Abstract
In spite of being spin-forbidden, some enzymes are capable of catalyzing the incorporation of O2 (3Σ−g) to
organic substrates without needing any cofactor. It has been established that the process followed by these
enzymes starts with the deprotonation of the substrate forming an enolate. In a second stage, the peroxidation
of the enolate formation occurs, a process in which the system changes its spin multiplicity from a triplet state
to a singlet state. In this article, we study the addition of O2 to enolates using state-of-the-art multi-reference
and single-reference methods. Our results confirm that intersystem crossing is promoted by stabilization of
the singlet state along the reaction path. When multi-reference methods are used, large active spaces are
required, and in this situation, Semistochastic Heat-Bath Configuration Interaction (SHCI) emerges as a
powerful method to study these multi-configurational systems and is in good agreement with LCCSD(T)
when the system is well-represented by a single-configuration.
organic substrates without needing any cofactor. It has been established that the process followed by these
enzymes starts with the deprotonation of the substrate forming an enolate. In a second stage, the peroxidation
of the enolate formation occurs, a process in which the system changes its spin multiplicity from a triplet state
to a singlet state. In this article, we study the addition of O2 to enolates using state-of-the-art multi-reference
and single-reference methods. Our results confirm that intersystem crossing is promoted by stabilization of
the singlet state along the reaction path. When multi-reference methods are used, large active spaces are
required, and in this situation, Semistochastic Heat-Bath Configuration Interaction (SHCI) emerges as a
powerful method to study these multi-configurational systems and is in good agreement with LCCSD(T)
when the system is well-represented by a single-configuration.
Supplementary materials
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