Decomplexation and complexation of alkali metal cations by a crown-ether-type podand in dichloromethane: a steered molecular dynamics study

Abstract

The decomposition of three complexes involving the alkali metal cations Li ? , Na ? and K ? and a potentially octadentate polyethylene-glycol-type podand(1,2-bis-{2-[2-(2-methoxy-ethoxy)-ethoxy]-ethoxy}-benzene, hereafter b33) in dichloromethane was studied by steered molecular dynamics (SMD). This technique proved applicable to the problem. Analysis of the resulting trajectories allowed phenomenological descriptions of the decomposition processes. Use of the Jarzynski identity allowed the estimation of the corresponding free energies, which in turn allowed the estimation of the complex formation free energies in dichloromethane. These are very similar to the experimental values determined by liquid-liquid extraction, as long as a strong reduction of the podand denticity is considered, possibly due to the presence of competing water molecules. To the best of our knowledge, the present study is the first to use SMD to address the problem of determination of the free energies involved in the complexation of alkali cations by an extraction agent (here a podand), in a bulk solvent (here dichloromethane).

Ion Transport through a Water–Organic Solvent Liquid–Liquid Interface: A Simulation Study

“…Our observations of the magnitude of hydration and the consistent partial loss of the second solvation shell are in excellent agreement with prior studies; dos Santos and Gomes report cesium and Chorny and Benjamin report sodium losing comparable amounts of its second solvation shell when entering nitrobenzene, but they report persistent first shell hydration. Furthermore, refs and discuss similar water wedge formation and encapsulation of cation K + at the water–dichloromethane interface.…”

A Quantitative Metric for the Design of Selective Supercritical CO2 Extraction of Lithium from Geothermal Brine

“…Valente et al. showed that H 2 O will initially cross the interface as a water droplet around the cation, before returning to the bulk H 2 O phase on the order of 1–2 ns . Based on this time scale relative to the time scale for experimental extraction, we could confidently conclude all superfluous H 2 O molecules will dissipate prior to selectivity measurements.…”

“…A more recent MD study by Valente et al. in 2012 used a custom crown ether in dichloromethane solvent to calculate the binding free energies of lithium, sodium, and potassium . They found that the selectivity of their crown ethers to alkali metals increased with decreasing ionic radius.…”

“…They found that the selectivity of their crown ethers to alkali metals increased with decreasing ionic radius. This work used steered molecular dynamics (SMD) to find the reaction coordinate, rather than assume a coordinate perpendicular to the plane of the crown ether . This allows SMD to provide a relatively unbiased insight into a viable reaction coordinate (see the Supporting Information for method details).…”

Synthesis and complexing properties of diglycol resorcinarene podands

“…The excellent binding properties of biological receptors are still assigned to self-assembly, molecular recognition and multivalency. Multiple-interaction ligands are useful both for cation binding and protein surface recognition, cell transfection or crystal engineering [ 1 – 5 ]. All these many possibilities are associated also with a wide panel of scaffolds used for the synthesis of modern podands.…”