Abstract: Principal N-15 hyperfine interaction (hfi) values in N-15-substituted nitroxide spin probe 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-oxyl dissolved in nematic liquid crystal 4-pentyl-4'-cyanobiphenyl (5CB) were measured in a wide temperature range of 10-210 K, for 5CB frozen to a glassy state. X-band continuous-wave electron paramagnetic resonance (CW EPR) and pulse X- and Q-band N-15 electron-nuclear double resonance (ENDOR) techniques were employed. To avoid microwave saturation at low temperatures in CW EPR studies, a holmium complex Ho(Dbm)(3)Bpy (where Dbm is dibenzoylmethane and Bpy is 2,2'-bipyridine) was added. X-and Q-band N-15-ENDOR data have shown that the nitroxide hfi tensor is axially symmetric. The combination of data from all techniques allowed us to obtain the temperature dependence of isotropic and anisotropic parts of the nitroxide hfi tensor. Above similar to 100 K, a linear dependence of the anisotropic hfi value was observed, whereas below 30 K it was found to be nearly temperature independent. Such a behavior can be interpreted using the model of restricted orientational motions (librations) of a spin probe in a glassy matrix, with quantum effects occurring at low temperature ("freezing" of the librations). The energy quantum for the libration motion estimated from the temperature dependence of hfi of the spin probe is 84 cm(-1). Low-frequency Raman spectra of 5CB were also obtained, which provided the mean vibrational frequency of 76 cm(-1) for glassy 5CB.

Cite: Pivtsov A.V. , Kulik L.V. , Surovtsev N.V. , Adichtchev S.V. , Kirilyuk I.A. , Grigor'ev I.A. , Fedin M.V. , Dzuba S.A.
Temperature Dependence of Hyperfine Interaction for N-15 Nitroxide in a Glassy Matrix at 10-210 K
Applied Magnetic Resonance. 2011. V.41. N2-4. P.411-429. DOI: 10.1007/s00723-011-0272-y WOS Scopus

Dates:

Published online:	Sep 25, 2011
Published print:	Dec 1, 2011

Identifiers:

Web of science	WOS:000299295600024
Scopus	2-s2.0-81155128537
OpenAlex	W2072286620

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