2.1.1. FTIR

The FTIR spectra of THEOS–chitosan and MeTHEOS–chitosan films present similar characteristics in terms of their band frequencies for –OH (3500–3200 cm<sup>−</sup>1), –CH, –CH2, and –CH3 (3000–2840 and 1460–1350 cm<sup>−</sup>1), amide N–C=O (1655 cm<sup>−</sup><sup>1</sup> and 1580 cm<sup>−</sup>1), amine –NH2 (1320 cm<sup>−</sup>1), and the Si–O–Si network (1110–1000 cm<sup>−</sup>1). The main difference is due the presence of the bands at 1270 and 770 cm<sup>−</sup><sup>1</sup> (Si–CH3 and –C–Si–O, respectively) in the MeTHEOS–chitosan film (Figure S1).
