Introducing Positive Charges in an Artificial Enzyme Increases CO2 Hydrogenation
Metalloenzymes play central roles in many energy transduction reactions by facilitating the storage of energy in chemical bonds until the energy needs to be used. Because metalloenzymes are very efficient, fast, and selective in the conversion and storage of energy under ambient conditions, they are ideal models upon which to base synthetic mimics capable of efficiently interconverting electrical and chemical energies.
One of the critical features responsible for the high reactivity and specificity of metalloenzymes is the protein scaffold surrounding the metal at the active site. Protein scaffolds are composed of elements of secondary structure dominated by α-helices and β-sheets which, in turn, fold into higher order tertiary structures with a well-defined spatial arrangement of hydrophobic and hydrophilic residues. These highly evolved three-dimensional spaces tune specific chemical reactions catalyzed by the metal at the active site.
A research group at Washington State University has synthesized an artificial enzyme capable of CO2 hydrogenation containing the small molecular complex [Rh(PEt2NglycinePEt2)2]– bound to a protein scaffold.
Point mutations were made in the outer coordination spheres for several complexes, producing positive charges at various distances from the Rh center. The structures were solved using data acquired on beam line 12-2 at the Stanford Synchrotron Radiation Lightsource.
The structure of a complex with a 3-fold greater turnover rate showed that its positive charges were close (8-9 Å) and oriented towards the Rh site. This work should expand the synthetic toolset for the development of more efficient enzymes.
Laureanti, J. A. et al. 2020. “A Positive Charge in the Outer Coordination Sphere of an Artificial Enzyme Increases CO2 Hydrogenation,” Organometallics 39(9), 1532–44. [DOI:10.1021/acs.organomet.9b00843]