First Electrical Connection Between Hydrogenase Enzymes and Nanotubes; Potential Biohybrid Catalyst for Hydrogen Production and Use

National Renewable Energy Laboratory (NREL) in Colorado are reporting the first successful electrical connection between hydrogenase enzymes and carbon nanotubes.Their work, which shows that surfactant-suspended carbon single-walled nanotubes (SWNTs) spontaneously self-assemble with [FeFe] hydrogenases in solution to form catalytically active biohybrids Hydrogenase enzymes, comprising a polypeptide chain and abundant first-row transition metals, show promise as catalysts for use in hydrogen production and in fuel cells. However, establishing a robust electrical connection for use in an electric device between the enzyme and a support in a manner that does not compromise catalytic activity has proven difficult. Currently, precious metals such as platinum perform the requisite catalysis in devices. the [FeFe] hydrogenase I (CaHydI) from the anaerobic bacterium Clostridium acetobutylicum. Neither CaHydI nor the SWNTs were specially modified to facilitate formation of complexes. The hydrogenase remains catalytically active so long as anaerobic conditions are maintained.

Molecular model of CaHydI hydrogenase enzyme bound to a SWNT, one of several plausible arrangements. The yellow and green units show the FeS clusters. There are many possible geometries, but the existence of a strong electronic interaction demonstrates that at least one of the FeS clusters must be proximal to the tubes.

By carefully designed synthesis, it should be possible to tune the catalytic biohybrids for use as electrochemical probes for in vivo detection of hydrogenase activities. More importantly, this work offers the first step toward the construction of functional hydrogenase/SWNT hybrids for application in a variety of hydrogen production and fuel cell technologies.