Site-specific attachment of a H2-evolving artificial metalloenzyme onto carbon nanotubes via electrografting of a protected thiophenolate diazonium salt

Abstract

The development of efficient and stable electrodes for hydrogen evolution is a key challenge in the field of artificial enzymes and bioelectrocatalysis. We report the tuning of an artificial metalloenzyme–electrode interface using a covalent near-monolayered thiophenolate functionalisation of multiwalled carbon nanotubes (MWCNT). To this end, we synthesized, characterized, and electrografted 4-diazophenyl disulfide bis(tetrafluoroborate) to the surface of carbon-nanotube electrodes. A subsequent deprotection step yields highly functionalized thiophenolate-modified CNTs, which were employed for the immobilization of ferrocene derivatives and rubredoxins either via disulfide or thiolene formation. Introduction of a surface-accessible cysteine residue via site-directed mutagenesis of rubredoxin – followed by Fe-to-Ni metal substitution – affords the site-specific immobilization of this H₂-evolving artificial metalloenzyme, which delivers up to 4 mA cm⁻² at 800 mV overpotential.