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151.
Leufgen K Mutter M Vogel H Szymczak W;TOF-SIMS Study 《Journal of the American Chemical Society》2003,125(29):8911-8915
Structure and orientation of molecules are key properties of functionalized surfaces. Using time-of-flight secondary ion mass spectrometry (TOF-SIMS), here we investigate how to modulate these parameters upon the immobilization process varying the conditions of self-assembly. The molecule of interest, a template-assembled synthetic protein (TASP), consists of a central peptide ring with orthogonally arranged residues. Thioalkane chains allow the directed self-assembly of the molecule on a gold surface; four serine residues on the opposite side of the ring can be used as anchoring sites for various functional sensing molecules. The TASP conformation and its orientation in self-assembled monolayers (SAMs) play a central role for the accessibility of these serine residues. To study the influence of the self-assembly conditions, two series of samples were prepared. Pure TASP monolayers of different surface densities are compared to mixed TASP/alkanethiol monolayers prepared by sequential adsorption varying sequence and particular incubation times as well as by coadsorption modifying incubation times and TASP/alkanethiol mass ratios. Switching the TASP orientation from a state where the molecules are lying flat on the surface to an upright orientation turned out to be possible by inserting the TASP into a preformed alkanethiol monolayer of an appropriate surface density. This study demonstrates that TOF-SIMS is an excellent tool not only to investigate the surface composition, but also the molecular structure of functionalized surfaces. 相似文献
152.
Jürgen Dnnecke Wilfried A. Knig Olle Gyllenhaal Jrgen Vessman Christian Schulze 《Journal of separation science》1994,17(11):779-783
Heptakis(2,6-di-O-methyl-3-O-pentyl) (2-O-methyl-6-O-oct-1-enyl-3-O-pentyl)-γ-cyclodextrin was immobilized to narrow-bore fused silica capillaries after selective modification. One tert-butyldimethylsilyl group was introduced into octakis-(2-O-methyl-3-O-pentyl)-γ-cyclodextrin in order to get a pure monofunctionalized cyclodextrin derivative. During synthesis the tert-butyldimethylsilyl group was replaced by an anchoring group to bind the cyclodextrin to a polysiloxane. After thermal immobilization of the modified polysiloxane this new chiral stationary phase was applied in GC and SFC. High efficiency separations were obtained in GC. In SFC very polar compounds could be chromatographed at low temperatures resulting in higher separation factors as compared to GC. 相似文献
153.
Udo Huber Wilhelm Boland Wilfried A. Knig Brbel Gehrcke 《Helvetica chimica acta》1993,76(5):1949-1955
Optically pure(+)-(4S, 4aS, 8aS)-1,2,3,4,4a,5,8,8a-octahydro-4,8a-dimethylnaphthalen-4a-ol((+)- 1 ; dehydrogeosmin) is released from flower heads of the two cactaceae Rebutia marsoneri and Dolichothele spharica. The absolute configuration of (+)- 1 is identical with that of the known microbial metabolial geosmin (?)- 2 . The key reactions of the synthesis of 1 are the kinetically controlled transesterification of the primary alcohol 4 using a lipase from Candida cyclindracea and the stereo-and regiospecific angular alkylation of a cis-decalin skeleton by a Lewis-acid-assisted ring opening of the quaternary epoxy-alcohol 3 with MeMgBr/Cul. The sequence provides a new entry into the class of bis-angularly substituted trans-decalins. 相似文献
154.
Enantiomeric composition of the chiral constituents of essential oils—part 3: Diterpene hydrocarbons
Enantiomeric diterpene hydrocarbons were isolated from different plants and identified by mass spectrometric and NMR investigations. All enantiomeric pairs could be resolved by capillary gas chromatography using either heptakis(2,6-di-O-methyl-3-O-pen-tyl)-β-cyclodextrin or heptakis(6-O-tert-butyldimethylsilyl-2,3-di-O-methyl)-β-cyclodextrin as chiral stationary phases. 相似文献
155.
IfY is a finite graph then it is known that every sufficiently large groupG has a Cayley graph containing an induced subgraph isomorphic toY. This raises the question as to what is sufficiently large. Babai and Sós have used a probabilistic argument to show that |G| > 9.5 |Y|3 suffices. Using a form of greedy algorithm we strengthen this to
(2 + \sqrt 3 )|Y|^3 $$
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. Some related results on finite and infinite groups are included. 相似文献
156.
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159.
Heinz-Dieter Kurland Janet Grabow Gisbert Staupendahl Wilfried Andrä Silvio Dutz Matthias Erich Bellemann 《Journal of magnetism and magnetic materials》2007
Magnetic iron oxide nanopowders were produced with the laser evaporation technique under normal process gas pressure. In addition, the generated particles were coated in situ with stearic acid and separated on magnets. The methods and the used laboratory setup are briefly described. Influences of essential process conditions, particularly the use of continuous and pulsed laser radiation as well as the properties of the process gas, were experimentally investigated. The produced nanopowders were analysed with TEM, XRD, and magnetic measurements and confirmed the in-principle suitability of the presented method. 相似文献
160.
Kpotin Gaston A. Bédé Affoué Lucie Houngue-Kpota Alice Anatovi Wilfried Kuevi Urbain A. Atohoun Guy S. Mensah Jean-Baptiste Gómez-Jeria Juan S. Badawi Michael 《Structural chemistry》2019,30(6):2301-2310
Structural Chemistry - Malaria is an important disease causing many death in several countries of Africa and Asia. In these continents, some plants such as Garcinia cola are used to fight against... 相似文献