Exploring the Molecular Driving Forces for f-Element Complexation and Organization in Mixed Solvents at Interfaces

This project will examine changes in the solvation of trivalent actinide (An3+) and lanthanide (Ln3+) cations in binary solvents during complexation with an emphasis on characterizing the speciation in the bulk liquid versus at liquid:vapor and liquid:liquid interfaces.
1. Understand the solvation and de-solvation processes for An3+ and Ln3+ cations during complexation by simple organic ligands in binary solvents,
2. Define the molecular species formed as a function of solvent composition, and
3. Determine their subsequent organization at interfaces.
The organic ligands of interest are alpha-hydroxy and alpha-amino carboxylate ligands, and the binary solvents will involve mixtures of water:methanol (MeOH) and water:dimethylformamide (DMF). The liquid:liquid interface we will pursue will be the binary solvents and hexane. A combination of optical spectroscopic techniques (absorption, time-resolved fluorescence and sum-frequency generation) and computational methods (both classical molecular dynamics (MD) and ab-initio MD (AIMD) will be utilized.
The proposed project closely aligns with BER's mission to provide a molecular understanding of complex environmental systems and the fate of radionuclides within such systems. This basic knowledge is essential for designing effective remediation strategies for contaminated DOE legacy sites, and understanding biological processes such as bioaccumulation and biological remediation. The impact of the proposed studies will be to provide a molecular foundation for understanding complex environmental systems and the fate of radionuclides within such systems. Our studies are designed to quantify the impact of increased covalency for the 5f period of elements compared to the 4f period on complexation in mixed solvent systems.
The facilities and infrastructure at EMSL are essential for success in this project because of the integration of experimental and computational tools necessary to address the problem. Conducting the work under the EMSL umbrella provides a collaborative environment that will be essential for this project, as described. In addition, the proposed studies using laser fluorescence spectroscopy and SFG will build on completed experimental work from Washington State University involving other experimental tools, such as nuclear magnetic resonance, absorption spectroscopy, and calorimetry. This integration of information from multiple spectroscopic and computational tools will enable us to more fully define the role of f-element solvation in lanthanide and actinide biogeochemistry.