TY - JOUR
T1 - Comparative study of the electron spin resonance behavior of doxyl-labeled and (minimum steric perturbation) azethoxyl-labeled fatty acids in several liquid crystalline mesophases
AU - Broido, Michelle S.
AU - Belsky, Igai
AU - Meirovitch, Eva
PY - 1982
Y1 - 1982
N2 - We report on temperature- and angular-dependent ESR spectra of two types of nitroxide-labeled fatty acid chains, the commonly used but sterically bulky doxyl nitroxides and the recently prepared "minimum steric perturbation" azethoxyl nitroxides, dissolved in various liquid crystalline phases. The main spectral feature examined was the effective hyperfine splitting of the nitroxide radical, which in almost all cases was found to exceed the isotropic value of this parameter. The interpretation of this result in terms of deviations from an extended-chain conformation is shown to be unique with the azethoxyls and ambiguous with the doxyls, as it is based on the inherent geometric molecular feature β, the tilt angle of the free-electron π orbital relative to the main chain axis. In the various mesophases studied, β was found to range from 30° to 50°, as compared to 60° for an extended chain. Use of azethoxyl probes, rather than doxyl probes, in addressing questions related to the conformation of flexible chains in locally ordered media is thus suggested, for with the azethoxyl probes valuable information is available before detailed line-shape analysis.
AB - We report on temperature- and angular-dependent ESR spectra of two types of nitroxide-labeled fatty acid chains, the commonly used but sterically bulky doxyl nitroxides and the recently prepared "minimum steric perturbation" azethoxyl nitroxides, dissolved in various liquid crystalline phases. The main spectral feature examined was the effective hyperfine splitting of the nitroxide radical, which in almost all cases was found to exceed the isotropic value of this parameter. The interpretation of this result in terms of deviations from an extended-chain conformation is shown to be unique with the azethoxyls and ambiguous with the doxyls, as it is based on the inherent geometric molecular feature β, the tilt angle of the free-electron π orbital relative to the main chain axis. In the various mesophases studied, β was found to range from 30° to 50°, as compared to 60° for an extended chain. Use of azethoxyl probes, rather than doxyl probes, in addressing questions related to the conformation of flexible chains in locally ordered media is thus suggested, for with the azethoxyl probes valuable information is available before detailed line-shape analysis.
UR - http://www.scopus.com/inward/record.url?scp=33845555242&partnerID=8YFLogxK
U2 - 10.1021/j100218a022
DO - 10.1021/j100218a022
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AN - SCOPUS:33845555242
SN - 0022-3654
VL - 86
SP - 4197
EP - 4205
JO - Journal of Physical Chemistry
JF - Journal of Physical Chemistry
IS - 21
ER -