The broad goals of my research program are to develop chemical knowledge that will help us to predict the dynamics of nutrient and toxic metal bioavailablility and mobility in the environment and to develop analytical methods that will enhance our ability to explore the kinetics and mechanism of governing reactions.

The biovailability and transport of metal ions in the environment is often controlled by kinetics of governing reactions. For example, iron is an essential micronutrient for plants but because it is insoluble in many soils plants have evolved strategies to capture their requirement of iron from the soil surrounding their roots. Grasses (including wheat, oats, barley, rye, etc.) have evolved to periodically realease chelating agents to strongly bind iron and mobilize it from surrounding soil. Chelating agents are ligands that bind metal ions with more than one Lewis base and form highly stable complexes with metal ions. How fast the chelating agent can capture iron determines whether the plant captures sufficient iron. The kinetics of this process is also influenced by the presence of other, potentially toxic, metal ions, organic acids, and mineral surfaces. 

Synthetic chelating agents are used widely in industrial and domestic applications including scale-inhibition in cooling pipes and fracking wells, paper pulp processing, food preservation, builders in detergents, and buffers in personal care products. Given the wide use of synthetic chelating agents it is not suprising that they have been detected in natural waters around the world. Indeed, both natural and synthetic chelating agents dominate dissolved metal ion speciation in the environment. 

Adjunctive-Semijunctive-Disjunctive Ligand Exchange

Ligand exchange is the principal reaction that leads to the formation of stable metal ion complexes. Ligand exchange involves the exchange of one ligand (L) with another (Y) in the inner-coordiation sphere of a metal ion (M). Pathways of ligand exchange control whether reactions occur on timescales relevant to bio-uptake. Predicting pathways where both L and Y are chelating agents is complicated by the fact that these pathways are a function of the properties of M, L, and Y. Furthermore, reactions may be very fast, complete in fractions of a second, or very slow, taking many weeks. By studying reactions with an array of structurally-related chelating agents we seek to develop structure-reactivity relationships that will help us predict the kinetics of ligand exchange reactions. Furthermore, we seek to improve the conceptual framework used to categorize ligand exchange pathways.

My research group uses a novel capillary electrophoresis (CE) method to separate and monitor several metal-chelating agent and free chelating agent species through the course of a reaction. Combining CE separations with suites of structurally-related chelating agents and kinetic modelling, we have a powerful tool for elucidating reaction pathways.

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