Molecular dynamics simulations of BSA absorptions on pure and formatecontaminated rutile (110) surface

Titanium dioxide is easily contaminated by carboxylic acid (mainly formate) in ambient environments. Although numerous studies have proven that the removal of contamination will enhance the adsorption of albumin and then the hemocompatibility of the TiO2 surface, recontamination makes further experimental investigation difficult. Previous molecular dynamics (MD) studies have elucidated the mechanisms of protein on the pure TiO2 surface, but no focus was given to the contamination of carboxylic acid. Here, we are the first to examine formate-contamination, and to deduce the forcefield parameters of the contaminated surface. We then simulated adsorptions of BSA on pure and formate-contaminated rutile (110) surface. On the pure surface, strong polarity makes water molecules exhibit a layered structure and generate local dipole moment distribution, which attracts charged groups. Compared with other proteins, BSA possesses a high content of charge residues, and thus BSA can stably adsorb on the pure surface. When the surface is contaminated, however, the formate ions form bonds to five-fold-coordinated titanium atoms and only expose C-H bonds, and surface polarity is consequently decreased. Therefore, the interaction between BSA and the surface is diminished, and stable adsorption cannot be established in the time scale of hundreds of nanoseconds.