Inst. Chemie

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Theoretical studies for the development of a better understanding of cofactor-structure and mechanistic properties of photoreceptors and metallo-enzymes with quantum chemical and molecular dynamical approaches

Belger, Dennis Heinz (2020)

In this work two phytochromes, namely Cyanobacterial phytochrome Cph1 and Agrobacterium tumefaciens phytochrome Agp2, as well as formate dehydrogenase of Rhodobacter Capsulatus (RcFDH), are investigated. Part III shows the development and its application of a new polarized force field (polff) for the chromophore-binding domain (CBD) of Cph1, derived by QM-computations of Mulliken charges. This ...

Graphene Quantum Dot-Based Electrochemical Immunosensors for Biomedical Applications

Mansuriya, Bhargav D. ; Altintas, Zeynep (2019-12-23)

In the area of biomedicine, research for designing electrochemical sensors has evolved over the past decade, since it is crucial to selectively quantify biomarkers or pathogens in clinical samples for the efficacious diagnosis and/or treatment of various diseases. To fulfil the demand of rapid, specific, economic, and easy detection of such biomolecules in ultralow amounts, numerous nanomateria...

The Alanine World Model for the Development of the Amino Acid Repertoire in Protein Biosynthesis

Kubyshkin, Vladimir ; Budisa, Nediljko (2019-11-05)

A central question in the evolution of the modern translation machinery is the origin and chemical ethology of the amino acids prescribed by the genetic code. The RNA World hypothesis postulates that templated protein synthesis has emerged in the transition from RNA to the Protein World. The sequence of these events and principles behind the acquisition of amino acids to this process remain elu...

O−O Bond Formation and Liberation of Dioxygen Mediated by N5‐Coordinate Non‐Heme Iron(IV) Complexes

Kroll, Nicole ; Speckmann, Ina ; Schoknecht, Marc ; Gülzow, Jana ; Diekmann, Marek ; Pfrommer, Johannes ; Stritt, Anika ; Schlangen, Maria ; Grohmann, Andreas ; Hörner, Gerald (2019-08-13)

Formation of the O−O bond is considered the critical step in oxidative water cleavage to produce dioxygen. High‐valent metal complexes with terminal oxo (oxido) ligands are commonly regarded as instrumental for oxygen evolution, but direct experimental evidence is lacking. Herein, we describe the formation of the O−O bond in solution, from non‐heme, N5‐coordinate oxoiron(IV) species. Oxygen evo...

A Reaction‐Induced Localization of Spin Density Enables Thermal C−H Bond Activation of Methane by Pristine FeC4+

Geng, Caiyun ; Li, Jilai ; Weiske, Thomas ; Schwarz, Helmut (2019-08-13)

The reactivity of the cationic metal‐carbon cluster FeC4+ towards methane has been studied experimentally using Fourier‐transform ion cyclotron resonance mass spectrometry and computationally by high‐level quantum chemical calculations. At room temperature, FeC4H+ is formed as the main ionic product, and the experimental findings are substantiated by labeling experiments. According to extensive...

Direct Identification of Acetaldehyde Formation and Characterization of the Active Site in the [VPO4].+/C2H4 Couple by Gas‐Phase Vibrational Spectroscopy

Li, Ya-Ke ; Debnath, Sreekanta ; Schlangen, Maria ; Schöllkopf, Wieland ; Asmis, Knut R. ; Schwarz, Helmut (2019-11-08)

The gas‐phase reaction of the heteronuclear oxide cluster [VPO4].+ with C2H4 is studied under multiple collision conditions at 150 K using cryogenic ion‐trap vibrational spectroscopy combined with electronic structure calculations. The exclusive formation of acetaldehyde is directly identified spectroscopically and discussed in the context of the underlying reaction mechanism. In line with comp...

Influence of Adding Molybdenum on Structure and Performance of FexOy/SBA‐15 Catalysts in Selective Oxidation of Propene

Genz, Nina Sharmen ; Ressler, Thorsten (2019-08-21)

Mixed iron and molybdenum oxide catalysts supported on nanostructured silica, SBA‐15, were synthesized with various Mo/Fe atomic ratios ranging from 0.07/1.0 to 0.57/1.0. Structural characterization of as‐prepared MoxOy_FexOy/SBA‐15 samples was performed by nitrogen physisorption, X‐ray diffraction, and DR‐UV‐Vis spectroscopy. Adding molybdenum resulted in a pronounced dispersion effect on supp...

Vinylene-Linked Covalent Organic Frameworks by Base-Catalyzed Aldol Condensation

Acharjya, Amitava ; Pachfule, Pradip ; Roeser, Jérôme ; Schmitt, Franz-Josef ; Thomas, Arne (2019-09-09)

Two 2D covalent organic frameworks (COFs) linked by vinylene (−CH=CH−) groups (V‐COF‐1 and V‐COF‐2) are synthesized by exploiting the electron deficient nature of the aromatic s‐triazine unit of C3‐symmetric 2,4,6‐trimethyl‐s‐triazine (TMT). The acidic terminal methyl hydrogens of TMT can easily be abstracted by a base, resulting in a stabilized carbanion, which further undergoes aldol condensa...

Boosting water oxidation through in situ electroconversion of manganese gallide: an intermetallic precursor approach

Menezes, Prashanth W. ; Walter, Carsten ; Hausmann, Jan Niklas ; Beltrán-Suito, Rodrigo ; Schlesiger, Christopher ; Praetz, Sebastian ; Yu. Verchenko, Valeriy ; Shevelkov, Andrei V. ; Driess, Matthias (2019-10-15)

For the first time, the manganese gallide (MnGa4) served as an intermetallic precursor, which upon in situ electroconversion in alkaline media produced high‐performance and long‐term‐stable MnOx‐based electrocatalysts for water oxidation. Unexpectedly, its electrocorrosion (with the concomitant loss of Ga) leads simultaneously to three crystalline types of MnOx minerals with distinct structures...

Lewis acid catalyzed transfer hydromethallylation for the construction of quaternary carbon centers

Walker, Johannes C. L. ; Oestreich, Martin (2019-09-12)

The design and gram‐scale synthesis of a cyclohexa‐1,4‐diene‐based surrogate of isobutene gas is reported. Using the highly electron‐deficient Lewis acid B(C6F5)3, application of this surrogate in the hydromethallylation of electron‐rich styrene derivatives provided sterically congested quaternary carbon centers. The reaction proceeds by C(sp3)−C(sp3) bond formation at a tertiary carbenium ion ...

Catalytic difunctionalization of unactivated alkenes with unreactive hexamethyldisilane through regeneration of silylium ions

Wu, Qian ; Roy, Avijit ; Irran, Elisabeth ; Qu, Zheng-Wang ; Grimme, Stefan ; Klare, Hendrik F. T. ; Oestreich, Martin (2019-10-23)

A metal‐free, intermolecular syn‐addition of hexamethyldisilane across simple alkenes is reported. The catalytic cycle is initiated and propagated by the transfer of a methyl group from the disilane to a silylium‐ion‐like intermediate, corresponding to the (re)generation of the silylium‐ion catalyst. The key feature of the reaction sequence is the cleavage of the Si−Si bond in a 1,3‐silyl shift...

Copper‐Catalyzed Enantio‐ and Diastereoselective Addition of Silicon Nucleophiles to 3,3‐Disubstituted Cyclopropenes

Zhang, Liangliang ; Oestreich, Martin (2019-10-22)

A highly stereocontrolled syn‐addition of silicon nucleophiles across cyclopropenes with two different geminal substituents at C3 is reported. Diastereomeric ratios are excellent throughout (d.r.≥98:2) and enantiomeric excesses usually higher than 90 %, even reaching 99 %. This copper‐catalyzed C−Si bond formation closes the gap of the direct synthesis of α‐chiral cyclopropylsilanes.

X-ray Crystallography and Vibrational Spectroscopy Reveal the Key Determinants of Biocatalytic Dihydrogen Cycling by [NiFe] Hydrogenases

Ilina, Yulia ; Lorent, Christian ; Katz, Sagie ; Jeoung, Jae-Hun ; Shima, Seigo ; Horch, Marius ; Zebger, Ingo ; Dobbek, Holger (2019-10-25)

[NiFe] hydrogenases are complex model enzymes for the reversible cleavage of dihydrogen (H2). However, structural determinants of efficient H2 binding to their [NiFe] active site are not properly understood. Here, we present crystallographic and vibrational‐spectroscopic insights into the unexplored structure of the H2‐binding [NiFe] intermediate. Using an F420‐reducing [NiFe]‐hydrogenase from ...

Chiral Modification of the Tetrakis(pentafluorophenyl)borate Anion with Myrtanyl Groups

Pommerening, Phillip ; Oestreich, Martin (2019-11-14)

The synthesis and characterization of chiral [B(C6F5)4]– derivatives bearing a myrtanyl group instead of a fluoro substituent in the para position are described. These new chiral borates were isolated as their bench‐stable lithium, sodium, and cesium salts. The corresponding trityl salts were prepared and tested as catalysts in representative counteranion‐directed Diels–Alder reactions and Muka...

A Simple Nickel Catalyst Enabling an E‐Selective Alkyne Semihydrogenation

Thiel, Niklas Olof ; Kaewmee, Benyapa ; Tran Ngoc, Trung ; Teichert, Johannes F. (2019-11-06)

Stereoselective alkyne semihydrogenations are attractive approaches to alkenes, which are key building blocks for synthesis. With regards to the most atom economic reducing agent dihydrogen (H 2 ), only few catalysts for the challenging E ‐selective alkyne semihydrogenation have been disclosed, each with a unique substrate scope profile. Here, we show that a commercially available nickel cataly...

Stereospecific and chemoselective copper-catalyzed deaminative silylation of benzylic ammonium triflates

Scharfbier, Jonas ; Gross, Benjamin M. ; Oestreich, Martin (2019-12-04)

A method for the synthesis of benzylsilanes starting from the corresponding ammonium triflates is reported. Silyl boronic esters are employed as silicon pronucleophiles, and the reaction is catalyzed by copper(I) salts. Enantioenriched benzylic ammonium salts react stereospecifically through an SN2‐type displacement of the ammonium group to afford α‐chiral silanes with inversion of the configur...

Changes in Phase Behavior from the Substitution of Ethylene Oxide with Carbon Dioxide in the Head Group of Nonionic Surfactants

Spiering, Vivian Jeannette ; Ciapetti, Aurora ; Tupinamba Lima, Michelle ; Hayward, Diminic W. ; Noirez, Laurence ; Appavou, Marie-Sousai ; Schomäcker, Reinhard ; Gradzielski, Michael (2019-11-25)

Nonionic ethylene oxide (EO)‐based surfactants are widely employed in commercial applications and normally form gel‐like liquid crystalline phases at higher concentrations, rendering their handling under such conditions difficult. By incorporating CO2 units in their hydrophilic head groups, the consumption of the petrochemical EO was reduced, and the tendency to form liquid crystals was suppres...

Extensive structure‐activity relationship study of albicidin’s C‐terminal dipeptidic p‐aminobenzoic acid moiety

Behroz, Iraj ; Durkin, Patrick ; Grätz, Stefan ; Seidel, Maria ; Rostock, Lida ; Spinczyk, Marcello ; Weston, John B. ; Süßmuth, Roderich D. (2019-12-12)

Albicidin is a recently described natural product that strongly inhibits bacterial DNA gyrase. The pronounced activity, particularly against Gram‐negative bacteria, turns it into a promising lead structure for an antibacterial drug. Hence, structure–activity relationship studies are key for the in‐depth understanding of structural features/moieties affecting gyrase inhibition, antibacterial act...

Influence of calcination conditions on structural and solid‐state kinetic properties of iron oxidic species supported on SBA‐15

Genz, Nina Sharmen ; Ressler, Thorsten (2019-10-17)

Iron oxidic species supported on silica SBA-15 were synthesized with various iron loadings using two different FeIII precursors. The effect of varying powder layer thickness during calcination on structural and solid-state kinetic properties of FexOy/SBA-15 samples was investigated. Calcination was conducted in thin (0.3 cm) or thick (1.3 cm) powder layer. Structural characterization of resulti...

Bis(N-heterocyclic silylene)xanthene in transition-metal catalysis and main group chemistry

Wang, Yuwen (2020)

This dissertation is devoted to the synthesis of the first bis(N-heterocyclic silylene)xanthene compound [Xant(SiIIL)2] [Xant = 9,9-dimethyl-xanthene-4,5-diyl, L = PhC(NtBu)2] and its application in transition-metal catalysis and main group chemistry. At first, the novel bis(silylenes) compound [Xant(SiIIL)2] was successfully synthesized and utilized as a strong σ donor ligand in transition-me...