α‐D Nucleoside Based Self‐Healing Supramolecular Hydrogels Derived from the α‐D Anomers of 2’‐Deoxyguanosine and Fluorescent 8‐Azapurine 2’‐Deoxyribofuranosides

Self-assembly of α-D nucleosides to supramolecular hydrogels is described in detail. Hydrogel formation is studied on α-D 2'-deoxyguanosine (α-dG), and the fluorescent 8-azapurine α-D nucleosides 2-amino-8-aza-2'-deoxyadenosine (α-2-NH₂-z⁸A_d) and 8-aza-2'-deoxyisoguanosine (α-z⁸iG_d). These compounds were prepared from α-D 8-aza-2'-deoxyguanosine by an activation/amination protocol followed by deamination. Protonation and deprotonation pK_a values of monomeric nucleosides were determined. Fluorescence measurements displayed the pH-dependent fluorescence intensity of α-D 8-azapurine nucleosides. α-dG and α-z⁸iG_d self-assemble to gels that are selective for K⁺-ions. The α-dG gel is transparent and the α-z⁸iG_d gel shows fluorescence. α-2-NH₂-z⁸A_d forms fluorescent gels in the presence of alkali metal ions of different size. SEM images expose a large condensed and flat structure for the α-dG gel, whereas the α-2-NH₂-z⁸A_d gel consists of flakes that are connected to bundles. A porous structure generated by helical cylindric fibers was found for the α-z⁸iG_d gel. All α-D hydrogels show long-term lifetime stability. The α-z⁸iG_d hydrogel in KCl solution has the highest T_gel value. The minimum gelation concentration of the hydrogels is 0.3-0.5 mg nucleoside/100 μL alkali ion solution. In periodical step-strain experiments, the hydrogels of α-dG, α-2-NH₂-z⁸A_d and α-z⁸iG_d displayed thixotropy. Based on their self-healing and shear-thinning properties the hydrogels are injectable.