Impact of Water Extraction on Malonamide Aggregation: A Molecular Dynamics and Graph Theoretic Approach

Abstract

Solution structure in liquid−liquid extraction affects the efficacy of separation; however, even for simplified organic phases, structural characterization and attribution of aggregation to intermolecular interactions are fundamental challenges. We investigate water uptake into organic phases for two malonamides commonly applied to actinide and lanthanide separations. Extracted water induces reorganization of the amphiphilic extractant molecules, although we find this rearrangement is not strongly manifested in small-angle X-ray scattering making it challenging to probe without methods such as atomistic simulation. Using a graph theoretic approach to define hydrogen bonded water/malonamide aggregates from molecular dynamics simulations, we find evidence of a characteristic aggregate size by water number that results from geometric accommodation of the surrounding malonamide molecules. This implies a degree of size selectivity inherent to these water-in-oil aggregates. Conversely, we find no evidence of a characteristic size of the aggregates with respect to their malonamide number. By defining a separate graphical representation of self-association of the amphiphilic malonamides, we quantify how water affects the local and nonlocal topology of the malonamide network, providing a basis for characterization of the structure and impact of polar solutes in increasingly complex organic phases.

Critical fluctuations in liquid–liquid extraction organic phases controlled by extractant and diluent molecular structure

“…Extractant aggregation is quantified by using both geometric and thermodynamic descriptions. For the geometric description, a graph-theoretic cluster analysis is performed on the extractant molecules 59,61,100 using the position of the carbon connecting the two amide groups and a distance cutoff of 10 Å, taken from the first minimum in the radial distribution function (RDF) for pairs of that atom type (see Fig. 11).…”

Molecular Dynamics Study of the Aggregation Behavior of N,N,N′,N′-Tetraoctyl Diglycolamide

“…Our aim in this article is to study the metal-free i-SANEX system, exploring the link between molecular interactions and the aggregates that result. Previous simulations of metal-free systems have shown that diglycolamides form reverse structures in a non-polar diluent, and there has been extensive analysis of the molecular organization of these clusters and the distributions of cluster sizes and compositions. ,,− A very recent article reports the results of large-scale simulations of the TODGA/ n -dodecane/water/nitric acid system as well as providing a detailed description of the molecular structure of the aggregates …”

Aggregation Behavior of Nitrilotriacetamide (NTAmide) Ligands in Thorium(IV) Extraction from Acidic Medium: Small-Angle Neutron Scattering, Fourier Transform Infrared, and Theoretical Studies

“…The overall size of the aggregates increases for the acid-equilibrated L I /L II system because of the accumulation of HNO 3 and H 2 O in the aggregate core. The co-extraction of acid and water along with the metal ions are well reported for different ligands used in the NFC. ,,− ,,− The aggregation of the ligand in the nonpolar medium is mainly driven by the extraction of acid, metal ions, sand water in the organic phase. ,,− ,,, For example, the selectivity of the trivalent metal ion by TODGA is driven by the spherical aggregate formation by the extraction of the acid and water in the organic phase . We have also determined the uptake of water and acid by the L I /L II dissolved in the 20% isodecanol +80% n -dodecane at 3 M HNO 3 (for experimental details, see ESI).…”

“…12,13,15−18,36,70−72 The aggregation of the ligand in the nonpolar medium is mainly driven by the extraction of acid, metal ions, sand water in the organic phase. 11,12,[14][15][16][17]36,70,71 For example, the selectivity of the trivalent metal ion by TODGA is driven by the spherical aggregate formation by the extraction of the acid and water in the organic phase. 9 We have also determined the uptake of water and acid by the L I /L II dissolved in the 20% isodecanol +80% ndodecane at 3 M HNO 3 (for experimental details, see ESI).…”