TY - JOUR
T1 - Zero field splitting fluctuations induced phase relaxation of Gd3+ in frozen solutions at cryogenic temperatures
AU - Raitsimring, A.
AU - Dalaloyan, A.
AU - Collauto, A.
AU - Feintuch, A.
AU - Meade, T.
AU - Goldfarb, D.
N1 - Funding Information:
AR is deeply thankful to Dr. A. Astashkin and Prof. S. Vega for numerous discussions on the possible nature of phase relaxation mechanism of GdSL, and to Dr. M.E. Raisglid for help in editing this manuscript. This work was supported by the Israel–USA BSF science foundation (Grant No. 2010130 ). DG holds the Erich Klieger professorial chair in Chemical Physics.
Publisher Copyright:
© 2014 Elsevier Inc. All rights reserved.
PY - 2014/11
Y1 - 2014/11
N2 - Distance measurements using double electron-electron resonance (DEER) and Gd3+ chelates for spin labels (GdSL) have been shown to be an attractive alternative to nitroxide spin labels at W-band (95 GHz). The maximal distance that can be accessed by DEER measurements and the sensitivity of such measurements strongly depends on the phase relaxation of Gd3+ chelates in frozen, glassy solutions. In this work, we explore the phase relaxation of Gd3+-DOTA as a representative of GdSL in temperature and concentration ranges typically used for W-band DEER measurements. We observed that in addition to the usual mechanisms of phase relaxation known for nitroxide based spin labels, GdSL are subjected to an additional phase relaxation mechanism that features an increase in the relaxation rate from the center to the periphery of the EPR spectrum. Since the EPR spectrum of GdSL is the sum of subspectra of the individual EPR transitions, we attribute this field dependence to transition dependent phase relaxation. Using simulations of the EPR spectra and its decomposition into the individual transition subspectra, we isolated the phase relaxation of each transition and found that its rate increases with |ms|. We suggest that this mechanism is due to transient zero field splitting (tZFS), where its magnitude and correlation time are scaled down and distributed as compared with similar situations in liquids. This tZFS induced phase relaxation mechanism becomes dominant (or at least significant) when all other well-known phase relaxation mechanisms, such as spectral diffusion caused by nuclear spin diffusion, instantaneous and electron spin spectral diffusion, are significantly suppressed by matrix deuteration and low concentration, and when the temperature is sufficiently low to disable spin lattice interaction as a source of phase relaxation.
AB - Distance measurements using double electron-electron resonance (DEER) and Gd3+ chelates for spin labels (GdSL) have been shown to be an attractive alternative to nitroxide spin labels at W-band (95 GHz). The maximal distance that can be accessed by DEER measurements and the sensitivity of such measurements strongly depends on the phase relaxation of Gd3+ chelates in frozen, glassy solutions. In this work, we explore the phase relaxation of Gd3+-DOTA as a representative of GdSL in temperature and concentration ranges typically used for W-band DEER measurements. We observed that in addition to the usual mechanisms of phase relaxation known for nitroxide based spin labels, GdSL are subjected to an additional phase relaxation mechanism that features an increase in the relaxation rate from the center to the periphery of the EPR spectrum. Since the EPR spectrum of GdSL is the sum of subspectra of the individual EPR transitions, we attribute this field dependence to transition dependent phase relaxation. Using simulations of the EPR spectra and its decomposition into the individual transition subspectra, we isolated the phase relaxation of each transition and found that its rate increases with |ms|. We suggest that this mechanism is due to transient zero field splitting (tZFS), where its magnitude and correlation time are scaled down and distributed as compared with similar situations in liquids. This tZFS induced phase relaxation mechanism becomes dominant (or at least significant) when all other well-known phase relaxation mechanisms, such as spectral diffusion caused by nuclear spin diffusion, instantaneous and electron spin spectral diffusion, are significantly suppressed by matrix deuteration and low concentration, and when the temperature is sufficiently low to disable spin lattice interaction as a source of phase relaxation.
KW - Gd3+
KW - Phase relaxation
KW - Spin labels
KW - W-band EPR
KW - Zero field splitting
UR - http://www.scopus.com/inward/record.url?scp=84907976881&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84907976881&partnerID=8YFLogxK
U2 - 10.1016/j.jmr.2014.09.012
DO - 10.1016/j.jmr.2014.09.012
M3 - Article
C2 - 25442776
AN - SCOPUS:84907976881
VL - 248
SP - 71
EP - 80
JO - Journal of Magnetic Resonance
JF - Journal of Magnetic Resonance
SN - 1090-7807
ER -