Systematic Optimization of a Force Field for Classical Simulations of TiO₂–Water Interfaces

Abstract

Atomistic force field parameters were developed for the TiO 2 −water interface by systematic optimization with respect to experimentally determined crystal structures (lattice parameters) and surface thermodynamics (water adsorption enthalpy). Optimized force field parameters were determined for the two cases where TiO 2 was modeled with or without covalent bonding. The nonbonded TiO 2 model can be used to simulate different TiO 2 phases, while the bonded TiO 2 model is particularly useful for simulations of nanosized TiO 2 and biomatter, including protein− surface and nanoparticle−biomembrane simulations. The procedure is easily generalized to parametrize interactions between other inorganic surfaces and biomolecules. ■ INTRODUCTIONBiomolecules interacting with inorganic objects are fundamental in nanobiotechnological applications such as surfaceattached biomolecules for target delivery of drug molecules, 1 protein adsorption to medical implants, 2 protein−nanoparticle interactions 3 and, not least, to understand the molecular mechanisms of nanotoxicity. 4 The contact points between inorganic surfaces and biomatter (the nanobio interface 5 ) can be tracked with experimental techniques like dynamic light scattering (DLS), 6−8 chromatography 9,10 and/or spectroscopy, 11,12 but only by indirect measurements.On the other hand, computer simulations can in principle be used to directly calculate interactions at the nanobio interface, covering system sizes ∼1000 Å and time scales ∼1000 ns. These windows are highly relevant when modeling the nanobio interface, but outside the realm of quantum mechanics. This calls for "classical" models with atomistic or semiatomistic (atoms being grouped into effective interaction centers) representations in computer simulations of nanobio interactions, parametrized to reproduce properties relevant to the nanobio interface. Substantial effort has been invested during the last decades to develop classical molecular models for biomolecules (proteins, lipids, nucleic acids, carbohydrates, etc.), but there has been no comparable endeavor to include inorganic materials into the models. The state of classical models aimed to describe the nanobio interface remains underdeveloped, largely because of the difficulties involved with representing the electronic structure of the inorganic material by interacting point particles. The present work is an attempt to close this modeling gap by developing atomistic force field parameters for the TiO 2 −water interface. We use an automated algorithm that is extended to accept arbitrary experimental data as targets in the parameter fitting. The method can easily be generalized to develop force field parameters for other inorganic surfaces and biomolecules. In an accompanying paper, 13 we use the optimized force field parameters to address the other long-standing problem in nanobio simulationsaccurate sampling of biomolecules near inorganic surfacesand to compute binding free energies of amino acid side chain analogues and a peptide to the TiO 2 surface.T...

Molecular Dynamics Simulations of Adsorption of Amino Acid Side Chain Analogues and a Titanium Binding Peptide on the TiO2 (100) Surface

“…(17) is a variant of a well-known matrix approximation 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 agreement with density functional theory (DFT). 16 The force field parameters are summa- Side chain analogs (SCAs) are the molecules corresponding to truncating amino acid side chains at the protein backbone and replacing the C α -carbon by a hydrogen. The present work covered 19 SCAs (Fig.…”

“…The first problem is addressed by us in an accompanying paper 16 where the aim is to develop robust force field parameters for interactions between TiO 2 surfaces and biomolecules.…”

“…To mimic such conditions, we used a model with oxygen-terminated TiO 2 (100) surface slabs, consisting of layers of 2-coordinated oxygens on top of 5-coordinated titaniums (Ti-O-Ti bridges on the surface, same setup as used in an accompanying TiO 2 forcefield parameterization by us16 and similar to that of Ref. 32]).…”

Transferable force-field for modelling of CO2, N2, O2and Ar in all silica and Na+exchanged zeolites

“…After each iteration the difference in between computed and experimental values at high and low pressures is evaluated, and a heuristic script (more advanced optimization procedure can be found in papers [71,72]) suggests changes of parameters which would provide better agreement between computed and experimental adsorption isotherms. On the initial stages of the iterative procedure a general scaling of either partial charges or Lennard-Jones parameters were done, in the later stage tuning of parameters of individual atom types (Si, Al, and oxygens of the framework) was done to satisfy individual isotherms of the considered set of structures.…”

Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics

“…Such calculations rely on empirical potentials obtained from fitting ab initio data 54 or experimental measurements. 55 The major limitations of classical MD simulations are the ineptitude to model surface reactivity due to predetermined covalent bonds and the poor representation of surface polarization when fixed partial charges are used to treat electrostatic interactions. An additional complication is the pH-dependence of TiO 2 surface chemistry (the point of zero charge is around 5).…”