Secondary structure of three amyloid b-peptides [Aβ(1-28), Aβ(1-40) and Aβ(1-42)] in the solid state was respectively determined by Fourier transform infrared (FT-IR) microspectroscopy. Their thermal-dependent structural transformation were also investigated by FT-IR microspectroscopy equipped with a thermal analyzer. The present result demonstrates that the solid-state Aβ(1-28), Aβ(1-40) and Aβ(1-42) peptides showed a significant IR spectral difference in the amide I and II bands. The secondary conformation of Aβ(1-28) peptide was the combination of major β-sheet and minor α-helix with little random coil structures, but Aβ(1-40) peptide showed the co-existence of major β-sheet and minor random coil with little α-helix structures. Aβ(1-42) peptide mainly consisted of the predominant β-sheet structure. Although the intact Aβ(1-28), Aβ(1-40) or Aβ(1-42) peptide exhibits a different secondary structure, a similar β-conformation may form after thermal treatment. A thermal-dependent transition was found for solid Aβ(1-28) and Aβ(1-40) peptides near 40° C and 45° C, respectively. There was no transition temperature for solid Aβ(1-42) peptide, however, due to only a very little level of α-helix and random coil structure containing in the solid Aβ(1-42) peptide. The thermal denaturation plays an important role in the structural transformation from α-helix/random coil to β-sheet.

Key words: amyloid β-peptide [Aβ(1-28), Aβ(1-40) and Aβ(1-42)], secondary structure, FT-IR, heating, conformational transformation.