Figure 4.

2D-IR spectra of VEALYL after the pH of the solution has been lowered from 7 to 2.5. The increasing signal strength at ∼1622 and 1682 cm⁻¹ indicates that amyloid β-sheets are formed, and the decreasing inverted slope of the modes with time indicates that the heterogeneity is decreasing. The spectrum labeled “44 h^∗” is measured at a spot in the IR sample cell ∼500 μm away from the four preceding spectra (all of a 11.75 mM VEALYL sample). The mature fibril is measured of a 26.5 mM solution that was incubated for 5 days. We did not observe a strong dependency of the spectral line shape once the concentration threshold for aggregation was exceeded. To see this figure in color, go online.