The rising interest on pathway complexity in supramolecular polymerization has prompted the finding of novel monomer designs able to stabilize kinetically trapped species and generate supramolecular polymorphs. In the present work, the exploitation of the Z/E (geometrical) isomerism of squaramide (SQ) units to produce various self‐assembled isoforms and complex supramolecular polymerization pathways in methylcyclohexane/CHCl3 mixtures is reported for the first time. This is achieved by using a new bissquaramidic macrocycle (MSq) that self‐assembles into two markedly different thermodynamic aggregates, AggA (discrete cyclic structures) and AggB (fibrillar structures), depending on the solvent composition and concentration. Remarkably, UV–vis, 1H NMR, and FT‐IR experiments together with quantum‐chemical calculations indicate that these two distinct aggregates are formed via two different hydrogen bonding patterns (side‐to‐side in AggA and head‐to‐tail in AggB) due to different conformations in the SQ units (Z,E in AggA and Z,Z in AggB). The ability of MSq to supramolecularly polymerize into two distinct aggregates is utilized to induce the kinetic‐to‐thermodynamic transformation from AggA to AggB, which occurs via an on‐pathway mechanism. It is believed that this system provides new insights for the design of potential supramolecular polymorphic materials by using squaramide units.
Supramolecular hydrogels with tunable properties have innovative applications in biomedicine, catalysis, and materials chemistry. Minimalist low-molecular-weight hydrogelators based on squaramide and squaramic acid motifs have been designed. This approach benefits from the high acidity of squaramic acids and the aromaticity of squaramides. Moreover, substituents on the aryl ring tune the π density of the arylsquaramide motif. Thus, materials featuring distinct thermal and mechanical properties have been successfully prepared. The hydrogel (G'≈400 Pa, G''≈57 Pa; at 1.0 % w/v; 1 Hz) obtained from 4-nitrophenylsquaramide motif 1 is thermoreversible (T=57 °C at 0.2 % w/v), thixotropic, self-healable, and undergoes irreversible shrinking in response to saline stress. Furthermore, the hydrogel is injectable and can be loaded with substantial amounts (5:1 excess molar ratio) of zwitterionic biomolecules, such as l-carnitine, γ-aminobutyric acid (GABA), or d,l-Ala-d,l-Ala, without any loss of structural integrity. Then, the release of these molecules can be modulated by saline solutions.
Herein we report the design, synthesis and assessment of the first example of a squaramide-based self-immolative system triggered by an enzymatic reduction. We have proved that the release of the...
Five new compounds have been synthesized and characterized by elemental analysis, IR, NMR and single-crystal X-ray diffraction. They present interesting assemblies in the solid state dominated by H-bonding and anion–π interactions.
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