Technical University of Dortmund

About: Technical University of Dortmund is a education organization based out in Dortmund, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Context (language use) & Large Hadron Collider. The organization has 13028 authors who have published 27666 publications receiving 615557 citations. The organization is also known as: Dortmund University & University of Dortmund.

18F-labeling of peptides by means of an organosilicon-based fluoride acceptor.

Abstract: Fluorine-18 is among the most commonly used radionuclides for positron emission tomography (PET). This non-invasive imaging technique is capable of providing in vivo information about the distribution of radiolabeled biomolecules by 1808 coincidence detection of two simultaneously emitted photons from positron–electron annihilation. Although a number of different radiotracers have been successfully employed in PET, only a few, such as 2-[F]fluoro-2-deoxy-d-glucose (FDG) and [F]fluorodopa, have gained widespread application in nuclear medicine. The reason for this is that the regioselective introduction of F into tracer molecules is often non-specific and radiochemical yields (RCY) of the Flabelled product are low. The introduction of F into tracer molecules requires high temperatures and often leads to undesired by-products. The research over the last decade clearly indicates that the success of PET in nuclear medicine justifies the intense search for versatile labeling formulations for the syntheses of F-radiopharmaceuticals. Especially the development of rational F-labelling strategies for peptides, until now characterized by multistep procedures, is considered to be one of the most important tasks. As an alternative to conventional F-labelling chemistry, the use of [F]fluorosilanes as labeling synthons was first proposed by Rosenthal et al. who treated chlorotrimethylsilane with n.c.a. (no carrier added) F in aqueous acetonitrile isolating the corresponding [F]fluorosilane in 65% yield. A preliminary in vivo evaluation revealed fast hydrolysis of the compound accompanied by high radioactivity (F) uptake by the bone making it unsuitable as a labeling synthon. Another approach is based on the work by Pilcher et al. who fluorinated organosilanoles with nonradioactive HF in high yields. An analogous labeling strategy was proposed in a symposium abstract. However, so far no labeling experiments using aqueous F /[F]HF solutions have been reported. Most recently Ting et al. used organotriethoxysilanes as labeling precursors for the synthesis of [F]fluorosilanes but no practical application for the synthesis of potential radiopharmaceuticals has been demonstrated. Herein we report the syntheses of substituted [F]organofluorosilanes using organochlorosilanes as labeling precursors and their in vitro and in vivo stability. As an alternative labeling approach we also describe the F–F isotopic exchange using [F]di-tert-butylphenyl fluorosilane as a highly efficient silicon-based fluoride acceptor (SiFA compound). As proof of applicability we transferred the SiFA approach to the development of a simple and practical formulation for the synthesis of a F-labelled SiFA derivatized Tyr-octreotate, a peptide used in oncology for the visualization of neuro-endocrine tumors. We synthesized three [F]organofluorosilanes, namely [F]fluorotriphenylsilane (1), [F]fluoro-tert-butyldiphenylsilane (2), and [F]fluorodi-tert-butylphenylsilane (3), and evaluated their in vitro stability in human serum as well as their in vivo stability in rats, studied by animal-PET. These data are essential for finding the most suitable compound and for evaluating the labeling concept. The reaction in acetonitrile of the triorganochlorosilanes (5–11.8 mmolmL ) Ph3SiCl, tBuPh2SiCl, and tBu2PhSiCl, with the azeotropically dried complex F /Kryptofix2.2.2./ K at room temperature provided almost quantitatively the corresponding [F]triorganofluorosilanes 1–3 (Figure 1), as demonstrated by means of radio-HPLC. Their identities were confirmed by coelution of the radioactive probes spiked with the related nonradioactive F-analogues. The specific activity of 1, 2, and 3 was determined using UV-calibration curves and was in the range 1500–1700 GBqmmol . To investigate the applicability of the F-labelled compounds for the development of Si–F containing radiopharmaceuticals, their in vitro stability in human serum was investigated (Figure 1). In agreement with previously published data, the [F]triphenylfluorosilane 1 was found to be stable for 4 h in neutral water (data not shown) but unstable at pH 7.4–7.6 in human serum. In contrast, the tert[*] Dr. R. Schirrmacher, Dr. E. Schirrmacher, J. Tillmanns, Dr. T. Siessmeier, Dipl.-Ing. H. G. Buchholz, Prof. Dr. P. Bartenstein Klinik und Poliklinik f1r Nuklearmedizin Johannes Gutenberg Universit6t Mainz 55131 Mainz (Germany) Fax: (+49)6131-172386 E-mail: schirrmacher@klinik.nuklearmedizin.uni-mainz.de Dipl.-Chem. G. BradtmBller, Prof. Dr. K. Jurkschat Lehrstuhl f1r Anorganische Chemie Universit6t Dortmund 44221 Dortmund (Germany) Fax: (+49)231-755-5048 E-mail: klaus.jurkschat@uni-dortmund.de

Search for heavy Majorana neutrinos with the ATLAS detector in pp collisions at √s 8 TeV

Abstract: A search for heavy Majorana neutrinos in events containing a pair of high-p(T) leptons of the same charge and high-p(T) jets is presented. The search uses 20.3 fb(-1) of pp collision data collected with the ATLAS detector at the CERN Large Hadron Collider with a centre-of-mass energy of root s = 8TeV. The data are found to be consistent with the background-only hypothesis based on the Standard Model expectation. In the context of a Type-I seesaw mechanism, limits are set on the production cross-section times branching ratio for production of heavy Majorana neutrinos in the mass range between 100 and 500 GeV. The limits are subsequently interpreted as limits on the mixing between the heavy Majorana neutrinos and the Standard Model neutrinos. In the context of a left-right symmetric model, limits on the production cross-section times branching ratio are set with respect to the masses of heavy Majorana neutrinos and heavy gauge bosons W-R and Z'.

Dynamic heterogeneity in supercooled ortho-terphenyl studied by multidimensional deuteron NMR

Abstract: Using deuteron NMR, we have studied molecular reorientation rates and rate exchange processes in supercooled ortho-terphenyl. We monitor the re-equilibration of differently selected subensembles through four-time stimulated echo experiments. A comparison of the two-time with the four-time echoes suggests that the characteristic time scales for reorientation and dynamical exchange are relatively similar. The four-time correlation functions were described using various multi-state rate exchange models.

Propagation kernels: efficient graph kernels from propagated information

Abstract: We introduce propagation kernels, a general graph-kernel framework for efficiently measuring the similarity of structured data. Propagation kernels are based on monitoring how information spreads through a set of given graphs. They leverage early-stage distributions from propagation schemes such as random walks to capture structural information encoded in node labels, attributes, and edge information. This has two benefits. First, off-the-shelf propagation schemes can be used to naturally construct kernels for many graph types, including labeled, partially labeled, unlabeled, directed, and attributed graphs. Second, by leveraging existing efficient and informative propagation schemes, propagation kernels can be considerably faster than state-of-the-art approaches without sacrificing predictive performance. We will also show that if the graphs at hand have a regular structure, for instance when modeling image or video data, one can exploit this regularity to scale the kernel computation to large databases of graphs with thousands of nodes. We support our contributions by exhaustive experiments on a number of real-world graphs from a variety of application domains.

Tunable Hydrophobic Eutectic Solvents Based on Terpenes and Monocarboxylic Acids

Abstract: Recently, some works claim that hydrophobic deep eutectic solvents could be prepared based on menthol and monocarboxylic acids. Despite of some promising potential applications, these systems were poorly understood, and this work addresses this issue. Here, the characterization of eutectic solvents composed of the terpenes thymol or l(−)-menthol and monocarboxylic acids is studied aiming the design of these solvents. Their solid–liquid phase diagrams were measured by differential scanning calorimetry in the whole composition range, showing that a broader composition range, and not only fixed stoichiometric proportions, can be used as solvents at low temperatures. Additionally, solvent densities and viscosities close to the eutectic compositions were measured, showing low viscosity and lower density than water. The solvatochromic parameters at the eutectic composition were also investigated aiming at better understanding their polarity. The high acidity is mainly provided by the presence of thymol in the m...