Fig. 1.

(a) 2D IR spectrum of the human islet amyloid polypeptide fibril with a single ¹³C=¹⁸O isotope label at the L16 position with diagonal and off-diagonal doublet features highlighted. (b) Pulse sequence for measurement of 2D IR spectra. The mid-IR pulse shaper generates k₁ and k₂ and controls the delay between them. Pulses k₃ and k_LO refer to the probe pulse before and after the sample, respectively, while k_S is the signal.