Spectroscopy of Electron Paramagnetic Resonance (EPR) is widely used in the studies of physico-chemical and biological phenomena. EPR enables investigation of various bioenergetic processes, which involve energy or electron transfer, radiation damage to biological objects, and obtaining certain structural information. The entire area of EPR applicability cannot be described even roughly, because EPR is one of the universal spectroscopic techniques.

A necessary condition for a molecule to be EPR-detectable is that it should possess a magnetic moment, which comprises its spin and orbital moments. It means that such (paramagnetic) molecules should contain one or more unpaired electrons. If such molecules are subjected to a constant magnetic field, additional (magnetic) energy sublevels appear. Application of a second, electromagnetic field may result in transitions between the sublevels, somewhat similar to the transitions in optical spectroscopy. EPR technique makes use of the detection of power absorption accompanying such transitions. Recording the absorption changes with magnetic field sweep provides an EPR spectrum, characteristic of the molecules studied, their dynamics and interactions.

The proposed laboratory work includes sample preparation and measurement of EPR signals from solutions containing so-called spin-probes (in our case, of stearic acid molecules with an attached paramagnetic fragment). Spin-probes are widely used in a multitude of studies in molecular biology, and in particular for determination of local viscosity, as their EPR spectral shape depends on the environment viscosity. In this work measurements of spin-probes in solutions of different viscosity will be performed, followed by a simple calculation. Spectra will be recorded using a modern EPR spectrometer Bruker EMX-6.