We present a multiscale modeling approach for studying interactions of organic molecules with metal surfaces in explicit water. The approach is based on combining adsorption energies of isolated molecules on transition metal surfaces calculated by ab initio density functional methods and classical molecular dynamics simulations using atomistically detailed force fields. The interaction of benzene with Ni(111) and Au(111) surfaces was studied. It is shown that a strong affinity of water for the hydrophilic surfaces makes benzene adsorption on Au thermodynamically unfavorable, while on Ni there is no preference. The work presented here serves as a first step in modeling the interactions of larger organic molecules with metal surfaces.
We report a computer simulation study on the hydration of benzene, which, despite being hydrophobic, is a weak hydrogen bond acceptor. The effect of benzene-water hydrogen bonding on the hydration free energy has been analyzed in terms of solute-solvent energies and entropies. Our calculations show that benzene-water hydrogen bonding restricts the number of arrangements possible for the water molecules resulting in a more unfavorable (negative) solute-solvent entropy change than observed for a 'nonpolar benzene' not capable of accepting water hydrogen bonds. More favorable hydration free energies of aromatic hydrocarbons in comparison with aliphatic hydrocarbons observed experimentally as well as in our calculations must therefore be a result of more favorable solute-solvent interaction energies. This result supports the view that lower aqueous solubilities of nonpolar molecules compared to polar molecules are due to a lack of favorable electrostatic interactions with water molecules. The calculated hydration free energy, enthalpy, entropy, and hydration heat capacity of benzene are in good agreement with experimentally reported values.
We present a multiscale modeling procedure that offers the opportunity to study hydrated biomolecules at
metal surfaces. First principle DFT calculations and classical atomistic simulations are used interactively in
order to account for both quantum and statistical aspects of molecular conformations at the surface. We
present models for water, benzene, phenol, alanine, and phenylalanine at the (111) surface of nickel. These
models are subsequently used in classical atomistic simulations to study physical−chemical aspects of amino
acids at a Ni(111)/water interface. Application of this method to a larger set of “molecular building blocks”
opens a computational route for molecular engineering of bio/inorganic hybrid systems.
We performed molecular simulations to study ion pairing in aqueous solutions. Our results indicate that ion specific interactions of Li(+), Na(+), and K(+) with the dimethyl phosphate anion are solvent-mediated. The same mechanism applies to carboxylate ions, as has been illustrated in earlier simulations of aqueous alkali acetate solutions. Contact ion pairs play only a minor role--or no role at all--in determining the solution structure and ion specific thermodynamics of these systems. On the basis of the Kirkwood-Buff theory of solution we furthermore show that the well-known reversal of the Hofmeister series of salt activity coefficients, comparing chloride or bromide with dimethyl phosphate or acetate, is caused by changing from a contact pairing mechanism in the former system to a solvent-mediated interaction mechanism in the latter system.
A first principle density functional study of the adsorption of neutral and zwitterionic alanine on the Ni͑111͒ surface is presented. Adsorption energies and geometries are reported for a set of possible initial orientations of both alanine forms with respect to the surface. The most energetically favorable adsorption of neutral alanine occurs via the bonding of the nitrogen to the top site. Adsorption of zwitterionic alanine is possible only via the bonding of one oxygen to the bridge site. Application of the current results to a multiscale modeling of oligopetides interacting with metal surfaces is discussed.
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