A supramolecular gel based on a glycosylated amino acid derivative with the properties of gel to crystal transition

Abstract

Here we report the generation of a novel gelator from a glycosylated amino acid derivative, which contained three structural units, an aromatic residue, a carbohydrate moiety and a tert-butyl group in a single molecule. These structural units can promote the supramolecular self-assembly of this gelator in both aprotic and protic solvents via coordinated π-π stacking, multiple hydrogen binding and van der Waals interactions. More importantly, due to their non-equilibrium natures, the organogels formed in DCM, chloroform and ethanol can undergo gel to crystal transition in storage, driven by unbalanced gelator-gelator and solvent-gelator interactions. In this process, the gelators were firstly trapped in a kinetically favorable gel state, and then transferred into a more thermodynamically stable crystal state upon ageing, with the generation of microcrystals in different morphologies.

Transformation of Dipeptide‐Based Organogels into Chiral Crystals by Cryogenic Treatment

“…Thev iscoelastic properties of the gels were measured by oscillatory rheology experiments.G enerally,t he viscoelastic behavior of ag el is determined by two key parameters,t he storage modulus (G')a nd the loss modulus (G''), which represent the ability of agel to return to its original geometry and the tendency of amaterial to flow under applied stress. [34] Foragel, G' is greater than G'',a nd G' is very weakly dependent on the oscillatory frequency,d emonstrating the dominant elastic behavior of the gel. Ther esults shown in Figure 3a confirm the formation of an organogel and its elastic properties.Importantly,asthe cryogenic treatment was repeated for several additional cycles,t he mechanical strength increased.…”

“…[26] Owing to the weakness of the non-covalent interactions exploited to maintain the aforementioned equilibrium, such metastable physical gels can be converted into thermodynamically stable crystals.The gel-crystal transitions in several systems have been observed to be triggered by various stimuli, such as light irradiation, pH changes,heating/ cooling, ac hange in ionic strength or solvent, or even storage. [27][28][29][30][31][32][33][34][35] Fori nstance,o ur group has demonstrated that the structural transition from an organogel to flower-like microcrystals can be induced in the dipeptide self-assembly system by using ethanol as ac o-solvent. [18] Herein, we explore cryogenic treatment as an approach to achieve at unable transition from ad ipeptide-based selfassembled organogel to aw ell-ordered crystal (Scheme 1).…”

“…[40] Thus the cryogenic treatment mediates the rebalancing effect, enabling the transformation of am etastable gel phase into athermodynamically stable crystal phase. [34] Interestingly,d uring the transition process,t he wellordered FF crystals exhibited enhanced emission properties. Specifically,a ss hown in Figure 4a,u pon excitation at l = 250 nm, the photoluminescence emission peak of the FF/ HFIP solution at l = 285 nm shifted to 295 nm in FF-toluene gel as the molecules aggregated into gels.A st he number of cryogenic treatments was increased, the emission intensity increased gradually but significantly (Figure 4b).…”

Transformation of Dipeptide‐Based Organogels into Chiral Crystals by Cryogenic Treatment

“…Owing to the weakness of the non‐covalent interactions exploited to maintain the aforementioned equilibrium, such metastable physical gels can be converted into thermodynamically stable crystals. The gel–crystal transitions in several systems have been observed to be triggered by various stimuli, such as light irradiation, pH changes, heating/cooling, a change in ionic strength or solvent, or even storage . For instance, our group has demonstrated that the structural transition from an organogel to flower‐like microcrystals can be induced in the dipeptide self‐assembly system by using ethanol as a co‐solvent …”

“…The viscoelastic properties of the gels were measured by oscillatory rheology experiments. Generally, the viscoelastic behavior of a gel is determined by two key parameters, the storage modulus ( G′ ) and the loss modulus ( G′′ ), which represent the ability of a gel to return to its original geometry and the tendency of a material to flow under applied stress . For a gel, G′ is greater than G′′ , and G′ is very weakly dependent on the oscillatory frequency, demonstrating the dominant elastic behavior of the gel.…”