One

Kekule
 

KOPO 2017

 

 

Wichtige Termine im Wintersemester 2017/2018
  • Beginn der Vorlesungszeit: 09.10.2017
  • Ende der Vorlesungszeit: 02.02.2018
  • Die Vorlesungen fallen aus: 23.12.2017 - 07.01.2018
  • Dies acdemicus: 06.12.2017
  • Feiertage: 31.10.2017, 01.11.2017
BIGS Chemistry

GDCh Ortsverband Bonn

 

GDCh-Logo


Vorsitzender: Prof. Dr. A. Lützen
Jungchemikerforum Bonn


logo

KOPO 2017

KOPO 2017 logo.jpg

 
Two
FG Chemie auf uni-bonn.tv

Die 7. Folge der uni-bonn.tv-Serie "Frag
die Bonner Forscher" beschäftigt sich
mit der Frage, warum die Elemente im
Periodensystem genau auf diese Weise
angeordnet sind. Im Videoclip wird u. a.
der Schalenaufbau der Elektronenhülle
und der daraus resultierende Aufbau
des Periodensystems erklärt.

 

Veröffentlichungen
Bonner Chemiker berechnen zentrale Eigenschaft von Wasser
E. Perlt, M. von Domaros, B. Kirchner, R. Ludwig, F. Weinhold, Scientific Reports 7 2017, Article number: 10244. doi:10.1038/s41598-017-10156-w
Dr. Eva Perlt, Michael von Domaros und Prof. Dr. Barbara Kirchner vom Institut für Physikalische und Theoretische Chemie ist es in Kooperation mit Forschern der Universitäten Wisconsin-Madison und Rostock gelungen, das Ionenprodukt von Wasser mit theoretischen Methoden zu bestimmen. Die Arbeit ist kürzlich in der Zeitschrift Scientific Reports erschienen (link). Darin gelang es den Wissenschaftlern auch, die Temperaturabhängigkeit dieser Konstante, die im Zusammenhang mit dem pH-Wert steht, zu berechnen.
Weitere Informationen: (link)

*****
Chemists from Bonn evaluate fundamental property of water
Dr. Eva Perlt, Michael von Domaros, and Prof. Dr. Barbara Kirchner from the Institute for Physical and Theoretical Chemistry were able to predict the ion product of water from theoretical methods in cooperation with researchers from the universities Wisconsin-Madison and Rostock. The article has just been published in the journal Scientific Reports (link).
Furthermore, the researchers were able to reproduce the temperature dependence of this constant, which is responsible for all pH-related phenomena.
Further information (German): (link)
 
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Willkommen

auf der Homepage des Kekulé-Institut für Organische Chemie und Biochemie der Rheinischen Friedrich-Wilhelms-Universität Bonn.


Anschrift:
Gerhard-Domagk-Straße 1
D-53121 Bonn

Geschäftsführung:
Prof. Dr. D. Menche
Tel.: +49 (0) 228 73-2653
Fax: +49 (0) 228 73-5813

Verwaltung:
Frau A. Schmidt / Frau E. Kuneck
Tel.: +49 (0) 228 73- 5785 / -2650
Fax: +49 (0) 228 73- 4583 / -5683
 

 

Aktuelles 

Aziridine radical opening
 

Gansäuer Aziridines.png

Y.-Q. Zhang, E. Vogelsang, Z.-W, Qu, S. Grimme, A. Gansäuer, Angew. Chem. Int. Ed. 2017, 56, 12654-12657. (link)
 
The first catalytic generation of β-amido substituted radicals from N-acyl aziridines is described. The radicals that are generated with excellent regioselectivity are useful intermediates for intermolecular additions, reductions, and cyclizations to yield functionalized amides. Through calculations we have shown that the ring opening is concerted and not step-wise as previously postulated.
 
 
Inside or outside?
 
Lützen Inside or outside.png       
 
 
 
 
Simultaneous endo and exo Complex Formation of Pyridine[4]arene Dimers with Neutral and Anionic Guests
A. Kiesilä, L. Kivijärvi, N. Kodiah Beyeh, J. O. Moilanen, M. Groessl, T. Rothe, S. Götz, F. Topić, K. Rissanen, A. Lützen,  E. Kalenius, Angew. Chem. Int. Ed. 2017, 56, 10942-10946. (link)
 
The formation of noncovalent complexes between hexafluorophosphate (PF6) and tetraisobutyloctahydroxypyridine[4]arene has been studied in the gas phase, in the solid state, and in solution. In all states of matter, simultaneous endo complexation of solvent molecules and exo complexation of PF6 anions with the pyridine[4]arene dimers was observed.
 
 
 
 
Tetrahedral cages
Two supramolecular cages based on a trifluoromethyl-substituted pyridylimine ligand have been synthesised where the iron(II) complex shows host–guest chemistry and complex-to-complex transformations.
Lützen Tetra cages.gif                              Lützen tetra cages Titelblatt.gif
Electron-deficient trifluoromethyl-substituted sub-components affect the properties of M4L4 tetrahedral cages 

N. Struch, F. Topić, K. Rissanen,  A. Lützen, Dalton Trans. 2017, 46, 10809-10813. (link)

 

 
 
 
 
SN2 at Tertiary Carbons by Epoxide Hydrosilylation
 
TOC for SN2 at tertiary-2.jpg
Y.-Q. Zhang, C. Poppel, A. Panfilova, F. Bohle, S. Grimme, A. Gansäuer, Angew. Chem. Int. Ed. 2017, 56, 9719-9722.
 
SN2 reactions at tertiary carbon centers in epoxides are possible when the angle of ‘backside attack’ is controlled! This is achieved by binding of the reagent and its activation to hydride transfer by fluoride. The reaction proceeds with excellent regioselectivity and allows the synthesis of many acetate and propionate derived 1,3-diol units pertinent to natural product synthesis.
 
 
 
Metallosupramolecular Chemistry
 
Lützen anie201781861-toc-0001.png
 
 
 
 
 
 
 
N. Struch, C. Bannwarth, T. Ronson, Y. Lorenz, B. Mienert, N. Wagner, M. Engeser, E. Bill, R. Puttreddy, K. Rissanen, J. Beck, S. Grimme, J. R. Nitschke, A. Lützen
An Octanuclear Metallosupramolecular Cage Designed to Exhibit Spin-Crossover Behavior
Angew. Chem. Int. Ed. 2017, 56, 4930-4935. DOI: 10.1002/anie.201700832. (link)
By employing the subcomponent self-assembly approach utilizing 5,10,15,20-tetrakis(4-aminophenyl)porphyrin or its zinc(II) complex, 1H-4-imidazolecarbaldehyde, and either zinc(II) or iron(II) salts, we were able to prepare O-symmetric cages having a confined volume of ca. 1300 Å3. The use of iron(II) salts yielded coordination cages in the high-spin state at room temperature, manifesting spin-crossover in solution at low temperatures, whereas corresponding zinc(II) salts led to the corresponding diamagnetic analogues. The new cages were characterized by synchrotron X-ray crystallography, high-resolution mass spectrometry, and NMR, Mössbauer, IR, and UV/Vis spectroscopy. The cage structures and UV/Vis spectra were independently confirmed by state-of-the-art DFT calculations. A remarkably high-spin-stabilizing effect through encapsulation of C70 was observed. The spin-transition temperature T1/2 is lowered by 20 K in the host–guest complex.
 
 
 
A Liquid-Crystalline Phenylene-Based Shape-Persistent Molecular Spoked Wheel
ja-2016-13020q_0008.gif
A. Idelson, C. Sterzenbach, S.-S. Jester, C. Tschierske, U. Baumeister, S. Höger
A Liquid-Crystalline Phenylene-Based Shape-Persistent Molecular Spoked Wheel
J. Am. Chem. Soc. 2017, 139, 4429–4434. (link)
 
Molecular spoked wheels with an all-phenylene backbone and different alkoxy side chain substitution patterns were synthesized using a cobalt-catalyzed [2+2+2] cycloaddition and subsequent template-directed cyclization via Yamamoto coupling. The two-dimensional organization of the molecules at the solid/liquid interface was investigated by means of scanning tunneling microscopy allowing imaging the molecular structure with submolecular resolution. With the right proportion of the flexible alkyl corona to the rigid core, mesomorphic behavior of one compound could be observed over a wide temperature range.
 
  
Terpene Biosynthesis
DickschatTOC Graphic4-17.jpg                                                               
 


P. Rabe, J. Rinkel, E. Dolja, T. Schmitz, B. Nubbemeyer, T. H. Luu, J. S. Dickschat, Mechanistic investigantions on two bacterial diterpene cyclases:
Spiroviolene Synthase and Tsukubadiene Synthase, Angew.
Chem. Int. Ed.
2017, 56, 2776-2779. (link)
The mechanisms of two diterpene cyclases from streptomycetes - one with an unknown product that was identified as the spirocyclic hydrocarbon spiroviolene and one with the known product tsukubadiene - were investigated in detail by isotope labeling experiments. Although the structures of the products were very different, the cyclization mechanisms of both enzymes proceed through the same initial cyclization reactions, before they diverge towards the individual products, which is reflected in the close phylogenetic relationship of the enzymes.

  
 
Nachruf Prof. Dr. Fritz Vögtle
Fritz Vögtle.JPG
Am 3. Januar 2017 ist unser lieber Freund und Kollege Prof. Dr. rer. nat. Dr. phil. h.c. Fritz Vögtle im Alter von 77 Jahren verstorben. Er war uns menschlich und wissenschaftlich immer ein Vorbild, und er hat die Bonner Chemie in den vergangenen vier Jahrzehnten entscheidend mitgeprägt. Wir werden ihn stets in ehrender Erinnerung halten.
 
 Bent π-systems: 
Angewandte_Chemie_International_Edition cover klein.jpg







P. Wilhelm, J. Vogelsang, G. Poluektov, N. Schönfelder, T. J. Keller, S.-S. Jester, S. Höger, J. M. Lupton
Molecular polygons probe the role of intramolecular strain in the photophysics of π-conjugated chromophores
Angew. Chem. Int. Ed. 2017, 56, 1234–1238. (link)
Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.
The π-system of conjugated macromolecules can be bent in a controlled fashion by incorporating chromophores in molecular polygon templates. Bending leads to isotropic polarization in absorption and fluorescence but also influences excited-state properties. On the single-molecule level, a correlation emerges between luminescence spectrum and lifetime, which arises from subtle variations in the bending radius of the molecules.

Terpen-Biosynthese
Dickschat komp 2





P. Rabe, J. Rinkel, B. Nubbemeyer, T. G.
Köllner, F. Chen, J. S. Dickschat, Terpene Cyclases from Social Amoebae, Angew. Chem. Int. Ed. 2016, 55, 15420-15423. (link)
 

Genome sequences of social amoebae reveal the presence of terpene cyclases (TCs) in these organisms. Two TCs from Dictyostelium discoideum converted farnesyl diphosphate into (2S,3R,6S,9S)-(−)-protoillud-7-ene and (3S)-(+)-asterisca-2(9),6-diene. The enzyme mechanisms and EI-MS fragmentations of the products were studied by labeling experiments.
 
Natural products in synthesis and biosynthesis II
Dickschat komp













                                                                 

Jeroen S. Dickschat, Beilstein J. Org. Chem. 2016, 12, 413–414. (link)
Natural products continue to be an inspiring field of research and an important source of potent biologically active compounds. Currently, also in the pharmaceutical industry, natural products are experiencing a revival as viable drug candidates, which is a pleasing development since many infectious diseases continue to threaten human health. From the numerous articles in daily newspapers, it is obvious that politicians have also realised the urgent need for new drugs and the potential associated with natural products and their derivatives. Certainly, the recent technological advances in many fields related to natural products, analytical chemistry, gene synthesis, and genome sequencing and editing offer an efficient toolbox to natural products chemists. In addition, classical methods such as isotopic labelling experiments continue to be important.
 
Metal-Free Room-Temperature Dual Singlet–Triplet Emitters
Höger TOC 2016
Reprinted with permission from J. Phys. Chem. Lett. 2016, 7, 4802–4808. Copyright 2016 American Chemical Society.



W. Ratzke, L. Schmitt, H. Matsuoka, C. Bannwarth, M. Retegan, S. Bange, P. Klemm, F. Neese, S. Grimme, O. Schiemann, J. M. Lupton, S. Höger
Effect of Conjugation Pathway in Metal-Free Room-Temperature Dual Singlet–Triplet Emitters for Organic Light-Emitting Diodes
J. Phys. Chem. Lett. 2016, 7, 4802–4808.
DOI: 10.1021/acs.jpclett.6b01907  (link)

Management of spin statistics is crucial to the operation of OLEDs. Electrons and holes recombine as bright singlet and dark triplet excitations. To maximize efficiency, one has to make triplets bright. This can be achieved by either increasing spin-orbit coupling, which increases singlet-triplet mixing, raising the transition rate; or by decreasing non-radiative triplet relaxation by blocking internal conversion.
Perplexingly, only the former approach is used in OLED technology. This is all the more surprising, since the most efficient OLEDs are not strictly “organic” at all – they only work because of the incorporation of organometallic emitters.
The alternative approach has, in principle, been known for a long time, but has never been applied systematically to OLEDs. Orthogonalization of molecular orbitals effectively inhibits internal conversion and provides modest spin-orbit coupling to enable phosphorescence. A simple way to achieve this is to design molecules with transitions involving npi* orbitals. As we demonstrate here, such purely organic molecules show strong electrophosphorescence, at room temperature – with no metal ion in sight! The present letter discusses design rules to jumpstart this research direction. In particular, we explore the effect of extended conjugation and non-trivial isomerization on electrophosphorescence.
 
Terpen-Biosynthese
Dickschat TOC Graphic 8-11.jpg    
 





J. Rinkel, P. Rabe, P. Garbeva, J. S. Dickschat, Lessons from 1,3-Hydride Shifts in Sesquiterpene Cyclisations, Angew. Chem. Int. Ed. 2016, 55, 13593-13596. (link)
Stereospecifically labelled precursors were subjected to conversion by seven bacterial sesquiterpene cyclases to investigate the stereochemistry of their initial 1,10-cyclisation-1,3-hydride shift cascades. Enzymes with products of known absolute configuration showed a coherent stereochemical course, except for (-)-α-amorphene synthase, for which the obtained results are better explained by an initial 1,6-cyclisation. The link between the absolute configuration of the product and the stereochemical course of the 1,3-hydride shifts enabled assignment of the absolute configurations of three enzyme products, which were confirmed independently through the absolute configuration of the common byproduct germacrene D-4-ol.
 
 
 Die regiodivergente Epoxidöffnung: Kann links wie rechts
Abb Gansäuer AC  
N. Funken, F. Mühlhaus, A. Gansäuer
General, Highly Selective Synthesis of 1,3- and 1,4-Difunctionalized Building Blocks by Regiodivergent Epoxide Opening, Angew. Chem. Int. Ed. 2016, 55, 12030-12034. (link)
 Die Synthese enantiomerenreiner, linearer und unverzweigter 1,3- und 1,4-difunktionalisierter Verbindungen stellt einen wichtigen, aber noch recht unerforschten Teil der Organischen Synthese dar. Hier präsentieren wir eine zuverlässige und hoch selektive Synthese von sowohl 1,3- als auch 1,4-difunktionalisierten Verbindungen ausgehend von β-epoxy-funktionalisierten Substraten. Die hervorragenden Selektivitäten resultieren aus der Titan(III) katalysierten regiodivergenten Epoxidöffnung (REO) mit Kagan-Komplex. Durch den Einsatz verschiedener Pyridiniumsalze kann über Anioneneffekte Einfluss auf Selektivität und Dauer der Reaktion genommen und letztere um bis zu 97% gesenkt werden. Damit handelt es sich bei der REO um eine hervorragende Reaktion sowohl für die TOS (target oriented synthesis) als auch für die DOS (diversity oriented synthesis).  
 
 
 Naturstoffe als Spinsonden
Menche cover
 
 
EPR and DEER studies of V-ATPase complexes with spin labeled inhibitors DCC and archazolid enable insights into non-covalent binding dynamics and analysis of the key functional subunit c and demonstrate the general usefulness of natural product derived spin labels as innovative tools for chemical biology.

 J. P. Gölz, S. Bockelmann, K. Mayer, H.-J. Steinhoff, H. Wieczorek, M. Huss, J. P. Klare, D. Menche, EPR Studies of V-ATPase with Spin-Labeled Inhibitors DCC and Archazolid: Interaction Dynamics with Proton Translocating Subunit c, ChemMedChem 2016, 11, 420-428. (link)

 
 Terpen-Biosynthese
Dickschat TOC Graphic.jpg






 
  T. A. Klapschinski, P. Rabe, J. S. Dickschat,
  Pristinol, a Sesquiterpene Alcohol with
  Unprecedented Skeleton from Streptomyces
  pristinaespiralis
, Angew. Chem. Int. Ed. 2016,
  55, 10141-10144. (link)
 
A terpene cyclase from Streptomyces pristinaespiralis was characterised as
(+)-(2S,3S,9R)-pristinol synthase. The structure of this sesquiterpene alcohol with a new carbon skeleton was established by NMR spectroscopy and single-wavelength anomalous dispersion X-ray crystallography. Extensive isotopic labelling experiments were performed to distinguish between various possible cyclisation mechanisms of the terpene cyclase and to decipher the EI-MS fragmentation mechanism of pristinol.

 
 Katalytisch, effizient, atom-ökonomisch: Ein neuer Zugang zu Alkaloidgerüsten
Gansäuer AC-2
 
S. Hildebrandt, A. Gansäuer, Angew. Chem. Int. Ed. 2016, 55, 9719–9722. (link)
        
Die katalytische C-H-Funktionalisierung aromatischer Verbindungen ist eines der aktivsten Gebiete der Organischen Synthese. Eine katalytische radikalische Funktionalisierung von Pyrrolen wurde nun durch Titanocen(III)-Katalyse ermöglicht. Da die Reaktion atom- ökonomisch, unter milden Bedingungen, mit einem ungiftigen und gut verfügbaren Metall unter niedriger Katalysatorbeladung verläuft, genügt sie den modernen Anforderungen an nachhaltige Chemie. Die entstehenden Alkaloidstrukturen sind wertvolle Intermediate in der Synthese komplexer Naturstoffe.
 
 
Terpen-Biosynthese
 
Dickschat Literatur






I. Burkhardt, T. Siemon, M. Henrot, L. Studt, S. Rösler, B. Tudzynski, M. Christmann, J. S. Dickschat, Mechanistic Characterisation of two Sesquiterpene Cyclases from the Plant Pathogenic Fungus Fusarium fujikuroi, Angew. Chem. Int. Ed. 2016, 55, 8748-8751. (link)
Two sesquiterpene cyclases from Fusarium fujikuroi were expressed in Escherichia coli and purified. The first enzyme was inactive because of a critical mutation, but activity was restored by sequence correction through site-directed mutagenesis. The mutated enzyme and two naturally functional homologues from other fusaria converted farnesyl diphosphate into guaia-6,10(14)-diene. The second enzyme produced eremophilene. The absolute configuration of guaia-6,10(14)-diene was elucidated by enantioselective synthesis, while that of eremophilene was evident from the sign of its optical rotation and is opposite to that in plants but the same as in Sorangium cellulosum. The mechanisms of both terpene cyclases were studied with various 13C- and 2H-labelled FPP isotopomers.
 
Epoxid-Hydrosilylierung: Hydroborierung vor dem wohlverdienten Ruhestand? 
 Gansäuer Klare weiss 2

D. Schwarz G. Henriques, K. Zimmer, S. Klare, A. Meyer, E. Rojo-Wiechel, M. Bauer, R. Sure, S. Grimme, O. Schiemann, R. A. Flowers II, A. Gansäuer
Highly Active Titanocene Catalysts for Epoxide Hydrosilylation: Synthesis, Theory, Kinetics, EPR Spectroscopy
Angew.Chem. Int. Ed
. 2016, 55, 7671 –7675. (link)
Epoxid-Hydrosilylierungen ermöglichen die lang begehrte anti-Markownikow-Addition von Wasser an Alkene in zwei Stufen. DFT- Rechnungen zusammen mit kinetischen, EPR-spektroskopischen und synthetischen Untersuchungen führten zu einer neuartigen, einfach durchführbaren Katalysatorgenerierung. Sie erlaubten ferner einen tiefen Einblick in den Reaktionsmechanismus mit einem ungewöhnlichen Resting State.
Dank der hohen Ausbeuten kombiniert mit hohen Regio- und Diastereoselektivitäten mit Silanen als umweltfreundliches Reduktionsmittel wird sich die Epoxid-Hydro-silylierung als nachhaltige Konkurrenz zur klassischen Hydroborierung etablieren.
 

Wie formstabil ist „formstabil”?

TOC AC Schweez groß
Bei neuartigen Phenylen-Ethinylen-Butadiinyl-Rotaxanen, die über einen kovalenten Templatansatz synthetisiert wurden, wird ein Abfädeln der Rad- von der Achskomponente beobachtet (siehe Bild). Der Abfädelungsmechanismus wurde durch DFT-basierte Molekülmechanikrechnungen und eine String-Methode zur Simulation seltener Ereignisse untersucht.
C. Schweez, P. Shushkov, S. Grimme, S. Höger
Synthesis and Dynamics of Nanosize Phenylene-Ethynylene-Butadiynylene Rotaxanes and the Role of Shape Persistence
Angew. Chem. 2016, 128, 3389-3394 (pdf); Angew. Chem. Int. Ed. 2016, 53, 3328-3333 (pdf).  DOI: 10.1002/anie.201509702R2 and 10.1002/ange.201509702R2
 
Gansäuer cover d
Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.
Katalytischer Tango: Die Katalysezyklen
greifen ineinander wie der Tanz eines
Tangopaars. Durch kooperative Katalyse können Radikale generiert und dann reduziert werden. Der milde Prozess eignet sich auch für gezielte Modifikation von Naturstoffen.
Y.-Q. Zhang, V. Jakoby, K. Stainer, A. Schmer, S. Klare, M. Bauer, S. Grimme, J. M. Cuerva, A. Gansäuer
Amid-substituierte Titanocene für die H-Atom-Transfer-Katalyse
Angew. Chem. 2016,128, 1546-1550. (link)
DOI: 10.1002/ange.201509548
(Pressemitteilung der UBonn)
 
Wagenrad

 
 
Ein π-konjugiertes molekulares Wagenrad mit 6nm Durchmesser liefert neue Einsichten in die Photophysik konjugierter Polymere.
V. Aggarwal, A. Thiessen, A. Idelson, D. Kalle, D. Würsch, T. Stangl, F. Steiner, S.-S. Jester, J. Vogelsang, S. Höger, J. M. Lupton
Fluctuating exciton localization in giant π-conjugated spoked-wheel macrocycles
Nat. Chem. 2013, 5, 964-970. (link)
 
 
 
 

 

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