Publications by authors named "Stefan Wiedemann"

6 Publications

  • Page 1 of 1

Unified prebiotically plausible synthesis of pyrimidine and purine RNA ribonucleotides.

Science 2019 10;366(6461):76-82

Center for Integrated Protein Science, Department of Chemistry, LMU München, Butenandtstrasse 5-13, 81377 München, Germany.

Theories about the origin of life require chemical pathways that allow formation of life's key building blocks under prebiotically plausible conditions. Complex molecules like RNA must have originated from small molecules whose reactivity was guided by physico-chemical processes. RNA is constructed from purine and pyrimidine nucleosides, both of which are required for accurate information transfer, and thus Darwinian evolution. Separate pathways to purines and pyrimidines have been reported, but their concurrent syntheses remain a challenge. We report the synthesis of the pyrimidine nucleosides from small molecules and ribose, driven solely by wet-dry cycles. In the presence of phosphate-containing minerals, 5'-mono- and diphosphates also form selectively in one-pot reactions. The pathway is compatible with purine synthesis, allowing the concurrent formation of all Watson-Crick bases.
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http://dx.doi.org/10.1126/science.aax2747DOI Listing
October 2019

A one-pot, water compatible synthesis of pyrimidine nucleobases under plausible prebiotic conditions.

Chem Commun (Camb) 2019 Feb;55(13):1939-1942

Center for Integrated Protein Science (CiPSM) at the Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München, Germany.

Herein, we report a new prebiotically plausible pathway towards a pyrimidine nucleobase in continuous manner. The route involves simultaneous methylation and carbamoylation of cyanoacetylene-derived α,β-unsaturated thioamide with N-methyl-N-nitrosourea (MNU) in aqueous media. This provides S-methylpyrimidinone in one-pot, which can be converted into a variety of 4-substituted pyrimidine nucleobases including cytosine and uracil.
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http://dx.doi.org/10.1039/c8cc09435gDOI Listing
February 2019

Freeze fracture approach to directly visualize wetting transitions on nanopatterned superhydrophobic silicon surfaces: more than a proof of principle.

Langmuir 2013 Jan 9;29(3):913-9. Epub 2013 Jan 9.

Institute of Solid State Physics, Ulm University, Ulm, Baden-Württemberg, Germany.

Freeze fracturing is applied to make the wetting behavior of artificially nanopatterned Si surfaces directly visible. For this purpose, almost hexagonally arranged nanopillars of fixed areal density (127 μm(-2)) and diameters (35 nm) but varying heights (40-150 nm) were fabricated on silicon. Measurement of contact angles (CAs) including hysteresis allowed to distinguish between the Wenzel (W) and the Cassie-Baxter (CB) states with droplets completely wetting the pillars or residing on top of them, respectively. Providing additional depth contrast by evaporating the ice replica with thin carbon and (typically 3 nm) platinum layers under 45° allowed resolving 3D features of 5 nm within the ice replica. In this way, laterally sharp transitions from CB- to W-states could be revealed, indicating the formation of zero-curvature water surfaces even on the nanoscale.
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http://dx.doi.org/10.1021/la304791qDOI Listing
January 2013

Plasmonic nanostructures fabricated using nanosphere-lithography, soft-lithography and plasma etching.

Beilstein J Nanotechnol 2011 16;2:448-58. Epub 2011 Aug 16.

Ulm University, Institute of Experimental Physics, Albert-Einstein-Allee 11, 89069 Ulm, Germany.

We present two routes for the fabrication of plasmonic structures based on nanosphere lithography templates. One route makes use of soft-lithography to obtain arrays of epoxy resin hemispheres, which, in a second step, can be coated by metal films. The second uses the hexagonal array of triangular structures, obtained by evaporation of a metal film on top of colloidal crystals, as a mask for reactive ion etching (RIE) of the substrate. In this way, the triangular patterns of the mask are transferred to the substrate through etched triangular pillars. Making an epoxy resin cast of the pillars, coated with metal films, allows us to invert the structure and obtain arrays of triangular holes within the metal. Both fabrication methods illustrate the preparation of large arrays of nanocavities within metal films at low cost.Gold films of different thicknesses were evaporated on top of hemispherical structures of epoxy resin with different radii, and the reflectance and transmittance were measured for optical wavelengths. Experimental results show that the reflectivity of coated hemispheres is lower than that of coated polystyrene spheres of the same size, for certain wavelength bands. The spectral position of these bands correlates with the size of the hemispheres. In contrast, etched structures on quartz coated with gold films exhibit low reflectance and transmittance values for all wavelengths measured. Low transmittance and reflectance indicate high absorbance, which can be utilized in experiments requiring light confinement.
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http://dx.doi.org/10.3762/bjnano.2.49DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3190615PMC
August 2012

Expedient construction of the vibsanin E core without the use of protecting groups.

Org Lett 2005 Mar;7(7):1327-9

School of Molecular and Microbial Sciences, University of Queensland, St. Lucia, 4072 Queensland, Australia.

[reaction: see text] The tricyclic core of vibsanin E was constructed without the use of a protecting group in six steps. The El Gaïed Baylis-Hillman variant was key to allowing the Brønsted acid induced tandem cyclization forming rings B and C in one operation.
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http://dx.doi.org/10.1021/ol0501222DOI Listing
March 2005

Primary 1-arylcyclopropylamines from aryl cyanides with diethylzinc and titanium alkoxides.

Org Lett 2003 Mar;5(5):753-5

Institut für Organische Chemie der Georg-August-Universität Göttingen, Tammannstrasse 2, 37077 Göttingen, Germany.

1-Aryl-substituted primary cyclopropylamines are conveniently prepared from aromatic nitriles and diethylzinc. The yields range from 40 to 56% for donor-substituted (five examples) to 62-82% for non- and acceptor-substituted substrates (nine examples).
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http://dx.doi.org/10.1021/ol034021kDOI Listing
March 2003