Abstract
Dissipative particle dynamics (DPD) can be used to simulate the self-assembly properties of surfactants in aqueous solutions, but in order to simulate a new compound, a large number of new parameters are required. New methods for the calculation of reliable DPD parameters directly from chemical structure are described, allowing the DPD approach to be applied to a much wider range of organic compounds. The parameters required to describe the bonded interactions between DPD beads were calculated from molecular mechanics structures. The parameters required to describe the nonbonded interactions were calculated from surface site interaction point (SSIP) descriptions of molecular fragments that represent individual beads. The SSIPs were obtained from molecular electrostatic potential surfaces calculated using density functional theory and used in the SSIMPLE algorithm to calculate transfer free energies between different bead liquids. This approach was used to calculate DPD parameters for a range of different types of surfactants, which include ester, amide, and sugar moieties. The parameters were used to simulate the self-assembly properties in aqueous solutions, and comparison of the results for 27 surfactants with the available experimental data shows that these DPD simulations accurately predict critical micelle concentrations, aggregation numbers, and the shapes of the supramolecular assemblies formed. The methods described here provide a general approach to determining DPD parameters for neutral organic compounds of arbitrary structure.
Highlights
Molecular modeling is a powerful tool for investigating molecular self-assembly in the liquid phase.[1,2] These calculations can provide information at the molecular level about how intermolecular interactions affect macroscopic properties
Each dissipative particle dynamics (DPD) bead is described as a set of surface site interaction points (SSIPs), each of which corresponds to 9 Å2 of the van der Waals surface and is assigned an interaction parameter ε based on polarity
The parameters required to describe the bonded interactions between DPD beads were calculated from molecular mechanics structures of the surfactant molecules
Summary
Molecular modeling is a powerful tool for investigating molecular self-assembly in the liquid phase.[1,2] These calculations can provide information at the molecular level about how intermolecular interactions affect macroscopic properties. The self-interaction parameters can be obtained by matching simulations to experimental liquid densities using a method introduced by Anderson et al.[16] The transfer free energies required in eq 5 can be estimated by using values for the mixing of liquids that most closely approximate the chemical structures of the relevant beads.[18,19] A number of different approaches to deriving aij repulsion parameters experimental or calculated transfer have free been described energies.[14,18−20] using Groot and Warren matched the equilibrium distance with the maximum in the radial distribution function to develop a soft sphere model for linear polymers (aij = 25 and ρ = 3).[20] Since it has become common practice to choose values depending on the situation requirements.[15,21−27]. The approach has been tested on 27 different surfactants, and the DPD simulations are shown to provide an excellent description of the critical micelle concentration (CMC), the aggregation number (Nagg), and aggregate shape when compared with experimental data
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