Rapid Reaction of Nanomolar Mn(II) with Superoxide Radical in Seawater and Simulated Freshwater

Abstract

Superoxide radical (O2-) has been proposed to be an important participant in oxidation-reduction reactions of metal ions in natural waters. Here, we studied the reaction of nanomolar Mn(II) with O2- in seawater and simulated freshwater, using chemiluminescence detection of O2- to quantify the effect of Mn(II) on the decay kinetics of O2-. With 3-24 nM added [Mn(II)] and <0.7 nM [O2-], we observed effective second-order rate constants for the reaction of Mn(II) with O2- of 6×10(6) to 1×10(7) M(-1)·s(-1) in various seawater samples. In simulated freshwater (pH 8.6), the effective rate constant of Mn(II) reaction with O2- was somewhat lower, 1.6×10(6) M(-1)·s(-1). With higher initial [O2-], in excess of added [Mn(II)], catalytic decay of O2- by Mn was observed, implying that a Mn(II/III) redox cycle occurred. Our results show that reactions with nanomolar Mn(II) could be an important sink of O2- in natural waters. In addition, reaction of Mn(II) with superoxide could maintain a significant fraction of dissolved Mn in the +III oxidation state.

Mn(II) oxidation by an ascomycete fungus is linked to superoxide production during asexual reproduction

“…Taken together, these results indicate that ROS and Mn oxide formation are colocalized at the base of synnemata. Although H 2 O 2 can readily reduce Mn(III) and Mn oxides, it does not have a demonstrated ability to oxidize Mn(II) (16,30). Taking into account that superoxide has the demonstrated ability to rapidly oxidize Mn(II) (16) forming Mn oxides (19), this codistribution of the Mn oxides and superoxide indicates that Mn(II) is being oxidized by superoxide.…”

“…Here, the localization of Mn oxides at the base of reproductive structures implicates processes associated with cell differentiation in Mn(II) oxidation. In particular, superoxide, a known oxidant of Mn(II) (16), is believed to act as both an intracellular and extracellular cell signal for the initiation of asexual and sexual reproductive structures in fungi (28).…”

“…Superoxide is a powerful and versatile redox reactant that has been shown to play a significant role in the cycles of numerous metals, including the reduction of Fe(III) and Cu(II), as well as oxidation of Mn(II) (16)(17)(18) ] by molecular oxygen is not thermodynamically viable below a pH of 9, oxidation by superoxide is favorable over all pH conditions (4). Indeed, oxidation of Mn(II) to Mn oxides by a common marine bacterium, Roseobacter AzwK-3b, was found to be a consequence of enzymatic extracellular production of O 2 − , which served as the terminal oxidant of Mn(II) (19).…”

Profiling Microbial Communities in Manganese Remediation Systems Treating Coal Mine Drainage

“…Recent studies have demonstrated that although abiotic Mn(II) oxidation is thermodynamically inhibited below pH 9 when oxygen is the oxidant (6), Mn oxide surfaces (7) and reactive oxygen species (8,9) catalyze oxidation of Mn(II) at near-neutral pH. Mineral surface-catalyzed Mn(II) oxidation was shown to occur in simulated CMD treatment bioreactors, although microbial activity dominated the oxidation of Mn(II) to Mn(III/IV) oxides under certain treatment conditions (2).…”

Hydrogen peroxide dynamics in an agricultural headwater stream: Evidence for significant nonphotochemical production

“…Both H 2 O 2 and its precursor, superoxide radical (O . { 2 ), are involved in the redox cycling of Fe, Mn, and Cu (Voelker et al 1997;Scott et al 2002;Hansard et al 2011). In addition, the strong oxidants produced by the reaction of H 2 O 2 with Fe(II), known as Fenton's reaction, can oxidize organic contaminants and natural organic matter (NOM), converting NOM into more readily bioavailable compounds (Southworth and Voelker 2003;Pullin et al 2004;Vermilyea and Voelker 2009).…”