Yes / We investigate how the presence of Ca2+ ions at the aqueous TiO2 interface influences the binding modes two experimentally-identified titania-binding peptides, Ti-1 and Ti-2, using replica exchange with solute tempering molecular dynamics simulations. We compare our findings with available experimental data and contrast our results with those obtained under NaCl solution conditions. We find that for Ti-1, Ca2+ ions enhances the adsorption of the negatively-charged Asp8 residue in this sequence to the negatively-charged surface, via Asp{Ca2+{TiO2 bridging. This appears to generate a non-local impact on the adsorption of Lys12 in Ti-1, which then pins the peptide to the surface via direct surface contact. For Ti-2, fewer residues were predicted to adsorb directly to the surface in CaCl2, compared with predictions made for NaCl solution, possibly due to competition between the other peptide residues and Ca2+ ions to adsorb to the surface. This reduction in direct surface contact gives rise to a more extensive solvent-mediated contact Ti-2. In general, the presence of Ca2+ ions resulted in a loss of conformational diversity of the surface-adsorbed conformational ensembles of these peptides, compared to counterpart data predicted for NaCl solution. Our findings provide initial insights into how peptide{TiO2 interactions might be tuned at the molecular level via modification of the salt composition of the liquid medium. / Air Office of Scientific Research, grant number FA9550-12-1- 0226.

Yes / Materials-binding peptides offer promising routes to the production of tailored Pd nanomaterials in aqueous media, enabling the optimization of catalytic properties. However, the atomic-scale details needed to make these advances are relatively scarce and challenging to obtain. Molecular simulations can provide key insights into the structure of peptides adsorbed at the aqueous Pd interface, provided that the force-field can appropriately capture the relevant bio-interface interactions. Here, we introduce and apply a new polarizable force field, PdP-CHARMM, for the simulation of biomolecule–Pd binding under aqueous conditions. PdP-CHARMM was parametrized with density functional theory (DFT) calculations, using a process compatible with similar polarizable force-fields created for Ag and Au surfaces, ultimately enabling a direct comparison of peptide binding modes across these metal substrates. As part of our process for developing PdP-CHARMM, we provide an extensive study of the performance of ten different dispersion-inclusive DFT functionals in recovering biomolecule–Pd(111) binding. We use the functional with best all-round performance to create PdP-CHARMM.We then employ PdP-CHARMM and metadynamics simulations to estimate the adsorption free energy for a range of amino acids at the aqueous Pd(111) interface. Our findings suggest that only His and Met favor direct contact with the Pd substrate, which we attribute to a remarkably robust interfacial solvation layering. Replica-exchange with solute tempering molecular dynamics simulations of two experimentally-identified Pd-binding peptides also indicate surface contact to be chiefly mediated by His and Met residues at aqueous Pd(111). Adsorption of these two peptides was also predicted for the Au(111) interface, revealing distinct differences in both the solvation structure and modes of peptide adsorption at the Au and Pd interfaces. We propose that this sharp contrast in peptide binding is largely due to the differences in interfacial solvent structuring. / Air Force Office for Scientfi c Research (Grant #FA9550-12-1-0226)