Hierarchical Self-Assembly of Chiral Complementary Hydrogen-Bond Networks in Water:  Reconstitution of Supramolecular Membranes

Abstract

Spontaneous formation of complementary hydrogen-bond pairs and their hierarchical self-assembly (reconstitution) into chiral supramolecular membranes are achieved in water by mixing amphiphilic pairs of glutamate-derived melamine 6 and ammonium-derivatized azobenzene cyanuric acid 4. Electron microscopy is used to observe formation of helical superstructures, which are distinct from the aggregate structures observed for each of the single components in water. In addition, a spectral blue-shift and induced circular dichroism (ICD) with exciton coupling are observed for the pi-pi* absorption of the azobenzene chromophores. These observations are consistent with the reconstitution of the hydrogen-bond-mediated supramolecular membrane 6-4. Spectral titration experiments indicate the stoichiometric integration of the complementary subunits with an association constant of 1.13 x 10(5) M(-1). This value is considerably larger than those reported for the artificial hydrogen-bonding complexes in aqueous media. The remarkable reconstitution efficiency is ascribed to the hydrophobically driven self-organization of the amphiphilic, linear hydrogen-bond networks in water. Molecular structure of the complementary subunits plays an important role in the complexation process since it is restricted by the photoisomerized cis-azobenzene subunit. On the other hand, thermally regenerated trans-isomer 4 undergoes facile complexation with the counterpart 6. The present reconstitution of supramolecular membranes provides the first example of complementary hydrogen-bond-directed formation of soluble, mesoscopic supramolecular assemblies in water.

Hierarchical formation of helical supramolecular polymers via stacking of hydrogen-bonded pairs in water

“…The analogy might be made here to nucleic acid oligomers; whereas single mononucleotides do not form a hydrogen-bonded supramolecular structure in water, covalently connected oligonucleotides do (1). That stacking is observed already at concentrations as low as 5⅐10 Ϫ6 M indicates that it precedes hydrogen bonding and concomitant formation of helical columns, which occurs around 10 Ϫ4 M. The use of a hydrophobic interaction as the driving force for self assembly, generating a hydrophobic microenvironment to allow expression of hydrogen bonding, has also recently nicely been demonstrated for the hierarchical formation of membranes (24).…”

“…Natural molecules use a hydrophobic microenvironment that shields the hydrogen bonding from the water such as in the double helix of DNA (1) and the interior of proteins (31, 32). Synthetic systems using this principle have been demonstrated (21)(22)(23)(24)(25)(33)(34)(35)(36)(37)(38)(39)(40)(41). It was anticipated that such a microenvironment, which is required for the creation of multimolecular helical columnar architectures in water analogous to those observed for 2 in dodecane, would be created by the arene-arene stacking of the hydrophobic aromatic surfaces of the molecules.…”

“…Peripheral chiral centers in assemblies (8)(9)(10)(11) and chiral side chains attached to a polymer backbone (12)(13)(14)(15)(16)(17)(18)(19)(20) have been shown to bias chirality at the supramolecular level. Highly ordered multimolecular supramolecular structures stable in water, held together by hydrophobic interactions or with additional hydrogen bonding, are also known (21)(22)(23)(24)(25). However, it remains difficult to exploit directional noncovalent interactions in a cooperative way for the formation of discrete multimolecular assemblies stable in water.…”

Induced Circular Dichroism of Anionic Porphyrin TPPS Aggregates in DNA Solutions

“…[1][2][3] There are many achiral molecules reported to show chirality induced by certain chiral templates, [4][5][6][7] in which the chirality of achiral molecules can be induced through the interactions of achiral molecules with the chiral templates and the chirality of achiral molecules usually follows the chirality of the templates.…”

Urea Route to Homoleptic Cyanates—Characterization and Luminescence Properties of [M(OCN)2(urea)] and M(OCN)2 with M=Sr, Eu

“…Whitesides et al have extensively studied the hydrogenbonded adducts of cyanuric acid (C 3 N 3 (OH) 3 , CA) and melamine (CA·M) as an outstanding example of noncovalent synthesis. [1,2] Such weak interactions have received considerable attention (for example self-assembly, [3] nanostructures, [4] and supermolecular architectures [5] ).…”