Photodegradable coumarin-derived amphiphilic dendrons for DNA binding: Self-assembly and phototriggered disassembly in water and air-water interface.

In this article, we demonstrate the self-assembly and photoresponive behavior of a novel coumarin-based amphiphilic dendron in both aqueous solution and air-water interface. The dendritic structure, namely C-IG, was composed of a lipophilic cholesterol and hydrophilic poly(amido amine) (PAMAM) dendron, and the amphiphilic counterpart is interconnected by a photolabile coumarin carbonate ester, enabling the photoinduced degradation of the amphiphiles in protic solvents via S1-like mechanism. A Nile red solubilization fluorescence assay suggests a low critical aggregation concentration for the micelle formation of C-IG in aqueous solutions (3.9 × 10 M); the Langmuir analysis further indicates that C-IG possesses significant compressibility in air-water interface, eventually forming homogeneous monolayers with a final molecular area (A) of 36 Å. Notably, the micelles and Langmuir monolayer are quite stable until photo-triggered dissociation based on the photocleavage of C-IG amphiphile activated by 365-nm incident light. Moreover, the transition in interfacial morphology of the Langmuir monolayer during the assembly and photodegradation processes also can be visually analyzed by incorporating Nile red probes with in situ monitoring through fluorescence microscopy. The thin film deposited on a glass substrate by the Langmuir-Blodgett technique also shows a photoresponsive behavior based on the change in the contact angles of a water droplet on the surface upon light stimulation. The binding affinity of C-IG and cyclic DNA determined by the fluorescence quenching analysis of the coumarin reporter suggests a ground-state macromolecular complexation process occurring through polyvalent interactions between the pseudodendrimers and biomacromolecules. The ethidium bromide displacement assay further indicates thus dendriplex formation at low nitrogen-to-phosphorous value (N/P < 1) and confirms that the decomplexation accompanied by DNA release can be achieved through an active phototriggered route under spatiotemporal control.