
Although lipid structures tend to be very strong, defects are functionally important in a range of biophysical processes. We use computer simulations to study the properties of defects, which are difficult to access by experimental techniques. In bilayers, a large energetic barrier prevents pore formation, which is largely dependent on the composition and structure of the lipid bilayer. We have used molecular dynamics simulations with atomistic detail to study the thermodynamics, kinetics and mechanism of pore formation and dissipation in DLPC, DMPC, and DPPC bilayers, with pore formation free energy barriers of 17 kJ/mol, 45 kJ/mol and 78 kJ/mol. By using atomistic computer simulations, we are able to determine not only the free energy for pore formation, but also the enthalpy and entropy, which yields significant new insights in the molecular driving forces behind membrane defects. In monolayers, collapse and other large-scale changes are important in lung surfactant and of general biophysical interest. We have previously shown that the shape of defects can be predicted based on measurable mechanical properties in homogeneous monolayers (Baoukina et al, PNAS 2008). We are now extending this to study monolayers in which two phases coexist, using coarse-grained simulations with the MARTINI model. In these mixtures breakdown is significantly more complicated and depends on the location of initial defects, rates, and other properties.

Although lipid structures tend to be very strong, defects are functionally important in a range of biophysical processes. We use computer simulations to study the properties of defects, which are difficult to access by experimental techniques. In bilayers, a large energetic barrier prevents pore formation, which is largely dependent on the composition and structure of the lipid bilayer. We have used molecular dynamics simulations with atomistic detail to study the thermodynamics, kinetics and mechanism of pore formation and dissipation in DLPC, DMPC, and DPPC bilayers, with pore formation free energy barriers of 17 kJ/mol, 45 kJ/mol and 78 kJ/mol. By using atomistic computer simulations, we are able to determine not only the free energy for pore formation, but also the enthalpy and entropy, which yields significant new insights in the molecular driving forces behind membrane defects. In monolayers, collapse and other large-scale changes are important in lung surfactant and of general biophysical interest. We have previously shown that the shape of defects can be predicted based on measurable mechanical properties in homogeneous monolayers (Baoukina et al, PNAS 2008). We are now extending this to study monolayers in which two phases coexist, using coarse-grained simulations with the MARTINI model. In these mixtures breakdown is significantly more complicated and depends on the location of initial defects, rates, and other properties.