Amino Acids and Peptides

This chapter presents an overview of the dielectric properties of amino acids and oligopeptides in aqueous solutions. Two relaxation processes identified in the aqueous solutions of amino acids are ascribed to the molecular motion of the solute and water molecules. The relaxation characteristics (i.e., the dielectric strength and relaxation time) of the process related to amino acids strongly depend on the chemical nature (polar/charged/aromatic) and size of the side groups. The dielectric properties of water are changed by the presence of solute molecules. The relaxation process for water in amino acid solutions becomes wider in comparison with pure water and is well described by the phenomenological Cole–Cole spectral function. A discussion is also presented regarding the effect of molecular mass/length of chain and composition of the polypeptide, the pH of the solution and concentration on the dielectric properties of oligopeptides and polypeptide solutions. Finally, the mechanism of triple-helix-to-single-coil transition in model collagen polypeptides is discussed.