Infrared Absorption Study of Peptide Fragments of Human Hemoglobin α-Chain (123–136) in the Solid State

Abstract

Abstract In order to evaluate the influence of polar amino acid residues on peptide conformations, IR absorption spectroscopic analysis of peptide fragments of human hemoglobin α-chain (123–136) and Boc–Leun–OBzl (n=3–6,9, and 12) was performed in the solid state. The polar amino acid residues involved in the peptide fragments are in the following: Asp(OBzl), Lys(Z), Ser(Bzl), and Thr(Bzl). Regardless of the amino acid composition, all of the peptides equal to or larger than a pentapeptide level exhibited a high potential for the formation of a β-sheet structure in the solid state. Conformational behaviors of peptides having polar amino acid residues are similar to those of Boc–Leun–OBzl, indicating that polar side chains can not cause disturbance of the formation of β-sheet structures. The fine relationship among the conformation, solubility, and 〈Pc〉 value of the peptide fragments strongly supports the propriety of the solubility prediction method for peptide intermediates. The influence of shear stress on peptide conformations in the solid state was also investigated precisely, and it was suggested that a heptapeptide size had the potential for the development of a helical structure in the solid state.