Temperature-induced conformational changes in amyloid beta(1-40) peptide investigated by simultaneous FT-IR microspectroscopy with thermal system

Temperature-dependent secondary structures of the amyloid beta(1-40) peptide in the solid state were studied by simultaneous Fourier transform infrared/differential scanning calorimetry (FT-IR/DSC) microspectroscopic system with the heating-cooling-reheating cycle. The result indicates that a thermal transition temperature at 45 degrees C was easily obtained from the three-dimensional plot of the transmission FT-IR spectra as a function of temperature. Furthermore, the thermal-dependent conformational transformations, due to denaturation and aggregation, of solid amyloid beta(1-40) were mainly evidenced by reducing the compositions from 37 to 20-24% for alpha-helical and random coil structures but increasing the components from 27 to 45% for intermolecular beta-sheet structures. Thermal-irreversible behavior and a poor thermal stability of solid amyloid beta(1-40) were also observed from the poor restoration of the secondary conformational changes in the heated sample.