Ultrastable and Responsive Foams Based on 10-Hydroxystearic Acid Soap for Spore Decontamination.

Currently, there is renewed interest in using fatty acid soaps as surfactants. Hydroxylated fatty acids are specific fatty acids with a hydroxyl group in the alkyl chain, giving rise to chirality and specific surfactant properties. The most famous hydroxylated fatty acid is 12-hydroxystearic acid (12-HSA), which is widely used in industry and comes from castor oil. A very similar and new hydroxylated fatty acid, 10-hydroxystearic acid (10-HSA), can be easily obtained from oleic acid by using microorganisms. Here, we studied for the first time the self-assembly and foaming properties of R-10-HSA soap in an aqueous solution. A multiscale approach was used by combining microscopy techniques, small-angle neutron scattering, wide-angle X-ray scattering, rheology experiments, and surface tension measurements as a function of temperature. The behavior of R-10-HSA was systematically compared with that of 12-HSA soap. Although multilamellar micron-sized tubes were observed for both R-10-HSA and 12-HSA, the structure of the self-assemblies at the nanoscale was different, which is probably due to the fact that the 12-HSA solutions were racemic mixtures, while the 10-HSA solutions were obtained from a pure R enantiomer. We also demonstrated that stable foams based on R-10-HSA soap can be used for cleaning applications, by studying spore removal on model surfaces in static conditions via foam imbibition.

Aqueous Binary Mixtures of Stearic Acid and Its Hydroxylated Counterpart 12-Hydroxystearic Acid: Cascade of Morphological Transitions at Room Temperature.

Here, we describe the behavior of mixtures of stearic acid (SA) and its hydroxylated counterpart 12-hydroxystearic acid (12-HSA) in aqueous mixtures at room temperature as a function of the 12-HSA/SA mole ratio R. The morphologies of the self-assembled aggregates are obtained through a multi-structural approach that combines confocal and cryo-TEM microscopies with small-angle neutron scattering (SANS) and wide-angle X-ray scattering (WAXS) measurements, coupled with rheology measurements. Fatty acids are solubilized by an excess of ethanolamine counterions, so that their heads are negatively charged. A clear trend towards partitioning between the two types of fatty acids is observed, presumably driven by the favorable formation of a H-bond network between hydroxyl OH function on the 12th carbon. For all R, the self-assembled structures are locally lamellar, with bilayers composed of crystallized and strongly interdigitated fatty acids. At high R, multilamellar tubes are formed. The doping via a low amount of SA molecules slightly modifies the dimensions of the tubes and decreases the bilayer rigidity. The solutions have a gel-like behavior. At intermediate R, tubes coexist in solution with helical ribbons. At low R, local partitioning also occurs, and the architecture of the self-assemblies associates the two morphologies of the pure fatty acids systems: they are faceted objects with planar domains enriched in SA molecules, capped with curved domains enriched in 12-HSA molecules. The rigidity of the bilayers is strongly increased, as well their storage modulus. The solutions remain, however, viscous fluids in this regime.

Aqueous Binary Mixtures of Stearic Acid and Its Hydroxylated Counterpart 12-Hydroxystearic Acid: Fine Tuning of the Lamellar/Micelle Threshold Temperature Transition and of the Micelle Shape.

This study examines the structures of soft surfactant-based biomaterials which can be tuned by temperature. More precisely, investigated here is the behavior of stearic acid (SA) and 12-hydroxystearic acid (12-HSA) aqueous mixtures as a function of temperature and the 12-HSA/SA molar ratio (R). Whatever R is, the system exhibits a morphological transition at a given threshold temperature, from multilamellar self-assemblies at low temperature to small micelles at high temperature, as shown by a combination of transmittance measurements, Wide Angle X-ray diffraction (WAXS), small angle neutron scattering (SANS), and differential scanning calorimetry (DSC) experiments. The precise determination of the threshold temperature, which ranges between 20 °C and 50 °C depending on R, allows for the construction of the whole phase diagram of the system as a function of R. At high temperature, the micelles that are formed are oblate for pure SA solutions (R = 0) and prolate for pure 12-HSA solutions (R = 1). In the case of mixtures, there is a progressive continuous transition from oblate to prolate shapes when increasing R, with micelles that are almost purely spherical for R = 0.33.

Influence of critical micelle concentration of choline-based long chain fatty acid soaps on their antibacterial activity against Methicillin resistant Staphylococcus aureus.

HYPOTHESIS: Antimicrobial resistance (AMR) is a pressing global health concern. ESKAPEE pathogens, such as Methicillin-resistant Staphylococcus aureus (MRSA) are notable of concern in healthcare settings due to their resistance to critical antibiotics. To combat AMR, the development of alternatives such as bacterial membrane-active agents is crucial. Fatty acids (FAs) have emerged as a sustainable, antibiotic-free solution with inherent antibacterial activity. However, long chain saturated fatty acids (LCFAs) sodium soaps exhibit poorly antibacterial properties in comparison to short chain FAs, believed to be linked to limited solubility in aqueous media. EXPERIMENTS: We employed choline as a chaotropic organic counter-ion to enhance the solubility of LCFAs and investigated their antibacterial effects against MRSA. The optimal medium conditions for micelle formation for LCFAs was first investigated. Then, we determined the critical micelle concentration (CMC), micellar morphology, and aggregation number through surface tension measurements and small angle neutron scattering experiments. Antimicrobial activity was assessed using minimum bactericidal concentration (MBC) assays and time-kill experiments. FINDINGS: We have identified conditions where LCFAs are effective against MRSA for the first time, providing valuable insights for developing new antibacterial agents to fight AMR. LCFAs need to be used above their Krafft temperatures and CMC to exhibit antibacterial efficacy.

12-hydroxystearic acid-mediated in-situ surfactant generation: A novel approach for organohydrogel emulsions.

HYPOTHESIS: Organohydrogel emulsions display unique rheological properties and contain hydrophilic and lipophilic domains highly desirable for the loading of active compounds. They find utility in various applications from food to pharmaceuticals and cosmetic products. The current systems have limited applications due to complex expensive formulation and/or processing difficulties in scale-up. To solve these issues, a simple emulsification process coupled with unique compounds are required. EXPERIMENTS: Here, we report an organohydrogel emulsion based only on a low concentration of 12-hydroxystearic acid acting as a gelling agent for both oil and water phases but also as a surfactant. The emulsification process is based on in-situ surfactant transfer. We characterize the emulsification process occurring at the nanoscale by using tensiometry experiments. The emulsion structure was determined by coupling Small Angle X-ray and neutron scattering, and confocal Raman microscopy. FINDINGS: We demonstrate that the stability and unique rheological properties of these emulsions come from the presence of self-assembled crystalline structures of 12-hydroxystearic acid in both liquid phases. The emulsion properties can be tuned by varying the emulsion composition over a wide range. These gelled emulsions are prepared using a low energy method offering easy scale-up at an industrial level.

Norovirus capsid proteins self-assemble through biphasic kinetics via long-lived stave-like intermediates.

The self-assembly kinetics for a norovirus capsid protein were probed by time-resolved small-angle X-ray scattering and then analyzed by singular value decomposition and global fitting. Only three species contribute to the total scattering intensities: dimers, intermediates comprising some 11 dimers, and icosahedral T = 3 capsids made up of 90 dimers. Three-dimensional reconstructions of the intermediate robustly show a stave-like shape consistent with an arrangement of two pentameric units connected by an interstitial dimer. Upon triggering of self-assembly, the biphasic kinetics consist of a fast step in which dimers are assembled into intermediates, followed by a slow step in which intermediates interlock into capsids. This simple kinetic model reproduces experimental data with an excellent agreement over 6 decades in time and with nanometer resolution. The extracted form factors are robust against changes in experimental conditions. These findings challenge and complement currently accepted models for the assembly of norovirus capsids.

4-Sulfonatocalix[6]arene-induced aggregation of ionic liquids.

The interaction of 4-sulfonatocalix[6]arene (SCX6) macrocycle with 1-alkyl-3-methylimidazolium type of ionic liquids possessing dodecyl, tetradecyl, or hexadecyl substituent was studied in aqueous solution at 298 K. Host-guest complexation promoted the spontaneous self-assembly into nanoparticles of 7:1 ionic liquid:SCX6 stoichiometry. Positively charged and stable nanoparticles were produced in solutions of 7-200-fold excess of ionic liquid as compared to the amount of SCX6. The negatively charged nanoparticles formed in solutions having 2-7 ionic liquid:SCX6 molar ratios evolved into larger species. The stability of the nanoparticles increased with the lengthening of aliphatic chain of the ionic liquid. Cryo-TEM experiments showed dense particles generally with spherical shape and multilayered structure, which has been confirmed by small-angle neutron scattering.

Polymer-metal-organic framework self-assembly (PMOFSA) as a robust one-step method to generate well-dispersed hybrid nanoparticles in water.

A new process, PMOFSA, is described here, that opens the way for the one-pot straightforward and versatile manufacture of polymer-MOF nanoparticles in water. It can be expected that this study will not only expand the scope of in situ preparation of polymer-MOF nano-objects but also inspire researchers in the field to prepare a new generation of polymer-MOF hybrid materials.

Unexpected Slow Kinetics of Poly(Methacrylic Acid) Phase Separation in the Semi-Dilute Regime.

Poly (methacrylic acid) (PMAA) solutions are known to exhibit a lower critical solution temperature (LCST). A temperature-composition phase diagram of PMAA has been constructed by standard cloud point determination through transmittance measurements, and also by studying the steady states reached under phase separation. This allows us to reconstruct the binodal curve describing the phase behavior of PMAA for both low and high concentration regimes, and to determine accurately the LCST temperature. In a second step, the structures formed following a temperature jump above the cloud point and their evolution in time have been investigated at the nanoscale using small angle neutron scattering (SANS). This approach shows that the formation of phase-separated nanostructures is a slow process, requiring more than 12 h. The formed structures are then shown to depend on the amplitude of the temperature jump above the cloud point. An original mechanism of phase separation is identified in the semi-dilute regime. The growth of micrometric-size droplets with an inner structure displaying the rheological properties of a gel leads to the formation of a percolating network which hinders the influence of gravity. Such a result can explain the slow kinetics of the PMAA LCST transition.