Long-range 1H-19F distance measurement in peptides by solid-state NMR.

A new NMR technique for determining long-range 1H-19F distances in solids is demonstrated. Using a modified rotational-echo double resonance (REDOR) sequence involving 1H homonuclear decoupling and composite 19F pulses, we show that it is possible to determine 1H-19F distances to approximately 8 A. The detrimental effect of the large 19F chemical shift to REDOR dephasing is partially compensated for by the composite pulse, 90 degrees 225 degrees 315 degrees . The 1HNLeu-19FPhe distance in the peptide f-MLF-OH was found to be 7.7 A. This was used to refine the Phe side chain conformation. The 1H-19F REDOR technique should be useful for restraining the three-dimensional structure of proteins.