Molecular machines? The factors involved in and the fundamental nature of a “mechanical” action within molecular catalysis is explored in detail. Such mechanical homogeneous catalysts are rare but not unknown (see graphic). The spatial and temporal nature of their catalytic action is considered. Potential implications for mimicry of enzymes are discussed.
Chemical reactions may be controlled by either: 1) the minimum threshold energy that must be overcome during collisions between reactant molecules/atoms (the activation energy, Ea), or: 2) the rate at which reactant collisions occur (the collision frequency, A)—for reactions with low Ea. Reactions of type 2 are governed by the physical, mechanical interaction of the reactants. Such mechanical processes are unusual, but not unknown in molecular catalysts. In this work we examine the machine-like nature of the action in various abiological mechanical catalysts and consider the implications for mimicry of biological catalysts.