8-Aza-2'-deoxyisoguanosine Forms Fluorescent Hydrogels whereas 8-Aza-2'-deoxyguanosine Assembles into Nucleoside Nanotubes.

Fluorescent hydrogels have attracted attention for applications in tissue engineering, drug delivery or as molecular machines. This study describes a nucleoside hydrogel formed by 8-aza-2'-deoxyisoguanosine (z8 isoGd ). The new hydrogel is the first guanosine gel that has intrinsic fluorescence. It has long-term stability and a higher thermal stability (Tgel =77 °C) than gels of 2'-deoxyisoguanosine (Tgel =67 °C) and 2'-deoxyguanosine (Tgel =50 °C). Furthermore, the minimum gel concentration is lower at 0.3 mg per 100 μL for z8 isoGd compared to 0.7 mg for 2'-deoxyisoguanosine. Scanning electron microscopy images show that the z8 isoGd gel forms dense bundles of fibers. The related nucleoside 8-aza-2'-deoxyguanosine does not form a hydrogel but forms nanotube-like structures in the solid state. The fluorescence of the z8 isoGd hydrogel responds to external stimuli such as the addition of alkali metal ions, pH change, heat, and UV irradiation. In binary mixtures with nucleoside shape mimics such as 7-deaza-2'-deoxyisoguanosine, the z8 isoGd hydrogel disintegrates.