Spin labeling is a technique used in molecular biology and biochemistry to study the dynamics and interactions of proteins and other biomolecules. It involves attaching a stable free radical, known as a spin label, to a specific site on a molecule. This label can be detected using electron paramagnetic resonance (EPR) spectroscopy, allowing researchers to gather information about the molecule's structure and behavior in different environments. The spin label provides unique insights into the local environment of the attached site, revealing details about molecular motion and interactions. By analyzing the EPR spectra, scientists can infer information about the flexibility, conformational changes, and proximity of other molecules, contributing to our understanding of complex biological processes involving proteins and lipids.