The Use of Multi-frequency EPR Techniques to Identify the Radicals Produced in Irradiated β-Blockers

Abstract

The identification of radicals trapped in irradiated drugs can be very intricate. A multi-frequency electron paramagnetic resonance (EPR) study is proposed to resolve this problem. The Q-band (ca. 34 GHz) comparison with X-band (ca. 9 GHz) did not show significant differences for the four beta-blockers studied (atenolol, esmolol, nadolol and propranolol). The use of a higher frequency (285 GHz) was required. It enabled us to determine the g-tensor values of the radicals present in atenolol and esmolol, respectively, g1 = 2.0086, g2 = 2.0059 and g3 = 2.0021 and g1 = 2.0066, g2 = 2.0044 and g3 = 2.0021. The latter was assigned as a phenoxyl radical, which can not be the case for the former. Therefore, radicals produced in esmolol may result from a more complex mechanism than the abstraction followed by the diffusion of an H atom inside the solid. In addition, two molecules as similar as atenolol and esmolol hydrochloride do not contain the same radicals after irradiation. These two conclusions drawn from the EPR results on beta-blockers show clearly the importance of continuing the investigations on radiolytic mechanisms in solid-state drugs.

Free radicals and their electron spin relaxation in cellobiose. X-band and W-band ESR and electron spin echo studies

“…We also took into account results from previous extensive ESR studies of cellobiose, cellulose, and other disaccharides (Kawano and Logarezzi 1995;Kuzuya and Yamauchi 1998;Ershov 1998;Wach et al 2004;Mohanty and Singh 1988;Wach et al 2003;Hon 1975;Ershov and Isakova 1984;Yamauchi et al 1999;Kuzina et al 2004;Engalytcheff et al 2004;Kuzuya et al 1999;Ershov et al 1977). The X-band ESR spectra were typical of radicals in saccharides with a relatively low total radical concentration (approx.…”

“…To obtain more convincing results it is necessary to record ESR spectra at higher frequency where spectral components differing in g-factor become resolved and anisotropic spectra can be well separated. Such measurements have not been performed on cellobiose but have been performed with the D-band (130 GHz) on irradiated wood and lignin (Kuzina et al 2004) and on irradiated drugs using both the Q-band (34 GHz) and the 285-GHz band (Engalytcheff et al 2004).…”

Sample Holders for Sub-THz Electron Spin Resonance Spectroscopy

“…The advances in m.w. technologies have been driving the development of new methodologies in ESR [33], resulting in the commercially available ESR spectrometers operating at J-band frequencies (263 GHz, 9.395 T for g = 2) (Bruker, USA) and custom made spectrometers working in a broad range of frequencies up to the THz range [34], [35]. These ESR spectrometers work either in a pulsed or in a continuous wave (cw) regime.…”

Determination of the g Tensors for the Dominant Stable Radicals in X-Irradiated β-d-Fructose Single Crystals

“…In order to enhance g tensor resolution, we performed the experiments at the microwave Q-band (34 GHz). Knowledge of the radical g tensors is also necessary if one aims at reproducing powder spectra, , e.g. in order to determine the contributions of various radicals for dose assessment.…”

“…Knowledge of the radical g tensors is also necessary if one aims at reproducing powder spectra 19,20 , e.g. in order to determine the contributions of various radicals for dose assessment.…”