Triplet dioxygen

Binding of dioxygen to the water-free iron complex 4a leads to 5a (Fig. 10), which has a septet ground state originating from the triplet dioxygen and the quintet iron complex 4a and which is... 

The addition reaction of normal, triplet dioxygen to Vaska s complex, fra/is-Ir(CO)Cl(PPh3)2, has been well studied (126,127). The kinetics... 

The reaction sequence at the heme active site starts with the binding of unactivated triplet dioxygen forming the so-called oxy-heme complexes. The iron center in 02-activating heme enz5maes is then thought to be converted into a peroxo anion species. It can be protonated to form a ferric hydroperoxo intermediate usually termed compormd 0 (183), which is a crucial reactive species in catalase and peroxidase enz5nne catalysis (Fig. 21). These hydroperoxo intermediates of hemoproteins are important... 

Formation of 1,2-Dioxetanes by Cation Radical Additions to Triplet Dioxygen... 

The arrows represent electron spins represents a singlet molecule with all electron spins paired t f represents a triplet molecule with two unpaired electrons and I (which we will see in Reaction 5.13) represents a doublet molecule, also referred to as a free radical, with one unpaired electron. The pathways that do not violate the spin restriction are all costly in energy, resulting in high activation barriers. For example, the reaction of ground-state triplet dioxygen,... 

With increasing knowledge and experience on the reactivity of singlet and triplet carbenes (see Sect. 8.1), and of singlet and triplet dioxygen (see Sect. 8.5) in the 1960 s and 1970 s, it seemed to be feasible to consider that a 02-molecule, as a highly electrophilic reagent, may attack the nucleophilic C (a)-atom of diazoalkanes... 

Many coordinatively unsaturated organometallic complexes are known to react with triplet dioxygen to form metal-dioxygen complexes. The oxidative addition of triplet oxygen to Vaska s Complex (Ir(CO)Cl(PPh3)2,1) to give the stable oxygen complex 2 was one of the first of these reactions to be discovered. ... 

Activation of Triplet Dioxygen by Bio-inspired Cuprous Complexes... 

Fig. 2 Molecular orbital diagram and iron-oxygen n orbitals for an octahedral ferryl model, with four equatorial amine ligands and an axial acetonitrile, illustrating a high degree of covalence and a triplet dioxygen-like electronic structure [22]...

All the preceding substrates, even oxyheme, are expected to form carbanions readily. In fact, under solution conditions, in a mixture of f-butanol, dimethylformamide and base, the indole and flavonol derivatives undero oxygenation biomimetically to cleave the C-2, C-3 bond. Like indole itself, the C-3-substituted indoles, on enzymic catalysis, are structurally pre-disposed to yield tetrahedral carbanionic centers at C-3, suitably soft for easy and efficient addition to triplet dioxygen 139). The resulting peroxide (53) (Scheme 24) could possibly cleave its C-2, C-3 bond by the expedient of hydration (54) followed by cleavage to the keto-aldehyde (55). 

In his review on potential use of iron chelators against oxidative damage, Galey (1997) recalled that although triplet dioxygen cannot directly react with biomolecules in the ground state, iron, as well as other transition metals, can relieve the spin restriction of oxygen and dramatically enhances the rates of oxidation (Miller et al. 1990). 

The fitness of dioxygen as a fuel is shown, from the theimodynamic point of view, by the fiee energy decrease in the formation of the bonds with hydrogen, which is lower only than that of fluorine. On the other hand, from a kinetic point of view, the reduction of triplet dioxygen can be conveniently controlled when a stepwise reaction is considered. The uptake of the first electron in a chemical reaction with substrates in a singlet states is foibidden by spin restriction, and the "activation" of O2 molecule is necessary 1]. 

Prabhakar, R., Siegbahn, P. E. M., Minaev, B. R, 8c Agren, H. (2002). Activation of triplet dioxygen by glucose oxifase Spin-orbit coupling in the superoxide ion. Journal of Physical Chemistry B, 106, 3742. 

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