2D N-15-N-15 isotropic chemical shift correlation established by H-1-H-1 dipolar coherence transfer in biological solids

A 2D N-15-N-15 chemical shift correlation method is proposed to assign reso nances in non-selectively or uniformly N-15 labeled biological solids. A re verse cross-polarization sequence is used to transfer N-15 magnetization to the directly bonded amide-protons through the H-1-N-15 dipolar coupling an d a longitudinal proton magnetization transfer via H-1-H-1 dipolar coupling s is used to mix amide-H-1 resonances. It is shown that this procedure allo ws the observation of cross-peaks between N-15 chemical shift resonances of adjacent amino acid residues with a proton mixing time as short as 10 mus in a polycrystalline sample of N-acetyl-L-N-15-valyl-L-N-15-leucine. (C) 20 01 Published by Elsevier Science B.V.