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181.
Dr. Biao Yang Kaifeng Niu Nan Cao Dr. Nitika Grover Wenchao Zhao Alexander Riss Prof. Dr. Jonas Björk Prof. Dr. Willi Auwärter Prof. Dr. Johannes V. Barth Prof. Dr. Mathias O. Senge 《Angewandte Chemie (International ed. in English)》2023,62(19):e202218211
Bicyclo[1.1.1]pentane (BCP) motifs are of growing importance to the pharmaceutical industry as sp3-rich bioisosteres of benzene rings and as molecular building blocks in materials science. Herein we explore the behavior of 1,3-disubstituted BCP moieties on metal surfaces by combining low-temperature scanning tunneling microscopy / non-contact atomic force microscopy studies with density functional theory modeling. We examine the configuration of individual BCP-containing precursors on Au(111), their supramolecular assembly and thermally activated dehalogenative coupling reactions, affording polymeric chains with incorporated electronically isolating units. Our studies not only provide the first sub-molecular insights of the BCP scaffold behavior on surfaces, but also extend the potential application of BCP derivatives towards integration in custom-designed surface architectures. 相似文献
182.
Abas SA Hossain MB van Der Helm D Schmitz FJ Laney M Cabuslay R Schatzman RC 《The Journal of organic chemistry》1996,61(8):2709-2712
Two new alkaloids, polycarpine (1) and N,N-didesmethylgrossularine-1 (4), have been isolated from extracts of the ascidian Polycarpa aurata collected in Chuuk, Federated States of Micronesia. Three degradation products of 1 were also isolated. The structures of 1, 2, and 4 were determined by X-ray crystallography. The dimeric disulfide 1 inhibited the enzyme inosine monophosphate dehydrogenase, but the inhibition could be reversed by addition of excess dithiothreitol suggesting that 1 reacts with sulfhydryl groups on the enzyme. 相似文献
183.
184.
Hettmann E Brand WA Gleixner G 《Rapid communications in mass spectrometry : RCM》2007,21(24):4135-4141
A low dead volume oxygen scrubbing system was introduced in a commercially available liquid chromatography/isotope ratio mass spectrometry (LC/IRMS) interface to enhance the analytical capability of the system. In the LC/IRMS interface carbon from organic samples is converted into CO(2) inside the mobile phase by wet chemical oxidation using peroxodisulfate (Na(2)S(2)O(8)). After passing the hot reaction zone, surplus oxygen (O(2)) remains dissolved in the liquid phase. Both CO(2) and O(2) diffuse through a transfer membrane into the helium carrier and are transferred to the mass spectrometer. The presence of O(2) in the ion source may have detrimental effects on measurement accuracy and precision as well as on filament lifetime. As a remedy, a new on-line O(2)-removing device has been incorporated into the system.The new O(2) scrubber consists of two parallel hot copper reduction reactors (0.8 mm i.d., active length 120 mm) and a switch-over valve between them. One reactor is regenerated using He/H(2) while the other is actively scavenging O(2) from the gas stream. The capacity of each reduction reactor, expressed as usage time, is between 40 and 50 min. This is sufficient for a single LC run for sugars and organic acids. A further increase of the reduction capacity is accompanied by a peak broadening of about 100%. After switching to a freshly reduced reactor the oxygen background and the delta(13)C values of the reference gas need up to 500 s to stabilize. For repeated injections the delta(13)C values of sucrose remain constant (+/-0.1 per thousand) for about 3000 s. The long-term stability for measurements of sucrose was 0.11 per thousand without the reduction oven and improved slightly to 0.08 per thousand with the reduction oven. The filament lifetime improved by more than 600%, thereby improving the long-term system stability and analytical efficiency. In addition the costs per analysis were reduced considerably. 相似文献
185.
Dr. José I. Urgel Prof. David Écija Dr. Saranyan Vijayaraghavan Mathias Pörtner Prof. Marie-Laure Bocquet Prof. Willi Auwärter Prof. Johannes V. Barth 《Chemphyschem》2019,20(18):2301-2304
We report a low-temperature scanning tunneling microscopy investigation of the in-situ growth of gadolinium phthalocyaninato complexes by combined deposition of free-base phthalocyanines and gadolinium atoms on a smooth Ag(111) substrate. A careful control of the stoichiometry allows the expression of a multilevel structurecomposed of irregularly distributed Gdx-1(Pc)x complexes, x=2–5, thus paving new avenues for surface-confined columnar growth. 相似文献
186.
Willi Desens Marleen Winterberg Dirk Michalik Peter Langer 《Helvetica chimica acta》2016,99(5):361-372
The reaction of perfluorinated 3,5‐dioxoesters with 1,2‐diaminobenzenes or 2,3‐diaminonaphthalenes afforded two types of 1H‐benzo‐1,5‐diazepine derivatives containing a perfluorinated side chain. 2,5‐Dihydro‐1H‐benzo‐1,5‐diazepin‐2‐ones were formed by cyclocondensation via the central keto and the ester group, whereas 1H‐benzo‐1,5‐diazepines resulted from cyclocondensation via the two keto groups. The tautomerism and isomerization of these compounds have been investigated by 1H‐, 13C‐, and 19F‐NMR spectroscopy. The 1,5‐diazepines appear in CDCl3 solution as mixtures of two tautomeric forms, the enaminoimine I and diaminodiene II . In DMSO solution, besides I and II , two further species, III and IV , are formed by (E/Z) isomerization on the exocyclic C=C bond. 相似文献
187.
Michael J. Dick Brian J. Drouin Timothy J. Crawford John C. Pearson 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(9-10):628-638
A new spectroscopic experiment has been constructed at the Jet Propulsion Laboratory. This experiment employs the collisional cooling technique to study gases at temperatures below their condensation points. Specifically, the experiment has been designed to mimic the temperatures of the interstellar medium for the study of water under these conditions. The ultimate purpose is to measure state-to-state excitation rates under equilibrium conditions to provide insights into the interpretation of interstellar water spectra obtained from space-borne platforms such as the Herschel Space Observatory. This paper presents an overview of the new experiment including a discussion of its design and a detailed explanation of the system. In addition, we report a pressure broadening study of the J=5←4 transition of CO at 576 GHz used as a system validation. The new results are compared with measurements from the literature as a validation of the new experiment. In addition, the non-classical behavior of the pressure broadening of CO at low temperature observed in the measurements will be discussed. 相似文献
188.
A previous calculation of Green's function (E-H)-1 for an interface Hamiltonian which interpolates between two and three dimensions is generalized to include scattering from perturbations both on and off the interface. 相似文献
189.
Antici P Fuchs J Borghesi M Gremillet L Grismayer T Sentoku Y d'Humières E Cecchetti CA Mancić A Pipahl AC Toncian T Willi O Mora P Audebert P 《Physical review letters》2008,101(10):105004
The characteristics of fast electrons laser accelerated from solids and expanding into a vacuum from the rear target surface have been measured via optical probe reflectometry. This allows access to the time- and space-resolved dynamics of the fast electron density and temperature and of the energy partition into bulk (cold) electrons. In particular, it is found that the density of the hot electrons on the target rear surface is bell shaped, and that their mean energy at the same location is radially homogeneous and decreases with the target thickness. 相似文献
190.
We report on the first observations of periodic structures caused by the filamentation instability. These structures were observed on 0.35 μm laser irradiated planar target experiments. Comparison of these observations with self-focusing theory indicates that even though thermal filamentation may initiate the instability, ponderomotive force effects eventually dominate the actual filamentation process. 相似文献