Cationic gemini surfactants based on tartaric acid : synthesis, aggregation, monolayer behaviour, and interaction with DNA

The synthesis of three novel cationic gemini surfactants (10, 12, and 14) based on tartaric acid appended with biocompatible palmitoyl tails and head groups is described, and their aggregation in water, monolayer behaviour, DNA binding, and gene transfection activities are reported. The monolayer studies showed that the molecular area of the surfactants is determined by the head group, as it increased going from the ethylenediamine head group of 10 via the lysine head group of 12 to the combined lysine/ethylenediamine head group of 14. Electron microscopy showed that the surfactants with the smaller head groups (10 and 12) form plate-like structures, probably stacked bilayers, in line with the shape-structure concept, whereas no structures are observed for the largest surfactant 14. A CD spectroscopic titration of -phage DNA with surfactants 12 and 14 showed that there was some interaction, although the secondary structure of the DNA was hardly affected. The effects of the novel surfactants and commercially available DOTAP [N-(2,3-dioleoyloxypropyl)-N,N,N-trimethylammonium methyl sulfate] were identical when compared on the basis of charge complimentarity, indicating that the complexation of DNA with the surfactant is a process of ion exchange. DNA binding was confirmed by the ability of all surfactants (10, 12, and 14) to release ethidium bromide from its complex with DNA in an agarose gel electrophoresis experiment. Both lysine-containing surfactants 12 and 14 showed activity in a luciferase gene-transfection assay but this was accompanied by a considerable toxicity.