Rates of rotational diffusion and Heisenberg spin exchange as obtained from CW ESR and ESR tomographic experiments on model systems and human skin

Abstract

The purpose of the present paper is to describe p ossibilities and limitations for the determination of the rates of rotational diffusion and Heisenberg spin exchange, obtained from eontinuous-wave electron spin resonance (cw ESR) and ESR tomographic experiments. Model systems including nitroxides as paramagnetic reporter molecules have been examined in order to verify data, which have been obtained from cw ESR and ESR tomography. This has been done with particular emphasis on checking the influence of concentration, temperature, and viscosity on the spectral-spatial properties. These findings have been applied to the evaluation of penetration and permeation studies on human skin, The extracted full spectral information from ESR tomography allows the determination of the above mentioned dynamic parameters for model systems of definite geometry and for samples of human skin. It has been found that the signal-to-noise ratio is critical for all discussed applications.

Structural Dynamics in a “Breathing” Metal–Organic Framework Studied by Electron Paramagnetic Resonance of Nitroxide Spin Probes

“…The agreement between theory and experiment at the sharp high-field features (Figure a, T = 200–293 K) is not so good due to the imperfection of the orienting potential used (see the Supporting Information, Figure S11), but otherwise, the agreement is very reasonable. While at T = 80 K the nitroxide is immobilized, its τ c value at room temperature approaches that typical of nitroxides freely rotating in viscous solutions . In the NP state, the situation is quite different, and EPR spectra at T = 80–293 K (Figure b) can be well simulated assuming an immobile nitroxide, whose A zz splitting slightly decreases with temperature (3.7 → 3.5 mT at 80 → 293 K).…”

“…While at T = 80 K the nitroxide is immobilized, its τ c value at room temperature approaches that typical of nitroxides freely rotating in viscous solutions. 18 In the NP state, the situation is quite different, and EPR spectra at T = 80−293 K (Figure 2b) can be well simulated assuming an immobile nitroxide, whose A zz splitting slightly decreases with temperature (3.7 → 3.5 mT at 80 → 293 K). Such a decrease can be explained by intensive librations (small angle tumbling) of nitroxide growing in amplitude at higher temperature, which partially average anisotropic interactions.…”

Spin Exchange in Solutions of TEMPOL in n-Octanol and 1-Methyl-3-octylimidazolium Hexafluorophosphate in the Temperature Range from 300 to 500 K

“…Values of the rotational correlation time τ R and the spin exchange ω ss can be obtained by spectra simulations using suitable algorithms . In previous studies, the microviscosity and micropolarity of ILs have been investigated by determining τ R of different nitroxide spin probes. − (The terms microviscosity and micropolarity have been used in order to differentiate from the macroscopic terms viscosity and polarity. In most cases, the term viscosity is associated with the dynamic viscosity, measured in mPa·s.…”

Electron paramagnetic resonance and mass spectrometry: Useful tools to detect ultraviolet light induced skin lesions on a molecular basis – A short review

“…After a certain incubation period, the radical concentration reaches a steady-state level. Figures 3 and 4 make clear the enrichment of some spin probes in the hydrophilic or lipophilic vicinity in model experiments and in skin biopsies, which corresponds to the Nernst distribution law [4,[28][29][30].…”