Polymer Tacticity Effects in Polymer-Lanthanide Chelation Thermodynamics

Metal-chelating polymers are critical components in numerous applications. However, despite the known influence of polymer tacticity on both bulk and solution properties, most materials used in metal-chelation applications are atactic. Here, we investigate the relationship between polymer tacticity and polymer-lanthanide interactions in aqueous solution. We synthesized a series of five poly(methacrylic acid)s with systematic variations in tacticity (20-99% m diads) and used isothermal titration calorimetry to measure the thermodynamics of lanthanide binding to each material (Delta H, Delta G, Delta S, K-a, and stoichiometry). We observed enthalpy-entropy compensation across this tacticity series, finding that both |Delta H| and |Delta S| decreased with decreasing m diad content while Delta G remained similar. Molecular dynamics simulations of the polymer-metal interactions revealed that the observed differences in binding thermodynamics may be largely ascribed to differences in polymer flexibility. These combined experimental and computational results demonstrate that metal binding can be influenced by altering the polymer stereochemistry, ultimately influencing the design of more efficient metal-chelating materials.