C₃-Symmetrical Supramolecular Architectures:  Fibers and Organic Gels from Discotic Trisamides and Trisureas

Abstract

Hydrogen bonded C(3)-symmetrical molecules that associate into supramolecular stacks are described. Structural mutation on these molecules has been performed to elucidate the contribution of the different secondary interactions (hydrogen bonding, pi-pi stacking) to the self-assembly of the disks into chiral stacks. Twelve C(3)-symmetrical molecules have been investigated, six of which contain three central amide functionalities (1a-f) and six of which contain three central urea groups (2a-f). Peripheral groups of the disks are "small", "medium", or "large", half of them being achiral and the other half being chiral, to enable investigation of the supramolecular architectures with CD spectroscopy. In all of the cases, elongated, helical stacks are formed in apolar solution, except for the "medium" amide disks 1c/d. The elongated stacks of the C(3)-symmetrical disks form gels, which are visualized by AFM and SANS, and this confirms the directionality of the interactions. For the "large" urea disk, 2f, fibers with a length of up to 2 microm are observed. Temperature dependent and "sergeants-and-soldiers" CD measurements reveal that the urea stacks are much more rigid than the corresponding amide ones. In case of the "medium" urea disks, 2c/d, a true rigid rod, is formed. Where amide disks immediately reach their thermodynamic equilibrium, kinetic factors seem to govern urea aggregation. In a number of experiments aimed at reversibility with the urea stacks, hysteresis is observed, implying that these urea disks initially form a poorly defined stack, which subsequently transforms slowly into a well-defined, chiral architecture.

Induction and control of supramolecular chirality by light in self-assembled helical nanostructures

“…5 for calculation details). The structure resembles the C3 symmetric helical supramolecular structures based on 1,3,5-benzenetricarboxylic acid and others thoroughly studied by Meijer and colleagues [33][34][35] .…”

Self‐assembly of supramolecular polymers into tunable helical structures

“…4). 58 Molecuar modeling studies and an X-ray structural analysis strongly supported the curved and coplanar conformation of the helical backbone. This curvature lead to a helical arrangement for longer oligomers with lengths exceeding 7-9 units, where it is proposed that p-p interactions further stabilize the helical architecture once a turn is completed.…”

“…[53][54][55][56] and Meijer and coworkers, [57][58][59] where p-p stacking interactions combined with hydrogen-bonding interactions direct folding. Huc and coworkers reported that oligoamide strands composed of alternating 2,6-bis(carbonylamino) pyridine units and 2,6-pyridinedicarboxamide units selforganized into single stranded helical structures upon forming intramolecular hydrogen bonds (Fig.…”

Toward poly(aminophthalimide), structures of dimers and trimers

“…Examples are binding of mercury ions to helical oligomeric cholates 23 and the induction of helicity in oligo-(meta-ethynylpyridine)s upon binding of saccharides. 24 From a fundamental point of view, the intrinsic folding dynamics 25 of these molecules can provide insight into the more complex folding behavior of proteins as foldamers are composed of a single monomer.…”

“…Recently, we reported a new class of poly(ureidophthalimides) (PUP, 1) illustrated in Figure 1, which was shown to fold in apolar and polar media [25][26][27] depending on the nature of the R* group. The NH-groups of the ureas, which are positioned at the 3,6-positions of phthalimide ring, preferentially adopt a conformation in which intramolecular hydrogen bonding of the NH protons with the adjacent imide oxygens is operational.…”