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181.
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
182.
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
183.
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
184.
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
185.
R. White P. S. Thomas M. R. Philips R. Wuhrer J. P. Guerbois 《Journal of Thermal Analysis and Calorimetry》2007,88(1):181-184
The deleterious interaction
of some traditional sulphide artists pigments and copper ions results in the
formation of black copper sulphides, in particular, covellite (CuS), and,
hence, the discolouration of valuable artworks. In this paper the interaction
of malachite, a source of copper(II) ions, with the pigment cadmium yellow,
a sulphide pigment comprising of a solid solution of cadmium and zinc sulphides,
is investigated by XRD and TG-MS. XRD showed the presence of the copper sulphide
and cadmium carbonate phases, produced by a simple ion exchange mechanism.
TG-MS showed the complexity of the range of metastable phases produced. The
identification of these phases, however, requires further work. 相似文献
186.
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 $$
" align="middle" border="0">
. Some related results on finite and infinite groups are included. 相似文献
187.
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190.
David A. Philips Riccardo Rossi Gianluca Iaccarino 《International Journal of Heat and Fluid Flow》2011,32(5):943-963
A numerical study of scalar dispersion is presented to investigate the effectiveness of pairing the v2–f turbulence model with algebraic models for the scalar flux. This approach is contrasted with utilizing a full Second Moment Closure (SMC) as the flow field input to the scalar model. Predictions of scalar transport in a turbulent channel and over a wavy wall are compared to available DNS databases. The latter case includes a scalar release from a point source and therefore detailed comparisons of the three-component turbulent scalar flux are reported. It is found that the transported variable v2, representing the near wall turbulent velocity fluctuation scale, can be used to increase the level of normal stress anisotropy provided to algebraic scalar models and thereby improve mean scalar prediction over that of the Standard Gradient Diffusion Hypothesis (SGDH). Improvement is most significant in the near wall region. Three specifications of the normal stresses, derived from v2, are considered to provide the link from the v2–f model to the algebraic flux models used to close the scalar transport equation. Barycentric maps are used to examine the state of turbulence anisotropy in each case. As the anisotropy in the normal stress specification becomes more accurate, improvements are realized in the prediction of the spanwise flux as well as the mean concentration. 相似文献