Interaction between Sophorolipids and β-glucan in Aqueous Solutions

Skin disorders, including acne vulgaris, atopic dermatitis, and rosacea, are characterized by the presence of biofilms, which are communities of microorganisms. The mechanical stability of biofilms is attributed to one of their constituents-polysaccharides-which are secreted by microorganisms. Sophorolipids are biosurfactants with biofilm disruption and removal abilities and are expected to become alternatives for classical petrochemical-based surfactants in cosmetics. In this study, we investigated the influence of sophorolipids on β-glucan such as dispersion status, interaction mechanism, and configuration change as a model polysaccharide of biofilm in aqueous solution. Dynamic light scattering measurements showed that sophorolipids interfere with the aggregation of β- glucan in aqueous solutions. In contrast, sodium dodecyl sulfate (SDS), which is used as a typical surfactant reference, promotes the aggregation of β-glucan. The interaction between sophorolipids and β-glucan were investigated using surface tension measurements and isothermal titration calorimetry (ITC). Surface tension increased only near critical micelle concentration (CMC) region of sophorolipids in the presence of β-glucan. This suggests that the interaction occurred in the solution rather than at the air-liquid interface. Moreover, the results of ITC indicate that hydrophobic interactions were involved in this interaction. In addition, the results of optical rotation measurements indicate that sophorolipids did not unfold the triple helical structure of β-glucan. β-glucan dispersion was expected to be caused steric hindrance and electrostatic repulsion when sophorolipids interacted with β-glucan via hydrophobic interactions owing to the unique molecular structure of sophorolipids attributed by a bulky sugar moiety and a carboxyl functional group. These results demonstrated unique performances of sophorolipids on β-glucan and provided more insights on the efficacy of sophorolipids as good anti-biofilms.

Effects of Counterion on the Formation and Hydration Behavior of α-Form Hydrated Crystals (α-Gels)

α-Form hydrated crystals form a lamellar gel in which the alkyl chains of the amphiphilic molecules are hexagonally arranged within bilayers below the gel-liquid crystal phase transition temperature. In practice, the lamellar gel network with excess water is called an "α-gel", particularly in the cosmetics industry. In this study, the hydration or water sorption of amphiphilic materials in water vapor was assessed using a humidity-controlled quartz crystal microbalance with dissipation monitoring (QCM-D) technique. The amphiphilic materials used in this study were hexadecyl phosphate salts neutralized with L-arginine (C16P-Arg), CsOH (C16P-Cs), KOH (C16P-K), and NaOH (C16P-Na). Small- and wide-angle X-ray scattering measurements revealed that C16P-Arg and C16P-Cs yielded α-form hydrated crystals. Humidity-controlled QCM-D measurements demonstrated that C16P-Arg and C16P-Cs more readily underwent hydration or water sorption than C16P-K and C16P-Na. The key conclusion is that the significant hydration ability of C16P-Arg and C16P-Cs promotes the formation of the corresponding α-form hydrated crystals.

Enhanced Removal of Photoresist Films through Swelling and Dewetting Using Pluronic Surfactants

Organic photoresist coatings, primarily composed of resins, are commonly used in the electronics industry to protect inorganic underlayers. Conventional photoresist strippers, such as amine-type agents, have shown high removal performance but led to environmental impact and substrate corrosiveness. Therefore, this trade-off must be addressed. In this study, we characterized the removal mechanism of a photoresist film using a nonionic triblock Pluronic surfactant [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)] in a ternary mixture of ethylene carbonate (EC), propylene carbonate (PC), and water. In particular, the removal dynamics determined by using a quartz crystal microbalance with dissipation monitoring was compared with those determined by performing confocal laser scanning microscopy and visual observation to analyze the morphology, adsorption mass, and viscoelasticity of the photoresist film. In the absence of the Pluronic surfactant, the photoresist film in the ternary solvent exhibited a three-step process: (i) film swelling caused by the penetration of a good solvent (EC and PC), (ii) formation of photoresist particles through dewetting, and (iii) particle aggregation on the substrate. This result was correlated to the Hansen solubility parameters. The addition of the Pluronic surfactant not only prevented photoresist aggregation in the third step but also promoted desorption from the substrate. This effect was dependent on the concentration of the Pluronic surfactant, which influenced diffusion to the interface between the photoresist and the bulk solution. Finally, we proposed a novel photoresist stripping mechanism based on the synergy between dewetting driven by an EC/PC-to-water mixture and adsorption by the Pluronic surfactant.

Time-Resolved Structural Analysis of Fast-Photoresponsive Surfactant Micelles by Stroboscopic Small-Angle Neutron Scattering

Photoresponsive materials are garnering attention because of their applications toward building a sustainable society. A recently developed fast-photoresponsive amphiphilic lophine dimer (3TEG-LPD) responds rapidly to light, making it a promising candidate for drug-delivery systems. In this study, the mechanism of structural changes induced by ultraviolet (UV) irradiation in 3TEG-LPD micelles in an aqueous solution was investigated via an in situ time-resolved small-angle neutron scattering (SANS) technique. Since subsecond resolution was necessary to observe the structural changes in the 3TEG-LPD micelles, stroboscopic SANS analysis was employed to obtain scattering profiles with a time width of 0.5 s. The structural parameters were quantitatively determined by performing a model-fitting analysis of the SANS results. The stroboscopic SANS results showed that upon UV irradiation, the axial ratio and pseudo-aggregation number of the 3TEG-LPD micelles increased by 1.8 and 1.6 times, respectively, whereas the number of water molecules per surfactant molecule decreased. This finding suggested that the change in the shape of the micelles from spherical to ellipsoidal shape was accompanied by dehydration. Under the present UV irradiation conditions, this structural change of the micelle occurred rapidly during the first 30 s after the start of UV irradiation. Each structural parameter recovered exponentially and reversibly during the recovery process after the cessation of UV irradiation. The changes in these parameters were analyzed in terms of kinetics by comparing them with the changes in the molecular structure. We found that the change of the micelles proceeds approximately twice as fast as the association of the molecule. Furthermore, from the perspective of the critical packing parameter consideration, the SANS analysis revealed that the UV-induced changes in 3TEG-LPD micelles are dominated by the enthalpy contribution. This finding is expected to be useful for developing new materials for various applications.

Anti-adsorption Mechanism of Photoresist by Pluronic Surfactants: An Insight into Their Adsorbed Structure

Photoresist stripping is the final step in the photolithography process that forms fine patterns for electronic devices. Recently, a mixture of ethylene carbonate (EC) and propylene carbonate (PC) has attracted attention as a new stripper based on its eco-friendliness and anti-corrosiveness. However, the EC/PC mixture causes re-adsorption of the photoresist during a process of subsequent water rinsing. In this study, we characterized the adsorption/desorption of the photoresist and a triblock Pluronic surfactant [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)] as a blocking agent on an indium tin oxide (ITO) substrate. In addition, we evaluated the dispersion of photoresist particles. The photoresist polymer formed a thin and rigid adsorption layer on an ITO substrate in the EC/PC mixture. When water was injected into the EC/PC mixture and the photoresist solutions, the photoresist polymer aggregated and was then deposited on the substrate. In contrast, the addition of Pluronic surfactant F-68 (PEO₇₉PPO₃₀PEO₇₉) into the EC/PC mixture remarkably decreased the residual amount of the photoresist on the ITO after water injection. This variation was attributed to the PEO blocks of F-68 extended to the solution phase, whereas the PPO blocks of F-68 functioned as anchors for adsorption onto the photoresist. Therefore, the F-68-adsorbed layer prevented interaction between the photoresist particles or the photoresist and the ITO surface, which provides potential for future applications as new stripping agents with high removal performance.

Anion-π Interactions in Monolayers Formed by Amphiphilic Electron-Deficient Aromatic Compounds at Air/Water Interfaces

Biological systems precisely and selectively control ion binding through various chemical reactions, molecular recognition, and transport by virtue of effective molecular interactions with biological membranes and proteins. Because ion binding is inhibited in highly polar media, recognition systems for anions in aqueous media, which are relevant to biological and environmental systems, are still limited. In this study, we explored the anion binding of Langmuir monolayers formed by amphiphilic naphthalenediimide (NDI) derivatives with a series of substituents at air/water interfaces via anion-π interactions. Density functional theory (DFT) simulations revealed that the binding of anions originating from anion-π interactions is related to the electron density of the anions. At the air/water interfaces, amphiphilic NDI derivatives formed Langmuir monolayers, and the addition of anions caused expansion of the Langmuir monolayers. The anions with larger hydration energies related to electron density showed larger binding constants (K_a) for 1:1 stoichiometry with the NDI derivatives. The loosely packed monolayer formed by the amphiphilic NDI derivatives with bromine groups showed a better anion response. In contrast, the binding of NO₃^- was significantly enhanced in the highly packed monolayer. These results indicate that the packing of NDI derivatives with rigid aromatic rings influenced the binding of the anions. These results provide insight into ion binding using the air/water interface as a promising recognition site for mimicking biological membranes. In future, sensing devices can be developed using Langmuir-Blodgett films on electrodes. Furthermore, the capture of anions on electron-deficient aromatic compounds can lead to doping or composition technologies for n-type semiconductors.

Inner and Interfacial Environmental Nanoarchitectonics of Supramolecular Assemblies Formed by Amphiphiles: from Emergence to Application

The inner and interfacial environments of self-assemblies provide fascinating nano-space for selective and efficient chemical reactions and processes. In biological systems, various chemical reactions, molecular recognition, and transport occur precisely and selectively by virtue of effective molecular interactions on biological membranes and proteins. Considering these advantages and the concept of nanoarchitectonics, we demonstrated that the photochromism of a lophine dimer was accelerated by using confined nano-spaces formed by surfactant micelles. The photoresponsive micelles were used for the rapid controlled release of a model drug upon ultraviolet light irradiation. Furthermore, selective ion recognition inside the self-assembled molecular films at the interfaces was investigated. The anion-π interaction between the anion and an electron-deficient aromatic ring was evaluated on a solid substrate modified with a naphthalenediimide (NDI) analog. Force curve measurements afforded a quantitative analysis of anion-π interactions on the NDI film. The strength of anion-π interactions is regulated by the electric fields on the electrode. An optical probe was developed to visualize the distribution of Cs ions in the soil, plant bodies, and aqueous media using an optode system. Advances in the development of molecular functional systems are expected based not only on molecular structures but also on the spaces and environments produced by them.

New measurement system based on small-angle neutron scattering for structural analysis of light-responsive materials

With the increasing importance of light-responsive materials, it is vital to analyze the relationship between function and structural changes induced by light irradiation. Small-angle scattering (SAS) is effective for such structural analysis. However, quantitatively capturing local molecular structure formation and molecular reactions at a scale of less than 1 nm via SAS is difficult. In this study, to analyze the structure of non-equilibrium phenomena in light-responsive materials, a new sample environment has been developed for a time-of-flight small- and wide-angle neutron scattering instrument (TAIKAN), comprising a UV–Vis irradiation system, UV–Vis absorption measurement equipment and photodetector. Simultaneous measurement of small-angle neutron scattering and UV–Vis absorption was achieved. This system was used to demonstrate the in situ observation of UV–Vis irradiation-induced structural change of micelles formed by 4-butylazobenzene-4′-(oxyethyl)trimethylammonium bromide, which is a light-responsive surfactant, in an aqueous solution. The results showed that the present measuring system provides direct information on the interplay between changes in micelle structure and changes in molecular configuration.

Adsorption and Lubrication of Glutamic Acid-Based Surfactant with Calcium Ions

The adsorption and lubrication of an amino acid-based surfactant at the solid/liquid interface were studied in the presence of calcium ions. The surfactant used here was disodium N-dodecanoylglutamate (C12Glu-2Na). The solid surface used in this study was hydrophobically modified to mimic the hydrophobicity of the skin surface. Quartz crystal microbalance with dissipation monitoring (QCM-D) measurements revealed that the anionic surfactant was adsorbed on the hydrophobically modified solid surface. The replacement of the surfactant solution with CaCl₂ aqueous solution resulted in the desorption of the surfactant to some extent; however, a rigid and elastic adsorption film interacting with calcium ions remained on the solid surface. The adsorption film containing calcium ions lowered the kinetic friction coefficient in aqueous media. The insoluble calcium salt of the surfactant, dispersed in the solution phase, also contributed to lubrication. We expect that the usability of personal care products formulated using amino acid-based surfactants is relevant to such adsorption and lubrication properties.

Preparation of Highly Stable Oil-in-Water Emulsions with High Ethanol Content Using Polyglycerol Monofatty Acid Esters as Emulsifiers

Oil-in-water (O/W) emulsions containing ethanol have been used in food, cosmetics, paints, and other applications. However, O/W emulsions with long-term stability are difficult to produce at high ethanol concentrations because the adsorption of the emulsifier at the O/W interface is restricted by ethanol. In this study, to resolve this issue, we prepared ethanol-containing O/W emulsions with high dispersion stability using a series of polyglycerol monofatty acid esters (PGFEs) with different fatty acid chain lengths, which are bio-safe nonionic surfactants, as emulsifiers. First, aqueous PGFE solutions containing 0-50 wt% ethanol were prepared and then O/W emulsions were formed using limonene as the oil phase. When decaglycerol stearic acid ester (DGMS, C18) was used as the emulsifier, an O/W emulsion with fine droplets (~30 nm in size) was successfully obtained at an ethanol concentration of 35 wt%. This emulsion remained stable for more than four weeks, during which no phase separation occurred, indicating its high dispersion stability. Furthermore, aqueous DGMS solutions containing 30-40 wt% ethanol were viscous, and a lamellar liquid crystal phase was observed to be dispersed in these solutions. The formation of this lamellar liquid crystal phase at the O/W interface led to an interfacial film with superior viscoelastic properties. The results suggested that the stability of the emulsions was determined by the balance between the decrease in interfacial tension caused by the addition of ethanol and the density (rigidity) of the DGMS film formed at the O/W interface. Finally, to further improve the dispersion stability of the ethanol-containing O/W-type emulsions, O/W emulsions were prepared using a mixture of two PGFEs with different degrees of glycerol polymerization, that is, systems having different hydrophilic-lipophilic balance values.

Removal of a Model Biofilm by Sophorolipid Solutions: A QCM-D Study

Biofilms are communities of microorganisms that have been widely studied because they can cause hospital-acquired infections and skin disorders. Polysaccharides secreted by microorganisms are constituents of biofilms, contributing to their adhesion and mechanical stability. Sophorolipids are biosurfactants with the ability to disrupt and remove biofilms. Biosurfactants have been targeted as potential substitutes for classical petrochemical-based surfactants in cosmetics. In this study, we fabricate a β-glucan film as a model biofilm, and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements are used to assess the biofilm removal. The viscoelasticity of the β-glucan films is monitored while sophorolipid solutions are introduced into the system, and we found that the film removal performance increases with the sophorolipid concentration. In addition, Δf (change in frequency)-ΔD (change in energy dissipation) plot analyses reveal that two processes are involved in the removal mechanism. The first process involves the adsorption of water (hydration) on the β-glucan film. The second process involves the removal of the β-glucan film from the sensor surface. Furthermore, it is suggested that sophorolipids interfere with the hydration of the β-glucan film and suppress increases in its viscosity. This is expected to be an essential factor for the removal of the β-glucan film. Sophorolipids, therefore, show potential for use in cosmetics as an eco-friendly agent for biofilm removal.

Interaction between Hydrophilic Ionic Liquid and Phospholipid/Cholesterol Mixed Film

Surface pressure (π)-area (A) isotherms were studied to analyze the interactions between a hydrophilic ionic liquid (IL) (ethyl(2-hydroxyethyl)dimethylammonium methanesulfonate) and a pure dipalmitoylphosphatidylcholine (DPPC) film or a DPPC-cholesterol mixed film. When the hydrophilic IL was added to an underlayer solution, the isotherm shifted toward higher areas. Intriguingly, when the hydrophilic IL was added, the packing of the film materials became loose and the elastic modulus decreased, resulting in increased flexibility. This phenomenon was most evident under a cholesterol mole fraction of 0.2. This composition resembles that of cell membranes, which typically comprise phospholipids and cholesterol, suggesting that this hydrophilic IL may be able to interact significantly with biological membranes.

Lubrication by Adsorption Films of Hydrophilic Amine-based Protic Ionic Liquids: Effect of Anion Species

In this study, we synthesize hydrophilic amine-based protic ionic liquids (PILs) with hydroxy groups in a cation and different anions. Subsequently, we evaluate the kinetic friction coefficients of iron oxide in aqueous solutions of the PILs under different sliding conditions. Ditriethanolamine malate, triethanolamine lactate, triethanolamine methoxyacetate, and triethanolamine acetate are used as PIL samples in this study. Among them, ditriethanolamine malate exhibits the lowest kinetic friction coefficient. As the number of sliding cycles increases, the excellent lubrication capability remains. Subsequently, we characterize the adsorption of the PILs on an iron oxide surface to investigate the lubrication behavior on the basis of quartz crystal microbalance with dissipation monitoring and force curve data. We expect hydrophilic PILs to be excellent water-soluble lubricants and additives for use in metal surface treatments.

Contrast Variation Small-Angle Neutron Scattering Study of Solubilization of Perfumes in Cationic Surfactant Micelles

Perfume solubilization is an important process in the production of commercial products such as beverages, foods, and cosmetics. In the present study, small-angle neutron scattering (SANS) experiments were performed to investigate the solubilization behavior of perfumes in cetyltrimethylammonium bromide (CTAB) micelles. The solubilization of linalool (LL) and l-menthol (MT), which are relatively hydrophilic perfumes, did not change the size of the CTAB micelles although the perfumes were incorporated in the micelles, as indicated by a decrease in scattering length density. On the other hand, the solubilization of d-limonene (LN), a hydrophobic perfume, led to the swelling of CTAB micelles. An internal contrast variation SANS study was performed by the deuteration of CTAB molecules to directly observe the perfumes in the micelles. The radius of d-CTAB micelles solubilizing LL or MT corresponds to that of h-CTAB, which indicates that these perfumes are accommodated in the palisade layers of the micelles and are homogeneously distributed in the micelles. On the other hand, LN formed small droplets, as indicated by the SANS profile, which implies the solubilization of LN molecules in the core of the CTAB micelles. We found that the relatively hydrophilic perfumes (LL and MT) show less impact on the sizes of the cationic micelles in comparison to nonionic micelles. Thus, the internal contrast variation method of SANS allowed the direct observation of the solubilization sites of perfumes with different hydrophilicity-hydrophobicity balances. This method is a powerful tool to determine the solubilization states that affect the solubilization capacity, volatilization, or release speed of perfumes.

Adsorption and Lubrication of α-Gel (α-Form Hydrated Crystal) Dispersion at Solid/Liquid Interfaces

We characterized the adsorption and desorption of α-gel (α-form hydrated crystal) dispersions in aqueous media using a quartz crystal microbalance with dissipation monitoring (QCM-D) technique. The α-gel was formed from a mixture of N-[3-(dimethylamino)propyl]docosanamide (APA-22) L-lactic acid salt, 1-octadecanol (C₁₈OH), and water. The solid substrate employed in this study as a model for hair was silica. The QCM-D measurements revealed that the α-gel dispersions yielded a rigid adsorption film on the negatively charged silica surface. The adsorption mass decreased with decreasing domain size (on the micrometer scale) of the α-gel dispersions. The adsorption film highly restricted the desorption of the α-gel from the silica surface even after rinsing with water. The adsorption film also exhibited excellent lubrication ability in aqueous media both before and after rinsing with water. We expect that the α-gel formed by APA-22 L-lactic acid is a potential ingredient for formulating an environment-friendly hair conditioner owing to its high adsorption, limited desorption, and excellent lubrication abilities on the solid surface.

Impact of Doping a Phytosteryl Sulfate on the Properties of Liposomes Made of Saturated and Unsaturated Phosphatidylcholines

The size, dispersibility, and fluidity of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine), POPC (1-palmitoy-2-oleoyl-sn-glycero-3-phosphocholine), and DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) liposomes doped with β-sitosteryl sulfate (PSO₄) were comparatively studied. In all three types of liposomes, PSO₄ reduced sizes and enhanced the negative values of the ζ-potential. However, the effect on sizes quantitatively differed in the three cases in a manner dependent on their phase behaviors. PSO₄ rigidified each type of membrane in its liquid crystalline phase and fluidized the gel phase. It enhanced the glucose trapping efficiency (TE) of both DPPC and DOPC liposomes. The TE of DPPC first increased with the increasing concentration of PSO₄, then decreased gradually. On the other hand, in the case of DOPC, the TE increased significantly upon addition of PSO₄, then remained nearly constant. Though the exact dependence of TE on the PSO₄ concentration differed in the two cases, its effect, in each case, was more than the effect of β-sitosterol (POH). The ability of PSO₄ for reducing the size and enhancing dispersibility and TE of liposomes can be useful for preparing cosmetics and pharmaceutical formulations.

Rheology of α-Gel Formed by Amino Acid-Based Surfactant with Long-Chain Alcohol: Effects of Inorganic Salt Concentration

Mixtures of surfactants, long-chain alcohols, and water sometimes yield lamellar gels with hexagonally packed alkyl chains. This assembly is called "α-gel" or "α-form hydrated crystal." In this study, we characterized the rheological properties of α-gel prepared using disodium N-dodecanoylglutamate (C12Glu-2Na), 1-hexadecanol (C16OH), and water at different NaCl concentrations. The α-gel structure was assessed using small- and wide-angle X-ray scattering (SWAXS). The SWAXS measurements revealed that an increased NaCl concentration (0-200 mmol dm^-3) resulted in a decreased d-spacing caused by the screening of electrostatic repulsion between lamellar bilayers. This led to an increased amount of excess water (i.e., the water present between the α-gel domains), and hence, the viscosity of the α-gel decreased in the range of the NaCl concentration. A further increase in the NaCl concentration (200-1000 mmol dm^-3) resulted in decreased electrostatic repulsion between the α-gel domains and/or an increased number of α-gel domains (multilamellar vesicles). These effects increased the domain-to-domain interactions, leading to increased viscosity. Therefore, we concluded that the viscosity of the α-gel was controlled by the amount of excess water and the domain-to-domain interactions. Once the network structure collapsed under the strain, it was difficult to recover the original network structure. The low recoverability resulted from increased cohesion between the domains at high NaCl concentrations.

Rapid controlled release by photo-irradiation using morphological changes in micelles formed by amphiphilic lophine dimers

Photo-induced rapid control of molecular assemblies, such as micelles and vesicles, enables effective and on-demand release of drugs or active components, with applications such as drug delivery systems (DDS) and cosmetics. Thus far, no attempts to optimize the responsiveness of photoresponsive molecular assemblies have been published. We previously reported photoresponsive surfactants bearing a lophine dimer moiety that exhibit fast photochromism in confined spaces, such as inside a molecular assembly. However, rapid control of the micelle structures and solubilization capacity have not yet been demonstrated. In the present work, photo-induced morphological changes in micelles were monitored using in-situ small-angle neutron scattering (SANS) and UV/Vis absorption spectroscopy. An amphiphilic lophine dimer (3TEG-LPD) formed elliptical micelles. These were rapidly elongated by ultraviolet light irradiation, which could be reversed by dark treatment, both within 60 s. For a solution of 3TEG-LPD micelles solubilizing calcein as a model drug molecule, fluorescence and SANS measurements indicated rapid release of the incorporated calcein into the bulk solvent under UV irradiation. Building on these results, we investigated rapid controlled release via hierarchical chemical processes: photoisomerization, morphological changes in the micelles, and drug release. This rapid controlled release system allows for effective and on-demand DDS.

Anion-π interaction at the solid/water interfaces

Anion-π interaction has been found to play a key role in interfacial phenomena. In this study, we evaluated the anion-π interactions at the solid/water interface. Anion adsorption originating from anion-π interaction at the interfaces followed the hydration energy and the presence of conjugated systems of the anions by the QCM measurements. Force curve measurements revealed that the single-molecule force of anion-π interaction between an NDI unit and the negatively charged surface of the cantilever was ∼40 pN. To the best of our knowledge, this is the first example of obtaining a single-molecule force for anion-π interactions.

Adsorption of Hydrophilic Amine-Based Protic Ionic Liquids on Iron-Based Substrates

We synthesized hydrophilic amine-based protic ionic liquids (PILs) with hydroxy groups in their cations and anions, and characterized their adsorption at a solid (iron-based substrate) / aqueous solution interface. The IL samples employed in this study were triethanolamine lactate, diethanolamine lactate, and monoethanolamine lactate. Quartz crystal microbalance with dissipation monitoring (QCM-D) measurements revealed that the adsorption mass of the hydrophilic PILs was larger than that of the comparative materials, including a non-IL sample (1,2,6-hexanetriol) and an OH-free sample in the cations (triethylamine lactate). Additionally, an increase in the number of hydroxy groups in the cations resulted in an increased adsorption mass. Force curve measurements by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) measurements proved the high adsorption density of the hydrophilic PILs on the iron-based substrate. A decreased kinetic friction coefficient was also observed in the hydrophilic PIL systems. Moreover, hydrophilic PILs are expected to have potential applications as water-soluble lubricants and additives for metal surface treatments.

Effects of Domain Size on Viscosity of α-Gel (α-Form Hydrated Crystal) Prepared from Eco-friendly Cationic Surfactant

We determine the effects of the α-gel (α-form hydrated crystal) domain size on the viscosity of water-diluted α-gels consisting of the N-[3-(dimethylamino)propyl]docosanamide (APA-22) L-lactic acid salt, 1-octadecanol (C₁₈OH), and water. A decrease in the C₁₈OH mole content results in increased domain size and viscosity of the water-diluted α-gel system. Additionally, when a sample is prepared by slow cooling and/or at low stirring speed, the domain size and viscosity of the water-diluted α-gel system increase. A similar increase in the domain size and viscosity of the α-gel system is observed for annealed samples. The observed change in the α-gel domain size is explained by the crystal growth theory.

α-Gel (α-Form Hydrated Crystal) Prepared by Eco-Friendly Cationic Surfactant

We studied the structures and properties of gel samples prepared by mixtures of N-[3-(dimethylamino)propyl]docosanamide (APA-22) acid salt (APA-22 L-lactic acid), 1-octadecanol (C₁₈OH), and water. The gel samples prepared at the mole ratios [APA-22 L-lactic acid]:C₁₈OH = 1:3, 1:4, and 1:5 yielded two phases; one being the α-gel (α-form hydrated crystal) phase, incorporating a significant quantity of water between lamellar bilayers, and the other being the excess water phase. The lamellar d-spacing remained practically unaltered at these mole ratios, thus maintaining the quantity of water incorporated between the lamellar bilayers relatively constant. Starting at 30°C, the gel samples transformed into a lamellar liquid crystal phase at high temperatures (85°C) and a β-gel phase at low temperatures (5°C). Interestingly, following dilution by pure water, the viscosity of the gel samples decreased with increasing C₁₈OH content. We expect that the viscosity change affects the performance of the gel samples as hair conditioners.

Physicochemical Properties of Acylglutamic Acid-Alkylamine Complexes in Aqueous Media

We studied the physicochemical properties of 1:1 stoichiometric complexes of acylglutamic acids (CnGlu) with tertiary alkylamines (CnDMA) in water at their low and high concentrations. Static surface tensiometry suggested that the critical micelle concentration (cmc) decreased with increasing hydrophobic chain length of the complexes. In addition, CnGlu-CnDMA yielded lower cmc than the C12Glu single system. In the region of high concentrations, several phase states including isotropic liquid (L₁) phase, hexagonal liquid crystal (H₁) phase, bicontinuous cubic liquid crystal (V₁) phase, and lamellar liquid crystal (L_α) phase were observed. Assemblies with lesser positive curvature tend to be formed with increasing complex concentration, increasing temperature, and increasing hydrophobic chain length. Additionally, the complex formation resulted in the molecular assemblies with lesser positive curvature.

Phase Behavior of the Bilayers Containing Hydrogenated Soy Lecithin and β-Sitosteryl Sulfate

The phase behaviors of systems containing saturated phosphatidylcholine (PC) and plant steroids can be important for designing new alternative delivery methods. In our previous studies, we found that even a small amount of β-sitosteryl sulfate (PSO₄) significantly affects the phase behavior, hydration properties, and liposomal properties of pure saturated phosphatidylcholines [Kafle, A.; Colloids Surf., B 2018, 161, 59-66; Kafle, A.; J. Oleo Sci. 2018, 67 (12), 1511-1519]. In the current paper, we are reporting the phase behavior of a more complex system consisting of hydrogenated soy lecithin (HLC), which is useful as a carrier in drug delivery systems or in cosmetics, and PSO₄. HLC, which is composed of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidic acid (PA), and lysophosphatidylcholine (LPC), demonstrated a versatile phase behavior. The PC component of HLC was found to separate from the PE and PA components as a result of nonideal mixing. At room temperature, these two domains represented two distinct gel phases denoted L_β1 and L_β2. The L_β1 phase selectively underwent transition into the liquid crystalline phase (L_α) at a lower temperature than L_β2. Upon addition of PSO₄, at room temperature, the PC fraction gradually converted into the liquid-ordered (L_o) phase, while the (PE + PA) fraction remained unaffected. When heated above 60 °C, the whole material converted into the liquid crystalline phase. The observed fluidizing effect of PSO₄ on HLC can find applications in preparing vehicles for moisture or drugs in cosmetic and pharmaceutical formulations.

Structural Change of an α-Gel (α-Form Hydrated Crystal) Induced by Temperature and Shear Flow in an Oleic Acid Based Gemini Surfactant System

We studied the effects of temperature and shear flow on the structures of α-gel bilayers and domains. The α-gel samples were prepared by a carboxylate-type gemini surfactant synthesized from oleic acid and a long-chain alcohol (1-tetradecanol) with water. The structural change as a function of temperature was investigated using small- and wide-angle X-ray scattering (SWAXS) measurements, spin-spin relaxation time (T₂) measurements, and optical microscopy observations. SWAXS measurements suggested that the decreased temperature yielded the α-gel phase from a lamellar liquid-crystal phase. We also found that the lamellar d-spacing drastically decreased at the phase transition temperature. The T₂ measurements suggested that two kinds of protons with different mobilities coexisted in amphiphiles consisting of lamellar bilayers. The abundance of the protons with low mobility increased with decreasing temperature. Optical microscopy results indicated that the size of the α-gel domains increased with decreasing temperature. We assumed that the increased abundance of the low-mobility protons, indicating low flexibility of lamellar bilayers, led to a decreased lamellar d-spacing and increased size of the α-gel domains. Shear-induced structural changes in the α-gel were also studied using simultaneous small-angle neutron scattering and rheological measurements. The α-gel can maintain bilayer structures even at high shear rates. We also found that the lamellar d-spacing was independent of the shear rate.

Phase Behavior and Polymerization of the Ternary Polymerizable Cationic Gemini Surfactant/Fatty Alcohol/Water System

We studied the phase behavior of a ternary polymerizable gemini surfactant (PC11-6-11)/1-undecanol/water system and stabilized these liquid crystalline structures through the polymerization of surfactants. The addition of 1-undecanol to a PC11-6-11/water system formed bicontinuous cubic (V₁) and reversed hexagonal (H₂) liquid crystal phases in addition to hexagonal (H₁) and lamellar (L_α) phases, which were also formed using the binary system of PC11-6-11/water. These new phases were formed because the fatty alcohol penetrated the palisade layer of the PC11-6-11 micelles. The polymerization of PC11-6-11 with a thermal initiator successfully preserved the L_α and H₂ phases. Layered or honeycomb structures of these liquid crystals were clearly observed by transmission electron microscopy. The nanomaterials have potential applications as membranes for nano- or microfiltration and catalyst support materials.

A mechanical model reveals that non-axisymmetric buckling lowers the energy barrier associated with membrane neck constriction

Membrane neck formation is essential for scission, which, as recent experiments on tubules have demonstrated, can be location dependent. The diversity of biological machinery that can constrict a neck such as dynamin, actin, ESCRTs and BAR proteins, and the range of forces and deflection over which they operate, suggest that the constriction process is functionally mechanical and robust to changes in biological environment. In this study, we used a mechanical model of the lipid bilayer to systematically investigate the influence of location, symmetry constraints, and helical forces on membrane neck constriction. Simulations from our model demonstrated that the energy barriers associated with constriction of a membrane neck are location-dependent. Importantly, if symmetry restrictions are relaxed, then the energy barrier for constriction is dramatically lowered and the membrane buckles at lower values of forcing parameters. Our simulations also show that constriction due to helical proteins further reduces the energy barrier for neck formation when compared to cylindrical proteins. These studies establish that despite different molecular mechanisms of neck formation in cells, the mechanics of constriction naturally leads to a loss of symmetry that can lower the energy barrier to constriction.

Accelerated recombination of lophyl radicals and control of the surface tension with amphiphilic lophine dimers

We report the accelerated photoisomerization of amphiphilic lophine dimers based on the inner environments of molecular assemblies and rapid control of the interfacial properties of aqueous solution with photoirradiation. This novel photoisomerization system enables on-demand controlled release of drugs, perfumes, and other active compounds.

Accelerated Recombination of Lophyl Radicals with Self-Assembled Amphiphilic Lophine Dimer

This report focuses on acceleration of the recombination of lophyl radicals with a lophine dimer derivative by forming molecular assemblies. A newly synthesized cationic amphiphilic lophine dimer formed molecular assemblies with a diameter of ~220 nm in an aqueous medium. When the molecular assemblies were formed, the rate of recombination of lophyl radicals, produced by ultraviolet light irradiation, was accelerated 50,000-fold compared to that in an organic solvent. The rate enhancement is likely derived from the short diffusion distance of the lophyl radicals in the molecular assemblies. These results revealed that accumulation of the lophine dimers via self-assembly remarkably accelerated the recombination of lophyl radicals. This novel photoisomerization system could rapidly control the interfacial properties or morphologies of molecular assemblies when used for applications, such as efficient delivery of drugs or active components.

Friction and Adsorption Properties of Oleic Acid-Based Gemini Amphiphile at Silica/Ester Oil Interfaces

We characterized the friction and adsorption properties of an oleic acid-based gemini amphiphile having two carboxylic acid headgroups. We employed silica as a solid material, and diethyl sebacate and bis (2-ethylhexyl) sebacate as polar ester oils. Oleic acid and stearic acid were used as comparative amphiphilic materials. These amphiphiles were soluble in the ester oils, and the solubility of the gemini amphiphile was lower than that of the other two amphiphiles. Quartz crystal microbalance with dissipation monitoring measurements suggested that the gemini amphiphile had greater adsorption capability than the two comparative amphiphiles. The greater adsorption density of the gemini amphiphile resulted in the formation of a rigid interfacial film, as suggested by the normal force curves obtained by atomic force microscopy (AFM). We assessed the friction property of these systems using a ball-on-plate-type friction analyzer and by friction-mode AFM (friction force curve). These measurements confirmed that the gemini amphiphile had a smaller kinetic friction coefficient than that of the other two amphiphiles. These results suggest the potential of the gemini amphiphile as a friction modifier in polar oils.

Adsorption of Pluronic Surfactants in Alkylene Carbonates on Silica

Adsorption of triblock Pluronic surfactants bearing poly(ethylene oxide) (PEO) chains of different lengths, L-62 (5 EO groups on each end), L-64 (13 EO groups on each end), and F-68 (79 EO groups on each end), on silica has been characterized using atomic force microscopy (AFM). The solvent used herein was a mixture of ethylene carbonate (EC) and propylene carbonate (PC). The three Pluronic surfactants were dissolved in the mixed solvent, with the PEO chain acting as a solvophilic group and the poly(propylene oxide) (PPO) chain acting as a solvophobic group. The approaching force curve measurements for the three Pluronics (at 10 mmol dm^-3) revealed repulsive forces from an apparent separation of 20-30 nm. The most solvophilic Pluronic surfactant with the longest PEO chain (F-68) showed continuously increasing repulsive interaction with decreasing separation. The Milner-Witten-Cates (MWC) theory described the repulsive force curve data of F-68, suggesting that F-68 forms a polymer brush on the silica surface. The retracting force curve measurements detected stretching forces for the three Pluronic systems. These stretching forces were observed more frequently for the L-62 system than for the F-68 system, but the pull-off distance was shorter for L-62 than for F-68.

Effects of β-Sitosteryl Sulfate on the Properties of DPPC Liposomes

The effect of β-sitosteryl sulfate (PSO₄) on the liposomal size, stability, fluidity, and dispersibility of DPPC liposomes prepared by vortex mixing, bath-sonication, and probe-sonication has been studied. PSO₄ significantly decreases the particle size of the multilamellar liposomes (MLVs). The sizes of the vortexmixed and the bath-sonicated liposomes vary as a function of PSO₄ concentration. On the other hand, PSO₄ has only little effect on the particle sizes of probe sonicated liposomes. In some cases, the liposomal stability at higher PSO₄ concentrations depends on the preparation method. PSO₄ improves the dispersibility of the DPPC liposomes and enhances their hydration. It also increases the fluidity of the liposomes prepared by each method. Our results suggest that liposomes consisting of DPPC and PSO₄ can be suitable as a cosmetic or pharmaceutical ingredient for the effective delivery of the active components into the body.

The Emergence of Anion-π Catalysis

The objective of this Account is to summarize the first five years of anion-π catalysis. The general idea of anion-π catalysis is to stabilize anionic transition states on aromatic surfaces. This is complementary to the stabilization of cationic transition states on aromatic surfaces, a mode of action that occurs in nature and is increasingly used in chemistry. Anion-π catalysis, however, rarely occurs in nature and has been unexplored in chemistry. Probably because the attraction of anions to π surfaces as such is counterintuitive, anion-π interactions in general are much younger than cation-π interactions and remain under-recognized until today. Anion-π catalysis has emerged from early findings that anion-π interactions can mediate the transport of anions across lipid bilayer membranes. With this evidence for stabilization in the ground state secured, there was no reason to believe that anion-π interactions could not also stabilize anionic transition states. As an attractive reaction to develop anion-π catalysis, the addition of malonic acid half thioesters to enolate acceptors was selected. This choice was also made because without enzymes decarboxylation is preferred and anion-π interactions promised to catalyze selectively the disfavored but relevant enolate addition. Concerning anion-π catalysts, we started with naphthalene diimides (NDIs) because their intrinsic quadrupole moment is highly positive. The NDI scaffold was used to address questions such as the positioning of substrates on the catalytic π surface or the dependence of activity on the π acidity of this π surface. With the basics in place, the next milestone was the creation of anion-π enzymes, that is, enzymes that operate with an interaction rarely used in biology, at least on intrinsically π-acidic or highly polarizable aromatic amino-acid side chains. Electric-field-assisted anion-π catalysis addresses topics such as heterogeneous catalysis on electrodes and remote control of activity by voltage. On π-stacked foldamers, anion-(π) _n-π catalysis was discovered. Fullerenes emerged as the scaffold of choice to explore contributions from polarizability. On fullerenes, anionic transition states are stabilized by large macrodipoles that appear only in response to their presence. With this growing collection of anion-π catalysts, several reactions beyond enolate addition have been explored so far. Initial efforts focused on asymmetric anion-π catalysis. Increasing enantioselectivity with increasing π acidity of the active π surface has been exemplified for enamine and iminium chemistry and for anion-π transaminase mimics. However, the delocalized nature of anion-π interactions calls for the stabilization of charge displacements over longer distances. The first step in this direction was the formation of cyclohexane rings with five stereogenic centers from achiral acyclic substrates on π-acidic surfaces. Moreover, the intrinsically disfavored exo transition state of anionic Diels-Alder reactions is stabilized selectively on π-acidic surfaces; endo products and otherwise preferred Michael addition products are completely suppressed. Taken together, we hope that these results on catalyst design and reaction scope will establish anion-π catalysis as a general principle in catalysis in the broadest sense.

Why Does the Single Neuron Activity Change from Trial to Trial during Sensory-Motor Task?

Single neuron activities from cortical areas of a monkey were recorded while performing a sensory-motor task (a choice reaction time task). Quantitative trial-by-trial analysis revealed that the timing of peak activity exhibited large variation from trial to trial, compared to the variation in the behavioral reaction time of the task. Therefore, we developed a multi-unit dynamic neural network model to investigate the effects of structure of neural connections on the variation of the timing of peak activity. Computer simulation of the model showed that, even though the units are connected in a cascade fashion, a wide variation exists in the timing of peak activity of neurons because of parallel organization of neural network within each unit.

Oil-in-Water Emulsions Stabilized by Acylglutamic Acid-Alkylamine Complexes as Noncovalent-Type Double-Chain Amphiphiles

We have studied the preparation and stabilization mechanism of oil-in-water-type emulsions in the presence of amphiphilic 1:1 stoichiometric complexes of acylglutamic acids (CnGlu) with tertiary alkylamines (CnDMA). Relatively stable emulsions were obtained when C16Glu-C16DMA (or C18Glu-C18DMA), hexadecane, and water were homogenized at 80 °C and then stored at room temperature. The gel-liquid crystal phase transition temperatures (T_c) of C16Glu-C16DMA and C18Glu-C18DMA dispersed in water were determined to be ca. 39 and 53 °C, respectively. This indicates that the complexes form an adsorbed layer at the oil/water interface during the homogenization process above the T_c and then change into a gel during storage at room temperature. The gel phase formed at the oil/water interface prevents the oil droplets from coalescing. In contrast, shorter chain analogues (C10Glu-C10DMA and C12Glu-C12DMA) did not yield stable emulsions because their adsorption layers were not able to prevent coalescence of the oil droplets (i.e., the T_c of these analogues was below the room temperature). We have also demonstrated that the dispersion stability of these emulsion systems can be controlled by changing the aqueous pH.