共查询到20条相似文献,搜索用时 0 毫秒
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H. Tsuruda M. MitoH. Deguchi S. TakagiA.A. Leitch K. LekinS.M. Winter R.T. Oakley 《Polyhedron》2011,30(18):2997-3000
The hydrostatic pressure response of TC of the bisdiselenazolyl radical ferromagnet 1 up to 5 GPa was investigated by AC magnetic susceptibility measurements using a SQUID magnetometer and a miniature diamond anvil cell. It was found that the ambient pressure value of TC = 17 K could be raised to 21 K at a pressure of 0.9 GPa. The experimental technique is described in detail and the pressure response is compared to that observed in related systems. 相似文献
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The photoelectrochemical behaviour of several chlorinated nitrobenzenes has been investigated using steady state channel flow cell methods. It has been shown that, in acetonitrile+0.1 M TBAHFP, 4-chloronitrobenzene (p-CNB), 2-chloronitrobenzene (o-CNB), 2,4-dichloronitrobenzene (2,4-DCNB), 2,6-dichloronitrobenzene (2,6-DCNB) and 1,3,5-trichloro-2-nitrobenzene (TCNB) can undergo reversible one-electron reductions to form radical anions that are stable on the timescale of at least tens of seconds under dark conditions. When the electrode surface is irradiated with light of intensity 2 mW cm−2, the electrochemically formed radical anions can absorb light to form an excited state from which dechlorination is favoured. Reactivity orders of o-CNB>p-CNB>2,4-DCNB>2,6-DCNB>TCNB at 330 nm, and o-CNB>2,4-DCNB>2,6-DCNB>p-CNBTCNB at 470 nm have been determined. The relative order is rationalised in terms of radical anion lifetime effects and the role of heavy atom subsituents in reducing the excited state lifetime. 相似文献
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Leitch AA Brusso JL Cvrkalj K Reed RW Robertson CM Dube PA Oakley RT 《Chemical communications (Cambridge, England)》2007,(32):3368-3370
A pair of isostructural bis-selenathiazolyl and bis-diselenazolyl radical conductors display weak (spin-canted) ferromagnetism with Tc values of 18 K and 27 K respectively. 相似文献
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E. S. Klimchuk B. P. Makarov Yu. A. Serebrennikov I. V. Khudyakov 《Russian Chemical Bulletin》1989,38(8):1627-1630
The effect of an external heavy atom on the EPR spectra of radicals in homogeneous liquid solutions was investigated. Broadening of the lines in the EPR spectrum of the fluorescein semiquinone radical in water-ethanol solution was found under the effect of the external heavy atom. It was hypothesized that this broadening is due to an increase in the anisotropy of the g-factor due to potentiation of the spinorbital interaction on contact with the external heavy atom.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1778–1781, August, 1989.We would like to thank V. A. Roginskii for his assistance in the research and valuable advice, and B. F. Minaev for his useful discussion of the mechanism. 相似文献
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《Comptes Rendus de l'Academie des Sciences Series IIC Chemistry #》1999,327(1):133-138
Strong compression effects are experimentally demonstrated by acting magnetic forces upon a cold cesium atom cloud. Atoms released from an optical molasses at a temperature of 5 μK experience during their fall a pulsed longitudinal force. Magnetic state selection occurs and time-of-flight spectrum compressions are obtained for definite experimental parameters. Corresponding spatial or velocity compressions are reported. 相似文献
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A significantly increased polymer growth rate was observed during a surface-initiated ATRP reaction in the presence of DNA molecules. To investigate this phenomenon, thiolated single-stranded DNA molecules (ssDNAs) with ATRP initiators coupled at the distal point were used as the model molecule in the study. In comparison, a small molecule, HS-(CH(2))(11)NHCOC(CH(3))(2)Br, was used to provide a less-polar surface coating for polymer grafting. 2-Hydroxyethyl methacrylate (HEMA) and monomethoxy-capped oligo(ethylene glycol) methacrylate (OEGMA) were used as the ATRP monomers. The polymer growth rates were monitored by measuring the thickness of the polymer films formed at different times. Our results show that the presence of DNA molecules, although at a less-than-1% surface coverage, significantly accelerated the growth rates of both poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(oligoethylene glycol methacrylate) (POEGMA) at the beginning of the ATRP reactions. This accelerating effect was suspected to be a combined result of the highly charged sugar-phosphate backbones of DNA molecules and the formation of Cu complexes with DNA bases. After the initial polymer growth, a smaller yet constant polymer growth rate was observed, suggesting the reduced influence of DNA molecules as the ATRP reaction centers moved farther away from the surface. Similar to conventional ATRP reactions, the polymer growth from surface-anchored DNA molecules was found to be strongly dependent on the composition and the concentration of the catalysts used. Specifically, a catalyst mixture of CuCl/30% CuBr(2)/bpy with 23 mM CuCl was found to provide the optimal reaction condition to yield the fastest polymer film growth among the conditions tested. 相似文献
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Krzysztof Matyjaszewski 《Macromolecular Symposia》2002,182(1):209-224
Kinetics of atom transfer radical polymerization (ATRP) with the special emphasis on dynamics of activation and deactivation is discussed. Various mechanistic features of ATRP related to electron transfer processes are presented. Elementary reactions of ATRP process are analyzed. 相似文献
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Yannick Borguet 《Tetrahedron letters》2007,48(36):6334-6338
The first monomode microwave-assisted atom transfer radical additions (ATRA) of carbon tetrachloride to various olefins were successfully performed, affording the adducts with almost quantitative yields in less than 10 min at 160 °C. 相似文献
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Simplified electrochemical atom transfer radical polymerization (seATRP) using CuII–N-propyl pyridineimine complexes (CuII(NPPI)2) is reported for the first time. In aqueous solution, using oligo(ethylene glycol) methyl ether methacrylate (OEGMA), standard electrolysis conditions yield POEGMA with good control over molecular weight distribution (Đm < 1.35). Interestingly, the polymerizations are not under complete electrochemical control, as monomer conversion continues when electrolysis is halted. Alternatively, it is shown that the extent and rate of polymerization depends upon an initial period of electrolysis. Thus, it is proposed that seATRP using CuII(NPPI)2 follows an electrochemically-triggered, rather than electrochemically mediated, ATRP mechanism, which distinguishes them from other CuIIL complexes that have been previously reported in the literature.Simplified electrochemical atom transfer radical polymerization (seATRP) using CuII-pyridineimine complexes is reported and follows a previously unreported electrochemically triggered mechanism. 相似文献
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Mei Li Krzysztof Matyjaszewski 《Journal of polymer science. Part A, Polymer chemistry》2003,41(22):3606-3614
An improved atom transfer radical polymerization (ATRP) process was developed for use in a waterborne miniemulsion system. To conduct a successful ATRP in a heterogeneous waterborne system, it is of great importance to ensure control over the polymerization process while preserving colloidal stability. Efforts devoted to optimization of reaction conditions and improvement in the overall productivity of the process allowed the development of a novel, practical initiation system for ATRP suitable for use in a miniemulsion procedure that can provide copolymers of well-defined composition (e.g., block copolymers) and topologies (e.g., multiarm polymer). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3606–3614, 2003 相似文献
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Kohji Ohno Yoshinobu Tsujii Takeshi Fukuda 《Journal of polymer science. Part A, Polymer chemistry》1998,36(14):2473-2481
Controlled free radical polymerization of sugar-carrying methacrylate, 3-O-methacryloyl-1,2 : 5,6-di-O-isopropylidene-d-glucofuranose (MAIpGlc) was achieved by the atom transfer radical polymerization (ATRP) technique with an alkyl halide/copper-complex system in veratrole at 80°C. The time–conversion first-order plot was linear and the number-average molecular weight increased in direct proportion to the ratio of the monomer conversion to the initial initiator concentration, providing PMAIpGlc with a low polydispersity. The sequential addition of the two monomers styrene (S) and MAIpGlc afforded a block copolymer of the type PS-b-PMAIpGlc. The acidolysis of the homo- and block copolymers gave well-defined glucose-carrying water-soluble polymers PMAGlc and PS-b-PMAGlc, respectively. The amphiphilic PS-b-PMAGlc block copolymer exhibited a microdomain surface morphology with spherical PS domains in a PMAGlc matrix. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2473–2481, 1998 相似文献
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Li W Barton PT Kiran MS Burwood RP Ramamurty U Cheetham AK 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(44):12429-12436
Hybrid inorganic-organic framework materials exhibit unique properties that can be advantageously tuned through choice of the inorganic and organic components and by control of the crystal structure. We present a new hydrothermally prepared 3D hybrid framework, [Mn(2-methylsuccinate)](n) (1), comprising alternating 2D manganese oxide sheets and isolated MnO(6) octahedra, pillared via syn, anti-syn carboxylates. Powder magnetic characterization shows that the compound is a homospin Mn(II) ferrimagnet below 2.4 K. The easy-axis is revealed by single-crystal magnetic susceptibility studies and a magnetic structure is proposed. Anisotropic elastic moduli and hardness, observed through nanoindentation on differing crystal facets, were correlated with specific structural features. Such measurements of anisotropy are not commonly undertaken, yet allow for a more comprehensive understanding of structure-property relationships. 相似文献
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Intramolecular hydrogen atom transfer in hydrogen-deficient polypeptide radical cations 总被引:1,自引:0,他引:1
Michael L. Nielsen Bogdan A. Budnik Kim F. Haselmann Jesper V. Olsen Roman A. Zubarev 《Chemical physics letters》2000,330(5-6):558-562
Irradiation of protonated polypeptides NH2–RH+–COOH by >10 eV electrons leads to further ionization and fast intramolecular charge transfer to the free N-terminus. The resulting species may undergo further hydrogen atom rearrangement to form distonic ions N+H3–RH+–COO√. Such transfer is exothermic but can involve an appreciable barrier, e.g., 2.3±0.5 eV for MH2+√ ions of the peptide ACTH 1–10. Radical polypeptide dications can, therefore, be viewed as hydrogen atom wires. Subsequent capture of low energy electrons results in fragmentation. The pattern of this electronic excitation dissociation (EED) is consistent with hydrogen transfer prior to electron capture. 相似文献
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Ten solvents containing heavy atoms were examined for suitability for use in the external heavy atom effect for routine phosphorimetry. In previous work only iodine-containing solvent systems have been used, and the incongruity of enhancement results for structurally similar compounds suggests that the ultraviolet transmission characteristics of the solvent systems may be responsible for fractional enhancements. In this study the effect of chlorine-, bromine-, and iodine-containing solvent systems on phosphorescence and fluorescence intensities was investigated. Generally, chlorine-, and bromine-containing solvent systems showed a significant improvement in phosphorimetric enhancements with slightly longer lifetimes than in solvent systems containing iodine. As expected from their smaller spin-orbit coupling, chlorine-containing solvent systems yield smaller enhancements than bromine-containing solvent systems. Solvent systems containing bromine seem to offer the best compromise between ultraviolet transmission characteristics and large spin-orbit coupling constants. 相似文献
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We have synthesized a complex in which a pyridyliminonitroxide radical is coordinated to a vanadyl ion. ESR studies of this complex show that the radical's unpaired spin is tightly coupled to the vanadium spin to form a ground singlet state with a thermally accessible triplet state. The vanadium hyperfine splitting in the triplet state of the complex is found to be one half of that of isolated vanadyl complexes. 相似文献
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MO LCAO results are presented for the interatomic contribution to the anisotropy of the diamagnetic susceptibility; values of d=–23.5 · 10–6 and d=–13.8 · 10–6 cm3/mole are obtained for the cyclopropane and epoxide ring systems, respectively. The results are used to interpret PMR spectra in terms of the configuration and conformation of the and forms of caran-4-ol and two stereoisomers of caranone. 相似文献
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Stevens CV Van Meenen E Eeckhout Y Vanderhoydonck B Hooghe W 《Chemical communications (Cambridge, England)》2005,(38):4827-4829
The halogen atom transfer radical cyclization (HATRC) has been evaluated on N-(indolylmethyl)trichloroacetamides under Cu(I)Cl catalysis using nitrogen containing ligands. The ring closure leads to the formation of 3,3-spiro-3H-indoles in moderate to good yields by a 5-exo-mechanism. Derivatives with an N-electron withdrawing substituent also lead to a 5-exo-trig and not to a 6-endo-trig cyclization. 相似文献