A W/Cu Synthetic Model for the Mo/Cu Cofactor of Aerobic CODH Indicates That Biochemical CO Oxidation Requires a Frustrated Lewis Acid/Base Pair.

Constructing synthetic models of the Mo/Cu active site of aerobic carbon monoxide dehydrogenase (CODH) has been a long-standing synthetic challenge thought to be crucial for understanding how atmospheric concentrations of CO and CO2 are regulated in the global carbon cycle by chemolithoautotrophic bacteria and archaea. Here we report a W/Cu complex that is among the closest synthetic mimics constructed to date, enabled by a silyl protection/deprotection strategy that provided access to a kinetically stabilized complex with mixed O2-/S2- ligation between (bdt)(O)WVI and CuI(NHC) (bdt = benzene dithiolate, NHC = N-heterocyclic carbene) sites. Differences between the inorganic core's structural and electronic features outside the protein environment relative to the native CODH cofactor point to a biochemical CO oxidation mechanism that requires a strained active site geometry, with Lewis acid/base frustration enforced by the protein secondary structure. This new mechanistic insight has the potential to inform synthetic design strategies for multimetallic energy storage catalysts.

High Nucleobase-Solubilizing Ability of Low-Viscous Ionic Liquid/Water Mixtures: Measurements and Mechanism.

Research on nucleobases has always been on the forefront owing to their ever-increasing demand in the pharmaceutical, agricultural, and other industries. The applications, however, became limited due to their poor solubility in water. Recently, ionic liquids (ILs) have emerged as promising solvents for nucleobase dissolution, as they exhibit >100-fold increased solubility compared to water. But the high viscosity of ILs remains as a bottleneck in the field. Here, by solubility and viscosity measurements, we show that addition of low-to-moderate quantity of water preserves the high solubilizing capacity of ILs, while reducing the viscosity of the solution by several folds. To understand the mechanism of nucleobase dissolution, molecular dynamics simulations were carried out, which showed that at low concentrations water incorporates into the IL-nucleobase network without much perturbing of the nucleobase-IL interactions. At higher concentrations, increasing numbers of IL anion-water hydrogen bonds replace IL-nucleobase interactions, which have been confirmed by (1)H- and (13)C NMR chemical shifts of the IL ions.