normal Nonionic Surfactants

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5 months 2 weeks ago #7816 by cmluft
Nonionic Surfactants was created by cmluft
Hello Experts,

I was attempting to model the aggregation properties of various nonionic glycolipid derivatives and ran into a problem. The molecules I am interested in are typically a sugar head group and a nonpolar tail(s), these were not difficult to construct from various published MARTINI topologies. However, they seem to be behaving in unphysical ways. The biggest issue is that even small aggregates seem to want to form bilayer structures. This seems unlikely since it leaves a considerable portion of the aliphatic tails exposed to water. All-atom simulation on the same molecules raises suspicion as well since these show the formation of more spherical micellar aggregates with much less of the hydrocarbons exposed to solvent.

Is this an artifact of the force field since it is intended to model bilayer systems? Most of the published work on surfactants with the MARTINI force field seems to focus on ionic molecules with much smaller head groups. Has anyone run into this problem? Is there any solution?



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5 months 1 week ago #7832 by Pim
Replied by Pim on topic Nonionic Surfactants
Hi Charles, I don't think I can help you much. I've worked with some ionic surfactants and the micelles they formed had the right size according to SAXS. I'd imagine that for non-ionic surfactants, the aggregate shape is still largely based on the packing parameter (relative head and tail group sizes). Considering the aliphatic tail can't really be the problem, it is not unlikely the sugar Martini topology is suboptimal. Sugars have always been tricky to model and are an ongoing improvement project in the group. With the release of the Martini 3 force field (open beta available in Downloads/Particle definitions) we hope to combat some of their overaggregation which may allow a somewhat more spherical size for your system too. However, as mentioned, it is still work in progress and I'm not sure how much of the sugar topologies have been updated and tested, so you might have to do the work yourself.

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