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Density Functional Restricted-Unrestricted/Molecular Mechanics Theory for Hyperfine Coupling Constants of Molecules in Solution
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. (Swedish e-science Research Centre (SeRC))ORCID iD: 0000-0003-2729-0290
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0003-0185-5724
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
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2011 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 7, no 10, 3261-3271 p.Article in journal (Refereed) Published
Abstract [en]

A density functional restricted unrestricted approach, capable of evaluating hyperfine coupling constants with the inclusion of spin polarization effects in a spin-restricted Kohn-Sham method, has been extended to incorporate environmental effects. This is accomplished by means of a hybrid quantum mechanics/molecular mechanics formalism which allows for a granular representation of the polarization and electrostatic interactions with the classically described medium. By this technique, it is possible to trace the physical origin of hyperfine coupling constants in terms of spin polarization and spin density contributions and disentangle the dependence of these contributions on molecular geometry and solvent environment, something that increases the prospects for optimal design of spin labels for particular applications. A demonstration is given for the nitrogen isotropic hyperfine coupling constant in di-tert-butyl nitroxide solvated in water. The results indicate that the direct spin density contribution is about 5 times smaller than the spin polarization contribution to the nitrogen isotropic hyperfine coupling constant and that the latter contribution is solely responsible for the solvent shift of the constant. The developed approach is found capable of achieving satisfactory accuracy in prediction of the hyperfine coupling constants of solvated di-tert-butyl nitroxide and other similar nitroxides without the inclusion of solvent molecules in the quantum region provided polarizable force fields are used for the description of these molecules.

Place, publisher, year, edition, pages
2011. Vol. 7, no 10, 3261-3271 p.
Keyword [en]
NITROXIDE SPIN-LABEL, ELECTRONIC G-TENSORS, INTEGRATED COMPUTATIONAL APPROACH, LARGE FREE-RADICALS, CAR-PARRINELLO, MAGNETIC-PROPERTIES, SOLVATED MOLECULES, DYNAMICS SIMULATIONS, SOLVENT POLARITY, AQUEOUS-SOLUTION
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-47984DOI: 10.1021/ct2003572ISI: 000295655000023Scopus ID: 2-s2.0-80053960691OAI: oai:DiVA.org:kth-47984DiVA: diva2:457082
Funder
Swedish e‐Science Research Center
Note

QC 20111116

Available from: 2011-11-16 Created: 2011-11-15 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Theoretical studies of EPR parameters of spin-labels incomplex environments
Open this publication in new window or tab >>Theoretical studies of EPR parameters of spin-labels incomplex environments
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis encloses quantum chemical calculations performed in the framework of density functional response theory for evaluating electron paramagnetic resonance (EPR) spin Hamiltonian parameters of various spin-labels in different environments. These parameters are the well known electronic g-tensor and the nitrogen hyperfine coupling constants, which are extensively explored in this work for various systems. A special attention was devoted to the relationships that form between the structural and spectroscopic properties that can be accounted for as an environmental inuence. Such environmental effects were addressed either within a fully quantum mechanical formalism, involving simplified model structures that still capture the physical properties of the extended system, or by employing a quantum mechanics/molecular mechanics (QM/MM) approach. The latter implies that the nitroxide spin label is treated quantum mechanically, while the environment is treated in a classical discrete manner, with appropriate force fields employed for its description. The state-of- the art techniques employed in this work allow for an optimum accounting of the environmental effects that play an important role for the behaviour of EPR properties of nitroxides spin labels. One achievement presented in this thesis includes the first theoretical con_rmation of an empirical assumption that is usually made for inter-molecular distance measurement experiments in deoxyribonucleic acid (DNA), involving pulsed electron-electron double resonance (PELDOR) and site-directed spin labeling (SDSL) techniques. This refers to the fact that the EPR parameters of the spin-labels are not affected by their interaction with the nucleobases from which DNA is constituted. Another important result presented deals with the inuence of a supramolecular complex on the EPR properties of an encapsulated nitroxide spin-label. The enclusion complex affects the hydrogen bonding topology that forms around the R2NO moiety of the nitroxide. This, on the other hand has a major impact on its structure which further on governs the magnitude of the spectroscopic properties. The projects and results presented in this thesis offer an example of successful usage of modern quantum chemistry techniques for the investigation of EPR parameters of spin-labels in complex systems.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. iv, 57 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2013:6
Keyword
EPR, DFT, spin-labels, QM/MM, Breit-Pauli Hamiltonian
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-119515 (URN)978-91-7501-681-8 (ISBN)
Public defence
2013-04-05, FB 54, AlbaNova University Center, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130318

Available from: 2013-03-18 Created: 2013-03-15 Last updated: 2013-03-18Bibliographically approved

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Natarajan Arul, MuruganÅgren, Hans

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