Pyrene-anchored boronic acid receptors on carbon nanoparticle supports: Fluxionality and pore effects

Pyrene-appended boronic acids self-assemble onto graphitic surfaces and are shown here to self-assemble also around negatively charged carbon nanoparticles of ca. 8-18 nm diameter (Emperor 2000, Cabot Corp.). The resulting boronic acid modified nanoparticles are water-insoluble and readily deposited onto graphite electrodes, for example for electroanalytical applications. Boronic acid binding to the ortho-quinol caffeic acid is demonstrated and the mechanism based on ligand fluxionality is further investigated. Electrodes based on nanoparticle aggregates are sensitive to caffeic acid with Langmuirian binding constants estimated as 106 mol-1 dm3. The molecular structure of the pyrene-appended boronic acid affects the ability to bind caffeic acid as well as, more importantly, the fluxional transformation of the strongly bound (high oxidation potential) into the weakly bound (low oxidation potential) form. The resulting design principles for improved boronic acid receptors are discussed.