Spin‐Forbidden Branching in the Mechanism of the Intrinsic Haber–Weiss Reaction

Abstract

The mechanism of the O2 ⋅− and H2O2 reaction (Haber–Weiss) under solvent‐free conditions has been characterized at the DFT and CCSD(T) level of theory to account for the ease of this reaction in the gas phase and the formation of two different set of products (Blanksby et al., Angew. Chem. Int. Ed. 2007, 46, 4948). The reaction is shown to proceed through an electron‐transfer process from the superoxide anion to hydrogen peroxide, along two pathways. While the O3 ⋅− + H2O products are formed from a spin‐allowed reaction (on the doublet surface), the preferred products, O⋅−(H2O)+3O2, are formed through a spin‐forbidden reaction as a result of a favorable crossing point between the doublet and quartet surface. Plausible reasons for the preference toward the latter set are given in terms of the characteristics of the minimum energy crossing point (MECP) and the stability of an intermediate formed (after the MECP) in the quartet surface. These unique results show that these two pathways are associated with a bifurcation, yielding spin‐dependent products.

Reactive Oxygen Species and Mitochondrial Dynamics: The Yin and Yang of Mitochondrial Dysfunction and Cancer Progression

“…As a membrane-diffusible species, mitochondrially-generated H 2 O 2 has been implicated in cell-wide redox signal transduction [ 72 , 73 , 74 , 75 , 76 , 77 ]. H 2 O 2 can be further reduced by divalent metal ions or superoxide in the Fenton [ 78 ] or Haber-Weiss reactions [ 79 ], respectively, to produce the hydroxyl radical ( ● OH). This highly toxic molecule promiscuously reacts with a broad range of metabolites, thus inducing oxidative damage [ 80 ].…”

Iron Homeostasis Disorder and Alzheimer’s Disease

“…The excessive accumulation of iron ions will increase the permeability of the BBB, induce inflammation, affect the redistribution of iron ions in the brain, and then change brain iron metabolism [47]. Iron ions can act as both electron acceptors and electron donors; therefore, when iron ions accumulate in the brain, they will produce reactive oxygen free radicals through Fenton and Haber-Weiss chemical reactions [41,83,84]. Free radicals are highly active substances, which may promote protein oxidation, membrane lipid peroxidation and nucleic acid modification.…”

Gas-Phase Deprotonation of Benzhydryl Cations: Carbene Basicity, Multiplicity, and Rearrangements

“…For these diarylcarbenes, the experimental enthalpy of deprotonation correlates best to the calculated enthalpy of deprotonation to the singlet carbene. We do know, from other studies of proton transfer in the gas phase, that spin-forbidden proton transfer is possible. ,− Tian and Kass showed that the methyl cation is deprotonated to yield the more stable triplet carbene, in bracketing experiments in the gas phase . Triplets are more stable for diarylcarbenes 1a–1e ; therefore, it is possible that we could also see spin-forbidden proton transfer to yield these triplet ground states but our calculations imply otherwise, for 1c and 1e…”