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71.
D Jiang I Rauda S Han S Chen F Zhou 《Langmuir : the ACS journal of surfaces and colloids》2012,28(35):12711-12721
Amyloid β (Aβ) fibrils are present as a major component in senile plaques, the hallmark of Alzheimer's disease (AD). Diffuse plaques (nonfibrous, loosely packed Aβ aggregates) containing amorphous Aβ aggregates are also formed in brain. This work examines the influence of Cu(2+) complexation by Aβ on the aggregation process in the context of charge and structural variations. Changes in the surface charges of Aβ molecules due to Cu(2+) binding, measured with a ζ-potential measurement device, were correlated with the aggregate morphologies examined by atomic force microscopy. As a result of the charge variation, the "colloid-like" stability of the aggregation intermediates, which is essential to the fibrillation process, is affected. Consequently, Cu(2+) enhances the amorphous aggregate formation. By monitoring variations in the secondary structures with circular dichroism spectroscopy, a direct transformation from the unstructured conformation to the β-sheet structure was observed for all types of aggregates observed (oligomers, fibrils, and/or amorphous aggregates). Compared to the Aβ aggregation pathway in the absence of Cu(2+) and taking other factors affecting Aβ aggregation (i.e., pH and temperature) into account, our investigation indicates that formations of amorphous and fibrous aggregates diverge from the same β-sheet-containing partially folded intermediate. This study suggests that the hydrophilic domain of Aβ also plays a role in the Aβ aggregation process. A kinetic model was proposed to account for the effects of the Cu(2+) binding on these two aggregation pathways in terms of charge and structural variations. 相似文献
72.
DA Rusling IS Nandhakumar T Brown KR Fox 《Chemical communications (Cambridge, England)》2012,48(77):9592-9594
The triplex approach to DNA recognition is exploited to direct covalent inter-strand cross-links to unique locations within a pre-assembled DNA nanostructure. This approach can be used to improve the stability of DNA nanostructures and demonstrates the feasibility of directing other reactive groups to unique locations within these complexes. 相似文献
73.
Norbert Moszner Juraj Pavlinec Iris Lamparth Frank Zeuner Jrg Angermann 《Macromolecular rapid communications》2006,27(14):1115-1120
Summary: 1,3‐Bis(methacrylamido)propane‐2‐yl dihydrogen phosphate ( 1 ) was synthesised by phosphorylation of 1,3‐bis(methacrylamido)‐2‐hydroxypropane ( 2 ) with phosphorus oxychloride in tetrahydrofuran (THF) in the presence of triethylamine (TEA). The structure of the new monomer 1 was characterised by IR, 1H NMR, 13C NMR and 31P NMR spectroscopies, elemental analysis and mass spectrometry. The monomer dissolves well in water, ethanol or aqueous THF and shows an improved hydrolytic stability compared to the corresponding methacrylate‐based dihydrogen phosphates. 1 was homopolymerised in ethanol with 2,2′‐azoisobutyronitrile (AIBN) as the initiator at 55–75 °C under the formation of an insoluble, cross‐linked product. Aqueous solutions of 1 are strongly acidic and enable to etch enamel and dentin. Nevertheless, 1 did not show any cytotoxic effect. Furthermore, the adhesive properties of 1 were measured.
74.
75.
Cyprian M. Chunkang Iris E. Ikome Emmanuel N. Nfor Yuta Mitani Natsuki Katsuumi Tomoyuki Haraguchi Takashiro Akitsu 《Molecules (Basel, Switzerland)》2020,25(23)
Single crystals of two achiral and planar heterocyclic compounds, C9H8H3O(CA1) and C8H5NO2 (CA4), recrystallized from ethanol, were characterized by single crystal X-ray analysis, respectively, and chiral crystallization was observed only for CA1 as P212121 (# 19), whereas it was not observed for CA4 P21/c (# 14). In CA1, as a monohydrate, the hydrogen bonds were pronounced around the water of crystallization (O4), and the planar cyclic sites were arranged in parallel to slightly tilted positions. On the other hand, an anhydride CA4 formed a dimer by hydrogen bonds between adjacent molecules in the crystal, which were aggregated by van der Waals forces and placed in parallel planar cyclic sites. 相似文献
76.
A. Carel N. Kwamen Marcel Schlottmann Dr. David Van Craen Dr. Elisabeth Isaak Julia Baums Li Shen Ali Massomi Dr. Christoph Räuber Benjamin P. Joseph Prof. Dr. Gerhard Raabe Dr. Christian Göb Prof. Dr. Iris M. Oppel Dr. Rakesh Puttreddy Dr. Jas S. Ward Prof. Dr. Kari Rissanen Dr. Roland Fröhlich Prof. Dr. Markus Albrecht 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(6):1396-1405
The dissociation of hierarchically formed dimeric triple lithium bridged triscatecholate titanium(IV) helicates with hydrocarbyl esters as side groups is systematically investigated in DMSO. Primary alkyl, alkenyl, alkynyl as well as benzyl esters are studied in order to minimize steric effects close to the helicate core. The 1H NMR dimerization constants for the monomer–dimer equilibrium show some solvent dependent influence of the side chains on the dimer stability. In the dimer, the ability of the hydrocarbyl ester groups to aggregate minimizes their contacts with the solvent molecules. Due to this, most solvophobic alkyl groups show the highest dimerization tendency followed by alkenyls, alkynyls and finally benzyls. Furthermore, trends within the different groups of compounds can be observed. For example, the dimer is destabilized by internal double or triple bonds due to π–π repulsion. A strong indication for solvent supported London dispersion interaction between the ester side groups is found by observation of an even/odd alternation of dimerization constants within the series of n-alkyls, n-Ω-alkenyls or n-Ω-alkynyls. This corresponds to the interaction of the parent hydrocarbons, as documented by an even/odd melting point alternation. 相似文献
77.
78.
Iris Blankenhorn Dirk Meijer Robert J. Delft 《Fresenius' Journal of Analytical Chemistry》1992,343(6):497-504
Summary In view of the investigation of contaminated model sites in Baden-Württemberg an inter-laboratory comparison was organized for the methods used for analysing polycyclic aromatic hydrocarbons (PAHs). The laboratories performing chemical and physical analyses at the model sites participated at the request of the Landesanstalt für Umweltschutz, Baden-Württemberg. This inter-laboratory comparison was meant as a first laboratory evaluation, and not as the search for the best method available. Furthermore, it was to show the difficulties in comparing results from different laboratories, which have analysed identical samples. The results of the inter-laboratory comparison between the nine laboratories showed a reproducibility coefficient of variation, for the total of the 16 PAHs according to the EPA, between 48.8 and 61.1% in the concentration range of 5 to 55 mg/kg in the soil samples. One of the laboratories reported significantly lower values compared with the true value. This was probably due to an ill-suited (sample) preparation method. Although the results of the inter-laboratory comparison are, in general, satisfactory, the reproducibility can be improved by standardizing the analytical method for the determination of PAHs in solid environmental samples. 相似文献
79.
Wolfbeis Otto S. Ziegler Erich Knierzinger Andreas Wipfler Helmut Trummer Iris 《Monatshefte für Chemie / Chemical Monthly》1980,111(1):93-112
In a two step procedure and in usually good yield an -pyrone ring can be annelated to (enolized) cyclic -dicarbonyl compounds like 4-hydroxy-2-pyrones, 4-hydroxycoumarins, 4-hydroxy-2-quinolones and more complex malonylheterocycles, but also to -naphthole.In a first step the combined action of triethyl orthoformate and arylamines upon the dicarbonyl system affords the anilinomethylene derivativesB in usually high yields.B is reacted with an active methylene nitrile (like alkyl cyano-acetates) and one equivalent of a strong base (like sodium methoxide or potassium hydroxide) in a polar aprotic solvent (like dimethylformamide). Subsequent acidification with dilute aqueous acid gives the corresponding -pyroneD with yields from 18 to 84%.The reaction sequence is broadly applicable, which is demonstrated by the synthesis of a series of known (3, 7, 16, 31) and novel (10, 19, 22, 25, 28, 34) heterocyclic systems. Most of them exhibit strong fluorescence in the visible with emission maxima between 450 and 510 nm.
208. Mitt.:H. Wittmann undF. Günzl, Z. Naturforsch.33b, 1540 (1978). 相似文献
80.
Roland A. Fischer Dana Weiß Iris Müller Nikolaus Fröhlich Gernot Frenking 《Journal of organometallic chemistry》2004,689(24):4611-4623
The reactions of the sterically demanding group-13 alkyls ER3 (E = Al, Ga, In; R = CH2t-Bu, CH2SiMe3) with the platinum-complex [(dcpe)Pt(H)(CH2t-Bu)] were re-investigated. The bimetallic compounds [(dcpe)Pt(ER2)(R)] (3: E = Ga, R = CH2SiMe3; 5: E = In, R = CH2t-Bu; dcpe = bis(dicyclohexylphosphino)ethane) with direct σ(Pt-E) bonds were obtained by oxidative addition of an E-C bond to the coordinatively unsaturated fragment [(dcpe)Pt] produced in situ by thermolysis of the starting complex [(dcpe)Pt(CH2t-Bu)(H)]. The single crystal structure determination reveals a Pt-Ga bond length of 2.376(2) Å and a Pt-In bond length of 2.608(1) Å. All new compounds were characterised by elemental analysis, 31P and 195Pt NMR spectroscopy. Interestingly, the Pt-Ga compound 3 slowly transforms into the platinum alkyl/hydride isomer {(dcpe)Pt(μ2-H)[CH2Si(CH3)2 CH2Ga(CH2SiMe3)2]} (4) during crystallization from solution at room temperature. The X-ray single crystal structure analysis revealed both complexes 3 and 4 coexisting in the unit cell in a 1:1 relation. The inaccessibility of analytically pure samples of the Pt-Al complex {(dcpe)Pt[Al(CH2t-Bu)2](CH2t-Bu)} (6), postulated as intermediate of the reaction of [(dcpe)Pt(H)(CH2t-Bu)] with Al(CH2t-Bu) on the basis of 31P and 195Pt NMR data, is attributed to an enhanced tendency to isomerisation into the alkyl/hydride Pt/Al congener of 4. A brief DFT analysis of the bonding situation of the model complex [(dhpe)Pt(GaMe2)(Me)] (1M) revealed, that the contribution of π(Pt-Ga) back-bonding is negligible. 相似文献