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991.
Prof. Dariush Ajami Giannoula Theodorakopoulos Ioannis D. Petsalakis Prof. Julius Rebek Jr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(50):17092-17096
Encapsulation complexes permit the observation of molecules under conditions of limited motion. Inside capsules, molecular encounters are prolonged, prearranged, and protected from the medium, in contrast to the short‐lived and random encounters that occur in bulk solution. Herein, the interaction of α‐, β‐, and γ‐picolines in a cylindrical capsule is described. Two picolines were taken up, and NMR spectra indicated dynamic combinations of various social isomers. The stabilities of the complexes are interpreted through computational methods. The shape of the space in the capsule allowed the alignment of molecules and revealed delicate, atom‐to‐atom interactions and attractive forces that elude observation in dilute solution. These weak forces were amplified in the isolated small space of the capsule. 相似文献
992.
Jean-Pierre Cuif Azzedine Bendounan Yannicke Dauphin Julius Nouet Fausto Sirotti 《Analytical and bioanalytical chemistry》2013,405(27):8739-8748
Organic compounds have been extracted from calcium carbonate skeletons produced by three invertebrate species belonging to distinct phyla. The soluble parts of these skeleton matrices were isolated and analysed by synchrotron-based X-ray spectroscopy (XPS). The presence of calcium associated with these organic materials was revealed in every sample studied, with important variations in Ca 2p binding energy from species to species. Measured Ca 2p binding energy values are more related to compositional diversity of the mineralizing matrices of the skeletons, whose taxonomic dependence has long been established, than to the Ca carbonate polymorph selected to build the skeletal units. This suggests a physical bond between species-specific mineralizing organic assemblages and the associated calcium. Remarkably, the binding energy of 2p electrons in calcium associated with mineralizing matrices is consistently higher than Ca 2p values obtained in purely mineral carbonate (both calcite and aragonite). The ability both to identify and measure the effect of organic matrices on their mineral counterpart in calcareous biominerals opens a new perspective for a functional approach to the biomineralization process. 相似文献
993.
Embrechts A Velders AH Schönherr H Vancso GJ 《Langmuir : the ACS journal of surfaces and colloids》2011,27(23):14272-14278
The recognition of self-complementary quadruple urea-aminotriazine (UAT)-based hydrogen-bonded arrays was investigated in solution and at surfaces. For this purpose, an UAT-based donor-acceptor-donor-acceptor (DADA) array and complementary receptors were synthesized. Two-dimensional proton nuclear magnetic resonance ((1)H NMR) measurements in CDCl(3) pointed at an intramolecular hydrogen-bond stabilization of the UAT, which promotes a planar molecular geometry and, thereby, results in a significant stabilization of the dimeric complex. The bond strength of the UAT dimers at surfaces was determined by atomic force microscopy-based single molecule force spectroscopy (AFM-SMFS) in hexadecane. The UAT receptor was immobilized on gold surfaces using an ultrathin layer of ethylene glycol terminated lipoic acid and isocyanate chemistry. The layers obtained and the reversible self-complementary recognition were thoroughly characterized with contact angle measurements, grazing angle Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and AFM. Loading rate-dependent SMFS measurements yielded a barrier width x(β) and a bond lifetime at zero force t(off)(0) of 0.29 ± 0.02 nm and 100 ± 80 ms, respectively. The value of the corresponding off-rate constant k(off) suggests a substantially larger value of the dimerization constant compared to theoretical predictions, which is fully in line with the additional intramolecular hydrogen-bond stabilization detected in solution by (1)H NMR spectroscopy. 相似文献
994.
A deep water-soluble cavitand was functionalized with a carboxylic acid directed toward the hydrophobic interior of the host. The buried salt-bridge interaction formed with a quinuclidium cationic guest was determined to be worth -3 kcal/mol using a free energy cycle. The strength of the interaction correlates well with buried salt bridges in proteins, indicating that the cavitand interior mimics the hydrophobic inner space of proteins. 相似文献
995.
Guibin Ma Andrey Ilyukhin Julius Glaser 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(12):1473-1475
The title compound, [H2bipy](ClO4)2 or C10H10N22+·2ClO4?, was obtained at the interface between an organic (2,2′‐bipyridine in methanol) and an aqueous phase (perchloric acid in water). The compound crystallizes in space group P and comprises discrete diprotonated trans‐bipyridinium cations, [H2bipy]2+, and ClO4? anions. The cations and anions are connected through N—H?O and C—H?O hydrogen bonds [distances N?O 2.817 (4) and 2.852 (4) Å, and C?O 3.225 (6)–3.412 (5)Å]. The C—C bond distance between the two rings is 1.452 (5) Å. The bipyridinium cation has a trans conformation and the N—C—C—N torsion angle is 152.0 (3)°. 相似文献
996.
Christelle TD Hussainb H Dongo E Julius OE Hussain J 《Natural product communications》2011,6(8):1135-1136
Cordia platythyrsa Baker is known for its medicinal value. This paper deals with a phytochemical investigation of this species, from which cordioxime (1), a new dioxime y-lactam has been isolated. Its structure was determined by comprehensive analyses of its 1H and 13C NMR, COSY, HMQC, and HMBC spectroscopic, and HREIMS data. The remaining two known compounds were identified as beta-sitosterol, and beta-sitosterol glucopyranoside. 相似文献
997.
The natural automorphism group of a translation surface is its group of translations. For finite translation surfaces of genus g ≥ 2 the order of this group is naturally bounded in terms of g due to a Riemann–Hurwitz formula argument. In analogy with classical Hurwitz surfaces, we call surfaces which achieve the maximal bound Hurwitz translation surfaces. We study for which g there exist Hurwitz translation surfaces of genus g. 相似文献
998.
999.
Julius Löwe 《Fresenius' Journal of Analytical Chemistry》1875,14(1):117-130
Ohne Zusammenfassung 相似文献
1000.
Balázs Imre Dániel Bedő Attila Domján Peter Schön G. Julius Vancso Béla Pukánszky 《European Polymer Journal》2013
Polyurethane elastomers are promising candidates for the impact modification of PLA producing blends for example for biomedicine. Poly(lactic acid) (PLA)/polyurethane elastomer (PU) blends were prepared by reactive processing and physical blending as comparison. The blends were characterized by a number of techniques including microscopy (scanning electron microscopy, SEM, and atomic force microscopy, AFM), rotational viscometry, thermal (dynamic mechanical analysis, DMA), and mechanical (tensile) measurements. The analysis and comparison of the structure and properties of physical and reactor blends proved the successful coupling of the phases. Coupling resulted in more advantageous structure and superior mechanical properties compared to those of physical blends as confirmed by morphology, macroscopic properties and the quantitative estimation of interfacial interactions. Structural studies and the composition dependence of properties indicated the formation of a submicron, phase-in-phase structure which positively influenced properties at large PU contents. The results strongly support that reactive processing is a convenient, cost-effective and environmentally friendly technique to obtain blends with superior properties. 相似文献