HEADER

Next, investigate the effect of changes in the lipid tails and in the headgroups on the properties of the bilayer. We will i) introduce a double bond in the lipid tails, and ii) change the lipid head groups from PC to PE.

Unsaturated tails

To introduce a double bond in the tail, we will replace the DSPC lipids by DOPC (compare the Martini topologies of these two lipids). Replace DSPC by DOPC in your .top and .mdp files, and grompp will do the rest for you (you can ignore the ”atom name does not match” warnings of grompp).

Changing the headgroups

Starting again from the final snapshot of the DSPC simulation, change the head groups from PC to PE. For both new systems, run 15-ns MD simulations and compare the above properties (area per lipid, thickness, order parameter, diffusion) between the three bilayers (DSPC, DOPC, DSPE). Do the observed changes match your expectations? Why/why not? Discuss.