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Maya Doicheva Bojana Jeliazkova 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1998,54(14):2385-2392
The EPR technique has been used to study the photolysis of the mixed-ligand complex CuII(Et2dtc)Br in a 1:1 solvent mixture of chloroalkane and alcohol, where the chloroalkane is CCl4, CHCl3 or CH2Cl2 and the alcohol is MeOH, EtOH, i-PrOH or i-BuOH, in comparison with CuII(Et2dtc)Cl photolysis in CHBr3:ROH. It was found that while CuII(Et2dtc)Br photolysis in chloroalkane:ROH yielded CuII(Et2dtc)Cl as an intermediate, the opposite conversion of CuII(Et2dtc)Cl to CuII(Et2dtc)Br proceeded via CuII(Et2dtc)Cl photolysis in CHBr3:ROH. The final photolytic products in both cases were tetraethylthiuramdisulphide and the corresponding copper(II) salt (CuCl2 or CuBr2, respectively). The results obtained by EPR allowed to get some insight into the behaviour of the primary photolytic products towards both components of the mixed solvent. 相似文献
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IntroductionThespinexchangebetweenparamagneticparticlesmakesitpossibletoobtainuniqueinformationonthekineticsandmechanismofint... 相似文献
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A new series of tetrathiafulvalene-based organogelators endowed with four hydrophobic chains incorporating amide groups was synthesised and characterised. The resulting transparent organogels were obtained with organic solvents such as cyclohexane, carbon tetrachloride and chlorobenzene. Additionally, the length of the alkyl chain influenced the gelation ability of organogels. Considering the results, we concluded that compounds were ‘super gelators’. Interestingly, the gelators reacted with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane to form charge-transfer (CT) complexes and binary organogels. 1HNMR and FT-IR revealed that cooperation of hydrogen bonding, π–π and CT interactions was the main driving force for formation of the native and CT gels. The scanning electron microscopy images of native xerogels revealed characteristic gelation morphologies of three-dimensional cross-linking networks, whereas the morphologies of CT complex xerogels showed amorphous rod-like aggregates. X-ray powder diffraction studies suggested that both gelator and CT complex maintained lamellar molecular packing mode in organogel phase. 相似文献
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The effects of pressure, solvent on the intramolecular spin exchange of biradicals having two nitroxide fragments linked by a long flexible chain were studied by means of highpressure EPR technique. It was found that the intramolecular exchange interaction between nitroxides of biradical took place through the direct contact between them. By analyzing the observed EPR spectra, we have estimated the ratio(Τin/Τout) value of the average lifetime of the radical fragments inside a cage(Τin) to that outside the cage(Τout). The Τin/Τout values decreased with decreasing temperature, increasing pressure. The results suggest that the nearly cyclic conformation in a cage is favorable in solution. Fur ther, the rotational correlation time of individual nitroxide was estimated from the anisotropic EPR signal,, the information on the segmental motion of the nitroxide group in biradical was obtained. 相似文献
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Zun-Yun Li Hai-Long Wang Tian-Jing He Fan-Chen Liu Dong-Ming Chen 《Journal of Molecular Structure》2006,778(1-3):69-76
The ground-state structure of the charge-transfer complex formed by pyridine (Py) as electron donor and chloranil (CA) as acceptor has been studied by full geometry optimization at the MP2 and DFT levels of theory. Binding energies were calculated and counterpoise corrections were used to correct the BSSE. Both MP2 and DFT indicate that the pyridine binds with chloranil to form an inclined T-shape structure, with the pyridine plane perpendicular to the chloranil. The CP and ZPE corrected binding energies were calculated to be 14.21 kJ/mol by PBEPBE/6-31G(d) and 23.21 kJ/mol by MP2/6-31G(d). The charge distribution of the ground state Py–CA complex was evaluated with the natural population analysis, showing a net charge transfer from Py to CA. Analysis of the frontier molecular orbitals reveals a σ–π interaction between CA and Py, and the binding is reinforced by the attraction of the O7 atom of CA with the H23 atom of Py. TD-DFT calculations have been performed to analyze the UV–visible spectrum of Py–CA complex, revealing both the charge transfer transitions and the weak symmetry-relieved chloranil π–π* transition in the UV–visible region. 相似文献
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EPR study of the relationship between ultra high molecular weight polyethylene structure and radicals formed during irradiation with high energy sources 下载免费PDF全文
Valentina Brunella Maria Cristina Paganini 《Magnetic resonance in chemistry : MRC》2015,53(3):194-199
Three different samples of ultra high molecular weight polyethylene have been irradiated with a high energy source (electron beam), and radicals have been generated. Different radical species have been assigned on the basis of their electron paramagnetic resonance spectra. Electron paramagnetic resonance data have been used also to evaluate the amount of each kind of radical that has been generated on different starting materials. The structure of the polymer (number of double bonds or crystallinity) is strictly connected to the response of the sample itself to the irradiation. A rationalization between these different parameters has been performed in order to evaluate the stability of polymer samples toward high energy irradiation processes. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Yulia N. Pushkar Dietmar Stehlik Maurice van Gastel Wolfgang Lubitz 《Journal of Molecular Structure》2004,700(1-3):233-241
Hydrogen bonding to the photoaccumulated secondary acceptor radical anion A1√− in photosystem (PS) I has been studied using pulsed Q-band ENDOR spectroscopy. With deuterated quinone in protonated PS I particles it is demonstrated that the observed radical anion has only one hydrogen-bond hyperfine coupling (hfc) tensor with tensor components above the 2 MHz range. Below 2 MHz the protein matrix protons dominate and a second weak H-bond could not be detected. The spectral resolution of pulsed Q-band ENDOR is critically required to separate the signals of the H-bond proton from those of the primary chlorophyll acceptor, A0√−, which cannot be avoided to be formed to some extent in the photoaccumulation procedure. The determined H-bond hfc tensor of A1√− is found to be close to axial symmetry with a small isotropic component, as expected from a predominantly dipolar electron–proton spin interaction in a hydrogen-bond. The principal tensor components are A=(+)7.7, MHz A=(−)4.9 MHz, Aiso=(−)0.7 MHz. The magnitude of the dipolar tensor corresponds to an unusually short H-bond which can be estimated from the point-dipole approximation (1.5±0.1 Å). Based on previous studies with A- and B-branch specific site-directed mutants of the A1 site of PS I and the chosen photoaccumulation protocol, the observed A1√− radical anion can be assigned to the QK–A site of the A-branch. The observed H-bond hfc tensor is compared to those determined for related quinone radical anions observed in frozen protic solution as well as in the QA site of type II bacterial reaction centers. 相似文献
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Bures F Schweizer WB May JC Boudon C Gisselbrecht JP Gross M Biaggio I Diederich F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(19):5378-5387
A series of donor-acceptor chromophores was prepared in which the spacer separating 4-dimethylanilino (DMA) donor and C(CN)(2) acceptor moieties is systematically varied. All of the new push-pull systems, except 4 b, are thermally stable molecules. In series a, the DMA rings are directly attached to the central spacer, whereas in series b additional acetylene moieties are inserted. X-ray crystal structures were obtained for seven of the new, intensely colored target compounds. In series a, the DMA rings are sterically forced out of the mean plane of the residual pi system, whereas the entire conjugated pi system in series b is nearly planar. Support for strong donor-acceptor interactions was obtained through evaluation of the quinoid character of the DMA ring and by NMR and IR spectroscopy. The UV/Vis spectra feature bathochromically shifted, intense charge-transfer bands, with the lowest energy transitions and the smallest optical gap being measured for the two-dimensionally extended chromophores 6 a and 6 b. The redox behavior of the push-pull molecules was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). In the series 1 b, 2 b, 4 b, 5 b, in which the spacer between donor and acceptor moieties is systematically enlarged, the electrochemical gap decreases steadily from 1.94 V (1 b) to 1.53 V (5 b). This decrease is shown to be a consequence of a reduction in the D-A conjugation with increasing spacer length. Degenerate four-wave mixing experiments reveal high third-order optical nonlinearities, pointing to potentially interesting applications of some of the new chromophores in optoelectronic devices. 相似文献
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蛋白质—四氯苯醌荷移反应的分光光度研究 总被引:5,自引:0,他引:5
本文用分光光度法研究了蛋白质—四氯苯醌荷移反应。通过对影响反应各因素的研究,确立了以四氯苯醌形成荷移络合物的方法测定蛋白质的最佳条件,测定了最大结合数及反应平衡常数。 相似文献
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Franciska Könczöl Nelli Farkas Tímea Dergez J. Belágyi D. Lőrinczy 《Journal of Thermal Analysis and Calorimetry》2005,80(1):201-206
Summary DSC and EPR experiments were performed on human erythrocyte membranes and DPPC vesicles in order to study the effect of the
anaesthetic drug tetracaine on structure and dynamics of the lipid region. Experiments using spin label technique showed that
tetracaine induced fluidity changes of the lipid region in the environment of the fatty acid probe molecules incorporated
into the membranes in the vicinity of the lipid-water interface. Similarly to EPR observations, DSC measurements reported
decrease of the main melting and the pretransition temperature in comparison to control DPPC vesicles, which is the sign of
destabilisation of the structure in the head group region of the lipids. Similar effect was observed in the case of erythrocytes
where the protein conformation was also controlled in the presence of drug. A separated membrane melting with well distinguished
membrane protein phase transition was found that was affected significantly by tetracaine. These results suggest that tetracaine
is able to modify not only the internal dynamics of erythrocyte membranes and produce destabilisation of the lipid structure,
but the protein system as well. These might lead to further damage of the biological functions. 相似文献
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用EPR方法测定了三氟甲基叔丁基氮氧自由基在16种溶剂中的顺磁参数αN和αFβ值.并对αN值与溶剂的极性参数ET、z进行了线性相关分析,讨论了这类低位阻含氟自旋探针对研究溶剂化和探针本身结构的作用. 相似文献
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Actinomycin D (AMD) is an anticancer antibiotic that can bind selectively to both double-stranded and single-stranded DNA, and this binding greatly enhances DNA photosensitization. Using electron paramagnetic resonance (EPR) in combination with spin trapping techniques, a systematic study was carried out on the reactive oxygen species generated in the photosensitization process of AMD. It was found that 1O2 and O2- are important reactive intermediates either insolution or in DNA complexes, and the generation of these species is in competition. This finding suggests that the photodynamic action of AMD proceeds via two pathways: energy transfer (type Ⅰ mechanism) and electron transfer (type Ⅱ mechanism). 1O2 is the main product formed via energy transfer reaction in solution while electron transfer between the excited states of AMD and DNA becomes the predominant pathway in DNA complexes. 相似文献
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FENG Wen-Lin ZHANG Shao-Wen WANG Yan WU Jun-Nan LI Zong-HeDepartment of Chemistry Beijing Normal University Beijing China 《中国化学》1995,13(5):391-395
The microcanonical rate constants for the hydrogen-transfer process of HCCF (reaction 7) and the fluoro-transfer process of FCCF (reaction 8) are carried out with tunneling correction and curvature correction. The results show that the tunneling effects and curvature effects on the rate constant of reaction 7 is quite different from that of reaction 8. The rate constants for different rotational states are also studied for these reactions. 相似文献
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左旋多巴与2,3-二氯-5,6-二氰-1,4-苯醌的荷移反应研究 总被引:1,自引:0,他引:1
研究了左旋多巴和2,3-二氯-5,6-二氰-1,4-苯醌(DDBQ)的反应条件,确定在硼砂溶液中,在60℃反应70 min可获得稳定的络合物,其λmax=346 nm,组成比为1∶1,表观摩尔吸收系数ε=1.1×104L.mol-1.cm-1,应用拟定的方法测定药物制剂测定结果与文献方法一致,回收率在97.25%~102.7%之间,相对标准偏差在0.7%以内。 相似文献
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The response of the cavity to the rotation of a concentrically positioned planar sample of variable width, w ∈ 〈1 mm, 10 mm〉, around the common cavity-sample x-axis in a Bruker single TE102 rectangular cavity (radial effect) has been analysed. The observed dependence of the EPR signal intensity, Ipp, on the rotation angle has a general ovaloid shape with an eccentricity, ?, which varies linearly with the width, w, of the sample, ? = 0.0246 + 0.0311 × w, correlation, R = 0.996, for samples with a width greater than 2 mm but shows a positive deviation from linearity for the 1 and 2 mm samples. The dependence of the Ipp value on the planar sample width, w, is non-linear for all polar-angle values investigated. These experimental observations are in a very good agreement with theoretical calculations in which the response is modelled using the Cassinian curves modified for planar sample geometry. Similar trends of the angular Ipp dependence were observed for any position of the planar sample as the centre was moved along the vertical x-axis of the cavity. In the longitudinal Ipp dependence for a planar sample whose length, L = 30 mm, is greater than that of the cavity, then (i) for the case where the whole cavity length is occupied by the sample a constant value for the Ipp (a plateau) is observed and (ii) for sample movement in and out of this plateau region the dependence varies according to the left and right halves of a modified “sine-squared” function. The variation in the signal amplitude along the cavity x-axis (longitudinal effect) can be calculated theoretically using a “sine-squared” curve, modified for an “over full-length cavity” planar sample. In general, the response of the cavity to a planar sample situated at any position on the common sample cavity x-axis can be represented as a product of a modified Cassinian curve and a modified “sine-squared” curve. The non-linear radial effect may give rise to serious sources of systematic error in quantitative EPR spectroscopy with planar sample geometry and shows that accurate and precise positioning of the sample in the microwave cavity is essential. 相似文献