Abstract
Nitroxide radicals are widely used in electron paramagnetic resonance (EPR) applications. Nitroxides are stable organic radicals containing the N–O˙ group with hyperfine coupled unpaired electron and nitrogen nuclear spins. In the past, much attention was devoted to studying nitroxide EPR spectra and electron spin magnetization evolution under various experimental conditions. However, the dynamics of nitrogen nuclear spin has not been investigated in detail so far. In this work, we performed quantitative prediction and simulation of nitrogen nuclear spin magnetization evolution in several magnetic resonance experiments. Our research was focused on fast rotating nitroxide radicals in liquid solutions. We used a general approach allowing us to compute electron and nitrogen nuclear spin magnetization from the same time-dependent spin density matrix obtained by solving the Liouville/von Neumann equation. We investigated the nitrogen nuclear spin dynamics subjected to various radiofrequency magnetic fields. Furthermore, we predicted a large dynamic nuclear polarization of nitrogen upon nitroxide irradiation with microwaves and analyzed its effect on the nitroxide EPR saturation factor.
Highlights
Organic nitroxide radicals play a vital role in electron paramagnetic resonance (EPR) spectroscopy.1,2 Nitroxides are stable molecules with an unpaired electron, which is usually localized in the middle of the N–O bond, featuring a strong hyperfine interaction with the nitrogen nuclear spin.3 Various materials, which are usually EPR silent, can be made suitable for EPR experiments by introducing nitroxides into investigated samples
Organic nitroxide radicals play a vital role in EPR spectroscopy
Nitroxides can be used as a polarizing agent for Dynamic Nuclear Polarization (DNP) to enhance Nuclear Magnetic Resonance (NMR) signals
Summary
Organic nitroxide radicals play a vital role in EPR spectroscopy. Nitroxides are stable molecules with an unpaired electron (see Fig. 1A), which is usually localized in the middle of the N–O bond, featuring a strong hyperfine interaction with the nitrogen nuclear spin. Various materials, which are usually EPR silent, can be made suitable for EPR experiments by introducing nitroxides into investigated samples. Organic nitroxide radicals play a vital role in EPR spectroscopy.. Nitroxides are stable molecules with an unpaired electron (see Fig. 1A), which is usually localized in the middle of the N–O bond, featuring a strong hyperfine interaction with the nitrogen nuclear spin.. Nitroxides can be used as a polarizing agent for Dynamic Nuclear Polarization (DNP) to enhance Nuclear Magnetic Resonance (NMR) signals.. Since nitroxides can be attached to large macromolecules, they are often employed as spin labels to access valuable information about the structure and dynamics of organic polymers and bio-molecular systems. Spin-labeled molecules can be effectively studied by the pulsed EPR technique at low temperatures.. Nitroxide spin labels combined with pulsed electron–electron double resonance can detect macromolecule conformational flexibility at the nanometer scale.. Spin-labeled molecules can be effectively studied by the pulsed EPR technique at low temperatures. For example, nitroxide spin labels combined with pulsed electron–electron double resonance can detect macromolecule conformational flexibility at the nanometer scale. Recent methodological developments aim to extend the sensitivity of this technique to the range above 10 nm.
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