with the water density at the given temperature. The overall
number of atoms in the simulated systems was around 33 000.
Our long-term goal is to model interactions of functionalized
AuNPs with cell (lipid) membranes, and the AuNP force-field
has to be consistent with the force-field for lipid membranes. As
follow-up simulations of AuNPs with lipid membranes are
currently in progress, we here describe the background related
to both simulation projects. We employ the well-known unitedatom
force-field by Berger et al.55 for the alkythiol side groups.
The force-field is essentially a mixture of OPLS (nonbonded
interactions) and GROMOS (bonded interactions) force-fields.
Partial charges for the ionized head groups of AuNP+ and
AuNP− were taken from the appropriate parts of POPE55,56
and POPS57 lipids, respectively. A common problem for
metallic NPs in a biologically relevant environment is the fact