Surface-Tuned and Metal-Ion-Responsive Supramolecular Gels Based on Nucleolipids

Supramolecular synthons based on nucleic acid components, nucleobases and nucleosides, and their derivatives have been highly useful in constructing wide varieties of nanoarchitectures. While most of the design strategies have focused on developing biocompatible delivery vehicles, the potential of nucleoside hybrids in assembling smart materials with tunable and sensing properties, though challenging, is gaining significant attention. Here, we describe the development of novel functional materials with surface tunability and metal-ion responsiveness by using simple nucleolipid supramolecular synthons derived by attaching various fatty acids to the 3′-<i>O</i> or 3′,5′-<i>O</i> positions of the sugar residue of thymidine nucleoside. 3′,5′-<i>O</i>-Difatty acid-substituted thymidines formed typical organogels in pure organic solvents, whereas, 3′-<i>O</i>-monofatty acid-substituted thymidine nucleolipids formed water-induced gels. A detailed morphological and structural analysis using microscopy, single-crystal and powder X-ray diffraction, and NMR techniques clearly revealed the molecular interactions invoked by nucleobase, sugar, fatty acid chain, and water in setting up the path for hierarchical self-assembly and gelation of thymidine nucleolipids. Interestingly, the surface property of the xerogel film fabricated using 3′-<i>O</i>-monosubstituted nucleolipid gels could be switched from highly hydrophobic to hydrophilic and <i>vice versa</i> depending on the nature of the organic solvent–water mixture used in the gelation process. On the contrary, the gelation process of disubstituted thymidine nucleolipids was highly sensitive to the presence of Hg<sup>2+</sup> ions as the metal ion formed a T–Hg–T base pair, thereby disrupting the H-bonding interactions that favored the gelation. Taken together, straightforward synthesis and modification-dependent gelation behavior, surface tunability, and metal-ion responsiveness underscore the potential of these supramolecular nucleolipid synthons in constructing novel functional materials.