Carbon-centered radicals as oxygen sensors for in vivo electron paramagnetic resonance: screening for an optimal probe among commercially available charcoals.
Jordan BF, Baudelet C, Gallez B
Laboratory of Medicinal Chemistry and Radiopharmacy, Catholic University of Louvain, Brussels, Belgium.
It is known that some charcoals possess paramagnetic centers with an
electron paramagnetic resonance (EPR) linewidth which can be broadened
by oxygen. In order to identify potential candidates as sensors for in
vivo EPR oximetry, we carried out a systematic study among commercially
available charcoals. A total of 34 charcoals were tested. The steps used
for the screening were: (1) to check the presence of paramagnetic centers
in the material; (2) to measure the EPR linewidth in nitrogen and in air
on the dry material and on a aqueous suspension of particles; (3) to calibrate
the oxygen sensitive materials (EPR linewidth vs. pO2); (4) to test the
sensitivity and stability of the response to changes of pO2 in a simple
model of hypoxia induced in mice. seventeen charcoals contained paramagnetic
centers detectable by low-frequency EPR (1.1 GHz). The EPR spectrum consist
of one single line which is typical of carbon-centered radicals (g-factor
approximately 2). Eight charcoals presented sufficient interesting EPR
properties (linewidth in nitrogen < 0.1 mT, linewidth in air for an
aqueous suspension of particles > 0.15 mT) to be further characterized
in vivo. Only three charcoals presented a stable, reproducible, and sensitive
response to pO2 for more than 2 months. These three coals should be considered
as good candidates to be used as oxygen sensor using in vivo EPR spectroscopy.
PMID: 9951772, UI: 99135243