We used a Bruker ALPHA system (Bruker, Bremen, Germany) to record FT-IR spectra of the mung bean flavonoids. Five samples were prepared, including vitexin monomer, isovitexin monomer, DES, vitexin-DES, and isovitexin-DES (prepared by dissolving a specific quantity of vitexin or isovitexin in DES, respectively). FT-IR measurements were carried out in a scan range of 400 to 4000 cm−1.
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