PNNL

Abstract

The utilization of CO2 to generate chemical fuels, such as formic acid, is a potentially beneficial route to balance carbon emissions and reduce dependence on fossil fuels. The development of efficient catalysts for CO2 hydrogenation is needed to implement this fuel generation. In the molecular catalyst design presented here, we utilize covalent attachment of a rhodium complex, ([Rh(PNglyP)2]+ where PNGlyP is defined as P^(Et_2 )-CH2-N^((CH_2 CO_2^-))-CH2-P^(Et_2 )) to a protein scaffold, lactococcal multidrug resistant regulator from Lactococcus lactis, to create an environment around the metal center that can be used to control substrate delivery and therefore enable and improve catalytic activity. The reactivity of the rhodium complex and the synthetic metalloenzyme were characterized by high pressure operando NMR techniques. The rhodium complex in solution is not a catalyst for CO2 hydrogenation. The incorporation of the molecular complex into the protein scaffold results in a gain of function, turning on CO2 hydrogenation activity. The metalloenzyme displays a turnover frequency of 0.38 h-1 at 58 atm and 298 K; and achieved an average turnover number of 14 3. Proposed catalytic intermediates generated and characterized indicate the protein scaffold enables catalysis by facilitating the interaction between CO2 and the hydride donor intermediate. Research was funded by the Laboratory Directed Research and Development program at Pacific Northwest National Laboratory. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy. This structural work is supported as part of the Biological and Electron Transfer and Catalysis (BETCy) EFRC, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science (DE-SC0012518) to J.W.P. and O.A.Z. No competing financial interests have been declared.This work was performed in part using the William R. Wiley Environmental Molecular Sciences Laboratory, a US Department of Energy (DOE) national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located and the Pacific Northwest National Laboratory (PNNL). Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The SSRL Structural Molecular Biology Program is supported by the DOE Office of Biological and Environmental Research, and by the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393).