Stable glycosylamines at the reducing ends of cellulose nanocrystals.

The reaction of reducing end groups in cellulose nanocrystals with dodecylamine was examined. Using a direct-dissolution solution-state NMR protocol, the regioselective formation of glucosylamines was shown. This provides an elegant approach to sustainably functionalize these bio-based nanomaterials, that may not require further reduction to more stable secondary amines.

Organogel Formation Rationalized by Hansen Solubility Parameters: Shift of the Gelation Sphere with the Gelator Structure.

To rationalize how the gelation ability of a low molecular weight gelator is influenced by its molecular structure, we performed extensive solubility tests of a group of thiazole-based gelators and made use of Hansen solubility parameter formalism. We observe that the increase of a linear alkyl chain in these gelators promotes an increase of the radius of the gelation sphere as well as a gradual shift of its center to lower values of the polar (δP) and hydrogen bonding (δH) components. The molecular packing within the fibers and the crystal habit were determined by a combination of X-ray diffraction and molecular modeling. We attribute the gradual and linear shift of the gelation sphere to the fact that all of the studied gelators share the same molecular packing, so that an increasing length of the alkyl chain reduces the proportion of polar groups at the surface, resulting in a gradual increase in the contact between apolar parts of the fiber and the solvent.

Two-Component Self-Assemblies: Investigation of a Synergy between Bisurea Stickers.

It is of interest to develop two-component systems for added flexibility in the design of supramolecular polymers, nanofibers, or organogels. Bisureas are known to self-assemble by hydrogen bonding into long supramolecular objects. We show here that mixing aromatic bisureas with slightly different structures can yield surprisingly large synergistic effects. A strong increase in viscosity is observed when a bisurea with the sterically demanding 2,4,6-trimethylbenzene spacer is combined with a bisurea bearing no methyl group in position 2 of the aromatic spacer (i.e., 4-methylbenzene or 4,6-dimethylbenzene). This effect is the consequence of a change in the supramolecular assembly triggered by the composition of the mixture. The mixture of complementary bisureas forms rodlike objects that are more stable by about 1 kJ/mol and that are thicker than the rodlike objects formed by both parent systems.

Rational Design of Urea-Based Two-Component Organogelators.

Low molecular weight gelators are versatile and responsive gel-forming systems. However, it is still a challenge to develop a new organogelator for a precise application, i.e., to gel a predetermined liquid. We propose a simple concept of a two-component gelling system that can be rationally adapted to gel liquids ranging in polarity from silicone oil to acetonitrile.