Palmitic acid sophorolipid biosurfactant: from self-assembled fibrillar network (SAFiN) to hydrogels with fast recovery

Harnessing Glycolipids for Supramolecular Gelation: A Contemporary Review

Within the scope of this review, our exploration spans diverse facets of amphiphilic glycolipid-based low-molecular-weight gelators (LMWGs). This journey explores glycolipid synthesis, self-assembly, and gelation with tailorable properties. It begins by examining the design of glycolipids and their influence on gel formation. Following this, a brief exploration of several gel characterization techniques adds another layer to the understanding of these materials. The final section is dedicated to unraveling the various applications of these glycolipid-based supramolecular gels. A meticulous analysis of available glycolipid gelators and their correlations with desired properties for distinct applications is a pivotal aspect of their investigation. As of the present moment, there exists a notable absence of a review dedicated exclusively to glycolipid gelators. This study aims to bridge this critical gap by presenting an overview that provides novel insights into their unique properties and versatile applications. This holistic examination seeks to contribute to a deeper understanding of molecular design, structural characteristics, and functional applications of glycolipid gelators by offering insights that can propel advancements in these converging scientific disciplines. Overall, this review highlights the diverse classifications of glycolipid-derived gelators and particularly emphasizes their capacity to form gels.

Self-Assembly of Rhamnolipid Bioamphiphiles: Understanding the Structure-Property Relationship Using Small-Angle X-ray Scattering

The structure-property relationship of rhamnolipids, RLs, well-known microbial bioamphiphiles (biosurfactants), is explored 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. Modeling 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 RhaRhaC10C10 and the micelle-to-vesicle transition found for RhaC10C10 are reasonably well explained by employing the packing parameter (PP) model, provided a good estimation of the surface area per RL. On the contrary, the PP model fails to explain the lamellar phase found for the protonated RhaRhaC10C10 at acidic pH. The lamellar phase can only be explained by values of the surface area per RL being counterintuitively small for a di-rhamnose group and folding of the C10C10 chain. These structural features are only possible for a change in the conformation of the di-rhamnose group between the alkaline and acidic pH.

Ca2+ and Ag+ orient low-molecular weight amphiphile self-assembly into "nano-fishnet" fibrillar hydrogels with unusual β-sheet-like raft domains

Low-molecular weight gelators (LMWGs) are small molecules (M_w < ∼1 kDa), which form self-assembled fibrillar network (SAFiN) hydrogels in water when triggered by an external stimulus. A great majority of SAFiN gels involve an entangled network of self-assembled fibers, in analogy to a polymer in a good solvent. In some rare cases, a combination of attractive van der Waals and repulsive electrostatic forces drives the formation of bundles with a suprafibrillar hexagonal order. In this work, an unexpected micelle-to-fiber transition is triggered by Ca²⁺ or Ag⁺ ions added to a micellar solution of a novel glycolipid surfactant, whereas salt-induced fibrillation is not common for surfactants. The resulting SAFiN, which forms a hydrogel above 0.5 wt%, has a "nano-fishnet" structure, characterized by a fibrous network of both entangled fibers and β-sheet-like rafts, generally observed for silk fibroin, actin hydrogels or mineral imogolite nanotubes, but not known for SAFiNs. The β-sheet-like raft domains are characterized by a combination of cryo-TEM and SAXS and seem to contribute to the stability of glycolipid gels. Furthermore, 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.

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

Low-molecular weight gelators (LMWGs) are small molecules (M_w < ∼1 kDa), which form self-assembled fibrillar network (SAFiN) hydrogels in water. A great majority of SAFiN gels are 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 which are added to its diluted micellar phase. The resulting SAFiN, which forms a hydrogel above 0.5 wt%, has a "nano-fishnet" structure, characterized by a fibrous network of both entangled fibers and β-sheet-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 maintains its properties up to 55 °C, while the Ag⁺-based gel shows a constant elastic modulus up to 70 °C, without the appearance of any gel-to-sol transition temperature. Furthermore, the glycolipid is obtained by fermentation from natural resources (glucose and rapeseed oil), thus showing that naturally engineered compounds can have unprecedented properties, when compared to the wide range of chemically derived amphiphiles.

Cation-Induced Fibrillation of Microbial Glycolipid Biosurfactant Probed by Ion-Resolved In Situ SAXS

Biological amphiphiles are molecules with a rich phase behavior. Micellar, vesicular, and even fibrillar phases can be found for the same molecule by applying a change in pH or by selecting the appropriate metal ion. The rich phase behavior paves the way toward a broad class of soft materials, from carriers to hydrogels. The present work contributes to understanding the fibrillation of a microbial glycolipid, glucolipid G-C18:1, produced by Starmerella bombicola ΔugtB1 and characterized by a micellar phase at alkaline pH and a vesicular phase at acidic pH. Fibrillation and prompt hydrogelation is triggered by adding either alkaline earth, Ca²⁺, or transition metal, Ag⁺, Fe²⁺, Al³⁺, ions to a G-C18:1 micellar solution. A specifically designed apparatus coupled to a synchrotron SAXS beamline allows the performing of simultaneous cation- and pH-resolved in situ monitoring of the morphological evolution from spheroidal micelles to crystalline fibers, when Ca²⁺ is employed, or to wormlike aggregates, when Fe²⁺ or Al³⁺ solutions are employed. The fast reactivity of Ag⁺ and the crystallinity of Ca²⁺-induced fibers suggest that fibrillation is driven by direct metal-ligand interactions, while the shape transition from spheroidal to elongated micelles with Fe²⁺ or Al³⁺ rather suggest charge screening between the lipid and the hydroxylated cation species.

From bumblebee to bioeconomy: Recent developments and perspectives for sophorolipid biosynthesis

Sophorolipids are biobased compounds produced by the genera Starmerella and Pseudohyphozyma that gain exponential interest from academic and industrial stakeholders due to their mild and environmental friendly characteristics. Currently, industrially relevant sophorolipid volumetric productivities are reached up to 3.7 g∙L^-1∙h^-1 and sophorolipids are used in the personal care and cleaning industry at small scale. Moreover, applications in crop protection, food, biohydrometallurgy and medical fields are being extensively researched. The research and development of sophorolipids is at a crucial stage. Therefore, this work presents an overview of the state-of-the-art on sophorolipid research and their applications, while providing a critical assessment of scientific techniques and standardisation in reporting. In this review, the genuine sophorolipid producing organisms and the natural role of sophorolipids are discussed. Subsequently, an evaluation is made of innovations in production processes and the relevance of in-situ product recovery for process performance is discussed. Furthermore, a critical assessment of application research and its future perspectives are portrayed with a focus on the self-assembly of sophorolipid molecules. Following, genetic engineering strategies that affect the sophorolipid physiochemical properties are summarised. Finally, the impact of sophorolipids on the bioeconomy are uncovered, along with relevant future perspectives.