Browsing by Author "Ringenberg, Mark"

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    Caging of a strongly pairing fluorescent thymidine analog with soft nucleophiles
    (2022) Eyberg, Juri; Ringenberg, Mark; Richert, Clemens
    Controlling the pairing strength of nucleobases in DNA through reactions with compounds found inside the cell is a formidable challenge. Here we report how a thiazolyl substituent turns a strongly pairing ethynylpyridone C‐nucleoside into a reactive residue in oligonucleotides. The thiazolyl‐bearing pyridone reacts with soft nucleophiles, such as glutathione, but not with hard nucleophiles like hydroxide or carbonate. The addition products pair much more weakly with adenine in a complementary strand than the starting material, and also change their fluorescence. This makes oligonucleotides containing the new deoxynucleoside interesting for controlled release. Due to its reactivity toward N, P, S, and Se‐nucleophiles, and the visual signal accompanying chemical conversion, the fluorescent nucleotide reported here may also have applications in chemical biology, sensing and diagnostics.
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    Crystalline anions based on classical N‐heterocyclic carbenes
    (2022) Merschel, Arne; Rottschäfer, Dennis; Neumann, Beate; Stammler, Hans‐Georg; Ringenberg, Mark; Gastel, Maurice van; Demirer, T. Ilgin; Andrada, Diego M.; Ghadwal, Rajendra S.
    Herein, the first stable anions K[SIPrBp] (4 a‐K) and K[IPrBp] (4 b‐K) (SIPrBp=BpC{N(Dipp)CH2}2, IPrBp=BpC{N(Dipp)CH}2; Bp=4‐PhC6H4; Dipp=2,6‐iPr2C6H3) derived from classical N‐heterocyclic carbenes (NHCs) (i.e. SIPr and IPr) have been isolated as violet crystalline solids. 4 a‐K and 4 b‐K are prepared by KC8 reduction of the neutral radicals [SIPrBp] (3 a) and [IPrBp] (3 b), respectively. The radicals 3 a and 3 b as well as [Me‐IPrBp] 3 c (Me‐IPrBp=BpC{N(Dipp)CMe}2) are accessible as crystalline solids on treatment of the respective 1,3‐imidazoli(ni)um bromides (SIPrBp)Br (2 a), (IPrBp)Br (2 b), and (Me-IPrBp)Br (2 c) with KC8. The cyclic voltammograms of 2 a-2 c exhibit two one‐electron reversible redox processes in -0.5 to -2.5 V region that correspond to the radicals 3 a-3 c and the anions (4 a-4 c)-. Computational calculations suggest a closed‐shell singlet ground state for (4 a-4 c)- with the singlet‐triplet energy gap of 17-24 kcal mol-1.
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    Kristalline Anionen auf Basis klassischer N‐heterocyclischer Carbene
    (2022) Merschel, Arne; Rottschäfer, Dennis; Neumann, Beate; Stammler, Hans‐Georg; Ringenberg, Mark; Gastel, Maurice van; Demirer, T. Ilgin; Andrada, Diego M.; Ghadwal, Rajendra S.
    Die ersten stabilen Anionen K[SIPrBp] (4 a-K) und K[IPrBp] (4 b-K) (SIPrBp=BpC{N(Dipp)CH2}2, IPrBp=BpC{N(Dipp)CH}2; Bp=4-PhC6H4; Dipp=2,6-iPr2C6H3), die von klassischen N-heterocyclischen Carbenen (NHCs) abgeleitet sind (d. h. SIPr und IPr), wurden als violette kristalline Feststoffe isoliert. 4 a-K und 4 b-K wurden durch die Reduktion der neutralen Radikale [SIPrBp] (3 a) bzw. [IPrBp] (3 b) mit KC8 hergestellt. Die Radikale 3 a und 3 b sowie [Me-IPrBp] (3 c) (Me-IPrBp=BpC{N(Dipp)CMe}2) liegen als kristalline Feststoffe vor, wenn die entsprechenden 1,3-Imidazoli(ni)umbromide (SIPrBp)Br (2 a), (IPrBp)Br (2 b) und (Me-IPrBp)Br (2 c) mit KC8 umgesetzt werden. Die Cyclovoltammogramme von 2 a-2 c zeigen zwei reversible Ein-Elektronen-Redoxprozesse im Bereich von -0.5 bis -2.5 V, die den Radikalen 3 a-3 c und den Anionen (4 a-4 c)- entsprechen. Quantenchemische Berechnungen deuten auf einen geschlossenschaligen Singulett-Grundzustand für (4 a-4 c)- mit einer Singulett-Triplett-Energielücke von 17-24 kcal mol-1 hin.
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    Oxo‐bridged Zr dimers as well‐defined models of oxygen vacancies on ZrO2
    (2023) Wimmer, Erik J.; Klostermann, Sina V.; Ringenberg, Mark; Kästner, Johannes; Estes, Deven P.
    While ZrO2 is known to have a large effect on the activity and selectivity of the Cu/ZrO2 catalyst for methanol synthesis, its role in this process is poorly understood. Surface defects such as oxygen vacancies could play a role in the strong metal-support interaction (SMSI) between Cu and ZrO2. However, due to the complexity of the surfaces, the exact molecular nature of this interaction is not at present known. Here, we make well-defined models of both reduced and coordinatively unsaturated surface oxygen vacancies on ZrO2 using the molecular precursor [Cp2ZrCl]2(μ2-O) (1). Complex 1 can be reduced to form a complex (2) containing one Zr(III) center and a bridging hydride ligand (according to EPR and IR spectroscopy) derived from C-H activation of either thf or the Cp ring. Complex 2 reacts with CO2 to largely produce CO, suggesting that surface defects with similar structures probably do not play a role in the industrial catalyst. Halide abstraction from complex 1 results in the Lewis acidic species 3, which has similar Lewis acid properties to acidic defects on the ZrO2 surface. Similarities of both of these model species to real surface oxygen vacancies and their role in the catalytic reaction are discussed.