Oxidation by molecular oxygen

In the first step, luciferin is converted into luciferyl adenylate by ATP in the presence of Mg2+. In the second step, luciferyl adenylate is oxidized by molecular oxygen resulting in the emission of yellow-green light, of which the mechanism is discussed in Sections 1.1.6 and 1.1.7. Both steps, (1) and (2), are catalyzed by luciferase. The reaction of the first step is slower than that of the second step, thus the first step is the rate-limiting step. 

Harvey (1952) demonstrated the luciferin-luciferase reaction with O. phosphorea collected at Nanaimo, British Columbia, Canada, and with O. enopla from Bermuda. McElroy (1960) partially purified the luciferin, and found that the luminescence spectrum of the luciferin-luciferase reaction of O. enopla is identical to the fluorescence spectrum of the luciferin (A.max 510 nm), and also that the luciferin is auto-oxidized by molecular oxygen without light emission. Further investigation on the bioluminescence of Odontosyllis has been made by Shimomura etal. (1963d, 1964) and Trainor (1979). Although the phenomenon is well known, the chemical structure of the luciferin and the mechanism of the luminescence reaction have not been elucidated. 

Catalysis by metalloporphyrins of reactions involving oxidation by molecular oxygen and oxygen-containing compounds. N. S. Enikolopyan, K. A. Bogdanova, L. V. Karmilova and K. A. Askarov, Russ. Chem. Rev. (Engl. Transl.), 1985,54,215 (188). 

Oxidation by molecular oxygen or NO2 converts this weak acid into H2 SO4, a major contributor to acid rain. 

In the second oxidation method, a metalloporphyrin was used to catalyze the carotenoid oxidation by molecular oxygen. Our focus was on the experimental modeling of the eccentric cleavage of carotenoids. We used ruthenium porphyrins as models of cytochrome P450 enzymes for the oxidation studies on lycopene and P-carotene. Ruthenium tetraphenylporphyrin catalyzed lycopene oxidation by molecular oxygen, producing (Z)-isomers, epoxides, apo-lycopenals, and apo-lycopenones. 

A similar system, but with a more hindered porphyrin (tetramesitylporphyrin = tetraphenylporphyrin bearing three methyl substituents in ortho and para positions on each phenyl group), was tested for P-carotene oxidation by molecular oxygen. This system was chosen to slow the oxidation process and thus make it possible to identify possible intermediates by HPLC-DAD-MS analysis. The system yielded the same product families as with lycopene, i.e., (Z)-isomers, epoxides, and P-apo-carotenals, together with new products tentatively attributed to diapocarotene-dials and 5,6- and/or 5,8-epoxides of P-apo-carotenals. The oxidation mechanism appeared more complex in this set-up. 

FIGURE 11.4 Hypothesis of the sequence of events when lycopene is oxidized by molecular oxygen in the presence of ruthenium tetraphenylporphyrin. 

FIGURE 11.6 Hypothesis of the sequence of events when (3-carotene is oxidized by molecular oxygen in the presence of ruthenium tetramesitylporphyrin. Parts of the chemical formula in dotted line indicate that length of the carbon chain may vary. 

The active enzyme abstracts a hydrogen atom stereospecifically from the intervening methylene group of a PUFA in a rate-limiting step, with the iron being reduced to Fe(II). The enzyme-alkyl radical complex is then oxidized by molecular oxygen to an enzyme-peroxy radical complex under aerobic conditions, before the electron is transferred from the ferrous atom to the peroxy group. Protonation and dissociation from... 

Lophine emits yellow CL upon oxidation by molecular oxygen in alkaline solution. The oxidation is believed to produce a free radical [3], which is further oxidized to a hydroperoxide, which is the light-emitting species [4-6], A number of chemiluminescent derivatives of lophine have been synthesized and have been shown to exhibit varying efficiencies of CL. Lophine has been used in the analysis of metal ions such as Co2+ that catalyze the chemiluminescent reaction between it and hydrogen peroxide [7], It has also been used as a chemiluminescent indicator in titrimetry [8],... 

IP Skibida. Homogeneous Catalysis by Compounds of Transition Metals in Liquid-Phase Oxidation by Molecular Oxygen. Doctoral Thesis Dissertation. RUDN, Moscow, 1997. 

A mild aerobic palladium-catalyzed 1,4-diacetoxylation of conjugated dienes has been developed and is based on a multistep electron transfer46. The hydroquinone produced in each cycle of the palladium-catalyzed oxidation is reoxidized by air or molecular oxygen. The latter reoxidation requires a metal macrocycle as catalyst. In the aerobic process there are no side products formed except water, and the stoichiometry of the reaction is given in equation 19. Thus 1,3-cyclohexadiene is oxidized by molecular oxygen to diacetate 39 with the aid of the triple catalytic system Pd(II)—BQ—MLm where MLm is a metal macrocyclic complex such as cobalt tetraphenylporphyrin (Co(TPP)), cobalt salophen (Co(Salophen) or iron phthalocyanine (Fe(Pc)). The principle of this biomimetic aerobic oxidation is outlined in Scheme 8. 

Several different tocopherols are known to have vitamin E activity, but a-tocopherol, a trimethyltocol (Figure 12.9) is the most biologically active. Other less potent forms are the /3-, y- and S-tocopherols, which contain fewer methyl groups. They all have antioxidant properties and a deficiency results in a lack of protection of the unsaturated fatty acids in the membrane phospholipids against oxidation by molecular oxygen. 

Oxidation by molecular oxygen of trifluoroacetyldiphenylphosphine in ether in a polythene vessel yields the compound (100),102 previously suggested as an intermediate in the reaction of chlorodiphenylphosphine with trifluoroacetic acid which gives (101).103 In a glass vessel, (100) rapidly isomerizes to (101). 

Soot can be oxidized by molecular oxygen, through the process described previously for pulverized coal char oxidation, but in combustion systems the dominant oxidation of soot is performed by radical species, especially the hydroxyl radical, OH. This discovery was made by Fenimore and Jones... 

A possible mechanism of oxidation of methylene groups to carbonyl groups involves autoxidation (oxidation by molecular oxygen) at the benzylic position. Autoxidation of arylalkanes is a facile reaction with low activation energies for example, 6.0 kcal/mole for 1,1-diphenylethane and 13.3 kcal/mole for toluene. ... 

The first variant works with isobutane as the hydroperoxide precursor, which is oxidized to TBHP by molecular oxygen. During the epoxidation of propene, TBHP is transformed to ferf-butanol, which is converted to methyl ferf-butyl ether. The second procedure employs ethylbenzene, which is oxidized by molecular oxygen to phenyl ethyl hydroperoxide, which transfers an oxygen to propene and so is reduced to phenylethanol. This by-product of the process is converted to styrene, a versatile bulk chemical. 

The oxidation by molecular oxygen or the base-catalyzed oxidative decarboxylation of saturated 5(4//)-oxazolones 278 yields diacylamines and provides an efficient procedure to prepare imides 279 from Al-acylamino acids (Scheme 7.90). 

Oxidation by molecular oxygen most likely occurs via a radical mechanism 10-13 and the reaction rates are generally slow unless traces of metal ions are present which are known to drastically affect the reaction rate 14 thus making control of the air-oxidation reaction rather difficult. The rates can also be significantly enhanced by adding charcoal to induce a surface-assisted catalysis of the intramolecular disulfide bond formation 15 Nonetheless the difficult control of this oxidation procedure can lead to partial oxidation of Met and Trp residues when peptides are exposed for longer periods of time to air oxygen 16 ... 

The three-dimensional structures, or part of it, are also known for Desulfovibrio vulgaris and Anacystis nidulans flavodoxins. These results, including those obtained on C.MP., were recently summarized by Adman . Hence, these results will be discussed only briefly. The x-ray structures show that the isoalloxazine ring is embedded in a hydrophobic pocket of the apoprotein, i.e. flanked by at least one aromatic amino acid residue. During the redox transitions, especially from the oxidized to the semiquinone state, small conformational changes occur and contacts with the isoalloxazine ring are formed or broken. These conformational transitions form probably a kinetic barrier so that the semiquinone state is trapped by the apoprotein and, therefore, rather stable towards oxidation by molecular oxygen. 

NADPH—undergo oxidation by molecular oxygen. These reactions take place on the lumenal face of the smooth ER. A similar pathway, but with different electron carriers, occurs in plants. 

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