The aim of this work was to elucidate the structure-activity relationship of new peptide-modified gemini surfactant-based carriers. Glycyl-lysine modified gemini surfactants that differ in the length and degree of unsaturation of their alkyl tail were used to engineer DNA nano-assemblies. To probe the optimal nitrogen to phosphate (N/P) ratio in the presence of helper lipid, in vitro gene expression and cell toxicity measurements were carried out. Characterization of the nano-assemblies was accomplished by measuring the particle size and surface charge. Morphological characteristics and lipid organization were studied by small angle X-ray scattering technique. Lipid monolayers were studied using a Langmuir-Blodgett trough. The highest activity of glycyl-lysine modified gemini surfactants was observed with the 16-carbon tail compound at 2.5 N/P ratio, showing a 5- to 10-fold increase in the level of reporter protein compared to the 12 and 18:1 carbon tail compounds. This ratio is significantly lower compared to the previously studied gemini surfactants with alkyl or amino- spacers. In addition, the 16-carbon tail compound exhibited the highest cell viability (85%). This high efficiency is attributed to the lowest critical micelle concentration of the 16-tail gemini surfactant and a balanced packing of the nanoparticles by mixing a saturated and unsaturated lipid together. At the optimal N/P ratio, all nanoparticles exhibited an inverted hexagonal lipid assembly. The results show that the length and nature of the tail of the gemini surfactants play an important role in determining the transgene efficiency of the delivery system. We demonstrated here that the interplay between the headgroup and the nature of tail is specific to each series, thus in the process of rational design, the contribution of the latter should be assessed in the appropriate context.

The phase separation of immiscible surfactants in mixed monolayer films provides an approach to physically manipulate important properties of thin films, including surface morphology, microscale composition, and mechanical properties. In this work, we predict, based upon existing miscibility studies and their thermodynamic underpinnings described in the literature, the miscibility and film morphology of mixed monolayers comprised of behenic acid (C21H43COOH) and perfluorotetradecanoic acid (C13F27COOH) in various molar ratios. Predictions are tested using a combination of experimental surface characterization methods for probing miscibility and film morphology at the solid/air and air/water interfaces. Film components were immiscible and phase-separated into chemically well-defined domains under a variety of experimental conditions, with monolayer morphology consistent with initial predictions. The extensibility of these basic predictions to other systems is discussed in the context of using these works for different perfluorinated surfactant molecules.

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Mixed monolayer surfactant films of perfluorotetradecanoic acid and the photopolymerizable diacetylene molecule 10,12-pentacosadiynoic acid were prepared at the air-water interface and transferred onto solid supports via Langmuir-Blodgett (LB) deposition. The addition of the perfluoroacid to the diacetylene surfactant results in enhanced stabilization of the monolayer in comparison with the pure diacetylene alone, allowing film transfer onto a solid substrate without resorting to addition of cations in the subphase or photopolymerization prior to deposition. The resulting LB films consisted of well-defined phase-separated domains of the two film components, and the films were characterized by a combination of atomic force microscope (AFM) imaging and fluorescence emission microscopy both before and after photopolymerization into the highly emissive "red form" of the polydiacetylene. Photopolymerization of the monolayer films resulted in the formation of diacetylene bilayers, which were highly fluorescent, with the apparent rate of photopolymerization and the fluorescence emission of the films being largely unaffected by the presence of the perfluoroacid.

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