Hydroxyl radical hydrazine reactions

Relative rate experiments were carried out in a 50 litre FEP Teflon reaction chamber. The chamber was surrounded by blacklamps and sunlamps. Temperature was maintained at 298 K. Hydroxyl radicals were produced by photolysis of methyl nitrite in air with NO added or by the dark reaction of hydrazine with O3. The generated OH radicals react with the substrate compound, RH, and the reference compound, REF ... 

In the one-electron oxidation of hydrazine with hydroxyl radicals, the reaction rates are dependent on the state of protonation of the molecule,... 

The reported measured rate constant for reaction of hydrazine with atmospheric hydroxyl (OH) radicals producing ammonia and nitrogen gas was 6.lx 10 cm molecule s (Harris et al. 1979). The rate constant for 1,1-dimethylhydrazine was not measured since the chemical decomposed rapidly in the test system, but the value was estimated at 5 /10 cm molecule s . Assuming an average OH radical concentration of about 10 molecLile/cm . the tropospheric half-lives ofboth chemicals due to reaction with OH were estimated to be about 3 hours. The half-lives are expected to range from less than 1 hour in polluted urban air to 3-6 hours in less polluted atmospheres (Tuazon et al. 1981). 

The observation of 4 -hydroxylated abasic site 23 allowed to propose the mechanism summarized in Fig. 7 in association to the observation of similar oxidation products previously characterized with Fe-bleomycin or neocarzi-nostatin (4,7). It results in the initial formation of a C4 radical 6 due to H4 abstraction by activated Cu(phen)2. Then a C4 -hydroxylated compound is probably formed. It allows the release of the nucleobase and the formation of 4 -hydroxylated abasic site 23 that is not associated to DNA cleavage. This site was trapped by the authors as a pyridazine after reaction with hydrazine followed by an enzymatic digestion to nucleosides. Oyushi and Sugiyama proposed that a C4 carbocation was involved as intermediate in the reaction, as for Cl -DNA oxidation performed by activated Cu(phen)2. This hypothesis needs, however, to be confirmed since other evolutions of the C4 radical 6, producing also C4 -hydroxylated site, have been proposed with other chemical nucleases (4). However, in the case of DNA oxidation by activated Cu(phen)2 this oxidation pathway seemed minor when compared to the pathway leading to the formation of phosphoglycolate fragment 11. 

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