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Molecular dynamics of nitroxides in glasses as studied by multi‐frequency EPR
Author(s) -
Kirilina Evgeniya P.,
Prisner Thomas F.,
Bennati Marina,
Endeward Burkhard,
Dzuba Sergei A.,
Fuchs Martin R.,
Möbius Klaus,
Schnegg Alexander
Publication year - 2005
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1677
Subject(s) - chemistry , electron paramagnetic resonance , relaxation (psychology) , nitroxide mediated radical polymerization , molecular dynamics , glass transition , spin probe , chemical physics , spectral line , nuclear magnetic resonance , molecular physics , analytical chemistry (journal) , computational chemistry , chromatography , polymer , organic chemistry , physics , psychology , social psychology , radical polymerization , astronomy , copolymer
Pulsed multi‐frequency EPR was used to investigate orientational molecular motion of the nitroxide spin probe (Fremy's salt) in glycerol glass near the glass transition temperature. By measuring echo‐detected EPR spectra at different pulse separation times at resonance frequencies of 3, 9.5, 95 and 180 GHz, we were able to discriminate between different relaxation mechanisms and characterize the timescale of molecular reorientations (10 −7 –10 −10 s). We found that near the glass transition temperature, the orientation‐dependent transverse relaxation is dominated by fast reorientational fluctuations, which may be overlapped with fast modulations of the canonical g‐matrix values. The data was interpreted using a new simulation program for the orientation‐dependent transverse relaxation rate 1/ T 2 of nitroxides based on different models for the molecular motion. The validity of the different models was assessed by comparing least‐square fits of the simulated relaxation behaviour to the experimental data. Copyright © 2005 John Wiley & Sons, Ltd.