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Encapsulation Influence on EPR Parameters of Spin-Labels: 2,2,6,6-Tetramethyl-4-methoxypiperidine-1-oxyl in Cucurbit[8]uril
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0003-2729-0290
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0003-0185-5724
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0002-9123-8174
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2012 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 8, no 1, 257-263 p.Article in journal (Refereed) Published
Abstract [en]

Encapsulation of a nitroxide spin label into a host cavity can prolong the lifetime of the spin label in biological tissues and other environments. Although such paramagnetic supramolecular complexes have been extensively studied experimentally, there is yet little understanding of the role of the encapsulation on the magnetic properties of the spin labels and their performance at the atomistic level. In this work, we approach this problem by modeling encapsulation induced changes of the magnetic properties of spin labels for a prototypical paramagnetic guest host complex, 2,2,6,6-tetramethyl-4-methoxypiperidine-1-oxyl, enclosed in the hydrophobic cavity of cucurbit[8]uril, using state-of-the-art hybrid quantum mechanics/molecular mechanics methodology. The results allow a decomposition of the encapsulation shift of the electronic g-tensor and the nitrogen isotropic hyperfine coupling constant of nitroxide radical into a set of distinct contributions associated with the host cavity confinement and with changes of the local solvent environment of the spin label upon encapsulation. It is found that the hydrophobic cavity of cucurbit[8]uril only weakly influences the electronic g-tensor of the 2,2,6,6-tetramethyl-4-methoxypiperidine-1-oxyl but induces a significant encapsulation shift of the nitrogen hyperfine coupling constant. The latter is caused by the change of topology of the hydrogen bonding network and the nature of the hydrogen bonds around the spin label induced by the hydrophobic cavity of the inclusion host. This indirect effect is found to be more important than the direct influence of the cavity exerted on the radical. The ramification of this finding for the use of approximate methods for computing electron paramagnetic resonance spectra of spin labels and for designing optimal spin labels based on guest-host templates is discussed.

Place, publisher, year, edition, pages
2012. Vol. 8, no 1, 257-263 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-75528DOI: 10.1021/ct200816zISI: 000298908500027Scopus ID: 2-s2.0-84855660084OAI: oai:DiVA.org:kth-75528DiVA: diva2:490884
Funder
Swedish e‐Science Research Center
Note

QC 20120206

Available from: 2012-02-06 Created: 2012-02-06 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, MuruganVahtras, OlavÅgren, Hans

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