Understanding the Spin Crossover Dynamical Effects of the Dioxygen Binding and Activation on HOD enzyme

TL;DR

This study investigates the spin crossover effects during dioxygen activation in the HOD enzyme, emphasizing the importance of non-adiabatic dynamics in the process and providing insights into the underlying physics of spin state transitions.

Contribution

It demonstrates the critical role of non-adiabatic effects in O2 activation and compares different dynamical methods to elucidate spin crossover mechanisms in enzymatic reactions.

Findings

Non-adiabatic effects are essential for O2 activation.

Triplet to singlet conversion occurs within hundreds of femtoseconds.

Dynamical methods reveal the importance of spin state transitions.

Abstract

For the cofactor-free 1-H-3-hydroxy-4-oxoquinaldine-2,4-dioxygenase (HOD), the dioxygen (O2) dependent steps are rate-limiting along with a spin state crossover to the singlet spin state. Here, the primary triplet O2 molecule activation on the 2-methyl-3-hydroxy-4(1H)-quinolone (MHQ) is investigated, and the catalytic role of the intersystem crossing effects is highlighted by directly comparing results from the Born-Oppenheimer dynamics and non-adiabatic surface hopping dynamics. This work confirms non-adiabatic dynamical effects are essential to modulate the O2 activation on the substrate MHQ. The time scale of the equilibration and conversion from triplet to singlet state should be in the range of a few hundreds of femtoseconds. We hope this work provides us a fresh look at the underlying physics of dioxygen activation reactions involving more than one spin state.