Polymer Radicals - Free-Radical-Induced DNA Damage and Its Repair - page 189

Fig. 9.3. Pulse radiolysis of N 2 O-saturated solutions of poly(acrylic acid). First-order rate constant
of the β - to α -radical conversion as a function of pH. Source: Ulanski et al. (1996c), with permission
The rate of this reaction strongly depends on the pH (Fig. 9.3), i.e., the proton-
ation state of the polymer. With increasing pH, the rate of reaction slows down
considerably, an indication that the f flexibility of the polymer chain is of impor-
tance for this reaction to occur efficiently. Whether this implies that H-abstrac-
tion mainly occurs from distant sites and not from a neighboring subunit [as
shown in reaction (4)], cannot be decided yet on the basis of the existing data.
A similar H-abstraction takes place in poly(methacrylic) acid, converting the
primary radical into a secondary one [reaction (5); k = 350 s − 1 at pH 7.5; Ulanski
et al. 1999b].
When in the poly(acrylic acid) system radical the tertiary radical is converted by
O 2 into the corresponding peroxyl radical, a chain reaction sets in which yields
CO 2 and a acetylacetone-like product [reactions (6)−(9); Ulanski et al. 1996a; for
the formation of acetylacetone in the model system 2,4-dimethylglutaric acid,
see Ulanski et al. 1996b].