Radical oxidizing properties

The antioxidant property of ferulic acid and related compounds from rice bran was reported by Kikuzaki et al, (2002). Their results indicated that these compounds elicit their antioxidant function through radical scavenging activity and their affinity with lipid substrates. Another recent study reported by Butterfield et al, (2002) demonstrated that ferulic acid offers antioxidant protection against hydroxyl and peroxyl radical oxidation in synaptosomal and neuronal cell culture systems in vitro. The effect of ferulic acid on blood pressure (BP) was investigated in spontaneously hypertensive rats (SHR). After oral administration of ferulic acid the systolic blood pressure (SBP) decreased in a dose-dependent manner. There was a significant correlation between plasma ferulic acid and changes in the SBP of the tail artery, suggesting... 

El-Agamey, A., Carotenoid radical chemistry and antioxidant/pro-oxidant properties. Arch. Biochem. Biophys., 430, 37, 2004. 

Another mechanistically useful nucleophile is acetate ion and related carboxylates. Acetate ion is difficult to oxidize (Eberson, 1963) and reacts with radical cations in a bond-forming reaction (Eberson and Nyberg, 1976). The oxidation product, the acetoxyl radical, has properties which make trapping it very unlikely in that its decarboxylation rate constant is 1.3 X 109 s 1 (Hillborn... 

While using the trap method, one should take into account the oxidation properties of a trap with respect to radicals or other electron donors that are present in the system. Because spin traps can be electron donors themselves, their oxidation potentials should be more positive than that of the participants of the reaction under study. 

Measurement of ionization potentials has shown that 2,4,6-triphenylpyrylium salts undergo a thermal reduction in the mass spectrometer giving the corresponding free radicals. Steric properties preclude dimerization (74OMS(9)80>. This type of reduction appears to be largely independent of the nature of the anion the bromide and iodide salts behave identically. However, in the case of the tetrafluoroborate salt, adduct formation between a cation and a fluoride ion gave a minor peak. Anomalous behaviour is displayed by the perchlorates the anion effects oxidation of the cation upon evaporation giving a base peak which corresponds to [M + 0-H]+. 

The other important property affecting lipid oxidation is the chelating effect of chlorogenic acids. It is important to keep in mind that the influence of biometals (Fe, Cu etc.) on lipid free radical oxidation is essential. It is well known that iron can react with hydrogen peroxide by the Fenton reaction (Equation 3). The hydroxyl radical formed in the Fenton reaction is capable of reacting with lipid and PUFA as the initiation stage. Iron can also participate in alkyl peroxide or lipid peroxide decomposition. Therefore, the nature of iron chelation in a biological system is an important aspect in disease prevention. 

Photooxidative degradation of LLDPE at ambient temperature under sunlight is also a radical oxidation reaction. It causes change in color and drastic deterioration of mechanical and dielectric properties of LLDPE articles. Photooxidation can be prevented by using Light stabilizers. 

The oxidative properties of iodosylbenzene in the presence of Mn(TPP)Cl towards hydroxylation of alkanes478,479 and epoxidation of alkenes478 were simultaneously reported by Hill479 and Groves.478 These oxidations have the characteristics of a stepwise radical reaction. 

Besides their free-radical trapping properties, flavonoids can interfere with the capacity of oxidants to reach the bilayer. A study from our laboratory demonstrated that the adsorption of water-soluble ( )-epicatechin oligomers (dimer to hexamer) to membranes prevents lipid oxidation initiated by the azocompound 2,2 -azobis (2,4-dimethylvaleronitrile), (AMVN), a hydrophobic molecule that upon its incorporation into the bilayer decomposes yielding peroxyl radicals [Verstraeten et al., 2003], In this case, given that the oxidant... 

All these radicals have oxidizing properties, but there are also some inorganic radicals which have reducing properties (E < 0 V cf. Table 5.2). 

The mesomeric forms of the pyrimidine C(6)-adduct radicals may be written with the free spin at a heteroatom and hence have as oxidizing properties. 

These reactions are real tautomerization reactions, but the quite common water elimination reactions can also completely change the redox property of a radical. A case in point is the radical derived from ethylene glycol which is a reducing a-hydroxyalkyl radical which is transformed by water elimination into the fomylmethyl radical (see below) whose oxidizing property has been discussed above [reaction (20)]. Similarly, the phenol OH-adduct is a reason-... 

Radical cations are strongly oxidizing intermediates, but also after deprotonation at a heteroatom (in the present systems at nitrogen) some of this oxidizing property remains. Thus a common feature of these intermediates is that they are readily reduced by good electron donors. Since the heteroatom-centered radicals and the radical cations are always in equilibrium, it is, at least in principle, possible that such intermediates react with water at another site (canonical mesomelic form), that is at carbon. This reaction leads to OH-adduct radicals. Although deprotonation at a heteroatom is usually faster (but also reversible) than deprotonation at carbon, the latter reaction is typically "irreversible". This also holds for a deprotonation at methyl (in Thy). 

On the other hand, the C(6)- OH-adduct formed in reaction (61) has oxidizing properties (note its mesomeric form with the radical at oxygen quantum-mechanical calculations indicate that it is the most oxidizing radical among all conceivable OH- and H-adducts of the nudeobases Colson and Sevilla 1995). The yield of this oxidizing radical can be determined with the help of a strong re-ductant such as TMPD [reaction (63) the TMPD radical cation is monitored e(565 nm) = 12,500 dm3 mol-1 cm-1]. 

The allylic radical formed upon H-abstraction from the methyl group [reaction (60)] has neither reducing nor oxidizing properties, and its yield may be deducted from the difference of the sum of reducing and oxidizing radicals with respect to the total OH yield. A series of such experiments has been carried out (Fujita and Steenken 1981 Al-Sheikhly and von Sonntag 1983 Hazra and Steen-ken 1983), and their results are compiled in Table 10.7. 

Of these radicals, 60-70% have oxidizing properties (for the reactions of purine- OH-adducts with a number of reductants see, e.g., O Neill 1983, 1984 O Neill et al. 1985 Shi et al. 1999a Candeias and Steenken 2000). This includes the -OH-adducts that eliminate rapidly water yielding G (Steenken 1989). Its main precursor has been has been suggested to be the C(4)- OH-adduct (-60-70% Vieira et al. 1993 Candeias and Steenken 2000). This radical eliminates water leading to the even more strongly oxidizing G- [cf. reaction (77)]. 

---