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111.
Dietrich PM Horlacher T Girard-Lauriault PL Gross T Lippitz A Min H Wirth T Castelli R Seeberger PH Unger WE 《Langmuir : the ACS journal of surfaces and colloids》2011,27(8):4808-4815
Carbohydrate films on gold based on dimannoside thiols (DMT) were prepared, and a complementary surface chemical analysis was performed in detail by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), near-edge X-ray absorption fine structure (NEXAFS), FT-IR, and contact angle measurements in order to verify formation of ω-carbohydrate-functionalized alkylthiol films. XPS (C 1s, O 1s, and S 2p) reveals information on carbohydrate specific alkoxy (C-O) and acetal moieties (O-C-O) as well as thiolate species attached to gold. Angle-resolved synchrotron XPS was used for chemical speciation at ultimate surface sensitivity. Angle-resolved XPS analysis suggests the presence of an excess top layer composed of unbound sulfur components combined with alkyl moieties. Further support for DMT attachment on Au is given by ToF-SIMS and FT-IR analysis. Carbon and oxygen K-edge NEXAFS spectra were interpreted by applying the building block model supported by comparison to data of 1-undecanethiol, poly(vinyl alcohol), and polyoxymethylene. No linear dichroism effect was observed in the angle-resolved C K-edge NEXAFS. 相似文献
112.
Pierre-Luc Girard-Lauriault Juan-Carlos Ruiz Thomas Gross Michael R. Wertheimer Wolfgang E. S. Unger 《Plasma Chemistry and Plasma Processing》2011,31(4):535-550
Nitrogen (N)-rich organic thin films were deposited using both low-pressure plasma- and vacuum-ultraviolet-based techniques, from mixtures of ammonia (NH3) and ethylene (C2H4). These films were investigated using angle-resolved and excitation energy resolved X-ray photoelectron spectroscopy (ARXPS and ERXPS, respectively) in order to determine their sub-surface chemical profiles. These two techniques enable one to tune the ??XPS 95%?? information depth, z 95%, by varying either the angle or the excitation energy. Using a combination of both techniques, z 95% can be varied continuously from 0.7 to 11 nm. The surface-near chemistry is investigated using both high-resolution C 1s spectra and elemental concentrations derived from elemental peak intensities. Results show that while laboratory XPS, and even ARXPS, suggest homogenous surface chemistries, the novel combination of ARXPS and ERXPS points to the existence of a compositional profile in the extreme outer surface layer. Our conclusions are supported by simulations using SESSA software. 相似文献
113.
Börner J Vieira Idos S Pawlis A Döring A Kuckling D Herres-Pawlis S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(16):4507-4512
Zinc bis(chelate) guanidine complexes promote living lactide polymerization at elevated temperatures. By means of kinetic and spectroscopic analyses the mechanism has been elucidated for these special initiators that make use of neutral N-donor ligands. The neutral guanidine function initiates the polymerization by a nucleophilic ring-opening attack on the lactide molecule. DFT calculations on the first ring-opening step show that the guanidine is able to act as a nucleophile. Three transition states were located for ligand rearrangement, nucleophilic attack, and ring-opening. The second ring-opening step was modeled as a representation for the chain growth because here, the lactate alcoholate opens the second lactide molecule via two transition states (nucleophilic attack and ring-opening). Additionally, the resulting reaction profile proceeds overall exothermically, which is the driving force for the reaction. The experimental and calculated data are in good agreement and the presented mechanism explains why the polymerization proceeds without co-initiators. 相似文献
114.
Stanković S Catak S D'hooghe M Goossens H Abbaspour Tehrani K Bogaert P Waroquier M Van Speybroeck V De Kimpe N 《The Journal of organic chemistry》2011,76(7):2157-2167
The synthetic utility of N-alkylidene-(2,3-dibromo-2-methylpropyl)amines and N-(2,3-dibromo-2-methylpropylidene)benzylamines was demonstrated by the unexpected synthesis of 3-methoxy-3-methylazetidines upon treatment with sodium borohydride in methanol under reflux through a rare aziridine to azetidine rearrangement. These findings stand in contrast to the known reactivity of the closely related N-alkylidene-(2,3-dibromopropyl)amines, which are easily converted into 2-(bromomethyl)aziridines under the same reaction conditions. A thorough insight into the reaction mechanism was provided by both experimental study and theoretical rationalization. 相似文献
115.
Unger EL Morandeira A Persson M Zietz B Ripaud E Leriche P Roncali J Hagfeldt A Boschloo G 《Physical chemistry chemical physics : PCCP》2011,13(45):20172-20177
The hole transporting medium in solid-state dye-sensitized solar cells can be utilized to harvest sunlight. Herein we demonstrate that a triphenylamine-based dye, used as hole-transporting medium, contributes to the photocurrent in a squaraine-sensitized solid-state dye-sensitized solar cell. Steady-state photoluminescence measurements have been used to distinguish between electron transfer and energy transfer processes leading to energy conversion upon light absorption in the hole-transporting dye. 相似文献
116.
Background
The extent of similarity between consolidation and reconsolidation is not yet fully understood. One of the differences noted is that not every brain region involved in consolidation exhibits reconsolidation. In trace fear conditioning, the hippocampus and the medial prefrontal cortex (mPFC) are required for consolidation of long-term memory. We have previously demonstrated that trace fear memory is susceptible to infusion of the protein synthesis inhibitor anisomycin into the hippocampus following recall. In the present study, we examine whether protein synthesis inhibition in the mPFC following recall similarly results in the observation of reconsolidation of trace fear memory. 相似文献117.
118.
Weakly hyperbolic involutions are introduced and a proof is given of the following local–global principle: a central simple
algebra with involution of any kind is weakly hyperbolic if and only if its signature is zero for all orderings of the ground
field. Also, the order of a weakly hyperbolic algebra with involution is a power of two, this being a direct consequence of
a result of Scharlau. As a corollary an analogue of Pfister's local–global principle is obtained for the Witt group of hermitian
forms over an algebra with involution.
Received: 29 October 2001; in final form: 9 August 2002 /
Published online: 16 May 2003
Mathematics Subject Classification (2000): 16K20, 11E39 相似文献
119.
We consider a continuum model describing steady flows of a miscible mixture of two fluids. The densities ϱ
i
of the fluids and their velocity fields u
(i) are prescribed at infinity: ϱ
i
|∞ = ϱ
i∞ > 0, u
(i)|∞ = 0. Neglecting the convective terms, we have proved earlier that weak solutions to such a reduced system exist. Here we
establish a uniqueness type result: in the absence of the external forces and interaction terms, there is only one such solution,
namely ϱ
i
≡ ϱ
i∞, u
(i) ≡ 0, i = 1, 2.
This work was supported by the SFB 611 at the University of Bonn and the European HYKE network (contract no. HPRN-CT-2002-00282).
The third author was also supported by the project CSF 201/03/0934, and by MSM 0021620839. 相似文献
120.
Ernst Binz Sonja Pods Walter Schempp 《Journal of Applied Mathematics and Computing》2003,11(1-2):1-57
Vector fields in three-space admit bundles of internal variables such as a Heisenberg algebra bundle. Information transmission along field lines of vector fields is described by a wave linked to the Schrödinger representation in the realm of time-frequency analysis. The preservation of local information causes geometric optics and a quantization scheme. A natural circle bundle models quantum information visualized by holographic methods. Features of this setting are applied to magnetic resonance imaging. 相似文献