Intermolecular nuclear shielding due to the aromatic amino acids of proteins and to porphyrins

Abstract

The chemical shifts of protons due to ring currents in neighbouring aromatic amino acids of proteins and in porphin are evaluated for several planes parallel to the conjugated rings of these compounds. The calculated values reproduce correctly the order of magnitude of the measured shifts as well as the variations of the effect with the structure of the compounds studied. Presented in the form of curves of isoshielding, the results should be helpful in the analysis of n.m.r. studies on the conformation of polypeptides and proteins.