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161.
We show that if a manifold $M$ admits a contact structure, then so does $M \times S^2$ . Our proof relies on surgery theory, a theorem of Eliashberg on contact surgery and a theorem of Bourgeois showing that if $M$ admits a contact structure then so does $M \times T^2$ . 相似文献
162.
163.
Kristensen EM Nederberg F Rensmo H Bowden T Hilborn J Siegbahn H 《Langmuir : the ACS journal of surfaces and colloids》2006,22(23):9651-9657
The structure of a biomimetic phosphorylcholine (PC)-functionalized poly(trimethylene carbonate) (PC-PTMC-PC), linked to a silicon substrate through an aminolysis reaction at 120 degrees C with (3-aminopropyl)trimethoxysilane (APTMS), was studied using photoelectron spectroscopy. Two chemical states were found for the unreacted APTMS amine, a neutral state and a protonated state, where the protonated amine on average was situated closer to the silicon substrate than the neutral amine. The experiments also indicated the presence of a third chemical state, where amines interact with unreacted silanol groups. The PTMC chains of the grafted films were found to consist of only 2-3 repeat units, with the grafted chains enriched in the zwitterionic end group, suggesting that these groups are attracted to the surface. This was further supported by the experiments showing that the PC groups were situated deeper within the film. 相似文献
164.
The contact domain utilized by horse cytochrome c when adsorptively bound to a C(10)COOH self-assembled monolayer (SAM) was delineated using a chemical method based on differential modification of surface amino acids. Horse cytochrome c was adsorbed at low ionic strength (pH 7.0, 4.4 mM potassium phosphate) onto 10 microm diameter gold particles coated with HS(CH(2))(10)COOH SAMs. After in situ modification of lysyl groups by reductive Schiff-base methylation, the protein was desorbed, digested using trypsin, and the peptide mapped using LC/MS. Relative lysyl reactivities were ascertained by comparing the resulting peptide frequencies to control samples of solution cytochrome c modified to the same average extent. The least reactive lysines in adsorbed cytochrome c were found to be 13, 72, 73, 79, and 86-88, consistent with a contact region located up and to the left (Met-80 side) of the solvent-exposed heme edge (conventional front face view). The most reactive lysines were 39, 53, 55, and 60, located on the lower backside. The proposed orientation features a heme tilt angle of approximately 35-40 degrees with respect to the substrate surface normal. Factors that can complicate or distort data interpretation are discussed, and the generality of differential modification relative to existing in situ methods for protein orientation determination is also addressed. 相似文献
165.
The Grubbs' first and second generation catalysts were occluded into cross-linked slabs of polydimethylsiloxane with volumes from 1 mm3 to 1 cm3 by swelling the polymer with catalyst and methylene chloride. Methylene chloride was evaporated under vacuum to yield occluded catalysts where their solvent was polydimethylsiloxane. These occluded catalysts were reacted with alkenes dissolved in H2O or H2O/MeOH mixtures that diffused into the polydimethylsiloxane to react by ring-closing metathesis and cross metathesis. Control experiments revealed that the catalysts remained occluded and metathesis did not occur in the solvent. Occlusion of these catalysts allowed commercially available Grubbs' catalysts to be used with H2O as the solvent while isolating the H2O sensitive ruthenium methylidene from exposure to H2O. Functional group selective experiments were carried out where the polydimethylsiloxane was an "active" membrane to exclude salts. Polydimethylsiloxane is a hydrophobic polymer, so the deprotonated salt of diallylmalonic acid did not diffuse into it while a diallylether diffused into it and reacted by metathesis. Thus, by controlling the polarity of reagents their reactivity can be controlled owing to the properties of polydimethylsiloxane rather than those of the Grubbs' catalysts. Occlusion of catalysts in polydimethylsiloxane has been shown to add new selectivities to mature catalysts. 相似文献
166.
Dr. Biao Jin Ying Chen Jinhui Tao Dr. Kacper J. Lachowski Mark E. Bowden Zihao Zhang Dr. Lilo D. Pozzo Nancy M. Washton Karl T. Mueller James J. De Yoreo 《Angewandte Chemie (International ed. in English)》2023,62(28):e202303770
Hierarchical nucleation pathways are ubiquitous in the synthesis of minerals and materials. In the case of zeolites and metal–organic frameworks, pre-organized multi-ion “secondary building units” (SBUs) have been proposed as fundamental building blocks. However, detailing the progress of multi-step reaction mechanisms from monomeric species to stable crystals and defining the structures of the SBUs remains an unmet challenge. Combining in situ nuclear magnetic resonance, small-angle X-ray scattering, and atomic force microscopy, we show that crystallization of the framework silicate, cyclosilicate hydrate, occurs through an assembly of cubic octameric Q38 polyanions formed through cross-linking and polymerization of smaller silicate monomers and other oligomers. These Q38 are stabilized by hydrogen bonds with surrounding H2O and tetramethylammonium ions (TMA+). When Q38 levels reach a threshold of ≈32 % of the total silicate species, nucleation occurs. Further growth proceeds through the incorporation of [(TMA)x(Q38)⋅n H2O](x−8) clathrate complexes into step edges on the crystals. 相似文献