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131.
A. S. Culf M. Čuperlović‐Culf R. J. Ouellette 《Magnetic resonance in chemistry : MRC》2009,47(2):158-164
Highly coloured Janovsky complexes have been known for over 120 years, being used in many colourimetric analytical procedures. In this present study, two novel and stable nitrocyclohexadienyl spirobicyclic, zwitterionic Janovsky anionic hydantoin σ‐complexes, rac‐1,3‐diisopropyl‐6‐nitro‐2,4‐dioxo‐1,3‐diazaspiro[4.5]deca‐6,9‐dien‐8‐ylideneazinate, ammonium internal salt (1) and 1,3‐diisopropyl‐2,4‐dioxo‐1,3‐diazaspiro[4.5]deca‐6,9‐dien‐8‐ylideneazinate, ammonium internal salt (2) have been prepared and characterised by NMR, electrospray ionization mass spectrometry (ESI‐MS) and UV/visible methods. For the p‐mononitro‐substituted complex (2), we discovered chemical exchange behaviour using 1D saturation transfer and 2D exchange spectroscopy (EXSY) 1H NMR techniques. The coalescence temperature was determined to be 62 °C in d3‐acetonitrile. Analysis of these data provided a Gibbs free energy of activation, ΔG ?, of + 67 kJ mole?1, a rate constant, k, coalescence of 220 Hz and an equilibrium constant, Keqm, of 0.98 as estimates of the exchange process in this solvent. Of the two mechanisms proposed for this fluxional behaviour, ring opening to a substituted benzene or proton exchange, a further theoretical modelling study of 1D 1H NMR spectra was able to confirm that simple proton exchange between the two nitrogen sites of the hydantoin ring provided an accurate simulation of the observed experimental evidence. Interestingly, the o,p‐dinitro‐substituted complex (1) did not show any chemical exchange behaviour up to 150 °C in d3‐acetonitrile (to 75 °C) and d6‐dimethyl sulfoxide (DMSO). Molecular modelling at the MM2 level suggests that steric collisions of an N‐acyl isopropyl substituent of the hydantoin ring with the ortho‐nitro group of the spirofused cyclohexadienyl ring prevents the proposed proton exchange mechanism occurring in this case. Copyright © 2008 Crown in the right of Canada. Published by John Wiley & Sons, Ltd 相似文献
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133.
Mirjana M. Radanović Marko V. Rodić Stevan Armaković Sanja J. Armaković Ljiljana S. Vojinović-Ješić Vukadin M. Leovac 《Journal of Coordination Chemistry》2017,70(16):2870-2887
Two nitrate salts of the well-known, and due to its significant biological activity very important, compound pyridoxylidene aminoguanidine (PLAG) were obtained in the form of single crystals. Thus this ligand is structurally characterized for the first time. In addition, the first data on the structure of a Schiff base of aminoguanidine with the active form of vitamin B6, i.e. pyridoxal-phosphate, of the formula PLPAG·HCl·2H2O, are presented. Two new square-pyramidal Cu(II) complexes of PLAG were synthesized and their physicochemical and structural properties analyzed. In these complexes, PLAG is coordinated as a zwitter-ion, in a tridentate ONN manner, via the oxygen atom of the deprotonated phenolic OH-group and nitrogen atoms of the azomethine and imino group of the aminoguanidine moiety. For the first time it was possible to make a comparative analysis of the structural properties of ligand salts and the coordinated ligand, so the effects of coordination could be unequivocally pointed out. Common fragments encountered in ligand structures were compared by half-normal probability plots. Density functional theory calculations have been conducted in order to gain insight into reactive properties of the investigated molecules. Molecular electrostatic potential, average local ionization energy surfaces, and Fukui functions have been calculated in order to obtain further information on the reactive properties. 相似文献
134.
This work presents a comparison of convective interaction media (CIM) and controlled pore glass (CPG) as solid supports for
immunoglobulin antibodies used in bioanalytical detection of allergens in foodstuffs. A flow-injection manifold with highly
sensitive thermal lens spectrometric detection was used for this purpose. Using beta-lactoglobulin, a milk allergen, as a
model analyte, CIM disc supports had a higher linear range (0.2–3.5 μg L−1), better reproducibility (intra-day RSD = 1%, inter-day RSD = 10%), lower consumption of reagents, and better immunocolumn
stability (1 month, over 240 injections of substrate), while providing comparable LODs (0.1 μg L−1). Application of CIM discs as solid supports in immunocolumns for allergen detection enables fast and sensitive screening
of allergens in foodstuffs with sample throughput of up to eight samples per hour. 相似文献
135.
Jakub Plášil Elena Buixaderas Jiří Čejka Jiří Sejkora Jan Jehlička Milan Novák 《Analytical and bioanalytical chemistry》2010,397(7):2703-2715
The uranyl sulphate mineral zippeite was studied by Raman spectroscopy. The phase purity of the sample was initially checked
by X-ray powder diffraction and its chemical composition was defined by electron microprobe (wavelength dispersive spectroscopy,
WDS) analysis. The Raman spectroscopy research focused on the low wavenumber and uranyl stretching vibration regions. Vibration
bands down to 50 cm–1 were tentatively assigned. The U–O bond lengths were calculated based on empirical relations. Inferred values are consistent
with those obtained from the crystal structure analysis of synthetic zippeite. Number of bands was interpreted on the basis
of factor group analysis. 相似文献
136.
Alexander Popkov Jiří Hanusek Jiří Čermák Vratislav Langer Robert Jirásko Michal Holčapek Milan Nádvorník 《Journal of Radioanalytical and Nuclear Chemistry》2010,285(3):621-626
In this communication the evaluation of eleven new metallocomplex alanine synthons bearing C2-symmetric benzyl groups with electron-donating and electron-withdrawing substituents is described. α-Methylated glycine synthons (alanine complexes) were evaluated alongside alanine synthons in order to obtain a deeper understanding of the relationship between their structures and stereochemistry of monoalkylated products and to choose several candidates for their further tests for stereospecific preparation of 6-[18F]FDOPA. Glycine-derived analogues of the complexes 3–5 are the best candidates for the development of a 6-[18F]FDOPA preparation procedure. In the model epimerisation reaction they demonstrated the best performance, much better compared to the previously described compound 2. Complexes 3, 5 and 8 are the best in asymmetric preparation of β-13C monolabelled α-aminoisobutyric acid. They have to be tested in the preparation of α-methyl amino acids like 6-[18F]-α-methylDOPA and 2-[18F]-α-methyltyrosine. 相似文献
137.
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139.
Gajath Gunatillake Mirjana Jovovic Wayne Smith 《Journal of Mathematical Analysis and Applications》2014
The operator that takes the function f to ψf°φ is a weighted composition operator. We study numerical ranges of some classes of weighted composition operators on H2, the Hardy–Hilbert space of the unit disc. We consider the case where φ is a rotation of the unit disc and identify a class of convexoid operators. In the case of isometric weighted composition operators we give a complete classification of their numerical ranges. We also consider the inclusion of zero in the interior of the numerical range. 相似文献
140.
Current waveforms induced by prebreakdown streamers have been measured in a short positive point-to-plane gap in hydrogen
at pressures of (12.5–100) kPa over a wide range of gap voltage values. The current waveforms were measured using a small
central cathode probe. The cathode probe signal corresponding to the streamer arrival to the probe is interpreted in terms
of recent computer simulation models and consists of an initial sharp current spike due to displacement current followed,
some 20 ns later, by a lower current hump due to the ion arrival at the cathode.
Dedicated to Prof. Jan Janča on the occasion of his 60th birthday.
This work was supported by the Scientific Grant Agency of the Slovak Ministry of Education and Academy of Sciences of Slovak
Republic (Project No. 95/5195/136). 相似文献