An official website of the United States government
The organization of multiple subcellular compartments is controlled by liquid–liquid phase separation. Phase separation of this type occurs with the emergence of interfacial tension. Aqueous two-phase systems formed by two non-ionic polymers can be used to separate and analyze biological macromolecules, cells and viruses. Phase separation in these systems may serve as the simple model of phase separation in cells also occurring in aqueous media. To better understand liquid–liquid phase separation mechanisms, interfacial tension was measured in aqueous two-phase systems formed by dextran and polyethylene glycol and by polyethylene glycol and sodium sulfate in the presence of different additives. Interfacial tension values depend on differences between the solvent properties of the coexisting phases, estimated experimentally by parameters representing dipole–dipole, ion–dipole, ion–ion, and hydrogen bonding interactions. Based on both current and literature data, we propose a mechanism for phase separation in aqueous two-phase systems. This mechanism is based on the fundamental role of intermolecular forces. Although it remains to be confirmed, it is possible that these may underlie all liquid–liquid phase separation processes in biology.
more »
« less
Metastable precipitation and ion–extractant transport in liquid–liquid separations of trivalent elements
The extractant-assisted transport of metal ions from aqueous to organic environments by liquid–liquid extraction has been widely used to separate and recover critical elements on an industrial scale. While current efforts focus on designing better extractants and optimizing process conditions, the mechanism that underlies ionic transport remains poorly understood. Here, we report a nonequilibrium process in the bulk aqueous phase that influences interfacial ion transport: the formation of metastable ion–extractant precipitates away from the liquid–liquid interface, separated from it by a depletion region without precipitates. Although the precipitate is soluble in the organic phase, the depletion region separates the two and ions are sequestered in a long-lived metastable state. Since precipitation removes extractants from the aqueous phase, even extractants that are sparingly soluble in water will continue to be withdrawn from the organic phase to feed the aqueous precipitation process. Solute concentrations in both phases and the aqueous pH influence the temporal evolution of the process and ionic partitioning between the precipitate and organic phase. Aqueous ion–extractant precipitation during liquid–liquid extraction provides a reaction path that can influence the extraction kinetics, which plays an important role in designing advanced processes to separate rare earths and other minerals.
more »
« less
- Award ID(s):
- 1834750
- PAR ID:
- 10578090
- Publisher / Repository:
- Proceedings of the National Academy of Sciences
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 121
- Issue:
- 13
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract. Gas–particle partitioning of water-soluble organic compounds plays a significant role in influencing the formation, transport, and lifetime oforganic aerosols in the atmosphere, but is poorly characterized. In this work, gas- and particle-phase concentrations of isoprene oxidation products(C5-alkene triols and 2-methylterols), levoglucosan, and sugar polyols were measured simultaneously at a suburban site of the western Yangtze RiverDelta in east China. All target polyols were primarily distributed into the particle phase (85.9 %–99.8 %). Given the uncertainties inmeasurements and vapor pressure predictions, a dependence of particle-phase fractions on vapor pressures cannot be determined. To explore the impactof aerosol liquid water on gas–particle partitioning of polyol tracers, three partitioning schemes (Cases 1–3) were proposed based onequilibriums of gas vs. organic and aqueous phases in aerosols. If particulate organic matter (OM) is presumed as the only absorbing phase(Case 1), the measurement-based absorptive partitioning coefficients (Kp,OMm) of isoprene oxidation products and levoglucosan were more than 10 times greater than predicted values (Kp,OMt). The agreement betweenKp,OMm and Kp,OMt was substantially improved when solubility in a separate aqueous phase wasincluded, whenever water-soluble and water-insoluble OM partitioned into separate (Case 2) or single (Case 3) liquid phases,suggesting that the partitioning of polyol tracers into the aqueous phase in aerosols should not be ignored. The measurement-based effective Henry'slaw coefficients (KH,em) of polyol tracers were orders of magnitude higher than their predicted values in pure water(KH,wt). Due to the moderate correlations between log(KH,em/KH,wt) andmolality of sulfate ions, the gap between KH,em and KH,wt of polyol tracers could not be fullyparameterized by the equation defining “salting-in” effects and might be ascribed to mechanisms of reactive uptake, aqueous phase reaction,“like-dissolves-like” principle, etc. These study results also partly reveal the discrepancy between observation and modeling of organicaerosols.more » « less
-
The unprecedented liquid–liquid extraction of the dinegative chromate ion (CrO42–) from neutral aqueous solutions into aliphatic hydrocarbon solvents using nanojars as extraction agents is demonstrated. Transferring chromate from water into an organic solvent is extremely challenging due to its large hydration energy (ΔGh° = −950 kJ/mol) and strong oxidizing ability. Owing to their highly hydrophilic anion binding pockets lined by a multitude of hydrogen bond donor OH groups, neutral nanojars of the formula [cis-CuII(μ-OH)(μ-4-Rpz)]n (n = 27–33; pz = pyrazolate anion; R = H or n-octyl) strongly bind the CrO42– ion and efficiently transfer it from water into n-heptane or C11 – C13 isoalkanes (when R = n-octyl). The extracted chromate can easily be recovered from the organic layer by stripping with an aqueous acid solution. Electrospray ionization mass spectrometric, UV–vis and paramagnetic 1H NMR spectroscopic, X-ray crystallographic, and thermal stability studies in solution and chemical stability studies toward NH3, methanol, and Ba2+ ions are employed to explore the binding of the CrO42– ion by nanojars. Titration of carbonate nanojars [CO3 ⊂ {Cu(OH)(pz)}n]2– with H2CrO4 leads to anion exchange and the formation of chromate nanojars [CrO4 ⊂ {Cu(OH)(pz)}n]2–. Details of chromate binding by H-bonding based on single-crystal structures of (Bu4N)2[CrO4 ⊂ {Cu(OH)(pz)}28], four pseudopolymorphs of (Bu4N)2[CrO4 ⊂ {Cu(OH)(pz)}31], and also the methoxy-substituted derivative (Bu4N)2[CrO4 ⊂ {Cu31(OH)30(OCH3)(pz)31}] are presented.more » « less
-
The A. aeolicus intrinsically disordered protein FlgM has four well-defined α-helices when bound to σ 28 , but in water FlgM loses structure. In this work, we investigate the structure of FlgM in aqueous solutions of the ionic liquid [C 4 mpy][Tf 2 N]. We find that FlgM is induced to fold by the addition of the ionic liquid, achieving average α-helicity values similar to the bound state. Analysis of secondary structure reveals significant similarity with the bound state, but the tertiary structure is found to be more compact than the bound state. Interestingly, the ionic liquid is not homogeneously dispersed in the water, but instead aggregates near the protein. Separate simulations of aqueous ionic liquid do not show ion clustering, which suggests that FlgM stabilizes ionic liquid aggregation.more » « less
-
Abstract Organic semiconductors based on liquid crystal (LC) molecules have attracted increasing interest. In this work, two linear LCs based on 2,5‐bis(thien‐2‐yl)thieno[3,2‐b]thiophene (BTTT) mesogen are designed and synthesized, including BTTT/dEO3 with two symmetrically attached tri(ethylene oxide) groups and BTTT/mEO6 with one asymmetrically attached hexa(ethylene oxide) group. These two molecules have comparable functional‐group compositions but different molecular geometries, leading to their moderately different material performances. Both LCs show smectic mesophases with relatively low transition temperatures as confirmed by differential scanning calorimetry and polarized optical microscopy. A combination of experimental grazing incidence wide‐angle X‐ray scattering and molecular dynamics (MD) simulations reveals a herringbone packing motif of BTTT segments in both LCs while a smaller molecular tilt angle in BTTT/mEO6. Ionic conductivities are measured by doping LCs with different amounts of ionic dopants, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). BTTT/mEO6 shows better smectic phase stability to higher LiTFSI doping ratios. Both LCs exhibit similar ionic conductivities in the smectic phases, but BTTT/mEO6 outperforms BTTT/dEO3 by a factor of three in the amorphous phase at higher temperatures. MD simulations, performed to examine the ion solvation environment, reveal that BTTT/mEO6 is more efficient in coordinating Li‐ions and screening their interactions with TFSI‐ions which further promote ionic transport.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1073/pnas.2315584121
