Effect of alkyl chain asymmetry on catanionic mixtures of hydrogenated and fluorinated surfactants

Accumulation and glucocorticoid signaling suppression by four emerging perfluoroethercarboxylic acids based on animal exposure and cell testing

Various perfluoroethercarboxylic acids (PFECA) have emerged as next-generation replacements of legacy per- and polyfluoroalkyl substances (PFAS). However, there is a paucity of information regarding their bioaccumulation ability and hazard characterization. Here, we explored the accumulation and hepatotoxicity of four PFECA compounds (HFPO-DA, HFPO-TA, PFO4DA, and PFO5DoDA) in comparison to perfluorooctanoic acid (PFOA) after chronic low-dose exposure in mice. Except for HFPO-DA, the levels of all tested PFAS in the liver exceeded that in serum. High molecular weight PFECA compounds (PFO5DoDA and HFPO-TA) showed stronger accumulation capacity and longer half-lives (t1/2) than low molecular weight PFECA compounds (HFPO-DA and PFO4DA) and even legacy PFOA. Although hepatomegaly is a common apical end point of PFAS exposure, the differentially expressed gene (DEG) profiles in the liver suggested significant differences between PFOA and the four PFECA compounds. Gene enrichment analysis supported a considerable inhibitory effect of PFECA, but not PFOA, on the glucocorticoid receptor (GR) signaling pathway. Both HFPO-TA and PFO5DoDA demonstrated a more pronounced ability to perturb RNA expression profiles in vivo and to suppress GR signaling in vitro compared to HFPO-DA and PFO4DA. Calculated reference doses (RfDs) emphasized the potential hazard of PFECA to human health. Overall, our findings indicate that PFECA alternatives do not ease the concerns raised from legacy PFAS pollution.

Tailoring microstructural, drug release properties, and antichagasic efficacy of biocompatible oil-in-water benznidazol-loaded nanoemulsions

This study explored the transition of lamellar-type liquid crystal (LLC) to biocompatible oil-in-water nanoemulsions able to modify benznidazole (BNZ) release and target the drug to cells infected with the T. cruzi parasite. Three cosolvents (2methylpyrrolidone [NMP], polyethylene glycol [POL], and propylene glycol [PRO] were tested to induce the transition of anisotropic LLC systems to isotropic nanoemulsions. Mixtures of soy phosphatidylcholine with sodium oleate stabilized the dispersions of medium chain triglyceride in water. Rheological measurements, polarized microscopy, and small angle X-ray scattering demonstrated that there is a phase transition from LLC to desired nanoemulsions. These small and narrow droplet-sized nanocarriers exhibited some advantages and promising features, such as the enhanced BNZ aqueous solubility and slow drug release rate. In vitro cell biocompatibility of formulations was assessed in the Vero E6 and SiHa cell lines. Drug-loaded nanoemulsions inhibited the epimastigote growth of the T. cruzi parasite (IC50 0.208 ± 0.052 μg mL^-1) and reduced its infective life form trypomastigote (IC50 0.392 ± 0.107 μg mL^-1). The oil-in-water nanoemulsions were demonstrated as promising biocompatible liquid drug delivery systems capable of improving the BNZ trypanocidal activity for the treatment of Chagas disease.

Formation of polyhedral vesicle gels from catanionic mixtures of hydrogenated and perfluorinated surfactants: effect of fluoro-carbon alkyl chain lengths

The effects of alkyl chain length of anionic fluorinated fatty acid surfactants, CnF2n+1COOH (n = 7-11), mixed with one cationic hydrocarbon surfactant, tetradecyltrimethylammonium hydroxide (TTAOH), on the formation of polyhedral vesicle gels were investigated in aqueous solutions. On the basis of phase behavior mapping, C8F17COOH, C9F19COOH, C10F21COOH and C11F23COOH except C7F15COOH all formed polyhedral vesicle gels when they were mixed with TTAOH under certain mixed ratios, which was demonstrated by freeze-fracture transmission electron microscopy (FF-TEM) measurements. Meanwhile, the following observation was not observed: the longer the fluorinated alkyl chain, the more effective the formation of gels by fluorinated fatty acids. The formation of the faceted vesicle gels was determined both by the rigidity of the fluorinated alkyl chain and the co-crystallization of fluorocarbon chains and hydrocarbon chains, as revealed by the results of differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS) and 19F NMR measurements. Furthermore, the polyhedral vesicle gels showed high viscoelasticity, which increased clearly with increasing fluorinated alkyl chain length, indicating that the viscoelastic property of the polyhedral vesicle gel was a result of the crystalline state of the polyhedral vesicle bilayers at room temperature. As far as we know, such polyhedral vesicle gels formed from perfluorinated and hydrocarbon surfactant mixtures have been rarely reported. Our study can be a great advancement in fundamental research of surfactant vesicle gels.

Rheological Characterization of Mixed Surfactant Films at Droplet Interfaces via Micropipette Aspiration

Cationic and anionic surfactant mixtures can form viscous films that dominate the rheology and stability of micrometer-sized droplet suspensions. In this work, we use micropipette aspiration to study the mechanical properties of mixed surfactant surface films of anionic sodium dodecyl sulfate (SDS) and cationic dodecylamine hydrochloride (DAH) on alkane and lipid droplets. For octane droplets, SDS was found to decrease the surface tension until a minimum of 5 ± 1 mJ/m² was reached after the critical micelle concentration (cmc). The surface viscosity of the droplets was found to be on the order of 10^-3 mN s/m at an SDS concentration of 10 mM. An addition of 0.2 mM of DAH was found to increase this viscosity to a peak of 0.24 ± 0.01 mN s/m. Similar to octane, the surface tension of dodecane decreased to a value of 7.7 ± 0.4 mJ/m² at SDS concentrations above cmc. Unlike with octane, however, the dodecane droplets had a significant surface viscosity of 0.37 ± 0.01 mN s/m when only the 10 mM SDS film was present. An addition of DAH caused a decrease in this viscosity initially, before rising to a peak viscosity of 0.45 ± 0.01 mN s/m at a DAH concentration of 0.15 mM. We speculate that the peaks in viscosities were the result of the completions of a phase change associated with microcrystalline SDS/DAH grains growing in the film at the surface of the droplets. Fluorescence microscopy and visual observations provided further evidence that these films can show rigid microcrystalline-like structure. Further work done with soybean oil in the same conditions and with a lipid film, simulating biological lipid droplets, confirmed that lipid droplets behave rheologically similar to alkanes in the presence of these mixed surfactant and lipid films. These results imply that droplet mechanics may be heavily influenced by the presence of microcrystalline grains in the oil-water systems with complex surfactant mixtures.

Synergistic Adsorption and Flotation of New Mixed Cationic/Nonionic Collectors on Muscovite

The mixed cationic collector cetyltrimethylammonium chloride (CTAC) and nonionic collector octanol (OCT) was found to exhibit a synergistic effect on the flotation and adsorption of muscovite. To understand the underlying synergistic mechanism, flotation, contact angle, surface tension, and adsorption measurements were carried out. The results obtained from flotation measurements indicated that the mixed CTAC/OCT exhibits a better collecting ability than CTAC or OCT. The recovery of muscovite with CTAC only rapidly decreased from 97.25% at pH 2.64 to 75.26% at pH 5.82, followed by a flat horizontal at a pH is higher than 6. In contrast, a high recovery of greater than 85% muscovite was observed using mixed CTAC/OCT at α CTAC = 0.67 (the mole ratio of CTAC:OCT = 2:1) over the investigated pH range. From the surface activity parameters (CMC, γ CMC, Γmax, Amin) estimated from surface measurements and interaction parameters (βm, βσ), in addition to the micellar and interfacial compositions ( x 1 m , x 1 σ ) obtained from the theory of regular solutions, a synergistic effect is evident in the mixed micelle and at the water/air interface. Moreover, the mixed CTAC/OCT at α CTAC = 0.67 exhibited the maximum synergistic interaction. The results obtained from surface tension measurements indicated that the mixed CTAC/OCT exhibits considerably higher surface activities compared to single CTAC or OCT. The contact angle results confirmed that the mixed CTAC/OCT is a better collector than the individual CTAC or OCT for the flotation of muscovite. According to the results obtained from adsorption experiments, compared with that of individual CTAC or OCT, the amounts of CTAC and OCT adsorbed on the muscovite surface are considerably increase in the mixed systems because of co-adsorption. Based on these results, the mixed CTAC/OCT exhibits a remarkable synergistic effect during the flotation and adsorption of muscovite.

Formation and rheological behavior of wormlike micelles in a catanionic system of fluoroacetic acid and tetradecyldimethylaminoxide

From catanionic fluoro-/hydro-carbon mixtures of fluoroacetic acid (CF₃COOH) and tetradecyldimethylaminoxide (C₁₄DMAO) in water, viscoelastic wormlike micelles are successfully constructed which are determined by cryo-TEM measurements. It is found that the formation and rheological behavior of the wormlike micelles are greatly affected by the total concentration and mixing ratio of CF₃COOH and C₁₄DMAO as well as temperature. The driving force for the formation of wormlike micelles here is considered to be the electrostatic attractive interaction between the two molecules which is confirmed by ¹H NMR measurements. As far as we know, such wormlike micelles formed from the catanionic mixtures of fluorofatty acids and hydrocarbon surfactants have been rarely reported. Our work provides a simple method through mixing a perfluorofatty acid with a hydrocarbon surfactant to construct and understand the formation mechanism of catanionic fluoro-/hydro-carbon wormlike micelles, which should be a great advance in the fundamental research of wormlike micelles.

Vesicle formation of catanionic mixtures of CTAC/SDS induced by ratio: a coarse-grained molecular dynamic simulation study

A vesicle was formed by disk-like bilayer curling.

Synthesis of Branch Fluorinated Cationic Surfactant and Surface Properties

A novel fluorinated quaternary ammonium salt cationic surfactant N,N,N-trimethyl-2-[[4-[[3,4,4,4-tetrafluoro-2-[1,2,2,2-tetrafluoro-1-(trifluoromethyl)ethyl]-1,3-bis(tri-fluoromethyl)-1-buten-1-yl]oxy]-benzoyl]amino]-iodide (FQAS) was synthesized successfully, and its structure was characterized by FTIR,1H-NMR,19F-NMR, and MS. The surface activities of FQAS and the effect of temperature, electrolyte, and combination with hydrocarbon surfactant were investigated. The results showed that FQAS exhibited excellent surface activity and combination with hydrocarbon surfactant.

Polyhedral vesicles with crystalline bilayers formed from catanionic surfactant mixtures of fluorocarbon and hydrocarbon amphiphiles

Salt-free catanionic mixtures of perfluorononanoic acid (C8F17COOH) and tetradecyltrimethylammonium hydroxide (TTAOH) in aqueous solution show rich and interesting self-assembly properties. With the addition of TTAOH to a C8F17COOH solution, a structural transition from polyhedral vesicles with crystalline bilayers to spherical vesicles with fluid bilayers was observed at room temperature, which was demonstrated by cryo- and FF-TEM observations, DSC and WAXS measurements. It is interesting that both uni-lamellar and multi-lamellar polyhedral vesicles were formed in these fluoro- and hydrocarbon catanionic surfactant mixtures. SAXS measurements were performed to determine the interlamellar spacing of the multi-lamellar polyhedral vesicles. The driving force for the formation of the polyhedral vesicles was the crystallization of the C8F17COO(-) - TTA(+) ion pairs in the bilayers, which induced the excess anionic surfactants to be segregated and concentrated to produce the vertices of the polyhedral vesicles. Besides, the rheological results show that the rheological properties of the C8F17COOH/TTAOH system are greatly affected by the fluorocarbon chains due to their high rigidity and Krafft point. The solutions consisting of polyhedral vesicles have high viscoelasticity and high yield stress values while spherical vesicle solutions are not viscoelastic.

Hydrogenated/fluorinated catanionic surfactants as potential templates for nanostructure design

The structure and physicochemical properties of the nanoparticles spontaneously formed within aqueous mixtures of the hydrogenated/fluorinated catanionic surfactant cetyltrimetylammonium perfluorooctanoate in the absence of counterions as a function of its concentration are investigated by a combined experimental/computational study at room temperature. Apparent molar volumes, isentropic apparent molar compressibilities, and dynamic light scattering measurements together with transmission and cryo-scanning electron as well as confocal laser microscopy images, and computational molecular dynamics simulations indicate that a variety of structures of different sizes coexist in solution with vesicles of ∼160 nm diameter. Interestingly, the obtained nanostructures were observed to self-assemble from a random distribution of monomers in a time scale easily accessible by atomistic classical molecular dynamics simulations, allowing to provide a comprehensive structural and dynamic characterization of the surfactant molecules at atomic level within the different aggregates. Overall, it is demonstrated that the use of mixed fluorinated hydrogenated surfactant systems represents an easy strategy for the design of specific nanoscale structures. The detailed structural analysis provided in the present work is expected to be useful as a reference to guide the design of new nanoparticles based on different hydrogenated/fluorinated catanionic surfactants.