RUI: Effect of Multidentate Ligand Exchange Pathways on Metal Ion Uptake

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The Environmental Chemical Sciences Program in the Division of Chemistry funds Professor Nathan Boland at Whitman College. Professor Boland and his students study chemical reactions that affect the availability of metal ions in living organisms. Metal ions can be essential nutrients or toxic contaminants depending on identity and concentration. The chemical form of a metal ion affects how readily the metal is absorbed into an organism. Researchers use chelating resins, which are synthetic compounds that also absorb metal ions, to estimate bioavailability in particular natural waters. This project studies the chemical reactions where chelating resins capture metal ions bound by different organic molecules. The goal of this project is to better understand these reactions and build better predictive tools. The project provides a unique opportunity for undergraduate students to participate as researchers, collaborators, and co-authors of presentations and papers. The project will immerse Whitman undergraduate students in cutting-edge environmental chemistry research. The project will contribute to a growing network of research-active faculty at Whitman with interests in environmental chemistry and transition metal chemistry. This project will enhance Dr. Boland's ability to integrate teaching and research by informing his courses with current and relevant issues in the field. Dr. Boland is committed to continued involvement with Whitman-based science outreach and educational activities engaging local elementary and middle school students and teachers.Multidentate ligand exchange reactions are important in controlling transition metal ion speciation and biouptake. However, there is limited mechanistic understanding of how reaction pathways affect reaction kinetics. The technique of diffusive gradients in thin films (DGT) was designed to mimic bio-uptake and is a useful tool for evaluating metal ion bioavailability in situ. The project uses the adjunctive-semijunctive-disjunctive framework for classifying multidentate ligand exchange reactions to evaluate common assumptions in both DGT and biouptake models. Initial rates of nickel uptake into a suite of DGT chelating resin layers are quantified under varied reaction conditions. Results are used to evaluate new combined kinetic-mass transfer models for each multidentate ligand exchange pathway. Additionally, the project evaluates the effect of low molecular weight organic acids (e.g. oxalate) and the common constituent ion calcium on rates and pathways of metal ion uptake.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.