Water homolytic dissociation mechanism

Figure 19.1. Left Schematic diagram depicting the homolytic dissociation mechanism for vapor-phase water activation over a metal surface. Right Corresponding diagram for the heterol5dic dissociation mechanism for aqueous-phase water activation.

The coverage of water influences the mechanism for water dissociation. At low coverage, a single H2O molecule binds atop a single metal atom and dissociates homolytically to form adsorbed OH and H species ... 

Bernhard and co-workers have performed a series of experiments to determine the mechanisms of DNA strand breakage by direct ionization of plasmid DNA. A big surprise in this work was the discovery that the total yield of single strand breaks exceeds the yield of trapped sugar radicals. Even at very low hydration levels (2.5 waters per nucleotide residue) nearly 2/3 of the strand breaks are derived from precursors other than deoxyribose radicals [74], The authors conclude that a majority of the strand breaks observed do not result from dissociative electron capture, homolytic bond cleavage from excited states, or from hydroxyl radical attack. Rather, the authors conclude that doubly oxidized deoxyribose is responsible for the high yield of strand breaks. 

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