Self-Assembled Fluorinated Organogelators for Surface Modification

Fluorine Effect in the Gelation Ability of Low Molecular Weight Gelators

The three gelators presented in this work (Boc-D-Phe-L-Oxd-OH F0, Boc-D-F₁Phe-L-Oxd-OH F1 and Boc-D-F₂Phe-L-Oxd-OH F2) share the same scaffold and differ in the number of fluorine atoms linked to the aromatic ring of phenylalanine. They have been applied to the preparation of gels in 0.5% or 1.0% w/v concentration, using three methodologies: solvent switch, pH change and calcium ions addition. The general trend is an increased tendency to form structured materials from F0 to F1 and F2. This property ends up in the formation of stronger materials when fluorine atoms are present. Some samples, generally formed by F1 or F2 in 0.5% w/v concentration, show high transparency but low mechanical properties. Two gels, both containing fluorine atoms, show increased stiffness coupled with high transparency. The biocompatibility of the gelators was assessed exposing them to fibroblast cells and demonstrated that F1 and F2 are not toxic to cells even in high concentration, while F0 is not toxic to cells only in a low concentration. In conclusion, the presence of even only one fluorine atom improves all the gelators properties: the gelation ability of the compound, the rheological properties and the transparency of the final materials and the gelator biocompatibility.

Multi-responsive organo- and hydrogelation based on the supramolecular assembly of fluorocarbon- and hydrocarbon-containing hybrid surfactants

HYPOTHESIS

Novel photoresponsive hybrid surfactants, in which a combination of perfluoroalkyl and alkyl chains and cationic head groups are connected via azobenzene moieties, are excellent candidates for assembling low-molecular-weight organogels (LMOGs) with reversibly switchable viscoelasticities triggered by external stimuli.

EXPERIMENTS

The structure-composition-property relationships of gels assembled with the hybrid surfactants were investigated by UV-vis and NMR spectroscopy, SEM, XRD, and rheology.

FINDINGS

Hybrid surfactants containing perfluorohexyl chains with more than six carbons gelled in a variety of organic solvents at concentrations of less than a few percent. In particular, compositions with the perfluorooctyl and somewhat shorter hydrocarbon chains (C1-C4) gelled in both organic solvents and water. The gellable solvent species can be well grouped according to their solubility parameters, suggesting that gelation properties can be predicted from the chemical structure of the surfactant. Mechanical and structural investigations revealed that gel viscoelasticity can be reversibly altered by applying photo, shear, and heat stimuli, which is achieved through the formation and deformation of lamella-like molecular aggregates. The multi-responsive gelation and facile molecular design of the present hybrid surfactants will expand the fields in which fluorinated LMOGs can be applied.

A fluorous sodium l-prolinate derivative as low molecular weight gelator for perfluorocarbons

We report the first study dealing with the self-assembly of an α-amino acid derivative in perfluorocarbons. Rheology, microscopy, and spectroscopy studies reveal that the fluorous sodium l-prolinate derivative 1 self-assembles in perfluorocarbons to form a three-dimensional network of left-handed nano-helices resulting in solvent gelation. Singlet oxygen lifetime measured in a gel of perfluorodecalin is about 1000 times longer than in pure water.

Micro-flow synthesis of β-amino acid derivatives via a rapid dual activation approach

Rapid dual activation (≤3.3 s) of both β-amino acid N-carboxy anhydride and alkyl chloroformate for the synthesis of a β-amino acid-derived scaffold was demonstrated. The key to success was the use of rapid mixing enabled by using a micro-flow reactor. The one-flow synthesis of 22 β-amino acid derivatives was achieved.