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Abstract

Spectroscopic and biophysical methods for structural determination at atomic resolution are fundamental in studies of biological function. Here we introduce an approach to measure molecular distances in bio-macromolecules using 19 F nuclear spins and nitroxide radicals in combination with high-frequency (94 GHz/ 3.4 Tesla) electron-nuclear double resonance (ENDOR). The small size and large gyromagnetic ratio of the 19 F label enables to access distances up to about 1.5 nm with accuracy 0.1 - 1 Å. The experiment is not limited by the size of the bio-macromolecule. Performance is illustrated on synthesized, fluorinated model compounds as well as spin-labelled RNA duplexes. The results demonstrate that our simple but strategic spin labelling procedure combined with state-of-the-art spectroscopy accesses a distance range crucial to elucidate active sites of nucleic acids or proteins in solution state.