The energy minimum position for quinone head group of the molecules was around 13-14 Åaway from the center of membrane which lies below the phosphate head group, at approximately the level of the lipid carbonyl groups in the surrounding membrane. This is similar to the position determined from equilibrium simulations (Fig. ). As discussed with the equilibrium results, the preferred depth for the quinone headgroup is driven largely by the hydrogen bonds that the quinones make with the surrounding environment. The reduced hydrogen bonding for sorgoleone when compared with its precursors (Fig. ) manifests in Fig. as the lowest barrier to interleaflet exchange when the compound crosses the membrane midplane. The sorgoleone precursors, by contrast, need to break additional hydrogen bonds, and thus have larger barriers inhibiting the transition between states.