Temperature dependence of amplitudes of libration motion of guest spin-probe molecules in organic glasses

Abstract

Electron paramagnetic resonance (EPR) lineshapes of nitroxide spin probes in a variety of organic supercooled liquids and glasses were analyzed within the framework of the fast librational motion model. Computer simulation confirmed that the EPR lineshape may be fitted well by the librational model. For all systems studied, a mean-squared amplitude of this motion, 〈α2〉, was found to depend linearly on temperature in the low-temperature region, which is typical of harmonic solids. The slope of the linear dependence varies from glass to glass and does not change for different nitroxides in the same glass. This slope seems to correlate with the strength of the intermolecular bonds and with a degree of the fragility of the glass. Steep rises in 〈α2〉 were observed at high temperature.

Microscopic rigidity and heterogeneity of ionic liquids probed by stochastic molecular librations of the dissolved nitroxides

“…As was shown previously, the librations can be essentially described by two parameters: angular amplitude of motion a and its characteristic correlation time t c ; however, experimentally one obtains their combination ha Such a linear behavior is typical for previous studies of stochastic molecular librations in organic glasses and biological membranes. [49][50][51][52][53][54] At the temperature range 80-150 K the librations systematically appear to be more intensive in ILs compared to common organic solvents. Here we used glycerol, o-terphenyl and squalane as representatives of common solvents because they preserve the glass state at a very large range of temperatures, whereas many other organic solvents (e.g.…”

“…harmonic-anharmonic dynamical transitions. 46,[48][49][50] In addition, the same approaches allowed important conclusions on structural organization of some biological membrane systems. 47 4 ) were purchased from Sigma-Aldrich and used without additional purification (Scheme 1a).…”

The Temperature Dependence of Nitroxide Spin–Label Interaction Parameters: a High-Field EPR Study of Intramolecular Motional Contributions

“…The temperature dependence of the dipolar (anisotropic) hyperfine coupling could be explained by the model of fast librations of the nitroxide molecule in the host matrix [18,64]. On the other hand, the pronounced change of the isotropic hyperfine coupling with temperature is not due to an overall motion of the nitroxide molecule in the matrix, but rather originates in an intramolecular motion of the nitroxide skeleton [44].…”

“…5). Another implication of the temperature-dependent out-of-plane motion of the nitroxide label for EPR studies of multi-mode molecular motion under the constraints of the guestmatrix system is the suggestion to disentangle this complex motion at a fixed temperature by using a multi-frequency EPR approach [19,63,65,66] rather than at a fixed EPR frequency and varying the temperature [64,[67][68][69][70][71].…”

Pulsed EPR Spin-Probe Study of Intracellular Glasses in Seed and Pollen

“…This technique has been applied in the study of rotational and librational motions of spin probes in glass-forming substances, such as supercooled ethanol (6), polymers (7), sugar-water systems (8,9), and biological materials (5, 10). Echo-detected EPR (ED EPR) of nitroxide spin probes in organic glasses revealed that the molecules undergo librational motion (orientational oscillations of a molecule) (6,11). This kind of motion appeared to be a general property of guest molecules in glass-forming liquids (6,12).…”