PEGylation of Nanosubstrates (Titania) with Multifunctional Reagents: At the Crossroads between Nanoparticles and Nanocomposites

Titania (anatase) nanoparticles were successfully PEGylated through the use of catechol (dopamine)-terminated PEG derivatives. The resulting materials were characterized by excellent stability at neutral pH and extremely low toxicity (phagocytic and nonphagocytic cell lines). In particular, we focused on the comparison between mono- and bis-catechol PEGs. Due to the double terminal anchorage on the titania surface, bis-catechol ligands can produce chains differing from classical monoanchored PEG in conformation (horseshoe-shaped vs brush) and thus the possibility of interactions with biomolecules. At the same time, less than quantitative catechol binding may lead to the presence of dangling chains with unbound catechols which can polymerize and eventually produce PEG/titania nanocomposite colloids. Our results on double-functional PEG2000 show the latter to be the case. Pluronic F127 was also used as a bifunctional ligand, leading to nanocomposite aggregates with an even larger organic content

Adsorption Studies of <i>p</i>‑Aminobenzoic Acid on the Anatase TiO₂(101) Surface

The adsorption of <i>p</i>-aminobenzoic acid (pABA) on the anatase TiO₂(101) surface has been investigated using synchrotron radiation photoelectron spectroscopy, near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT). Photoelectron spectroscopy indicates that the molecule is adsorbed in a bidentate mode through the carboxyl group following deprotonation. NEXAFS spectroscopy and DFT calculations of the adsorption structures indicate the ordering of a monolayer of the amino acid on the surface with the plane of the ring in an almost upright orientation. The adsorption of pABA on nanoparticulate TiO₂ leads to a red shift of the optical absorption relative to bare TiO₂ nanoparticles. DFT and valence band photoelectron spectroscopy suggest that the shift is attributed to the presence of the highest occupied molecular orbitals in the TiO₂ band gap region and the presence of new molecularly derived states near the foot of the TiO₂ conduction band