Investigation of slow molecular dynamics using R-CODEX.

A solid state NMR experiment is introduced for probing motions on the millisecond time scale, based on dephasing and refocusing (1)H-(13)C or (1)H-(15)N dipolar couplings. The method is related to the previously described Centerband-Only Detection of Exchange or CODEX experiment. The use of an R-type dipolar recoupling sequence takes advantage of the strong (1)H-(13)C or (1)H-(15)N dipolar coupling, while suppressing the effect of (1)H-(1)H homonuclear coupling. This approach paves the way to detect both the correlation time and reorientational angle of the dynamics in fully protonated samples. The performance of this pulse sequence is demonstrated using imidazole methyl sulfonate.