Hydride and hydrogen transfer activity in enzymatic and nonenzymatic systems through the lens of three-component thermodynamics - study of the role of enzymatic microenvironments

The crucial step for selective cleavage and formation of C-H bonds is a concerted transfer of proton (PT) and electron(s) (ET): hydrogen atom abstraction (HAA) or hydride transfer (HT).

The HAA and HT processes can be employed to various chemical transformations: from activation of inert bonds to reduction of CO2. This approach, however, requires a strict control of the regioselectivity of the reaction. Notably, enzymes - catalysts developed by Nature, are characterised by high activity and selectivity.

In this project, we would like to provide insight into the interplay of reaction thermodynamics and sterics given by the microenvironment of prototypical enzymatic active sites (employing HAA or HT as a key step in catalysis) and to decipher which of these effects is more important in enzymatic selectivity.The focal point of the project is the novel three component thermodynamic-based model for reactivity, developed for concerted H+/e abstraction.

The model captures the coupled nature of PT and ET by the relative magnitutes of redox potentials and acidity constants of the reactants - their values determine not only the the reaction driving force but also the two novel contributions: asynchronicity and frustration with opposing effects on the barrier for the reaction.

An asynchronous process, featuring a large disparity in ET and PT components of the reaction driving force, is more efficient.

In contrast, a common large size of these ET and PT components makes HAA more frustrated and hence less effective.Based on this model we would like to look into systems capable of CO2 reduction and C-H bond activation to assess to what extent their reactivity is tweaked by the local conditions given by the enzymatic microenvironment versus the canonical factors affecting enzymatic activity, such as sterics and specific interactions.

The studies may serve as a guide for design for systems capable of effective reduction of CO2 and rational redesign of C-H activating enzymes.