Gemini surfactants with a disaccharide spacer

A gemini surfactant is an amphiphile possessing tin sequence) the following : hydrocarbon tail/polar group/spacer/polar group/hydrocarbon tail. Widespr ead interest in geminis has emerged recently from both industrial and acade mic laboratories. In the present contribution, two related families of gemi nis have been synthesized, both with trehalose, a disaccharide, as a polar spacer. One family, Series-A, is nonionic and has amide groups separating t he long chains from the trehalose spacer. The other family, Series-B, has q uaternary ammonium ions connecting the long chains to the trehalose spacer. It was found that Series-A geminis are water insoluble despite the two ami des and multiple hydroxyls. When hydrated or extruded, these geminis form m icroscopically visible vesicular and tubular structures above their transit ion temperatures (which were determined calorimetrically). Insoluble monomo lecular films, constructed from these geminis, have interfacial areas that are dominated by the sugar spacer although intermolecular chain/chain inter actions seem to stabilize the films. Thus, the behavior of Series-A geminis in many ways parallels that of phospholipids and simple double-chain surfa ctants. It is as if the trehalose is less of a spacer than a large but conv entional headgroup. In contrast, cationic Series-B geminis are water solubl e and form micelles with critical micelle concentrations an order of magnit ude lower than that of corresponding conventional surfactants. Molecular mo deling using the Amber* force field explains the difference in properties b etween the two families of geminis. Series-A are tubular in shape and thus prefer bilayer packing as do other amphiphiles in which the headgroups are similar in width to the sum of the tail diameters. Series-B geminis are con ical-shaped and pack more readily into spherical micelles. This work entail s synthesis, tensiometry, conductance, microscopy, surface balance studies, calorimetry, light scattering, and molecular modeling. In colloid chemistr y, a balanced perspective cannot be achieved by one methodology alone but o nly through the pursuit of consilience among multiple approaches.