Reversible self-assembly in water of small molecules into ordered structures is an essential process that underlies many biological functions and developmental strategies for biomedical materials. We report that low molecular weight monomers containing triaminopyrimidine and cyanuric acid recognition elements can be used to generate supramolecular polymers and hydrogels. Mimicking the base pairing interactions of nucleic acids, hydrogen bonding directs assembly of monomers into bimolecular rosettes which stack into micron length supramolecular polymers (containing tens of thousands of monomers). The hydrophobic effect drives the assembly of the small water-soluble monomers into long noncovalent structures and is responsible for the observed cooperative assembly mechanism. Monomer assembly exhibits the ultimate achievable sensitivity to pH change for a supramolecular polymerization system, with bidirectional response and maximum assembly occurring at physiological pH (see figure). Results will be presented that demonstrate how this was achieved with controlled, precise and predictable outcomes by employing pKa-matched acidic and basic hydrogen bonded recognition elements. Additionally, precipitation, which causes gel collapse, severely limits the utility of many supramolecular gels. We demonstrate that polymer heterogeneity resulting from the co-assembly of additional monomers with small structural differences extend gel lifetimes by frustrating regular packing between assemblies. These results illustrate the advantages of using pKa-matched recognition elements and multi-component assemblies in the development of environmentally responsive and well-behaved molecular self-assembly systems.

Aqueous assembly and ultrasensitive pH control of biomimetic supramolecular polymers and hydrogels

250th National Meeting (2015)

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