Cartoon representations of the Marcelja-Radic theory with water molecules oriented in a symmetrical way (a) and in an asymmetrical way (b), with respect to the axis O’O.
(a) An initial structure of a system having two PC-headgroup plates immersed in water, when the separation distance is 2.5 nm. (b) Charge distribution of the zwitterionic PC headgroup. (c) Charge distribution of the cationic headgroup in the C-plate. (d) An initial structure of a system having a C-plate (left) and a PC-headgroup plate (right) in water at a separation of 1.5 nm. To neutralize the whole system, chloride ions (orange) are introduced as counterions but frozen at the given positions. Water molecules are not presented for clarity.
PMF between a C-plate and a PC-headgroup plate, and its decomposition into contributions from the direct and solution-mediated interactions.
Comparison of solution-mediated interactions when interactions are between: (i) two zwitterionic PC-headgroup plates, (ii) two hydrophobic CRPC plates, (iii) one zwitterionic PC-headgroup plate and one cationic C-plate.
Enthalpic (ΔH) and entropic (−TΔS) contributions to the solution-mediated interaction for the system containing a zwitterionic PC-headgroup plate and a cationic C-plate. The error bars are calculated from standard deviation. For clarity, we only display the error bars at every 10 data points (1 nm interval).
Profiles of the dipole moment orientation (blue) and the number density (red) of water molecules at the interplate distance of 1.6 nm. (Upper panel) The plots are for the case of C-plate (z < 0) opposing the PC-headgroup plate (z > 0). (Lower panel) The plots are for the case of two PC-headgroup plates. Only the column of the water molecules within the x-y dimensions of the plates is considered for the analysis. The number density is normalized by the bulk water number density and the dipole moment orientation profile is in dimensionless units.
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