Despite clear evidence of sudden translational jump occurrence of a solute in supercooled water, a detailed mechanism of this jump is still lacking. A previous work [ Indra , S. ; Daschakraborty , S. Chem. Phys. Lett. 2017 , 685 , 322 - 327 ] put forward a mechanism of this jump from an initial solvent cage to a final one. The proposed mechanism is astoundingly similar to that of the electron/proton transfer reaction in aqueous solution. The above study identified the spatial prearrangement (rearrangement before the jump occurrence) of cage forming water solvent molecules as the actual reaction coordinate. However, the study completely ignored the contribution of the orientational prearrangement of solvent water molecules. In this study, we have monitored both the spatial and the orientational prearrangements of water solvent molecules at subzero temperatures during the jump occurrence of the solute. We have found overwhelming contributions of both the spatial and orientational prearrangements of water, which symmetrize the hydration structure at the initial and final cage positions to facilitate the jump event. Through a systematic temperature dependence study (from T = 240 to 270 K), we have found clear evidence that a strong synchronization between translational and rotational prearrangements of the solvent water molecules is crucial for the solute's jump from one solvent cage to another in supercooled water (below T = 252 K). The above translation-rotation synchronization is probably due to the cooperative movement of solvent water molecules forming clusters in the supercooled region. Since these cooperative dynamics are the consequence of the spatiotemporal heterogeneity in the medium, we infer that the large-amplitude translational jump of the nonpolar solute probably stems from the spatiotemporal heterogeneity of supercooled water. At temperatures above the melting point, this cooperativity is partly lost since the translational and orientational prearrangements become somewhat independent of each other.
Much is understood about electrolyte liquid/liquid interfaces, yet the relationships between ion solvation, adsorption, and the instantaneous surface have not been the topic of significant study. The thermally corrugated capillary wave characteristics of the instantaneous aqueous surface contribute to heterogeneous interfacial structural and dynamic properties. Those properties are sensitive the nature of the immiscible nonpolar solvent. In this work, we examine the role of interfacial heterogeneity upon ion behavior and further, how this is influenced by a partially polar solvent relative to a vapor phase analog. We compare and contrast ion solvation in electrolyte/vapor and electrolyte/octanol biphasic systems, focusing upon the changes to interfacial heterogeneity in the presence of the octanol solvent and the variations of ion concentration at different interfacial regions. The interplay between competing forces introduced by strong octanol water interactions at the interface is examined, with a new understanding of how such competition may lead to tailored interfacial properties.
Liquid/liquid extraction is one of the most widely used separation and purification methods, where a forefront of research is the study of transport mechanisms for solute partitioning and the relationships...
Uranyl (UO2+ 2 ) speciation at the liquid/liquid interface is an essential aspect of the mech?anism that underlies its extraction as part of spent nuclear fuel reprocessing schemes and environmental remediation of contaminated legacy waste sites. Of particular importance is a detailed perspective of how changing ion concentrations at the liquid interface alter the distribu?tion of hydrated uranyl ion and its interactions with complexing electrolyte counterions relative to the bulk aqueous solution. In this work, classical molecular dynamics simulations have ex?amined uranyl in bulk LiNO3(aq) and in the presence of a hexane interface. UO2+ 2 is observed to have both direct coordination with NO− 3 and outer-sphere interactions via solvent-separated ion-pairing (SSIP), whereas the interaction of Li+ with NO− 3 (if it occurs) is predominantly as a contact ion-pair (CIP). The variability of uranyl interactions with nitrate is hypothesized to prevent dehydration of uranyl at the interface, and as such the cation concentration is un?perturbed in the interfacial region. However, Li+ loses waters of solvation when it is present in the interfacial region, an unfavorable process that causes a Li+ depletion region. Although significant perturbations to ion-ion interactions, solvation, and solvation dynamics are observed in the interfacial region, importantly, this does not change the association constants of uranyl with nitrate. Thus, the experimental association constants, in combination with knowledge of the interfacial ion concentrations, can be used to predict the distribution of interfacial uranyl nitrate complexes. The enhanced concentration of uranyl dinitrate at the interface, caused by excess adsorbed NO− 3 , is highly relevant to extractant ligand design principles as such nitrate complexes are the reactants in ligand complexation and extraction events. File list (2) download file view on ChemRxiv Uranyl_complexation_and_solvation_in_nitrate_f.pdf (1.59 MiB) download file view on ChemRxiv Uranyl_complexation_and_solvation_in_nitrate_SI.pdf (4.00 MiB)
Described in this work are calix [4]pyrrole-based ionpair receptors, cis/trans-1 and cis/trans-2, designed for the extraction of sodium hydroxide. An X-ray diffraction analysis of a single crystal of the cis-1•NaOH isomer isolated from a mixture of cis/trans-1 revealed a unique dimeric supramolecular structure. An average dimer in toluene-d 8 solution was inferred on the basis of diffusion-ordered spectroscopy (DOSY). Support for the proposed stoichiometry came from density functional theory (DFT) calculations. The structural stability of the dimeric cis-1•NaOH complex in toluene solution was further confirmed by ab initio molecular dynamics (AIMD) simulation with explicit representation of solvent. Under conditions of liquid−liquid extraction (LLE), purified receptors cis-and trans-2 were both found to remove NaOH from a pH 11.01 aqueous source phase into toluene with extraction efficiencies (E%) of 50−60% when used equimolar to NaOH. However, in all cases, precipitation was observed. Complexities associated with precipitation could be avoided by immobilization of the receptors onto a chemically inert poly(styrene) resin by means of solvent impregnation. The use of solvent-impregnated resins (SIRs) eliminated precipitation in solution while retaining the extraction efficiency toward NaOH. This allowed both the pH and salinity of the alkaline source phase to be lowered.
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