The distance between g-tensors of nitroxide biradicals governs MAS-DNP performance : The case of the bTurea family

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Bis-nitroxide radicals are common polarizing agents (PA), used to enhance the sensitivity of solid-state NMR experiments via Magic Angle Spinning Dynamic Nuclear Polarization (MAS-DNP). These biradicals can increase the proton spin polarization through the Cross-Effect (CE) mechanism, which requires PAs with at least two unpaired electrons. The relative orientation of the bis-nitroxide moieties is critical to ensure efficient polarization transfer. Recently, we have defined a new quantity, the distance between g-tensors, that correlates the relative orientation of the nitroxides with the ability to polarize the surrounding nuclei. Here we analyse experimentally and theoretically a series of biradicals belonging to the bTurea family, namely bcTol, AMUPol and bcTol-M. They differ by the degree of substitution on the urea bridge that connects the two nitroxides. Using quantitative simulations developed for moderate MAS frequencies, we show that these modifications mostly affect the relative orientations of the nitroxide, i.e. the length and distribution of the distance between the g-tensors, that in turn impacts both the steady state nuclear polarization/depolarization as well as the build-up times. The doubly substituted urea bridge favours a large distance between the g-tensors, which enables bcTol-M to provide ∊on/off>200 at 14.1 T/600 MHz/395 GHz with build-up times of 3.8 s using a standard homogenous solution. The methodology described herein was used to show how the conformation of the spirocyclic rings flanking the nitroxide function in the recently described c- and o-HydrOPol affects the distance between the g-tensors and thereby polarization performance.

Medienart:

E-Artikel

Erscheinungsjahr:

2021

Erschienen:

2021

Enthalten in:

Zur Gesamtaufnahme - volume:329

Enthalten in:

Journal of magnetic resonance (San Diego, Calif. : 1997) - 329(2021) vom: 10. Aug., Seite 107026

Sprache:

Englisch

Beteiligte Personen:

Mentink-Vigier, Frédéric [VerfasserIn]
Dubroca, Thierry [VerfasserIn]
Van Tol, Johan [VerfasserIn]
Sigurdsson, Snorri Th [VerfasserIn]

Links:

Volltext

Themen:

8W8T17847W
Bis-nitroxides
Cross-effect
Density functional theory
Dynamic nuclear polarization
GFQ4MMS07W
Journal Article
Liouville space
MAS-DNP
Magic angle spinning
Nitrogen Oxides
Nitroxyl
Research Support, N.I.H., Extramural
Research Support, U.S. Gov't, Non-P.H.S.
Simulations
Spin diffusion
Urea

Anmerkungen:

Date Completed 17.01.2022

Date Revised 02.08.2022

published: Print-Electronic

Citation Status MEDLINE

doi:

10.1016/j.jmr.2021.107026

funding:

Förderinstitution / Projekttitel:

PPN (Katalog-ID):

NLM327927208