Chemistry and Structure
via Solid-State NMR
The versatility of NMR derives from the dual modulation of local magnetic fields by induced electron currents and nearby nuclear spins. The induced electron currents are the source of chemical shifts, the degree of which reflect local electron distributions. The nearby nuclear spins provide dipolar interactions, the strengths of which reflect the internuclear distances. Between the two, NMR provides both chemical and spatial information. This chapter illustrates both of these modes of applying NMR. The use of the chemical information in chemical shifts is illustrated by studies of the vectoriality mechanism of the light-driven ion pump, bacteriorhodopsin. These studies have followed the migration of the absorbed energy to bond torsion in the active site and the irreversible release of this torsion on ion transfer. The use of the spatial information in dipolar interactions is illustrated by studies of the structures of gas vesicles, the floatation organelles of aquatic microorganisms. These studies have shown that the vesicles are functional amyloids and that deep water organisms add strength to their vesicles by folding half of the constituent monomers in a different way, presumably of higher energy, than the other half.