Figure 3.

Characterizing free-energy surface profiles for BBB translocation for the solute library. (A) Group 1 solutes have an energy barrier located in the hydrophobic core in the center of the bilayer (ΔG₂ ≥ kT). In some cases, there are energy minima located in the head group regions, with a barrier to escape from the bilayer (ΔG₁ ≤ 2kT) and an energy barrier between the two minima (ΔG₃ ≤ kT). (B) Group 2 solutes have two energy minima located in the head group regions of the bilayer separated by a small energy barrier in the hydrophobic core. This profile results in a barrier to escape from the bilayer ΔG₁ ≥ 2kT and an energy barrier associated with hopping between the two minima in the hydrophobic core (ΔG₃ ≤ kT). (C) Group 3 solutes have an energy minimum in the center of the bilayer, resulting in a barrier to escape from the bilayer (ΔG₁ ≥ 4kT). (D) Energy minima in the head group regions result in an energy barrier to escape from the bilayer (ΔG₁). (E) Energy barrier in the center of the bilayer provides an energy barrier to translocation across the hydrophobic core (ΔG₂). (F) Energy minima in the head group regions combined with an energy barrier in the center of the bilayer result in an energy barrier for hopping between the energy minima (ΔG₃).