The need to revisit lipid areas

We have studied the structural properties of lipid bilayers made up of monounsaturated phosphatidylcholines (i.e. diCn:1PC, where n=14, 16, 18, 20, 22 and 24). High-resolution x-ray scattering data were analyzed in conjunction with contrast varied neutron scattering data, using the recently developed technique by Kučerka et al. [Biophys. J. 95, 2356 (2008)]. Analyses of the data show that with increasing n lipid bilayers do not thicken in a linear fashion, as is often assumed, but quadratically, and that lipid area assumes a maximum value for n∼18 bilayers. More importantly, compared to previous data our results strongly suggest that lipid areas are smaller by about 10%. This observation highlights the need to revisit lipid areas as they are extensively used in molecular dynamics simulations and for calibrating their force fields.