Theoretical Investigations on the Mechanistic Aspects of O₂ Activation by a Biomimetic Dinitrosyl Iron Complex

Abstract

Though dinitrosyl-iron complexes (DNICs) are largely believed to act as NO carriers, several experiments on model DNICs have suggested that they can also act as nitrating agents in presence of dioxygen. Oxygen activation by DNICs has been implicated as a possible route for protein tyrosine nitration (PTN), which leads to neurodegenerative disorders. Herein using static and dynamic theoretical techniques we unravel a previously unknown dual state mechanistic paradigm for dioxygen activation of a biomimetic nitrating DNIC complex leading to phenolic nitration. Our computations reveal that the model DNIC, the ground electronic state of which is singlet, has a low-lying triplet state and an inherent singlet-triplet spin-crossover of DNICs can be triggered by fluxional changes in the bite angle of the two NO ligands. The presence of a low-lying triplet state in the DNIC affords an avenue for O activation other than a direct O activation by O -induced spin-crossover of the singlet ground state. These two low-lying channels facilitate the formation of a peroxynitrite species. Nitration of phenolic substrates is facilitated by the release of NO . The corresponding minimum energy crossing points (MECP) have been located. Along the reaction path, the changes in the electronic structure scenarios have been studied and interpreted. Our report also sheds light on the plausible mechanistic pathway of PTN by reactive species formed once O activation by DNICs have been achieved.

Hydration dynamics gives the distinctive brown color in the "brown ring" nitrate test

“…Since we do not discuss physical/chemical processes where spin-orbit coupling is important in this study, we otherwise strictly confine our focus to the quartet manifold. is reflected in the fractional natural occupation in these orbitals in agreement with earlier studies [6,15,17,24].…”

“…Traditional inorganic chemists have also found the Fe-NO bond very interesting, as reflected by the detailed study on Hieber's anion [13,14]. Theoretical attempts have uni-vocally established the multiconfigurational character of the Fe-NO bond [15][16][17]. Pierloot and co-workers have also stressed upon the importance of dynamical correlation in description of the Fe-NO bond [15].…”

“…Multi-reference quantum chemical computations have also been used to show the O 2 activation by Dinitrosyl Iron Complexes (DNICs) which contains two Fe-NO bonds [17]. The first attempt in using multireference theories to describe the classic brown ring complex was only done by Monsch and co-workers in 2019 [6].…”

Hydration dynamics gives the distinctive brown color in the "brown ring" nitrate test

“…Traditional inorganic chemists have also found the Fe-NO bond very interesting, as reflected by the detailed study on Hieber's anion [13,14]. Theoretical attempts have uni-vocally established the multiconfigurational character of the Fe-NO bond [15][16][17]. Pierloot and co-workers have also stressed upon the importance of dynamical correlation in description of the Fe-NO bond [15].…”

Organoruthenium (II) complexes featuring pyrazole‐linked Schiff base ligands: Crystal structure, DNA/BSA interactions, cytotoxicity and molecular docking

“…Assiduous research in the area of organometallic chemistry has yielded various types of complexes with promising applications in the field of catalysis, photosensors, reagents for synthetic organic chemistry, polymer synthesis, dye‐sensitized solar cells, water splitting reactions, asymmetric synthesis, bio‐mimic reactions and medicinal chemistry . Over the last twenty years, organoruthenium compounds have captivated abundant notions of researchers due to their wide variety of applications .…”