Toward understanding the activity of cobalt carbonic anhydrase: A comparative study of zinc- and cobalt-cyclen

Renhu Ma, George F. Schuette, Linda J. Broadbelt*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Density functional theory (DFT) calculations were used to study the mechanism of CO2 hydrolysis by Co-(1, 4, 7, 10-tetrazacyclododecane), also referred to as cobalt-cyclen, and evaluate the associated thermodynamic and kinetic parameters. A microkinetic model was then built based on the kinetics and thermodynamics derived from first principles. The intrinsic reaction rate constant was calculated to be 10572 M-1 s-1, three times larger than that of zinc-cyclen. The high activity was ascribed to a very large pKa value of 13.3. The monodentate structure of a key intermediate along the reaction coordinate, [Cyclen-Co-HCO3]+, was more stable than the bidentate isomer, due to a hydrogen bond formed between bicarbonate and the ligand. The reaction rate constant decreased significantly over 0-12 ms, which was attributed to the fast decrease of the concentration of the catalytic form, Co-OH-. The conversion of CO2 at 1000 ms as a function of pH was calculated to compare the relative activity of zinc-cyclen and cobalt-cyclen, and zinc-cyclen was found to be a much better catalyst. Through calculating the ratio of the net rate to the forward rate of each elementary reaction, the rate-limiting step of the catalytic cycle was identified as the adsorption of CO2, which was the same as that for zinc-cyclen, though the product-releasing step was regarded as more difficult in cobalt-cyclen, compared to zinc-cyclen.

Original languageEnglish (US)
Pages (from-to)151-159
Number of pages9
JournalApplied Catalysis A: General
Volume492
DOIs
StatePublished - Feb 25 2015

Keywords

  • Biomimetic catalysis
  • Carbonic anhydrase
  • Cobalt cyclen
  • Density functional theory
  • Microkinetic modeling

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology

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