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- ItemDistinction of nucleobases - A tip-enhanced Raman approach(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2011) Treffer, R.; Lin, X.; Bailo, E.; Deckert-Gaudig, T.; Deckert, V.The development of novel DNA sequencing methods is one of the ongoing challenges in various fields of research seeking to address the demand for sequence information. However, many of these techniques rely on some kind of labeling or amplification steps. Here we investigate the intrinsic properties of tip-enhanced Raman scattering (TERS) towards the development of a novel, label-free, direct sequencing method. It is known that TERS allows the acquisition of spectral information with high lateral resolution and single-molecule sensitivity. In the presented experiments, single stranded adenine and uracil homopolymers were immobilized on different kinds of substrates (mica and gold nanoplates) and TERS experiments were conducted, which demonstrated the reproducibility of the technique. To elucidate the signal contributions from the specific nucleobases, TERS spectra were collected on single stranded calf thymus DNA with arbitrary sequence. The results show that, while the Raman signals with respect to the four nucleobases differ remarkably, specific markers can be determined for each respective base. The combination of sensitivity and reproducibility shows that the crucial demands for a sequencing procedure are met.
- ItemOrigins of high catalyst loading in copper(i)-catalysed Ullmann-Goldberg C-N coupling reactions(Cambridge : RSC, 2017) Sherborne, Grant J.; Adomeit, Sven; Menzel, Robert; Rabeah, Jabor; Brückner, Angelika; Fielding, Mark R.; Willans, Charlotte E.; Nguyen, Bao N.A mechanistic investigation of Ullmann-Goldberg reactions using soluble and partially soluble bases led to the identification of various pathways for catalyst deactivation through (i) product inhibition with amine products, (ii) by-product inhibition with inorganic halide salts, and (iii) ligand exchange by soluble carboxylate bases. The reactions using partially soluble inorganic bases showed variable induction periods, which are responsible for the reproducibility issues in these reactions. Surprisingly, more finely milled Cs2CO3 resulted in a longer induction period due to the higher concentration of the deprotonated amine/amide, leading to suppressed catalytic activity. These results have significant implications on future ligand development for the Ullmann-Goldberg reaction and on the solid form of the inorganic base as an important variable with mechanistic ramifications in many catalytic reactions.
- ItemControl of etch pit formation for epitaxial growth of graphene on germanium(Melville, NY : American Inst. of Physics, 2019) Becker, Andreas; Wenger, Christian; Dabrowski, JarekGraphene epitaxy on germanium by chemical vapor deposition is a promising approach to integrate graphene into microelectronics, but the synthesis is still accompanied by several challenges such as the high process temperature, the reproducibility of growth, and the formation of etch pits during the process. We show that the substrate cleaning by preannealing in molecular hydrogen, which is crucial to successful and reproducible graphene growth, requires a high temperature and dose. During both substrate cleaning and graphene growth, etch pits can develop under certain conditions and disrupt the synthesis process. We explain the mechanisms how these etch pits may form by preferential evaporation of substrate, how substrate topography is related to the state of the cleaning process, and how etch pit formation during graphene growth can be controlled by choice of a sufficiently high precursor flow. Our study explains how graphene can be grown reliably on germanium at high temperature and thereby lays the foundation for further optimization of the growth process. © 2019 Author(s).
- ItemOpen is not enough(Basingstoke : Nature Publishing Group, 2018) Chen, Xiaoli; Dallmeier-Tiessen, Sünje; Dasler, Robin; Feger, Sebastian; Fokianos, Pamfilos; Gonzalez, Jose Benito; Hirvonsalo, Harri; Kousidis, Dinos; Lavasa, Artemis; Mele, Salvatore; Rodriguez, Diego Rodriguez; Šimko, Tibor; Smith, Tim; Trisovic, Ana; Trzcinska, Anna; Tsanaktsidis, Ioannis; Zimmermann, Markus; Cranmer, Kyle; Heinrich, Lukas; Watts, Gordon; Hildreth, Michael; Lloret Iglesias, Lara; Lassila-Perini, Kati; Neubert, SebastianThe solutions adopted by the high-energy physics community to foster reproducible research are examples of best practices that could be embraced more widely. This first experience suggests that reproducibility requires going beyond openness.
- ItemHigh molecular weight mechanochromic spiropyran main chain copolymers via reproducible microwave-assisted Suzuki polycondensation(Cambridge : RSC Publ., 2015) Metzler, Lukas; Reichenbach, Thomas; Brügner, Oliver; Komber, Hartmut; Lombeck, Florian; Müllers, Stefan; Hanselmann, Ralf; Hillebrecht, Harald; Walter, Michael; Sommer, MichaelSuzuki–Miyaura polycondensation (SPC) is widely used to prepare a variety of copolymers for a broad range of applications. Although SPC protocols are often used in many instances, the limits of this method and issues of molecular weight reproducibility are not often looked at in detail. By using a spiropyran-based (SP) mechanochromic copolymer, we present an optimized protocol for the microwave-assisted synthesis of a mechanochromic, alternating copolymer P(SP-alt-C10) via SPC that allows the reproduction of molecular weight distributions. Several parameters such as microwave power, temperature, stoichiometry, and ligand are screened, leading to molecular weights up to Mw ∼ 174 kg mol−1. The process of optimization is guided by NMR end group analysis which shows that dehalogenation, oxidative deborylation and SP cleavage are the limiting factors that impede further increase of molar mass, while other classical side reactions such as protiodeborylation are not observed. Embossing films of P(SP-alt-C10) yields the colored merocyanine (MC) copolymer P(MC-alt-C10) that undergoes a thermally facilitated back reaction to P(SP-alt-C10). DFT suggests that the barrier of the SP → MC transition has two contributions, with the first one being related to the color change and the second one to internal bond reorganizations. The barrier height is 1.5 eV, which suggests that the ease of the thermally facilitated back reaction is either due to residual energy stored in the deformed polymer matrix, or arises from an MC isomer that is not in the thermodynamically most stable state.