Bringing New Chemistry to Guanosine Hydrogels

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Molecular self-assembly is a powerful method to construct functional materials such as supramolecular hydrogels. Hydrogels contain mostly water but show solid-like rheology. Nucleosides and nucleotides contain rich recognition information, which opens up opportunities for gelator design. Hydrogels derived from these natural products have seen a resurgence in the past decade due to the high biodegradability and biocompatibility. Guanosine (G 1) and its analogs are powerful supramolecular hydrogelators. The structural basis for most guanosine hydrogels is G4•M+ quartet with K+ being the best metal to stabilize such a structure. These hydrogen-bonded macrocycles further stack to form 1D G-quadruplex that traps water to give hydrogels. Guanosine hydrogels have been used for applications such as bioactive molecule trap and release, environmental remediation, sensing and cell culture.

While the H-bonded G-quadruplex is critical for gelation, G 1 can be synthetically modified to introduce new functions. The work presented here is focused on G-quartet hydrogels made from synthetic guanosine analogs. Guanosine analogs containing sulfur on 8- and 5ʹ-position are purified and their hydrogelation properties in water were examined. The resulting hydrogels can potentially be applied to environmental remediation.

Substitution of 5ʹ-OH in G 1 into a hydrazine group in HG 2 significantly improves the hydrogelation properties. The resulting HG 2 KCl hydrogel can be used to non-covalently bind anionic dyes and covalently trap toxic electrophiles such as acrolein.

A binary mixture of G 1 and HAG 15 forms a stable hydrogel with KCl. The hydroxamic acid group in HAG 15 serves as a pH-switchable group that can be applied as a carboxylic acid substitute in hydrogelator design. Furthermore, the hydrogel serves as a supramolecular siderophore and binds Fe3+ to generate patterns on the gel surface. The surface can be erased with a reducing agent and rewritten with Fe3+.