Straightforward, effective calibration of SPINAL-64 decoupling results in the enhancement of sensitivity and resolution of biomolecular solid-state NMR

We describe a simple yet highly effective optimization strategy for SPINAL-64 ¹H decoupling conditions for magic-angle spinning solid-state NMR. With adjustment of the phase angles in a coupled manner, the optimal conditions resulting from three parameter optimizations can be determined with adjustment of a single phase. Notably, echo T₂ relaxation times for ¹³C and ¹⁵N show significant enhancement (up to 64%), relative to the previous described SPINAL-64 conditions, under the moderate ¹H decoupling levels (60-100 kHz) and MAS rate (13.3 kHz) commonly employed for high-resolution SSNMR spectroscopy of proteins. Additionally, we also investigated the effect at higher spinning rate (33.3 kHz) and compared the results with other ¹H decoupling schemes (TPPM, XiX), as well as SPINAL-64 with the originally reported optimal values.