Diluting Abundant Spins by Isotope Edited Radio Frequency Field Assisted Diffusion

A new solid-state NMR method is described for obtaining long-range distance constraints in nanocrystalline samples of 13C-, 15N-, and 2H-enriched protein. The method selects only those 13C or 15N nuclei close to 1Hs for dipolar recoupling. When used with extensive deuteration, the bath of abundant 13C spins is made to appear dilute. Contacts over 4.5 A are readily observed in human ubiquitin.