Singlet dioxygen reactivity

Given that the myeloperoxidase enzyme see Peroxidases) within the neutrophils produces hypochlorous acid, an intriguing possibility is that it may combine with another hydrogen peroxide molecule. Such a reaction in the laboratory produces a stoichiometric quantity of singlet dioxygen ( O2), which is selectively reactive with conjugated polyenes. 

Zinc phthalocyanine complexes show good catalytic activity only upon simultaneous irradiation with visible light. Interaction between dioxygen and the long-lived triplet state of these complexes produces reactive singlet dioxygen, which also interacts with compounds containing sulfur in various oxidation states. 

Of the different oxygen species, the main interest has been in O-, Oj, and O3. Relatively little attention has been paid to the characterization and reactivity of singlet oxygen, O -, lattice or adsorbed O2- species, and most importantly polynuclear species. The work on dioxygen species is likely to be related to the studies of oxygen carriers. Features of special interest in the future on the characterization side are likely to be the detailed geometry of the adsorption site, how the oxygen species is bonded to the surface, and its mobility. 

Dioxygen could overcome the kinetic barrier of its unpaired electrons and triplet ground state by excitation to its first excited state (xAg), in which all electrons are paired. Unfortunately, this species, referred to as singlet oxygen, is generally too reactive and too short-lived for most situations (lb, lc). However, dioxygen complexation to a transition metal can also result in activation and create stable complexes that can be studied, modified, and used in further reactions in a controlled manner (2). This latter type of activation is the subject of this chapter. 

As predicted by molecular orbital theory dioxygen has two unpaired electrons and some of its chemistry shows diradical characteristics in particular, it reacts readily with other radicals. Singlet oxygen is an excited state in which the two electrons in the p anti-bonding orbitals have paired spins. It produced in some chemical reactions and has different chemical reactivity. 

Because the ground state of dioxygen is a triplet with two unpaired electrons with parallel spins, its reactivity with organic molecules in the singlet state is severely... 

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