Luminescent Helical Nanofiber Self-Assembled from a Cholesterol-Based Metalloamphiphile and Its Application in DNA...

Compared to pure organic amphiphiles, metalloamphiphiles display distinctive features, including luminescence, magnetism and catalytic properties. However, the self-organization of metalloamphiphiles is commonly driven by solvophobic effects. Alkyl chains and oligomeric ethylene glycol moieties are thus the most frequently used aggregation units to drive the self-assembly of metalloamphiphiles. We expect novel metallo-supramolecular structures with exciting functions to be created if additional noncovalent interaction modes are incorporated. In this work, a new type of metalloamphiphile, consisting of a Tb(III) complex head and a cholesteryl unit (TbL³⁺(I)), was designed and synthesized. TbL³⁺(I) spontaneously self-assembles into helical nanofibers (d = 6 nm) in water. This synthetic multivalent nanoscale binding array displays powerful capability for the recognition of DNA conformations through a turn-on luminescence sensing mechanism. ssDNA-kit1 triggered a 26-fold increase in the luminescence intensity of TbL³⁺(I). Its corresponding G-quadruplex structure (G-quadruplex-kit1), however, induced a 6.6-fold enhancement under the same conditions. Consequently, TbL³⁺(I) nanofibers can monitor DNA folding. In contrast, neither ssDNA-kit1 nor G-quadruplex-kit1 markedly promoted the luminescence of molecularly dispersed TbL³⁺(II), illustrating that the multivalent electrostatic interactions between the phosphate groups on the backbone of DNA and TbL³⁺(I) self-assembled into nanofibers could greatly improve the efficiency of the energy transfer between the guanine units and the organized TbL³⁺(I). The TbL³⁺(I) nanofibers could bind and distinguish not only the kit1-ssDNA/G-quadruplex but also the conformations of other G-rich DNA, such as spb1, htelo, and intermolec-htelo. The self-assembly of luminescent metalloamphiphiles thus provides a general and convenient strategy for the efficient recognition and conversion of molecular information.