A Novel Tautomeric Polymorph of Anhydrous Guanine and Its Reversible Water Harvesting Property

Tautomeric isomerism is very important in DNA/RNA research, especially base-pair mismatches. However, the tautomeric polymorph of anhydrous guanine (AG) composed of a N₇-G purine ring has never been reported in the literature. Herein, a novel crystal phase of anhydrous guanine consisting of a N₉-G purine ring was obtained by dehydration of guanine monohydrate (GM) at 111 °C, termed dehydrated-GM, the first reported tautomeric polymorph of AG (N₇-G). The dehydration/hydration transformation between GM and dehydrated-GM can be repeated more than 10 times without any observable phase damage. The dehydrated-GM can harvest 8 wt % water within 30 min at relative low humidity (below 20%). Furthermore, dehydrated-GM has long-term stability in a very dry environment when the temperature is in between RT and 150 °C. The channel structure of dehydrated-GM can enlighten the design of materials to harvest water from atmospheric air. The tautomeric polymorphism of N₇-G and N₉-G purine rings provides a new insight in nucleic acid bases crystals.