arXiv subjects

Niki Baccile

Publications and source records attributed to Niki Baccile.

At least 19 recordsLinked to original sources

arXiv2025

Orthogonality between cellulose nanocrystals and a low-molecular weight gelator

The development of multicomponent hydrogels has gained a lot of attention in the field of soft matter, as precise tuning of the chemical nature and colloidal properties of each component brings mechanical and functional benefits compared to one-component gels. Within the field, orthogonality between a self-assembled low-molecular weight gelator (LMWG) and a colloid is a domain that has received little attention. In this study, orthogonal LMWG-colloid hydrogels were developed with the additional constraint of sustainability: a bolaamphiphile glycolipid (G-C18:1) is selected as LMWG while cellulose nanocrystals (CNCs) as colloid. These compounds are chosen for their dual role. G-C18:1 is a LMWG but it can also be used, at lower concentrations, as surface stabilizer for CNCs and tune its aggregative properties. On the other hand, tuning surface properties of CNCs drives its bulk behavior: uncharged CNCs locally aggregate and act as reinforcing agent for the LMWG gel, while negatively-charged CNCs, cross-linked with Ca 2+ , naturally form a hydrogel, which can interpenetrate with the LMWG network. By means of rheometry, small-angle X-ray scattering (SAXS) and rheo-SAXS, it is shown here how the aggregative behavior of CNCs enhances the mechanical properties of G-C18:1 hydrogels, while G-C18:1 imparts pH and temperature responsiveness to CNC hydrogels. An interesting field of research in soft matter science is the development of orthogonal hydrogels containing cellulose and LMWGs, although, to the best of our knowledge, there are no existing reports. Since cellulose is among the most extensively studied macromolecules in the field of soft matter, particularly for biomedical applications, 22,23 developing and studying the properties of orthogonal hydrogels containing CNCs and a LMWG represents an intriguing avenue for research, and this for two reasons. First of all, CNCs are bio-based nanoparticles, relevant for the development of sustainable nanoscale science and engineering. Secondly, the surface chemistry of CNCs can be controlled in such a way to tune their aggregation and dispersion properties, making them interesting either as reinforcements in hydrogels, 24,25 or as hydrogel scaffold themselves. 26,27 These aspects were never explored in the context of orthogonal hydrogels. In this work, we then study orthogonality in fully bio-based hydrogels composed of a single glucose lipid LMWG (G-C18:1) and CNCs. G-C18:1 is selected for its multiphasic behavior in water at room temperature 28 and linked to its unique surfactant-lipid-gelator nature, 28,29 tuned by pH and/or type of ion. Below neutral pH and at concentrations under 5 wt%, G-C18:1 forms vesicles, displaying a lipid-like behavior. At pH above neutrality, it assembles into micelles, thus exhibiting a surfactant behavior. 30,31 When Ca 2+ is added to its micellar phase, 32,33 G-C18:1 forms fiber gels 30 (Figure 1). In particular, we focused on orthogonal G-C18:1/CNC hydrogels, in which CNCs either assembled into hydrogels (negatively-charged and cross-linked by calcium ions, referred to as SCNCs, Figure 1) or behaved as reinforcing agents (uncharged CNCs prepared via HCl hydrolysis, referred to as CNC$α$, and neutral surface stabilized by G-C18:1, 34 Figure 1). These two types of CNCs exhibit distinct roles in the hydrogel system: SCNCs actively participate in the formation of a percolated network, while CNC$α$ are used to reinforce the hydrogel matrix physically. Specific attention is paid to the impact of the assembled form of CNCs to the elastic properties of the LMWG hydrogel as well as how the responsivity to pH and temperature of the LMWG affect the elastic properties of CNC hydrogels. 33

cond-mat.soft↗

arXiv2025

Driving a stimuli-responsive wedge in the packing of phospholipid membranes using bolaamphiphile intercalants

Bolaamphiphilesamphiphilic molecules with polar groups at each of the two ends of a hydrophobic tail with pH-sensitive spontaneous molecular curvaturesendow membranes of extremophiles with an exquisite balance between stability (or robustness) and adaptability (or plasticity). But how the presence (or real-time insertion) of bolaamphiphiles influences lamellar lipid membranes is poorly understood. Using a combination of time-resolved confocal fluorescence microscopy, in situ small angle X-ray and neutron scattering (SAXS, SANS), and neutron spin echo (NSE) measurements, we monitor here the pH-dependent interactions of nanoscopic vesicles of a representative bolaamphiphilea glucolipid consisting of a single glucose headgroup and a C18:1 (oleyl) fatty acid tail (G-C18:1)with the membranes of an essentially cylindrical, fluid-phase phospholipid (dioleoylphosphatidylcholine, DOPC). We find that the two mesophases interact spontaneously at all pH values, producing large-scale morphological remodeling. Under neutral and acidic conditions, when the bolaamphiphile assumes a cylindrical shape, vesicles fuse with one another, producing invaginations, inner tubulation and vesicle-in-vesicle aggregates. Under basic pH, by contrast, when the carboxylic acid is deprotonated and the molecule is inverted-conical in shape, the bolaamphiphile causes phospholipid membranes to undergo poration, budding, and vesiculation. This pH-dependent, environmentally sensitive membrane remodeling without the disruption of the essential bilayer motif illustrates how local, molecular-level packing perturbations can translate into global system-level morphological changes, enabling membranes to acquire environmental sensitivity and real-time adaptability. These results support the notion that molecular fluxeswhich add (or remove) amphiphilic molecules to biological membranescan endow de novo functionalities (e.g., pH sensitivity) and influence global morphologies of cell-sized vesicles.

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arXiv2025

Electron conductive self-assembled hybrid low-molecular weight glycolipid-nanosilver gels

Low-molecular weight (LMW) hydrogels are gaining interest over macromolecular gels due to their reversible, dynamic and stimuli-responsive nature. They are potentially interesting functional materials for advanced applications such as catalysis, nanoelectronics or regenerative medicine. One common strategy to enhance the functional properties is to incorporate inorganic nanostructures. However, simultaneous control of the gel mechanics, shape and size of the nanostructures and functional properties is challenging. Here, a biobased, double amphiphilic, bolaform, single-glucose lipid (containing glucose and COOH in opposite directions) is able to coordinate silver ions, drive the formation of a self-assembled fibrous hydrogel and, after controlling the reduction time (seconds to hours) of the reduction process (NaBH4, ascorbate, $γ$-rays), stabilize Ag nanoparticles (NPs) of controlled size (2.8 nm $\pm$ 13%). The NPs are spontaneously embedded in the fibers' core following a two-dimensional anisotropic long-range order. Precise control of the reduction parameters (ascorbate) drives the formation of Ag nanowires, possibly due to an anisotropic coalescence process of the nanoparticles. Samples containing Ag nanowires have shown an electronic conductive response, observed with impedance spectroscopy. This works shows the potential of biological amphiphiles to develop under soft conditions (pseudo single step, water, room temperature) advanced hybrid organic/inorganic (O/I) materials with a multiscale structure, order and electron conductivity functionality

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arXiv2024

Myelin figures from microbial glycolipid biosurfactant amphiphiles

Myelin figures (MFs) -- cylindrical lyotropic liquid crystalline structures consisting of concentric arrays of bilayers and aqueous media -- arise from the hydration of the bulk lamellar phase of many common amphiphiles. Prior efforts have concentrated on the formation, structure, and dynamics of myelin produced by phosphatidylcholine (PC)-based amphiphiles. Here, we study the myelinization of glycolipid microbial amphiphiles, commonly addressed as biosurfactants, produced through the process of fermentation. The hydration characteristics (and phase diagrams) of these biological amphiphiles are atypical (and thus their capacity to form myelin) because unlike typical amphiphiles, their molecular structure is characterized by two hydrophilic groups (sugar, carboxylic acid) on both ends with a hydrophobic moiety in the middle. We tested three different glycolipid molecules: C18:1 sophorolipids and single-glucose C18:1 and C18:0 glucolipids, all in their nonacetylated acidic form. Neither sophorolipids (too soluble) nor C18:0 glucolipids (too insoluble) displayed myelin growth at room temperature (RT, 25 C). The glucolipid C18:1 (G-C18:1), on the other hand, showed dense myelin growth at RT below pH 7.0. Examining their growth rates, we find that they display a linear L $α$ t (L, myelin length; t, time) growth rate, suggesting ballistic growth, distinctly different from the L $α$ t^(1/2) dependence, characterizing diffusive growth such as what occurs in more conventional phospholipids. These results offer some insight into lipidic mesophases arising from a previously unexplored class of amphiphiles with potential applications in the field of drug delivery.

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arXiv2023

Measuring the bending rigidity of microbial glucolipid (biosurfactant) bioamphiphile self-assembled structures by neutron spin-echo (NSE): interdigitated vesicles, lamellae and fibers

Bending rigidity, k, is classically measured for lipid membranes to characterize their nanoscale mechanical properties as a function of composition. Widely employed as a comparative tool, it helps understanding the relationship between the lipid's molecular structure and the elastic properties of its corresponding bilayer. Widely measured for phospholipid membranes in the shape of giant unilamellar vesicles (GUVs), bending rigidity is determined here for three self-assembled structures formed by a new biobased glucolipid bioamphiphile, rather associated to the family of glycolipid biosurfactants than phospholipids. In its oleyl form, glucolipid G-C18:1 can assemble into vesicles or crystalline fibers, while in its stearyl form, glucolipid G-C18:0 can assemble into lamellar gels. Neutron spin-echo (NSE) is employed in the q-range between 0.3 nm-1 (21 nm) and 1.5 nm-1 (4.1 nm) with a spin-echo time in the range of up to 500 ns to characterize the bending rigidity of three different structures (Vesicle suspension, Lamellar gel, Fiber gel) solely composed of a single glucolipid. The low (k= 0.30 $\pm$ 0.04 kbT) values found for the Vesicle suspension and high values found for the Lamellar (k= 130 $\pm$ 40 kbT) and Fiber gels (k= 900 $\pm$ 500 kbT) are unusual when compared to most phospholipid membranes. By attempting to quantify for the first time the bending rigidity of self-assembled bioamphiphiles, this work not only contributes to the fundamental understanding of these new molecular systems, but it also opens new perspectives in their integration in the field of soft materials.

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arXiv2023

Aqueous self-assembly of a wide range of sophorolipid and glucolipid microbial bioamphiphiles (biosurfactants): considerations on the structure-properties relationship

Sophorolipids are well-known scaled-up microbial glycolipid biosurfactants with a strong potential for commercialization due to their biological origin and mildness in contact with the skin and the environment compared to classical surfactants. However, their association properties in water are still poorly understood, they cannot be predicted and their behavior in solution challenges half a century of knowledge generated in the field of surfactant science. By studying forty different types of sophorolipids and sophorosides in water using small angle X-ray scattering, and optical and cryogenic transmission electron microscopy, this work provides better understanding of their structure-property relationship and identifies which chemical groups in their molecular structure have a critical influence on their self-assembly properties. Structural features like the number of sugar headgroups, acetylation, end-chain functional group, (un)saturation, lactonization and length of chain are adjusted to both rationalize their impact and understand their effect on self-assembly. The number of sugar groups, pH, (un)saturation and lactonization were found to have a critical impact on sophorolipid self-assembly. The chemical nature of the end-chain functional group and chain length were also found to have a possibly critical impact, depending on the specific type of chemical function (COOH and long chains are critical). Mono- and diacetylation, as well as the position of sophorose in the fatty acid ($ω$, $ω$-1), are not critical, i.e., they did not significantly influence sophorolipid self-assembly.

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arXiv2023

Are microbial biosurfactants actually only surfactants?

The term biosurfactants refers to a complex mixture of metabolites with surface-active properties produced by specific microorganisms. However, nowadays trends moves towards isolation, screening and purifying single biocompatible, biodegradable biosurfactants with high commercialization potential. Current legislation limiting petrochemicals combined with environmentally concerned consumers did not only stimulate research and development but it also promoted large-scale production of this class of molecules. However, recent data recorded on single congeners question the actual pertinence of using the word ''biosurfactant'' associated to these molecules. By evaluating the accepted characteristics of surfactants and comparing them to the actual self-assembly and bulk properties in water of molecules traditionally called ''biosurfactants'', this opinion paper aims at showing that the term ''biosurfactant'' can be somewhat reductive when applied to specific individual compounds produced by fermentation. The use of a more generic term, like bioamphiphile could probably be more pertinent and appropriate for consideration in the future.

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arXiv2023

Self-Assembly of Rhamnolipids Bioamphiphiles: Understanding Structure-Properties Relationship using Small-Angle X-Ray Scattering

The structure-properties relationship of rhamnolipids, RLs, well known microbial bioamphiphiles (biosurfactants), is exlored in detail by coupling cryogenic transmission electron microscopy (cryo-TEM) and both ex situ and in situ small angle X-ray scattering (SAXS). The self-assembly of three RLs with reasoned variation of their molecular structure (RhaC10, RhaC10C10 and RhaRhaC10C10) and a rhamnose-free C10C10 fatty acid is studied in water as a function of pH. It is found that RhaC10 and RhaRhaC10C10 form micelles in a broad pH range and RhaC10C10 undergoes a micelle-to-vesicle transition from basic to acid pH occurring at pH 6.5. Modelling coupled to fitting SAXS data allows a good estimation of the hydrophobic core radius (or length), the hydrophilic shell thickness, the aggregation number and the surface area per RL. The essentially micellar morphology found for RhaC10 and

cond-mat.mtrl-sci↗

arXiv2022

Shear recovery and temperature stability of Ca2+ and Ag+ glycolipid fibrillar metallogels with unusual $β$-sheet-like domains

Low-molecular weight gelators (LMWG) are small molecules (Mw < ~1 kDa), which form self-assembled fibrillar networks (SAFiN) hydrogels in water. The great majority of SAFiN gels is described by an entangled network of self-assembled fibers, in analogy to a polymer in a good solvent. Here, fibrillation of a biobased glycolipid bolaamphiphile is triggered by Ca2+ or Ag+ ions, added to its diluted micellar phase. The resulting SAFiN, which forms hydrogel above 0.5 wt%, has a ``nano-fishnet'' structure, characterized by a fibrous network of both entangled fibers and $β$-sheets-like rafts, generally observed for silk fibroin, actin hydrogels or mineral imogolite nanotubes, but generally not known for SAFiN. This work focuses on the strength of the SAFIN gels, their fast recovery after applying a mechanical stimulus (strain) and their unusual resistance to temperature, studied by coupling rheology to small angle X-ray scattering (rheo-SAXS) using synchrotron radiation. The Ca2+-based hydrogel keeps its properties up to 55{\textdegree}C, while the Ag+-based gel shows a constant elastic modulus up to 70{\textdegree}C, without appearance of any gel-to-sol transition temperature. Furthermore, the glycolipid is obtained by fermentation from natural resources (glucose, rapeseed oil), thus showing that naturally-engineered compounds can have unprecedented properties, when compared to the wide range of chemically derived amphiphiles.

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arXiv2022

In situ stimulation of self-assembly tunes the elastic properties of interpenetrated glycolipid-biopolymer biobased hydrogels

Hydrogels are widespread soft materials, which can serve a wide range of applications. The control over the viscoelastic properties of the gel is of paramount importance. Ongoing environmental issues have raised the consumer's concern towards the use of more sustainable materials, including hydrogels. However, are greener materials compatible with high functionality? In a safe-by-design approach, this work demonstrates that functional hydrogels with in situ responsivity of their elastic properties by external stimuli can be developed from entirely ``sustainable'' components, a biobased amphiphile and biopolymers (gelatin, chitosan and alginate). The bioamphiphile is a stimuli-responsive glycolipid obtained by microbial fermentation, which can self-assemble into fibers, but also micelles or vesicles, in water under high dilution and by a rapid variation of the stimuli. The elastic properties of the bioamphiphile/biopolymer interpenetrated hydrogels can be modulated by selectively triggering the phase transition of the glycolipid and/or the biopolymer inside the gel by mean of temperature or pH.

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arXiv2022

Interpenetrated biosurfactant-biopolymer orthogonal hydrogels: the biosurfactant's phase controls the hydrogel's mechanics

Controlling the viscoelastic properties of hydrogels is a challenge for many applications. Low molecular weight gelators (LMWG) like bile salts and glycolipids, and biopolymers like chitosan and alginate, are good candidates for developing fully biobased hybrid hydrogels that combine the advantages of both components. Biopolymers lead to enhanced mechanics while LMWG add functionality. In this work, hybrid hydrogels are composed of biopolymers (gelatin, chitosan, alginate) and microbial glycolipid bioamphiphiles, known as biosurfactants. Besides their biocompatibility and natural origin, bioamphiphiles can present chameleonic behavior, as pH and ions control their phase diagram in water around neutrality under strongly diluted conditions (< 5 wt%). The glycolipid used in this work behaves like a surfactant (micellar phase) at high pH or like a phospholipid (vesicle phase) at low pH. Moreover, at neutral-to-alkaline pH in the presence of calcium, it behaves like a gelator (fiber phase). The impact of each of these phases on the elastic properties of biopolymers is explored by means of oscillatory rheology, while the hybrid structure is studied by small angle X-ray scattering. The micellar and vesicular phase reduce the elastic properties of the hydrogels, while the fiber phase has the opposite effect, it enhances the hydrogel's strength by forming an interpenetrated biopolymer-LMWG network.

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arXiv2022

Topological connection between vesicles and nanotubes in single-molecule lipid membranes driven by head-tail interactions

Lipid nanotube-vesicle networks are important channels for intercellular communication and transport of matter. Experimentally observed in neighboring mammalian cells, but also reproduced in model membrane systems, a broad consensus exists on their formation and stability. Lipid membranes must be composed of at least two molecular components, each stabilizing low (generally a phospholipid) and high curvatures. Strong anisotropy or enhanced conical shape of the second amphiphile is crucial for the formation of nanotunnels. Anisotropic driving forces generally favor nanotube protrusions from vesicles. In the present work, we report the unique case of topologically-connected nanotubes-vesicles obtained in the absence of directional forces, in single-molecule membranes, composed of an anisotropic bolaform glucolipid, above its melting temperature, Tm. Cryo-TEM and fluorescence confocal microscopy show the interconnection between vesicles and nanotubes in a single-phase region, between 60{\textdegree} and 90{\textdegree}C under diluted conditions. Solid-state NMR demonstrates that the glucolipid can assume two distinct configurations, head-head and head-tail. These arrangements, seemingly of comparable energy above the Tm, could explain the existence and stability of the topologically-connected vesicles and nanotubes, which are generally not observed for classical single-molecule phospholipid-based membranes above their Tm.

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arXiv2022

Energy Landscape of Sugar Conformation Controls the Sol-to-Gel Transition in Self-assembled Bola Glycolipid Hydrogels

Self-assembled fibrillar network (SAFIN) hydrogels and organogels are commonly obtained by a crystallization process into fibers induced by external stimuli like temperature or pH. The gel-to-sol-to-gel transition is generally readily reversible and the change rate of the stimulus determines the fiber homogeneity and eventual elastic properties of the gels. However, recent work shows that in some specific cases, fibrillation occurs for a given molecular conformation and the sol-to-gel transition depends on the relative energetic stability of one conformation over the other, and not on the rate of change of the stimuli. We observe such a phenomenon on a class of bolaform glycolipids, sophorosides, similar to the well-known sophorolipid biosurfactants, but composed of two symmetric sophorose units. A combination of oscillatory rheology, small-angle X-ray scattering (SAXS) cryogenic transmission electron microscopy (cryo-TEM) and in situ rheo-SAXS using synchrotron radiation shows that below 14$^\circ$C, twisted nanofibers are the thermodynamic phase. Between 14$^\circ$C and about 33$^\circ$C, nanofibers coexist with micelles and a strong hydrogel forms, the sol-to-gel transition being readily reversible in this temperature range. However, above the annealing temperature of about 40$^\circ$C, the micelle morphology becomes kinetically-trapped over hours, even upon cooling, whichever the rate, to 4$^\circ$C. A combination of solution and solid-state nuclear magnetic resonance (NMR) suggests two different conformations of the 1'', 1' and 2' carbon stereocenters of sophorose, precisely at the $β(1,2)$ glycosidic bond, for which several combinations of the dihedral angles are known to provide at least three energetic minima of comparable magnitude and each corresponding to a given sophorose conformation.

cond-mat.mtrl-sci↗

arXiv2021

pH Switchable Pickering Emulsions Stabilized by Polyelectrolyte Biosurfactant Complex Coacervate Colloids

Polyelectrolyte-surfactant complexes (PESCs) have long been employed as oil-in-water (o/w) emulsions stabilizers, but never in the structure of colloidal complex coacervates providing a Pickering effect. The complexed state of PESCs could make them unsuitable o/w Pickering emulsifiers, which instead require a balance between colloidal structure and stability, amphiphilicity and wettability. Here we hypothesize that PESCs coacervates are efficient Pickering stabilizers. Instead of classical surfactants, we employ sophorolipid (SL) biosurfactants, atypical anionic/neutral stimuli-responsive biosurfactants. Despite their tunable charge and mild amphiphilic character, they can be used in combination with cationic/neutral polyelectrolytes (chitosan, CHL, or poly-L-lysine, PLL) to form PESC coacervates for the development of biobased, but also pH-switchable, Pickering emulsions.Aqueous solutions of SL-CHL (or SL-PLL) complex coacervates are emulsified with dodecane. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy under cryogenic conditions (cryo-SEM) demonstrate the Pickering effect, while optical microscopy and oscillatory rheology respectively assess the emulsion formation and relative viscoelastic properties.Both SL-CHL and SL-PLL PESCs stabilize o/w emulsions up to $Φ$oil of 0.7 only in the pH region of complex coacervation (6 < pH < 9): outside this range, phase separation occurs. Rheology shows a typical solid-like response and mechanical recovery upon applying large deformations. CLSM and cryo-SEM highlight a colloidal structure, associated to the complex coacervates, of the oil/water interface and suggest a Pickering effect. These findings demonstrate the Pickering effect from PESC coacervates and the possibility to use biobased and biocompatible components, with application potential in cosmetics, food science, or oil recovery.

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arXiv2021

Self-Assembly, Interfacial Properties, Interactions with Macromolecules and Molecular Modelling and Simulation of Microbial Bio-based Amphiphiles (Biosurfactants). A Tutorial Review

Chemical surfactants are omnipresent in consumers' products but they suffer from environmental concerns. For this reason, complete replacement of petrochemical surfactants by biosurfactants constitute a holy grail but this is far from occurring any soon. If the "biosurfactants revolution" has not occurred, yet, mainly due to the higher cost and lower availability of biosurfactants, another reason explains this fact: the poor knowledge of their properties in solution. This tutorial review aims at reviewing the self-assembly properties and phase behavior, experimental (sections 2.3 and 2.4) and from molecular modelling (section 5), in water of the most important microbial biosurfactants (sophorolipids, rhamnolipids, surfacting, cellobioselipids, glucolipids) as well as their major derivatives. A critical discussion of such properties in light of the well-known packing parameter of surfactants is also provided (section 2.5). The relationship between the nanoscale self-assembly and macroscopic materials properties, including hydrogelling, solid foaming, templating or encapsulation is specifically discussed (section 2.7). We also present their self-assembly and adsorption at flat and complex air/liquid (e.g., foams), air/solid (adhesion), liquid/solid (nanoparticles) and liquid/liquid (e.g., emulsions) interfaces (section 3). A critical discussion on the use of biosurfactants as capping agents for the development of stable nanoparticles is specifically provided (section 3.2.4). Finally, we discuss the major findings involving biosurfactants and macromolecules, including proteins, enzymes, polymers and polyelectrolytes.

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arXiv2021

Palmitic Acid Sophorolipid Biosurfactant: From Self-Assembled Fibrillar Network (SAFiN) To Hydrogels with Fast Recovery

Nanofibers are an interesting phase into which amphiphilic molecules can self-assemble. Described for a large number of synthetic lipids, they were seldom reported for natural lipids like microbial amphiphiles, known as biosurfactants. In this work, we show that the palmitic acid congener of sophorolipids (SLC16:0), one of the most studied families of biosurfactants, spontaneously forms a self-assembled fiber network (SAFiN) at pH below 6 through a pH jump process. pH-resolved in-situ Small Angle X-ray Scattering (SAXS) shows a continuous micelle-to-fiber transition, characterized by an enhanced core-shell contrast between pH 9 and pH 7 and micellar fusion into flat membrane between pH 7 and pH 6, approximately. Below pH 6, homogeneous, infinitely long nanofibers form by peeling off the membranes. Eventually, the nanofiber network spontaneously forms a thixotropic hydrogel with fast recovery rates after applying an oscillatory strain amplitude out of the linear viscoelastic regime (LVER): after being submitted to strain amplitudes during 5 min, the hydrogel recovers about 80% and 100% of its initial elastic modulus after, respectively, 20 s and 10 min. Finally, the strength of the hydrogel depends on the medium's final pH, with an elastic modulus fivefold higher at pH 3 than at pH 6.

cond-mat.soft↗

arXiv2020

Synthesis and self-assembly of aminyl and alkynyl substituted sophorolipids

Sophorolipids are one of the most important microbial biosurfactants, because of their large-scale production and applications developed so far in the fields of detergency, microbiology, cosmetics or environmental science. However, the structural variety of native sophorolipids is limited/restricted, a limiting fact for the development of new properties and their potential applications. In their open acidic form, C18:1 sophorolipids (SL) are classically composed of a sophorose headgroup and a carboxylic acid (COOH) end-group. The carboxyl group gives them unique pH-responsive properties, but they are a poorly-reactive group and their charge can only be negative. To develop a new generation of pH-responsive, positively-charged, SL and to improve their reactivity for further functionalization, we develop here SLs with an amine (-NH2) or terminal alkyne (-C$\not\equiv$CH) end-group analogues. The amine group generates positively-charged SL and is more reactive than carboxylic acids, e.g. towards aldehydes; the alkyne group provides access to copper-based click chemistry. In this work, we synthesize (C18:1) and (C18:0) --NH2 and (C18:1) -C$\not\equiv$CH sophorolipid derivatives and we study their self-assembly properties in response to pH and/or temperature changes by means of static and dynamic light scattering, small angle (X-ray, neutron) scattering and cryogenic electron microscopy. Monounsaturated aminyl SL-C18:1-NH2 sophorolipids form a micellar phase in their neutral form at high pH and a mixed micellar-bilayer phase in their positively-charged form at low pH. Saturated aminyl SL-C18:0-NH2 sophorolipids form a micellar phase in their charged form at low pH and a twisted ribbon phase in their neutral form at high pH and monounsaturated alkynyl SL-C18:1-C$\not\equiv$CH sophorolipids form a main micellar phase at T> 51.8{\textdegree}C and a twisted ribbon phase at T< 51.8 {\textdegree}C.

cond-mat.soft↗

arXiv2020

Synthesis of multilamellar walls vesicles polyelectrolyte-surfactant complexes from pH-stimulated phase transition using microbial biosurfactants

Multilamellar wall vesicles (MLWV) are an interesting class of polyelectrolyte-surfactant complexes (PESCs) for wide applications ranging from house-care to biomedical products. If MLWV are generally obtained by a polyelectrolyte-driven vesicle agglutination under pseudo-equilibrium conditions, the resulting phase is often a mixture of more than one structure. In this work, we show that MLWV can be massively and reproductively prepared from a recently developed method involving a pH-stimulated phase transition from a complex coacervate phase (Co). We employ a biobased pH-sensitive microbial glucolipid biosurfactant in the presence of a natural, or synthetic, polyamine (chitosan, poly-L-Lysine, polyethylene imine, polyallylamine). In situ small angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) show a systematic isostructural and isodimensional transition from the Co to the MLWV phase, while optical microscopy under polarized light experiments and cryo-TEM reveal a massive, virtually quantitative, presence of MLWV. Finally, the multilamellar wall structure is not perturbed by filtration and sonication, two typical methods employed to control size distribution in vesicles. In summary, this work highlights a new, robust, non-equilibrium phase-change method to develop biobased multilamellar wall vesicles, promising soft colloids with applications in the field of personal care, cosmetics and pharmaceutics among many others.

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