Synthesis and solubility properties of peptide fragments of human hemoglobin α‐chain (123‐136)

The solubility prediction method for protected peptides was successfully applied to relatively small peptide fragments of human hemoglobin alpha-chain (123-136) which contained various polar amino acid residues such as Asp(OBzl), Glu(OBzl), Lys(Z), Ser(Bzl), and Thr(Bzl). As reported previously for hydrophobic peptides and human proinsulin C-peptide fragments, solubility data indicated that the insolubility of protected peptides having a mean value of Pc value below 0.90 appeared to begin at the octa- or nonapeptide sequence level and that beta-sheet structure played an important role in the insolubility of peptides. When a peptide has a beta-sheet structure in the solid state, we can clearly determine the critical chain length for peptide insolubility, the solubility dependence on solvent properties, and the solubility independence of amino acid compositions of peptides.