Drawing with Iron on a Gel Containing a Supramolecular Siderophore

Guanosine-5 '-hydroxamic acid (3) forms hydrogels when mixed with guanosine (1) and KCl. The 5 '-hydroxamic acid (HA) unit is pH-responsive and also chelates Fe3+. When gels are prepared under basic conditions, the 5 '-HA groups are deprotonated and the anionic hydrogel binds cationic thiazole orange (TO), signaled by enhanced fluorescence. The HA nucleoside 3, when immobilized in the G-quartet gel, acts as a supramolecular siderophore to form red complexes with Fe3+. We patterned the hydrogel's surface with FeCl3, by hand and by using a 3D printer. Patterns form instantly, are visible by eye, and can be erased using vitamin C. This hydrogel, combining self-assembled G-quartet and siderophore-Fe3+ motifs, is strong, can be molded into different shapes, and is stable on the bench or under salt water.