FTIR spectra collected during the disintegration of prefibrillar aggregates in solutions of BPI (20 mg mL−1, pH 1) after a temperature quench from 60°C to 25°C. Data are shown for spectra collected at times of 5 (○), 60 (□), 150 (▵), 500 (•), and 2100 min (▪) after the quench. The solid line is a spectrum taken from freshly dissolved insulin at 25°C.