## 4 Conclusions  
The sol-gel method was employed in this study to synthesize hybrid materials incorporating silica (S), polyethylene glycol (P), and quercetin (Q). Different percentages of P and Q were incorporated into the silica matrix to investigate their influence on the properties of the materials. The synthesized materials were characterized using FT-IR analysis and solid-state NMR spectroscopy, and their in vitro release behavior was evaluated.  
Insights into the interactions between the organic and inorganic components within the hybrids were obtained through the deconvolution of the main absorption band, as observed in the FT-IR analysis. The spectra revealed the presence of characteristic absorption bands corresponding to S, P, and Q. The shifts in absorption bands and the appearance of new peaks indicated the influence of the polyethylene glycol and quercetin on the silica matrix. Moreover, the shifts in Si-O-Si skeletal vibrations and the appearance of C-O-C aryl ketone vibrations suggested the interaction between the organic phases and the silica matrix. These results support the hypothesis of interactions between all the components inside the hybrid materials.  
Furthermore, solid-state NMR analysis confirmed the presence of P and Q in the hybrid systems. Indeed, the NMR spectra showed distinct peaks corresponding to the chemical shifts of P and Q, indicating their successful incorporation into the silica matrix. The condensation degree of silica in the composites was also assessed, providing valuable information about the structure of the materials.  
The in vitro release study highlights how the presence or absence of P (polyethylene glycol) has notable influences on the properties, specifically on the release behavior, of quercetin. In particular, the presence of P plays a vital role in restricting the movement of quercetin, leading to a slower release profile. Due to its configuration, P physically entraps Q inside the S matrix and interacts with quercetin by H-bonds, thus reducing its mobility and impeding diffusion out of the SP matrix.  
Thus, the results indicate that the SPQ-synthesized materials exhibited controlled release properties, suggesting their potential application in drug-delivery systems.  
Conceptualization, M.C. and P.M.; methodology, V.P., V.V. and A.D.; validation, V.P., V.V. and A.D.; formal analysis, A.D. and M.M.D.; investigation, V.P., V.V. and A.D.; resources, M.C. and P.M.; data curation, V.P., V.V. and A.D.; writing--original draft preparation, M.C., P.M. and A.D.; writing--review and editing, M.C.; P.M. and M.M.D.; visualization, V.P., V.V. and A.D.; supervision, M.C. and P.M.; project administration, M.C. and P.M. All authors have read and agreed to the published version of the manuscript.  
Figure 12: Possible mechanisms of release of high and low percentage of quercetin, with and without P. (A) SQ5 system; (B) SPxQ5 system; (C) SQ15 and (D) SPxQ15 systems.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.  
**Acknowledgments:** This work was supported in part by \"SCAVENGE\", financed by Universita degli Studi della Campania Luigi Vanvitelli in the framework of \"Piano Strategico di Ateneo 2021-2023--Azione strategica R1.S2\".  
**Conflicts of Interest:** The authors declare no conflict of interest.