Impact of Magnetic Field Strength on Resolution and Sensitivity of Proton Resonances in Biological Solids

Sensitivity and resolution together determine the quality of NMR spectra in biological solids. Higher magic angle spinning frequencies yield a more efficient suppression of the coupling network and enable atomic-level investigations of protonated protein samples. On the other hand, truncation effects induced by higher magnetic fields have an impact on the achievable sensitivity and resolution. In this work, we address the question of how the proton dipolar coupling network affects the magnetic field strength-dependent gains in sensitivity and resolution. We find that - beyond the canonical B03/2 dependence - an additional factor of 2 in sensitivity can be achieved for residues embedded in the core of the protein, when the static magnetic field induces a transition from the strong- to the weak-coupling limit. The experiments are carried out using a selectively methyl-protonated (13CH3) α-spectrin SH3 sample, at magnetic field strengths of 11.75 T (1H Larmor frequency of 500 MHz) and 23.5 T (1H Larmor frequency of 1 GHz).