Mechanistic insights into biomimetic carbonic anhydrase action catalyzed by doped carbon nanotubes and graphene.

Electronic structural analyses of hydrogen terminated metal doped carbon nanotube/graphene (M-CNT/Gr, MN-CNT/Gr, M = Ru/Rh) and ruthenium cluster decorated carbon nanotube/graphene (Ru-CNT/Gr) were carried out for examining the biomimetic catalytic activity towards CO hydration reaction. The carbonic anhydrase action was followed for the reaction of CO with HO resulting in a bicarbonate ion and a proton. All the catalysts were found to be active for CO hydration and the mechanism proved them to be biomimetic. Interconversion of CO to a HCO ion took place with five elementary steps viz. OH formation by HO dissociation, linear CO complexation, CO bending by nucleophilic attack of an OH ion over CO, HCO ion formation by intramolecular proton migration and HCO ion displacement by HO addition. Free energy landscapes over the catalysts were developed for CO hydration reaction. The activation energies of HO dissociation and CO bending were observed to be substantially smaller over Ru-CNT when compared to those over the other catalysts. Ru-CNT was found to be the best catalyst for CO hydration with the rate limiting step being HCO ion formation.