Compartmentalizing Supramolecular Hydrogels Using Aqueous Multi-phase Systems.

A generic method is used for compartmentalization of supramolecular hydrogels by using water-in-water emulsions based on aqueous multi-phase systems (AMPS). By forming the low-molecular-weight hydrogel throughout all phases of all-aqueous emulsions, distinct, micro-compartmentalized materials were created. This structuring approach offers control over the composition of each type of the compartments by directing the partitioning of objects to be encapsulated. Moreover, this method allows for barrier-less, dynamic exchange of even large hydrophilic solutes (MW≈60 kDa) between separate aqueous compartments. These features are expected to find use in the fields of, for instance, micro-structured catalysts, templating, and tissue engineering.

Spatial and directional control over self-assembly using catalytic micropatterned surfaces.

Catalyst-assisted self-assembly is widespread in nature to achieve spatial control over structure formation. Reported herein is the formation of hydrogel micropatterns on catalytic surfaces. Gelator precursors react on catalytic sites to form building blocks which can self-assemble into nanofibers. The resulting structures preferentially grow where the catalyst is present. Not only is a first level of organization, allowing the construction of hydrogel micropatterns, achieved but a second level of organization is observed among fibers. Indeed, fibers grow with their main axis perpendicular to the substrate. This feature is directly linked to a unique mechanism of fiber formation for a synthetic system. Building blocks are added to fibers in a confined space at the solid-liquid interface.

Variable gelation time and stiffness of low-molecular-weight hydrogels through catalytic control over self-assembly.

This protocol details the preparation of low-molecular-weight hydrogels (LMWGs) in which the gelation time and mechanical stiffness of the final gel can be tuned with the concentration of the catalyst used in the in situ formation of the hydrogelator. By altering the rate of formation of the hydrazone-based gelator from two water-soluble compounds--an oligoethylene functionalized benzaldehyde and a cyclohexane-derived trishydrazide--in the presence of acid or aniline as catalyst, the kinetics of gelation can be tuned from hours to minutes. The resulting materials display controllable stiffness in the 5-50 kPa range. This protocol works at ambient temperatures in water, at either neutral or moderately acidic pH (phosphate buffer, pH 5) depending on the catalyst used. The hydrazide and aldehyde precursors take a total of 5 d to prepare. The final gel is prepared by mixing aqueous solutions of the two precursors and can take between minutes and hours to set, depending on the catalytic conditions. We also describe analysis of the hydrogels by critical gel concentration (CGC) tests, rheology and confocal laser-scanning microscopy (CLSM).

Covalent stabilization: a sturdy molecular square from reversible metal-ion-directed self-assembly.

Supramolecular self-assembly using weak interactions under quasi-equilibrium conditions has provided easy access to very complex but often quite fragile molecules. We now show how a labile structure obtained from reversible transition-metal-directed self-assembly of rods and connectors serves as a template that can be converted into a sturdy structure of identical topology and similar geometry. The process consists of Cu(I)-catalyzed replacement of all rods or connectors terminated with pyridines for analogues terminated with ethynyls, converting dative N→Pt(+) bonds into covalent C-Pt bonds. The procedure combines the facility and high yield of reversible self-assembly with the robustness of covalent synthesis.

White-light-emitting self-assembled nanofibers and their evidence by microspectroscopy of individual objects.

The self-assembly of a blue-emitting light-harvesting organogelator and specifically designed highly fluorescent tetracenes yields nanofibers with tunable emissive properties. In particular, under near-UV excitation, white light emission is achieved in organogels and dry films of nanofibers. Confocal fluorescence microspectroscopy demonstrates that each individual nanofiber emits white light. A kinetic study shows that an energy transfer (ET) occurs between the blue-emitting anthracene derivative and the green- and red-emitting tetracenes, while inter-tetracene ETs also take place. Moreover, microscopy unravels that the nanofibers emit polarized emission in the blue spectral region, while at wavelengths higher than 500 nm the emission is not significantly polarized.

Time-resolved confocal fluorescence microscopy of trinitrobenzene-responsive organic nanofibers.

Time-resolved confocal fluorescence microscopy is used to image and analyze quantitatively the influence of 1,3,5-trinitrobenzene on the fluorescence of organic nanofibers. These nanofibers are formed by self-assembly of 2,3-didecyloxyanthracene in methanol or from solutions drop-casted onto glass surfaces. Amplification of the fluorescence quenching emerges in the nanofibers as compared to the constituting monomer thus leading to efficient detection of nanomolar concentrations of TNB. The emission of dry nanofibers on glass is also efficiently quenched by vapors of TNB.

Striking correlation between the unusual trigonal crystal packing and the ability to self-assemble into nanofibers of 2,3-di-n-alkyloxyanthracenes.

The space group of the crystals of derivatives of 2,3-dialkoxyanthracenes is monoclinic P2(1)/a (herringbone structure) with the linear ethyl or propyl chains but abruptly changes to the trigonal P3 or R3 space group for butyl to heptyl chains. Strikingly, this switch is correlated with the capacity of these compounds to self-assemble into nanofibers and organogels. Besides, compounds with a chain length exceeding seven carbon atoms could not be crystallized in accordance with the analysis of the projected crystal structure but are nevertheless excellent organogelators. The study of this series of compounds suggests a tight link between the molecular structure of the crystals and that of the organogels.

Energy transfer in self-assembled [N]-acene fibers involving > or =100 donors per acceptor.

Anthracene derivatives self-assemble into fibers with a high molecular order, as is evidenced by probing the structure with energy-trapping tetracene analogues. Efficient energy transfer processes involving tens to hundreds of donors per acceptor and high emission quantum yields are outstanding characteristics displayed in these self-assembled fibers.