Spin labeling refers to a chemical technique that integrates molecules containing unpaired electrons into another research framework. For the study of biomacromolecule structure, kinetics and conformational changes, this technique provides a relatively non-invasive technique. The combination of site-directed spin labeling (SDSL) and electron paramagnetic resonance spectroscopy (EPR) is a mature method and has been widely used in recent years. There are many applications in protein and peptide science.
In general, a paramagnetic substance can be used as a paramagnetic detection probe as long as it can be attached to a biological macromolecule such as a protein. Diamagnetic molecules can be studied by attaching a molecule containing an unpaired electron, which known as spin labelling. In the EPR study of peptide, the preferred paramagnetic probe is referred to as a peptide spin label. The peptide spin labels commonly found in biomacromolecules can be broadly classified into two types: metals having paramagnetism and organic radicals containing unpaired electrons.