Glycyl methylene chemical shift non-equivalence in small peptides. Diasteriomers of Leu-Gly-Phe

Abstract

Main possibilities for the origin of glycyl methylene chemical shift non-equivalence in Gly-containing small peptides are reviewed together with new data obtained at 300 and 360 MHz ¹H-nmr spectroscopy. An unexpected behaviour, both in glycyl methylene chemical shift non-equivalence as in the similarity of mean shift values of these protons in the diasteriomeric tripeptides Leu-Gly-Phe rules out the electric field gradient contributions being of major importance. Changes in conformational features, both of the back-bone as of the side chain rotation in function of pH are revealed, as follows from a study of coupling constants.