Chelidonic acid

The sample of Chelidonic acid (Sigma-Aldrich, part of Merck; assay, 98.0%; mp 265 °C) was used as received. The IR absorption spectrum of the sample was measured at room temperature using standard KBr pellet technique. The spectrum was measured at 2 cm⁻¹ resolution with 100 scans in the range 4000–400 cm⁻¹ on a Thermo-Fisher Nicolet 6700 FT-IR spectrometer equipped with a KBr beam splitter, a ETC EverGlo mid-IR radiation source, and a deuterated L-alanine doped triglycine sulfate (DLaTGS) detector. The Raman spectrum was measured from 3500 – 100 cm^-1 at a spectral resolution of 2 cm⁻¹ with a Thermo-Fisher NXR 6700 FT-Raman module spectrometer, equipped with a diode-pumped air cooled Nd:YVO₄ laser source (1064 nm excitation line) and a LN₂ cooled high-performance Ge detector. The spectra were averaged over 500 scans. Both the spectrometers were purged with nitrogen to remove the interference due to the atmospheric CO₂ and moisture. The solid-phase near-IR (NIR) spectrum of Chelidonic acid was measured in the 4000–8000 cm⁻¹ region and for the sake of brevity, the analysis has been presented in the section S10 (see also Fig. S10a).