## 3 Results and Discussion  
### FT-IR and Deconvolution Study  
In our previous work, both the absorption bands and the H-bonds between the organic and inorganic phases have been revealed by FT-IR and Raman spectroscopies [24, 37, 38]. Moreover, it has also been demonstrated that Q underwent an oxidation phenomenon [38]. Indeed, the quercetin molecule is formed by a carbonyl group in position 4, a double bond between carbons 2 and 3, and five hydroxy groups in positions 3, 5, 7, 3\({}^{\prime}\) and 4\({}^{\prime}\). The hydroxyl groups on the quercetin molecule can be oxidized by nitric acid, resulting in the formation of quinones and decomposition products. This oxidation process leads to a visible color change due to the distinct electronic structures of the newly formed chemical species, which, in turn, can affect the absorption and reflection of light [39, 40]. Starting from those results, to better comprehend the influence of the oxidized Q (Qox) and P on the S matrix, the deconvolution of the main absorption band in the range of 1650-750 cm\({}^{-1}\) (see green rectangle in Figure 4) is reported. Deconvoluted spectra (Figure 5A-D) shed light on the main absorption band contributes of both the organic and inorganic components within the hybrids, thus result  
Figure 4: FT-IR spectra of S, Q, P, and hybrid systems. Figure 3: Calibration curve of quercetin extracted from the synthesized SQ20 hybrid system. ing in the hypothesis of an interaction between the SiO\({}_{2}\) matrix, polyethylene glycol, and quercetin. In particular, the main absorption bands in the deconvoluted spectrum of the silica (Figure 5A) were detected at 1378, 1179, 1058, 956, and 916 cm\({}^{-1}\). The signal at 1378 cm\({}^{-1}\) could be assigned to the vibration coming from residual ethanol not completely removed from the synthesized SiO\({}_{2}\) matrix [41], whereas the bands at 1179, 1058, 956, and 916 cm\({}^{-1}\) are typical of the silica matrix [42; 43; 44]. In Figure 5A, the Si-O-Si asymmetric stretching vibration (transverse optical mode), attributed to the most dominant band, was detected at 1058 cm\({}^{-1}\)[45; 46], whereas the high-frequency shoulder at 1179 cm\({}^{-1}\) is assigned to the skeletal Si-O-Si stretching vibration (longitudinal optical mode) [42]. Even if this band is not typically IR active, because of the matrix porosity, this mode does exist, resulting in this visible signal. The absorption bands at 956 and 916 cm\({}^{-1}\) are due to the Si-O stretching of the surface silanol groups and to the Si-OH bending vibration [47; 48], respectively. In the SP50 deconvoluted spectrum (Figure 5B), new absorption bands, centered at 1034, 1224, 1302, 1367, 1456, and 1500 cm\({}^{-1}\), are assigned to polyethylene glycol. Indeed, 1500, 1456, and 1367 cm\({}^{-1}\) are due to the C-H vibrations [49; 50; 51], while the new signal at 1034 cm\({}^{-1}\) may be derived from C-O stretching. The absorption band of C-O stretching is generally located at 1080-1060 cm\({}^{-1}\)[52], so the observed red shift may be associated with the formation of H-bonds between the PEG oxygens and the silanol groups of the matrix. Indeed, the main skeletal Si-O-Si vibrations (centered at 1179 and 1058 cm\({}^{-1}\), in the silica matrix alone) also shifted to higher wavenumbers (1193 and 1073 cm\({}^{-1}\), respectively). Furthermore, the silica peak at 1073 cm\({}^{-1}\) is superimposed on the C-O-H stretching signal [53], generally located at 1080 cm\({}^{-1}\), thus enforcing the hypothesis. The influence of the quercetin drug on the FT-IR spectrum of silica is shown in Figure 5C. The new signal at 1224 cm\({}^{-1}\) could be assigned to the C-O-C aryl ketone vibration of the quercetin [54; 55; 56]. According to [PERSON] [57], this absorption band is found at 1260 cm\({}^{-1}\). The shift at lower wavenumbers could be due to the chemical environment of the silica matrix.