| Abstract
| - Organically complexed Cu can be a significant sink ofphotoproduced superoxide (O2-) in seawater. Using pulseradiolysis, we examined the rate constant of catalyticdismutation (kcat) of O2- in the presence of Cu complexedby strong (L1) and weaker (L2) organic ligands presentin coastal seawater samples and produced by cultures ofSynechococcus sp. In the coastal samples examined,CuL2 complexes were almost as reactive towards O2- asinorganically complexed Cu species (kcat = 2.9−8.1 × 108M-1 s-1). Furthermore, kcat was invariant with added Cu (5−60 nM), implying that the added Cu formed a singletype of Cu complex or a mixture of complexes with verysimilar O2- reactivities. Significant differences between kcatvalues of estuarine and coastal samples were observed,suggesting an effect of organic ligands from terrestrialsources. CuL1 complexes produced by Synechococcus sp.were found to be less reactive (kcat< 1 × 108 M-1 s-1).The high reactivity of CuL2 complexes decreases estimatesof steady-state concentrations of O2- in sunlit marinewaters by at least a factor of 10.
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