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71.
Complete 1H and 13C NMR assignments of aurasperone A and fonsecinone A, two bis-naphthopyrones produced by Aspergillus aculeatus 总被引:1,自引:0,他引:1
Campos FR Barison A Daolio C Ferreira AG Rodrigues-Fo E 《Magnetic resonance in chemistry : MRC》2005,43(11):962-965
Complete assignments of 1H and 13C NMR chemical shifts of the polyketides aurasperone A and fonsecinone A were made by means of nuclear Overhauser enhancement and heteronuclear NMR correlation experiments. These compounds were isolated for the first time from Aspergillus aculeatus, an endophytic fungus obtained from leaves of Melia azedarach(Meliaceae). 相似文献
72.
Gunnarsson M Abbas Z Ahlberg E Nordholm S 《Journal of colloid and interface science》2004,274(2):563-578
Statistical mechanics has been used to derive a model for the charging of a spherical particle in a salt solution to complement our experimental studies and gain a deeper understanding of the processes involved in surface complexation. Our chosen model goes beyond the equilibrium constants and the Gouy-Chapmann theory currently used in surface complexation models. The proton adsorption is taken to occur at a harmonic potential well on the surface characterized by a frequency v and a well depth u(0). Outside the particle surface there is a capacitor layer of width w(c) which is impenetrable to the salt ions. The diffuse screening of the charged particle is described by a corrected Debye-Hückel analysis accounting for ion size in the ion-ion interactions. To account also for nonlinear electrostatic response a layer of condensed counterions has been introduced. The criterion for the onset of ion condensation is that the electrostatic field exceeds a linear response criterion. Ion size effects are accounted for in terms of hole-corrected electrostatic energies and excluded volume. The model has been applied to titrated surface charge data on goethite (alpha-FeOOH) at various background concentrations and good agreement between the experimental data and the model was obtained. Both the size of the screening ions and the central particle size were shown to be of importance for the surface charge. 相似文献
73.
74.
Magnus G. Johnston 《Journal of solid state chemistry》2004,177(11):4316-4324
Three new hydrated scandium selenites have been hydrothermally synthesized as single crystals and structurally and physically characterized. Sc2(SeO3)3·H2O crystallizes as a new structure type containing novel ScO7 pentagonal bipyramidal and ScO6+1 capped octahedral coordination polyhedra. Sc2(SeO3)3·3H2O contains typical ScO6 octahedra and is isostructural with its M2(SeO3)3·3H2O (M=Al, Cr, Fe, Ga) congeners. CsSc3(SeO3)4(HSeO3)2·2H2O contains near-regular ScO6 octahedra and has essentially the same structure as its indium-containing analogue. All three phases contain the expected pyramidal [SeO3]2- selenite groups. Crystal data: Sc2(SeO3)3·3H2O, Mr=524.85, trigonal, R3c (No. 161), , , , Z=6, R(F)=0.018, wR(F2)=0.036; Sc2(SeO3)3·H2O, Mr=488.82, orthorhombic, P212121 (No. 19), , , , , Z=4, R(F)=0.051, wR(F2)=0.086; CsSc3(SeO3)4(HSeO3)2·2H2O, Mr=1067.60, orthorhombic, Pnma (No. 62), , , , , Z=4, R(F)=0.035, wR(F2)=0.070. 相似文献
75.
al-Khalili A Thomas R Ehlerding A Hellberg F Geppert WD Zhaunerchyk V af Ugglas M Larsson M Uggerud E Vedde J Adlhart C Semaniak J Kamińska M Zubarev RA Kjeldsen F Andersson PU Osterdahl F Bednarska VA Paál A 《The Journal of chemical physics》2004,121(12):5700-5708
Dimethyl disulfide (DMDS) and N-methylacetamide are two first choice model systems that represent the disulfide bridge bonding and the peptide bonding in proteins. These molecules are therefore suitable for investigation of the mechanisms involved when proteins fragment under electron capture dissociation (ECD). The dissociative recombination cross sections for both protonated DMDS and protonated N-methylacetamide were determined at electron energies ranging from 0.001 to 0.3 eV. Also, the branching ratios at 0 eV center-of-mass collision energy were determined. The present results give support for the indirect mechanism of ECD, where free hydrogen atoms produced in the initial fragmentation step induce further decomposition. We suggest that both indirect and direct dissociations play a role in ECD. 相似文献
76.
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79.
Xu Y Eilers G Borgström M Pan J Abrahamsson M Magnuson A Lomoth R Bergquist J Polívka T Sun L Sundström V Styring S Hammarström L Akermark B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(24):7305-7314
To mimic the electron-donor side of photosystem II (PSII), three trinuclear ruthenium complexes (2, 2a, 2b) were synthesized. In these complexes, a mixed-valent dinuclear Ru2(II,III) moiety with one phenoxy and two acetato bridges is covalently linked to a Ru(II) tris-bipyridine photosensitizer. The properties and photoinduced electron/energy transfer of these complexes were studied. The results show that the Ru2(II,III) moieties in the complexes readily undergo reversible one-electron reduction and one-electron oxidation to give the Ru2(II,III) and Ru2(III,III) states, respectively. This could allow for photooxidation of the sensitizer part with an external acceptor and subsequent electron transfer from the dinuclear ruthenium moiety to regenerate the sensitizer. However, all trinuclear ruthenium complexes have a very short excited-state lifetime, in the range of a few nanoseconds to less than 100 ps. Studies by femtosecond time-resolved techniques suggest that a mixture of intramolecular energy and electron transfer between the dinuclear ruthenium moiety and the excited [Ru(bpy)3]2+ photosensitizer is responsible for the short lifetimes. This problem is overcome by anchoring the complexes with ester- or carboxyl-substituted bipyridine ligands (2a, 2b) to nanocrystalline TiO2, and the desired electron transfer from the excited state of the [Ru(bpy)3]2+ moiety to the conduction band of TiO2 followed by intramolecular electron transfer from the dinuclear Ru2(II,III) moiety to photogenerated Ru(III) was observed. The resulting long-lived Ru2(III,III) state decays on the millisecond timescale. 相似文献
80.
Xiaolin Hou K. G. Andersson J. Roed A. Byskov T. Roed 《Journal of Radioanalytical and Nuclear Chemistry》2007,271(1):133-143
Hairless rats, clothes, human hair, filter paper and water were exposed to gaseous elemental iodine in a glass chamber for
60–120 minutes. The deposition of gaseous elemental iodine on skin and lung of rats, human hair, water, clothes and paper
were investigated by measuring iodine content in the exposed material by epithermal neutron activation analysis (ENAA). For
measurement of the iodine concentration in the chamber air, elemental iodine in the air was collected by continuously sucking
air through an active charcoal column. The trapped iodine in the active charcoal was then determined by ENAA. The measured
deposition velocity in the test chamber of gaseous elemental iodine on skin, clothing, hair and water ranges from 0.006 on
filter paper and water to about 0.05 cm/s on skin and clothes. The variation of elemental iodine concentration in air of the
glass chamber was investigated by collecting and analyzing air samples at various time intervals. The results show that the
variation with time in the concentration of the iodine can be described by an exponential function. 相似文献