Walter Thiel

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

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Publications (533)2257.77 Total impact

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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.
    Physical Chemistry Chemical Physics 11/2015; DOI:10.1039/C5CP04394H · 4.49 Impact Factor
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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.
    Journal of the American Chemical Society 10/2015; 137(41). DOI:10.1021/jacs.5b09484 · 12.11 Impact Factor
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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.
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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.
    ChemPhysChem 09/2015; DOI:10.1002/cphc.201500744 · 3.42 Impact Factor
  • 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.
    Journal of Computational Chemistry 09/2015; DOI:10.1002/jcc.24044 · 3.59 Impact Factor
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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.
    Angewandte Chemie 08/2015; 54(42). DOI:10.1002/ange.201506075
  • 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.
    Biochimica et Biophysica Acta 07/2015; 1847(12). DOI:10.1016/j.bbabio.2015.07.011 · 4.66 Impact Factor
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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.
    Chemistry - A European Journal 07/2015; 21(35). DOI:10.1002/chem.201502160 · 5.73 Impact Factor
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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.
    Molecular Physics 07/2015; 113:2026-2045. DOI:10.1080/00268976.2015.1048320 · 1.72 Impact Factor
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    ABSTRACT: Contemporary catalytic procedures involving alkylpalladium(II) have enriched the arsenal of synthetic organic chemistry. Those transformations usually rely on internal coordination through “directing groups”, carefully designed to maximize catalytic efficiency and regioselectivity. Herein, we report structural and reactivity studies of a series of internally coordinated monohaptoallylpalladium complexes. These species enable the direct spectroscopic observation and theoretical study of π-σ-π interconversion processes. They further display unusual dynamic behavior which should be of direct relevance to chemistries beyond catalytic allylic alkylation.
    Chemical Science 07/2015; 6(10). DOI:10.1039/C5SC01867F · 9.21 Impact Factor
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    ABSTRACT: The mechanism of enzymatic peptide hydrolysis in matrix metalloproteinase-2 (MMP-2) was studied at atomic resolution through quantum mechanics/molecular mechanics (QM/MM) simulations. An all-atom three-dimensional molecular model was constructed on the basis of a crystal structure from the Protein Data Bank (ID: 1QIB), and the oligopeptide Ace-Gln-Gly∼Ile-Ala-Gly-Nme was considered as the substrate. Two QM/MM software packages and several computational protocols were employed to calculate QM/MM energy profiles for a four-step mechanism involving an initial nucleophilic attack followed by hydrogen bond rearrangement, proton transfer, and CN bond cleavage. These QM/MM calculations consistently yield rather low overall barriers for the chemical steps, in the range of 5-10 kcal/mol, for diverse QM treatments (PBE0, B3LYP, and BB1K density functionals as well as local coupled cluster treatments) and two MM force fields (CHARMM and AMBER). It, thus, seems likely that product release is the rate-limiting step in MMP-2 catalysis. This is supported by an exploration of various release channels through QM/MM reaction path calculations and steered molecular dynamics simulations. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.
    Journal of Computational Chemistry 07/2015; 36(21). DOI:10.1002/jcc.23977 · 3.59 Impact Factor
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    Daniel Escudero · Walter Thiel · Benoit R. Champagne ·
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    ABSTRACT: In this communication we use the density functional theory-based multi-reference configuration interaction (DFT/MRCI) and the second-order algebraic diagrammatic construction (ADC(2)) methods to compute the spectroscopic and second-order nonlinear optical (NLO) properties of Ru(II)-based NLO-phores. For some of the complexes, an appropriate treatment of doubly excited states is essential to correctly describe their spectroscopic and photochemical properties. Geometrical and solvent relaxation effects are also assessed. An adequate treatment of solvent effects seems critical for an accurate description of the NLO properties of these complexes.
    Physical Chemistry Chemical Physics 07/2015; 17(29). DOI:10.1039/C5CP01884F · 4.49 Impact Factor
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    Journal of Molecular Spectroscopy 07/2015; DOI:10.1016/j.jms.2015.07.004 · 1.48 Impact Factor
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    ABSTRACT: Two new nine-dimensional potential energy surfaces (PESs) have been generated using high-level ab initio theory for the two main isotopologues of methyl chloride, CH3 35Cl and CH3 37Cl. The respective PESs, CBS-35 HL, and CBS-37 HL, are based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set (CBS) limit, and incorporate a range of higher-level (HL) additive energy corrections to account for core-valence electron correlation, higher-order coupled cluster terms, scalar relativistic effects, and diagonal Born-Oppenheimer corrections. Variational calculations of the vibrational energy levels were performed using the computer program TROVE, whose functionality has been extended to handle molecules of the form XY 3Z. Fully converged energies were obtained by means of a complete vibrational basis set extrapolation. The CBS-35 HL and CBS-37 HL PESs reproduce the fundamental term values with root-mean-square errors of 0.75 and 1.00 cm−1, respectively. An analysis of the combined effect of the HL corrections and CBS extrapolation on the vibrational wavenumbers indicates that both are needed to compute accurate theoretical results for methyl chloride. We believe that it would be extremely challenging to go beyond the accuracy currently achieved for CH3Cl without empirical refinement of the respective PESs.
    The Journal of Chemical Physics 06/2015; 142(24):244306. DOI:10.1063/1.4922890 · 2.95 Impact Factor
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    ABSTRACT: Mandelalide A and three congeners had recently been isolated as the supposedly highly cytotoxic principles of an ascidian collected off the South African coastline. Since these compounds are hardly available from the natural source, a concise synthesis route was developed, targeting structure 1 as the purported representation of mandelalide A. The sequence involves an iridium-catalyzed two-directional Krische allylation and a cobalt-catalyzed carbonylative epoxide opening as entry points for the preparation of the major building blocks. The final stages feature the first implementation of terminal acetylene metathesis into natural product total synthesis, which is remarkable in that this class of substrates had been beyond the reach of alkyne metathesis for decades. Synthetic 1, however, proved not to be identical with the natural product. In an attempt to clarify this issue, NMR spectra were simulated for 20 conceivable diastereomers by using DFT followed by DP4 analysis; however, this did not provide a reliable assignment either. The puzzle was ultimately solved by the preparation of three diastereomers, of which compound 6 proved identical with mandelalide A in all analytical and spectroscopic regards. As the entire "northern sector" about the tetrahydrofuran ring in 6 shows the opposite configuration of what had originally been assigned, it is highly likely that the stereostructures of the sister compounds mandelalides B-D must be corrected analogously; we propose that these natural products are accurately represented by structures 68-70. In an attempt to prove this reassignment, an entry into mandelalides C and D was sought by subjecting an advanced intermediate of the synthesis of 6 to a largely unprecedented intramolecular Morita-Baylis-Hillman reaction, which furnished the γ-lactone derivative 74 as a mixture of diastereomers. Whereas (24R)-74 was amenable to a hydroxyl-directed dihydroxylation by using OsO4 /TMEDA as the reagent, the sister compound (24S)-74 did not follow a directed path but simply obeyed Kishi's rule; only this unexpected escape precluded the preparation of mandelalides C and D by this route. A combined spectroscopic and computational (DFT) study showed that the reasons for this strikingly different behavior of the two diastereomers of 74 are rooted in their conformational peculiarities. This aspect apart, our results show that the OsO4 /TMEDA complex reacts preferentially with electron deficient double bonds even if other alkenes are present that are more electron rich and less encumbered. Finally, in a brief biological survey authentic mandelalide A (6) was found to exhibit appreciable cytotoxicity only against one out of three tested human cancer cell lines and all synthetic congeners were hardly active. No significant fungicidal properties were observed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Chemistry - A European Journal 06/2015; 21(29). DOI:10.1002/chem.201501491 · 5.73 Impact Factor
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    Alec Owens · Sergei N. Yurchenko · Walter Thiel · V.  pirko ·
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    ABSTRACT: A comprehensive study of the mass sensitivity of the vibration–rotation–inversion transitions of 14NH3, 15NH3, 14ND3 and 15ND3 is carried out variationally using the trove approach. Variational calculations are robust and accurate, offering a new way to compute sensitivity coefficients. Particular attention is paid to the Δk = ±3 transitions between the accidentally coinciding rotation–inversion energy levels of the ν2 = 0+, 0−, 1+ and 1− states, and the inversion transitions in the ν4 = 1 state affected by the ‘giant’ l-type doubling effect. These transitions exhibit highly anomalous sensitivities, thus appearing as promising probes of a possible cosmological variation of the proton-to-electron mass ratio μ. Moreover, a simultaneous comparison of the calculated sensitivities reveals a sizeable isotopic dependence which could aid an exclusive ammonia detection.
    Monthly Notices of the Royal Astronomical Society 05/2015; 450(3):3191-3200. DOI:10.1093/mnras/stv869 · 5.11 Impact Factor
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    ABSTRACT: Conical intersections are perhaps the most significant mechanistic features of chemical reactions occurring through excited states. By providing funnels for efficient non-adiabatic population transfer, conical intersections govern the branching ratio of products of such reactions, similar to what the transition states do for ground-state reactivity. In this regard, intersections between the ground and the lowest excited states play a special role, and the correct description of the potential energy surfaces in their vicinity is crucial for understanding the mechanism and dynamics of excited-state reactions. The methods of density functional theory, such as time-dependent density functional theory, are widely used to describe the excited states of large molecules. However, are these methods suitable for describing the conical intersections or do they lead to artifacts and, consequently, to erroneous description of reaction dynamics? Here we address the first part of this question and analyze the ability of several density functional approaches, including the linear-response time-dependent approach as well as the spin-flip and ensemble formalisms, to provide the correct description of conical intersections and the potential energy surfaces in their vicinity. It is demonstrated that the commonly used linear-response time-dependent theory does not yield a proper description of these features and that one should instead use alternative computational approaches.
    Topics in current chemistry 04/2015; 368. DOI:10.1007/128_2015_631 · 4.46 Impact Factor
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    ABSTRACT: A series of novel toroidal cyclo-2,9-tris-1,10-phenanthroline macrocycles with an unusual hexaaza cavity are reported. Nickel-mediated Yamamoto aryl-aryl coupling was found to be a versatile tool for the cyclotrimerization of functionalized 1,10-phenathroline precursors. Due to the now improved processability, both liquid-crystalline behavior in the bulk phase and two-dimensional self-assembly at the molecular level could be studied, for the first time, for a torand system. The macrocycles exhibited a strong affinity for the complexation of different metal cations, as evidenced by MALDI-TOF analysis and spectroscopic methods. Experimental results were correlated to an extensive computational study of the cyclo-2,9-tris-1,10-phenanthroline cavity and its binding mode for metal cations. Due to the combination of several interesting features, toroidal macrocycles may find future applications in the field of ion and charge transport through molecular channels, as well as for chemical sensing and molecular writing in surface-confined monolayers under STM conditions. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Chemistry - A European Journal 04/2015; 21(23). DOI:10.1002/chem.201406602 · 5.73 Impact Factor
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    ABSTRACT: We investigate possible improvements in the accuracy of semiempirical quantum chemistry (SQC) methods through the use of machine learning (ML) models for the parameters. For a given class of compounds, ML techniques require suciently large training sets to develop ML models that can be used for adapting SQC parameters to reflect changes in molecular composition and geometry. The ML-SQC approach allows the automatic tuning of SQC parameters for individual molecules, thereby improving the accuracy without deteriorating transferability to molecules with molecular descriptors very different from those in the training set. The performance of this approach is demonstrated for the semiempirical OM2 method using a set of 6095 constitutional isomers C7H10O2, for which accurate ab initio atomization enthalpies are available. The ML-OM2 results show improved average accuracy and a much reduced error range compared with standard OM2 results, with mean absolute errors in atomization enthalpies dropping from 6.3 to 1.7 kcal/mol. They are also found to be superior to the results from specic OM2 reparameterizations (rOM2) for the same set of isomers. The ML-SQC approach thus holds promise for fast and reasonably accurate high-throughput screening of materials and molecules.
    Journal of Chemical Theory and Computation 04/2015; 11(5):2120. DOI:10.1021/acs.jctc.5b00141 · 5.50 Impact Factor
  • Claudia Loerbroks · Andreas Heimermann · Walter Thiel ·
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    ABSTRACT: This article reports a combined quantum mechanics/molecular mechanics (QM/MM) investigation on the acid hydrolysis of cellulose in water using two different models, cellobiose and a 40-unit cellulose chain. The explicitly treated solvent molecules strongly influence the conformations, intramolecular hydrogen bonds, and exoanomeric effects in these models. As these features are largely responsible for the barrier to cellulose hydrolysis, the present QM/MM results for the pathways and reaction intermediates in water are expected to be more realistic than those from a former density functional theory (DFT) study with implicit solvent (CPCM). However, in a qualitative sense, there is reasonable agreement between the DFT/CPCM and QM/MM predictions for the reaction mechanism. Differences arise mainly from specific solute-solvent hydrogen bonds that are only captured by QM/MM and not by DFT/CPCM. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.
    Journal of Computational Chemistry 03/2015; 36(15). DOI:10.1002/jcc.23898 · 3.59 Impact Factor

Publication Stats

17k Citations
2,257.77 Total Impact Points


  • 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
    • NASA
      Вашингтон, West Virginia, United States
  • 1986-2010
    • Bergische Universität Wuppertal
      • • Inorganic Chemistry
      • • Department of Chemistry and Biology
      • • Physical and Theoretical Chemistry
      Wuppertal, North Rhine-Westphalia, Germany
  • 2009
    • The University of Calgary
      Calgary, Alberta, Canada
    • Heinrich-Heine-Universität Düsseldorf
      • Institute for Theoretical and Computational Chemistry
      Düsseldorf, North Rhine-Westphalia, Germany
    • University of St Andrews
      • School of Chemistry
      Saint Andrews, Scotland, United Kingdom
    • 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
  • 2007
    • California Pacific University
      Pinole, California, United States
  • 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