Application of 2D IR to Study h-IAPP Aggregation and Perovskite Films

Abstract

Since two-dimensional infrared (2D IR) spectroscopy was introduced in 1998, 2D IR has rapidly developed and is being applied to various fields. A variety of experimental methods are used nowadays. The pump−probe (PP) and the heterodyned photon echo (HPE) methods are the most widely used among them. In terms of experimental difficulty, HPE has an advantage over PP. However, PP has a relatively lower signal-to-noise ratio than HPE. When both techniques are applied to samples producing strong scatterings, such as metal−organic frameworks (MOFs), protein aggregates, and perovskite films, the spectra are severely contaminated by the scattered light. In the PP method, this problem can be circumvented by phase cycling. However, in the HPE method, phase cycling does not function as effectively as in the PP method. This presentation demonstrates that the scattering problem in the HPE approach can be solved mechanically by introducing choppers or shutters without moving any translation stages.[1] This scatter-removing technique was applied to investigate a perovskite film with a very rough surface and hIAPP protein aggregation. The perovskite film was found to contain a tiny amount of dimethylformamide and H2O. Temperature-dependent study on hIAPP shows that the proteins are denatured at 4 ºC from β-sheets to random coils and β-turns.