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. 2023 Jul 8;9(7):e18119. doi: 10.1016/j.heliyon.2023.e18119

Fig. 1.

Fig. 1

FTIR spectral analysis of the six lipid A analogues. The spectra from 3000 to 2500 cm−1 for biological and synthetic BECC438 (A), biological and synthetic BECC470 (B), MPL (C), and PHAD (C) at 25 °C are shown. In order to show the peak positions of the symmetric stretching vibration of the methylene groups sv (CH2) around 2850 cm−1more clearly, the spectra from 2910 to 2790 cm−1 for biological and synthetic BECC438 (D), biological and synthetic BECC470 (E), MPL (F), and PHAD (F) at 25 °C are also plotted. The peak positions of the symmetric stretching vibration of the methylene groups sv (CH2) were then monitored as a function of temperature from at 25 °C–90 °C for both forms of BECC438 (G), both forms of BECC470 (H), and MPL and PHAD (I).