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 was 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-z8Ad) and 8-aza-2'-deoxyisoguanosine (α-z8iGd). These compounds were prepared from α-D 8-aza-2'-deoxyguanosine by an activation/amination protocol followed by deamination. Protonation and deprotonation pKa values of monomeric nucleosides were determined. Fluorescence measurements displayed the pH-dependent fluorescence intensity of α-D 8-azapurine nucleosides. α-dG and α-z8iGd self-assemble to gels that are selective for K+-ions. The α-dG gel is transparent and the α-z8iGd gel shows fluorescence. α-2-NH2-z8Ad forms fluorescent gels in the presence of alkali metal ions of different size. SEM images exposed a large condensed and flat structure for the α-dG gel, whereas the α-2-NH2-z8Ad gel consists of flakes that are connected to bundles. A porous structure generated by helical cylindric fibers was found for the α-z8iGd gel. All α-D hydrogels showed long-term lifetime stability. The α-z8iGd hydrogel in KCl solution has the highest Tgel value. The minimum gelation concentration of the hydrogels was 0.3-0.5 mg nucleoside/100 µL alkali ion solution. In periodical step-strain experiments, the hydrogels of α-dG and α-2-NH2-z8Ad and α-z8iGd displayed thixotropy. Based on their self-healing and shear-thinning properties the hydrogels are injectable.