13 - Probing local molecular properties of self-assembled systems with electron paramagnetic resonance (EPR)

Abstract

One of the most powerful and promising tools for probing self-assembled systems is electron parametric resonance (EPR) spectroscopy. Although EPR is still relatively uncommon for soft-matter characterization, this technique has gained prominence during the recent years due to its ability to provide site-specific information about organic compounds through the use of site-directed spin labeling (SDSL) with stable nitroxide radicals. By measuring the absorbance of microwave radiation by a radical electron spin label in a magnetic field, EPR experiments can provide crucial information about dynamics and solvent conditions in the vicinity of the radical electron probe. Further, EPR spectroscopy is sensitive to incredibly low numbers of radical electrons enabling measurements to be made with minimally invasive probes. For these reasons, EPR provides unique information about self-assembled structures including phase transitions and conformational dynamics at specific sites. Here, we provide an overview of the use of EPR spectroscopy to probe local properties of self-assembled systems. While both pulsed EPR and multifrequency EPR can provide additional information, we will focus primarily on continuous-wave (CW) experiments performed at X band, that is, at the frequency of ~10GHz.