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Updated: Aug 2, 2026

Rapid Scan Electron Paramagnetic Resonance Opens New Avenues for Imaging Physiologically Important Parameters In Vivo
Published on: September 26, 2016
Application of the out-of-phase absorption mode to separating overlapping EPR signals with different T1 values
1Max-Planck-Institut für biophysikalische Chemie, Abt. Spektroskopie, 37077 Göttingen, Germany.
Abstract:
The use of 90 degrees-out-of-phase first-harmonic absorption (V1'-) EPR to resolve the spectra from nitroxide spin labels with differing T1-relaxation times is described. Non-linear V1'-EPR spectra recorded under moderate saturation have sharper lines compared with the in-phase V1-EPR spectra, and amplitudes that preferentially enhance components with longer T1-relaxation. Discrimination between V1'-spectral components can be increased further by means of selective paramagnetic relaxation enhancement agents. Examples are given of biophysical applications to double labelling in single-component membranes and phase separation in two-component membranes, to lipid-peptide complexes, and to binding of spin-labelled reagents. It is concluded that optimal resolution in V1'-EPR spectroscopy is obtained at relatively low Zeeman modulation frequencies (20-30 kHz) and moderate saturation (H1 approximately 0.2-0.3 G).
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