A Hydrogen-Bonded Organic Framework Equipped with a Molecular Nano-Valve

The concept of a molecular nano-valve is applied to a newly synthesized biocompatible hydrogen-bonded organic framework (HOF), termed RSS-140, in order to load, trap, and subsequently release an antioxidant on command. Specifically, we exploit the pore windows of RSS-140 (i.e., β-CD cavities) to first load and trap the antioxidant, Trolox, within the internal pores of the HOF (Trolox⊂RSS-140) and, to prevent it from leaching, utilize supramolecular chemistry to complex azobenzene (Azo) with β-CD (Trolox⊂Azo@RSS-140). The molecular nano-valve is fully realized upon exposing Trolox⊂Azo@RSS-140 to UV light with a specific wavelength, which induces Azo isomerization, Azo decomplexation from β-CD, and subsequent release of Trolox from the pores of RSS-140. The biocompatibility and non-toxicity of Trolox⊂Azo@RSS-140, together with the absolute control over the nano-valve opening, was established to yield a system that safely and slowly releases Trolox for longer-lasting antioxidant efficacy. As the field of supramolecular chemistry is rich with similar systems and many such systems can be used as building blocks to construct HOFs or other extended framework materials, we envision the molecular nano-valve concept to be applied widely for controllably delivering molecular cargo for diverse applications.