Walter Thiel

Max Planck Institute for Coal Research, Mülheim-on-Ruhr, North Rhine-Westphalia, Germany

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Publications (550)2349.58 Total impact

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    ABSTRACT: The semiempirical orthogonalization-corrected OMx methods (OM1, OM2, OM3) go beyond the standard MNDO model by including additional interactions in the electronic structure calculation. When augmented with empirical dispersion corrections, the resulting OMx-Dn approaches offer a fast and robust treatment of noncovalent interactions. Here we evaluate the performance of the OMx and OMx-Dn methods for a variety of ground-state properties using a large and diverse collection of benchmark sets from the literature, with a total of 13035 original and derived reference data. Extensive comparisons are made with the results from established semiempirical methods (MNDO, AM1, PM3, PM6, and PM7) that also use the NDDO (neglect of diatomic differential overlap) integral approximation. Statistical evaluations show that the OMx and OMx-Dn methods outperform the other methods for most of the benchmark sets.
    No preview · Article · Jan 2016 · Journal of Chemical Theory and Computation
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    ABSTRACT: Semiempirical orthogonalization-corrected methods (OM1, OM2, OM3) go beyond the standard MNDO model by explicitly including additional interactions into the Fock matrix in an approximate manner (Pauli repulsion, penetration effects, and core-valence interactions), which yields systematic improvements both for ground-state and excited-state properties. In this article, we describe the underlying theoretical formalism of the OMx methods and their implementation in full detail, and we report all relevant OMx parameters for hydrogen, carbon, nitrogen, oxygen, and fluorine. For a standard set of mostly organic molecules commonly used in semiempirical method development, the OMx results are found to be superior to those from standard MNDO-type methods. Parametrized Grimme-type dispersion corrections can be added to OM2 and OM3 energies to provide a realistic treatment of noncovalent interaction energies, as demonstrated for the complexes in the S22 and S66x8 test sets.
    No preview · Article · Jan 2016 · Journal of Chemical Theory and Computation
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    ABSTRACT: The interactions between diphenylcarbene DPC and the halogen bond donors CF3I and CF3Br were investigated using matrix isolation spectroscopy (IR, UV-vis, and EPR) in combination with QM and QM/MM calculations. Both halogen bond donors CF3X form very strong complexes with the singlet state of DPC, but only weakly interact with triplet DPC. This results in a switching of the spin state of DPC, the singlet complexes becoming more stable than the triplet complexes. CF3I forms a second complex (type II) with DPC that is thermodynamically slightly more stable. Calculations predict that in this second complex the DPC···I distance is shorter than the F3C···I distance, whereas in the first (type I) complex the DPC···I distance is, as expected, longer. CF3Br only forms the type I complex. Upon irradiation I or Br, respectively, are transferred to the DPC carbene center and radical pairs are formed. Finally, on annealing, the formal C-X insertion product of DPC is observed. Thus, halogen bonding is a powerful new principle to control the spin state of reactive carbenes.
    No preview · Article · Jan 2016 · Journal of the American Chemical Society
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    ABSTRACT: The chemical locking of the central single bond in core chromophores of green fluorescent proteins (GFPs) influences their excited-state behavior in a distinct manner. Experimentally, it significantly enhances the fluorescence quantum yield of GFP chromophores with an ortho-hydroxyl group, while it has almost no effect on the photophysics of GFP chromophores with a para-hydroxyl group. To unravel the underlying physical reasons for this different behavior, we report static electronic structure calculations and nonadiabatic dynamics simulations on excited-state intramolecular proton transfer, cis-trans isomerization, and excited-state deactivation in a locked ortho-substituted GFP model chromophore (o-LHBI). On the basis of our previous and present results, we find that the S1 keto species is responsible for the fluorescence emission of the unlocked o-HBI and the locked o-LHBI species. Chemical locking does not change the parts of the S1 and S0 potential energy surfaces relevant to enol-keto tautomerization; hence, in both chromophores, there is an ultrafast excited-state intramolecular proton transfer that takes only 35 fs on average. However, the locking effectively hinders the S1 keto species from approaching the keto S1/S0 conical intersections so that most of trajectories are trapped in the S1 keto region for the entire 2 ps simulation time. Therefore, the fluorescence quantum yield of o-LHBI is enhanced compared with that of unlocked o-HBI, in which the S1 excited-state decay is efficient and ultrafast. In the case of the para-substituted GFP model chromophores p-HBI and p-LHBI, chemical locking hardly affects their efficient excited-state deactivation via cis-trans isomerization; thus, the fluorescence quantum yields in these chromophores remain very low. The insights gained from the present work may help to guide the design of new GFP chromophores with improved fluorescence emission and brightness.
    No preview · Article · Jan 2016 · Journal of Chemical Theory and Computation
  • Shu-Hua Xia · Ganglong Cui · Wei-Hai Fang · Walter Thiel
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    ABSTRACT: Photoswitchable azobenzene cross-linkers can control the folding and unfolding of peptides by photoisomerization and can thus regulate peptide affinities and enzyme activities. Using quantum mechanics/molecular mechanics (QM/MM) methods and classical MM force fields, we report the first molecular dynamics simulations of the photoinduced folding and unfolding processes in the azobenzene cross-linked FK-11 peptide. We find that the interactions between the peptide and the azobenzene cross-linker are crucial for controlling the evolution of the secondary structure of the peptide and responsible for accelerating the folding and unfolding events. They also modify the photoisomerization mechanism of the azobenzene cross-linker compared with the situation in vacuo or in solution.
    No preview · Article · Jan 2016 · Angewandte Chemie International Edition
  • Shu-Hua Xia · Ganglong Cui · Wei-Hai Fang · Walter Thiel
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    ABSTRACT: Photoswitchable azobenzene cross-linkers can control the folding and unfolding of peptides by photoisomerization and can thus regulate peptide affinities and enzyme activities. Using quantum mechanics/molecular mechanics (QM/MM) methods and classical MM force fields, we report the first molecular dynamics simulations of the photoinduced folding and unfolding processes in the azobenzene cross-linked FK-11 peptide. We find that the interactions between the peptide and the azobenzene cross-linker are crucial for controlling the evolution of the secondary structure of the peptide and responsible for accelerating the folding and unfolding events. They also modify the photoisomerization mechanism of the azobenzene cross-linker compared with the situation in vacuo or in solution.
    No preview · Article · Jan 2016 · Angewandte Chemie
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    ABSTRACT: A new nine-dimensional potential energy surface (PES) and dipole momentsurface (DMS) for silane have been generated using high-level ab initio theory. The PES, CBS-F12HL, reproduces all four fundamental term values for 28SiH4 with sub-wavenumber accuracy, resulting in an overall root-mean-square error of 0.63 cm−1. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit, and incorporates a range of higher-level additive energy corrections to account for core-valence electron correlation, higher-order coupled cluster terms, and scalar relativistic effects. Systematic errors in computed intra-band rotational energy levels are reduced by empirically refining the equilibrium geometry. The resultant Si–H bond length is in excellent agreement with previous experimental and theoretical values. Vibrational transition moments, absolute line intensities of the ν3 band, and the infrared spectrum for 28SiH4 including states up to J = 20 and vibrational band origins up to 5000 cm−1 are calculated and compared with available experimental results. The DMS tends to marginally overestimate the strength of line intensities. Despite this, band shape and structure across the spectrum are well reproduced and show good agreement with experiment. We thus recommend the PES and DMS for future use.
    Full-text · Article · Dec 2015 · The Journal of Chemical Physics
  • Mahendra Patil · Walter Thiel
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    ABSTRACT: We report a computational study on the mechanism of the reaction of ethyl acetoacetate (1) with two sulfur reagents: Martin's sulfurane (Ra) and a mixture of diphenyl sulfide and triflic anhydride (Rb). These reagents are able to provide a sulfonium ion [Ph2S-OX]+ and an anionic nucleophile –OX as active species [X = C(CF3)2Ph for Ra and X = SO2CF3 for Rb] in the reaction. Experimentally, the reaction of Ra with carbonyl compounds provides an S-ylide as the only product whereas a low yield of S-ylide is obtained in the case of Rb. To elucidate the mechanism of these reactions with prototype substrate 1, different plausible pathways have been investigated using density functional theory (DFT), mostly at the B3LYP-D/6-31+G** level. According to DFT calculations, initial deprotonation of 1 may furnish either an enolate (with Ra) or an O-sulfenylated enolate (with Rb). Subsequent nucleophilic addition of the enolate to the sulfonium ion provides the simplest route to S-ylide product, which is favored when using reagent Ra. In the case of reagent Rb, the preferentially formed O-sulfenylated enolate may undergo either a series of nucleophilic displacements or a [1,3] sigmatropic shift or a [3,3] sigmatropic rearrangement, all followed by a final deprotonation to yield the product. These conversions are highly exothermic and involve thermodynamically stable products. The [3,3] sigmatropic rearrangement that directly produces an arylated carbonyl compound is computed to be the kinetically most facile reaction with Rb. Overall, the computational results unveil detailed mechanistic scenarios detailing possible transformations and providing qualitative explanations for some of the experimental findings.
    No preview · Article · Dec 2015 · European Journal of Organic Chemistry
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    ABSTRACT: Two new light driven molecular rotary motors based on the N-alkylated indanylidene benzopyrrole frameworks are proposed and studied using quantum chemical calculations and non-adiabatic molecular dynamics simulations. These new motors perform pure axial rotation, and the photochemical steps of the rotary cycle are dominated by the fast bond-length-alternation motion that enables ultrafast access to the S1 /S0 intersection. The new motors are predicted to display a higher quantum efficiency than the currently available synthetic all-hydrocarbon motors. Remarkably, the quantum efficiency is not governed by the topography (peaked vs. sloped) of the minimum energy conical intersection, whereas the S1 decay time depends on the topography as well as on the energy of the intersection relative to the S1 minimum. It is the axial chirality (helicity), rather than the point chirality, that controls the sense of rotation of the motor.
    Preview · Article · Dec 2015 · Journal of Physical Chemistry Letters
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    ABSTRACT: The mass sensitivity of the vibration–rotation–inversion transitions of H316O+, H318O+, and D316O+ is investigated variationally using the nuclear motion program trove (Yurchenko, Thiel & Jensen). The calculations utilize new high-level ab initio potential energy and dipole moment surfaces. Along with the mass dependence, frequency data and Einstein A coefficients are computed for all transitions probed. Particular attention is paid to the Δ|k| = 3 and Δ|k − l| = 3 transitions comprising the accidentally coinciding |J, K = 0, v2 = 0+〉 and |J, K = 3, v2 = 0−〉 rotation–inversion energy levels. The newly computed probes exhibit sensitivities comparable to their ammonia and methanol counterparts, thus demonstrating their potential for testing the cosmological stability of the proton-to-electron mass ratio. The theoretical trove results are in close agreement with sensitivities obtained using the non-rigid and rigid inverter approximate models, confirming that the ab initio theory used in the present study is adequate.
    No preview · Article · Dec 2015 · Monthly Notices of the Royal Astronomical Society
  • Berit Heggen · Walter Thiel
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    ABSTRACT: Iron is a versatile catalyst for cross coupling reactions. These reactions may proceed either via classical redox cycles involving low-valent iron species or via highly alkylated organoferrate complexes. Experimentally, it is difficult to trap reactive intermediates, but it has been possible to prepare iron complexes similar to the supposed active catalyst that are able to methylate activated electrophiles (J. Am. Chem. Soc. 130 (2008) 8773–8787). Motivated by these experiments we studied the methylation of 4-chlorobenzoyl chloride by the organoferrate complex [(Me)4 Fe(MeLi)][Li(OEt2)]2 employing density functional theory at the OPBE/6-311+G** level, as well as B3LYP/6-311+G** calculations with explicit inclusion of dispersion and solvent effects (describing iron with the QZVP basis and SDD pseudopotential). In the preferred mechanism, methyl transfer takes place via substitution at the organoferrate complex, with the leaving methyl group being replaced by chloride. In line with the experimental findings, up to four methyl groups can be transferred in this manner. By locating all conceivable transition states and intermediates, the calculations shed light on the relative ease of substitution at the various positions of the organoferrate complex, both in the first and subsequent methyl tranfers. Transition states for an alternative redox mechanism could not be located.
    No preview · Article · Dec 2015 · Journal of Organometallic Chemistry
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    ABSTRACT: Time-resolved photoelectron spectroscopy is performed on aqueous guanosine solution to study its excited-state relaxation dynamics. Experimental results are complemented by surface hopping dynamic simulations and evaluation of the excited-state ionization energy by Koopmans' theorem. Two alternative models for the relaxation dynamics are discussed. The experimentally observed excited-state lifetime is about 2.5 ps if the molecule is excited at 266 nm and about 1.1 ps if the molecule is excited at 238 nm. The experimental probe photon energy dependence of the photoelectron kinetic energy distribution suggests that the probe step is not vertical and involves a doubly-excited autoionizing state.
    No preview · Article · Nov 2015 · Physical Chemistry Chemical Physics
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    ABSTRACT: A highly enantioselective Brønsted acid catalyzed intramolecular carbonyl-ene reaction of olefinic aldehydes has been developed. Using a confined imidodiphosphate catalyst, the reaction delivers diverse trans-3,4-disubstituted carbo- and heterocyclic five-membered rings in high yields and with good to excellent diastereo- and enantioselectivities. ESI-MS, NMR, and DFT mechanistic studies reveal that the reaction proceeds via a stepwise pathway involving a novel covalent intermediate.
    No preview · Article · Oct 2015 · Journal of the American Chemical Society
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    ABSTRACT: Insights into the mechanism of the unusual trans-hydrogenation of internal alkynes catalyzed by {CpRu} complexes were gained by para-hydrogen (p-H2) induced polarization (PHIP) transfer NMR spectroscopy. It was found that the productive trans-reduction competes with a pathway in which both H atoms of H2 are delivered to a single alkyne C atom of the substrate while the second alkyne C atom is converted into a metal carbene. This "geminal hydrogenation" mode seems unprecedented; it was independently confirmed by the isolation and structural characterization of a ruthenium carbene complex stabilized by secondary inter-ligand interactions. A detailed DFT study shows that the trans alkene and the carbene complex originate from a common metallacyclopropene intermediate. Furthermore, the computational analysis and the PHIP NMR data concur in that the metal carbene is the major gateway to olefin isomerization and over-reduction, which frequently interfere with regular alkyne trans-hydrogenation. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    No preview · Article · Oct 2015 · Angewandte Chemie International Edition
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    ABSTRACT: We show by quantum mechanical/molecular mechanical (QM/MM) simulations that phenylbenzothiazoles undergoing an excited-state proton transfer (ESPT) can be used to probe protein binding sites. For 2-(2'-hydroxy-4'-aminophenyl)benzothiazole (HABT) bound to a tyrosine kinase, the absolute and relative intensities of the fluorescence bands arising from the enol and keto forms of HABT are found to be strongly dependent on the active-site conformation. The emission properties are tuned by hydrogen-bonding interactions of HABT with the neighboring amino acid T766 and with active-site water. The use of ESPT tuners opens the possibility of creating two-color fluorescent markers for protein binding sites, with potential applications to detection of mutations in cancer cell lines. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Full-text · Article · Sep 2015 · ChemPhysChem
  • Berit Heggen · Mahendra Patil · Walter Thiel
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    ABSTRACT: Density functional theory is used to study the mechanism of the title reaction, one of the first catalytic asymmetric 6π-electrocyclizations observed experimentally. The benzylideneacetone-derived phenyl hydrazone is chosen as model substrate for the cyclization reaction, both in the protonated (A) and unprotonated (B) form, while the isoelectronic carbon analogue, 1,5-diphenylpentadienyl anion (C), serves as a reference for comparisons. The barrier to cyclization is computed to be more than 15 kcal/mol lower in A compared with B, in line with the observed acid catalysis. The relevant transition states to cyclization are characterized for A and C using orbital inspection, natural bond orbital analysis, nucleus independent chemical shifts, and stereochemical indicators. The cyclization of C is confirmed to be pericyclic, while that of A can be described as pseudopericyclic ring closure involving an intramolecular nucleophilic addition. © 2015 Wiley Periodicals, Inc.
    No preview · Article · Sep 2015 · Journal of Computational Chemistry
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    ABSTRACT: Insights into the mechanism of the unusual trans-hydrogenation of internal alkynes catalyzed by {Cp*Ru} complexes were gained by para-hydrogen (p-H2 ) induced polarization (PHIP) transfer NMR spectroscopy. It was found that the productive trans-reduction competes with a pathway in which both H atoms of H2 are delivered to a single alkyne C atom of the substrate while the second alkyne C atom is converted into a metal carbene. This "geminal hydrogenation" mode seems unprecedented; it was independently confirmed by the isolation and structural characterization of a ruthenium carbene complex stabilized by secondary inter-ligand interactions. A detailed DFT study shows that the trans alkene and the carbene complex originate from a common metallacyclopropene intermediate. Furthermore, the computational analysis and the PHIP NMR data concur in that the metal carbene is the major gateway to olefin isomerization and over-reduction, which frequently interfere with regular alkyne trans-hydrogenation. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Preview · Article · Aug 2015 · Angewandte Chemie
  • Jan P Götze · Bora Karasulu · Mahendra Patil · Walter Thiel
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    ABSTRACT: We present a computationally derived energy transfer model for the peridinin-chlorophyll a-protein (PCP), which invokes vibrational relaxation in the two lowest singlet excited states rather than internal conversion between them. The model allows an understanding of the photoinduced processes without assuming further electronic states or a dependence of the 2Ag state character on the vibrational sub-state. We report molecular dynamics simulations (CHARMM22 force field) and quantum mechanics/molecular mechanics (QM/MM) calculations on PCP. In the latter, the QM region containing a single peridinin (Per) chromophore or a Per-Chl a (chlorophyll a) pair is treated by density functional theory (DFT, CAM-B3LYP) for geometries and by DFT-based multireference configuration interaction (DFT/MRCI) for excitation energies. The calculations show that Per has a bright, green light absorbing 2Ag state, in addition to the blue light absorbing 1Bu state found in other carotenoids. Both states undergo a strong energy lowering upon relaxation, leading to emission in the red, while absorbing in the blue or green. The orientation of their transition dipole moments indicates that both states are capable of excited-state energy transfer to Chl a, without preference for either 1Bu or 2Ag as donor state. We propose that the commonly postulated partial intramolecular charge transfer (ICT) character of a donating Per state can be assigned to the relaxed 1Bu state, which takes on ICT character. By assuming that both 1Bu and 2Ag are able to donate to the Chl a Q band, one can explain why different chlorophyll species in PCP exhibit different acceptor capabilities. Copyright © 2015 Elsevier Inc. All rights reserved.
    No preview · Article · Jul 2015 · Biochimica et Biophysica Acta
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    ABSTRACT: The cyclization of the hydroxy-allene 2 to the tetrahydrofuran 3 catalyzed by the gold-phosphoramidite complex 1, after ionization with an appropriate silver salt AgX, is one of the most striking cases of enantioinversion known to date. The major reason why the sense of induction can be switched from (S) to (R) solely by changing either the solvent or the temperature or the nature of the counterion X is likely found in the bias of the organogold intermediates to undergo assisted proto-deauration. Such assistance can be provided by a protic solvent, a reasonably coordinating counterion or even by a second substrate molecule itself; in this case, the reaction free energy profile gains a strong entropic component that can ultimately dictate the stereochemical course. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    No preview · Article · Jul 2015 · Chemistry - A European Journal
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    ABSTRACT: We present two new modifications of the second-order polarization propagator approximation (SOPPA), SOPPA(SCS-MP2) and SOPPA(SOS-MP2), which employ either spin-component-scaled or scaled opposite-spin MP2 correlation coefficients instead of the regular MP2 coefficients. The performance of these two methods, the original SOPPA method as well as SOPPA(CCSD) and RPA(D) in the calculation of vertical electronic excitation energies and oscillator strengths is investigated for a large benchmark set of 28 medium-sized molecules with 139 singlet and 71 triplet excited states. The results are compared with the corresponding CC3 and CASPT2 results from the literature for both the TZVP set and the larger and more diffuse aug-cc-pVTZ basis set. In addition, the results with the aug-cc-pVTZ basis set are compared with the theoretical best estimates for this benchmark set. We find that the original SOPPA method gives overall the smallest mean deviations from the reference values and the most consistent results.
    No preview · Article · Jul 2015 · Molecular Physics

Publication Stats

18k Citations
2,349.58 Total Impact Points

Institutions

  • 2000-2015
    • Max Planck Institute for Coal Research
      Mülheim-on-Ruhr, North Rhine-Westphalia, Germany
  • 2010
    • Friedrich-Alexander-University of Erlangen-Nürnberg
      • Computer-Chemistry-Center
      Erlangen, Bavaria, Germany
    • ETH Zurich
      Zürich, Zurich, Switzerland
  • 1993-2010
    • University of Zurich
      • Institut für Organische Chemie
      Zürich, ZH, Switzerland
  • 1986-2010
    • Bergische Universität Wuppertal
      • • Inorganic Chemistry
      • • Department of Chemistry and Biology
      • • Physical and Theoretical Chemistry
      Wuppertal, North Rhine-Westphalia, Germany
  • 2009
    • University of St Andrews
      • School of Chemistry
      Saint Andrews, Scotland, United Kingdom
    • The University of Calgary
      Calgary, Alberta, Canada
    • Heinrich-Heine-Universität Düsseldorf
      • Institute for Theoretical and Computational Chemistry
      Düsseldorf, North Rhine-Westphalia, Germany
    • IT University of Copenhagen
      København, Capital Region, Denmark
  • 2003-2009
    • Hebrew University of Jerusalem
      • • Lise Meitner Minerva Center for Computational Quantum Chemistry
      • • Department of Organic Chemistry
      • • Institute of Chemistry
      Yerushalayim, Jerusalem District, Israel
  • 2005
    • Universität Paderborn
      • Department of Physics
      Paderborn, North Rhine-Westphalia, Germany
    • University of Minnesota Duluth
      • Department of Chemistry and Biochemistry
      Duluth, Minnesota, United States
  • 2004
    • Athens State University
      Athens, Alabama, United States
  • 1998
    • Ruhr-Universität Bochum
      Bochum, North Rhine-Westphalia, Germany
    • University of Strasbourg
      Strasburg, Alsace, France