Optimization of 15N–13C double-resonance NMR experiments under low temperature magic angle spinning dynamic nuclear polarization conditions

Dynamic nuclear polarization (DNP) enhanced magic angle spinning (MAS) solid-state NMR carried out at 25 K enables rapid acquisition of multi-dimensional ¹³C–¹⁵N correlation spectra for protein structure studies and resonance assignment. Under commonly used DNP conditions, solvent deuteration reduces ¹H–¹⁵N cross polarization (CP) efficiencies, necessitates more careful optimization, and requires longer high-power ¹⁵N radio-frequency pulses. The sensitivity of 2D heteronuclear correlation experiments is potentially impaired. Here we show that 2D ¹⁵N-¹³C experiments based on ¹³C-¹⁵N transferred echo double resonance (TEDOR) methods outperform 2D experiments based on CP transfers in a fully deuterated solvent, and are competitive with CP-based experiments when the solvent is only partially deuterated. Additionally, we show that optimization of TEDOR-based 2D experiments is simpler than optimization of CP-based experiments under 25 K MAS conditions.