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Systematic theoretical investigation of the zero-field splitting in Gd(III) complexes: Wave function and density functional approaches
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
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2015 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 3, article id 034304Article in journal (Refereed) Published
Abstract [en]

The zero-field splitting (ZFS) of the electronic ground state in paramagnetic ions is a sensitive probe of the variations in the electronic and molecular structure with an impact on fields ranging from fundamental physical chemistry to medical applications. A detailed analysis of the ZFS in a series of symmetric Gd(III) complexes is presented in order to establish the applicability and accuracy of computational methods using multiconfigurational complete-active-space self-consistent field wave functions and of density functional theory calculations. The various computational schemes are then applied to larger complexes Gd(III)DOTA(H2O)(-), Gd(III)DTPA(H2O)(2-), and Gd(III)(H2O)(8)(3+) in order to analyze how the theoretical results compare to experimentally derived parameters. In contrast to approximations based on density functional theory, the multiconfigurational methods produce results for the ZFS of Gd(III) complexes on the correct order of magnitude.

Place, publisher, year, edition, pages
2015. Vol. 142, no 3, article id 034304
National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
URN: urn:nbn:se:su:diva-114354DOI: 10.1063/1.4905559ISI: 000348302900024PubMedID: 25612706OAI: oai:DiVA.org:su-114354DiVA, id: diva2:793670
Note

AuthorCount:5;

Available from: 2015-03-09 Created: 2015-03-02 Last updated: 2018-04-27Bibliographically approved
In thesis
1. Combined Quantum Mechanical and Molecular Dynamics study of paramagnetic complexes: Towards an understanding of electronic spin relaxation
Open this publication in new window or tab >>Combined Quantum Mechanical and Molecular Dynamics study of paramagnetic complexes: Towards an understanding of electronic spin relaxation
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The prime objectives of contrast agents in Magnetic Resonance Imaging (MRI) is to accelerate the relaxation rate of the solvent water protons in the surrounding tissue. Paramagnetic relaxation originates from dipole-dipole interactions between the nuclear spins and the fluctuating magnetic field induced by unpaired electrons. Currently Gadolinium(III) chelates are the most widely used contrast agents in MRI, and therefore it is incumbent to extend the fundamental theoretical understanding of parameters that drive the relaxation mechanism in these complexes. In compounds such as Gadolinium(III) complexes with total electron spins higher than 1 (in this case S=7/2) the Zero-Field Splitting (ZFS) plays a significant role in influencing the electron spin dynamics and nuclear spin dynamics. For this purpose, the current research delves into an understanding of the relaxation process, focusing on ZFS in various complexes of interest, using multi-scale modelling by combining quantum, semi-quantum and newtonian methods.

We compare and contrast Density Function Theory (DFT) with multi-configurational quantum chemical calculation and find that DFT is highly functional dependent and unreliable in accurately reproducing experimental data for the static ZFS. It was found that long-range corrected functionals (in particular LC-BLYP) perform significantly better as compared to other functionals in predicting the magnitude of the static ZFS. We study hydrated Gd(III) and Eu(II) systems to compare and contrast these isoelectronic complexes (both contain 7 unpaired electrons in their valence shell) and through ab-initio molecular dynamics (AIMD) sampling followed by multi-reference quantum chemical calculations, it was established that inclusion of the first shell has a dominant influence (over 90%) on the ZFS. We also studied the complex [Gd(III)(HPDO3A)(H2O)], which is of clinical relevance as a contrast agent for MRI, through post-Hartree-Fock and DFT calculations by utilizing configurations derived from AIMD trajectories. From the fluctuations in the ZFS tensor, we extract a correlation time of the transient ZFS which is on the sub-picosecond time scale, showing a faster decay than experimental data.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2018. p. 58
Keyword
molecular dynamics, quantum chemistry, zero-field splitting
National Category
Other Physics Topics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-155519 (URN)978-91-7797-320-1 (ISBN)978-91-7797-321-8 (ISBN)
Public defence
2018-06-12, FB53, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
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Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2018-05-18 Created: 2018-04-23 Last updated: 2018-05-09Bibliographically approved

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Khan, ShehryarKowalewski, JozefOdelius, Michael
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