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Characterization of Aqueous Lower Polarity Solvation Shells Around Amphiphilic TEMPO Radicals in Water

preprint
submitted on 21.05.2020 and posted on 22.05.2020 by Johannes Hunold, Jana Eisermann, Martin Brehm, Dariush Hinderberger
Solvation of the stable nitroxide radicals 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) and 4-Oxo-TEMPO (TEMPONE) in water and THF is studied. With electron paramagnetic resonance (EPR) spectroscopy at X- and Q-band as well as spectral simulations, the existence of pure water shells enclosing TEMPO in aqueous solution that lead to significantly reduced local polarity at the nitroxide is shown. These aqueous lower polarity solvation shells (ALPSS) offer TEMPO a local polarity that is similar to that in organic solvents like THF. Furthermore, using double electron-electron resonance (DEER) spectroscopy, local enrichment and inhomogenous distribution without collisions of dissolved TEMPO in water is found that can be correlated with potentially attractive interactions mediated through ALPSS. However, no local enrichment of TEMPO is found in organic solvents such as THF. These results are substantiated by MD and metadynamics simulations and physical methods like DLS and MS.

Funding

DFG Br5494/1-1

Fonds der chemischen Industrie (FCI)

History

Email Address of Submitting Author

dariush.hinderberger@chemie.uni-halle.de

Institution

Martin-Luther-Universität Halle-Wittenberg

Country

Germany

ORCID For Submitting Author

0000-0002-6066-7099

Declaration of Conflict of Interest

no conflicts of interest

Version Notes

initial version 1

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