Authors: Ortega, P.; Gil-Guerrero, S.; Veselinova, A.; Zanchet, A.; Gonzalez-Sanchez, L.; Jambrina, P. G.; Sanz-Sanz, C.


Publication date: 2021/04/14

DOI: 10.1063/5.0046906

Abstract: In spite of being spin-forbidden, some enzymes are capable of catalyzing the incorporation of O-2(Sigma g-3) 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 O-2 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 emerges as a powerful method to study these multi-configurational systems and is in good agreement with PNO-LCCSD(T) when the system is well-represented by a single-configuration.