TY - JOUR
T1 - Multifrequency EPR study of the mobility of nitroxides in solid-state calixarene nanocapsules
AU - Bagryanskaya, Elena G.
AU - Polovyanenko, Dmitriy N.
AU - Fedin, Matvey V.
AU - Kulik, Leonid
AU - Schnegg, Alexander
AU - Savitsky, Anton
AU - Möbius, Klaus
AU - Coleman, Anthony W.
AU - Ananchenko, Gennady S.
AU - Ripmeester, John A.
PY - 2009
Y1 - 2009
N2 - Multifrequency continuous wave (cw) and echo-detected (ED) electron paramagnetic resonance (EPR) was employed to study the mobility of nitroxides confined in nanocapsules. The complexes p-hexanoyl calix[4]arene with 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl (MT) and N-(2-methylpropyl)-N-(1- diethylphosphono-2,2-dimethylpropyl)-aminoxyl (DEPN) were studied by X-, W-band and 360 GHz cw EPR at temperatures between 90 and 370 K. Thereby we were able to extract the canonical values of the hyperfine and g-tensors of the encapsulated radicals as well as information on restricted orientational dynamics of the caged spin probes. Comparing cw and ED-EPR data obtained on MT@C6OH we found that between 90 and 200 K the caged nitroxide undergoes isotropic small-angle fluctuations (librations), whereas at higher temperatures restricted rotations of the radical with correlation times of 0.75 × 10-10 s and 1.2 × 10-10 s dominate at 325 and 300 K, respectively. The activation energy of the rotational motion of encapsulated MT radicals was evaluated as Ea = 1.0 kcal mol-1, which is comparable to the magnitude of van der Waals interactions. Compared to MT, the reorientational motion of DEPN was found to be slower and more isotropic.
AB - Multifrequency continuous wave (cw) and echo-detected (ED) electron paramagnetic resonance (EPR) was employed to study the mobility of nitroxides confined in nanocapsules. The complexes p-hexanoyl calix[4]arene with 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl (MT) and N-(2-methylpropyl)-N-(1- diethylphosphono-2,2-dimethylpropyl)-aminoxyl (DEPN) were studied by X-, W-band and 360 GHz cw EPR at temperatures between 90 and 370 K. Thereby we were able to extract the canonical values of the hyperfine and g-tensors of the encapsulated radicals as well as information on restricted orientational dynamics of the caged spin probes. Comparing cw and ED-EPR data obtained on MT@C6OH we found that between 90 and 200 K the caged nitroxide undergoes isotropic small-angle fluctuations (librations), whereas at higher temperatures restricted rotations of the radical with correlation times of 0.75 × 10-10 s and 1.2 × 10-10 s dominate at 325 and 300 K, respectively. The activation energy of the rotational motion of encapsulated MT radicals was evaluated as Ea = 1.0 kcal mol-1, which is comparable to the magnitude of van der Waals interactions. Compared to MT, the reorientational motion of DEPN was found to be slower and more isotropic.
UR - http://www.scopus.com/inward/record.url?scp=68349101209&partnerID=8YFLogxK
U2 - 10.1039/b906827a
DO - 10.1039/b906827a
M3 - Article
C2 - 19639143
AN - SCOPUS:68349101209
SN - 1463-9076
VL - 11
SP - 6700
EP - 6707
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
IS - 31
ER -