The effect of varying carboxylate ligation on the electronic environment of N2Ox (x = 1–3) nonheme iron: A DFT analysis

摘要: Mononuclear nonheme iron oxygenase (MNO) enzymes contain a subclass of metalloproteins capable catalyzing the O2-dependent hydroxylation unactivated substrates at ferrous ion center coordinated to highly conserved His-His-Glu/Asp motif. These enzymes, which utilize additional reducing equivalents obtained from decarboxylation α-ketoglutarate (αKG) cofactor, do not readily interact with O2 in absence αKG binding. Density functional theory calculations B3LYP were performed gain insight into electrochemical behavior three sets FeII/III complexes containing core N, O facial binding motif number carboxylate ligands was systematically altered, provide one, two (cis) or (fac) labile sites. The calculated trend FeII/IIIreduction potentials observed parallel that cyclic voltammetry experiments, showing decrease potential (stabilized oxidized state) increasing ligation. This does appear be result differential charge on metal complex. Changes redox-active molecular orbital (RAMO) energy due covalent effects dominate across series when chloride is modeled as ligand, π anti-bonding nature RAMO being an important factor. With water molecules ligands, however, much steeper redox dependence and this effect seems largely electrostatic origin. Differential relaxation occupied orbitals ferric appears contribute well. Finally, these observations are placed context MNO enzyme mechanisms.