Persistent Radicals of Self-assembled Benzophenone bis-Urea Macrocycles: Characterization and Application as a Polarizing Agent for Solid-state DNP MAS Spectroscopy.

Autor: DeHaven BA; Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina, 29208, USA., Tokarski JT 3rd; Department of Chemistry, University of Florida, Gainesville, Florida, 32611, USA., Korous AA; Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina, 29208, USA., Mentink-Vigier F; National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida, 32310, USA., Makris TM; Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina, 29208, USA., Brugh AM; Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio, 43403, USA., Forbes MDE; Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio, 43403, USA., van Tol J; National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida, 32310, USA., Bowers CR; Department of Chemistry, University of Florida, Gainesville, Florida, 32611, USA., Shimizu LS; Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina, 29208, USA.
Jazyk: angličtina
Zdroj: Chemistry (Weinheim an der Bergstrasse, Germany) [Chemistry] 2017 Jun 16; Vol. 23 (34), pp. 8315-8319. Date of Electronic Publication: 2017 May 19.
DOI: 10.1002/chem.201701705
Abstrakt: UV-irradiation of a self-assembled benzophenone bis-urea macrocycle generates μm amounts of radicals that persist for weeks under ambient conditions. High-field EPR and variable-temperature X-band EPR studies suggest a resonance stabilized radical pair through H-abstraction. These endogenous radicals were applied as a polarizing agent for magic angle spinning (MAS) dynamic nuclear polarization (DNP) NMR enhancement. The field-stepped DNP enhancement profile exhibits a sharp peak with a maximum enhancement of ϵ on/off =4 superimposed on a nearly constant DNP enhancement of ϵ on/off =2 over a broad field range. This maximum coincides with the high field EPR absorption spectrum, consistent with an Overhauser effect mechanism. DNP enhancement was observed for both the host and guests, suggesting that even low levels of endogenous radicals can facilitate the study of host-guest relationships in the solid-state.
(© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)
Databáze: MEDLINE
Externí odkaz:
Nepřihlášeným uživatelům se plný text nezobrazuje