Superoxide conjugated base

Proton-containing admixtures in a solvent or in benzaldehyde can act like water. The superoxide ion abstracts such labile protons and generates a conjugated base. The base in its turn abstracts protons from the solvent, acetonitrile, for example. If benzaldehyde is present, it is converted into cinnamyl nitrile according to Scheme 1-75 ... 

Fe and Cu catalyze, through the cycling of Fe(II)/Fe(III) and Cu(I)/Cu(II) species, respectively, the destruction of superoxide radical (HO2 ) and its conjugate base, the superoxide anion (O2 "), yielding hydrogen perox-... 

Reactive oxygen species (ROS) is a term that describes (i) free radicals, e.g. the hydroxyl radical OH (NB it differs from the hydroxyl ion OH ) (ii) ions, e.g. the hypochlorite ion C10 , the conjugate base formed from the dissociation of hypochlorous acid and the active component of domestic bleach (iii) a combined free radical and ion, e.g. the superoxide anion 02 or (iv) molecules, e.g. hydrogen peroxide H2O2. 

ROS are formed as byproducts of energy production and storage in aerobic microorganisms, animals, and plants. Some are intermediates in essential biolc ical processes such as intracellular signaling, but others damage cell membranes and DNA. They include not only molecules in which all of the electrons are paired, hydrogen peroxide and its conjugate base, for example, but also species with unpaired electrons such as hydroxyl ( ()—H), alkoxyl (-0—R), and superoxide ( ()—07) radicals. 

Based on the mechanistic and kinetic investigation described above, it may be concluded that the semiquinone radical species, particularly its conjugate base, of anthracyclines serves as a catalyst for the reduction of oxygen in aqueous media. In addition, the disproportionation reaction of the generated superoxide radical plays an important role in this reaction mechanism, though a true reaction mechanism of superoxide radical might be more complicated than that proposed here. 

The disproportionation is crucial in determining the action of superoxide anion as a base. According to equation 1, in aqueous solution stoichiometric amounts of the strong bases HO and HO are formed, and the equilibrium constant for this process indicates that superoxide is effective in extracting protons from acids of pK up to 24. In contrast O itself is a weak base (the pK of its conjugate acid, HOj, is 4.69). 

These radicals constitute an acid-base pair (pKa = 4.8 [34]) and, although the superoxide radical anion (Oj ) is the dominating species in most surface waters, its conjugated acid cannot be neglected because of its much higher standard reduction potential ... 

Bullock et al. characterized PEGylated superoxide dismutase (SOD) by CZE using a low-pH separation buffer (pH 2.05) [133]. At low pH, protein molecules are completely protonated and the charge differences between individual PEG-mers (i.e., mono-, di-, or tri-PEGmers) are minimized due to neutralization of lysine residues modified by PEG attachment. This results in a predominantly size-based separation of PEGylated proteins. Under low pH conditions, PEG-SOD conjugates were size-dependently separated and the separation pattern was very similar to the MALDI-TOF MS spectrum. 

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