Reaction networks in environmental systems: connecting reactive oxygen species generation and particle formation during the oxidation of ferrous iron

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The Environmental Chemical Sciences Program in the Chemistry Division at the National Science Foundation supports the research of Professor John L. Ferry at the University South Carolina at Columbia. There have been several important works describing the oxidation of dilute (nanomolar) Fe(II) by oxygen and many describing electron transfer from ferrous/ferric solids in anoxic solutions. However, these have not been integrated into a predictive, Fe-based continuous model for estimating ROS production. In the natural environment, Fe(III) can be reduced to the Fe(II) state through photochemical processes, direct reaction with reductants (e.g. sulfides) or via microbially mediated reduction. The net cycling between the two oxidation states leads to the apparent catalytic production of ROS (which include hydroperoxyl radical and its conjugate base superoxide, hydroxyl radical and hydrogen peroxide) and provides kinetically and energetically facile connections between the elemental Fe, O, C, S and N cycles. The researchers have developed a high throughput, combinatorial approach to explore the effect of solution variation on Fe(II) oxidation and ROS yield in the presence of Fe(III). Work proposed will test the specific hypothesis that ROS production is maximized when resulting Fe(III) is sequestered in phases that can undergo atom transfer as well as electron transfer with reactants in the solution phase. ROS will be measured in the aqueous phase through the addition of a series of organic probes. The concentration of dissolved metals will be determined by a combination of spectrophotometric and mass spectrometric techniques. Solids will be characterized for 56Fe to 58Fe to O ratios using electron backscatter and mass spectrometric techniques. The exchange of isotopically labeled Fe(II) with particulate Fe will be determined using high resolution mass spectrometric techniques. These observables will be correlated to the conditional initiating matrix to develop response surfaces describing the systemic ROS generation response to oxygen addition.The outcomes of this study will result in a new understanding of how rapid Fe(II)/Fe(III) cycling is affected by co-solutes and colloids. These outcomes have significance to the general public in the context of carbon turnover driven by the by-product ROS (and hence climate change) as well as public health concerns. Results from this work will be incorporated into workshops designed to educate students and faculty outside of the field. The workshops will be developed in collaboration with the Hanse Institute for Advanced Study in Delmenhorst; Germany, and extended to the South Carolina State Museum. The proposed work will provide support for two graduate and two undergraduate students. Professors John Ferry and Tim Shaw have a well-documented record of mentoring underrepresented minorities and female students; 34 out of the 60 researchers in their laboratories have been female, and nine have been from underrepresented groups.