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Bordignon E, Nalepa AI, Savitsky A, et al. Changes in the Microenvironment of Nitroxide Radicals around the Glass Transition Temperature. J Phys Chem B. 2015;119(43):13797-806doi: 10.1021/acs.jpcb.5b04104.
Bordignon, E., Nalepa, A. I., Savitsky, A., Braun, L., & Jeschke, G. (2015). Changes in the Microenvironment of Nitroxide Radicals around the Glass Transition Temperature. The journal of physical chemistry. B, 119(43), 13797-806. https://doi.org/10.1021/acs.jpcb.5b04104
Bordignon, Enrica, et al. "Changes in the Microenvironment of Nitroxide Radicals around the Glass Transition Temperature." The journal of physical chemistry. B vol. 119,43 (2015): 13797-806. doi: https://doi.org/10.1021/acs.jpcb.5b04104
Bordignon E, Nalepa AI, Savitsky A, Braun L, Jeschke G. Changes in the Microenvironment of Nitroxide Radicals around the Glass Transition Temperature. J Phys Chem B. 2015 Oct 29;119(43):13797-806. doi: 10.1021/acs.jpcb.5b04104. Epub 2015 Aug 20. PMID: 26266707.
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J Phys Chem B. 2015 Oct 29;119(43):13797-806. doi: 10.1021/acs.jpcb.5b04104. Epub 2015 Aug 20.

Changes in the Microenvironment of Nitroxide Radicals around the Glass Transition Temperature.

The journal of physical chemistry. B

Enrica Bordignon, Anna I Nalepa, Anton Savitsky, Lukas Braun, Gunnar Jeschke

Affiliations

  1. Laboratory of Physical Chemistry, ETH Zurich , Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland.
  2. Berlin Joint EPR Laboratories, Department of Experimental Physics, Free University of Berlin , Arnimallee 14, 14195 Berlin, Germany.
  3. Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany.

PMID: 26266707 DOI: 10.1021/acs.jpcb.5b04104

Abstract

For structural characterization by pulsed EPR methods, spin-labeled macromolecules are routinely studied at cryogenic temperatures. The equilibration of the conformational ensemble during shock-freezing occurs to a good approximation at the glass transition temperature (Tg). In this work, we used X-band power saturation continuous wave (cw) EPR to obtain information on the glass transition temperatures in the microenvironment of nitroxide radicals in solvents or bound to different sites in proteins. The temperature dependence of the saturation curve of nitroxide probes in pure glycerol or ortho-terphenyl showed detectable transitions at the respective Tg values, with the latter solvent characterized by a sharper change of the saturation properties, according to its higher fragility. In contrast, nitroxide probes in a glycerol/water mixture showed a discontinuity in the saturation properties close to the expected glass transition temperature, which made the determination of Tg complicated. Low-temperature W-band cw EPR and W-band ELDOR-detected NMR experiments demonstrated that the discontinuity is due to local rearrangements of H-bonds between water molecules and the nitroxide reporter group. The change in the network of H-bonds formed between the nitroxide and water molecules that occurs around Tg was found to be site-dependent in spin-labeled proteins. This effect can therefore be modulated by neighboring residues with different steric hindrances and/or charge distributions and possibly by the glycerol enrichment on protein surfaces. In conclusion, if the thermal history of the sample is carefully reproduced, the nitroxide probe is extremely sensitive in reporting site-specific changes in the H-bonding to water molecules close to Tg and local glass transition temperatures in spin-labeled macromolecules.

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