Dioxygen cleavage

The presently accepted model1555 for the reaction of bleomycin with DNA involves the binding of an Fen-bleomycin complex to DNA, and the reduction of iron-bound dioxygen. Cleavage of DNA is known to occur by the action of the 1,10-phenanthroline complex of Cu1 in the presence of hydrogen peroxide, and this reaction is sustained by the presence of NADH.1556 This provides a useful parallel for the bleomycin reaction. 

The ozonolysis of cyclohexene to 1,6-dioxygenated compounds is shown in Figure 17.28. Other cycloalkenes similarly afford other l,y-dioxygenated cleavage products. With the three methods for workup (Figure 17.27), this ozonolysis provides access to 1,6-hexanediol, 1,6-hexanedial, or to 1,6-hexanedicarboxylic acid. Each of these compounds contains two functional groups of the same kind. 

Bassan A, Blomberg MRA, Siegbahn PEM Mechanism of dioxygen cleavage in tetrahydrobiopterin-dependent amino acid hydroxylases. Chem Eur J 9 106-115,2003. 

A dramatic discovery in this area was made in 1996 when a dicopper-dioxygen adduct was found to have two isomeric forms which featured either a side-on bridging unit Cu(/r ), ) -02)-Cu) " or a cyclic (Cu(/r-0)2Cu) " core depending on whether it was crystallized from CH2CI2 or thf, respectively. The two forms could be readily interconverted by reversible 0-0 bond cleavage and reformation, the 0-0 distance being 141 pm and 229 pm in the two isomers.The... 

Caris-Veyrat, C. et al., Cleavage products of lycopene produced by in vitro oxidations characterization and mechanisms of formation, J. Agric. Food Chem., 51, 7318, 2003. Caris-Veyrat, C. et al., Mild oxidative cleavage of beta, beta-carotene by dioxygen induced by a ruthenium porphyrin catalyst characterization of products and of some possible intermediates, New J. Chem., 25, 203, 2001. 

Figure 2.7 Surface oxidation at Zn(0001) in an ammonia-rich NH3-02 mixture at 120, 160, 200 and 240 K compared with 02(g) at 200 K as a function of 02 exposure. An (NH3-02) complex (transient) provides a low-energy pathway to dioxygen bond cleavage. The rate of dioxygen bond cleavage is increased by a factor of up to 300 in the presence of ammonia. (Reproduced from Ref. 46).

The results obtained for carbazole degradation by Pseudomonas strain LD2 indicate that carbazole is oxidized initially by angular dioxygenation at position 2, 3 [317] to form 2,9-aminobiphenyl-2,3-diol (via an unstable intermediate), which is further degraded by meta-cleavage of the diol ring to form 2-hydroxy-6-oxo-6-(29-aminophenyl)hexa-2,4-dienoic acid [316], The degradation steps are shown in Fig. 17. 

Alkyl radicals can break down through the cleavage of C—C bonds. Since these radicals are reactive to dioxygen, their concentration must decline with increasing p02 and,... 

Another gradient-corrected density functional study of reversible dioxygen binding and reversible 0-0 bond cleavage has been carried out for Cu2(p-T 2 r 2... 

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