Fluorous gallic acid derivatives as versatile gelators. Self-assembly into nanosized fibers or balls

Helical nanofibers of N-(perfluorooctanoyl)cysteine ethyl ester in coordination polymers of Ag. Chem Commun (Camb) 2020;56:15133-15136. [PMID: 33165457 DOI: 10.1039/d0cc05989g]

We propose using the formation of coordination polymers of Ag+ to probe differences between the perfluorinated alkyl chain and the alkyl chain by deriving a thiol ligand, N-(perfluoroalkanoyl)cysteine. Rapid formation in EtOH of P-/M-helical nanofibrils of high thermostability was found for N-(perfluorooctanoyl)-l-/d-cysteine ethyl esters at the μM level upon mixing with Ag+, but not for the octanoyl counterpart. This difference was also observed in terms of circular dichroism-enantiomeric excess dependence.

Sustainable sorbitol-derived compounds for gelation of the full range of ethanol-water mixtures

During the development of soft material systems inspired by green chemistry, we show that naturally occurring starting materials can be used to prepare mono- and di-benzylidene sorbitol derivatives. These compounds gelate a range of organic, aqueous (including with mono and divalent metal salt solutions) and ethanolic (ethanol-water) solutions, with the equimolar mixture of two of the gelators gelling all compositions from 100% ethanol to 100% water (something neither of the individual components do). We explored the influence of modifications to the acetal substituents on the formation of the compounds as well as the impact of steric bulk on self-assembly properties of the gelators. The effect of solvent on the self-assembly, morphology, and rheology of the 1,3:2,4-di(4-isopropylbenzylidene)-d-sorbitol (DBS-iPr), 2,4(4-isopropylbenzylidene)-d-sorbitol (MBS-iPr) and the equimolar multicomponent (DBS-MBS-iPr) gels have been investigated. DBS-iPr gelates polar solvents to form smooth flat fibres, whereas in non-polar solvents such as cyclohexane helical fibres grow where the chirality is determined by the stereochemistry of the sugar. Oscillatory rheology revealed that MBS-iPr gels have appreciable strength and elasticity, in comparison to DBS-iPr gels, regardless of the solvent medium employed. Powder X-ray diffraction was used to probe the arrangement of the gelators in the xerogels they form, and two single crystal X-ray structures of related MBS derivatives give the first precise structural information concerning layering and hydrogen bonding in the monobenzylidene compounds. This kind of layering could explain the apparent self-sorting behaviour of the DBS-MBS-iPr multicomponent gels. The combination of sorbitol-derived gelators reported in this work could find potential applications as multicomponent systems, for example, in soft materials for personal care products, polymer nucleation/clarification, and energy technology.

Stereochemical effects on dynamics in two-component systems of gelators with perfluoroalkyl and alkyl chains as revealed by vibrational circular dichroism

The VCD method was applied to the gelation processes of chiral two-component gel systems.

Rapid self-healing and anion selectivity in metallosupramolecular gels assisted by fluorine–fluorine interactions

Metal complexes from perfluoroalkylamide terpyridine self-assemble into anion selective gels, which manifest self-healing and thermal rearrangement in aqueous dimethyl sulfoxide.

Fluorous 'ponytails' lead to strong gelators showing thermally induced structure evolution

Appending perfluoroalkyl substituents to bis(urea) gelators results in significantly decreased inter-chain interactions with markedly thinner fibres and hence more cross-linked and more transparent gels with potential applications in the crystallisation of fluorinated pharmaceuticals. Gel structure has been probed by detailed SANS measurements which indicate a surprising structure evolution on thermal cycling, not seen for hydrocarbon analogues. The SANS data are complemented by the single crystal X-ray structure of one fluorinated gelator.

Perfluorinated gelators for solidifying fluorous solvents: effects of chain length and molecular chirality

With a purpose of solidifying fluorous solvents, a novel series of perfluorinated gelators based on 1,2-diaminocyclohexane (denoted as CFn: n = the number of carbon chain in perfluoroalkanoyl moiety) were developed.