly, neither phenanthrene nor anthracene (C14H10) was found, which indicates that the HACA mechanism does not lead to cyclization of the third aromatic ring as expected but rather undergoes ethynyl substitution reactions instead. 相似文献
19.
John P. Maier 《Angewandte Chemie (International ed. in English)》1981,20(8):638-646
The radiative decay of over a hundred open-shell organic radical cations has now been established. As a result, the spectral structure of such cations in their ground and excited electronic states can be probed with resolutions of the order of ? 1 cm?1. This is achieved by means of emission and laser-induced fluorescence techniques. The analysis of the emission and excitation spectra provides the vibrational frequencies of many of the totally symmetric fundamentals of the cations in the two electronic states. In order to study the relaxation behavior of these cations under “isolated conditions”, the lifetimes and fluorescence quantum fields can be obtained by means of photoelectron-photon coincidence measurements. These data yield the radiative and non-radiative rate constants as a function of the internal energy of the cations. The structural and decay information obtained from each of these techniques is illustrated using the 1,3-pentadiyne radical cation as example. 相似文献