Electrical communication of redox proteins by means of electron relay-tethered polymers in photochemical, electrochemical and photoelectrochemical systems

Redox polymers act as macromolecular interfaces that electrically communicate redox centers in proteins with their macroscopic environment. N-Methyl-N′-carboxyalkyl-4,4′-bipyridinium-derivatized polylysine (1) acts as an electron mediator from photoexcited Ru(bpy)₃²⁺ to the redox enzyme glutathione reductase (GR). The rate of electron transfer from the redox polymer to GR is controlled by the chain lengths linking the bipyridinium units to the polymer. Nitrate reductase (NR) immobilized in an acrylamide-N-methyl-N′-acrylamido-4,4′-bipyridinium copolymer (4) reveals electrical communication with photoexcited Ru(bpy)₃²⁺ and stimulates the photoinduced biocatalyzed reduction of nitrate (NO₃^-) to nitrite (NO₂^-). Electrobiocatalyzed reduction of nitrate to nitrite is accomplished by immobilization of NR in polythiophene-4,4′-bipyridinium associated with an Au electrode. The rate of electrocatalyzed reduction of NO₃^- relates to the bulk concentration of nitrate, and thus the enzyme electrode acts as a biosensor for NO₃^-. Photoelectrochemical biocatalyzed reduction of nitrate to nitrite is accomplished by electrostatic or covalent attachment of NR to a N-methyl-N′-propionyl-4,4′-bipyridinium-derivatized polyethyleneimine associated with semiconductor TiO₂ colloids or powders. The polymer acts as electron trap of conduction band electrons and electrically communicates the semiconductor photocatalyst with nitrate reductase.