Paramagnetic Systems in Biochemistry: Solid-State NMR Studies

Paramagnetic phenomena arise due to the presence of one or more unpaired electrons in a system. In this article, we shall be concerned with the effects of unpaired electrons upon nuclear spins in biological systems and the resultant effects upon the NMR spectra in the solid state. In particular, the effects of paramagnetic ions upon proteins studied using magic angle spinning (MAS) NMR will be considered, highlighting both the difficulty and utility of their presence. Paramagnetism can be a rich source of long-range information, which may be applied to structural and dynamical characterization of biomolecules and of their intermolecular interactions. The enhancement of longitudinal relaxation rates by paramagnetic relaxation enhancement can also be exploited to reduce interscan delays and thus improve overall sensitivity.