Accurate Determination of 1H‐15N Dipolar Couplings using inaccurate settings of the Magic Angle in Solid State NMR

Magic Angle Spinning is an essential ingredient in a wide variety of solid‐state NMR experiments. The standard procedures to adjust the rotor angle are not highly accurate resulting in a slight mis‐adjustment of the rotor from the magic angle (𝜃𝑅𝐿= Arctan(√2)) on the order of a few millidegrees. This small missetting has no significant impact on the overall spectral resolution, but is sufficient to reintroduce anisotropic interactions. We show here that site specific 1H‐15N dipolar couplings can be accurately measured in a heavily deuterated protein. This method can be applied at arbitrarily high MAS frequencies, since neither rotor synchronization nor particularly high radiofrequency field strengths are required. The off‐magic angle spinning (off‐MAS) method allows to quantify order parameters for very dynamic residues, which often escape an analysis using existing methods.

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