Using Tension to Map Free-Energy Landscapes that Govern Pore Nucleation in Membranes

Abstract

Because of the large energy, thermal activation is needed to open nanopores in membranes yet activation energy can change significantly with tension. Although models exist describing the impact of tension, experiments have failed to cover the ranges of tension and pore nucleation rate required to examine theories. Hence, a micromechanical method was established to assay rates at which unstable nanopores form in giant single-bilayer vesicles in relation to tension, covering rates from 100/s. Plotted as logarithms, rates of nanopore nucleation yield changes in activation energy (scaled by thermal energy kBT). Derivatives of activation energy with respect to tension establish the critical-pore areas that couple with tension to lower activation energy. When correlated to pore area, changes in activation energy can be transformed to free energies along a reaction coordinate defined by pore size. In this way, we have mapped free-energy landscapes for pore nucleation in several types of fluid-lipid bilayer systems (cf. figure), beginning near the symmetry break and rising by 10-20 kBT when pore sizes reach a few nm. [E. Evans and B.A. Smith, New Journal of Physics13 (2011)].View Large Image | View Hi-Res Image | Download PowerPoint Slide