Infrared Absorption Study of Human Hemoglobin α-Chain (123–136) Fragments in Dichloromethane

In connection with the relationship between the conformation and solubility of peptide intermediates having polar side chains, IR spectroscopic conformational analysis of peptide fragments of human hemoglobin α-chain (123–136) was performed in dichloromethane. In dichloromethane, the conformational behavior of the peptide fragments was, in essence, dependent on their amino acid sequences, and Boc–Ser(Bzl)–Thr(Bzl)–Val–Leu–OPac through Boc–Ala–Ser(Bzl)–Val–Ser(Bzl)–Thr(Bzl)–Val–Leu–OPac had predominantly unordered structures including some intramolecular hydrogen bonds, while Boc–Ala–Ser(Bzl)–Leu–Asp(OBzl)–Lys(Z)–Phe–Leu–OPac had successive intramolecular hydrogen bonds, probably corresponding to an α-helical structure. On the other hand, in carbon tetrachloride, the conformation of Boc–Val–Ser(Bzl)–Thr(Bzl)–Val–Leu–OPac and Boc–Ser(Bzl)–Val–Ser(Bzl)–Thr(Bzl)–Val–Leu–OPac had a typical β-sheet structure. These results are discussed on the basis of the amino acid sequences of the peptide fragments.