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71.
Olivia Bistri 《Tetrahedron letters》2006,47(25):4137-4139
An expeditious synthesis of a cyclodextrin with three pairs of functionalities on its primary rim is presented. Compared to the previous one, this improved synthetic route yields the product in four steps and 70% yield, instead of six steps and 35% yield; it also bypasses two metathesis reactions and avoids the use of tin reagent. 相似文献
72.
Anne‐Catherine Servais Anne Rousseau Marianne Fillet Ketevan Lomsadze Antonio Salgado Jacques Crommen Bezhan Chankvetadze 《Journal of separation science》2010,33(11):1617-1624
In the present study the migration order of the propranolol enantiomers with various native CDs and neutral and charged CD derivatives was examined in capillary electrophoresis (CE). The reversal of the enantiomer migration order was observed due to sulfation of β‐CD on its primary hydroxy groups. The structures of intermolecular selector‐select and temporary diastereomeric associates in solution were elucidated based on 1D rotating frame nuclear Overhauser effect spectroscopy (1D ROESY) experiments. Major structural differences were observed between the propranolol complexes with native β‐CD and heptakis(6‐O‐sulfo)‐β‐CD. 相似文献
73.
Massimo Peruffo Pablo Contreras-Carballada Paolo Bertoncello Ren M. Williams Luisa De Cola Patrick R. Unwin 《Electrochemistry communications》2009,11(10):1885-1887
A method for assembling Pt nanoparticles (5 nm diameter) on indium tin oxide (ITO) and highly oriented pyrolytic graphite (HOPG) electrodes, via the potential-assisted deposition of pre-formed perthiolated-β-cyclodextrin-capped Pt nanoparticles is described. Cyclic voltammetry allowed control over the surface coverage of monodisperse Pt nanoparticles in a simple fashion, as evidenced by the voltammetric response and atomic force microscopy of the resulting electrode surface. The Pt nanoparticle arrays formed in this way were electrocatalytically active towards proton reduction-hydrogen evolution. The methodology described thus opens up a new approach for the deposition of metal nanoparticles with controlled surface density for the investigation of electrocatalytic processes. 相似文献
74.
Santana Rodríguez JJ Halko R Betancort Rodríguez JR Aaron JJ 《Analytical and bioanalytical chemistry》2006,385(3):525-545
The use of organized supramolecular systems—including micellar media and cyclodextrin inclusion complexes—combined with luminescence techniques in the study and determination of compounds and elements of environmental interest from 1990 to 2005 is reviewed. Analyses of environmental samples performed using fluorescence, photochemically induced fluorescence and phosphorescence spectroscopy as well as liquid chromatography, capillary electrophoresis and flow injection with luminescence detection in the presence of these organized media are described in detail. 相似文献
75.
Nilsson C Nilsson F Turner P Sixtensson M Nordberg Karlsson E Holst O Cohen A Gorton L 《Analytical and bioanalytical chemistry》2006,385(8):1421-1429
In this work, a real-time sampling/analytical method for on-line measurements of two newly discovered cyclomaltodextrinases
(CDases) has been developed and evaluated. This novel methodology not only allows the final products to be investigated, but
it also reveals enzyme-specific differences in the degradation pathways during the hydrolysis of different substrates, which
is a great advantage in the important tasks of investigating the mechanisms of and classifying new hydrolases, and is an advantage
that conventional techniques cannot offer. Two different enzymes, one CDase from Laceyella
sacchari (LsCda13) and one from Anoxybacillus flavithermus (AfCda13), were investigated during the hydrolysis of α-, β- and γ-cyclodextrin, and the hydrolysis products were sampled via
a microdialysis probe and injected on-line every 30 min into a high-performance anion exchange chromatography system equipped
with a pulsed amperometric detector (HPAEC–PAD), where they were identified. The enzymes yielded the same end-products, maltose
and glucose, in an approximate molar ratio of 2:1, but they exhibited distinctly different patterns of intermediate product
formation before reaching the end-point. LsCda13 had a more random distribution of the intermediate products, whereas AfCda13 showed the distinct intermediate production of maltotriose, which in some cases accumulated. 相似文献
76.
The influence of temperature on the solvolysis of substituted benzoyl chlorides in the presence of dimethyl-β-cyclodextrin (DM-β-CD) was studied. Based on the influence of the DM-β-CD concentration on chemical reactivity in this process, the cyclodextrin has a catalytic effect on the solvolysis of 4-nitrobenzoyl chloride (4-NO2) but an inhibitory effect on that of 4-methoxy-(4-MeO), 3-chloro-(3-Cl) and 3-trifluoromethyl-(3-CF3) benzoyl chlorides. These disparate effects are related to a difference in reaction mechanism; thus, DM-β-CD catalyses associative solvolysis and inhibits dissociative solvolysis. Examining the influence of temperature on the solvolytic process allowed the stoichiometry of the host-guest complexes formed to be established. The formation constants for the complexes of meta-substituted benzoyl chlorides increased with increasing temperature. On the other hand, the equilibrium formation constants for the 1:1 host-guest complexes of para-substituted benzoyl chlorides exhibited the opposite trend. The equilibrium formation constant for 2:1 host-guest complexes for the para-substituted benzoyl chlorides increased with increasing temperature. These differences are ascribed to the release of water from the DM-β-CD cavity during the formation of the host-guest complex. 相似文献
77.
用分子光谱法研究了甲基-β-环糊精(M-CD)和羟丙基-β-环糊精(HP-CD)与4-(N,N-二甲氨基)-苯甲酸-2′-乙基己基酯(EHDAB)分子间的包结作用.结果表明,柔性的2′-乙基己基和刚性的芳香端都包结在M-CD和HP-CD空腔中,形成了2∶1笼型主-客体包结物.疏水性2′-乙基己基在包结物的热力学稳定性中起重要作用,亲水性M-CD和HP-CD将EHDAB增溶在水中,提高了EHDAB分子的紫外吸收程度,M-CD和HP-CD空腔抑制了光诱导EHDAB分子内扭转电荷转移,显著提高了EHDAB的光化学稳定性,增强了其抗氧化性,降低了酸碱性水解程度,包结物的热稳定性与所用主体环糊精相当. 相似文献
78.
Iványi T Pál K Lázár I Massart DL Vander Heyden Y 《Journal of chromatography. A》2004,1028(2):325-332
Two new diaza-crown ether derivatives (R-1, RS-1) have been synthesized from 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane and tested as potential chiral selectors in capillary electrophoresis (CE) for the chiral separation of five amino acid derivatives. The individual use of the selectors did not lead to chiral differentiation. However, they enhanced the enantioselective effect of different cyclodextrins in dual selector systems. In this paper, we report the effect of different substituted diaza-crown ether derivatives on the separation results obtained in dual systems with cyclodextrins. 相似文献
79.
L. Omar M. I. El-Barghouthi N. A. Masoud A. A. Abdoh M. M. Al Omari M. B. Zughul A. A. Badwan 《Journal of solution chemistry》2007,36(5):605-616
The extent and mode of solubility enhancement exerted by the cyclodextrins (α-, β-, γ-, and HP-β-CDs) on loratadine (Lort) have been experimentally measured under controlled conditions in buffered aqueous solutions. Rigorous
nonlinear regression analysis of the phase solubility diagrams obtained in 0.1 mol⋅L−1 phosphate buffer at pH=7.0 and 25 °C revealed the following: neutral Lort (pK
a
=4.6) tends to form soluble 1:1 and 1:2 Lort/CD complexes with all four of the examined CDs, where complex stability follows
the decreasing order β-CD>HP-β-CD>γ-CD>α-CD. The hydrophobic character of Lort constitutes about 66% of the driving force for complex formation whereas specific interactions
contribute 11.2 kJ⋅mol−1 towards the stability of the complexes. Thermodynamic studies showed that Lort/CD complex formation was favored by large
enthalpic contributions but was impeded by negative entropic changes. Dissolution studies indicate that the dissolution rate
of Lort from the freeze-dried Lort/β-CD complex is significantly higher than that of the corresponding physical mixture. Both DSC studies and molecular mechanical
modeling of Lort/β-CD interactions were carried out to explore the possible formation of inclusion complexes. 相似文献
80.
The effect of β-CD and α-CD on the electrochemical behaviour of H2A and HA− on platinum is studied. The adsorption of β-CD on this electrode is demonstrated and proved to be dependent on the base electrolyte composition. The maximum adsorption coverage was reached in phosphate solution at pH 6.95. The homogeneous H2A---β-CD complex formation produced a decrease in the oxidation current and a positive shift in the oxidation peak potential. These effects are predominant in acid solutions. In neutral solutions the opposite behaviour is observed, i.e. an increase in the oxidation current at lower oxidation potentials. The presence of a parallel oxidation route for the vitamin involving strongly adsorbed CO residues is considered, and evidence for a decrease in COad in the presence of β-CD was given by variations in hydrogen adsorption charges. This fact, more important in neutral solutions, must be responsible for the catalytic effect observed. α-CD was not adsorbed, neither did it modify the electro-oxidation behaviour of H2A and HA−. 相似文献