[super 15]N solid-state NMR provides a sensitive probe of oxidized flavin reactive sites

The [super 15]N solid-state nuclear magnetic resonance (SS-NMR) is proposed as a tool for directly observing reactive positions of the flavin ring and thereby obtaining information on their frontier orbitals. The [super 15]N chemical shift principal values are valuable tools for understanding electronic differences that underlie variations in flavin reactivity, as well as the reactivities of other heterocyclic cofactors.