Adsorption of tripeptide RGD on rutile TiO2 nanotopography surface in aqueous solution

Molecular dynamics simulations were carried out to investigate the adsorption mechanisms of tripeptide Arg-Gly-Asp (RGD) on the nanotopography and perfect rutile TiO2 (1 1 0) surfaces in aqueous solution. It is shown that the amino groups (NH2 and NH3+) and carboxyl group (COO−) of RGD are the main groups bonding to hydrophilic TiO2 surface by electrostatic and van der Waals interactions. It is also demonstrated that RGD adsorbs much more rapidly and stably on the nanotopography surface than the perfect surface. On the hydrophilic TiO2 surface, the water molecules occupy the adsorption sites to form hydration layers, which have a significant influence on RGD adsorption. On the perfect surface, since the fivefold titanium atom is surrounded by surface bridging oxygen atoms above it and has a water molecule bonding to it, the amino group NH2 is the adsorption group. However, because the pit surface exposes more adsorption sites and has higher surface energy, RGD can adsorb rapidly on the surfaces by amino groups NH2 and NH3+, and the carboxyl group COO− may edge out the adsorbed water molecules and bond to the surface titanium atom. Moreover, the surface with higher surface energy has more adsorption energy of RGD.