We present a set of Coulomb point charges and van der Waals parameters for molecular dynamics simulations of interfaces between natively deprotonated amorphous SiO2 surfaces and liquid water, to be used in combination with standard biomolecular force fields. We pay particular attention to the extent of negative charge delocalisation in the solid that follows the deprotonation of terminal silanol groups, as revealed by extensive Bader analysis of electronic densities computed by density functional theory (DFT). The absolute charge values in our force field are determined from best‐fitting to the electrostatic potential computed ab initio (ESP charges). Our proposed parameter set is found to reproduce the energy landscape of single water molecules over neutral and deprotonated amorphous SiO2 surfaces and, after a minor adjustment, over thin oxide films on Si. Our analysis reveals a certain degree of arbitrariness in the choice of the DFT scheme used as the reference for the force‐field optimisation procedure, highlighting its intrinsic limits. Interaction between a water molecule and an oxidised Si surface calculated with several DFT and force‐field schemes, and delocalisation of the negative charge upon deprotonation of an amorphous SiO2 surface.

Stable adsorption configurations of several amino acid monomers on anatase (101) and (001) and rutile (110) as well as (100) were found in Car-Parrinello simulations of aqueous solutions. Adsorption energies were calculated by averaging over trajectories of the adsorbed and desorbed configuration, taking into account thermal fluctuations of the potential energy. The small adsorption energy of the cysteine on the stoichiometric (110) rutile surface is largely enhanced by inserting the S into an oxygen vacancy. Values for glutamic acid and lysine were significantly higher in the previously identified hydroxyl contact points (160 and 110 kJ/mol, respectively) than on the stoichiometric rutile surfaces (70 and 40 kJ/mol). Adsorption of histidine and glutamic acid on anatase largely depended on the surface orientation. Glutamic acid binds strongly to (101), whereas histidine on (001) was so stably bound that no molecular desorption was achieved. These results coincide with recent experiments on the crystallization of anatase in amino acid solutions [

The adsorption of α-chymotrypsin and hen egg white lysozyme on amorphous silica is studied by molecular dynamics (MD) simulations in comparison with adsorption experiments. Protein–surface interaction profiles are computed in implicit solvent at the level of DLVO theory. These reveal a preferential adsorption orientation for chymotrypsin, driven by its large dipole moment, with its α-helical regions pointing toward the surface. Instead, a less clear orientational preference characterizes lysozyme adsorption, which approaches the surface in a side-on orientation, confirming previous results. Explicit-solvent MD simulations are then performed to analyze the formation and stability of protein–surface contacts. While no significant conformational changes take place in the short simulation time investigated (up to 300 ns), the simulations clearly reveal the presence of adsorption motifs comprising both positively charged, but also negatively charged, polar and even nonpolar residues. Stable adsorption originates from a favorable match between the adsorption motifs and the local subnanometer distribution of charged, strongly hydrophilic, and less hydrophilic surface regions. We conclude that intuitive arguments based on DLVO forces may be put forward to predict the expected adsorption orientation of the proteins. However, observed differences in the relative adsorption amount of the two enzymes can only be explained by taking into account also protein–protein interactions and the stability of the aforementioned specific adsorption motifs.

The adsorption of several small organic molecules on rutile (110) and (100) as well as on anatase (101) surfaces was investigated by Car-Parrinello molecular dynamics in aqueous solution and a new approach to the calculation of adsorption energies is proposed, taking into account the potential energy fluctuation of larger systems. Acetylene and ethylene insert into twin oxygen vacancies in the surface and form polarized covalent Ti-C bonds. In one case spontaneous coupling of two acetylene molecules to a C(4)H(3) molecule with a structure similar to trans-butadiene was observed. Neutral catechol and the singly charged anion were not reactive on any titanium dioxide surface, but the twofold-charged anion attained stable mono- and bidentated geometries on anatase. Methanol, ethanol, formaldehyde and acetaldehyde adsorbed with their functional groups. Very stable geometries provide a Ti-O bond and have adsorption energies of 60-200 kJ/mol. The adsorbates compete with water molecules for similar adsorption sites in point defects as well as on perfect surfaces.

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