Computation of Lipid Headgroup Interactions

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Biophysical Journal Supplement 1

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The equilibrium structure of lipid aggregates is determined by the balance of numerous forces between hydrophobic acyl chains, hydrophilic lipid headgroups, and the lipid's environment. Among these forces, lipid headgroup interactions are both important to the stability of lipid structures and responsible for many of the interactions between biological membranes and aqueous solutes including ions and soluble peptides. In order to model these headgroup interactions, we consider the electrical properties of the headgroup molecules via the multipole expansion. While common lipid headgroups such as phosphatidylcholine are electrically neutral, they are characterized by non-zero higher order terms in the multipole expansion. Making a dipole approximation, we employ a two dimensional lattice of classical dipoles to model the headgroup networks of lipid aggregates. Restrictions to each dipole's position and orientation are imposed to account for the effect of hydrocarbon chains which are not included in the model. A Monte Carlo algorithm is used to calculate headgroup-headgroup interactions and network energies in both dipole and point-charge approximations.


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