The lyophilized samples were mixed with KBr at a ratio of 1:100 (w/w), ground and pressed. FTIR spectroscopy (Bruker, Billerica, MA, USA) of the samples was conducted in accordance with Zhang et al. [16 (link)]. The FT-IR scan range was 400–4000 cm−1 with a resolution of 4 cm−1. The scan was performed 32 times with KBr as the background.
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