## 3 Results and Discussion
### NMR Study  
Figure 6A shows the \({}^{1}\)H-\({}^{13}\)C CP-MAS NMR spectrum of P used in this work, showing three peaks at 8 72.8, 8 70.5, and 8 61.2, attributable to HOCH\({}_{2}\)CH\({}_{2}\), to the backbone ether carbons, and to HOCH\({}_{2}\)CH\({}_{2}\), respectively. The FWMH of the peaks is ca. 49 Hz, and their integrals are 2:13.4:2, consistent with the mean molecular weight of 400 da. The \({}^{1}\)H-\({}^{13}\)C CP-MAS NMR spectra of the hybrid systems composed of S, P, and Q show, together with peaks attributable to P, signals at ca. 8 165, 8 58.3, and 8 14.5, attributable to the aerobic oxidation products of quercetin, Qox, whose antioxidant properties have been recently explored by [PERSON] et al. [40; 58]. The \({}^{1}\)H-\({}^{13}\)C CP-MAS NMR spectrum of pure (not oxidized) quercetin is reported in Figure 6B, for comparison.  
As a representative example, Figure 7 shows the \({}^{1}\)H-\({}^{13}\)C CP-MAS NMR spectrum of SP50Q20, while Figure 8 shows the comparison between the \({}^{1}\)H-\({}^{13}\)C CP-MAS NMR spectrum of pure polyethylene glycol with those of the hybrid systems.  
Figure 6: (**A**) \({}^{1}\)H-\({}^{13}\)C CP-MAS NMR spectrum of P; (**B**) \({}^{1}\)H-\({}^{13}\)C CP-MAS NMR spectrum of Q.  
It is apparent that SP50Q20 exhibits \({}^{13}\)C NMR peaks that are slightly high-field-shifted (\(\delta\) 71.8, \(\delta\) 69.9 and \(\delta\) 61.1) and that the peak due to the backbone carbons shows a larger FWMH (ca. 172 Hz), with respect to pure P. Such features can be attributed to weak interactions between P and SiO\({}_{2}\) and/or Qox. The \({}^{1}\)H-\({}^{13}\)C CP-MAS NMR spectrum of the composite made up of SiO\({}_{2}\) and polyethylene glycol confirms the S and P interactions since a similar peak shift, as observed in SP50Q20, is recorded. However, a weak interaction of Qox cannot be excluded given that the broadness of the \({}^{13}\)C NMR peaks in the SP50Q20 sample is larger than that of the SP50 composite (ca. 110 Hz). In order to gain insights into the effect of Qox charge onto the broadness of the P \({}^{13}\)C NMR peaks, we prepared hybrid systems containing 5% (SP50Q5), 10% (SP50Q10), and 15% (SP50Q15) of quercetin and recorded their \({}^{1}\)H-\({}^{13}\)C CP-MAS NMR spectra (Figure 9a-d), from which it appears that a higher amount of quercetin results in a larger FWMH.  
Figure 8: \({}^{1}\)H-\({}^{13}\)C CP-MAS NMR spectra of pure P (**a**); SP50 hybrid system (**b**); SP50Q20 hybrid system (**c**).  
Figure 7: \({}^{1}\)H-\({}^{13}\)C CP-MAS NMR spectrum of SP50Q20.  
Figure 10 shows the \({}^{1}\)H-\({}^{29}\)Si CP-MAS NMR spectra of S, SP50, and SP50Q20. In this case, all spectra are nearly superimposable, indicating that silicon atoms are not involved in strong interactions with PEG or quercetin. The peaks present in the spectra are at 5-87.5, 8-96.9, and 8-105.7 and are attributable to silicon atoms conventionally denoted as Q\({}_{2}\) [\(Si\)(OSi)\({}_{2}\)(OH)\({}_{2}\)], Q\({}_{3}\) [\(Si\)(OSi)\({}_{3}\)OH], and Q\({}_{4}\) [\(Si\)(OSi)\({}_{4}\)] due to bi-, tri-, and tetrabranching units, respectively. The condensation degree of the three samples (76 for SiO\({}_{2}\); 78 for SP50; and 77 for SP50Q20) calculated on the basis of the relative intensity of Q\({}_{2}\), Q\({}_{3}\), and Q\({}_{4}\) peaks [33] is almost identical.