Mechanism of Organogel Formation from Mixed-Ligand Silver (I) Carboxylates

Abstract

Ag(I) carboxylate gelators with mixed-ligands were systemically investigated to understand the mechanism of the organic gel formation. The gelators constructed 3-D networks of nanometer-sized thin fibers which facilitated gel formation in various aromatic organic solvents, even at very low concentrations. The loss of reflection peaks in the X-ray diffraction data indicated the reduction of strong interactions between the long alkyl chains as the Ag(I) carboxylates formed gels by maximizing their interactions with the organic solvents. The gelation temperature (Tgel) was measured to explore the interaction between the gelator molecules and solvents depending on their composition and concentration. Based on the gelation phenomena, a dissociation/ re-association mechanism was proposed.

Chameleonic amphiphile: The unique multiple self-assembly properties of a natural glycolipid in excess of water

“…The COOform of the carbonyl group strongly interacts with metal ions, most likely forming G-C18:1 dimers, in agreement with what has been reported in similar systems. (89,90) Meanwhile, the hydrophilic glucose group greatly improves solubilization in water, preventing the dimers to precipitate as a lamellar crystal, as classically found for metal salts of carboxylic acids. (89) According to ssNMR (Figure 5a,b), the 2'-5' and 6' signals of glucose are broad and centered at 75.1 and 61.2 ppm, respectively, thus indicating that conformation of glucose is poorly defined for both micellar (1,8) and fibrillar (7) structures.…”

“…Ions may induce the formation of rafts in lipid bilayers (95) and fibrillation in LMW gelators. (90,96) The effect of cations on biosurfactants has been less studied from a phase behavior point of view. Micellar solutions of sophorolipids seem to be poorly affected by mono and divalent cations,(66) just as rhamnolipids.…”

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

“…Origin of the fiber's b-sheet-like raft structure Fibrillar hydrogels, of which the elastic properties are driven by entanglement, are commonly observed for a large number of systems, including biopolymers, 14 surfactants, 66 peptides 67 and peptide amphiphiles, 10 and biosurfactants. 51,68 Fibrillation by mono and multivalent cations is also well known for bile salts, 69 low-molecular weight gelators, 5,70,71 peptides, peptidederivatives 41,42,72 and polymers. [73][74][75][76][77] If the magnitude of the elastic modulus varies from system to system and depends on the length, dispersion in size of the fiber's cross section, fibers content, spherulite formation, most amphiphilic systems are characterized by the absence of specific forces driving suprafibrillar interactions.…”

“…69 Fibrous networks based on a Ag + /COO À complex can be obtained in organic solvent by solubilization at high temperature and cooling. 69 In water, polymeric gels induced by Ag + bridging carboxylate groups have been described, mainly for the use of silver as an antimicrobial agent. 86 A natural tripeptide was found as a ligand to form a lamellar hydrogel by Ag + / sulfur complexation.…”

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

“…For surfactants, typical evolutions are observed from spheres to cylinders − and wormlike morphologies, , and from micelles to vesicles , or lamellae . For other LMW compounds, such as peptide amphiphiles, peptide derivatives, or bile salts, fibrillation often occurs. ,− By salt addition, one can differentiate several mechanisms, possibly occurring simultaneously, at the origin of the morphological changes: charge screening, bridging, or complexation. , …”