Double Electron−Electron Resonance Measured Between Gd3+ Ions and Nitroxide Radicals

Double electron−electron resonance has attracted growing attention as a technique to study structure and conformational changes of biomacromolecules. Here, a new combination of paramagnetic labels is experimentally tested, one being a commonly used nitroxide radical, and the other being a Gd 3+ ion. The Gd 3+ −nitroxide spin pair can serve as a good substitute for the nitroxide−nitroxide pair of spin labels and potentially provides a link to other experimental approaches dealing with structural information.