Hierarchical Ordering of Sugar Based Amphiphiles

Abstract

Colloidal aggregates of amphiphilic molecules provide an example of self-confined liquid crystal, being finite both in extension, nanometric scale, and in dimension, nearly-two dimensional. In fact, although disperse on the macroscopic scale, amphiphiles demix in dilute aqueous solution on the microscopic scale due to their bifunctional nature and form condensed assemblies with a complex internal structure, dictated by the compromise between hydrophobic and hydrophilic requirements. On raising the concentration, these amphiphile-aggregate containing solutions start to develop organised structures on the mesoscale, evidencing a long-range crystalline order, but still preserving the ability to rearrange on the nanoscale giving rise to rich phase diagrams.

We present here some peculiar and unexpected effects observed for aggregates of gangliosides, glycosidic amphiphiles with both an extended hydrophobic portion, a double-tailed ceramide, and a bulky saccharidic headgroup, displaying large conformational adaptability and showing relevant preferential interactions. While giving rise to a highly cooperative structural unit, with a strong conformational coupling between surface and core of the colloid, ganglioside aggregates respond to crowding in a counterintuitive fashion, exploiting their structural metamorphism.

Keywords:

• gangliosides
• self-confined liquid crystals
• sugar based amphiphiles

Acknowledgments

The authors are grateful to G. Karlsson (University of Uppsala) for the Cryo-TEM measurements. We thank J. Teixeira and T. Narayanan for their precious assistance on the beamlines PAXE at LLB and ID02 at ESRF.