For further understanding of conformational flexibility and presence of unfolded forms, investigation of the fluoride riboswitch structure in solution using, e.g., NMR or fluorescence methods is needed. Molecular dynamic simulations are complicated by the unusual cluster of Mg 2+ ions, but might lead to further insight. As a next step, extending the riboswitch from the sensing domain to the full-length expression platform will potentially allow forming the transcription terminator state in the absence of F -and observing the inherent conformational change by EPR methods, giving further insights into this intricate molecular mechanism of gene regulation. Finally, we have shown that the use of a fluorine bearing ligand allows to selectively the ligand bound form by F ENDOR in a complex mixture of bound and unbound molecules. In a more general context, similar strategies could be employed to study ligand binding of fluorinated pharmaceuticals to biological targets. F ENDOR complements PELDOR with more precise distances on a shorter length scale. Here, we first observed a F --nitroxide distance in the range of 2 nm, which completely closes the gap in the distance range accessible from pulse dipolar spectroscopies. Therefore, the combination of the two EPR-based methods, for distance measurements in frozen solution under similar sample conditions, provides valuable information on structure and conformational distributions, constituting a powerful tool for validation of structural models of complex biological systems.