Mar 23 – 24, 2009
KTH - Royal Institute of Technology
Europe/Stockholm timezone

Free energy of nano-pore formation and growth in membranes

Mar 24, 2009, 3:30 PM
45m
F3 (KTH - Royal Institute of Technology)

F3

KTH - Royal Institute of Technology

Lindstedtsväg 26

Speaker

Prof. Olle Edholm (Royal Institute of Technology KTH, Sweden)

Description

The free energy cost for creating water filled pores of different sizes in model membranes is discussed and calculated from molecular dynamics simulations. Clearly the free energy cost for creating a hydrophilic pore with the lipid head groups turned inwards towards that water is less than that for creating a hydrophobic pore with hydrocarbon towards the water. This depends, however, on the ratio between bending modulus and surface tension and one might think of systems in which the hydrophobic pore is more stable. There are also systems for which a vacuum pore would be more stable than the water filled one. The free energy was calculated from atomistic molecular dynamics simulations as a function of a reaction coordinate using a constraining potential. The free energy profile that came out of the simulations is quadratic for a radii less than about 0.3 nm, and linear shape for larger radii. In the outer region, a line tension can be calculated that is consistent with experimentally measured values. Further, this line tension can be rationalized and understood in terms of the bending energy to deform the bilayer. The region with small radii can be described and understood in terms of statistical mechanics of density fluctuations. In the region of cross over between a quadratic and linear free energy there was some hysteresis associated with filling and evacuation of the pore with water. The meta-stable pre-pore state hypothesized to interpret experiments was not observed in this region. Reference: Free energy of a trans-membrane pore calculated from atomistic molecular dynamics simulations, J. Wohlert, W.K. den Otter, O. Edholm and W. J Briels, J. Chem. Phys. 124(2006) 154905.

Primary author

Prof. Olle Edholm (Royal Institute of Technology KTH, Sweden)

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