Radicals perhydroxyl

These include the mitochondrial respiratory chain, key enzymes in fatty acid and amino acid oxidation, and the citric acid cycle. Reoxidation of the reduced flavin in oxygenases and mixed-function oxidases proceeds by way of formation of the flavin radical and flavin hydroperoxide, with the intermediate generation of superoxide and perhydroxyl radicals and hydrogen peroxide. Because of this, flavin oxidases make a significant contribution to the total oxidant stress of the body. 

Aikens, J. and Dix, T.A. (1991). Perhydroxyl radical initiated lipid peroxidation. J. Biol. Chem. 266, 15091-15098. 

HODE Hydroxyoctadecanoic acid HO Hydroxyl radical H02 Perhydroxyl radical HPETE, 5-HPETE 15-HPETE... 

An AOX-free alternative [316] is impregnation with 4 g/1 hydrogen peroxide, 8 g/1 urea and 2 g/1 nonionic wetting agent, then treatment for 60 minutes at 95 °C, pH 8 and 20 1 liquor ratio [316]. This results in a bleached fabric with excellent wettability and without serious fibre degradation. The urea interacts with hydrogen peroxide to form an unstable complex, which then decomposes to form hydroxyl and perhydroxyl radicals, according to Scheme 10.28 [316]. Urea exhibits undesirable environmental characteristics in some respects, however. 

As a result, we get a perhydroxyl radical. At the same time the TiO surface has returned to its initial state and the cycle is completed. The reaction as a whole looks like this ... 

Farhataziz and Ross, A. B. (1977), Selected Specific Rates of Reactions of Transients from Water in Aqueous Solution. III. Hydroxyl Radical and Perhydroxyl Radical and Their Radical Ions, NSRDS-NBS 59, National Bureau of Standards, Washington, D.C. 

D. Behar, G. Czapski, J. Rabani, L.M. Dorfman, and H.A. Schwarz, Acid dissociation constant and decay kinetics of the perhydroxyl radical. J. Phys. Chem. 74, 3209-3213 (1970). 

Recently, perhydroxyl (hydroperoxyl) radical HOO has been wittily named by de Grey [23] as the forgotten radical. Although the concentration of perhydroxyl radical should be many times lower than that of the superoxide (about 1000 times smaller at pH 7.8), this radical always presents in solution, in equilibrium with superoxide ... 

This conclusion is partly true because superoxide is unable to abstract hydrogen atom even from the most active bisallylic positions of unsaturated compounds, while perhydroxyl radical abstracts H atom from linoleic, linolenic, and arachidonic fatty acids with the rate constants of 1-3 x 1031 mol-1 s-1 [24], However, the superoxide damaging activity does not originate from hydrogen atom abstraction reactions but from one-electron reduction processes, leading to the formation of hydroxyl radicals, peroxynitrite, etc, and in these reactions perhydroxyl cannot compete with superoxide. 

Another reason for neglecting perhydroxyl radical is a big difficulty to distinguish it from the much more abundant and more reactive peroxyl radicals. Nonetheless, in several works perhydroxyl radical was considered as a possible initiator of lipid peroxidation (see Chapter 25). It should be noted that at least two biological systems were described where the participation of perhydroxyl radicals seems to be possible. Thus, it has been shown [25,26] that perhydroxyl radical is able to abstract hydrogen atom from NADH (Reaction 6) and the glyceraldehyde-3-phosphate dehydrogenase-NADH (GAPDH-NADH) complex (Reaction 7). 

Bedard et al. [7] studied quantitatively the initiation of the peroxidation of human low-density lipoproteins (LDL) with H00702 . In accord with the above findings the initiation rate increased when pH decreased from 7.6 to 6.5. It was suggested that initiation occurred via hydrogen atom abstraction by perhydroxyl radical from endogenous a-tocopherol, which in this process exhibited prooxidant and not antioxidant properties. Neutral, positively, and negatively charged alkyl peroxyl free radicals were the more efficient initiators of LDL peroxidation compared to superoxide. 

All unsaturated fatty acids contain highly reactive allylic positions, which are easily attacked by hydroxyl and peroxyl free radicals. Bielski et al. [3] studied the reactivity of unsaturated acid with perhydroxyl radical by the stopped flow technique. These authors... 

The influence of substituents on the rates of degradation of arylazo reactive dyes based on H acid, caused by the action of hydrogen peroxide in aqueous solution and on cellulose, has been investigated [43]. The results suggested that the oxidative mechanism involves attack of the dissociated form of the o-hydroxyazo grouping by the perhydroxyl radical ion [ OOH]. The mechanism of oxidation of sulphonated amino- and hydroxyarylazo dyes in sodium percarbonate solution at pH 10.6 and various temperatures has also been examined. The initial rate and apparent activation energy of these reactions were determined. The ketohydrazone form of such dyes is more susceptible to attack than the hydroxyazo tautomer [44]. 

Bielski BHJ, Cabelli D. 1991. Highlights of cnrrent research involving snperoxide and perhydroxyl radicals in aqneons solntion. Int J Radiat Biol 59 291-319. 

Eleetrons reaet with dissolved oxygen producing superoxid radical ion, 02, or its protonated form, perhydroxyl radical, H02, equations (22) and (23) ... 

Under anhydrous conditions, side reactions due to hydroxyl or perhydroxyl radical species can be avoided. Tetrahydropyran and tetrahydrofuran ethers were prepared in good to excellent yields (85-97%) from the corresponding primary and secondary alcohols and THP and THE as a solvent using (w-Bu4N)2S208. Under these reaction conditions the sulfide group and acid-sensitive groups such as aUylic hydroxyl or an acetal moiety remain intact (equation 27). 

Perhydroxyl radical, 75 thermal generation from PNA of, 75 Peroxy radical generation, 75 Peroxide crystal photoinitiated reactions, 310 acetyl benzoyl peroxide (ABP), 311 radical pairs in, 311, 313 stress generated in, 313 diundecanyl peroxide (UP), 313 derivatives of, 317 EPR reaction scheme for, 313 IR reaction scheme for, 316 zero field splitting of, 313 Peorxyacetyl nitrate (PAN), 71, 96 CH3C(0)00 radical from, 96 ethane oxidation formation of, 96 IR spectroscopy detection of, 71, 96 perhydroxyl radical formation of, 96 synthesis of, 97 Peroxyalkyl nitrates, 83 IR absorption spectra of, 83 preparation of, 85 Peroxymethyl reactions, 82 Photochemical mechanisms in crystals, 283 atomic trajectories in, 283 Beer s law and, 294 bimolecular processes in, 291 concepts of, 283... 

---