Sulfate-Radical-Induced Reactions

J-1 (Hildenbrand et al. 1993). It is interesting, that the Ade yield after heating exceeds that of strand breakage. Only the slow and minor strand-breaking process that is suppressed by cysteamine may be due to a radical transfer from the base to the sugar moiety. 

The spectral changes observed by pulse radiolysis have been attributed to unimolecular transformation reactions and the suppression of these reactions by cysteamine has been studied (Hankiewicz et al. 1992 Hankiewicz 1996,1998). Among the products the formation of 8-oxo-A, FAPY-A (Alexander et al. 1987) and cA were noticed, whereby at pH 7 the R isomer dominates over the S isomer by a factor of 2.5 (G(total) = 0.09 x 10 7 mol J Fuciarelli et al. 1986). This low yield is in contrast to a value of 1.4 x 10 7 mol J 1 obtained by an immunochemical assay (Fuciarelli et al. 1985). 

At low pH, poly (A) turns double-stranded, and at relatively high ionic strength and low doses per pulse cross-linking is observed, while DSBs are formed at low ionic strength and high doses per pulse (Denk et al. 1983). Similar results have been obtained with poly(A-t-U). With poly(A), also a dramatic effect of Mg2+ on these reactions has been noted. 

It is concluded that despite all this effort the free-radical chemistry of poly(A) is still poorly understood. 

Poly(A) and poly(G) react with S04 by ET (Wolf et al. 1993). In poly(A) this reaction does not give rise to noticeable strand breakage (3%). The decay kinetics of the poly(A)-derived radicals have been followed by EPR, and it has been shown that it is biphasic 60% decay at a rate of 2 s 1 and 40% at 50 s 1 (Schulte-Frohlinde and Hildenbrand 1989). 

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Niehaus H, Hildenbrand K (2000) Continuous-flow and spin-trapping EPR studies on the reactions of cytidine induced by the sulfate radical-anion in aqueous solution. Evidence for an intermediate radical cation. J Chem Soc Perkin Trans 2 947-952 Niles JC, Burney S, Singh SP, Wishnok JS, Tannenbaum SR (1999) Peroxynitrie reaction products of 3, 5 -di-0-acetyl-8-oxo-7,8-dihydro-2 -deoxyguanosine. Proc Natl Acad Sci USA 96 11729-11734... 

CHS, and nitric oxide (Chap. 15). Radicals have a typical set of reactions in the gaseous state, many will remove thin films of metals from hot glass, and in solution they often can induce polymerization of compounds having carbon-carbon double bonds. Thus, a solution of ferrous sulfate and hydrogen peroxide (such a mixture is called Fenton s reagent) qatalyzes the conversion of acrylonitrile, CH2=CH—CN, to its polymer neither H202 alone nor Fe2+ alone is effective as a catalyst. 

The most widely used method for chemical initiation for graft copolymerization on polysaccharides has been with ceric salts such as CAN or ceric ammonium sulfate. Free radical sites are generated on a polymeric backbone by direct oxidation through ceric metal ions (e.g., Ce "). The ceric ion with low oxidation potential is the proper choice for the reaction. The proposed mechanism for such processes has been depicted by an intermediate formation of metal ion polymer complex (chelate type) [17, 21-24]. Such a complex formation is not restricted to all polymers. The plausible mechanism for ceric ion induced graft copolymerization by direct oxidation method is shown in Scheme 3.1. A series of four grades of Ag-g-PAM copolymers have been synthesized by the conventional method. 

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