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

Abstract

Low-molecular weight gelators (LMWGs) are small molecules (Mw < ∼1 kDa), which form self-assembled fibrillar network (SAFiN) hydrogels in water.

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

“…In water at pH 8 and concentrations below 5 wt %, the biosurfactant G-C18:1 mainly forms a micellar phase, possibly coexisting with nanoscale flat objects, because of its negatively charged carboxylate group. , Below pH 8, a micelle-to-vesicle transition has been previously observed in the absence of added salt. , If the addition of a molar amount of NaCl at pH 8 under diluted G-C18:1 conditions has no specific effect on its phase diagram (Figure b), besides screening the charge of the micelles, the addition of alkaline earth and transition metal cations triggers a micelle-to-fiber phase transition , and prompt formation of metallogels for a number of cations. , In this work, we select to study four different systems, which are representative of the metallogel behavior of G-C18:1 found for a number of metal ions . Ca 2+ and Ag + generate hydrogels composed of self-assembled fibers (Figure b) with an analogous crystalline structure and tendency to form β-sheet-like rafts. , Fe 2+ and Al 3+ , on the contrary, form hydrogels with a wormlike micelle structure (Figure b) .…”

“…These data are partially summarized in Figure , where the corresponding cryo-TEM, SAXS, and rheology experiments are presented. A detailed description of the data in Figure can be found in refs − .…”

“…More specifically, the effect of controlled injections of salts of Ag + , Ca 2+ , Fe 2+ , or Al 3+ on the self-assembled morphology of G-C18:1 and pH are monitored in situ in a continuous fashion. The data are correlated with complementary cryo-TEM, oscillatory rheology, and calorimetry experiments performed elsewhere. , …”

“…Recent work has shown that microbial glycolipid amphiphiles self-assemble into micelles at basic pH, , but into vesicles and lamellar phase at acidic pH. − In particular, the monounsaturated glycolipid, glucolipid G-C18:1 (Figure a), obtained by the fermentation of Starmerella bombicola ΔugtB1 fed with glucose and vegetable oil, , was shown to form SAFiN metallogels upon the addition of a wide range of cations to its micellar phase, except for Na + , which has no impact on the phase behavior (Figure b). , This result is unusual because the fibrillation of surfactants driven by multivalent cations is not expected (literature survey can be found elsewhere) . Among all cations tested, two main structures could be observed by applying the combination of cryogenic transition electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS) on the metallogel samples.…”

Metallogels from a Glycolipid Biosurfactant

“…19,46,[60][61][62][63] The broad set of data in our possession (Figure 4 and Ref. 58,59,64 ) shows that self-assembly and gelling occurs at a well-defined ion-to-surfactant molar ratio.…”