The utility of small nutation angle 1H pulses for NMR studies of methyl-containing side-chain dynamics in proteins

We describe the utility of small nutation angle (acute; <90°) ¹H radiofrequency pulses for efficient manipulation of magnetization in selectively [¹³CH₃]-labeled methyl groups of otherwise deuterated proteins. Focusing primarily on NMR applications that target either fast (pico-to-nanosecond) motions of the methyl group three-fold rotation axis, or slow (micro-to-millisecond) processes associated with chemical exchange, we show that significant simplification of the ¹³CH₃ spin-system and, as a consequence, of NMR pulse schemes, may be achieved in certain cases by the proper choice of the flip-angle of the ¹H acute-angle pulse. In other instances, appropriate adjustment of acute-angle ¹H pulses permits optimization of the sensitivity of NMR experiments. The results of acute-angle pulse based NMR experiments are validated by comparison with well-established NMR techniques for the characterization of fast dynamics of methyl-containing side-chains and chemical exchange processes.