Ab Initio Investigation of Polyethylene Glycol Coating of TiO₂ Surfaces

Abstract

In biomedical applications, TiO2 nanoparticles are generally coated with polymers to prevent agglomeration, improve biocompatibility, and reduce cytotoxicity. Although the synthesis processes of such composite compounds are well established, there is still a substantial lack of information on the nature of the interaction between the titania surface and the organic macromolecules. In this work, the adsorption of polyethylene glycol (PEG) on the TiO2 (101) anatase surface is modeled by means of dispersion-corrected density functional theory (DFT-D2) calculations. The two extreme limits of an infinite PEG polymer [−(OCH2CH2)n], on one side, and of a short PEG dimer molecule [H(OCH2CH2)2OH], on the other, are analyzed. Many different molecular configurations and modes of adsorption are compared at increasing surface coverage densities. At low and medium coverage, PEG prefers to lay down on the surface, while at full coverage, the adsorption is maximized when PEG molecules bind perpendicularly to the surface and interact with each other through lateral dispersions, following a mushroom to brush transition. Finally, we also consider the adsorption of competing water molecules at different coverage densities, assessing whether PEG would remain bonded to the surface or desorb in the presence of the aqueous solvent.

Impact of surface curvature, grafting density and solvent type on the PEGylation of titanium dioxide nanoparticles

“…These densities and the relative number of PEG chains attached to the surface are reported in Table 1. DFT calculations on the adsorption of PEG dimers on the anatase (1 0 1) surface of TiO 2 [51] proved that the adsorption process is exothermic, with binding energies from about À1.0 to À2.0 eV depending on the adsorption mode and on the grafting density. Therefore, after functionalizing the NP, we performed an energy minimization and then we fixed the distance between the undercoordinated Ti atoms (involved in the binding with the PEG) and the terminal O atoms of each PEG.…”

“…From a computational point of view, many studies have been published in the last years regarding chemically modified low index flat surfaces of TiO 2 [47][48][49][50][51][52][53], however, only few of them report on the modelling of functionalized nanoparticles [54][55][56][57]. In particular, simulation of polymer functionalization of NPs is a complex task and requires sophisticated tools.…”

Optimizing PEGylation of TiO2 Nanocrystals through a Combined Experimental and Computational Study

“…From a computational point of view, surface functionalization of TiO 2 with PEG was studied for a periodic slab model of a flat surface. 24 Modeling PEGylated NPs, in general, and TiO 2 NPs, in particular, is a much more complex task and requires large realistic models and sophisticated tools. Studies on spherical PEG brushes based on Monte Carlo or coarse-grained molecular dynamics (MD) approaches are reported in the literature.…”

Water Multilayers on TiO2 (101) Anatase Surface: Assessment of a DFTB-Based Method

“…Recently, TiO 2 nanoparticles photoactivity and redox chemistry have attracted growing interest for biomedical applications . In this field, knowledge of the properties of this solid–liquid interface is of key importance since the interaction with biomolecules and polymer coatings is competitive with water adsorption or even mediated by it. − Rutile is the most stable bulk TiO 2 phase at normal conditions; however, sub-20 nm TiO 2 nanoparticles prefer the anatase phase …”