Utilization of dioxygen

It is interesting to note that in so many areas of oxygen chemistry, nature uses iron porphyrins for the transport, storage, and utilization of dioxygen and its reduced derivatives. 

Similarly, p-cyano-N,N-dimethylaniline N-oxide was introduced by Bruice in 1982 [53] and KHSO5 by Meunier [54] in 1985. More recently, Querci and Ricci [55] introduced the water-soluble magnesium monoperoxyphtbalate as an oxygen donor. Various systems were also developed for the direct utilization of dioxygen in these systems by employing a coreductant such as NaBH4, H2 and colloidal platinum, ascorbate and zinc and acetic acid [56]. 

In order to construct new types of binding and activating models of dioxygen molecules, Jitsukawa, Masuda and their co-workers have synthesized a novel group of tripodal tetradentate ligands and successfully utilized them in the formation of mononuclear copper(II) complexes with novel structural features (complexes (473)-(488)).395-403 This group of ligands has four... 

RW1 [143], In contrast, the Kodama pathway utilizes a 5,6 specific dioxygenase, keeping the thiophene ring intact and producing a product not amenable to further round of dioxygenation. 

How does nature prevent the release of hydrogen peroxide during the cytochrome oxidase-mediated four-electron reduction of dioxygen It would appear that cytochrome oxidase behaves in the same manner as other heme proteins which utilize hydrogen peroxide, such as catalase and peroxidase (vide infra), in that once a ferric peroxide complex is formed the oxygen-oxygen bond is broken with the release of water and the formation of an oxo iron(IV) complex which is subsequently reduced to the ferrous aquo state (12). Indeed, this same sequence of events accounts for the means by which oxygen is activated by cytochromes P-450. 

Electrochemical (24) and chemical (25, 26) techniques have been utilized to investigate the kinetics and the mechanisms of the addition of dioxygen to a metal center, and to follow its subsequent reduction to hydrogen peroxide when catalyzed by cobalt(III) complexes of macro-cyclic amine ligands. Such complexes have also been involved in the general investigation of dioxygen addition to cobalt complexes (27,28). 

Reduced flavins, unlike reduced nicotinamides, are reactive towards molecular oxygen, and an intermediate produced in this reaction is a more potent oxygenating agent than molecular oxygen is itself. A number of enzymes have evolved which utilize this intermediate to oxygenate certain metabolites. These reactions usually entail monooxygenation (Scheme 5). There are, however, at least two examples of dioxygenation that have been reported... 

Although hydronium ion (H30+) (Chapter 8) and dioxygen (02) (Chapter 9) are the most studied of the molecules and ions without metal atoms, several of the molecules that contain sulfur, nitrogen, or carbon also are electroactive. The results for representative examples are presented to illustrate the utility of electrochemical measurements for die evaluation of the redox thermodynamics and bond energies for non-metal-containing molecules. In particular, die electrochemistry for several sulfur compounds [S8, S02, HS(CH2)3SH], nitrogen compounds [-NO, HON=0, N20, H2NOH, hydrazines (/ NHNH/ ), amines, phenazine], and carbon compounds (C02, CO, NCT) is summarized and interpreted. 

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