Enhanced spectral resolution in immobilized peptides and proteins by combining chemical shift sum and difference spectroscopy

A two-dimensional correlation experiment is introduced that records the sum and difference chemical shift of two scalar or dipolar coupled nuclei. Statistical results indicate that the suggested pulse scheme can significantly increase the possibility of separating chemical shift contributions due to residue type and backbone conformation in immobilized peptides and proteins. Experimental applications demonstrate the theoretical concept and lead to the predicted resolution enhancement between different amino acid types and among protein residues of different secondary structure.