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1.
Radical anions of nitrobenzothiazoles: EPR study of conjugative properties of benzothiazolyl systems
Francesco Ciminale 《Tetrahedron letters》2004,45(30):5849-5852
The electrochemical reduction in DMSO of the five isomers of nitrobenzothiazole (NBTZ) gave quite persistent radical anions that could be easily characterised by EPR spectroscopy. By contrast, the chemical reduction in alkaline solution, that is by t-BuOK in DMSO or by glucose and MeOK in MeOH, presented some problems with 6- and 4-NBTZ, and in the case of 2-NBTZ did not provide any detectable paramagnetic species. The internal consistency of coupling constants of the nitrobenzothiazole radical anions is in good agreement with the conjugative properties of the various benzothiazolyl systems and allows rectifying a recent EPR characterisation of 6-NBTZ radical anion. 相似文献
2.
Elena V. Frolova M. Ivanovskaya V. Sadykov G. Alikina A. Lukashevich S. Neophytides 《Progress in Solid State Chemistry》2005,33(2-4):317-325
Structural peculiarities of Ce–Zr–La–O and Ce–Zr–La–O/Ru samples in mean of catalytic properties are compared. The samples (Ce:Zr = 1:1, La = 10÷30 mol.%, Ru = 1.5 wt.%) were obtained by sol–gel method (X-samples) and co-precipitation (P-samples). It is shown that Ce0.45Zr0.45La0.1O2−δ/Ru X-samples are characterized by high thermal stability and the highest catalytic activity in partial methane oxidation reaction. According to XRD, BET, FTIR, EPR and XPS data it is concluded that the difference in the samples catalytic activity is caused by various disposition of Ru-containing phase on the support surface. The distinction in the dimension of Ru-containing particles (3D or 2D) is conditioned by structural peculiarities of Ce0.45Zr0.45La0.1O2−δ and Ce0.35Zr0.35La0.3O2−δ P- and X-samples. 相似文献
3.
Temperature dependence of the EPR spectrum of 2-trifluoromethylnitrobenzene radical anion in anhydrous acetonitrile in the
temperature range 217 K ≤ T ≤ 296 K was studied and simulated. Temperature-dependent dynamic modulation of the fluorine isotropic hyperfine structure
is caused by slow hindered rotation of CF3 group with an activation energy of E
F* = 36.5±0.5 kJ mol−1, which is the highest value for motions in π-type free radicals studied to date.
Dedicated to the memory of Academician V. A. Koptyug on the occasion of the 75th anniversary of his birth.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 926–931, June, 2006. 相似文献
4.
Sihem Khaddar-Zine Abdelhamid Ghorbel Claude Naccache 《Journal of molecular catalysis. A, Chemical》1999,150(1-2):223-231
The oxidation state, the mobility and the molecular structure of chromium species present on CrOx–Al2O3 catalysts have been studied by combined diffuse reflectance spectroscopy, EPR and reduction–extraction by ethane 1,2 diol. CrO42− species exist on the alumina surface in the form of loosely-interacting species on hydrated surface (species A) and in the form of strongly bonded species on dehydrated Al2O3 surface (species B). The CrO42− species show high mobility and are probably responsible for the formation of CrOx clusters. 相似文献
5.
The adsorption of polybutadiene (PBR) on alumina and silica gel was studied at different temperatures from cyclohexane and toluene solutions. It shows that the adsorption process was dependent on temperature and solvent. The adsorption isotherm and the thermodynamic quantities of adsorption were determined and it was observed that the adsorption process from both solvents was similar and the amount of adsorption increased as temperature decreased. The silica gel-cyclohexane system was more exothermic than all other systems and was also relatively more ordered. 相似文献
6.
Alumina and silica were modified with alkylphosphonic acids and diethyl butylphosphonate. The boundaries of hydrolytic stability of the obtained surface-modified materials were determined. 相似文献
7.
The effect of modification of porous silica and alumina with a copolymer of styrene and vinylsilane on the porosity of oxides have been investigated by means of low temperature nitrogen sorption. Only small changes of the specific surface area and of the specific pore volume were observed on modification of oxides with non-cross-linked copolymer. The specific surface area significantly increased after the cross-linking of the deposited polymeric layer while the specific pore volume remains almost unaffected. A broad hysteresis loop appears in the nitrogen sorption isotherm for the alumina modified with the cross-linked polymer. The porosity of oxides modified by chemisorption method differed strongly from that observed for composites modified by physisorption of polymer. 相似文献
8.
Youqing Shen Shiping Zhu Faquan Zeng Robert Pelton 《Journal of polymer science. Part A, Polymer chemistry》2001,39(7):1051-1059
Silica‐gel particles grafted with tetraethyldiethylenetriamine were synthesized as support for CuBr for the heterogeneous atom transfer radical polymerization of methyl methacrylate (MMA). The immobilized CuBr mediated a living polymerization of MMA, demonstrated by an increase in molecular weight with conversion and low polydispersity. An excessive amount of catalyst (typically, CuBr/initiator = 1.5) was required to achieve a living process because of the limited mobility of the supported catalyst. The silica‐gel concentration had a strong effect on the polymerization. The recycled catalyst still mediated a living process but showed a reduced catalytic activity due to the presence of Cu(II). After being regenerated by a reaction with Cu(0), the catalyst regained its activity. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1051–1059, 2001 相似文献
9.
Polypropylene was cracked thermally and catalytically in the presence of kaoline and silica alumina in a semi batch reactor in the temperature range 400℃~550℃ in order to obtain suitable liquid fuels.The dependencies between process temperatures,types of catalyst,feed compositions and product yields of the obtained fuel fractions were found.It was observed that up to 450℃ thermal cracking temperature,the major product of pyrolysis was liquid oil and the major product at other higher temperatures(475℃~550℃) ... 相似文献
10.
B. L. Tumanskii V. F. Snegirev K. N. Makarov L. T. Lantseva S. P. Solodovnikov N. N. Bubnov T. V. Timofeeva Yu. T. Struchkov 《Russian Chemical Bulletin》1992,41(11):2008-2011
EPR spectra of radical adducts of phosphonyl radicals with 2-hydroperfluoro-4-methyl- and 4,4-dimethyl-2-pentene have been studied. The molecular mechanics method has been used to determine the preferred conformation of the (CF3)2CF-CF-HCF3P(O)(OMe)2 radical. The eclipsed conformation of the C–P bond and 2p
z
-orbital of an unpaired electron is stabilized due to steric factor and hyperconjugation.A. N. Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences, 117813 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2550–2554, November, 1992. 相似文献
11.
Manas Kumar Mondal Li Zhang Zhongtao Feng Shuxuan Tang Rui Feng Yue Zhao Gengwen Tan Huapeng Ruan Xinping Wang 《Angewandte Chemie (International ed. in English)》2019,58(44):15829-15833
The search for main‐group element‐based radicals is one of the main research topics in contemporary chemistry because of their fascinating chemical and physical properties. The Group 15 element‐centered radicals mainly feature a V‐shaped two coordinate structure, with a couple of radical cations featuring trigonal tricoordinated geometry. Now, nontrigonal compounds R3E (E=P, As, Sb) were successfully synthesized by introducing a new rigid tris‐amide ligand. The selective one‐electron reduction of R3E afforded the first stable tricoordinate pnictogen‐centered radical anion salts; the pnictogen atoms retain planar T‐shaped structures. EPR spectroscopy and calculations reveal that the spin density mainly resides at the p orbitals of the pnictogen atoms, which is perpendicular to the N3E planes. 相似文献
12.
Multinuclear low temperature solution NMR and FTIR has been used to monitor the hydrolysis and polymerisation chemistry involved in the preparation of multicomponent silica/alumina and silica/boric oxide monolithic gels. Pre-hydrolysis of the silicon component (tetraethylorthosilicate) in the presence of low levels of water is an important factor in obtaining transparent materials. In order to obtain high homogeneity and minimise the subsequent precipitation of the fastest hydrolysing component, ethylacetonate (etac) has been used to modify the aluminum alkoxides. Solid state nmr and FTIR studies show that the borosilicate system contains Si-O-B bonds during the early stages of polymerisation but they are absent on final gelation. Thermal treatment to around 500°C is required to generate mixed Si-O-B bonds. Length of prehydrolysis has little affect on the nature of the Si-O-B gel materials but has a significant effect on the chemical nature of Si-O-Al materials. Longer silicon alkoxide prehydrolysis times lead to better defined materials.formerly Carole C. Perry.formerly at Chemistry Department, Brunel University, Uxbridge, Middlesex. UB8 3PH UK. 相似文献
13.
The coupling reaction of 4-aminoantipyrine (4-AAP) with phenol using the superoxide anion radical (
) as oxidizing agent under the catalysis of horseradish peroxidase (HRP) was studied. Based on the reaction,
produced by irradiating vitamin B2 (VB2) was spectrophotometrically determined at 510 nm. Under the optimum experimental conditions, the relationship between A
510 and
concentration was linear in the range 9.14×10–6–1.2×10–4 mol L–1. The detection limit was determined to be 1.37×10–6 mol L–1. A possible reaction mechanism was discussed. The effect of interferences and surfactants on the determination of
was also investigated. The proposed method was applied to determine superoxide dismutase activity in garlic, scallion, and onion with satisfactory results. 相似文献
14.
The thermodynamic activation parameters of hindered rotation of the CF3 group in the 4-nitrophenyltrifluoromethylsulfone radical anion in DMF were determined from the temperature dependence of the EPR line widths and spin density distributions calculated by the U-B3LYP method in the 6-31+G* basis set. In the range 293 > T > 199 K, the activation energy of hindered rotation E F depends on the temperature and changes in the range 9.67 < E F < 18.95 kJ·mol?1; the changes in the activation enthalpy and entropy are 7.23 < ΔH ≠ < 17.30 kJ·mol?1 and ?53.45 < ΔS ≠ < ?11.37 J·(mol·K)?1, respectively. Based on the suggested method for evaluating the inner product of the g tensor and the tensor of anisotropic hfi with the 14N nucleus for nitrobenzene radical anions in the liquid state we calculated the correlation time and determined the activation energy of rotational diffusion of the 4-nitrophenyltrifluoromethylsulfone radical anion in DMF, E r = 20.175±0.54 kJ·mol?1. 相似文献
15.
D. V. Kazakov D. V. Mal’tsev G. Ya. Maistrenko S. L. Khursan M. Yu. Ovchinnikov V. P. Kazakov 《Russian Chemical Bulletin》2007,56(2):205-210
Decomposition of 1,4-dimethylnaphthalene endoperoxide supported on the silica gel and alumina surface is accompanied by chemiluminescence
(CL) in the IR and visible spectral regions. The CL emitter in the IR region is singlet oxygen. The 1O2 dimol contributes mainly to the emission at λmax = 630 and 700 nm. It was shown by the IR-CL method that endoperoxide decomposition on the sorbent surface follows the first-order
kinetics. The activation parameters of the process were determined. On the Al2O3 and silica gel surfaces a substantial acceleration of the decomposition of 1,4-dimethylnaphthalene endoperoxide is observed
compared to the solution.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 199–204, February, 2007. 相似文献
16.
Patsoukis N Papapostolou I Georgiou CD 《Analytical and bioanalytical chemistry》2005,381(5):1065-1072
The present study shows that hydroethidine (HE), used for in-vivo qualitative fluorescent detection of superoxide anion, can be also oxidized by H2O2 via non-specific peroxidase (horseradish peroxidase and myeloperoxidase) catalysis, forming fluorescent oxidation products. These products give broad excitation/emission peaks (490–495/580–600 nm) near the excitation/emission peaks (475/580 nm) of the HE-superoxide oxidation product, and this may pose serious interference problems to the fluorescent detection of the superoxide radical. The study suggests cautionary use of the HE-superoxide anion assay mainly for detection of reactive oxygen species. A byproduct of this study was the development of a simple and sensitive HE-horseradish peroxidase assay for the in-vitro quantification of H2O2 in biological tissues with a sensitivity of 1 mol L–1. 相似文献
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19.
Laura Hermosilla Paloma Calle Carlos Sieiro Nuria García Pilar Tiemblo Julio Guzmn 《Chemical physics》2007,340(1-3):237-244
The EPR spectral pattern observed in the bulk polymerization of methacrylic monomers was theoretically investigated by DFT methodology. The conformational analysis of the propagating radical by the rotation around the C–Cβ bond, was performed using the B3LYP/6-31G* computational scheme. To obtain accurate values of the isotropic hyperfine coupling constants (hfccs) a higher level protocol, B3LYP/TZVP//B3LYP/6-31G*, was applied. The experimental 13-line spectrum registered at the first stage of the polymerization was assumed to correspond to a free rotating radical in a fluid medium and it was simulated just considering the most stable conformation. The 9-line spectrum registered at high conversions was interpreted in terms of highly hindered rotational conformers frozen in the very viscous medium. This spectrum was well reproduced by a model which considers the sum of the individual spectra of the conformations spread around the most probable. Each of these contributing spectra was obtained on the basis of the computed hfccs for the considered conformations and weighted by his relative Boltzmann population according to the DFT analysis. Besides, the calculated hfccs showed an excellent agreement with those predicted by the Heller–McConnell relationship, which confirms the coherence of the DFT methodology for this kind of calculations. 相似文献
20.
V. B. Vol'eva A. I. Prokofev A. Yu. Karmilov N. L. Komissarova I. S. Belostotskaya T. I. Prokofeva V. V. Ershov 《Russian Chemical Bulletin》1998,47(10):1920-1923
The formation of semiquinone and phenoxazyl radicals and metallocomplexes with semiquinone ligands was observed by ESR during
the interaction of di-tert-butylpyrocatechol with Al2O3, ZnO, SiO2, and TiO2. In the case of different modifications of SiO2, admixtures of TiO2 exhibit a higher reactivity in complex formation with the organic substrate.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1975–1978, October, 1998. 相似文献