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

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 isoG_d ). The new hydrogel is the first guanosine gel that has intrinsic fluorescence. It has long-term stability and a higher thermal stability (T_gel =77 °C) than gels of 2'-deoxyisoguanosine (T_gel =67 °C) and 2'-deoxyguanosine (T_gel =50 °C). Furthermore, the minimum gel concentration is lower at 0.3 mg per 100 μL for z⁸ isoG_d compared to 0.7 mg for 2'-deoxyisoguanosine. Scanning electron microscopy images show that the z⁸ isoG_d 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 isoG_d 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 isoG_d hydrogel disintegrates.