Anion-triggered melamine based self-assembly and hydrogel.

We found that melamine in its protonated form could be triggered by oxoanions such as NO(3)(-), PO(4)(3-), ATP, and SO(4)(2-) to form superstructures and to gelate a large amount of water molecules, presumably resulting from the electrostatic and hydrogen bonding interactions operating in a synergistic manner; the gelation can be reversibly switched off/on by increasing/decreasing pH or temperature.