Ulrich Steiner

Universität Konstanz, Constance, Baden-Württemberg, Germany

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Publications (100)321.47 Total impact

  • Jannic Wolf, Thomas Huhn, Ulrich E Steiner
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    ABSTRACT: A recently reported protolytic gating effect on the ring closing reaction of an oligo(phenylene ethynylene) (OPE) embedded difurylperfluorocyclopentene (S) with a dimethylaminophenyl chain link in each of the side arms, was quantitatively analyzed in detail. The reaction system (So, SoH(+), SoH2(2+), Sc, ScH(+), ScH2(2+)) comprising three protolytic forms in both open and closed configuration, is characterized by four protolytic equilibrium constants and six photochemical quantum yields of ring closing and ring opening. The absorption spectra, conductivity, and effective photochemical quantum yields were measured in acetonitrile as functions of solvent acidity varied by addition of trifluoroacetic acid and triethylamine and characterized by an effective pHnon-aq. Based on the derivation of a rigorous method for assessing the individual quantum yields of ring closure and ring opening of the six species, it was shown that it is specifically the second protonation step that is responsible for a more than 10-fold increase in the quantum yield of ring closure.
    Physical Chemistry Chemical Physics 02/2015; 17(8). DOI:10.1039/c4cp05258g · 4.20 Impact Factor
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    ABSTRACT: The transmission of genetic information relies on Watson-Crick base pairing between nucleoside phosphates and template bases in template-primer complexes. Enzyme-free primer extension is the purest form of the transmission process, without any chaperon-like effect of polymerases. This simple form of copying of sequences is intimately linked to the origin of life and provides new opportunities for reading genetic information. Here, we report the dissociation constants for complexes between (deoxy)nucleotides and template-primer complexes, as determined by nuclear magnetic resonance and the inhibitory effect of unactivated nucleotides on enzyme-free primer extension. Depending on the sequence context, Kd's range from 280 mM for thymidine monophosphate binding to a terminal adenine of a hairpin to 2 mM for a deoxyguanosine monophosphate binding in the interior of a sequence with a neighboring strand. Combined with rate constants for the chemical step of extension and hydrolytic inactivation, our quantitative theory explains why some enzyme-free copying reactions are incomplete while others are not. For example, for GMP binding to ribonucleic acid, inhibition is a significant factor in low-yielding reactions, whereas for amino-terminal DNA hydrolysis of monomers is critical. Our results thus provide a quantitative basis for enzyme-free copying.
    Nucleic Acids Research 05/2014; 42(11). DOI:10.1093/nar/gku314 · 8.81 Impact Factor
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    ABSTRACT: Several difurylperfluorocyclobutenes showing reversible photochromism were synthesized. In comparison to their cyclopentene homologues they show enhanced quantum yields for ring opening but reduced quantum yields for ring closure. X-ray structure analysis and quantum chemical calculations provide a conclusive explanation for such a behaviour.
    Chemical Communications 10/2012; 48(92):11355-7. DOI:10.1039/c2cc35726g · 6.38 Impact Factor
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    ABSTRACT: We report on the experimental analysis of the charge transport through single-molecule junctions of the open and closed isomers of photoswitching molecules. Sulfur-free diarylethene molecules are developed and studied via electrical and optical measurements as well as density functional theory calculations. The single-molecule conductance and the current-voltage characteristics are measured in a mechanically controlled break-junction system at low temperatures. Comparing the results with the single-level transport model, we find an unexpected behavior of the current-dominating molecular orbital upon isomerization. We show that both the side chains and end groups of the molecules are crucial to understand the charge transport mechanism of photoswitching molecular junctions.
    Nano Letters 06/2012; 12(7):3736-42. DOI:10.1021/nl3015523 · 13.03 Impact Factor
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    ABSTRACT: The yield of chemical reactions involving intermediate radical pairs is influenced by magnetic fields well beyond the levels expected from energy considerations. This dependence can be traced back to the microscopic dynamics of electron spins and constitutes the basis of the chemical compass. Here we propose a new experimental approach based on molecular photoswitches to achieve additional control on the chemical reaction and to allow short-time resolution of the spin dynamics. Our proposal enables experiments to test some of the standard assumptions of the radical pair model and improves the sensitivity of chemical magnetometers by two orders of magnitude.
    Chemical Physics Letters 06/2012; 572. DOI:10.1016/j.cplett.2013.04.010 · 1.99 Impact Factor
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    ABSTRACT: In theories of spin-dependent radical pair reactions, the time evolution of the radical pair, including the effect of the chemical kinetics, is described by a master equation in the Liouville formalism. For the description of the chemical kinetics, a number of possible reaction operators have been formulated in the literature. In this work, we present a framework that allows for a unified description of the various proposed mechanisms and the forms of reaction operators for the spin-selective recombination processes. On the basis of the concept that master equations can be derived from a microscopic description of the spin system interacting with external degrees of freedom, it is possible to gain insight into the underlying microscopic processes and develop a systematic approach toward determining the specific form of the reaction operator in concrete scenarios.
    The Journal of Physical Chemistry A 03/2012; 116(16):4020-8. DOI:10.1021/jp209196a · 2.77 Impact Factor
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    ABSTRACT: Recently, photoswitchable molecules, i.e. diarylethene, gained significant interest due to their applicability in data storage media, as optical switches, and in novel logic circuits [1]. Diarylethene-derivative molecules are the most promising candidates to design electronic functional elements, because of their excellent thermal stability, high fatigue resistance, and negligible change upon switching [1]. Here, we present the preferential conductance of specifically designed sulfur-free diarylethene molecules [2] bridging the mechanically controlled break-junctions at low temperatures [3]. The molecular energy levels and electrode couplings are obtained by evaluating the current-voltage characteristics using the single-level model [4]. The charge transport mechanism of different types of diarylethene molecules is investigated, and the results are discussed within the framework of novel theoretical predictions. [4pt] [1] M. Del Valle etal., Nat Nanotechnol 2, 176 (2007) S. J. van der Molen etal., Nano. Lett. 9, 76 (2009).[0pt] [2] D. Sysoiev etal., Chem. Eur. J. 17, 6663 (2011).[0pt] [3] Y. Kim etal., Phys. Rev. Lett. 106, 196804 (2011).[0pt] [4] Y. Kim etal., Nano Lett. 11, 3734 (2011). L. Zotti etal., Small 6, 1529 (2010).
  • Dominik Wöll, Nikita Lukzen, Ulrich E Steiner
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    ABSTRACT: The kinetic rate equation for the photosensitized cleavage reaction of surface-bound photolabile chromophores with free diffusion of sensitizer molecules from the bulk of a solution to the surface is derived by determining the stationary solution of a diffusion equation with suitable boundary conditions. The relation between the phenomenological rate constant for the photosensitized reaction at the surface and in the bulk is established. Applying the result to the analysis of an experimental example, the origin of the quasi zeroth-order kinetics of the sensitized reaction is revealed. A theoretical comparison of intramolecular sensitization in photocleavable protecting groups with a molecular antenna and sensitization with the freely diffusing sensitizer shows that in a typical case sensitization with free diffusion is more effective than intramolecular sensitization for sensitizer concentrations higher than 5 mM.
    Photochemical and Photobiological Sciences 01/2012; 11(3):533-8. DOI:10.1039/c1pp05319a · 2.92 Impact Factor
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    Sergey Milikisiyants, Ulrich E. Steiner, Henning Paul
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    ABSTRACT: The triplet-sensitized photodecomposition of azocumene into nitrogen and cumyl radicals is investigated by time-resolved electron paramagnetic resonance and absorption spectroscopy. The radicals are found to be created spin polarized with a yield depending on the strength of the applied magnetic field. The phenomenon arises because in triplet azocumene, the decay into radicals competes with a fast triplet-sublevel selective intersystem crossing back to the azocumene ground state. The size of the initial spin polarization of the radicals and the magnetic field effect on their yield are determined in solvents of different viscosities. Data analysis yields rate constants for the intersystem crossing and the cleavage reaction of triplet azocumene as well as its zero-field splitting D ZFS. At room temperature in nonpolar solvents, the most probable values are: k x = k y = 1.2 × 1011 s−1 and k z = 1.9 × 1010 s−1 for the intersystem crossing from the energetically lower and upper triplet substates, respectively, k p = 1.6 × 109 s−1 for the cleavage reaction and for the zero-field splitting D ZFS = −3.4 × 1010 s−1 (0.18 cm−1).
    Applied Magnetic Resonance 12/2011; 41(2-4). DOI:10.1007/s00723-011-0263-z · 1.15 Impact Factor
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    ABSTRACT: Oxidation of dihydrorhodamine 123 (DHR) to rhodamine 123 (RH) by oxoperoxonitrite (ONOO(-)), formed through recombination of NO and O(2)(·-) radicals resulting from thermal decomposition of 3-morpholinosydnonimine (SIN-1) in buffered aerated aqueous solution at pH 7.6, represents a kinetic model system of the reactivity of NO and O(2)(·-) in biochemical systems. A magnetic-field effect (MFE) on the yield of RH detected in this system is explored in the full range of fields between 0 and 18 T. It is found to increase in a nearly linear fashion up to a value of 5.5±1.6 % at 18 T and 23 °C (3.1±0.7 % at 40 °C). A theoretical framework to analyze the MFE in terms of the magnetic-field-enhanced recombination rate constant k(rec) of NO and O(2)(·-) due to magnetic mixing of T(0) and S spin states of the radical pair by the Δg mechanism is developed, including estimation of magnetic properties (g tensor and spin relaxation times) of NO and O(2)(·-) in aqueous solution, and calculation of the MFE on k(rec) using the theoretical formalism of Gorelik at al. The factor with which the MFE on k(rec) is translated to the MFE on the yield of ONOO(-) and RH is derived for various kinetic scenarios representing possible sink channels for NO and O(2)(·-). With reasonable assumptions for the values of some unknown kinetic parameters, the theoretical predictions account well for the observed MFE.
    ChemPhysChem 06/2011; 12(9):1714-28. DOI:10.1002/cphc.201100178 · 3.36 Impact Factor
  • ChemPhysChem 06/2011; 12(9). DOI:10.1002/cphc.201190045 · 3.36 Impact Factor
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    ABSTRACT: In an attempt to design molecular optoelectronic switches functioning in molecular junctions between two metal tips, we synthesized a set of photochromic compounds by extending the π-system of 1,2-bis-(2-methyl-5-formylfuran-3-yl)perfluorocyclopentene through suitable coupling reactions involving the formyl functions, thereby also introducing terminal groups with a binding capacity to gold. Avoiding the presence of gold-binding sulphur atoms in the photoreactive centre, as they are present in the frequently used analogous thienyl compounds, the newly synthesized compounds should be more suitable for the purpose indicated. The kinetics of reversible photoswitching of the new compounds by UV and visible light was quantitatively investigated in solution. The role of conformational flexibility of the π-system for the width of the UV/Vis spectra was clarified by using quantum chemical calculations with time-dependent (TD)-DFT. As a preliminary test of the potential of the new compounds to serve as optoelectronic molecular switches, monolayer formation and photochemical switching on gold surfaces was observed by using surface plasmon resonance.
    Chemistry - A European Journal 06/2011; 17(24):6663-72. DOI:10.1002/chem.201003716 · 5.93 Impact Factor
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    ABSTRACT: In his Comment on a recent paper by two of us Kominis claims that the recently proposed quantum measurement model for spin-selective reactions of radical pairs leads to ambiguous predictions in a simple case. Here we show that this claim is based on a confusion between the unreacted and unrecombined portions of the radical pairs, and to an incorrect interpretation of the improper density matrices used in both our model and the conventional Haberkorn model of such reactions. We further show that if this error is corrected then the supposed ambiguity is resolved.
    Chemical Physics Letters 04/2011; 508(1). DOI:10.1016/j.cplett.2011.04.022 · 1.99 Impact Factor
  • Doklady Physical Chemistry 01/2011; 436(1):5-7. DOI:10.1134/S0012501611010027 · 0.48 Impact Factor
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    Keith A. McLauchlan, Ulrich Steiner
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    ABSTRACT: The concept of the spin-correlated radical pair has been used for some time in the interpretation of the results of magnetic polarization experiments in NMR and in ESR (CIDNP and CIDEP), and of the effects of magnetic fields on chemical reactions. It has, however, a much wider general significance as a reaction intermediate in all radical reactions, including photochemistry. Here the nature of the pair is introduced, and the evidence for it reviewed, and it is further shown how it can be treated theoretically, before some of the consequences of its existence are pointed out. Its recognition, and in particular the understanding of the processes which occur within it, notably the interplay of spin-mixing and diffusion, allow the design of new experiments in the absence or presence of an external magnetic field, and the optimization of reaction yields.
    ChemInform 10/2010; 73(2). DOI:10.1002/chin.199143258
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    ABSTRACT: Template-directed synthesis of complementary strands is pivotal for life. Nature employs polymerases for this reaction, leaving the ability of DNA itself to direct the incorporation of individual nucleotides at the end of a growing primer difficult to assess. Using 64 sequences, we now find that any of the four nucleobases, in combination with any neighboring residue, support enzyme-free primer extension when primer and mononucleotide are sufficiently reactive, with >or=93% primer extension for all sequences. Between the 64 possible base triplets, the rate of extension for the poorest template, CAG, with A as templating base, and the most efficient template, TCT, with C as templating base, differs by less than two orders of magnitude. Further, primer extension with a balanced mixture of monomers shows >or=72% of the correct extension product in all cases, and >or=90% incorporation of the correct base for 46 out of 64 triplets in the presence of a downstream-binding strand. A mechanism is proposed with a binding equilibrium for the monomer, deprotonation of the primer, and two chemical steps, the first of which is most strongly modulated by the sequence. Overall, rates show a surprisingly smooth reactivity landscape, with similar incorporation on strongly and weakly templating sequences. These results help to clarify the substrate contribution to copying, as found in polymerase-catalyzed replication, and show an important feature of DNA as genetic material.
    Proceedings of the National Academy of Sciences 07/2010; 107(27):12074-9. DOI:10.1073/pnas.0914872107 · 9.81 Impact Factor
  • Carbon-Centered Free Radicals and Radical Cations: Structure, Reactivity, and Dynamics, 01/2010: pages 205 - 220; , ISBN: 9780470584118
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    ABSTRACT: The formation of self-assembled monolayers (SAMs) on gold by 2-(5-iodo-2-nitrophenyl) propoxycarbonyl (I-NPPOC)-protected thymidine with an attached mercaptohexyl succinate linker and the kinetics of photochemical release of the I-NPPOC group were monitored using X-ray photoelectron spectroscopy (XPS) and surface plasmon resonance (SPR) detection. In the XPS spectra, the iodine peaks allowed for specific and accurate monitoring of the presence and loss of I-NPPOC groups on the surface. In the SPR experiment, the overall signal change on photoillumination is in accord with a theoretical estimation of the density of I-NPPOC groups in a dense monolayer. The kinetics roughly follow a biexponential time dependence with two very different time constants, corresponding to photochemical quantum yields of 0.22 and 0.0032, respectively.
    Langmuir 09/2009; 25(18). DOI:10.1021/la901346s · 4.38 Impact Factor
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    ABSTRACT: Novel photolabile protecting groups based on the 2-(2-nitrophenyl)propoxycarbonyl (NPPOC) group with a covalently linked thioxanthone as an intramolecular triplet sensitizer exhibit significantly enhanced light sensitivity under continuous illumination. Herein we present a detailed study of the photokinetics and photoproducts of nucleosides caged with these new protecting groups. Relative to the parent NPPOC group, the light sensitivity of the new photolabile protecting groups is enhanced by up to a factor of 21 at 366 nm and is still quite high at 405 nm, the wavelength at which the sensitivity of the parent compound is practically zero. A new pathway for deprotection of the NPPOC group proceeding through a nitroso benzylalcohol intermediate has been discovered to complement the main mechanism, which involves beta elimination. Under standard conditions of lithographic DNA-chip synthesis, some of the new compounds, while maintaining the same chip quality, react ten times faster than the unmodified NPPOC-protected nucleosides.
    Chemistry 02/2008; 14(21):6490-7. DOI:10.1002/chem.200800613 · 5.70 Impact Factor
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    ABSTRACT: Abstract— While studying the photoreduction of some dyes (D) by reducing agents (R), it was observed that the quantum yield of the photoreduction increases considerably upon addition of a third substance (C), whereas it is very small when the dye is photoreduced by C alone (catalytic effect), (see Table 1).The system thionine (D), allylthiourea (R), and azulene (C) was investigated in detail using both flash photolysis and continuous illumination. On photolysis, thionine is converted into its photo-reduced form, leucothionine. Azulene reacts with the basic form of the thionine triplet 3TH+ to produce the semithionine radical. In the system thionine and azulene, most of these radicals revert back to thionine. When ATU (˜ 102-M) is added to thionine and azulene (3 × 10-4M), the semithionine radicals are reduced to leucothionine; the quantum yield of this reduction is considerably higher than in the system thionine and allylthiourea. Flash experiments demonstrate that allylthiourea does not react with the semithionine radicals.At very high ATU concentrations (≥ 10-1M), however, the primary reaction is between thionine triplet and allylthiourea; under these conditions the quantum yield is not influenced by azulene (3 × 10-4M).
    Photochemistry and Photobiology 01/2008; 19(2):119 - 128. DOI:10.1111/j.1751-1097.1974.tb06487.x · 2.68 Impact Factor

Publication Stats

2k Citations
321.47 Total Impact Points

Institutions

  • 1983–2015
    • Universität Konstanz
      • Department of Chemistry
      Constance, Baden-Württemberg, Germany
  • 2012
    • University of Bristol
      Bristol, England, United Kingdom
  • 2011
    • Russian Academy of Sciences
      • Institute of Chemical Kinetics and Combustion
      Moskva, Moscow, Russia
  • 1975–2008
    • Universität Stuttgart
      Stuttgart, Baden-Württemberg, Germany
  • 2001
    • Weizmann Institute of Science
      • Department of Chemical Physics
      Israel
  • 1989
    • Osaka University
      Suika, Ōsaka, Japan