Perchlorinated Triarylmethyl Radical 99% Enriched 13C at the Central Carbon as EPR Spin Probe Highly Sensitive to Molecular Tumbling

<p>Soluble stable radicals are used as spin probes and spin labels for <i>in vitro</i> and <i>in vivo</i> Electron Paramagnetic Resonance (EPR) spectroscopy and imaging applications. We report the synthesis and characterization of a perchlorinated triarylmethyl radical enriched 99% at the central carbon, <b>¹³C₁-PTMTC</b>. The anisotropy of the hyperfine splitting with the ¹³C₁ (A_x=26, A_y=25, A_z=199.5 MHz) and the g (g_x=2.0015, g_y=2.0015, g_z=2.0040) are responsible for a strong effect of the radical tumbling rate on the EPR spectrum. The rotational correlation time can be determine by spectral simulation or via the linewidth after calibration. As spin probe <b>¹³C₁-PTMTC </b>can be used to measure media microviscosity with high sensitivity. Bound to a macromolecule as spin label, <b>¹³C₁-PTMTC </b>could be used to study local mobility and molecular interactions.</p>