共查询到20条相似文献,搜索用时 15 毫秒
1.
Dr. Dinar Abdullin Dr. Hideto Matsuoka Dr. Maxim Yulikov Nico Fleck Dr. Christoph Klein Dr. Sebastian Spicher Dr. Gregor Hagelueken Prof. Dr. Stefan Grimme Prof. Dr. Arne Lützen Prof. Dr. Olav Schiemann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(37):8820-8828
Pulsed EPR dipolar spectroscopy (PDS) offers several methods for measuring dipolar coupling and thus the distance between electron-spin centers. To date, PDS measurements to metal centers were limited to ions that adhere to the high-field approximation. Here, the PDS methodology is extended to cases where the high-field approximation breaks down on the example of the high-spin Fe3+/nitroxide spin-pair. First, the theory developed by Maryasov et al. (Appl. Magn. Reson. 2006 , 30, 683–702) was adapted to derive equations for the dipolar coupling constant, which revealed that the dipolar spectrum does not only depend on the length and orientation of the interspin distance vector with respect to the applied magnetic field but also on its orientation to the effective g-tensor of the Fe3+ ion. Then, it is shown on a model system and a heme protein that a PDS method called relaxation-induced dipolar modulation enhancement (RIDME) is well-suited to measuring such spectra and that the experimentally obtained dipolar spectra are in full agreement with the derived equations. Finally, a RIDME data analysis procedure was developed, which facilitates the determination of distance and angular distributions from the RIDME data. Thus, this study enables the application of PDS to for example, the highly relevant class of high-spin Fe3+ heme proteins. 相似文献
2.
Marianne Smits Yun Ling Prof. Dr. Silvia Lenaerts Prof. Dr. Sabine Van Doorslaer 《Chemphyschem》2012,13(18):4251-4257
Photocatalytic soot oxidation is studied on P25 TiO2 as an important model reaction for self‐cleaning processes by means of electron paramagnetic resonance (EPR) and Fourier transform infrared (FTIR) spectroscopy. Contacting of carbon black with P25 leads on the one hand to a reduction of the local dioxygen concentration in the powder. On the other hand, the weakly adsorbed radicals on the carbon particles are likely to act as alternative traps for the photogenerated conduction‐band electrons. We find furthermore that the presence of dioxygen and oxygen‐related radicals is vital for the photocatalytic soot degradation. The complete oxidation of soot to CO2 is evidenced by in situ FTIR spectroscopy, no intermediate CO is detected during the photocatalytic process. 相似文献
3.
Claire Mantel Hongyu Chen Robert H Crabtree Gary W Brudvig Jacques Pécaut Marie-No?lle Collomb Carole Duboc 《Chemphyschem》2005,6(3):541-546
The isolation, structural characterization, and electronic properties of two six-coordinated chloromanganese (III) complexes, [Mn(terpy)(Cl)3] (1) and [Mn(Phterpy)(Cl)3] (2), are reported (terpy = 2,2':6'2"-terpyridine, Phterpy = 4'-phenyl-2,2':6',2"-terpyridine). These complexes complement a series of mononuclear azide and fluoride Mn(lll) complexes synthesized with neutral N-tridentate ligands, [Mn(L)(X)3] (X = F- or N3 and L = terpy or bpea [N,N-bis(2-pyridylmethyl)-ethylamine)], previously described. Similar to these previous complexes, 1 and 2 exhibit a Jahn-Teller distortion of the octahedron, characteristic of a high-spin Mn(III) complex (S = 2). The analysis of the crystallographic data shows that, in both cases, the manganese ion lies in the center of a distorted octahedron characterized by an elongation along the tetragonal axis. Their electronic properties were investigated by multifrequency EPR (190-475 GHz) performed in the solid state at different temperatures (5-15 K). This study confirms our previous results and further shows that: i) the sign of D is correlated with the nature of the tetragonal distortion; ii) the magnitude of D is not sensitive to the nature of the anions in our series of rhombic complexes, contrary to the porphyrinic systems; iii) the [E/D] values (0.124 for 1 and 0.085 for 2) are smaller compared to those found for the [Mn(L)(X)3] complexes (in the range of 0.146 to 0.234); and iv) the E term increases when the ligand-field strength of the equatorial ligands decreases. 相似文献
4.
In situ ESR-UV/Vis spectroelectrochemistry is applied to obtain new insights into the intermediates and reaction products of the anodic oxidation of p-toluenediamine in aqueous solution at different pH values. A strong pH dependence of the stability of the cation radical is found. While the absence of a stable radical was proved by ESR spectroscopy at pH 2 and 10, this radical is detected at medium pH values and assigned to the semiquinonediimine structure. The UV/Vis absorption of the radical is observed at these pH values as well. The p-toluenediimine intermediate and the trimeric reaction product were followed during the electrode reaction by UV/Vis spectroscopy at all pH values. 相似文献
5.
Blanchard S Blain G Rivière E Nierlich M Blondin G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(17):4260-4268
A new dinuclear manganese(II) complex was synthesised with the biscompartimental ligand 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-nitrophenol (NO(2)BpmpH) and characterised by X-ray crystallography. Magnetic susceptibility measurements revealed that the two high-spin Mn(II) ions are antiferromagnetically coupled with a singlet-to-triplet separation of 7.2 cm(-1). The powder EPR spectra were recorded for both X- and Q-bands between 1.8 K and 35 K. A detailed analysis of these spectra led to the determination of three out of five individual spin-state zero-field splitting parameters. From the proposed simulations, the exchange coupling constant J and the intermetallic distance have been computed. 相似文献
6.
《Magnetic resonance in chemistry : MRC》2003,41(9):647-659
Free radicals generated from UV irradiation of simple aliphatic amides in anaerobic and nitric oxide (NO)‐saturated liquid mixtures or solutions gave EPR spectra of nitroxides. The application of isotopic effects to EPR spectra and the generation of radicals by transient radical attack on substrate molecules or by photolysing amine or acetoin were used to help identify photochemically produced radicals from the amides. The aliphatic amides used were formamide, acetamide and their N‐methyl‐ or deuterium‐substituted derivatives. Transient radicals used to attack the amides via hydrogen‐atom abstraction were generated from the initiator AIBN or AAPH. The observation of various nitroxides indicates the reactivity of NO for trapping acyl, carbamoyl and other carbon‐centered radicals. Possibly mechanistic pathways diagnosed with this trap are proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
7.
Hureau C Sabater L Anxolabéhère-Mallart E Nierlich M Charlot MF Gonnet F Rivière E Blondin G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(8):1998-2010
The dinuclear phenolato-bridged complex [(mL)Mn(II)Mn(II)(mL)](ClO(4))(2) (1(ClO(4))(2)) has been obtained with the new [N(4)O] pentadentate ligand mL(-) (mLH=N,N'-bis-(2-pyridylmethyl)-N-(2-hydroxybenzyl)-N'-methyl-ethane-1,2-diamine) and has been characterised by X-ray crystallography. X- and Q-band EPR spectra were recorded and their variation with temperature was examined. All spectra exhibit features extending over 0-800 mT at the X band and over 100-1450 mT at the Q band, features that are usually observed for dinuclear Mn(II) complexes. Cyclic voltammetry of 1 exhibits two irreversible oxidation waves at E(1)(p)=0.89 V and E(2)(p)=1.02 V, accompanied on the reverse scan by an ill-defined cathodic wave at E(1')(p)=0.56 V (all measured versus the saturated calomel electrode (SCE)). Upon chemical oxidation with tBuOOH (10 equiv) at 20 degrees C, 1 is transformed into the mono-mu-oxo species [(mL)Mn(III)-(mu-O)-Mn(III)(mL)](2+) (2), which eventually partially evolves into the di-mu-oxo species [(mL)Mn(III)-(mu-O)(2)-Mn(IV)(mL)](n+) (3) in which one of the aromatic rings of the ligand is decoordinated. The UV/Vis spectrum of 2 displays a large absorption band at 507 nm, which is attributed to a phenolate-->Mn(III) charge-transfer transition. The cyclovoltammogram of 2 exhibits two reversible oxidation waves, at 0.65 and 1.16 V versus the SCE, corresponding to the Mn(III)Mn(III)/Mn(III)Mn(IV) and Mn(III)Mn(IV)/Mn(IV)Mn(IV) oxidation processes, respectively. The one-electron electrochemical oxidation of 2 leads to the mono-mu-oxo mixed-valent species [(mL)Mn(III)-(mu-O)-Mn(IV)(mL)](3+) (2 ox). The UV/Vis spectrum of 2 ox exhibits one large band at 643 nm, which is attributed to the phenolate-->Mn(IV) charge-transfer transition. 2 ox can also be obtained by the direct electrochemical oxidation of 1 in the presence of an external base. The 2 ox and 3 species exhibit a 16-line EPR signal with first peak to last trough widths of 125 and 111 mT, respectively. Both spectra have been simulated by using colinear rhombic Mn-hyperfine tensors. Mechanisms for the chemical formation of 2 and the electrochemical oxidation of 1 into 2 ox are proposed. 相似文献
8.
9.
N,N-二甲基苯胺-对氨基二甲替苯胺氧化偶联反应催化分光光度法测定铬(Ⅵ) 总被引:11,自引:0,他引:11
在pH=3.2乙酸-乙酸钠缓冲介质中,研究了铬(Ⅵ)催化过氧化氢氧化对-氨基二甲替苯胺盐酸盐和N,N-二甲基苯胺的氧化偶联反应及其机理,建立了催化光度法测定痕量铬(Ⅵ)的新方法.该方法线性范围为0~0.12 mg/L;检出限为1.0×10-7 g/L;相对标准偏差为0.12%,直接用于水中铬(Ⅵ)的测定,结果满意. 相似文献
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11.
Summary In order to get better insight into the structural reasons for different properties of copper(II) complexes withL-threonine,L-allo-threonine,L-N,N-dimethyl-threonine, andL-N,N-dimethyl-allo-threonine, their EPR spectra were studied as a function ofpH and temperature. AtpD9.4, in all complexes a change in the copper(II) coordination sphere from the glycine to the hydroxy type was observed. Inbis(L-threoninato)copper(II), the hydroxy type formed atpD9.4 was found to be stablized by increasing the temperature of the solution from 280 to 320 K. In all other copper(II) complexes, the conformational change is accompanied by the disruption of the Cu-N bond of one chelate ring.
Vergleichende EPR-Untersuchungen von Kupfer(II)-Threonin-Komplexen
Zuzammenfassung Um einen besseren Einblick in die Beziehungen zwischen Struktur und Eigenschaften von Kupfer(II)-Komplexen mitL-Threonin,L-allo-Threonin,L-N,N-Dimethyl-Threonin undL-N,N-Dimethyl-allo-Threonin zu gewinnen, wurden ihre EPR-Spektren in Abhängigkeit vompH-Wert und von der Temperatur untersucht. Bei einempH-Wert von 9.4 (in deuterierter Lösung) wurde eine Veränderung in der Kupfer (II)-Koordinationssphäre festgestellt, die von einer Glycin-ähnlichen Konformation in eine vermutlich Hydroxy-ähnliche Konformation übergeht. Derbis(L-Threoninato)-Kupfer (II)-Hydroxy-Komplex wird durch eine Temperaturerhöhung von 280 auf 320K stabilisiert. Die Veränderung der Koordination vom Glycin-Typ wird von einem Bruch der Cu-N-Bindung eines Chelatrings begleitet.相似文献
12.
Dr. Wenyan Hao Yuchen Sha Dr. Yi Deng Yi Luo Li Zeng Shan Tang Dr. Yue Weng Prof. Dr. Chien-Wei Chiang Prof. Dr. Aiwen Lei 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(19):4931-4934
An in situ generated oxidation species of nickel quinolinylpropioamide intermediate was produced. Characterization by X-ray absorption near edge structure (XANES) and EPR provides complementary insights into this oxidized nickel species. With aliphatic amides and isocyanides as substrates, a nickel-catalyzed facile synthesis of structurally diverse five-membered lactams could be achieved. 相似文献
13.
Henk Hagen Santiago Reinoso Ed J. Reijerse Ernst E. van Faassen Martin Lutz Anthony L. Spek Gerard van Koten 《无机化学与普通化学杂志》2004,630(12):2097-2105
In order to study the effect of steric bulk on the vanadium coordination geometry in O, N‐chelated vanadium oxo (bis)phenolates, six different ortho‐aminophenolate ligands have been used. The ortho‐aminophenolate system was changed at three different places, i.e. 1) the second ortho position (C6) of the arene ring (R), 2) the substituents at the amino nitrogen (R′ and R″), and 3) the benzylic carbon atom (R*). The phenols were used in the preparation of the vanadium oxo (bis)phenolate complexes. In order to study whether it is possible to predict geometrical features of these vanadium complexes, UV/Vis, solution and frozen state EPR and 14N ESEEM spectroscopic data was measured and compared to the structural features of four structurally characterized vanadium oxo (bis)phenolates. Unfortunately, it turned out that is was not possible to correlate the EPR parameters, the UV/Vis HOMO‐LUMO transitions or 14N hyperfine couplings to the structural parameters. 相似文献
14.
Axel Klein Katharina Butsch Sait ElmasChristian Biewer Dominikus Heift Sara NitscheIrene Schlipf Helmut Bertagnolli 《Polyhedron》2012,31(1):649-656
The oxido-pincer ligand pydotH2 (2,6-bis(1-hydroxy-1-o-tolyl-ethyl-η2O,O′)pyridine) forms two different CuII containing complexes when prepared from anhydrous CuCl2. A combination of EPR spectroscopy and EXAFS allowed to structurally characterise the light-green dimer of the formula [(pydotH2)CuCl(μ-Cl)2ClCu(pydotH2)] and the penta-coordinate olive-green monomer [(pydotH2)CuCl2]. The molecular entities imply that the ligand remains protonated upon coordination. When dissolved in DMF both compounds form monomeric species [(pydotH2)CuCl2(DMF)] which could be characterised in detail by EPR, UV-Vis/NIR spectroscopy and electrochemical measurements. The assignments were supported by comparison with CuII complexes of the related ligands 2,6-bis(hydroxymethyl)pyridine (pydimH2) and 2,6-bis(1-hydroxy-1-methyl)pyridine (pydipH2). 相似文献
15.
Functionalized poly‐N,N‐dimethylaniline film was prepared by adsorption of ferrocyanide onto the polymer forming at the surface of carbon paste electrode (CPE) in aqueous solution by using potentiostatic method. The electrocatalytic ability of poly‐N,N‐dimethylaniline/ferrocyanide film modified carbon paste electrode (PDMA/FMCPE) was demonstrated by oxidation of cysteamine. Cyclic voltammetry and chronoamperometry techniques were used to investigate this ability. Results showed that pH 7.00 is the most suitable for this purpose. It is found that the catalytic reaction rate constant, (kh), is equal to 2.142×103 M?1 s?1 by the data of chronoamperometry. The catalytic reduction peak current was linearly dependent on the cysteamine concentration and the linearity range obtained was 8.00×10?5 M–1.14×10?2 M. Detection limit was determined 7.97×10?5 M (2σ). This method has been successfully employed for quantification of cysteamine in real sample. 相似文献
16.
Natalia Domracheva Anisoara Mirea Markus Schwoerer Laura Torre-Lorente Günter Lattermann 《Chemphyschem》2006,7(12):2567-2577
Copper(II) complexes formed by coordination of the Cu(II) ion with liquid-crystalline poly(propylene imine) dendrimer ligand (L) of the first (complex 1) and second (complex 2) generations with various Cu(II) contents (x = Cu/L) have been studied by electron paramagnetic resonance (EPR) spectroscopy. The existence of a redox-active blue complex 1 (x = 1.9) and the copper(II) nitrate electron transfer associated with the valence tautomerism are revealed for the first time in copper-based dendrimers. It has been shown that the electronic structure of the blue complex 1 (x = 1.9) is adequately described as a mixed-valence dimer containing d9- and diamagnetic d10-configurated copper ions, and an antiferromagnetically coupled NO3* radical arising on the nitrate-bridged counter ligand. The activation energy value found for the electron transfer is about 0.35 meV, which indicates a low-energy charge dynamic. The ability of the blue and green complexes 1 (x = 1.9) dissolved in isotropic solvents to orient themselves in the magnetic field was revealed by EPR spectroscopy. The degree of orientation of the molecular z axis (S(z)) of these complexes in the magnetic field differs, depending on the type of copper(II)-complexing site in the dendrimer ligand, and can reach 0.76, which is close to S(z) = 1 (completely aligned system). A combination of magnetic and orientational parameters indicates an NO4 environment of the Cu(II) ion in green complex 1 (x = 1.9), and confirms the chain structure with intermolecular Cu(II)-NO3-Cu(II) bridges between Cu(II) centres in columns. 相似文献
17.
Dr. Annalisa Pierro Dr. Alessio Bonucci Dr. Davide Normanno Dr. Mireille Ansaldi Dr. Eric Pilet Prof. Olivier Ouari Prof. Bruno Guigliarelli Dr. Emilien Etienne Dr. Guillaume Gerbaud Dr. Axel Magalon Prof. Valérie Belle Dr. Elisabetta Mileo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(66):e202202249
One of the greatest current challenges in structural biology is to study protein dynamics over a wide range of timescales in complex environments, such as the cell. Among magnetic resonances suitable for this approach, electron paramagnetic resonance spectroscopy coupled to site-directed spin labeling (SDSL-EPR) has emerged as a promising tool to study protein local dynamics and conformational ensembles. In this work, we exploit the sensitivity of nitroxide labels to report protein local dynamics at room temperature. We demonstrate that such studies can be performed while preserving both the integrity of the cells and the activity of the protein under investigation. Using this approach, we studied the structural dynamics of the chaperone NarJ in its natural host, Escherichia coli. We established that spin-labeled NarJ is active inside the cell. We showed that the cellular medium affects NarJ structural dynamics in a site-specific way, while the structural flexibility of the protein is maintained. Finally, we present and discuss data on the time-resolved dynamics of NarJ in cellular context. 相似文献
18.
Dr. Janine Wegner Dr. Gabriele Valora Dr. Karin Halbmair Annemarie Kehl Brigitte Worbs Prof. Dr. Marina Bennati Prof. Dr. Ulf Diederichsen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(9):2203-2207
β-Peptides are an interesting new class of transmembrane model peptides based on their conformationally stable and well-defined secondary structures. Herein, we present the synthesis of the paramagnetic β-amino acid β3-hTOPP (4-(3,3,5,5-tetramethyl-2,6-dioxo-4-oxylpiperazin-1-yl)-d -β3-homophenylglycine) that enables investigations of β-peptides by EPR spectroscopy. This amino acid adds to the, to date, sparse number of β-peptide spin labels. Its performance was evaluated by investigating the helical turn of a 314-helical transmembrane model β-peptide. Nanometer distances between two incorporated β3-hTOPP labels in different environments were measured by using pulsed electron/electron double resonance (PELDOR/DEER) spectroscopy. Due to the semi-rigid conformational design, the label delivers reliable distances and sharp (one-peak) distance distributions even in the lipid bilayer. The results indicate that the investigated β-peptide folds into a 3.2514 helix and maintains this conformation in the lipid bilayer. 相似文献
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20.
Lidie Rousseau Dr. Christian Herrero Dr. Martin Clémancey Arnaud Imberdis Dr. Geneviève Blondin Dr. Guillaume Lefèvre 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(11):2417-2428
Ate-iron(II) species such as [Ar3FeII]− (Ar=aryl) are key intermediates in Fe-catalyzed couplings between aryl nucleophiles and organic electrophiles. They can be active species in the catalytic cycle, or lead to Fe0 and FeI oxidation states, which can themselves be catalytically active or lead to unwished organic byproducts. Analysis of the reactivity of the intermediates obtained by step-by-step displacement of the mesityl groups in high-spin [Mes3FeII]− by less hindered phenyl ligands was performed, and uncovered the crucial role of both steric and electronic parameters in the formation of the Fe0 and FeI oxidation states. The formation of quaternized [Ar4FeIIMgBr(THF)]− intermediates allows the bielectronic reductive elimination energy required for the formation of Fe0 to be reduced. Similarly, the small steric pressure of the aryl groups in [Ar3FeII]− enables the formation of aryl-bridged [{FeII(Ar)2}2(μ-Ar)2]2− species, which afford the FeI oxidation state by bimetallic reductive elimination. These results are supported by 1H NMR, EPR, and 57Fe Mössbauer spectroscopies, as well as by DFT calculations. 相似文献