000097211 001__ 97211 000097211 005__ 20210902121924.0 000097211 0247_ $$2doi$$a10.1007/s00723-020-01278-y 000097211 0248_ $$2sideral$$a120980 000097211 037__ $$aART-2020-120980 000097211 041__ $$aeng 000097211 100__ $$aBracci, M. 000097211 245__ $$aEPR of Compound I: An Illustrated Revision of the Theoretical Model 000097211 260__ $$c2020 000097211 5060_ $$aAccess copy available to the general public$$fUnrestricted 000097211 5203_ $$aCompound I has been postulated to be the reactive species in many heme catalysts, which performs different chemistry and shows different properties in different enzymes. The aim of this review is to present a comprehensive model which has been successfully used to interpret the EPR spectra of various Compound I species. The theoretical approach established by seminal articles will be revisited and its ability to explain experimental results will be illustrated by simulating selected spectra from the literature. Compound I stores two oxidizing equivalents, one in the paramagnetic iron(IV)-oxo moiety, and another one as a free radical on the porphyrin ligand or an amino acid in the protein. To describe the interactions of the two paramagnetic species with each other and with their local environment, the spin Hamiltonian of the system is built step by step. The Fe(IV) center is described using a two-hole model. The effect of the crystal-field and spin–orbit coupling on the energy levels is calculated with this simple approach, which allows to obtain spin Hamiltonian parameters like zero-field splitting and effective g-values for the iron. The magnetic interaction between the Fe(IV) center and the free radical is considered and allowed to vary in sign (ferromagnetic to antiferromagnetic) and magnitude to interpret the EPR of Compound I species in different systems. Since orbital overlap is crucial for exchange interaction, special emphasis is made in obtaining the orientation of Fe semi-occupied orbitals by extending the counter-rotation concept, which relates the directions of magnetic, electronic, and molecular axes. 000097211 536__ $$9info:eu-repo/grantAgreement/EC/H2020/813209/EU/Paramagnetic Species in Catalysis Research. A Unified Approach Towards Heterogeneous, Homogeneous and Enzyme Catalysis/PARACAT$$9This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No H2020 813209-PARACAT 000097211 540__ $$9info:eu-repo/semantics/openAccess$$aby$$uhttp://creativecommons.org/licenses/by/3.0/es/ 000097211 590__ $$a0.831$$b2020 000097211 591__ $$aSPECTROSCOPY$$b36 / 43 = 0.837$$c2020$$dQ4$$eT3 000097211 591__ $$aPHYSICS, ATOMIC, MOLECULAR & CHEMICAL$$b35 / 37 = 0.946$$c2020$$dQ4$$eT3 000097211 592__ $$a0.205$$b2020 000097211 593__ $$aAtomic and Molecular Physics, and Optics$$c2020$$dQ4 000097211 655_4 $$ainfo:eu-repo/semantics/review$$vinfo:eu-repo/semantics/publishedVersion 000097211 700__ $$aVan Doorslaer, S. 000097211 700__ $$0(orcid)0000-0002-1827-1250$$aGarcía-Rubio, I.$$uUniversidad de Zaragoza 000097211 7102_ $$12003$$2395$$aUniversidad de Zaragoza$$bDpto. Física Materia Condensa.$$cÁrea Física Materia Condensada 000097211 773__ $$g51, 11 (2020), 1559-1589$$pAppl. magn. reson.$$tAPPLIED MAGNETIC RESONANCE$$x0937-9347 000097211 8564_ $$s1212000$$uhttps://zaguan.unizar.es/record/97211/files/texto_completo.pdf$$yVersión publicada 000097211 8564_ $$s21001$$uhttps://zaguan.unizar.es/record/97211/files/texto_completo.jpg?subformat=icon$$xicon$$yVersión publicada 000097211 909CO $$ooai:zaguan.unizar.es:97211$$particulos$$pdriver 000097211 951__ $$a2021-09-02-10:50:00 000097211 980__ $$aARTICLE