Investigating the use of conducting oligomers and redox molecules in CdS-MoFeP biohybrids

In this work we report the effect of incorporating conducting oligophenylenes and a cobaltocene-based redox mediator on photodriven electron transfer between thioglycolic acid (TGA) capped CdS nanorods (NR) and the native nitrogenase MoFe protein (MoFeP) by following the reduction of H⁺ to H₂. First, we demonstrate that the addition of benzidine-a conductive diphenylene- to TGA-CdS and MoFeP increased catalytic activity by up to 3-fold as compared to CdS-MoFeP alone. In addition, in comparing the use of oligophenylenes composed of one (p-phenylenediamine), two (benzidine) or three (4,4''-diamino-p-terphenyl)phenylene groups, the largest gain in H₂ was observed with the addition of benzidine and the lowest with phenylenediamine. As a comparison to the conductive oligophenylenes, a cobaltocene-based redox mediator was also tested with the TGA-CdS NRs and MoFeP. However, adding either cobaltocene diacid or diamine caused negligible gains in H₂ production and at higher concentrations, caused a significant decrease. Agarose gel electrophoresis revealed little to no detectable interaction between benzidine and TGA-CdS but strong binding between cobaltocene and TGA-CdS. These results suggest that the tight binding of the cobaltocene mediator to CdS may hinder electron transfer between CdS and MoFe and cause the mediator to undergo continuous reduction/oxidation events at the surface of CdS.