Biocatalytic hydrogenations on carbon supports.

We describe the use of carbon as a versatile support for H-2-driven redox biocatalysis for NADH-dependent C=X bond reductions in batch and flow reactions. In each case, carbon is providing an electronic link between enzymes for H-2 oxidation and reduction of the biological cofactor NAD(+), as well as a support for a multi-enzyme biocatalysis system. Carbon nanopowders offer high surface areas for enzyme immobilization and good dispersion in aqueous solution for heterogeneous batch reactions. Difficulties in handling multi-wall carbon nanotubes in aqueous solution are overcome by growing them on quartz tubes to form carbon nanotube column reactors, and we show that these facilitate simple translation of H-2-driven biocatalysis into flow processes. Using this flow reactor design, high conversions (90%) and total enzyme turnover numbers up to 54,000 could be achieved. Use of an entirely heterogeneous biocatalysis system simplifies recovery and re-use of the enzymes; combined with highly atom-efficient cofactor recycling, this means that high product purity can be achieved. We demonstrate these methods as platform approaches for overcoming challenges with NADH-dependent biocatalysis.