| 1. |
- Mondal, Arobendo, et al.
(författare)
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Large-Scale Computation of Nuclear Magnetic Resonance Shifts for Paramagnetic Solids Using CP2K
- 2018
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 14:1, s. 377-394
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale computations of nuclear magnetic resonance (NMR) shifts for extended paramagnetic solids (pNMR) are reported using the highly efficient Gaussian-augmented plane-wave implementation of the CP2K code. Combining hyperfine couplings obtained with hybrid functionals with g-tensors and orbital shieldings computed using gradient-corrected functionals, contact, pseudocontact, and orbital-shift contributions to pNMR shifts are accessible. Due to the efficient and highly parallel performance of CP2K, a wide variety of materials with large unit cells can be studied with extended Gaussian basis sets. Validation of various approaches for the different contributions to pNMR shifts is done first for molecules in a large supercell in comparison with typical quantum-chemical codes. This is then extended to a detailed study of g-tensors for extended solid transition-metal fluorides and for a series of complex lithium vanadium phosphates. Finally, lithium pNMR shifts are computed for Li3V2(PO4)(3), for which detailed experimental data are available. This has allowed an in-depth study of different approaches (e.g., full periodic versus incremental cluster computations of g-tensors and different functionals and basis sets for hyperfine computations) as well as a thorough analysis of the different contributions to the pNMR shifts. This study paves the way for a more-widespread computational treatment of NMR shifts for paramagnetic materials.
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| 2. |
- Noack, Holger, 1976-
(författare)
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Biomimetic Iron Complexes involved in Oxygenation and Chlorination : A Theoretical Study
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomimetic chemistry is directed towards the simulation of enzymatic reactivity with synthetic analogues. In this thesis a quantum chemical method has been employed to study the mechanism of highly reactive iron-oxo complexes involved in oxygenation and chlorination of organic substrates. The aim of this research is to gain greater understanding for the reactivity paradigm of the iron-oxo group. One reaction deals with the conversion of cyclohexane into adipic acid, a key chemical in industrial chemistry, catalyzed by an iron(II)-porphyrin complex in the presence of dioxygen. This process constitutes a ’green’ alternative to conventional adipic acid production, and is thus of great interest to synthetic chemistry. Another reaction investigated herein regards the selective chlorination observed for a new group of non-heme iron enzymes. With help of theoretical modeling it was possible to propose a mechanism that explains the observed selectivity. It is furthermore demonstrated how a biomimetic iron complex simulates the enzymatic reactivity by a different mechanism. Other topics covered in this thesis regard the structure-reactivity relationship of a binuclear iron complex and the intradiol C-C bond cleavage of catechol catalyzed by an iron(III) complex.
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| 3. |
- Schinzel, Sandra, et al.
(författare)
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Density Functional Calculations of Mn-55, N-14 and C-13 Electron Paramagnetic Resonance Parameters Support an Energetically Feasible Model System for the S-2 State of the Oxygen-Evolving Complex of Photosystem II
- 2010
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 16:34, s. 10424-10438
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Tidskriftsartikel (refereegranskat)abstract
- Metal and ligand hyperfine couplings of a previously suggested, energetically feasible Mn4Ca model cluster (SG2009(-1)) for the S, state of the oxygen-evolving complex (OEC) of photosystem II (PSII) have been studied by broken-symmetry density functional methods and compared with other suggested structural and spectroscopic models. This was carried out explicitly for different spin-coupling patterns of the S=(1)/(2) ground state of the Mn-III(Mn-IV)(3) cluster. By applying spin-projection techniques and a scaling of the manganese hyperfine couplings, computation of the hyperfine and nuclear quadrupole coupling parameters allows a direct evaluation of the proposed models in comparison with data obtained from the simulation of EPR. ENDOR, and ESEEM spectra. The computation of Mn-55 hyperfine couplings (HFCs) for SG2009(-1) gives excellent agreement with experiment. However, at the current level of spin projection, the Mn-55 HFCs do not appear sufficiently accurate to distinguish between different structural models. Yet, of all the models studied, SG2009(-1) is the only one with the Mn-III site at the Mn-C center, which is coordinated by histidine (D1-His332). The computed histidine N-14 HFC anisotropy for SG2009(-1) gives much better agreement with ESEEM data than the other models, in which Mn-C is an Mn-IV site, thus supporting the validity of the model. The C-13 HFCs of various carboxylates have been compared with C-13 ENDOR data for PSII preparations with C-13-labelled alanine.
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| 4. |
- Telyatnyk, Lyudmyla G., 1979-
(författare)
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Density functional studies of EPR and NMR parameters of paramagnetic systems
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Experimental methods based on the magnetic resonance phenomenon belong to the most widely used experimental techniques for investigations of molecular and electronic structure. The difficulty with such experiments, usually a proper interpretation of data obtained from high-resolution spectra, opens new challenges for pure theoretical methods. One of these methods is density functional theory (DFT), that now has an advanced position among a whole variety of computational techniques. This thesis constitutes an effort in this respect, as it presents theory and discusses calculations of electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) parameters of paramagnetic molecules. It is known that the experimental determination of the magnetic resonance parameters of such molecules, especially in the case of NMR, is quite complicated and requires special techniques of spectral detection. On the other hand, paramagnetics play an important role in many areas, such as molecular magnets, active centers in biological systems, and defects in inorganic conductive materials. Therefore, they have spurred great interest among experimentalists, motivating us to facilitate the interpretation of spectral data through theoretical calculations. This thesis describes new methodologies for the determination of magnetic properties of paramagnetic molecules in the framework of DFT, which have been developed in our laboratory, and their applications in calculations of a wide range of molecular systems. The first two papers of this thesis deal with the theoretical determination of NMRparameters, such as nuclear shielding tensors and chemical shifts, in paramagnetic nitroxides that form core units in molecular magnets. The developed methodology is aimed to realize a high calculational accuracy for these systems. The effects of hydrogen bonding are also described in that context. Our theory for the evaluation of nuclear shielding tensors in paramagnetic molecules is consistent up to second order in the fine structure constant and considers orbital, fully anisotropic dipolar, and isotropic contact contributions to the shielding tensor. The next projects concern electron paramagnetic resonance. The well-known EPR parameters, such as the g-tensors and the hyperfine coupling constants are explored. Calculations of electronic g-tensors were carried out in the framework of a spin-restricted open-shell Kohn-Sham method combined with the linear response theory recently developed in our laboratory and allowing us to avoid by definition the spin-contamination problem. The inclusion of solvent effects, described by the polarizable continuum model, extends the possibility to treat molecular systems often investigated in solution. For calculations of the hyperfine coupling constants a so-called restricted-unrestricted approach to account for the spin polarization effect has been developed in the context of DFT. To examine the validity of the approximations implicit in this scheme, the neglect ii of singlet operators, a generalized RU methodology was implemented, which includes a fully unrestricted treatment with both singlet and triplet operators. The small magnitude of the changes in hyperfine coupling constants confirms the validity of the original scheme.
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