Brominated ferracarboranes as diffuse redox mediators for glucose oxidase bioanodes

Two new brominated ferracarboranes, Li[Fe(3,1,2-C2B9H11) (8-Br-3,1,2-C2B9H10)] and Li[Fe(8-Br-3,1,2-C2B9H10)2] have been synthesized and characterized for use as redox mediators in a glucose oxidase (GOx) bioanode. These complexes were synthesized to more closely match the redox potential of the flavin adenine dinucleotide (FAD) cofactor in GOx as the parent complex, Li[Fe(3,1,2-C2B9H10)2], exhibited a redox potential too low to optimally oxidize FADH2 back to FAD. Hydrogen atoms attached to the carborane cage have been replaced with B–Br vertices to induce an anodic shift to the mediator Fe(III)/Fe(II) redox potential, making them stronger oxidizing agents. An anodic shift of ca. 150 mV in PBS and ca. 170 mV in MeCN was observed for each bromine added. Diffusion coefficients were determined for the complexes, with the heavier, brominated complexes showing decreased diffusion rates with respect to the parent non-brominated complex. These bromoferracarboranes were tested as diffuse mediators for a GOx-chitosan bioanode.