Oxidation, enzymic with halogens

Although the exact mechanism of degradation at metabolic level for each compound or group of compounds is not well known, the involvement of extracellular oxidative enzymes such as LAC, MnP, LiP, and versatile peroxidase (VP) (see Tables 1 and 2 of Chap. 6) and intracellular monooxygenases as cytochrome P-450 is well documented for pollutants such as hydrocarbons, dyes, and halogenated solvents [25]. To determine the actual role of the extracellular enzymes, many studies are performed in vitro experiments with purified enzymes. In the case of cytochrome P-450, usually inhibitors are used. 

Eliminations of hydrogen and a halogen occur sometimes during the metabolism of halogenated xenobiotics and lead to an alkene. The double bond may be oxidized into an epoxide by means of oxidative enzyme systems as discussed above. Dehydrogenation, dehydrochlorination and dechlorination are (with oxidation) the different metabolic pathways of the -isomer of the insecticide hexachloro-cyclohexane (lindane). ... 

Other 2,6-Disubstituted Monomers. Various poly(2,6-suhstituted-l,4-phenylene oxide)s possessing alkyl, aryl, alkoxyl, and halogen groups have been produced (see Polyethers, Aromatic). Recently, some functional polymers (36-39) were synthesized, one of which was converted to a heterocyclic ladder polymer (39). Poly(2,6-difluoro-l,4-phenylene oxide)s with crystallinity (40) and no crystallinity (41) were synthesized. By enzyme catalysis, oxidative polymerization of 3,5-disubstituted-4-hydroxybenzoic acids, with liberation of carbon dioxide, produced poly(2,6-disubstituted-l,4-phenylene oxide)s (42,43). 

There are a number of biological examples of halohydrin formation, particularly in marine organisms. As with halogenation (Section 8.2), halohydrin formation is carried out by haloperoxidases, which function by oxidizing Br or Cl ions to the corresponding HOBr or HOCl bonded to a metal atom in the enzyme. Electrophilic addition to the double bond of a substrate molecule then yields a bromonium or chloronium ion intermediate, and reaction with water gives the halohydrin. For example ... 

More recently, a novel type of halogenating enzyme, named hydroperoxide halolyase, which generates halogenated aldehydes, has been described in the marine diatom Stephanopyxis turris (Wichard and Pohnert 2006). In other microalgae, halogenation of organic compounds was shown to mainly involve methyl halide transferases (Moore et al. 1996 Manley 2002), and no vHPO has yet been identified on genomic data obtained from diatoms (Scala et al. 2002 Armbrust et al. 2004). Clearly, these emissions are not directly associated with an oxidative burst. 

Beryllium. Be metal is relatively unreactive at room temperature it does not react with water and steam even at red heat and it does not oxidize in air below 600°C. Powdered beryllium burns in air brilliantly on ignition forming BeO and Be3N2. It reacts with the halogens and dissolves easily in dilute aqueous acid solutions. It is passivated by cold concentrate HN03. The Be compounds, especially as dusts or smokes, are extremely toxic (possibly due to the ability of Be11 to displace Mg11 from Mg-activated enzymes). 

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