abstract
The deprotonation of an organic substrate is a common preactivation step for the enzymatic cofactorless addition of O-2 to this substrate, as it promotes charge-transfer between the two partners, inducing intersystem crossing between the triplet and singlet states involved in the process. Nevertheless, the spin-forbidden addition of O-2 to uncharged ligands has also been observed in the laboratory, and the detailed mechanism of how the system circumvents the spin-forbiddenness of the reaction is still unknown. One of these examples is the cofactorless peroxidation of 2-methyl-3,4-dihydro-1-naphthol, which will be studied computationally using single and multi-reference electronic structure calculations. Our results show that the preferred mechanism is that in which O-2 picks a proton from the substrate in the triplet state, and subsequently hops to the singlet state in which the product is stable. For this reaction, the formation of the radical pair is associated with a higher barrier than that associated with the intersystem crossing, even though the absence of the negative charge leads to relatively small values of the spin-orbit coupling.
keywords
CATALYTIC MECHANISMS; PHOTODYNAMIC THERAPY; SINGLET OXYGEN; ACTIVATION; OXIDATION; SUBSTRATE; DIOXYGEN; OXIDASE; AROMATICITY; PEROXIDE
subject category
Biochemistry & Molecular Biology; Chemistry
authors
Ortega, P; Gil-Guerrero, S; González-Sánchez, L; Sanz-Sanz, C; Jambrina, PG
Groups
acknowledgements
This research was funded by MCIN/AEI/10.13039/501100011033 (Ministerio de Ciencia e Innovacion) grant number PID2020-113147GA-I00, and by the Fundacion Salamanca City of Culture and Knowledge (a programme for attracting scientific talent to Salamanca). The PhD scholarship of P.O. was funded by Junta de Castilla y Leon and European Social Fund grant number EDU/601/2020. C.S.-S. acknowledges Ministerio de Ciencia e Innovacion for the funding with grant number PID2021-122549NB-C22.