Iron reaction with catechol

Later H-NMR (300 MHz) measurements on complex formation of iron(III) with catechol and 3-methylcatechol, as well as Mdssbauer investigations on complexation of 3,5-DTBC with iron(III) by Funabiki et al. [102] provided evidence indicating the existence of equilibria in Scheme 8. The semiquinonatoiron(II) complex 56 was regarded as the most probable active species for reaction with dioxygen. No iron-bonded dioxygen complexes have been inferred from these spectroscopic results. 

According to a recent study with iron(III) complexes of tripodal ligands, systematic variation of one ligand arm strongly affects the steric shielding of the iron(III) center and the bonding of catechol substrates (61). It was shown that the dioxygenation reactions of catechols... 

This enzyme [EC 1.13.11.1] catalyzes the reaction of catechol with dioxygen to produce d5, cK-muconate. Iron ions are used as a cofactor. Among its physiological roles, catechol 1,2-dioxygenase participates in the metabolism... 

The electron exchange rate constant of the iron(III) complex in DMSO was estimated from the cross reactions with hydroquinone and catechol, which was compared with the rate constant obtained electrochemically. The mechanism of the ascorbic acid oxidation reaction in DMSO is discussed based on the Marcus theory. 

METHYL STYRENE or 3-METHYL STYRENE or 4-METHYL STYRENE or m-METHYL STYRENE or p-METHYL STYRENE mixed Isomers (25013-15-4) C,H,o Flammable liquid. Forms explosive mixture with air (flash point 125°F/51°C). An inhibitor, usually 10 to 50 ppm of tert-butyl catechol, must be present in adequate concentrations to avoid explosive polymerization. Violent reaction with strong oxidizers, strong acids, peroxides and hydroperoxides. Incompatible with catalysts for vinyl or ionic polymers aluminum, aliuninum chloride, ammonia, aliphatic amines, alkanolamines, caustics, copper, halogens, iron chloride, metal salts (e.g., chlorides, iodides, sulfates, nitrates). The uninhibited monomer vapor may block vents and confined spaces by, forming a solid polymer material. On small fires, use dry chemical powder (such as Purple-K-Powder), foam, or CO extinguishers. a-METHYL STYRENE (98-83-9) C,H, Flammable liquid. Forms explosive mixture with air [explosion limits in air (vol %) 0.9 to 6.1 flashpoint 129°F/54°C autoignition temp 1066°F/574°C Fire Rating 2]. Easily polymerizable. Unless inhibited, forms unstable peroxides. Reacts with heat and/or lack of appropriate inhibitor concentration. Reacts with catalysts for vinyl or ionic polymerization, such as aluminum, iron chloride or 2,5-dimethyl-2,5-di(ieri-butylperoxy)hexane. Violent reaction with... 

Considerable effort has been expended in studies of the interaction of metal ions with catechols with a view to understanding oxygenase activity. In aprotic media, the electrochemical properties of substituted catechols have been examined. Reactions of 3,5-di-tert-butyl-o-quinone with manganese(II) result in stable tris-Mn(IV) or bis-Mn(III) complexes of the corresponding catecholate dianion, Bu C , depending on whether the initial ratio of reactants is 1 3 or 1 2. This flexible redox chemistry may be important for redox catalysis. The O2 oxidation of the iron-catechol complex [Fe(salen)(Bu2CH)] has also been examined in aprotic media. 

Oxygenation by SLO-1 is inhibited by various additives. Some of the reasons are (1) the reduction of active iron from the ferric form to the ferrous form, e,g, by N-alkylhydroxylamine [268], phenyldiazene [269], 2-benzyl-1-naphthol [270], diaryl-N-hydroxyurea [271] (2) oxidation of residues, e.g, methionine residues, by hexanal phenylhydrozone [272] (3) coordination to the active site, e.g. catechol [273], cysteine [274], hydroperoxy acids [275], chelating reagents [276], and Pt complex [277] (4) reaction with the active site, e.g. 12-iodo-ci5-9-octadecenoic acid [278]. In addition, it is reported that leukotriene A4, the electrophilic product of 5-lipoxygenases, irreversibly inactivates the enzyme [279]. 

Based on the EPR spectral changes of the model iron complexes, Fuji et al have described the importance of a monodentate dianionic catecholate Fe species (32) for the reaction with oxygen rather than (31), (33), (34) [92]. It is noticed that the E/D value is ca 0.30 with a monodentate monoanionic catecholate complex (31), ca 0.20 with a bidentate dianionic catecholate complex (33), and 0.12 with monodentate dianionic catecholate complex (32). Nishida et al. have argued that the bidentate complex (33) is inactive for oxygenation, while the monodentate form (31) which has a vacant site for coordination of oxygen is a reactive species, based on the ESR spectroscopy and molecular orbital considerations [93, 94]. 

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