Chapter 22 Polypeptides

Abstract

Synthetic polypeptides are interdisciplinary macromolecules that are important for research work in both polymer and protein science. Most of the peptides, polypeptides, and proteins considered in this chapter consist of repeating sequences of peptide bonds with 20 different types of substitutents at the C α carbon. In the solution state, the nuclear magnetic resonance (NMR) chemical shift of these biomolecules, with possible rotation around the bonds, becomes the averaged value because of rapid rotation about the peptide bonds on the NMR timescale. However, in the solid state, the chemical shift is characteristic of specific conformations because internal rotation around the peptide bonds is fixed. This shows that the NMR chemical shift can be used for elucidating the conformation of polypeptides and proteins in the solid state. It has been experimentally and theoretically shown that the NMR chemical shift of polypeptides and proteins is a very important NMR parameter for determining the main-chain conformation. Moreover, the 13 C chemical shift contour maps are very useful for predicting the dihedral angles of polypeptides and proteins in the solid state through the 13 C shifts of the amide carbonyl carbons of the Gly, L-Ala, L-Leu, L-Val, and L-Asp residues.