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51.
Viktoria S. Moskvina Olexander V. Turov Volodymyr P. Khilya Myroslav M. Garazd Ulrich M. Groth 《Monatshefte für Chemie / Chemical Monthly》2008,43(4):1391-1396
New functionalized derivatives of 8,8,10-trimethyl-4-phenyl-7,8-dihydro-2H,6H-pyrano[3,2-g]-chromene-2,6-dione – analogues of the natural compound graveolone – possessing hydrazine, hydroxylamine, and thiosemicarbazide
residues were synthesized and their reactions with acetic anhydride were studied. The structure of the obtained compounds
was confirmed by NMR spectroscopy. 相似文献
52.
Viktoria S. Moskvina Olexander V. Turov Volodymyr P. Khilya Myroslav M. Garazd Ulrich M. Groth 《Monatshefte für Chemie / Chemical Monthly》2008,139(11):1391-1396
New functionalized derivatives of 8,8,10-trimethyl-4-phenyl-7,8-dihydro-2H,6H-pyrano[3,2-g]-chromene-2,6-dione – analogues of the natural compound graveolone – possessing hydrazine, hydroxylamine, and thiosemicarbazide
residues were synthesized and their reactions with acetic anhydride were studied. The structure of the obtained compounds
was confirmed by NMR spectroscopy.
Correspondence: Viktoria Moskvina, Chemistry Department, Kyiv National Taras Shevchenko University, 60, ul. Vladimirskaya,
01033 Kyiv, Ukraine. 相似文献
53.
Milkova V Kamburova K Petkanchin I Radeva T 《Langmuir : the ACS journal of surfaces and colloids》2008,24(17):9495-9499
The effect of polyelectrolyte charge density on the electrical properties and stability of suspensions of oppositely charged oxide particles is followed by means of electro-optics and electrophoresis. Variations in the electro-optical effect and the electrophoretic mobility are examined at conditions where fully ionized pectins of different charge density adsorb onto particles with ionizable surfaces. The charge neutralization point coincides with the maximum of particle aggregation in all suspensions. We find that the concentration of polyelectrolyte, needed to neutralize the particle charge, decreases with increasing charge density of the pectin. The most highly charged pectin presents an exception to this order, which is explained with a reduction of the effective charge density of this pectin due to condensation of counterions. The presence of condensed counterions, remaining bound to the pectin during its adsorption on the particle surface, is proved by investigation of the frequency behavior of the electro-optical effect at charge reversal of the particle surface. 相似文献
54.
α‐Lithiated tertiary methylamines are important building blocks in all fields of chemistry, such as for the synthesis of new ligand or catalyst systems. However, the access to these compounds is still limited and the reaction mechanism, in general, not fully understood. We present herein X‐ray diffraction analyses of organolithium compounds with 1,2,3‐trimethyl‐1,3,5‐triazacyclohexane ( 1 ), such as a precoordination adduct of tert‐butyllithium, [(tBuLi)3?C6H15N3], which represents a potential intermediate of the lithiation of the methylene group of this ligand. By means of molecular structures and computational studies, the regioselectivity of this deprotonation reaction can be understood. Furthermore, the tBuLi adduct gives a hint to an alternative deaggregation process of organolithium compounds. 相似文献
55.
Thioflavin T: Electronic Circular Dichroism and Circularly Polarized Luminescence Induced by Amyloid Fibrils 下载免费PDF全文
Dr. Anna Rybicka Prof. Giovanna Longhi Prof. Ettore Castiglioni Prof. Sergio Abbate Dr. Wojciech Dzwolak Dr. Viktoria Babenko Dr. Magdalena Pecul 《Chemphyschem》2016,17(18):2931-2937
The circularly polarized luminescence (CPL) spectrum of thioflavin T (ThT) bound to insulin amyloid fibrils has been measured for the first time. It has been found that the samples exhibiting induced circular dichroism (CD) retain the optical activity in the CPL spectra, with the same sign of the rotatory strength. The fluorescence dissymmetry factor is substantial (of the order of magnitude 10?2). Unlike in the corresponding CD and absorption spectra, there is no shift of the CPL band with respect to the fluorescence band. It has been verified that the measured CPL spectra are free from artifacts from circularly polarized scattering of emitted light by conducting additional measurements in a medium with a refractive index similar to insulin (methylsalicylate). The CD and CPL spectra have been interpreted by means of density functional calculations carried out for ThT in its ground and first excited states in different dielectric environments and for ThT interacting with an aromatic ring. It has been found that the presence of an aromatic ring close to the ThT molecule induces Cotton effects of the same order of magnitude as the stabilization of one enantiomeric conformer. Thus, it is expected that both mechanisms contribute to the induced CD and CPL effect to a similar degree. 相似文献
56.
Katharina Dilchert Michelle Schmidt Angela Großjohann Kai‐Stephan Feichtner Robert E. Mulvey Viktoria H. Gessner 《Angewandte Chemie (International ed. in English)》2021,60(1):493-498
s‐Block metal carbenoids are carbene synthons and applied in a myriad of organic transformations. They exhibit a strong structure–activity relationship, but this is only poorly understood due to the challenging high reactivity and sensitivity of these reagents. Here, we report on systematic VT and DOSY NMR studies, XRD analyses as well as DFT calculations on a sulfoximinoyl‐substituted model system to explain the pronounced solvent dependency of the carbenoid stability. While the sodium and potassium chloride carbenoids showed high stabilities independent of the solvent, the lithium carbenoid was stable at room temperature in THF but decomposed at ?10 °C in toluene. These divergent stabilities could be explained by the different structures formed in solution. In contrast to simple organolithium reagents, the monomeric THF‐solvate was found to be more stable than the dimer in toluene, since the latter more readily forms direct Li/Cl interactions which facilitate decomposition via α‐elimination. 相似文献
57.
Viktoria Kazantzi Georgia Giakisikli 《International journal of environmental analytical chemistry》2017,97(6):508-519
A novel on-line flow injection solid phase extraction method for the preconcentration of trace toxic metals prior determination by flame atomic absorption spectrometry (FI-SPE-FAAS) was developed. The potential application of the hydrophobic reversed phase co-polymer sorbent StrataTM-X packed into an on-line microcolumn for the quantification of Cd(II), Pb(II), Cu(II) and Cr(VI) was demonstrated for the first time. The method was based on the on-line formation of metal complexes using sodium diethyl-dithiocarbamate (DDTC) and on the subsequent retention of them onto the sorbent material. The target analytes were completely eluted by methanol and, subsequently, directed to FAAS for quantification. All chemical and flow variables affecting the performance of the developed method were thoroughly studied and optimised. For a preconcentration time of 90 s and a sampling frequency of 28 h?1, enhancement factors of 72, 140, 185, 63 and detection limits of 0.18, 1.6, 0.20 and 1.2 μg L ?1 were obtained for Cd(II), Pb(II), Cu(II) and Cr(VI), respectively. The accuracy of the FI-SPE-FAAS method was evaluated by analysing certified reference materials as well as spiked environmental water samples. Furthermore, a comparative study of the analytical characteristics, the properties as well as the chemical structures of commercial polymeric based sorbent materials was employed. Strata-X sorbent was compared against HypersepTM SCX, Bond Elut® PlexaTM PCX, Oasis-HLBTM and NobiasTM PA-1, regarding the adaptation in on-line FI-SPE-FAAS systems for metal determination, and herein presented. 相似文献
58.
Reiter EV Cichna-Markl M Chung DH Shim WB Zentek J Razzazi-Fazeli E 《Analytical and bioanalytical chemistry》2011,400(8):2615-2622
The paper presents a new sample clean-up method based on immuno-ultrafiltration for the analysis of ochratoxin A in cereals.
In contrast to immunoaffinity chromatography, in immuno-ultrafiltration, the antibodies are used in non-immobilised form.
Ochratoxin A was extracted with ACN/water (60/40, v/v), and the extract was loaded onto the ultrafiltration device. After a washing step with phosphate-buffered saline, containing
0.05% Tween 20, ochratoxin A was eluted with MeOH/acetic acid (99/1, v/v). The detection of ochratoxin A was carried out with high-performance liquid chromatography and a fluorescence detector coupled
to an electrochemical cell (Coring cell). The electrochemical cell was used to eliminate matrix interferences by oxidising
matrix compounds. The method was validated by repeatedly analysing spiked barley and rye samples as well as a certified wheat
reference material. Recoveries and standard deviations (1 SD) were found to be 71 ± 9%, 77 ± 12% and 77 ± 8% in wheat, barley
and rye, respectively. The limit of detection (S/N = 3) and limit of quantitation (S/N = 10) were determined to be 0.4 μg kg-1 and 1 μg kg-1. The analysis of the certified reference material resulted in ochratoxin A concentrations which were in the range assigned
by the producer. Additionally, the effect of the electrochemical cell on other widely used clean-up techniques, namely the
immunoaffinity clean-up and multifunctional columns (Mycosep #229), was evaluated. In all clean-up methods, an improvement
of the chromatogram quality was registered. 相似文献
59.
Sol-gel immunoaffinity chromatography for the clean up of ochratoxin A contaminated grains 总被引:1,自引:0,他引:1
Reiter EV Cichna-Markl M Tansakul N Shim WB Chung DH Zentek J Razzazi-Fazeli E 《Journal of chromatography. A》2011,1218(42):7627-7633
This paper describes the application of sol-gel immunoaffinity columns for clean up of ochratoxin A contaminated cereal crops. Monoclonal antibodies selective for OTA have been entrapped into the pores of a sol-gel matrix in order to prepare immunoaffinity columns. Different parameters such as amount of entrapped antibodies and loading conditions were optimized to obtain highest possible recoveries of OTA. The method has been found to be a suitable tool in sample preparation prior to HPLC-FLD determination and as selective as conventional commercially available immunoaffinity columns. In the clean up of different cereals mean recoveries of 82±5%, 90±6% and 91±3%, were obtained for wheat, barley and rye, respectively, with sol-gel columns containing 1mg of anti-OTA antibodies. The detection limit (signal-to-noise ratio, 3) was 0.5 μg/kg and the limit of quantification (signal-to-noise ratio, 10) determined to be 1 μg/kg. Sol-gel columns can be reused 7 times without significant loss of recovery. After 10 applications the recovery decreased to approx. 50%. 相似文献
60.
Gessner VH Koller SG Strohmann C Hogan AM O'Shea DF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(10):2996-3004
This article addresses the mechanistic features of asymmetric carbolithiation of β‐methylstyrenes. While often the presence of functional groups is required to obtain high enantioselectivities in carbolithiation reactions, simple β‐methylstyrene also gives high selectivities in (?)‐sparteine‐mediated addition of alkyl lithium compounds. Computational studies on the carbolithiation of β‐methylstyrene with (?)‐sparteine show that the observed selectivities are the result of repulsion effects in the diastereomeric transition states between the (?)‐sparteine ? alkyl lithium adduct and the β‐methylstyrene, upon approximation of the two reactants. In contrast, for the ortho‐amino β‐methylstyrene (E)‐benzyl(2‐propenylphenyl)amine ( 4 ) X‐ray structure analyses of intermediate lithium amides indicate a carbolithiation mechanism in which one side of the double bond is shielded by the amide moiety, leaving only one side free for approach of the chiral alkyl lithium adduct. 相似文献