Anomalous phase behaviour of glycolipid self-assembly tuned by sugar headgroup surface arrangement

We present anomalous mesophase behavior of single component, non-added salt solutions of a family of membrane glycolipid bearing large headgroups: the gangliosides. Contrary to one of the mainstays of the colloid science, that the aggregation number of amphiphile aggregates grows with concentration, an anomalous region is found at intermediate concentrations of several of those glycolipid solutions, where a sharp decrease of the aggregation number occurs. The conventional picture of interacting micelles says that a reduction in the molecular surface area (increase of aggregate size) is paid to reduce intermicellar interactions when the solution is concentrated. Furthermore we present data on a bilayer forming glycolipid able to spontaneously vesiculate at high dilution and to concentrate in a more curved aggregate shapes (ribbons) opposite to usual paradigm telling that curvature can only decrease as concentration increases. The common point at the base of this rich phenomenology is that the amphiphilic surfaces made of bulky headgroups of more or less complex sugar chains, is able of modifying molecular surface area and protrusion from the aggregate, contributing to the energy balance between inter- and intra-aggregate interaction. This capability in the case of GM3 single component solutions have to be played non-homogeneously on the aggregate surface to account for edge energy cost of ribbons and finite membrane, and to allow for asymmetric curvature of the two monolayeres of the vesicles. We show that the different arrangements can be fine-tuned by physical condition as, very interestingly, counter-ion substitution.