Phase Separation Behavior Research Articles

Energy landscapes and heat capacity signatures for peptides correlate with phase separation propensity.

Phase separation plays an important role in the formation of membraneless compartments within the cell and intrinsically disordered proteins with low-complexity sequences can drive this compartmentalisation. Various intermolecular forces, such as aromatic-aromatic and cation-aromatic interactions, promote phase separation. However, little is known about how the ability of proteins to phase separate under physiological conditions is encoded in their energy landscapes and this is the focus of the present investigation. Our results provide a first glimpse into how the energy landscapes of minimal peptides that contain - and cation- interactions differ from the peptides that lack amino acids with such interactions. The peaks in the heat capacity () as a function of temperature report on alternative low-lying conformations that differ significantly in terms of their enthalpic and entropic contributions. The analysis and subsequent quantification of frustration of the energy landscape suggest that the interactions that promote phase separation lead to features (peaks or inflection points) at low temperatures in . More features may occur for peptides containing residues with better phase separation propensity and the energy landscape is more frustrated for such peptides. Overall, this work links the features in the underlying single-molecule potential energy landscapes to their collective phase separation behaviour and identifies quantities ( and frustration metric) that can be utilised in soft material design.

Sulfonated phenylamine ionic liquids as efficient phase-separation catalysts for the synthesis of trimethylolpropane triacrylate

PS3-PA with multi-SO3H exhibits excellent catalytic performance for the esterification of TMP with acrylic acidviahydrogen bond formation. The phase-separation behavior of PS3-PA plays an important role in catalyst recovery and stable reuse.

The role of microstructure on high‐temperature oxidation behavior of hafnium carbide

AbstractMicrostructure development of the products formed upon oxidation of hafnium carbide (HfCx, x = 0.65, 0.81, or 0.94) at 1300°C and 0.8 mbar oxygen pressure was investigated using Raman spectroscopy, X‐ray diffraction, electron microscopy, and electron energy‐loss spectroscopy. For all specimens a multilayered oxide scale was observed featuring an outermost porous hafnia layer and an interlayer adjacent to the parent carbide containing hafnia interspersed with carbon. The outermost hafnia features coarse pores presumably formed during initial stages of oxidation to allow rapidly evolving gaseous products to escape from the oxidation front. As the oxidation scale thickens, diffusional resistance results in slower oxidation rates and smaller quantities of gaseous products that are removed via networks of increasingly fine pores until the local oxygen partial pressure is sufficiently low to selectively oxidize the parent carbide. Electron microscopy studies suggest that the oxidation sequence at this stage begins with the transformation of parent carbide to an amorphous material having empirical formula HfO2Cx that subsequently phase separates into hafnia and carbon domains. Hafnia polymorphs in the phase‐separated region vary from cubic to monoclinic as grains coarsen from ca. 2–20 nm, respectively. Immediately adjacent to the phase‐separated region is carbon‐free mesoporous hafnia whose pore morphology is inherited from that of prior carbon domains. The average pore size and pore volume fraction observed in mesoporous hafnia are consistent with predictions from kinetic models that ascribe gaseous diffusion through a pore network as the rate determining step in oxidation behavior of hafnium carbide. These observations imply that high‐temperature oxidation behavior of hafnium carbide under the employed test conditions is linked to microstructure development via phase separation and coarsening behaviors of an initially formed amorphous HfO2Cx product.

Design and Synthesis of N‐Alkylaniline‐Substituted Low Band‐Gap Electron Acceptors for Photovoltaic Application

Comprehensive SummaryA novel electron donating unit, namely N‐octyl‐N‐phenyl‐thiophene (OPT), was designed in preparing electron acceptors with non‐fused ring chemical structures. By introducing different functional atoms/groups into the para‐position of phenyl in the OPT units, three non‐fused ring acceptors (NFREAs), C8‐2F, FC8‐2F and MeC8‐2F, were synthesized. The absorption spectrum of the three acceptors can be extended to about 950 nm with band‐gaps of 1.28—1.32 eV due to the strong electron donating ability of OPT. The frontier molecular orbital distribution of OPT based molecules obtained by quantum chemistry calculation results reveals that their energy alignment can be finely tuned to meet different requirements. Moreover, by changing the substituents on the OPT units, their Flory‐Huggins interaction parameter (χ) with the donor will be greatly influenced and different phase separation behavior can be accomplished. After blended with PBDB‐TF, the FC8‐2F‐based cell yields short circuit current density (Jsc) of 23.21 mA·cm–2, fill factor (FF) of 72.11% and the highest power conversion efficiency (PCE) of 12.42%. This work provides a new pathway for molecular design of new NFREAs, and demonstrates the application potential of OPT unit in realizing low band‐gap photovoltaic materials.

Phase separation of two-phase ammonia in horizontal T-junction at low mass velocity

Phase separation of a two-phase working fluid accompanies the thermal-hydraulic process in every system and device, with at least one T-junction used in a two-phase line. Adequate qualitative and quantitative prediction of phase separation in T-junction is critical for successful designing, e.g., refrigeration, thermal control, and fluid transport systems. Three simple T-junctions with different inlet and side diameters were tested in the horizontal position on two-phase ammonia at a saturation level of 40÷60 °C and mass velocities of 25÷150 kg·m−2s−1. Based on test data, it has been revealed that at the relative side branch mass flow rate above 0.6, the phase separation behaviour does not depend on inlet mass velocity, vapour quality, void fraction, flow patterns (stratified, slug and annular) and relative side branch diameter. A simplified empirical correlation has been proposed describing the ammonia test points with an error margin of ±15%.

Up/Down Tuning of Poly(ionic liquid)s in Aqueous Two-Phase Systems.

Thermally induced reversible up/down migration of poly(ionic liquid)s (PILs) in aqueous two-phase systems (ATPSs) was achieved for the first time in this study. Novel ATPSs were fabricated using azobenzene (Azo)- and benzyl (Bn)-modified PILs, and their upper and lower phases could be easily tuned using the grafting degree (GD) of the Azo and Bn groups. Bn-PIL with higher GDBn could go up into the upper phase and Azo-PIL come down to the lower phase when the temperature increased (>65 °C); this behavior was reversed at lower temperatures. Moreover, a reversible two-phase/single-phase transition was realized under UV irradiation. Experimental and simulation results revealed that the difference in the hydration capacity between Bn-PIL and Azo-PIL accounted for their unique phase-separation behavior. A versatile platform for fabricating ATPSs with tunable stimuli-responsive behavior can be realized based on our findings, which can broaden their applications in the fields of smart separation systems and functional material development.

Combined experimental and computational study on the effect of solvent structure on developing CO2 biphasic absorbents

To explore the regulatory factor of phase separation and the effect of solvent structure, the phase separation behavior, absorption/desorption performance, viscosity change, heat duty and ternary phase diagram of 3 monoethanolamine(MEA)-based phasic absorbents using 3 alcohols with various carbon chain lengths and isomers were determined by comprehensive experiments. The tunable phase separation behavior of MEA-based biphasic absorbents can be achieved by adjusting the mass concentration ratio of solvent and water, and the CO2 loading of phase separation point was much more impacted by the effect of the carbon chain length than that of isomerism. The intermolecular interactions between species in solutions before and after CO2 absorption were analyzed by the classical molecular dynamics simulations and independent gradient model analysis. Based on the experimental and computational results, the fundamental mechanism of phase separation was elucidated, which is related to the broken of hydrogen bonds between solvent with H2O or MEA, and the enhanced interaction among MEACOO−, MEAH+ and H2O. This study highlights the effect of structure effect on developing advanced CO2 biphasic absorbents, which may reduce the energy consumption of regeneration significantly.

Hydrophobicity of arginine leads to reentrant liquid-liquid phase separation behaviors of arginine-rich proteins

Intrinsically disordered proteins rich in cationic amino acid groups can undergo Liquid-Liquid Phase Separation (LLPS) in the presence of charge-balancing anionic counterparts. Arginine and Lysine are the two most prevalent cationic amino acids in proteins that undergo LLPS, with arginine-rich proteins observed to undergo LLPS more readily than lysine-rich proteins, a feature commonly attributed to arginine’s ability to form stronger cation-π interactions with aromatic groups. Here, we show that arginine’s ability to promote LLPS is independent of the presence of aromatic partners, and that arginine-rich peptides, but not lysine-rich peptides, display re-entrant phase behavior at high salt concentrations. We further demonstrate that the hydrophobicity of arginine is the determining factor giving rise to the reentrant phase behavior and tunable viscoelastic properties of the dense LLPS phase. Controlling arginine-induced reentrant LLPS behavior using temperature and salt concentration opens avenues for the bioengineering of stress-triggered biological phenomena and drug delivery systems.

Dynamic Assembly of Viscoelastic Networks by Aqueous Liquid-Liquid Phase Separation and Liquid-Solid Phase Separation (AqLL-LS PS2 ).

Living cells comprise diverse subcellular structures, such as cytoskeletal networks, which can regulate essential cellular activities through dynamic assembly and synergistic interactions with biomolecular condensates. Despite extensive efforts, reproducing viscoelastic networks for modulating biomolecular condensates in synthetic systems remains challenging. Here, a new aqueous two-phase system (ATPS) is proposed, which consists of poly(N-isopropylacrylamide) (PNIPAM) and dextran (DEX), to construct viscoelastic networks capable of being assembled and dissociated dynamically to regulate the self-assembly of condensates on-demand. Viscoelastic networks are generated using liquid-liquid phase-separated DEX droplets as templates and the following liquid-to-solid transition of the PNIPAM-rich phase. The resulting networks can dissolve liquid fused in sarcoma (FUS) condensates within 5 min. This work demonstrates rich phase-separation behaviors in a single ATPS through incorporating stimuli-responsive polymers. The concept can potentially be applied to other macromolecules through other stimuli to develop materials with rich phase behaviors and hierarchical structures.

Architecting dual coordination interactions in polyimide for constructing structurally controllable high-performance nanofiltration membranes

Polyimide-based nanofiltration membranes (NF) featuring customizable chemical structure and outstanding comprehensive performance have garnered tremendous interest for potential applications in ions rejection. Coordinated interactions can build supramolecular networks in polyimide that reshuffle phase separation behavior during membrane formation, thus conferring microstructural flexibility to nanofiltration membranes. In this paper, novel nanofiltration membranes were prepared by constructing dual coordination interactionsin polyimide, and the structures were confirmed by NMR, FTIR, EDX, and XPS analyses. As expected, the skin and supporting layers of the PI-based NF membranes can be controlled by designing coordination conditions during membrane formation. A promising result is that the resulted NF membranes occur higher reject of metal ions than the pristine membranes prepared by conventional non-solvent induced phase separation methods. The optimized performance showed significantly higher permeability for removing Mg2+ions, giving water permeance of 477.7 L m−2 h−1·bar−1and a rejection of over 80%. Moreover, the resulted PI-based NF membranes occur better solvent resistance than the pristine NF membranes due to the enhanced coordination structures. As a preliminary study, this work gives a new strategy to regulate the microstructure of nanofiltration membranes, promising further potential for applications in ion removal.

The combined effects of NaCl-pH and urea-pH on the phase separation of type-A gelatin and dextran

Understanding the phase separation behavior and the interaction mechanism under different conditions is important for the microstructure regulation of macromolecule systems via the induction or inhibition of phase separation. NaCl is widely used to flavor foods and urea is often used as a plasticizer in food packaging materials. In this work, the combined effects of NaCl-pH and urea-pH on phase separation of the model system of type-A gelatin-dextran (GE/DE, 4.0 wt%/4.0 wt%) were investigated. The macroscopic and microscopic structures and phase separation rate of GE/DE with different concentrations of NaCl or urea at pH 3.00, 4.00, 5.00 and 8.00 were investigated using static multiple light scattering (S-MLS), fluorescence microscopy and macroscopic observations. The results showed that NaCl promoted GE/DE phase separation at the above four pHs, and the phase separation rates were significantly increased at pH 5.00 and 8.00 even at quite low concentration of NaCl (5.0 mM). Urea seemed to inhibit the phase separation at all urea concentrations at pH 3.00–5.00 and at high urea concentration of 6.0 M at pH 8.00, while promoted the phase separation only at low concentrations of 0.5–4.0 M at pH 8.00. The effects of NaCl and urea on GE/DE phase separation at different pHs might be related with the zeta potential and transparency of gelatin. This work quantitatively characterized the induction or inhibition effect of NaCl and urea on GE/DE phase separation at different pHs, which was useful for the stability of mixed macromolecules added with NaCl or urea.

Phase separation and formation of sodium caseinate/pectin complex coacervates: effects of pH on the complexation

BackgroundThe electrostatic interactions between polysaccharides and proteins are an interesting field in the complex coacervation. PH and mixing ratio have major effect on the complexation and the coacervates structure. Hence, it is necessary to find the optimum pH and mixing ratio of the coacervates as well as understanding the thermal, mechanical, and structural characterization of the coacervates. Thus, structural changes of the complexes of sodium caseinate (NaCas) and high methoxyl pectin as a function of pH (2.00–7.00), biopolymer ratios (1:1, 2:1, 4:1, and 8:1), and total biopolymer concentration (0.1, 0.2, and 0.4% w/v) were evaluated by light scattering and ζ-potential measurements. The phase separation behavior of the NaCas/HMP coacervate and its kinetics turbidity were also investigated via monitoring the turbidity profiles. Moreover, the thermal, rheological and structural behavior of the coacervates was evaluated at the selected pH values.ResultsThe highest turbidity, particle size, and viscosity were achieved at pHmax = 3.30 and formation or dissociation around the pHmax was confirmed by particle size and FTIR. The optimum condition for the coacervation of NaCas and HMP was obtained at ratio 4:1 and 0.4% w/v. Thermal and mechanical stability of the NaCas/HMP coacervates was improved at pH 3.30. By increasing the total concentration of biopolymers, the NaCas/pectin ratio shifted to higher pH values. Furthermore, the maximum coacervate yield was achieved at 39.8% w/w at a ratio of 4:1 of NaCas/HMP and a total biopolymer concentration of 0.4% w/v.ConclusionPhase separation behavior of the coacervates exhibited the optimum pH in coacervation between NaCas and HMP. Furthermore, the rheological, thermal and structural stability of the coacervates were improved in comparison with the single biopolymers.Graphical

Study on the compounding of sodium N-lauroyl glutamate and cationic cellulose

Abstract In this work, sodium N-lauroyl glutamate (SLG) was mixed with cationic cellulose JR30 M. The rapidly occurring change in surface tension and the mass action law of the mixed (compound) system were investigated using dynamic and equilibrium surface tension methods. The behaviour of the system during phase separation was investigated by turbidimetry. The results showed that in the presence of JR30 M, the surface tension of SLG was reduced to a lower level in the given time interval due to the strong interaction compared to that of a solution with the same concentration of SLG but without JR30 M. The largest decrease was obtained with a JR30 M concentration of 0.2 g L−1, which reduced the equilibrium surface tension of SLG from 38.4 mN m−1 to 31.7 mN m−1. The rate of decrease in surface tension increased from 37.61 mN m−1 s−1 to 74.7 mN m−1 s−1. An association complex formed between SLG and JR30 M, and the equilibrium surface tension curve showed a double platform. As the concentration of JR30 M increased, the first platform broadened and the CMC value increased. The phase separation behaviour of the compound system disappeared with the increase of SLG concentration, and the area became narrower with the decrease of JR30 M concentration.

Effect of natural convection and diffusion on liquid-liquid phase separation behaviors of partially miscible solutions with lower critical solution temperature

Partially miscible solutions with lower critical solution temperature (LCST) have significant potential in improving the cooling performance of microchannel heat sinks, reducing pressure drop, and ensuring stable operation of the cooling system. Thereby, it is essential and meaningful to clearly understand the liquid-liquid phase separation process driven by natural convection and diffusion to enhance the cooling performance in microchannels further. In this paper, the liquid-liquid phase separation behaviors of 2-Butoxyethanol/water solutions in a slit cavity were visually investigated. Moreover, the effect of driven force was discussed on the temperature distribution, motion of boundaries and phase separation rate. Furthermore, the effect of the mass fraction was discussed on the phase separation temperature range and phase separation rate. The results proved that the phase separation rate was kept at 0.39%·s−1 on average in the whole slit cavity by the natural convection, whereas the driving force of diffusion was so weak that the phase separation rate rapidly decreased along the vertical direction. That means reasonable enhancements of the disturbance in the microchannel could significantly increase the phase separation rate. Moreover, the phase separation rate increased with an increase in the mass fraction, and the solution with the best cooling performance could be found at 27.4%≤ω2-BE≤35%. The results are expected to provide theoretical guidance to prepare solutions with suitable phase separation temperature range and excellent cooling performance.

Enhancing mechanical properties of flash-spun filaments by pressure-induced phase separation control in supercritical high-density polyethylene solution

Flash-spun nonwoven (FS-NW) is gaining attention in the PPE field due to its excellent barrier and mechanical properties resulting from its non-uniform diameter distribution and unique filament morphology. The unique network structure of flash-spun filaments (FSF) comprising the FS-NW can be controlled by phase separation behavior in the supercritical fluid (SCF) process. This study proposes a simple method to control the microstructure of FSFs by controlling the pressure-induced phase separation (PIPS) process in polymer/SCF solution. This phase separation behavior of an HDPE/SCF solution was confirmed by using a high-pressure view cell. A multistage nozzle allowing for phase-separated pressure to form different phases was also designed. HDPE-FSFs were synthesized by flash-spinning, and their morphology, crystallinity, and mechanical properties were investigated. The results demonstrated that the filaments obtained by PSP control at 220 °C and with an HDPE concentration of 8 wt% showed a network structure composed of strands, wherein the diameters ranged from 1.39 to 40.9 μm. Optimal FSF was obtained at 76 bar, with a crystallinity of 64.0% and a tenacity of 2.88 g/d. The PIPS method can thus effectively control the microstructure more feasibly than temperature- or solvent-induced techniques and can allow the effective synthesis of various products.

Two-dimensional demixing within multilayered nanoemulsion films.

Benefiting from the demixing of substances in the two-phase region, a smart polymer laminate film system that exhibits direction-controlled phase separation behavior was developed in this study. Here, nanoemulsion films (NEFs) in which liquid nanodrops were uniformly confined in a polymer laminate film through the layer-by-layer deposition of oppositely charged emulsion nanodrops and polyelectrolytes were fabricated. Upon reaching a critical temperature, the NEFs exhibited a micropore-guided demixing phenomenon. A simulation study based on coarse-grained molecular dynamics revealed that the perpendicular diffusion of oil droplets through the micropores generated in the polyelectrolyte layer is crucial for determining the coarsening kinetics and phase separation level, which is consistent with the experimental results. Considering the substantial advantages of this unique and tunable two-dimensional demixing behavior, the viability of using the as-proposed NEF system for providing an efficient route for the development of smart drug delivery patches was demonstrated.

A numerical investigation of the hydrodynamic and mass transfer behavior of a liquid-liquid semi-partition bioreactor (SPB) designed for in-situ extractive fermentation

Organisms used in fermentation processes are sometimes inhibited by accumulation of products or by-products. One route to circumvent this is via extractive fermentation. To facilitate this, novel bioreactor designs are required, such as the semi-partition bioreactor (SPB) which has been designed for in-situ extractive fermentation. This study reports on the numerical investigation of an SPB, considering phase separation, hydrodynamics and mass transfer behaviour. Key findings illustrate that a minimum agitation speed is necessary to attain system homogeneity in the mixer section. Furthermore, the results indicate that the working principle of the bioreactor will be effective for liquid-liquid partitioning and mass transfer followed by flux exchange between the mixer and settler sections and subsequent phase separation in the settler section. This mechanism has a shorter characteristic time than the replenishment of the bioreactor with recycled (and back-extracted) extractant. The reactor thus shows promise as a route for fermentations susceptible to product inhibition.

Reentrant phase separation of a sparse collection of nonreciprocally aligning self-propelled disks.

We study a model of aligning self-propelled disks that nonreciprocally reorient the self-propulsion directions along the interparticle separation and towards the other disks. In the limit of small inertia and large softness, where conventional motility-induced phase separation is absent, we demonstrate that the homogeneous system at a small area fraction phase-separates into clusters and a low-density phase that, eventually, reenters the homogeneous phase with a monotonic increase in alignment strength. The disks inside the clusters move with a finite space-dependent speed, constantly shuttling between clusters through the surrounding low-density homogeneous phase while maintaining the hexatic structure properties within the clusters. The area fraction gradually increases from the periphery towards the center of the clusters with a negligible correlation of the velocity and propulsion direction inside the clusters. The novel collective behavior of reentrant phase separation is found to follow from both the limits of hard disks and extremely small inertia, tending towards the overdamped limit. However, important differences in the structural and dynamical properties are shown in the limit of hard disks and extremely small inertia, as compared to that for soft disks at finite inertia. We show that the cluster phase is associated with an effective temperature for a wide range of values of alignment strength, whereas an effective temperature is associated with the specific range of alignment in the low-density phase. We believe that the reentrant phase behavior in the limit of small area fraction and the remarkable properties of the clusters should be useful in understanding a wide range of physics issues, ranging from clogging and unclogging to information exchange and transport, in biological and synthetic self-propelled systems.

Sedimentation Assays to Assess the Impact of Posttranslational Modifications on Phase Separation of RNA-Binding Proteins In Vitro and In Cells.

In the last years, RNA-binding proteins (RBPs) have been highlighted for their capacity to undergo liquid-liquid phase separation (LLPS). Aberrant phase transitions of RBPs from a liquid to a solid state are believed to underlie the formation of pathological RBP aggregates in several neurodegenerative diseases. Both in the physiological and the disease state, RBPs are often decorated with diverse posttranslational modifications (PTMs) that can influence the phase separation behavior, the physiological function, and the pathological behavior of the RBP. Here we describe two simple methods, sedimentation assays in vitro and in cells, that allow the analysis of RBP solubility as a measure of RBP phase separation in the absence or presence of a certain PTM.

Targeting androgen receptor phase separation to overcome antiandrogen resistance.

Patients with castration-resistant prostate cancer inevitably acquire resistance to antiandrogen therapies in part because of androgen receptor (AR) mutations or splice variants enabling restored AR signaling. Here we show that ligand-activated AR can form transcriptionally active condensates. Both structured and unstructured regions of AR contribute to the effective phase separation of AR and disordered N-terminal domain plays a predominant role. AR liquid-liquid phase separation behaviors faithfully report transcriptional activity and antiandrogen efficacy. Antiandrogens can promote phase separation and transcriptional activity of AR-resistant mutants in a ligand-independent manner. We conducted a phase-separation-based phenotypic screen and identified ET516 that specifically disrupts AR condensates, effectively suppresses AR transcriptional activity and inhibits the proliferation and tumor growth of prostate cancer cells expressing AR-resistant mutants. Our results demonstrate liquid-liquid phase separation as an emerging mechanism underlying drug resistance and show that targeting phase separation may provide a feasible approach for drug discovery.