TiO₂@SiO₂ nanoparticles functionalized with para-aminobenzoic acid (PABA) by Fisher esterification reaction

In this work, hybrid TiO₂ nanoparticles embedded in SiO₂ were obtained by means of sol-gel process, testing different proportions of the silicon and titanium oxides to obtain TiO₂ particles with a high surface content of hydroxyl groups. Anatase crystalline form of TiO₂ is a widely used material in active-substance release studies, due to its optimal properties for the transport, distribute and release of different molecules into biological systems. According to the X-ray diffraction analysis, all the proportions of evaluated hybrid systems presented the anatase phase, however, the molar proportion (20:80, TiO₂:SiO₂) contains a high quantity of hydroxyl groups according to infrared spectroscopy. The spherical morphology of the particles were observed by scanning electron microscopy forming agglomerates. The functionalization of these surfaces was carried out using para-aminobenzoic acid as a drug-binding model that generated a covalent bond between the TiO₂@SiO₂ system, likewise, thermogravimetric analysis identified the content of functionalized PABA. Dynamic light scattering showed particles and agglomerates around 25609 nm and negative value of zeta (¦)-potential in the molar ratio TiO₂:SiO₂ 20:80-PABA. Finally, we demonstrated that PABA hydrolyzes in the presence of human plasma, recovering the nanoparticularized systems with the hydroxyl groups. The hydroxyl groups on the particle surface promote the incorporation of organic molecules that contain carboxyl groups in their structure.