A Shuttle for the Transport of Protons Based on a [2]Rotaxane
A [2]rotaxane shuttle for (light-driven) proton transport has been designed and synthesized. The rotaxane contains a macrocyclic ring that carries a pyridine nitrogen atom as a basic center to bind and to transport a proton. The axis includes an amide binding site for the macrocycle and a positive charge in close vicinity. Upon protonation of the pyridine nitrogen atom, the hydrogen bond is broken and Coulomb repulsion between the protonated pyridine and the permanent positive charge in the axis pushes the protonated macrocycle to the other end of the axis. By variation of the pH the ring can shuttle to and fro. Its locations on the axis were determined by NMR spectroscopy.