Voltage Gating in Nanopores Containing Anthraquinone Mimics Biological Membrane Proteins

Ion channels formed by membrane bound proteins play a key role in the proper functioning of the human body. These membrane proteins are able to regulate the transport of water, ions, and larger molecules through small openings in the protein under a transmembrane potential. Much study has gone into illuminating how these membrane proteins sense voltage. Some mechanisms include charged residues in proteins that can reorient in an electric field or side chains that have an intrinsic dipole moment. Here we report the first synthetic nanopore to mimic and explore these possible mechanisms.We chemically attached a 9, 10 Anthraquinone (AQ) to the interior of an Alumina nanopore. In the presence of an applied voltage we found the AQ responds in a manner similar to biological pores exhibiting voltage gating. The conductivity verse voltage of the AQ modified nanopore followed a classic sigmoidal gating curve, identical to biological membrane proteins. Through this plot, it is possible determine the exact mechanism of the gating effect. In our system, we determined that the AQ was gaining one electron when the applied voltage reached a certain level. At this voltage level the AQ was reduced to form a radical semiquinone. The potential required to form the semiquinone state can be determined from the conductivity plot. This technique can also be applied to other molecules where the chemical reaction changes it response to an electric field, such as deprotonation, cation incorporation and radical formation.