Walter Thiel

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

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Publications (509)2168.97 Total impact

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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; DOI:10.1007/128_2015_631 · 4.61 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; DOI:10.1002/chem.201406602 · 5.70 Impact Factor
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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; DOI:10.1002/jcc.23898 · 3.60 Impact Factor
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    ABSTRACT: We present a hybrid quantum mechanics/molecular mechanics/coarse-grained (QM/MM/CG) multiresolution approach for solvated biomolecular systems. The chemically important active-site region is treated at the QM level. The biomolecular environment is described by an atomistic MM force field, and the solvent is modeled with the CG Martini force field using standard or polarizable (pol-CG) water. Interactions within the QM, MM, and CG regions, and between the QM and MM regions, are treated in the usual manner, whereas the CG-MM and CG-QM interactions are evaluated using the virtual sites approach. The accuracy and efficiency of our implementation is tested for two enzymes, chorismate mutase (CM) and p-hydroxybenzoate hydroxylase (PHBH). In CM, the QM/MM/CG potential energy scans along the reaction coordinate yield reaction energies that are too large, both for the standard and polarizable Martini CG water models, which can be attributed to adverse effects of using large CG water beads. The inclusion of an atomistic MM water layer (10 Å for uncharged CG water and 5 Å for polarizable CG water) around the QM region improves the energy profiles compared to the reference QM/MM calculations. In analogous QM/MM/CG calculations on PHBH, the use of the pol-CG description for the outer water does not affect the stabilization of the highly charged FADHOOH-pOHB transition state compared to the fully atomistic QM/MM calculations. Detailed performance analysis in a glycine-water model system indicates that computation times for QM energy and gradient evaluations at the density functional level are typically reduced by 40-70% for QM/MM/CG relative to fully atomistic QM/MM calculations.
    Journal of Chemical Theory and Computation 03/2015; DOI:10.1021/ct500956u · 5.31 Impact Factor
  • Daniele Fazzi, Mario Barbatti, Walter Thiel
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    ABSTRACT: Ultrafast excited-state processes play a key role in organic electronics and photovoltaics, governing the way on how excitons can relax and separate. Through the use of nonadiabatic excited-state dynamics, relaxation processes were investigated at the sub-picosecond timescale in thiophene and oligothiophenes (nT, n = 2,3,4), prototype oligomers for efficient π-electron conjugated polymers adopted in photovoltaics. For thiophene, TDDFT and TDA nonadiabatic excited-state dynamics revealed ultrafast nonradiative relaxation processes through ring opening and ring puckering, bringing the system to an S1/S0 conical intersection seam. The computed relaxation time is 110 fs, matching well the experimental one (~105 fs). In oligothiophenes (n = 2-4), high-energy (hot) excitations were considered. Exciton relaxation through the manifold of excited states to the lowest excited state is predicted to occur within ~150-200 fs, involving bond stretching, ring puckering, and torsional oscillations. For the longer oligomer (4T), the ultrafast relaxation process leads to exciton localization over three thiophene rings in 150 fs. These data agree with the self-localization mechanism (~100-200 fs) observed for poly(3-hexylthiophene) (P3HT) and shed light on the complex exciton relaxation dynamics occurring in π-conjugated oligomers of potential interest for optoelectronic applications.
    Physical Chemistry Chemical Physics 02/2015; DOI:10.1039/C5CP00019J · 4.20 Impact Factor
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    ABSTRACT: We explore the influence of two solvents, namely water and the ionic liquid 1-ethyl-3-methylimidazolium acetate (EmimAc), on the conformations of two cellulose models (cellobiose and a chain of 40 glucose units) and the solvent impact on glycosidic bond cleavage by acid hydrolysis by using molecular dynamics and metadynamics simulations. We investigate the rotation around the glycosidic bond and ring puckering, as well as the anomeric effect and hydrogen bonds, in order to gauge the effect on the hydrolysis mechanism. We find that EmimAc eases hydrolysis through stronger solvent-cellulose interactions, which break structural and electronic barriers to hydrolysis. Our results indicate that hydrolysis in cellulose chains should start from the ends and not in the centre of the chain, which is less accessible to solvent. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Chemistry - A European Journal 02/2015; 21(14). DOI:10.1002/chem.201405507 · 5.70 Impact Factor
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    ABSTRACT: Excited-state intramolecular proton transfer (ESIPT) between two highly electronegative atoms, for example oxygen and nitrogen, has been intensely studied experimentally and computationally, whereas there has been much less theoretical work on ESIPT to other atoms such as carbon. We have employed CASSCF, MS-CASPT2, RI-ADC(2), OM2/MRCI, DFT, and TDDFT methods to study the mechanistic photochemistry of 2-phenylphenol, for which such ESIPT has been observed experimentally. According to static electronic structure calculations, irradiation of 2-phenylphenol populates the bright S1 state, which has a rather flat potential in the Franck-Condon region (with a shallow enol minimum at the CASSCF level) and may undergo an essentially barrierless ESIPT to the more stable S1 keto species. There are two S1/S0 conical intersections that mediate relaxation to the ground state, one in the enol region and one in the keto region, with the latter one substantially lower in energy. After S1 → S0 internal conversion, the transient keto species can return back to the S0 enol structure via reverse ground-state hydrogen transfer in a facile tautomerization. This mechanistic scenario is verified by OM2/MRCI-based fewest-switches surface-hopping simulations that provide detailed dynamical information. In these trajectories, ESIPT is complete within 118 fs; the corresponding S1 excited-state lifetime is computed to be 373 fs in vacuum. Most of the trajectories decay to the ground state via the S1/S0 conical intersection in the keto region (67%), and the remaining ones via the enol region (33%). The combination of static electronic structure computations and nonadiabatic dynamics simulations is expected to be generally useful for understanding the mechanistic photophysics and photochemistry of molecules with intramolecular hydrogen bonds.
    Physical Chemistry Chemical Physics 02/2015; DOI:10.1039/C5CP00101C · 4.20 Impact Factor
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    ABSTRACT: An efficient catalytic one-step conversion of benzene to phenol was achieved recently by selective photooxidation under mild conditions with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) as the photocatalyst. Herein, high-level electronic structure calculations in the gas phase and in acetonitrile solution are reported to explore the underlying mechanism. The initially populated 1ππ* state of DDQ can relax efficiently through a nearby dark 1nπ* doorway state to the 3ππ* state of DDQ, which is found to be the precursor state involved in the initial intermolecular electron transfer from benzene to DDQ. The subsequent triplet-state reaction between DDQ radical anions, benzene radical cations, and water is computed to be facile. The formed DDQH and benzene-OH radicals can undergo T1S0 intersystem crossing and concomitant proton-coupled electron transfer (PCET) to generate the products DDQH2 and phenol. Two of the four considered nonadiabatic pathways involve an orientation-dependent triplet PCET process, followed by intersystem crossing to the ground state (S0). The other two first undergo a nonadiabatic T1S0 transition to produce a zwitterionic S0 complex, followed by a barrierless proton transfer. The present theoretical study identifies novel types of nonadiabatic PCET processes and provides detailed mechanistic insight into DDQ-catalyzed photooxidation.
    ChemPhysChem 01/2015; 16(5). DOI:10.1002/cphc.201402897 · 3.36 Impact Factor
  • Bora Karasulu, Walter Thiel
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    ABSTRACT: Amine oxidation, a process widely utilized by flavoprotein oxidases, is the rate-determining step in the three-step demethylation of N-methyltryptophan (NMT) catalyzed by N-methyltryptophan oxidase (MTOX), which employs a covalently bound flavin adenine dinucleotide (FAD) as cofactor. For the required transfer of a hydride ion equivalent, three pathways (direct/concerted, radical, and adduct-forming/polar nucleophilic) have been proposed, without a consensus on which one is commonly used by amine oxidases. We combine theoretical pKa analysis, classical molecular dynamics (MD) simulations, and pure quantum mechanics (QM) and hybrid QM/molecular mechanics (QM/MM) calculations to provide molecular-level insights into the catalytic mechanism of NMT oxidation and to analyze the role of MTOX active-site residues and covalent FAD incorporation for NMT binding and oxidation. The QM(B3LYP-D2/6-31G(d))/CHARMM results clearly favor a direct concerted hydride transfer (HT) mechanism involving anionic NMT as the reactive species. On the basis of classical canonical MD simulations and QM/MM calculations of wild-type MTOX and two mutants (K341Q and H263N), we propose that the K341 residue acts as an active-site base and electrostatically, whereas H263 and Tyr249 only support substrate alignment. Covalent FAD binding leads to a more bent isoalloxazine moiety, which facilitates the binding of anionic NMT but increases the catalytic activity of FAD only slightly.
    ACS Catalysis 01/2015; 5(5):1227-1239. DOI:10.1021/cs501694q · 7.57 Impact Factor
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    ABSTRACT: The reactivitiy of tetrakis(trifluoromethyl)cyclopentadienone towards different C-based Lewis bases, such as N-heterocyclic carbenes (NHC), ylides and isonitriles, are reported. While sterically not hindered carbenes were found to yield kinetic adducts by regiospecific nucleophilic attack at the position adjacent to the carbonyl group of the ketone, bulkier nucleophiles afforded the thermodynamically more stable O-bridged zwitterions. Interestingly, isonitriles were found to dimerize and trimerize under the same reaction conditions, forming bicyclic products that evolve differently depending on the nature of the substituents.
    Chemistry - A European Journal 12/2014; 21(7). DOI:10.1002/chem.201405418 · 5.70 Impact Factor
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    ABSTRACT: Direct arylation (DA) is emerging as a highly promising method to construct inexpensive conjugated materials for large-area electronics from simple and environ-mentally benign building blocks. Here, we show that exclusive α-C−H selectivity is feasible in the DA of π-extended monomers having unsubstituted thiophene or furan units, leading to fully linear materials. Two new naphthalene diimide-based conjugated copolymersP(FuNDIFuF 4) and P(ThNDIThF 4), composed of naphthalene diimide (NDI), furan (Fu) or thiophene (Th), and tetrafluorobenzene (F 4)are synthesized. Insight into structure−function relationships is given by density functional theory (DFT) calculations and variety of experimental techniques, whereby the effect of the heteroatom on the optical, structural, and electronic properties is investigated. The use of furan (Fu) allows for enhanced solubilities, a smaller dihedral angle between NDI and Fu as a result of the smaller size of Fu, and a smaller π−π-stacking distance in the solid state. P(FuNDIFuF 4) also exhibits a more edge-on orientation compared to P(ThNDIThF 4). Despite these advantageous properties of P(FuNDIFuF 4), P(ThNDIThF 4) exhibits the highest electron mobility: ∼1.3 cm 2 /(V s), which is a factor of ∼3 greater than that of P(FuNDIFuF 4). The enhanced OFET performance of P(ThNDIThF 4) is explained by reduced orientational disorder and the formation of a terrace-like thin-film morphology.
    Chemistry of Materials 12/2014; DOI:10.1021/cm503033j · 8.54 Impact Factor
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    ABSTRACT: We address the performance of the vertical and adiabatic Franck–Condon (VFC/AFC) approaches combined with time-independent or time-dependent (TI/TD) formalisms in simulating the one-photon absorption spectra of three flavin compounds with distinct structural features. Calculations were done in the gas phase and in two solvents (water, benzene) for which experimental reference measurements are available. We utilized the independent mode displaced harmonic oscillator model without or with frequency alteration (IMDHO/IMDHO-FA) and also accounted for Duschinsky mixing effects. In the initial validation on the first excited singlet state of riboflavin, the range-separated functionals, CAM-B3LYP and ωB97xD, showed the best performance, but B3LYP also gave a good compromise between peak positions and spectral topology. Large basis sets were not mandatory to obtain high-quality spectra for the selected systems. The presence of a symmetry plane facilitated the computation of vibrationally broadened spectra, since different FC variants yield similar results and the harmonic approximation holds rather well. Compared with the AFC approach, the VFC approach performed equally well or even better for all three flavins while offering several advantages, such as avoiding error-prone geometry optimization procedures on excited-state surfaces. We also explored the advantages of curvilinear displacements and of a Duschinsky treatment for the AFC spectra in cases when a rotatable group is present on the chromophore. Taken together, our findings indicate that the combination of the VFC approach with the TD formalism and the IMDHO-FA model offers the best overall performance.
    Journal of Chemical Theory and Computation 11/2014; DOI:10.1021/ct500830a · 5.31 Impact Factor
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    ABSTRACT: Photoswitching of simple photochromic molecules attracts substantial attention because of its possible role in future photon-driven molecular electronics. Here we model the full photoswitching cycle of a minimal photochromic Schiff base - salicylidene methylamine (SMA). We perform semi-empirical non-adiabatic on-the-fly photodynamics simulations at the OM2/MRCI level and thoroughly analyze the structural time evolution and switching efficiency of the system. We also identify and examine in detail the crucial steps in the SMA photochemistry ruled by excited-state intramolecular proton transfer. The results place the investigated model aromatic Schiff base among the promising candidates for novel photoswitching molecular materials. Our study also shows the potential of the semi-empirical multireference photodynamics simulations as a tool for early-stage molecular photo-device design.
    The Journal of Physical Chemistry B 10/2014; 119(6). DOI:10.1021/jp5095678 · 3.38 Impact Factor
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    ABSTRACT: It is proposed that xanthophylls, and carotenoids in general, may assist in energy transfer from the chlorophyll Soret band to the Q band. Ground-state (1Ag) and excited-state (1Bu) optimizations of violaxanthin (Vx) and zeaxanthin (Zx) are performed in an environment mimicking the light-harvesting complex II (LHCII), including the closest chlorophyll b molecule (Chl). Time-dependent density functional theory (TD-DFT, CAM-B3LYP functional) is used in combination with a semi-empirical description to obtain the excited-state geometries, supported by additional DFT/multireference configuration interaction calculations, with and without point charges representing LHCII. In the ground state, Vx and Zx show similar properties. At the 1Bu minimum, the energy of the Zx 1Bu state is below the Chl Q band, in contrast to Vx. Both Vx and Zx may act as acceptors of Soret-state energy; transfer to the Q band seems to be favored for Vx. These findings suggest that carotenoids may generally mediate Soret-to-Q energy flow in LHCII.
    ChemPhysChem 10/2014; 15(15). DOI:10.1002/cphc.201402233 · 3.36 Impact Factor
  • Daniel Escudero, Walter Thiel
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    ABSTRACT: In this Article, we address the complexity of the emissive processes of a square-planar heteroleptic Pt(II) complex bearing 2-phenylpyridine (ppy) as cyclometalated ligand and an acetylacetonate derivative (dbm) as ancillary ligand. The origins of emission were identified with the help of density functional theory (DFT) and quadratic response (QR) time-dependent (TD)-DFT calculations including spin-orbit coupling (SOC). To unveil the photodeactivation mechanisms, we explored the triplet potential energy surfaces and computed the SOCs and the radiative decay rates (kr) from possible emissive states. We find that emission likely originates from a higher-lying (3)MLCT/(3)LLCT state and not from the Kasha-like (3)MLCT/(3)LCdbm state. The temperature-dependent nonradiative deactivation mechanisms were also elucidated. The active role of metal-centered ((3)MC) triplet excited states is confirmed for these deactivation pathways.
    Inorganic Chemistry 10/2014; 53(20). DOI:10.1021/ic501430x · 4.79 Impact Factor
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    ABSTRACT: Quantum-chemical computational methods are benchmarked for their ability to describe conical in- tersections in a series of organic molecules and models of biological chromophores. Reference results for the geometries, relative energies, and branching planes of conical intersections are obtained us- ing ab initio multireference configuration interaction with single and double excitations (MRCISD). They are compared with the results from more approximate methods, namely, the state-interaction state-averaged restricted ensemble-referenced Kohn-Sham method, spin-flip time-dependent den- sity functional theory, and a semiempirical MRCISD approach using an orthogonalization-corrected model. It is demonstrated that these approximate methods reproduce the ab initio reference data very well, with root-mean-square deviations in the optimized geometries of the order of 0.1 Å or less and with reasonable agreement in the computed relative energies. A detailed analysis of the branching plane vectors shows that all currently applied methods yield similar nuclear displacements for escap- ing the strong non-adiabatic coupling region near the conical intersections. Our comparisons support the use of the tested quantum-chemical methods for modeling the photochemistry of large organic and biological systems.
    The Journal of Chemical Physics 09/2014; 141(12):124122. DOI:10.1063/1.4896372 · 3.12 Impact Factor
  • Ganglong Cui, Walter Thiel
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    ABSTRACT: Trajectory-based fewest-switches surface-hopping (FSSH) dynamics simulations have become a popular and reliable theoretical tool to simulate nonadiabatic photophysical and photochemical processes. Most available FSSH methods model internal conversion. We present a generalized trajectory surface-hopping (GTSH) method for simulating both internal conversion and intersystem crossing processes on an equal footing. We consider hops between adiabatic eigenstates of the non-relativistic electronic Hamiltonian (pure spin states), which is appropriate for sufficiently small spin-orbit coupling. This choice allows us to make maximum use of existing electronic structure programs and to minimize the changes to available implementations of the traditional FSSH method. The GTSH method is formulated within the quantum mechanics (QM)/molecular mechanics framework, but can of course also be applied at the pure QM level. The algorithm implemented in the GTSH code is specified step by step. As an initial GTSH application, we report simulations of the nonadiabatic processes in the lowest four electronic states (S0, S1, T1, and T2) of acrolein both in vacuo and in acetonitrile solution, in which the acrolein molecule is treated at the ab initio complete-active-space self-consistent-field level. These dynamics simulations provide detailed mechanistic insight by identifying and characterizing two nonadiabatic routes to the lowest triplet state, namely, direct S1 → T1 hopping as major pathway and sequential S1 → T2 → T1 hopping as minor pathway, with the T2 state acting as a relay state. They illustrate the potential of the GTSH approach to explore photoinduced processes in complex systems, in which intersystem crossing plays an important role.
    The Journal of Chemical Physics 09/2014; 141(12):124101. DOI:10.1063/1.4894849 · 3.12 Impact Factor
  • Bora Karasulu, Walter Thiel
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    ABSTRACT: The photophysical properties of a push-pull flavin derivative, roseoflavin (RoF), are investigated in different surroundings at the molecular level, with focus on intra-molecular charge transfer (ICT). Time-dependent density functional theory (TD-DFT, CAM-B3LYP functional) and DFT-based multi-reference configuration interaction (DFT/MRCI) are used to compute excited-state energies and one-electron properties of a truncated RoF model, roseolumiflavin (RoLF). Solvent effects are taken into account implicitly by the conductor-like polarizable continuum model and explicitly through a micro-solvation scheme. In the gas phase, the calculations predict no crossing between the lowest locally-excited (LE) and charge-transfer (CT) states upon twisting the dimethylamine donor group relative to the plane of the isoalloxazine acceptor moiety, whereas this crossing is found to be facile in solution (i.e., in water or benzene). Crossing of the LE and CT states facilitates ICT, which is the main cause of the fluorescence quenching and dual fluorescence character experimentally observed for roseoflavin in solution. The barrier for the ICT process is computed to be lower in water than in benzene, consistent with the enhanced ICT rates observed in more polar solvents. We present a detailed study of the molecular mechanism of the photoinduced ICT process in RoLF. For a typical donor-acceptor chromophore, three such mechanisms are discussed in the literature, which differ in the alignment of the donor and acceptor planes, namely planar ICT (PICT), perpendicular-twisted ICT (TICT), and wagging ICT (WICT). Our theoretical results suggest that the TICT mechanism is favored in RoLF.
    The Journal of Physical Chemistry B 09/2014; DOI:10.1021/jp506101x · 3.38 Impact Factor
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    ABSTRACT: The reaction FeO+ + H2 → Fe+ + H2O is a simple model for hydrogen abstraction processes in biologically important heme systems. The geometries of all relevant stationary points on the lowest sextet and quartet surfaces were optimized using several density functionals as well as the CASSCF method. The corresponding energy profiles were computed at the following levels: density functional theory using gradient-corrected, hybrid, meta, hybrid-meta, and perturbatively corrected double hybrid functionals; single-reference coupled cluster theory including up to single, double, triple, and perturbative quadruple excitations [CCSDT(Q)]; correlated multireference ab initio methods (MRCI, MRAQCC, SORCI, SORCP, MRMP2, NEVPT2, and CASPT2). The calculated energies were corrected for scalar relativistic effects, zero-point vibrational energies, and core−valence correlation effects. MRCI and SORCI energies were corrected for size-consistency errors using an a posteriori Davidson correction (+Q) leading to MRCI+Q and SORCI+Q. Comparison with the available experimental data shows that CCSDT(Q) is most accurate and can thus serve as benchmark method for this electronically challenging reaction. Among the density functionals, B3LYP performs best. In the correlated ab initio calculations with a full-valence active space, SORCI+Q yields the lowest deviations from the CCSDT(Q) reference results, with qualitatively similar energy profiles being obtained from MRCI+Q and MRAQCC. SORCI+Q benefits from the quality of the approximate average natural orbitals used in the final step of the SORCI procedure. Many of the tested methods show surprisingly large errors. The present results validate the common use of B3LYP in computational studies of heme systems and offer guidance on which correlated ab initio methods are most suitable for such studies.
    Journal of Chemical Theory and Computation 09/2014; 10(9):3807−3820. DOI:10.1021/ct500522d · 5.31 Impact Factor
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    ABSTRACT: We report the first X-ray structure of a spiroaminal hydrochloride. The chiral spiroaminal crystallizes as a racemic hydrochloride in the monoclinic space group P21/n and adopts the thermodynamically most stable conformation. Density functional calculations on several spiroaminals were used to establish correlations between trends in conformational energies, steric repulsions, and anomeric effects and to reveal the mechanism of the ring-opening tautomerization reaction. In the unsubstituted and backbone-substituted spiroaminals, the aminal tautomer is thermodynamically preferred. N-Substituted spiroaminals favor the amine/imine form for steric reasons, except for those with bridging N,N′ groups. The tautomerization from the aminal to the amine/imine is endergonic and kinetically hindered in the neutral species but quite facile after protonation. Anomeric effects lower the barriers but are less important than steric factors for relative energies.
    European Journal of Organic Chemistry 09/2014; 2014(25):5476-5486. DOI:10.1002/ejoc.201402576 · 3.15 Impact Factor

Publication Stats

15k Citations
2,168.97 Total Impact Points

Institutions

  • 2000–2015
    • Max Planck Institute for Coal Research
      Mülheim-on-Ruhr, North Rhine-Westphalia, Germany
    • University of British Columbia - Vancouver
      • Department of Chemistry
      Vancouver, British Columbia, Canada
  • 2013
    • University College London
      • Department of Physics and Astronomy
      Londinium, England, United Kingdom
  • 2010–2012
    • ETH Zurich
      • Laboratory of Physical Chemistry
      Zürich, ZH, 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
    • The University of Calgary
      Calgary, Alberta, Canada
    • IT University of Copenhagen
      København, Capital Region, Denmark
  • 2005–2009
    • Heinrich-Heine-Universität Düsseldorf
      • • Institute for Theoretical and Computational Chemistry
      • • Institut für Molekulare Enzymtechnologie (IMET)
      Düsseldorf, North Rhine-Westphalia, Germany
    • Universidad de Huelva
      Huelva, Andalusia, Spain
    • University of St Andrews
      Saint Andrews, Scotland, United Kingdom
    • Universität Paderborn
      • Department of Physics
      Paderborn, North Rhine-Westphalia, Germany
    • University of Minnesota Duluth
      • Department of Chemistry and Biochemistry
      Duluth, Minnesota, United States
    • University of Bergen
      • Department of Chemistry
      Bergen, Hordaland, Norway
  • 2002–2009
    • Hebrew University of Jerusalem
      • • Lise Meitner Minerva Center for Computational Quantum Chemistry
      • • Department of Organic Chemistry
      Yerushalayim, Jerusalem District, Israel
    • Universität Heidelberg
      • Interdisciplinary Center for Scientific Computing
      Heidelberg, Baden-Wuerttemberg, Germany
    • University of Texas at Austin
      Austin, Texas, United States
  • 2007
    • California Pacific University
      Pinole, California, United States
  • 2004
    • Athens State University
      Athens, Alabama, United States
  • 2003–2004
    • University of Rostock
      Rostock, Mecklenburg-Vorpommern, Germany
    • Technische Universität Dortmund
      Dortmund, North Rhine-Westphalia, Germany
    • Xiamen University
      • Department of Chemistry
      Xiamen, Fujian, China
    • University of Georgia
      • Center for Computational Chemistry
      Athens, GA, United States
  • 2001
    • Friedrich-Alexander Universität Erlangen-Nürnberg
      • Computer-Chemistry-Center
      Erlangen, Bavaria, Germany
  • 1998
    • University of Strasbourg
      Strasburg, Alsace, France