Investigation on the self-assembled behaviors of C₁₈unsaturated fatty acids in arginine aqueous solution

Abstract

In the field of drug delivery, there is growing concern over the self-assembly of fatty acids, since their structures and properties are similar to liposomes, which are characteristically nontoxic for humans, possess good biocompatibility and biodegradation, and are without immunogenicity. Changes in pH, temperature, concentration, molecular structure of the amphiphilic molecule, head group type and hydrocarbon chain length have significant effects on the self-assembled structures; however, the degree of unsaturation can also influence the self-assembled structures of fatty acids. The aggregation behaviors of the mixtures of arginine and three kinds of unsaturated fatty acids (UFAs, oleic acid, linoleic acid and linolenic acid) in aqueous solutions have been investigated. Phase transition from transparent micelles (L 1 phase) to birefringent bilayer structures (L a phase) occurred with increasing amounts of UFAs. However, the L a phase was different for macro and micro structures. Oleic acid with only one double bond was regarded as less flexible and curved, but with higher stacking, leading to a gradual phase transition process from the vesicle phase to the stacked lamellar phase in the L a phase region, which could be proved by cryogenic transmission electron microscopy (cryo-TEM) and polarizing microscopy observations combined with 2 H-nuclear magnetic resonance ( 2 H NMR) and rheological properties. The turbid vesicle phase with weak viscoelastic properties were only observed in linoleic acid and linolenic acid systems because UFAs with more than one double bond are easier to bend, indicating that highly curved vesicles are likely to form. Through the analysis of the proposed mechanism and FT-IR spectra, the synergistic effects of non-covalent interactions, including hydrogen bonding, electrostatic interaction, and hydrophobicity, were considered to be responsible for the aggregation behaviors. Finally, vesicles displayed their potential in encapsulating water-soluble model drugs such as calcein. The results show that drug-loaded vesicles could play a role in the potential applications in drug sustained delivery systems.

Adsorption Behavior and Wettability of Rhodochrosite Surface: Effect of C18 Fatty Acid Unsaturation

“…For unsaturated fatty acids, OA has the smallest value of γ CMC , while ALA has the largest γ CMC , which may be due to that the greater number of C=C bond in ALA, the less hydrophobic of the carbon chain, resulting in higher γ LG when micelles are formed, indicating that the unsaturation degree also affects the self-assembly of fatty acids. This conclusion is supported by other literature [46]. It is considered that small micelles may be formed in the range of fatty acid concentrations ranging from the premicellar concentration to CMC, while spherical micelles may be formed at the CMC.…”

Controlling Foam Stability with the Ratio of Myristic Acid to Choline Hydroxide

“…In fatty acid systems, different studies have clearly evidenced the effect of the molar ratio in bulk. 1,[35][36][37][38][39][40][41] For the myristic acid/choline hydroxide system, facetted vesicles, unilamellar and multilamellar vesicles, lamellar phases and spherical micelles have been observed as a function of R.…”

“…R sets the pH of the aqueous solution, which in turns governs the ionization state of the fatty acids and the headgroup interactions leading to the broad polymorphism in bulk. In fatty acid systems, different studies have clearly evidenced the effect of the molar ratio in bulk. ,− For the myristic acid/choline hydroxide system, faceted vesicles, unilamellar and multilamellar vesicles, lamellar phases, and spherical micelles have been observed as a function of R .…”

Methods for Forming Giant Unilamellar Fatty Acid Vesicles

“…As a rough guide, the pK a increases with fatty acid chain length, with decanoic acid (10 carbons) having an apparent pK a of approximately pH 7, and oleic acid (18 carbons) having an apparent pK a of approximately 8.5. The apparent pK a is also known to decrease with an increase in the solution's ionic strength, and in the lipid's unsaturation [8]. Some values from the literature are reported in Table 1.…”