title: A Systematic Account on Aromatic Hydroxylation by a Cytochrome P450 Model Compound I: A Low-Pressure Mass Spectrometry and Computational Study.
abstract: Cytochrome P450 enzymes are heme-containing mono-oxygenases that mainly react through oxygen-atom transfer. Specific features of substrate and oxidant that determine the reaction rate constant for oxygen atom transfer are still poorly understood and therefore, we did a systematic gas-phase study on reactions by iron(IV)-oxo porphyrin cation radical structures with arenes. We present herein the first results obtained by using Fourier transform-ion cyclotron resonance mass spectrometry and provide rate constants and product distributions for the assayed reactions. Product distributions and kinetic isotope effect studies implicate a rate-determining aromatic hydroxylation reaction that correlates with the ionization energy of the substrate and no evidence of aliphatic hydroxylation products is observed. To further understand the details of the reaction mechanism, a computational study on a model complex was performed. These studies confirm the experimental hypothesis of dominant aromatic over aliphatic hydroxylation and show that the lack of an axial ligand affects the aliphatic pathways. Moreover, a two-parabola valence bond model is used to rationalize the rate constant and identify key properties of the oxidant and substrate that drive the reaction. In particular, the work shows that aromatic hydroxylation rates correlate with the ionization energy of the substrate as well as with the electron affinity of the oxidant.
authors.affiliation: Manchester Institute of Biotechnology and School of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK.
authors.forename: Fabián G
authors.identifier: http://orcid.org/0000-0002-0916-6758
authors.initials: FG
authors.lastname: Cantú Reinhard
authors.affiliation: Manchester Institute of Biotechnology and School of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK.
authors.forename: Mala A
authors.identifier: http://orcid.org/0000-0003-4902-7960
authors.initials: MA
authors.lastname: Sainna
authors.affiliation: Department of Applied Physics, School for Physical Sciences, Babasaheb Bhimrao Ambedkar University, Vidya Vihar, Rae Bareilly Road, Lucknow (UP, 226025, India.
authors.forename: Pranav
authors.identifier: http://orcid.org/0000-0002-6151-1213
authors.initials: P
authors.lastname: Upadhyay
authors.affiliation: Manchester Institute of Biotechnology and School of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK.
authors.forename: G Alex
authors.identifier: http://orcid.org/0000-0003-1208-0880
authors.initials: GA
authors.lastname: Balan
authors.affiliation: Department of Applied Physics, School for Physical Sciences, Babasaheb Bhimrao Ambedkar University, Vidya Vihar, Rae Bareilly Road, Lucknow (UP, 226025, India.
authors.forename: Devesh
authors.identifier: http://orcid.org/0000-0001-5867-1905
authors.initials: D
authors.lastname: Kumar
authors.affiliation: Dipartimento di Chimica e Tecnologie del Farmaco, Università di Roma "La Sapienza", P.le A. Moro 5, 00185, Roma, Italy.
authors.forename: Simonetta
authors.identifier: http://orcid.org/0000-0002-6312-5738
authors.initials: S
authors.lastname: Fornarini
authors.affiliation: Dipartimento di Chimica e Tecnologie del Farmaco, Università di Roma "La Sapienza", P.le A. Moro 5, 00185, Roma, Italy.
authors.forename: Maria Elisa
authors.identifier: http://orcid.org/0000-0002-0991-5034
authors.initials: ME
authors.lastname: Crestoni
authors.affiliation: Manchester Institute of Biotechnology and School of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK.
authors.forename: Sam P
authors.identifier: http://orcid.org/0000-0002-2620-8788
authors.initials: SP
authors.lastname: de Visser
mesh_terms: D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D006900:Hydroxylation; D007700:Kinetics; D008024:Ligands; D013058:Mass Spectrometry; D008958:Models, Molecular; D016877:Oxidants / Q000737:chemistry*
chemical_list: D008024:Ligands; D016877:Oxidants; D006418:Heme; D003577:Cytochrome P-450 Enzyme System
keywords: arenes; density functional theory; fourier transform-ion cyclotron resonance; mass spectrometry; oxygen atom transfer