1: Free Radic Res.  2004 Jan;38(1):59-66.  

The use of multi-frequency EPR techniques to identify the radicals produced in
irradiated beta-blockers.

Engalytcheff A, Kolberg M, Barra AL, Andersson KK, Tilquin B.

Laboratory of Chemical and Physicochemical Analysis of Drugs (CHAM), UCL, Avenue
Mounier, 72.30, B. 1200 Bruxelles, Belgium. alix.engalytcheff@cham.ucl.ac.be

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.

PMID: 15061654 [PubMed - in process]