Interplay of Water and a Supramolecular Capsule for Catalysis of Reductive Elimination Reaction from Gold
Abstract
Supramolecular assemblies have gained tremendous attention due to their apparent ability to catalyze reactions with the efficiencies of natural enzymes. Using Born-Oppenheimer molecular dynamics and density functional theory, we identify the origin of the catalytic power of the supramolecular assembly Ga4L612- on the reductive elimination reaction from gold complexes and their similarity to enzymes. By comparing the catalyzed and uncatalyzed reaction in explicit solvent to identify the reaction free energies of the reactants, transition states, and products, we determine that a catalytic moiety -- an encapsulated water molecule -- generates electric fields that contribute significant reduction in the activation free energy. Although this is unlike the biomimetic scenario of catalysis through direct host-guest interactions, the nanocage host preconditions the transition state for greater sensitivity to electric field projections onto the breaking carbon bonds to complete the reductive elimination reaction with greater catalytic efficiency. However it is also shown that the nanocage poorly organizes the interfacial water, which in turn creates electric fields that misalign with the breaking bonds of the substrate, thus identifying new opportunities for catalytic design improvements in nanocage assemblies.