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991.
Lionel Excoffon Claire Andre Nadine Magy Samuel Limat Yves C. Guillaume 《Chromatographia》2009,70(11-12):1569-1573
In Alzheimer’s disease, it has been proposed that glycosaminoglycans facilitate amyloid fibril formation and/or stabilize the plaque aggregates. Chondroitin sulfates are sulfated glycosaminoglycans represented an ideal distribution of charge for amyloid-β (Aβ) interactions. Recent studies have suggested a possible link between the neurotoxicity of aluminum and the pathogenesis of Alzheimer’s disease. In this paper, the interaction of Aβ with chondroitin sulfates immobilized on a chromatographic column and the role of aluminum had been studied using a biochromatographic approach (molecular chromatography). A novel biochromatographic column was developed in our laboratory for studying this interaction. This study demonstrated that the aluminum interacted with Aβ and played a role in the Aβ/chondroitin sulfates association. For a Al3+ concentration (x) in the medium less than 30 μmM, the Aβ/chondroitin sulfates binding decreased with x due to a decrease of the charge–charge interactions between Aβ and its chondroitin sulfates binding site. Above 30 μmM of Al3+ in the medium, the affinity of Aβ to chondroitin sulfates increased slightly with x because the net number of ions (n) (Al3+ or Cl?) released or bound upon complex formation is low. As well, it was clearly demonstrated, that above 30 μmM the n value depend on the Al3+ concentration in the bulk solvent. This dependence was due to a gradual and conformational change of the Aβ which around 80 μmM adopted a less flexible structure; its binding site was thus less accessible to Aβ and Aβ/chondroitin sulfates association decreased slightly. 相似文献
992.
Hannah Johnson Claire E. Eyers Patrick A. Eyers Robert J. Beynon Simon J. Gaskell 《Journal of the American Society for Mass Spectrometry》2009,20(12):2211-2220
Quantification of the stoichiometry of phosphorylation is usually achieved using a mixture of phosphatase treatment and differential
isotopic labeling. Here, we introduce a new approach to the concomitant determination of absolute protein concentration and
the stoichiometry of phosphorylation at predefined sites. The method exploits QconCAT to quantify levels of phosphorylated
and nonphosphorylated peptide sequences in a phosphoprotein. The nonphosphorylated sequence is used to determine the absolute
protein quantity and serves as a reference to calculate the extent of phosphorylation at the second peptide. Thus, the stoichiometry
of phosphorylation and the absolute protein concentration can be determined accurately in a single experiment. 相似文献
993.
The synthesis and isolation of novel low oxidation state aluminium (Al) compounds has seen relatively slow progress over the 30 years since such species were first isolated. This is largely due to the significant challenges in isolating these thermodynamically unstable compounds. Despite challenges with isolation, their reactivity has been widely explored and they have been utilized in a wide range of processes including the activation of strong chemicals bonds, as ligands to transition metals and in the formation of heterobimetallic M–M compounds. As such, attempts to isolate novel low oxidation state Al compounds have continued in earnest and in the last few years huge advances have been made. In this review we highlight the remarkable recent developments in the low oxidation state chemistry of aluminium and discuss the variety of new reactions these compounds have made possible.Documenting the synthesis and isolation of novel low oxidation state aluminium (Al) compounds, which until recently has seen relatively slow progress over the 30 years since such species were first isolated. 相似文献
994.
Aromatic M?bius [4n]annulenes with 4n pi electrons, originally conceived by Heilbronner, are characterized computationally. These (CH)(12), (CH)(16), and (CH)(20) minima have nearly equal C-C bond lengths, small twist angles around the rings, and magnetic properties (NICS, nucleus-independent chemical shifts--see above at various positions in [16]annulene--and magnetic susceptibility exaltations) indicating significantly diatropic ring currents. The M?bius forms are not the most stable isomers but may contribute significantly to the chemistry of these annulenes. [structure: see text] 相似文献
995.
Hai T. Dong Amy L. Speelman Claire E. Kozemchak Debangsu Sil Carsten Krebs Nicolai Lehnert 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(49):17859-17863
Non‐heme high‐spin (hs) {FeNO}8 complexes have been proposed as important intermediates towards N2O formation in flavodiiron NO reductases (FNORs). Many hs‐{FeNO}8 complexes disproportionate by forming dinitrosyl iron complexes (DNICs), but the mechanism of this reaction is not understood. While investigating this process, we isolated a new type of non‐heme iron nitrosyl complex that is stabilized by an unexpected spin‐state change. Upon reduction of the hs‐{FeNO}7 complex, [Fe(TPA)(NO)(OTf)](OTf) ( 1 ), the N‐O stretching band vanishes, but no sign of DNIC or N2O formation is observed. Instead, the dimer, [Fe2(TPA)2(NO)2](OTf)2 ( 2 ) could be isolated and structurally characterized. We propose that 2 is formed from dimerization of the hs‐{FeNO}8 intermediate, followed by a spin state change of the iron centers to low‐spin (ls), and speculate that 2 models intermediates in hs‐{FeNO}8 complexes that precede the disproportionation reaction. 相似文献
996.
Abstract: A three step synthesis of the advanced glycosylation endproduct 2-(2′-furoyl)-4(5)-(2′-furanyl)-1H-imidazole (4, FFI) has been achieved from 2-acetylfuran. The key step in the synthesis was the rearrangement of the hydrazinium bromide 3 in refluxing methanol. 相似文献
997.
Hélène PLACE Bernard SÉBILLE Claire VIDAL-MADJAR 《Journal of Dispersion Science and Technology》2013,34(4):417-436
This work examines the adsorption of Human Serum Albumin (HSA) on a Reversed-Phase High Performance Liquid Chromatographic (RPLC) support. The adsorption experiments were performed by frontal analysis. Adsorption isotherms were determined in pure buffer and in the presence of acetonitrile. Saturation is always reached, even at the lower protein concentrations. In view of the pore size of the particles (80 Å), it is assumed that HSA is adsorbed on the external surface of silica In presence of acetonitrile, a variability in the amount of HSA adsorbed is found showing a maximum at 25% of acetonitrile. Slower adsorption kinetics are observed when the concentration of the organic modifier in the eluent is increased. The reversibility of HSA binding to the surface was investigated by desorbing the protein with 40% acetonitrile. The amount of HSA irreversibly adsorbed depends upon the experimental conditions used during the adsorption step. It is at a maximum when HSA is adsorbed with 25% acetonitrile. As the temperature is raised and only in the presence of acetonitrile, an important increase of the amount of HSA irreversibly adsorbed is observed. 相似文献
998.
Ribot F Escax V Roiland C Sanchez C Martins JC Biesemans M Verbruggen I Willem R 《Chemical communications (Cambridge, England)》2005,(8):1019-1021
Complexation affinity of laurate ligands (C(12)H(23)O(2)) grafted onto the surface of cerium(IV) oxide nanoparticles can be probed and quantified in situ, by pulsed field gradient (1)H NMR through the dependence of the diffusion coefficient on the size of a species. 相似文献
999.
Alkoxide-functionalized N-heterocyclic carbenes (NHCs) stabilise the potassium-imidazole-2-ylidene fragment against 1,2 alkyl rearrangement reactions; this allows the first structural characterisation of a potassium NHC complex, which reveals distorted and unusual bonding interactions between the imidazole ring and the potassium cation. 相似文献
1000.
Jacquet R Elfakir C Lafosse M 《Rapid communications in mass spectrometry : RCM》2005,19(21):3097-3102
A new methylated beta-cyclodextrin (Me-beta-CD) with a low degree of substitution (DS) was characterized by electrospray ionization mass spectrometry (ESI-MS) and liquid chromatography coupled with ESI-MS (LC/ESI-MS). For ESI-MS analyses, the composition of the infused sample solution was optimized in order to obtain only singly charged ammoniated CDs without fragmentation. The DS value (i.e. the number of methyl groups per glucopyranose unit) was found to be 0.7, which was in accordance with the values previously obtained by other methods. The LC/ESI-MS analysis, derived from a method using evaporative light scattering detection, allowed the study of the substitution isomers of each derivative and appears to be an easy and rapid tool for the accurate characterization of Me-beta-CD mixtures. 相似文献