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DpgC‐Catalyzed Peroxidation of 3,5‐Dihydroxyphenylacetyl‐CoA (DPA‐CoA): Insights into the Spin‐Forbidden Transition and Charge Transfer Mechanisms **
Author(s) -
Ortega Pablo,
Zanchet Alexandre,
SanzSanz Cristina,
GómezCarrasco Susana,
GonzálezSánchez Lola,
Jambrina Pablo G.
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202002993
Subject(s) - intersystem crossing , chemistry , photochemistry , singlet state , electron transfer , diradical , molecule , active site , protonation , singlet oxygen , redox , catalysis , chemical physics , oxygen , excited state , atomic physics , physics , inorganic chemistry , organic chemistry , ion
Despite being a very strong oxidizing agent, most organic molecules are not oxidized in the presence of O 2 at room temperature because O 2 is a diradical whereas most organic molecules are closed‐shell. Oxidation then requires a change in the spin state of the system, which is forbidden according to non‐relativistic quantum theory. To overcome this limitation, oxygenases usually rely on metal or redox cofactors to catalyze the incorporation of, at least, one oxygen atom into an organic substrate. However, some oxygenases do not require any cofactor, and the detailed mechanism followed by these enzymes remains elusive. To fill this gap, here the mechanism for the enzymatic cofactor‐independent oxidation of 3,5‐dihydroxyphenylacetyl‐CoA (DPA‐CoA) is studied by combining multireference calculations on a model system with QM/MM calculations. Our results reveal that intersystem crossing takes place without requiring the previous protonation of molecular oxygen. The characterization of the electronic states reveals that electron transfer is concomitant with the triplet–singlet transition. The enzyme plays a passive role in promoting the intersystem crossing, although spontaneous reorganization of the water wire connecting the active site with the bulk presets the substrate for subsequent chemical transformations. The results show that the stabilization of the singlet radical‐pair between dioxygen and enolate is enough to promote spin‐forbidden reaction without the need for neither metal cofactors nor basic residues in the active site.