Wolfgang Lubitz

Max Planck Institute for Chemical Energy Conversion, Mülheim-on-Ruhr, North Rhine-Westphalia, Germany

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Publications (469)2198.41 Total impact

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    ABSTRACT: Bis(p-methoxyphenyl)carbene is the first carbene that at cryogenic temperatures can be isolated in both its lowest energy singlet and triplet states. At 3 K both states coexist indefinitely under these conditions. The carbene is investigated in argon matrices by IR, UV-vis, and X-band EPR spectroscopy, and in MTHF glasses by W-band EPR and Q-band ENDOR spectroscopy. UV (365 nm) irradiation of the system results in formation of predominantly the triplet carbene, whereas visible (450 nm) light shifts the photostationary equilibrium towards the singlet state. Upon annealing at higher temperatures (> 10 K), the triplet is converted to the singlet, however, cooling back to 3 K does not restore the triplet. Therefore, depending on matrix temperature and irradiation conditions, matrices containing predominantly the triplet or the singlet carbene can be generated. Controlling the magnetic and chemical properties of carbenes by using light of different wavelengths might be of general interest for applications such as information storage and radical-initiated polymerization processes.
    No preview · Article · Jan 2016 · Journal of the American Chemical Society
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    ABSTRACT: Electron paramagnetic resonance (EPR) spectroscopy exploits an intrinsic property of matter, namely the electron spin and its related magnetic moment. This can be oriented in a magnetic field and thus, in the classical limit, acts like a little bar magnet. Its moment will align either parallel or antiparallel to the field, giving rise to different energies (termed Zeeman splitting). Transitions between these two quantized states can be driven by incident microwave frequency radiation, analogous to NMR experiments, where radiofrequency radiation is used. However, the electron Zeeman interaction alone provides only limited information. Instead, much of the usefulness of EPR is derived from the fact that the electron spin also interacts with its local magnetic environment and thus can be used to probe structure via detection of nearby spins, e.g., NMR-active magnetic nuclei and/or other electron spin(s). The latter is exploited in spin labeling techniques, an exciting new area in the development of noncrystallographic protein structure determination. Although these interactions are often smaller than the linewidth of the EPR experiment, sophisticated pulse EPR methods allow their detection. A number of such techniques are well established today and can be broadly described as double-resonance methods, in which the electron spin is used as a reporter. Below we give a brief description of pulse EPR methods, particularly their implementation at higher magnetic fields, and how to best exploit them for studying metallobiomolecules.
    No preview · Article · Dec 2015
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    ABSTRACT: In transition-metal complexes, the geometric structure is intimately connected with the spin state arising from magnetic coupling between the paramagnetic ions. The tetramanganese-calcium cofactor that catalyzes biological water oxidation in photosystem II cycles through five catalytic intermediates, each of which adopts a specific geometric and electronic structure and is thus characterized by a specific spin state. Here, we review spin-structure correlations in Nature's water-splitting catalyst. The catalytic cycle of the Mn4O5Ca cofactor can be described in terms of spin-dependent reactivity. The lower "inactive" S states of the catalyst, S0 and S1, are characterized by low-spin ground states, SGS = (1)/2 and SGS = 0. This is connected to the "open cubane" topology of the inorganic core in these states. The S2 state exhibits structural and spin heterogeneity in the form of two interconvertible isomers and is identified as the spin-switching point of the catalytic cycle. The first S2 state form is an open cubane structure with a low-spin SGS = (1)/2 ground state, whereas the other represents the first appearance of a closed cubane topology in the catalytic cycle that is associated with a higher-spin ground state of SGS = (5)/2. It is only this higher-spin form of the S2 state that progresses to the "activated" S3 state of the catalyst. The structure of this final metastable catalytic state was resolved in a recent report, showing that all manganese ions are six-coordinate. The magnetic coupling is dominantly ferromagnetic, leading to a high-spin ground state of SGS = 3. The ability of the Mn4O5Ca cofactor to adopt two distinct structural and spin-state forms in the S2 state is critical for water binding in the S3 state, allowing spin-state crossing from the inactive, low-spin configuration of the catalyst to the activated, high-spin configuration. Here we describe how an understanding of the magnetic properties of the catalyst in all S states has allowed conclusions on the catalyst function to be reached. A summary of recent literature results is provided that constrains the sequence of molecular level events: catalyst/substrate deprotonation, manganese oxidation, and water molecule insertion.
    No preview · Article · Dec 2015 · Inorganic Chemistry

  • No preview · Article · Dec 2015 · Biophysical Journal
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    ABSTRACT: Membrane type 1-matrix metalloproteinase (MT1-MMP or MMP-14) is a zinc-transmembrane metalloprotease involved in the degradation of extracellular matrix and tumor invasion. While changes in solvation of MT1-MMP have been recently studied, little is known about the structural and energetic changes associated with MT1-MMP while interacting with substrates. Steady-state kinetic and thermodynamic data (including activation energies and activation volumes) were measured over a wide range of temperatures and pressures by means of a stopped-flow fluorescence technique. Complementary temperature- and pressure-dependent Fourier-transform infrared measurements provided corresponding structural information of the protein. MT1-MMP is stable and active over a wide range of temperatures (10–55°C). A small conformational change was detected at 37°C, which is responsible for the change in activity observed at the same temperature. Pressure decreases the enzymatic activity until complete inactivation occurs at 2 kbar. The inactivation is associated with changes in the rate-limiting step of the reaction caused by additional hydration of the active site upon compression and/or minor conformational changes in the active site region. Based on these data, an energy and volume diagram could be established for the various steps of the enzymatic reaction.
    No preview · Article · Dec 2015 · Biophysical Journal
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    ABSTRACT: Direct spectroscopic evidence for a hydride bridge in the Ni–R form of [NiFe] hydrogenase has been obtained using iron-specific nuclear resonance vibrational spectroscopy (NRVS). The Ni–H–Fe wag mode at 675 cm −1 is the first spectroscopic evidence for a bridging hydride in Ni–R as well as the first iron-hydride-related NRVS feature observed for a biological system. Although density function theory (DFT) calculation assisted the determination of the Ni–R structure, it did not predict the Ni–H–Fe wag mode at ∼675 cm −1 before NRVS. Instead, the observed Ni–H–Fe mode provided a critical reference for the DFT calculations. While the overall science about Ni–R is presented and discussed elsewhere, this article focuses on the long and strenuous experimental journey to search for and experimentally identify the Ni–H–Fe wag mode in a Ni–R sample. As a methodology, the results presented here will go beyond Ni–R and hydrogenase research and will also be of interest to other scientists who use synchrotron radiation for measuring dilute samples or weak spectroscopic features.
    Preview · Article · Nov 2015 · Journal of Synchrotron Radiation
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    ABSTRACT: A new class of synthetic models for the active site of [NiFe]-hydrogenases are described. The Ni(I/II)(SCys)2 and Fe(II)(CN)2CO sites are represented with (RC5H4)Ni(I/II) and Fe(II)(diphos)(CO) modules, where diphos = 1,2-C2H4(PPh2)2(dppe) or cis-1,2-C2H2(PPh2)2(dppv). The two bridging thiolate ligands are represented by CH2(CH2S)2(2-) (pdt(2-)), Me2C(CH2S)2(2-) (Me2pdt(2-)), and (C6H5S)2(2-). The reaction of Fe(pdt)(CO)2(dppe) and [(C5H5)3Ni2]BF4 affords [(C5H5)Ni(pdt)Fe(dppe)(CO)]BF4 ([1a]BF4). Monocarbonyl [1a]BF4 features an S = 0 Ni(II)Fe(II) center with five-coordinated iron, as proposed for the Ni-SIa state of the enzyme. One-electron reduction of [1a](+) affords the S = (1)/2 derivative [1a](0), which, according to density functional theory (DFT) calculations and electron paramagnetic resonance and Mössbauer spectroscopies, is best described as a Ni(I)Fe(II) compound. The Ni(I)Fe(II) assignment matches that for the Ni-L state in [NiFe]-hydrogenase, unlike recently reported Ni(II)Fe(I)-based models. Compound [1a](0) reacts with strong acids to liberate 0.5 equiv of H2 and regenerate [1a](+), indicating that H2 evolution is catalyzed by [1a](0). DFT calculations were used to investigate the pathway for H2 evolution and revealed that the mechanism can proceed through two isomers of [1a](0) that differ in the stereochemistry of the Fe(dppe)CO center. Calculations suggest that protonation of [1a](0) (both isomers) affords Ni(III)-H-Fe(II) intermediates, which represent mimics of the Ni-C state of the enzyme.
    Full-text · Article · Sep 2015 · Inorganic Chemistry
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    ABSTRACT: The active site of [FeFe] hydrogenase contains a catalytic binuclear iron sub-site coordinated by CN(-) and CO ligands as well as a unique azadithiolate (adt(2-)) bridging ligand. It has been established that this binuclear cofactor is synthesized and assembled by three maturation proteins HydE,F,G. Using in vitro maturation in the presence of (15)N and (13)C labeled tyrosine it has been shown that the CN(-) and CO ligands originate from tyrosine. The source of the bridging adt(2-) ligand, however, remains as yet unknown. In order to identify the nitrogen of the bridging amine using HYSCORE spectroscopy and distinguish its spectroscopic signature from that of the CN(-) nitrogens we studied three isotope labeled variants of the H-cluster ((15)N-adt(2-)/C(14)N(-), (15)N-adt(2-)/C(15)N(-), and (14)N-adt(2-)/C(15)N(-)) and extracted accurate values of the hyperfine and quadrupole couplings of both CN(-) and adt(2-) nitrogens. This will allow to evaluate isotopologues of the H-cluster generated by in vitro bioassembly in the presence of various (15)N labeled potential precursors as possible sources of the bridging ligand.
    No preview · Article · Sep 2015 · Journal of the American Chemical Society
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    ABSTRACT: The metabolism of many anaerobes relies on [NiFe]-hydrogenases, whose characterization when bound to substrates has proven non-trivial. Presented here is direct evidence for a hydride bridge in the active site of the 57 Fe-labelled fully reduced Ni-R form of Desulfovibrio vulgaris Miyazaki F [NiFe]-hydrogenase. A unique ' wagging' mode involving H- motion perpendicular to the Ni(μ1/4-H)57 Fe plane was studied using 57 Fe-specific nuclear resonance vibrational spectroscopy and density functional theory (DFT) calculations. On Ni(μ1/4-D) 57 Fe deuteride substitution, this wagging causes a characteristic perturbation of Fe-CO/CN bands. Spectra have been interpreted by comparison with Ni(μ1/4-H/D) 57 Fe enzyme mimics [(dppe)Ni(μ1/4-pdt)(μ1/4-H/D) 57 Fe(CO)3 ]+ and DFT calculations, which collectively indicate a low-spin Ni(II)(μ1/4-H)Fe(II) core for Ni-R, with H- binding Ni more tightly than Fe. The present methodology is also relevant to characterizing Fe-H moieties in other important natural and synthetic catalysts.
    Full-text · Article · Aug 2015 · Nature Communications
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    Full-text · Dataset · Jul 2015
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    ABSTRACT: Das aktive Zentrum von Hydrogenasen inspiriert die Entwicklung molekularer Katalysatoren zur Wasserstoffumsetzung. Ein direkter Vergleich zwischen diesen Katalysatoren und dem Enzym war jedoch bisher nicht möglich, weil verschiedene Techniken zur Bewertung der Katalysatoreigenschaften verwendet wurden. Dies macht es schwierig zu beurteilen, inwieweit die synthetisierten Katalysatoren in ihrer Leistung an das Enzym heranreichen. Hier vergleichen wir die katalytischen Eigenschaften von Ni[(PCy2NGly2)2]+2 mit denen der [NiFe]-Hydrogenase aus Desulfovibrio vulgaris. Beide wurden auf funktionalisierten Elektroden unter identischen Bedingungen immobilisiert. Das Enzym zeigt bei pH 7 eine höhere Aktivität, geringere Überspannung und eine bessere Stabilität, während bei niedrigem pH-Wert der molekulare Katalysator das Enzym in jeder Hinsicht übertrifft. Dieser erste direkte Vergleich gibt Auskunft über die Vor- und Nachteile der beiden Systeme und Hinweise auf eine mögliche Verwendung bioinspirierter Komplexe in Brennstoffzellen.
    No preview · Article · Jul 2015 · Angewandte Chemie
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    ABSTRACT: The active site of hydrogenases has been a source of inspiration for the development of molecular catalysts. However, direct comparisons between molecular catalysts and enzymes have not been possible because different techniques are used to evaluate both types of catalysts, minimizing our ability to determine how far we have come in mimicking the enzymatic performance. The catalytic properties of the [Ni(P(Cy) 2 N(Gly) 2 )2 ](2+) complex with the [NiFe]-hydrogenase from Desulfovibrio vulgaris immobilized on a functionalized electrode were compared under identical conditions. At pH 7, the enzyme shows higher activity and lower overpotential with better stability, while at low pH, the molecular catalyst outperforms the enzyme in all respects. This is the first direct comparison of enzymes and molecular complexes, enabling a unique understanding of the benefits and detriments of both systems, and advancing our understanding of the utilization of these bio-inspired complexes in fuel cells. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    No preview · Article · Jul 2015 · Angewandte Chemie International Edition
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    ABSTRACT: Diamagnetic iron chloro compounds [(P(Ph)2N(Ph)2)FeCp*Cl] [1Cl] and [(P(Cy)2N(Ph)2)FeCp*Cl] [2Cl] and the corresponding hydrido complexes [(P(Ph2)N(Ph2))FeCp*H] [1H] and [(P(Cy)2N(Ph)2)FeCp*H] [2H] have been synthesized and characterized by NMR spectroscopy, electrochemical studies, electronic absorption, and (57)Fe Mössbauer spectroscopy (P(Ph)2N(Ph)2 = 1,3,5,7-tetraphenyl-1,5-diphospha-3,7-diazacyclooctane, P(Cy2)N(Ph2) = 1,5-dicyclohexyl-3,7-diphenyl-1,5-diphospha-3,7-diazacyclooctane, Cp* = pentamethylcyclopentadienyl). Molecular structures of [2Cl], [1H], and [2H], derived from single-crystal X-ray diffraction, revealed that these compounds have a typical piano-stool geometry. The results show that the electronic properties of the hydrido complexes are strongly influenced by the substituents at the phosphorus donor atoms of the P(R)2N(Ph)2 ligand, whereas those of the chloro complexes are less affected. These results illustrate that the hydride is a strong-field ligand, as compared to chloride, and thus leads to a significant degree of covalent character of the iron hydride bonds. This is important in the context of possible catalytic intermediates of iron hydrido species, as proposed for the catalytic cycle of [FeFe] hydrogenases and other synthetic catalysts. Both hydrido compounds [1H] and [2H] show enhanced catalytic currents in cyclic voltammetry upon addition of the strong acid trifluoromethanesulfonimide [NHTf2] (pKa(MeCN) = 1.0). In contrast to the related complex [(P(tBu)N(Bn))2FeCp(C6F5)H], which was reported by Liu et al. (Nat. Chem. 2013, 5, 228-233) to be an electrocatalyst for hydrogen splitting, the here presented hydride complexes [1H] and [2H] show the tendency for electrocatalytic hydrogen production. Hence, the catalytic direction of this class of monoiron compounds can be reversed by specific ligand modifications.
    No preview · Article · Jul 2015 · Inorganic Chemistry
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    Full-text · Dataset · Jun 2015
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    ABSTRACT: The preparation and spectroscopic characterization of a fully active [FeFe] hydrogenase with a selectively 57Fe-labeled binuclear subsite is described. The precursor [57Fe2(adt)(CN)2(CO)4]2- was synthesized from the 57Fe metal, S8, CO, [Et4N]CN, NH4Cl, and OCH2. (Et4N)2[57Fe2(adt)(CN)2(CO)4] was then used for the maturation of the [FeFe] hydrogenase HydA1 from Chlamydomonas reinhardtii, to yield the enzyme selectively labeled at the [2Fe]H subcluster. Complementary 57Fe enrichment of the [4Fe-4S]H cluster was realized by reconstitution with 57FeCl3 and Na2S. The Hox-CO state of [257Fe]H and [457Fe-4S]H HydA1 was characterized by Mössbauer, HYSCORE, ENDOR, and nuclear resonance vibrational spectroscopy.
    Full-text · Article · Jun 2015 · Journal of the American Chemical Society
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    ABSTRACT: Die Integration empfindlicher Katalysatoren in Redoxpolymere ist eine Möglichkeit, diese vor desaktivierenden Molekülen wie O2 zu schützen. [FeFe]-Hydrogenasen sind Enzyme, die die Oxidation sowie Produktion von H2 katalysieren. Da sie aber durch O2 irreversibel desaktiviert werden, war die Verwendung dieser Enzyme unter aeroben Bedingungen bisher unmöglich. Die Integration solcher Hydrogenasen in mit Viologenderivaten modifizierten Hydrogelfilmen ermöglicht auch in Gegenwart von O2 katalytische Ströme für die H2-Oxidation und demonstriert damit einen Schutzmechanismus unabhängig von Reaktivierungsprozessen. Im Hydrogel werden die Elektronen aus der durch die Hydrogenase katalysierten H2-Oxidation zur Hydrogel-Elektrolyt-Grenzfläche transportiert, um dort die schädlichen O2-Moleküle abzufangen, bevor sie die Hydrogenase desaktivieren können. Wir illustrieren mögliche Anwendungen dieses Schutzmechanismus für eine Biobrennstoffzelle bei gemischter H2/O2-Zufuhr.
    No preview · Article · Jun 2015 · Angewandte Chemie
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    ABSTRACT: The integration of sensitive catalysts in redox matrices opens up the possibility for their protection from deactivating molecules such as O2 . [FeFe]-hydrogenases are enzymes catalyzing H2 oxidation/production which are irreversibly deactivated by O2 . Therefore, their use under aerobic conditions has never been achieved. Integration of such hydrogenases in viologen-modified hydrogel films allows the enzyme to maintain catalytic current for H2 oxidation in the presence of O2 , demonstrating a protection mechanism independent of reactivation processes. Within the hydrogel, electrons from the hydrogenase-catalyzed H2 oxidation are shuttled to the hydrogel-solution interface for O2 reduction. Hence, the harmful O2 molecules do not reach the hydrogenase. We illustrate the potential applications of this protection concept with a biofuel cell under H2 /O2 mixed feed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    No preview · Article · Jun 2015 · Angewandte Chemie International Edition
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    ABSTRACT: The two resting forms of the active site of [NiFe] hydrogenase, Ni-A and Ni-B, have significantly different activation kinetics, but reveal nearly identical spectroscopic features which suggest the two states exhibit subtle structural differences. Previous studies have indicated that the states differ by the identity of the bridging ligand between Ni and Fe; proposals include OH-, OOH-, H2O, O2-, accompanied by modified cysteine residues. In this study, we use single crystal ENDOR spectroscopy and quantum chemical calculations within the framework of density functional theory (DFT) to calculate vibrational frequencies, 1H and 17O hyperfine coupling constants and g values with the aim to compare these data to experimental results obtained by crystallography, FTIR and EPR/ENDOR spectroscopy. We find that the Ni-A and Ni-B states are constitutional isomers that differ in their fine structural details. Calculated vibrational frequencies for the cyano and carbonyl ligands and 1H and 17O hyperfine coupling constants indicate that the bridging ligand in both Ni-A and Ni-B is indeed an OH- ligand. The difference in the isotropic hyperfine coupling constants of the β-CH2 protons of Cys-549 is sensitive to the orientation of Cys-549; a difference of 0.5 MHz is observed experimentally for Ni-A and 1.9 MHz for Ni-B, which results from a rotation of 7 degrees about the Cα-Cβ-Sγ-Ni dihedral angle. Likewise, the difference of the intermediate g value is correlated with a rotation of Cys-546 of about 10 degrees.
    No preview · Article · May 2015 · Physical Chemistry Chemical Physics
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    ABSTRACT: The regulatory hydrogenase (RH) from Ralstonia eutropha H16 acts as a sensor for the detection of environmental H2 and regulates gene expression related to hydrogenase-mediated cellular metabolism. In marked contrast to prototypical energy-converting [NiFe] hydrogenases, the RH is apparently insensitive to inhibition by O2 and CO. While the physiological function of regulatory hydrogenases is well established, little is known about the redox cycling of the [NiFe] center and the nature of the iron–sulfur (FeS) clusters acting as electron relay. The absence of any FeS cluster signals in EPR had been attributed to their particular nature, whereas the observation of essentially only two active site redox states, namely Ni-SI and Ni-C, invoked a different operant mechanism. In the present work, we employ a combination of Mössbauer, FTIR and EPR spectroscopic techniques to study the RH, and the results are consistent with the presence of three [4Fe–4S] centers in the small subunit. In the as-isolated, oxidized RH all FeS clusters reside in the EPR-silent 2+ state. Incubation with H2 leads to reduction of two of the [4Fe–4S] clusters, whereas only strongly reducing agents lead to reduction of the third cluster, which is ascribed to be the [4Fe–4S] center in ‘proximal’ position to the [NiFe] center. In the two different active site redox states, the low-spin FeII exhibits distinct Mössbauer features attributed to changes in the electronic and geometric structure of the catalytic center. The results are discussed with regard to the spectral characteristics and physiological function of H2-sensing regulatory hydrogenases.
    Full-text · Article · May 2015 · Chemical Science
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    ABSTRACT: The transfer of photosynthetic electrons by the ferredoxin PetF to the [FeFe] hydrogenase HydA1 in the microalga Chlamydomonas reinhardtii is a key step in hydrogen production. Electron delivery requires a specific interaction between PetF and HydA1. However, due to the transient nature of the corresponding electron-transfer complex, an X-ray-structure remains elusive. Therefore, we performed protein-protein docking based on new experimental data from solution NMR spectroscopy on native and Gallium-substituted PetF that provides valuable information about residues crucial for complex formation and electron transfer. The derived complex model may help pinpoint residue substitution targets for improved hydrogen production. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    No preview · Article · May 2015 · ChemBioChem

Publication Stats

13k Citations
2,198.41 Total Impact Points

Institutions

  • 2004-2015
    • Max Planck Institute for Chemical Energy Conversion
      Mülheim-on-Ruhr, North Rhine-Westphalia, Germany
    • Universidad Nacional del Litoral
      Ciudad de Santa Fe, Santa Fe, Argentina
  • 2003-2015
    • Max Planck Institute for Chemistry
      Mayence, Rheinland-Pfalz, Germany
  • 2007
    • Ruhr-Universität Bochum
      Bochum, North Rhine-Westphalia, Germany
    • Semenov Institute of Chemical Physics
      Moskva, Moscow, Russia
  • 1991-2007
    • Technische Universität Berlin
      • Department of Chemistry
      Berlín, Berlin, Germany
  • 1975-2007
    • Freie Universität Berlin
      • Institute of Experimental Physics
      Berlín, Berlin, Germany
  • 2001
    • VU University Amsterdam
      • Division of Theoretical Chemistry
      Amsterdamo, North Holland, Netherlands
  • 1996
    • Arizona State University
      • Department of Chemistry and Biochemistry
      Mesa, AZ, United States
  • 1995
    • Max Planck Institute for Biophysical Chemistry
      Göttingen, Lower Saxony, Germany
  • 1985-1995
    • University of California, San Diego
      • Department of Physics
      San Diego, California, United States
  • 1983
    • Goethe-Universität Frankfurt am Main
      • Institut für Anorganische und Analytische Chemie
      Frankfurt, Hesse, Germany
  • 1980
    • University of Jyväskylä
      • Department of Chemistry
      Jyväskylä, Western Finland, Finland