Aggregation Properties of Diacyl Lysine Surfactant Compounds: Hydrophobic Chain Length and Counterion Effect

New antimicrobial self-assembling short lipopeptides

Lipopeptides are an exceptional example of amphiphilic molecules that self-assemble into functional structures with applications in the areas of nanotechnology, catalysis or medicinal chemistry. Herein, we report a library of 21 short lipopeptides, together with their supramolecular characterization and antimicrobial activity against both Gram-negative (E. coli) and Gram-positive (S. aureus) strains. This study shows that simple lipoamino acids self-assemble into micellar or vesicular structures, while incorporating dipeptides capable of stablishing hydrogen bonds results in the adoption of advanced fibrilar structures. The self-assembly effect has proven to be key to achieve antimicrobial activity.

Design, synthesis and properties investigation of Nα-acylation lysine based derivatives

Amino acid-based compounds have attracted attention as environmentally friendly bio-based materials. Our group has recently developed a novel family of N^α-acylation lysine based derivatives. We introduced long chain acyl groups at the N^α position selectively by a new synthetic route that avoided the process of amino protection and deprotection. Sodium N^α-octanamide lysine (C8), sodium N^α-capramide lysine (C10) and sodium N^α-lauramide lysine (C12) can self-assemble into vesicles spontaneously. As a result, not only do they have potential in drug delivery system but also they may be used as bio-based surfactants applied in cosmetics and other industries.

A novel method has been developed for synthesizing N^α-acylation lysine based derivatives by introducing long chain acyl groups at the N^α position of lysine selectively.

Role of Capping Agent in Wet Synthesis of Nanoparticles

Aqueous-based synthesis is one of the most popular methods to prepare nanoparticles. In these procedures, surfactants are needed to regulate the growth and final particle size. While there are numerous evidence on the decisive role of surfactants, a quantitative description remains elusive. This study develops a theoretical model to correlate the surfactant activities to particle growth. In the model, the "penetrability" of ions within surfactant layer is used to combine surface reaction and adsorption/desorption processes. The penetrability was then directly correlated to surfactant size. The theory was verified by synthesis of iron oxide nanoparticles with series of cationic surfactants. Eight surfactants, with same headgroup and increasing hydrocarbon tail, were employed. The experimental data showed a deterministic correlation between surfactant tails and particle size. The experimental correlation between surfactant length and particle size was predicted by the model. The modeling results verify the role of surfactant as capping agent during particle growth. More importantly, it provides a theoretical framework to control particle size in wet synthesis.

Nioplexes encapsulated in supramolecular hybrid biohydrogels as versatile delivery platforms for nucleic acids

Supramolecular hydrogels based on N-protected phenylalanine (Fmoc–Phe–OH) were used to encapsulate non-ionic surfactant vesicles (niosomes).

Effect of fatty acids on self-assembly of soybean lecithin systems

With the increasing interest in natural formulations for drug administration and functional foods, it is desirable a good knowledge of the phase behavior of lecithin/fatty acid formulations. Phase structure and properties of ternary lecithin/fatty acids/water systems are studied at 37°C, making emphasis in regions with relatively low water and fatty acid content. The effect of fatty acid saturation degree on the phase microstructure is studied by comparing a fully saturated (palmitic acid, C16:0), monounsaturated (oleic acid, C18:1), and diunsaturated (linoleic acid, C18:2) fatty acids. Phase determinations are based on a combination of polarized light microscopy and small-angle X-ray scattering measurements. Interestingly, unsaturated (oleic acid and linoleic acid) fatty acid destabilizes the lamellar bilayer. Slight differences are observed between the phase diagrams produced by the unsaturated ones: small lamellar, medium cubic and large hexagonal regions. A narrow isotropic fluid region also appears on the lecithin-fatty acid axis, up to 8wt% water. In contrast, a marked difference in phase microsctructure was observed between unsaturated and saturated systems in which the cubic and isotropic fluid phases are not formed. These differences are, probably, a consequence of the high Krafft point of the C16 saturated chains that imply rather rigid chains. However, unsaturated fatty acids result in more flexible tails. The frequent presence of, at least, one unsaturated chain in phospholipids makes it very likely a better mixing situation than in the case of more rigid chains. This swelling potential favors the formation of reverse hexagonal, cubic, and micellar phases. Both unsaturated fatty acid systems evolve by aging, with a reduction of the extension of reverse hexagonal phase and migration of the cubic phase to lower fatty acid and water contents. The kinetic stability of the systems seems to be controlled by the unsaturation of fatty acids.

Self assembly of pH-sensitive cationic lysine based surfactants

Three cationic surfactants of the type N(ε)-acyl lysine methyl ester hydrochloride have been studied with respect to solution behavior and adsorption on the air/water interface, as well as the thermolyotropic behavior. The self-assembly of these surfactants, which have the cationic charge on amine protonated groups, was assessed by different physicochemical methods. Depending on the pH value, these surfactants can dissociate in aqueous solutions, losing the cationic charge. Therefore, knowledge of the pK(a) of these compounds is essential to explain their behavior in aqueous solutions. The bulk techniques, conductivity, and nuclear magnetic resonance diffusion (NMR) obtained similar critical micellar concentration (CMC) values, which were well above those obtained from surface tension. Surface tension measurements were strongly dependent on the technique used, namely, Wilhelmy plate and pendant drop. The phase behavior at medium to high concentrations has been studied by optical polarizing microscopy and small angle x-ray scattering (SAXS). The X-ray studies showed that the lysine-based surfactants at low hydration have rich thermotropic liquid crystalline behavior. The results are discussed in terms of the structure of the compounds and the cationic charge of the molecule. We will show how apparently small changes in molecule structure have a large influence on phase behavior.

Lysine-bisglycidol conjugates as novel lysine cationic surfactants

The synthesis of a novel class of lysine-based cationic amphiphilic derivatives of the type N(epsilon),N(epsilon)'-bis(n-acyloxypropyl)-l-lysine methyl ester salts combining several hydroxyl functions and aliphatic chains of 12 or 14 carbon atoms is described. The compounds have one, two, three, and four alkyl chains. Aggregation in water was studied by four different methods: surface tension, conductivity, chloride ion activity, and nuclear magnetic resonance ((1)H NMR). The critical aggregation concentration value of the new surfactants depends on both the number of alkyl chains and the alkyl chain length. The formation of vesicles at low concentrations was confirmed by H(1) NMR and optical microscopy. Antimicrobial activity was determined on the basis of the minimum inhibitory concentration (MIC) values. These novel lysine-based surfactants showed moderate antimicrobial activity which may be an important advantage for many biomedical applications.