**3. Results**

### *3.1. Sol–Gel Synthesis and Coating Application*

To obtain a controlled drug release fabric, 3-glycidoxypropyltriethoxysilane (GPTES) was employed in a sol–gel synthesis in the presence of an antioxidant/anti-inflammatory molecule, the N-Palmitoyl-(4-nitro-phenyl)-amine (PNPA) [28]. The simultaneous presence of both an epoxy group and a triethoxysilane functionalities makes this specific silica precursor able to cross-link to other GPTES molecules, to entrap the antioxidant doping molecule and still to coat the textile surface, respectively. In this regard, a GPTES-based sol was synthesized in acidic aqueous medium by addition of slight amount of HCl, as catalyst, and then added to a methanol solution containing the PNPA molecule. As reported in previous studies [15–21], the sol–gel synthesis leads to the formation of a hybrid polymeric 3D network through the opening of the epoxy ring of GPTES and interaction of the triethoxysilane end to form an extended polyethylene oxide network (PEO) [20], in whose holes the PNPA is physically and stably entrapped (Scheme 1).

**Scheme 1.** Reaction pathways toward the formation of the G-PNPA sol, as obtained in methanol solution at room temperature in slight acid conditions.

The so obtained G-PNPA functional sol was applied by padding on cotton fabrics and cured thermally with the aim to prepare a nano-hybrid coating for controlled release application (Scheme 2).

**Scheme 2.** Schematic representation of the application of the G-PNPA sol on cotton surface and the formation of the coating xerogel.

### *3.2. Sol NMR Characterization*

A reaction mixture relative to the G-PNPA sol as obtained in methanol for coating application, has been achieved in situ (1:0.1 = [GPTES]:[PNPA] molar ratio) in methanol-*d*4 and characterized by means of 1H one- and two-dimensional NMR spectroscopy. Figure 1 shows the 1H NMR spectra as recorded at time zero and after 24 h (in methanol-*d*4 at 298 K, 300 MHz). The comparison of the aliphatic regions of the 1H NMR spectra of the reaction mixtures recorded at different times clearly reveal the presence of the protonic pattern expected for the diol/PEO silylated (red squares in Figure 1) derivatives and the starting GPTES (black squares in Figure 1, [20]) as shown in Scheme 1. In particular, the aliphatic regions of the 1H NMR spectra in Figure 1 clearly show: (i) the presence of the expected protonic pattern for the GPTES open ring derivative, bringing a hydroxyl and an ether group bonded to two vicinal carbon Ce and Cf atoms (δ = 0.68, CH2a; 1.71, CH2b; 3.48, CH2c + CH2d + CH2f; 3.88 CH2e, red squares in lower spectrum) [30] (ii) the proton peaks relative to the starting GPTES in a decreased concentration (δ = 0.67, CH2a; 1.68, CH2b; 2.61+2.78, CH2f; 3.16, CH2e; 3.32 + 3.76, CH2d; 3.49, CH2c, black squares in upper spectrum); (iii) the presence of the upper-field methylene and the methyl proton resonances relative to free ethanol moieties, compared to those relative to the ethylic groups of GPTES (δ = 3.63, CH2, 1.19, CH3 vs 3.84, CH2, 1.22, CH3; cut signals in both spectra).

**Figure 1.** 1H NMR spectra relative to solutions of the G-PNPA sol, as obtained in methanol-*d*4 at 298 K, 300 MHz, at time zero (upper spectrum) and after 24 h reaction time in the presence of slight amount of HCl (lower spectrum).

Unfortunately, the long penta-decanoic protonic chain is buried under other signals, also due to the strong molar ratio exceed of GPTES. The aromatic region shows the expected and unchanged pattern of broad signals for para-substituted phenyl ring of the PNPA molecule.

The 1H NMR experiments clearly show that the GPTES epoxy ring opening reaction by a suitable nucleophilic group of the PNPA molecule is not occurring, as well as the formation of a stable ether covalent bond. As previously shown [20], the stable encapsulation of the PNPA molecule into the PEO silylated GPTES derivative is most likely due to the formation of weak bonds (i.e., van der Waals or electrostatic) between the polymerized GPTES (i.e., ether oxygen and hydroxyl group) and the N-Palmitoyl-(4-nitro-phenyl)-amine (i.e., nitrogen, oxygen, long alkyl chain, phenyl group).
