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201.
Douglas L. Cassimiro Leonardo M. B. Ferreira Ana Luiza R. de Souza Mariana Fonseca Suzy S. S. Kurokawa Jovan D. Alonso Victor Hugo V. Sarmento Clovis Augusto Ribeiro 《Journal of Thermal Analysis and Calorimetry》2018,134(3):1599-1609
Supramolecular gels are soft materials formed mainly by low molecular weight units held together by intermolecular interactions. Stabilizing these kinds of materials is quite a challenge due to the influence of multiple factors interfering with the integrity of the supramolecular structure. In our previous studies, we have shown that the aminocarbohydrate meglumine (MEG) interacts with organic acids by ion-pairing leading to the formation of MEG–carboxylate adducts. These adducts undergo supramolecular polymerization by heat treatment, but the macromolecular assembly was stable for a short period due to hydrogen bond (H-bond) breakup. Herein, we attempt to study the influence of hydrophobic building blocks on the formation of these compounds aiming to stabilize H-bonds to produce polymerizable supra-amphiphiles in water. Oleic acid and stearic acid are two analogous fatty acids differing only in the presence of unsaturation that were used in our studies. Results demonstrated that the presence of unsaturation hinders gelation in water by interfering with the self-assembly behavior of supra-amphiphiles. Thus, unsaturated supra-amphiphiles behave like traditional surfactants and gelify water at high concentrations (above 30% w/w). On the other hand, supramolecular gels with a polymer-like behavior could be produced with a saturated supra-amphiphile in water (above 4% w/w). The material was characterized by a lamellar arrangement that facilitates the alignment of H-bonds necessary to stabilize the self-assembled structure. These results have pivotal importance on the design of polymerizable supra-amphiphiles and demonstrate that the double bond of hydrophobic building blocks is an important design factor to be considered by scientists studying similar materials. 相似文献
202.
Hugo Hermann 《Fresenius' Journal of Analytical Chemistry》1905,44(11):686-698
Zusammenfassung Aus den angeführten Versuchen geht hervor, dass die analytische Bestimmung gasförmiger Verbindungen durch Absorption in Schiffchen, welche entsprechend beschickt und in die Bahn des Gasstromes gebracht werden, sehr gute Resultate liefern kann. (Siehe Stickstoff, Jod.)Bei der Elementaranalyse organischer Körper wurde jedoch der Einfluss des Glasrohres und der Kontaktsubstanz zu wenig gewürdigt und deshalb übersehen, dass infolge der Absorption von Schwefelsäure, beziehungsweise Halogenen, durch diese beiden beträchtliche Fehler gemacht werden können.Diese Untersuchung wurde auf Veranlassung des Herrn Professor Dr. Georg Vortmann ausgeführt. Es sei mir gestattet, meinem hochverehrten Lehrer auch an dieser Stelle für alle Förderung, die ich durch ihn erfahren, meinen tiefgefühlten Dank zu sagen.Wien, analytisches Laboratorium der technischen Hochschule. 相似文献
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205.
Lubin-Germain N Baltaze JP Coste A Hallonet A Lauréano H Legrave G Uziel J Augé J 《Organic letters》2008,10(5):725-728
Indium-mediated alkynylation reaction was studied for the direct preparation of C-glycosides. Easily available starting sugar derivatives with an acetyl group at the anomeric position were tested as electrophiles toward alkynylindium reagents under Barbier conditions. Good yields and stereoselectivities were observed during the reaction. The alkynylation was applied to the synthesis of an alpha-(1-->6)-C-disaccharide analogue of isomaltoside. 相似文献
206.
Hugo Aduén 《Journal of Mathematical Analysis and Applications》2008,337(1):348-359
Here we establish the existence of infinitely many nonradial solutions for a superlinear Dirichlet problem in annulii. Our proof relies on estimating the number of radial solutions having a prescribed number of nodal regions. We prove that, for k>0 large, there exist exactly two radial solutions with k nodal regions (connected components of ). The problem need not be homogeneous. 相似文献
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208.
Hugo Lachance 《Tetrahedron letters》2008,49(42):6061-6064
A synthetic approach to the polysubstituted pyran core and amide side chain of psymberin (irciniastatin A) using stereoselective organoboron methodology is described. An advanced oxyranyl pyran intermediate was prepared using a catalytic enantioselective and diastereoselective three-component reaction involving first an inverse electron-demand hetero [4+2] cycloaddition between 3-boronoacrolein pinacolate and 1-ethoxy-2-methylpropene, followed by an allylboration of ethyl glyoxylate. The amide side chain was prepared highly efficiently using the first example of a doubly diastereoselective allylboration of a chiral α-alkoxy aldehyde under the Lewis acid-catalyzed reaction manifold. 相似文献
209.
Victor Hugo Infante Patricia Maria Maia Campos Maxim Darvin Silke Lohan Johannes Schleusener Sabine Schanzer Juergen Lademann Martina Meinke 《Photochemistry and photobiology》2023,99(1):176-183
This aim of this study was to evaluate the penetration depth, antioxidant capacity and the clinical efficacy of Melaleuca alternifolia pure essential oil and in a nanoemulsion to prevent skin photoaging. For this, 2% of pure essential oil or 2% of this essential oil in a nanoemulsion were vehiculated in a formulation. The skin penetration was evaluated using confocal Raman microspectroscopy. The radical protection factor was evaluated using electron paramagnetic resonance spectroscopy. For a clinical study, 40 male participants, aged 18–28 years, were enrolled, being divided into three groups: vehicle formulation, M. alternifolia pure essential oil and M. alternifolia Nanoemulsion. All the participants also received a sunscreen SPF 50 to use during the day. Before and after 90 days of study, skin hydrolipidics and morphological characteristics were performed by skin imaging and biophysical techniques. The nanoemulsion presented a lower antioxidant capacity and a higher penetration through the stratum corneum, reaching the viable epidermis, improving the stratum granulosum morphology. The groups presented an increase in the papillary depth, improving in the dermis echogenicity and the collagen fibers. Melaleuca alternifolia essential provides the potential to improve photoaged skin, being the application of nanoemulsion able to reach deeper skin layers. 相似文献
210.